ENG 212 Farm Machinery and Power Notes PDF

Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Course Title: Farm Machinery and Power Course No.: ENG-212; Credit hours: 2(1+1) Course outline or syllabus Theory: Status of Farm Power in India, Sources of Farm Power, I.C. engines, working principles of I.C. engines, comparison of two stroke and four stroke cycle engines. Study of different components of I.C. engine, I.C. engine terminology and solved problems. Familiarization with different systems of I.C. engines: Air cleaning, fuel supply, cooling, lubrication. Tractor types, Cost analysis of tractor power and attached implement. Familiarization with Primary and Secondary Tillage implement, implement for intercultural operations, Familiarization with sowing and planting equipment, calibration of a seed drill and solved examples, Familiarization with Plant Protection equipment, Familiarization with harvesting and threshing equipment. Practical: 1. Study of different components of I.C. engine. 2. To study air cleaning and cooling system of engine, 3. Familiarization with lubrication and fuel supply system of engine, 4. Familiarization with brake, steering, learning of tractor driving, 5. Familiarization with operation of power tiller, 6. Familiarization with different types of primary and secondary tillage implements: mould plough, disc plough and disc harrow. 7. Familiarization with different types of sprayers and dusters. 8. Familiarization with different inter-cultivation equipment, 9. Familiarization with harvesting and threshing machinery. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 1 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Farm Power Sources of farm power There are different sources of farm power in India which are classified as below: A. Mobile Power 1. Human Power (men, women, children) 2. Draught animals (bullock, buffalo, camels, mules and donkeys) 3. Tractors 4. Power tiller 5. Self-propelled machines like: (i) Combines (ii) Transplanter (iii) Reapers (iv) Sprayers (v) Others B. Stationary Power 1. Diesel engines (For pump sets, thresher, sprayers, other stationary operation) 2. Electric motors (For pump sets, thresher, and other stationary operations) 3. Renewable energy (Biogas, Solar, Wind) Human power: Human power is an important source for operating: 1. Small tools and implements 2. Chaff cutter 3. Water lifting devices 4. Threshers 5. Winnower and many other devices A strong man can develop maximum power of about 75 watts (about 0.l hp) for doing farm work. The average human power availability in sustained working are as follows: (i) Male: 60 watts (0.06 kW) (ii) Female: 48 watts (0.048 kW) (iii) Children: 30 watts (0.030 kW) Draught animals: Power availability from draught animals are related to its body weight. Bullocks: About 10% of body weight; Buffaloes: About 12% of body weight; Camels: About 18% of body weight and Donkeys: About 32% of body weight. On the basis of body weight, draught animals are classified as: 1. Small: (200 to 300 kg) Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 2 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 2. Medium: (301 to 400 kg) 3. Large: (401 to 500 kg) 4. Heavy: (Above 500 kg) Mechanical power: Mechanical Power means power coming from machines. It may be classified as: (a) Tractors (b) Power tillers (c) Stationary I.C. engines (Diesel engines and petrol or kerosene engine) (d) Self-propelled machines Electrical power: Electrical power is used mostly in the form of electrical motors on the farms. Motor is very useful machine for farmers. It is clean, quiet and smooth running. Its maintenance and operation needs less attention and care. The operating cost remains almost constant throughout its life. Electrical power is used for water pumping, dairy industry, cold storage, farm product processing, fruit industry, poultry industry and many similar things for farmers. Renewable energy: It is the energy mainly obtained from biomass, sun and wind. Biomass energy, wind energy and solar energy are used in agricultural and domestic purposes with suitable devices. It can be used for lighting, cooking, water heating, water distillation, food processing, water pumping, diesel engine operation with supplementary fuel and electricity generation on small scale. Renewable energy is inexhaustible in nature. Merits and demerits different farm power sources Merits Demerits Human power 1. Easily available. 1. Costliest power compared to all other 2. Used for all types of work. forms of power. 2. Very low efficiency. 3. Requires full maintenance when not in use. 4. Affected by weather condition and seasons. Animal Power 1. Easily available. 1. Not very efficient. 2. Used for all types of work. 2. Seasons and weather affect the efficiency. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 3 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 3. Low initial investment. 3. Cannot work at a stretch. 4. Supplies manures to the field and fuels 4. Requires full maintenance when not in to farmers. use. 5. Lives on farm products. 5. Creates unhealthy and dirty atmosphere near the residence. 6. Very slow in doing work. Mechanical Power 1. Efficiency is high. 1. Initial capital investment high. 2. Not affected by weather. 2. Fuel is costly. 3. Cannot run at a stretch. 3. Repairs and maintenance needs technical knowledge. Electrical Power 1. Very cheap form of power. 1. Initial capital investment high. 2. High efficiency. 2. Requires good amount of technical 3. Can work at a stretch. knowledge. 4. Maintenance and operating cost is 3. If handled carelessly, it causes great very low. danger. 5. Not affected by seasons. Status of farm power in India Farm power is an important input in agriculture which helps in timely field operation by operating different types of farm equipment’s and stationary machines such as: (i) Threshers (ii) Shellers (iii) Cleaners (iv) Graders (v) Irrigation equipment’s (vi) Post harvest equipment Agriculture is the most important sector of Indian economy. Most of the farming is done on small holdings. About 75% farm holding belong to small and marginal farmers, about 25% belong to semi, medium and large farm holders. Draft animals and farm workers are important sources of farm power. Increasing farm power is strongly influenced by: (a) Farm size (b) Cost of farm labour Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 4 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) (c) Availability of suitable machines (d) Pressing need of farmers and socio economic compulsions of local people to have custom hiring services. The farming system continues to utilize manual labour, animal power and tractor based technology in almost all operations. Agricultural machinery and implements are capable of doing field operations of better quality and in lesser time. The economic progress of a nation depends directly upon availability of energy and its consumption for fruitful utilization. Increased energy input in agriculture directly or indirectly increases the production of crops. It is an established fact that inadequacy of power and machinery results in poor yield in general. In order to bring more land under cultivation and to improve productivity, it is necessary to introduce other sources of power like tractors, power tillers; oil engines, self-propelled machines, electric motors and renewable energy (specially wind mills for water pumping). More and more application of these devices call for more and more machinery to carry out the required operations in a short period. Table. Farm power availability on Indian Farms Year Farm power, kW/ha Total Agriculture Draught Tractors Power Diesel Electric power workers animals tillers engines power kW/ha 1971-72 0.045 0.133 0.020 0.001 0.053 0.041 0.293 1975-76 0.048 0.135 0.040 0.001 0.078 0.056 0.358 1981-82 0.051 0.128 0.090 0.002 0.112 0.084 0.467 1985-86 0.057 0.129 0.140 0.002 0.139 0.111 0.578 1991-92 0.065 0.126 0.230 0.003 0.177 0.159 0.760 1995-96 0.071 0.124 0.320 0.004 0.203 0.196 0.918 2001-02 0.079 0.122 0.480 0.006 0.238 0.250 1.175 2005-06 0.087 0.120 0.700 0.009 0.273 0.311 1.500 2011-12 0.100 0.119 0.804 0.014 0.295 0.366 1.698 2012-13 0.093 0.094 0.844 0.015 0.300 0.494 1.841 The ICAR projected the requirements of farm power for the year 2020 as 2.2 kW/ha. Average Command Area (i) One pair of draught animals: 2 ha Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 5 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) (ii) Power Tiller (7.46 kW): 5 ha (iii) Tractor (26.1 kW): 15 ha. I.C. engines and working principles of I.C. engines Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 6 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Engine An engine or motor is a machine designed to convert one form of energy into mechanical energy. Engines may be Heat engines or Electric motors. Heat engines are a machine for converting heat, developed by burning fuel into useful work. It can be said that heat engine is equipment which generates thermal energy and transforms it into mechanical energy. Electric motors convert electrical energy into mechanical motion. Heat engines are of two types: 1. Internal combustion engine: In this engine, the combustion of fuel takes place inside the engine cylinder and heat is generated within the cylinder of the engine. Ex: Present days engines (tractor, power tiller, truck, cars, buses, etc.). 2. External combustion engine: Here the combustion uses heat in form of steam, which is generated in a boiler, placed entirely separate from the working cylinder. Ex: Primitive locomotive engines. On the basis of ways in which combustion takes place in the cylinder, the internal combustion engine are of two type; 1. By rapid explosion of air-fuel mixture within the cylinder, when it is ignited by a spark, is called Spark Ignition (SI) engine or Otto engine or petrol engine or constant volume combustion engine. 2. Combustion takes place by slow burning when the fuel is injected into highly compressed heated air contained in the cylinder. This is called Compression Ignition (CI) engine or diesel engine or constant pressure combustion engine (because when the combustion takes place, the pressure in the cylinder is almost constant). On the basis of number of strokes or revolutions per cycle (mechanical cycle), the internal combustion engines are of two type; 1. When the cycle is completed in two revolutions of the crankshaft it is called four stroke cycle engines. 2. When the cycle is completed in one revolution of the crankshaft it is called two stroke cycle engines. Working principle of IC engines Four stroke cycle engine: In four stroke cycle engine, all the events taking place inside the engine cylinder are completed in four strokes of the piston. This engine has got valves for controlling the inlet of charge and outlet of exhaust gases. The opening and closing of the valve is controlled by cams, fitted on camshaft. The camshaft is driven by crankshaft with the Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 7 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) help of suitable gears and chains. The camshaft runs at half the speed of the crankshaft. The events taking place in IC engine are follows: 1. Air or air-fuel mixture (charge) is taken in the cylinder. 2. The charge is compressed in the cylinder by the piston. 3. If charge is only air, the fuel is injected at the end of compression. 4. The charge la ignited at a predetermined time under specified pressure inside the engine cylinder. 5. The power developed due to expansive forces of gases inside the cylinder is transferred to the crankshaft through the connecting rod. 6. Exhaust gases go out of the cylinder at regular interval of time. The complete cycle covers all these events in systematic manner. Four stroke cycle engines completes all these events in four strokes of the piston, whereas the two stroke cycle engines covers all these events in two strokes of the piston. The four strokes of the piston are: 1. Suction stroke; 2. Compression stroke; 3. Power stroke and 4. Exhaust stroke Suction stroke: During suction stroke, only air or mixture of air and fuel are drawn inside the cylinder. The charge enters the engine through the inlet valve which remains open during admission of the charge. The exhaust valve remains closed during this stroke. The pressure in the engine cylinder is less than atmospheric pressure during this stroke (Fig (a) below). Compression stroke: The charge taken in the cylinder is compressed by the piston during this stroke. The entire charge of the cylinder is compressed to a small volume contained in the clearance volume of the cylinder. If only air is compressed in the cylinder (as in case of diesel engine), the fuel is injected at the end of the compression stroke. The ignition takes place due to high pressure and temperature. If the mixture of air fuel is compressed in the cylinder (as in case of spark ignition engine) the mixture is ignited by spark plug. After ignition, tremendous amount of heat is generated, causing very high pressure in the cylinder which pushes the piston backward far useful work. Both valves are closed during this stroke (Fig (b) below). Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 8 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Power stroke: During power stroke, the high pressure developed due to combustion of fuel causes the piston to be forced forward or backward at regular intervals. The connecting rod with the help of crank shaft transmits the power to the transmission system for useful work. Both valves are closed during this stroke (as shown in Fig (c) above). Exhaust stroke: Exhaust gases go out through exhaust valves during this stroke. All the burnt gases go out of the engine and the cylinder becomes ready to receive the fresh charge. The inlet valve is closed and exhaust valve remains open during this stroke (as shown in Fig (d) above). Thus it is found that out of four strokes, there is only one power stroke and three idle strokes. The power stroke supplies necessary momentum for useful work. Two stroke cycle engine: In such engines, the whole sequence of events i.e. suction, compression, power and exhaust are completed in two strokes of the piston and one complete revolution of the crankshaft. There is no valve in this type of engine. Gas movement takes place through holes called ports in cylinder. The crankcase of the engine is gas tight in which the crankshaft rotates. First stroke (Suction + Compression): When the piston moves up the cylinder it covers two of the ports, the exhaust port and the transfer port, which are normally almost opposite to each other. This traps a charge of fresh mixture in the cylinder and further upward movement of the piston compresses this charge. Further movement of the piston also uncovers a third port in the cylinder suction port. More fresh mixture is drawn through this port into the crankcase. Just before the end of this stroke, the mixture in the cylinder is ignited as the four stroke cycle. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 9 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Second stroke (Power + Exhaust): The rise in pressure in the cylinder caused by the burning gases forces the piston to move down the cylinder. When the piston goes down, it covers and closes the suction port, trapping the mixture drawn into the crankcase during the previous stroke then compressing it. Further downward movement of the piston uncovers first the exhaust port and then transfer port. This allows the burnt gases to flow out through exhaust port. Also the fresh mixture under pressure in the crankcase is transferred into the cylinder through transfer port during this stroke. Special shaped piston crown deflect the incoming mixture up around the cylinder so that it can help in driving out the exhaust gases (Fig. below). Fig. Two stroke engine showing suction-compression and power-exhaust stokes Fig. below shows the two stroke engine with suction port, transfer port and exhaust port. Fig. Two stroke engine, (A) Suction port, (B) Transfer port, (C) Exhaust port Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 10 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Comparison between 4 stroke and 2 stroke engine S. No. Particulars 4 Stroke engine 2 Stroke engine 1 No. of power stroke One stroke for every One stroke for every one two revolution of revolution of crankshaft crankshaft 2 Power for the same cylinder Small Large (about 1.5 times of 4 volume stroke) 3 Valve mechanism Present Ports are there instead of valves 4 Construction and cost Complicated and Simple and cheap expensive 5 Fuel consumption Little High (about 15 % more) 6 Removal of exhaust gases Easy Difficult 7 Lubrication Equipped with an Using fuel mixed with independent lubricating lubricating oil oil circuit 8 Oil consumption Little Much 9 Carbon deposit inside Not so much Much because of mixed fuel cylinder 10 Durability Good Poor 11 Self-weight and size High and large Light and small 12 Air tightness of crankcase Unnecessary Must be sealed The difference between diesel and petrol engines Particulars Diesel engine (CI engine) Petrol engine/kerosine engine (SI engine) Cycle Diesel cycle Otto cycle Fuel Diesel fuel Petrol or kerosine Charge Only air is compressed in cylinder Air-fuel mixture is compressed in the cylinder Fuel supply Fuel is injected into the Air-fuel mixture is prepared in the Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 11 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) combustion chamber trough fuel carburetor & supplied to engine injection pump and fuel injector cylinder. Ignition By heat of compression By electric sparks Thermal efficiency 32 to 38 % 25 to 32 % Compression ratio 14:1 to 22:1 4:1 to 8:1 Specific fuel 160 to 200 g/hp-hr 200 to 280 g/hp-h consumption Compression 35 to 45 kg/cm2 6 to 10 kg/cm2 pressure Temperature About 5000C About 2600C Engine weight per High Comparatively low hp Operating cost Low Comparatively high Valve timing diagram A valve timing diagram is a diagram of crank rotation on which the time of Opening closing of inlet valve, exhaust valve are shown. Valve timing mechanism is concerned with relative closing and opening of valves and their duration with respect to the cylinder position and the degree of crankshaft rotation (as shown in Fig. below). Top dead centre (TDC) is the instant when a piston is at the top of its stroke i.e. it is on the point of changing from upward to downward motion. Bottom dead centre (BDC) is the instant when a piston is at the bottom of its stroke i.e. it is on the point of changing from downward to upward motion. Theoretically the intake valve should open on top dead centre (TDC) and close at bottom dead centre (BDC), whereas the exhaust valve should open on bottom dead centre and close on top dead centre, but in actual practice these angles differ. Valve timing is a function of engine speed. The best valve timing for any given engine can be determined only by actual test, as it depends greatly on the design of the intake and exhaust passage. For most of the average tractor engines of four stroke cycle, the inlet Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 12 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) valve opens about 5° before TDC and closes at about 300 after BDC (as shown in Fig. below), the exhaust valve opens about 400 before BDC and closes at about 5° after TDC. Fig. Valve timing diagram of four stroke engine Firing order The sequence in which the power stroke in each cylinder of an engine occurs is called firing order. The arrangement of the crank pin on the crankshaft and design of the camshaft both determine the firing order. For four cylinder engine the, most commonly used firing orders are 1-3-4-2 and 1-2-4-3. For six cylinder engines, firing order may be 1-4-2-6-3-5 or 1-5-3-6-2-4. Firing interval (FI) The interval between successive power strokes in different cylinders of the engine is called firing interval and is determined as below. Fig. below shows a diagram of firing order in a typical four stroke four cylinder engine. During the first 1800 rotation of crankshaft, the cylinder No. 1 has got the power stroke, cylinder No. 2 has got the compression stroke, cylinder No. 3 has got the exhaust stroke and cylinder No. 4 has got the suction stroke. Similarly during 3600 rotation of the crankshaft, the first cylinder has got exhaust stroke, second cylinder power stroke, third cylinder intake stroke and fourth cylinder compression stroke. Similar are the cases for 540 0 rotation of crankshaft and 7200 rotation of crankshaft. At one time, each cylinder has got different strokes and after two revolutions of the crankshaft, each cylinder has got only one power stroke for a four stroke four cylinder engine. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 13 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Fig. Chart showing occurrence of events in a four cylinder four stroke engine having 1-2-4-3 firing order. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 14 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Components of IC engines An internal combustion (IC) engine is the engine in which combustion (burning of fuel) takes place inside the cylinder of engine. By burning of the fuel, high temperature and pressure force generates. This pressure force use to move the vehicle or rotate wheels by use of some mechanism. In an engine many parts work together and achieve the goal of converting chemical energy of fuel into mechanical energy. These parts are bolted together and the combination of all these parts is known as engine. Below Fig. shows exploded view of engine. The main components of IC engines are described below one by one. Engine Block and cylinder: Engine block is a container fitted with cylinder liner and piston, where the fuel is burnt and power is produced. For cooling of cylinder, a water passage/water jacket (for liquid cooling) or fin (for air cooling as used in most of bikes) are situated within the block at the outer side of cylinder/cylinder liner. At the upper end of engine block/cylinder, cylinder head and at the bottom end crank case is bolted. Cylinder or cylinder liner is the main part of IC engine in which the intake of fuel, compression of fuel and burning of fuel take place. The main function of cylinder is to guide the piston. Cylinders are usually made of high grade cast iron. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 15 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Cylinder liners are classified as Dry liner (The dry liner makes metal to metal contact with the cylinder block casting) and Wet liner (The wet liners come in contact with the cooling water, whereas dry liner do not come in contact with cooling water). Cylinder Head: It is the detachable portion of an engine which covers the cylinder block. This consists of compression chamber, inlet valve for admitting air or air fuel mixture and exhaust valve for removing the products of combustion, spark plug, injector etc. The main function of cylinder head is to seal the cylinder block and not to permit entry and exit of gases on cover head valve engine. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 16 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Piston and piston rings: It is a cylindrical part closed at one end used to compress the air or air fuel mixture by reciprocating inside the cylinder. It is connected to the connecting rod by a piston pin and transmits the energy to crankshaft. Aluminium and its alloy are preferred material for piston due to its lightness. Piston rings are used to maintain a pressure tight seal between the piston and cylinder walls, it reduces contact area between cylinder wall and piston wall for preventing friction losses and excessive wear, and also it transfer the heat from the piston head to cylinder walls. These rings are fitted in grooves which have been cut in the piston. They are split at one end so they can expand or slipped over the end of piston. Connecting Rod and Piston pin: One end of the connecting rod is connected to piston through piston pin while the other is connected to crank of the crankshaft. It transmits the reciprocatory motion of piston to rotary motion of crankshaft. There are two end of connecting rod one is known as big end and other as small end. Big end is connected to the crankshaft and the small end is connected to the piston by use of piston pin/gudgeon pin/wrist pin. Connecting rod is usually made of drop forged steel. Crank Shaft: The function of crank shaft is to convert reciprocating motion of piston into rotary motion of the fly wheel with the help of connecting rod. Usually it is made of drop Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 17 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) forged steel or cast steel. The space that supports the crankshaft in the cylinder block is called main journal, whereas the part to which connecting rod is attached is known as crank journal. And crankshaft mounts in bearing so it can rotate freely. The shape and size of crankshaft depends on the number and arrangement of cylinders. Fly wheel: Fly wheel is a rotating mass used as an energy storing device and makes crankshaft rotation more uniform. A flywheel is secured on the crankshaft. The main function of flywheel is to rotate the shaft during preparatory stroke or idle stroke. It is made of cast iron. Many times it also carries ring gear that meshes with the pinion of starting motor. Cam Shaft: Camshaft is used in IC engine to control the opening & closing of valves and timing of spark or fuel injection at proper timing hence it is also called as timing gear shaft. The camshaft is operated by means of belt/chain/gear arrangement driven by the crankshaft or flywheel and it will be placed at the cylinder head or at the bottom of cylinder. For proper engine output, inlet valve should open at the end of exhaust stroke and closed at the end of intake stroke. So to regulate its timing, a cam is used which is oval in shape and it exerts a pressure on the valve to open and release to close. The cam converts rotary motion into linear motion that operates the rocker arm. The motion of the rocker arm operates the valves. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 18 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) The speed of the camshaft is exactly half the speed of the crankshaft in 4S engine, but is same as the speed as crankshaft in case of 2S engine. In addition to operate valves, camshaft also operates the ignition timing mechanism (in case of SI engine), fuel pump and injector pump (in case of CI engine), and lubricating oil pump. In most of the engine design, it is mounted in the crankcase, parallel to the crankshaft. Valve operating mechanism: Valve operating mechanism consists of several components such as; 1. Crankshaft gear 2. Cam gear 3. Camshaft 4. Push rod 5. Tappet and 6. Rocker arm Tappet & pushrods, Rocker Arm, and Poppet Valves: Tappet and pushrods are used when the camshaft is situated at the bottom end of cylinder. It carries the camshaft motion to the valves which are situated at the cylinder head. Rocker Arms are typically in between the pushrod and the intake and exhaust valves. They allow the pushrods to push up on the rocker arms and therefore push down on the valves. Valves are used to regulates, directs or controls the flow of a charge and burnt gases by opening and closing passageways. The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed. Arrangement of cams on camshaft, Tappet & Pushrods, Rocker Arm, and Poppet Valves are shown in below Fig. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 19 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Crank Case: It supports and covers the cylinder and the crank shaft. It is used to store the lubricating oil. The main body of the engine to which the cylinder are attached and which contains the crankshaft and crankshaft bearing is called crankcase. It serves as the lubricating system too and sometime it is called oil sump. All the oil for lubrication is placed in it. Manifolds: There are two types of manifolds: Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 20 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Inlet manifold: It is a pipe like structure that connects the carburettor (in case of petrol engine) or air cleaner with the inlet valves and air or air fuel mixture from the carburettor passes through the inlet manifold. Exhaust manifold: This pipe like structure connects the outlet valve to the atmosphere or to the silencer. The exhaust gas from the cylinder passes through the exhaust manifold into the atmosphere. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 21 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Terminologies connected with engine power Bore: Bore is the diameter of the engine cylinder. Stroke: It is the linear distance travelled by the piston from Top dead centre (TDC) to Bottom dead centre (BDC). Stroke-bore ratio: The ratio of length of stroke (L) and diameter of bore (D) of the cylinder is called stroke-bore ratio (L/D). In general, this ratio varies between 1 to 1.45 and for tractor engines, this ratio is about 1.25. Swept volume or Piston displacement: It is the volume (A x L) displaced by one stroke of the piston where A is the cross sectional area of piston and L is the length of stroke. Displacement volume: It is the total swept volume of piston or all pistons during power strokes occurring in one minute. It can be calculated as Displacement volume = A×L×n× (for 4 stroke engine) Displacement volume = A×L×n× (for 2 stroke engine) Where, L= length of stroke, mm A = cross sectional area of piston, mm2 n = engine speed, rev/min. x = number of cylinder Piston speed: It is the total length of travel of the piston in a cylinder in one minute, and can be determined as = 2×L×n. Fuel consumption and Specific fuel consumption: The quantity of fuel consumed per hour is fuel consumption of any engine, whereas the quantity of fuel consumed per kW-h output is the specific fuel consumption of the engine. Compression ratio: It is the ratio of the engine volume of the charge at the beginning of the compression stroke to that at the end of compression stroke, i.e. ratio of total cylinder volume to clearance volume. Compression ratio (r) = Compression ratio (r) = IHP: Indicated power (ip) or Indicated horse power (ihp) is the power generated in the engine cylinder and received by the piston. It is the power developed in the cylinder without friction or auxiliary unit. In SI unit, the indicated power is, Indicated power (ip), kW = [for 4 stroke engine] Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 22 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Indicated power (ip), kW = [for 2 stroke engine] Where, P = mean effective pressure (mep), Pa (Pascal) L= length of stroke, mm A = cross sectional area of piston, mm2 n = engine speed, rev/min. x = number of cylinder In metric unit, Indicated horse power (ihp) = [for 4 stroke engine] Indicated horse power (ihp) = [for 2 stroke engine] Where, P = mean effective pressure (mep), kg/cm2 L= length of stroke, m A = cross sectional area of piston, cm2 n = engine speed, rev/min. x = number of cylinder BHP: Brake power (bp) Brake horse power (bhp) is the power delivered by the engine and is available at the end of the crankshaft. Drawbar power (db): It is the power of a tractor, measured at the end of the drawbar. It is the power which is available for pulling loads at the drawbar. Power take-off power (pto power): It is the power delivered by a tractor through its pto shaft. In general, the belt and pto power of a tractor will approximately be the same. Frictional power (fp). It is the power required to run the engine at a given speed without producing any useful power. It represents the friction and pumping losses of an engine. Indicated power (ip) = brake power (bp) + friction power (fp) ip = bp + fp Mechanical efficiency: It is the ratio of the brake power (bp) to indicted power (ip) and is expressed as: Mechanical efficiency (Ƞmech) = Thermal efficiency (Ƞther): It is the ratio of the output in the form of useful mechanical power to the power value of the fuel consumed. Thermal efficiency (per cent) = Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 23 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Top dead centre (TDC) and bottom dead centre (BDC): the piston, while moving in the cylinder occupies two extreme positions. The upper most position of the piston is top dead centre and the lower most position is called bottom dead centre. IHP: Indicated power (ip) or Indicated horse power (ihp) is the power generated in the engine cylinder and received by the piston. It is the power developed in the cylinder without friction or auxiliary unit. In SI unit, the indicated power is, Indicated power (ip), kW = [for 4 stroke engine] Indicated power (ip), kW = [for 2 stroke engine] Where, P = mean effective pressure (mep), Pa (Pascal) L= length of stroke, mm A = cross sectional area of piston, mm2 n = engine speed, rev/mm. x = number of cylinder In metric unit, Indicated horse power (ihp) = [for 4 stroke engine] Indicated horse power (ihp), kW = [for 2 stroke engine] Where, P = mean effective pressure (mep), kg/cm2 L= length of stroke, m A = cross sectional area of piston, cm2 n = engine speed, rev/mm. x = number of cylinder Important conversions in SI unit 1 kg = 9.8 Newton (N) 1 N-m = 1 Joule (J) 1 N-m/s = 1 J/s = 1 Watt (W) 1 Pascal = 1 N/m2 1 kg/cm2 = 9.8×104 N/m2 = 9.8×104 Pascal (Pa) = 98 kPa 1 kg-m/s = 9.8 Joules/s = 9.8 Watt 1 Calorie = 4.186 Joules 1 kW-h = 860 k-Calories 1 kW = 1000 W = 1000 J/s = 1000 N-m/s = 102 kg-m/s Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 24 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Numerical on IC engine Example 1. Calculate the brake power of a 4 stroke 4 cylinder I.C engine, having following dimensions: (a) Cylinder bore (D) =125 mm (b) Stroke length (L) = 150 mm (c) Crankshaft speed (n) = 1000 rev/min (d) Friction power = 20 kW (e) Mean effective pressure (P) = 700 kPa (f) No. of cylinder (x) = 4 Example 2. Calculate the brake power of a 4 stroke 2 cylinders, 12×15 cm (D×L) I.C engine. The mean effective pressure is 700 kPa and speed of crankshaft is 1200 rpm. The mechanical efficiency is 75 %. Example 3: A four cylinder 4 stroke gas engine has cylinder diameter of 25 cm, stroke-bore ratio is 1.8, clearance volume 4500 cm3, engine speed 240 rpm, mean effective pressure 700 kPa and mechanical efficiency is 75%. Calculate (a) ip, (b) bp, (c) compression ratio and (d) swept volume. Example 4: Determine the power and compression ratio of the engine, working on four stroke cycle principle. When it runs at 400 rpm, the volume at the beginning of the compression is 0.032 m3 and at the end of compression is 0.005 m3. The work done per cycle is 650 kg-m. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 25 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Systems of IC engine Whole IC engine comprised of several system (which perform individual function) such as 1. Air cleaning and/or supply system 2. Fuel supply system 3. Lubrication system 4. Ignition system 5. Cooling system Air cleaning system Engines use a large quantity of air for fuel combustion. As the tractor engine has to work most of the time under dusty conditions, it is very much desirable that air supplied to the engine is kept free from impurities and abrasive materials. To remove dirt and abrasive materials, it is necessary to filter the air before admitting it to the engine. It is done by an air cleaner. The development of efficient air cleaner has been of great importance in extending the useful life of farm tractors and improving their operating efficiency. The dirt collected on the air cleaner increases the resistance to air flow. The dirtier the air cleaner becomes, the lesser the air flow to the engine and thus the performance of the engine is affected. A partially clogged air cleaner is a common cause of a diesel engine smoking. Abnormal wear on the top piston rings and on the intake valve indicates ineffective air cleaning. Air cleaning system consists an air cleaner assembly, the pipe connecting the engine and the cleaner. The characteristics of a good air cleaning system An air cleaner should have following characteristics: 1. It should have adequate cleaning capacity. 2. Low maintenance requirement. 3. It should create no obstruction to air entry. 4. It should be able to remove the maximum dust particles. 5. It should be robust in construction. 6. It should have less weight. Types of Air Cleaners There are three types of air cleaners used on farm engines: (i) dry type air cleaner and (ii) oil bath type. 1. Dry type air cleaner: The filtering element in this case is a type of felt. The air passes through the element. The element has got larger surface area so the air speed becomes Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 26 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) relatively low and consequently particle or dirt in the air is deposited on or stopped by its surface. Fig. Top: dry type air cleaner and Oil bath type tractor engine air cleaner (Middle Left: assembled view and Middle Right: dissembled view) 2. Oil bath type air cleaner: In this type of air cleaner, the incoming air impinges upon the surface of the oil, kept in a container in the lower part of the casing. The foreign particles of Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 27 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) the air are trapped in the oil and then the air passes through a wire element before reaching the inlet manifold of the engine. The wire element also arrests the remaining dirt particles of the air (as shown in Fig above). Engine Air Requirements The quantity of air passing through an air cleaner of a 4 stroke 4 cylinder engine is determined by the following formula: Volume of air (m3) = The volumetric efficiency of a petrol engine is taken as 75 to 80 per cent and that of diesel engine is taken as 85 to 90 per cent. For the same size of engine and efficiency, the air requirement of a 2 cylinder engine is multiplied by two and for a four cylinder engine, it is multiplied by four. Efficiency of Air Cleaner It is estimated as follows: Efficiency = Sometimes, an engine is provided with a precleaner. The total efficiency is calculated as follows; Let the efficiency of precleaner = 60%; The efficiency of oil bath cleaner = 95%; Total efficiency = 0.60 ÷ (0.40 x 0.95). The quantity of dust entering an engine is calculated as, Dust (gram/hour) = Volume of air (m3/ h) x Dust (g/m3) Example: Determine the quantity of air required for a 4 stroke 4 cylinder petrol engine having total displacement volume of 2.4 m3 and volumetric efficiency of 80 %. Volume of air (m3) = = = 0.96 m3. Care and Maintenance of Air Cleaner: 1. Oil level in the container should be up to the indicated mark. 2. An oil of proper viscosity should be used in the oil cleaner. It. Should be of recommended grade by the manufacturer. Normally SAE 40 oil is used in summer and SAE 30 oil is used in winter. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 28 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 3. Oil of the cleaner should be changed at proper interval depending on the type of work. 4. The filter should be washed and cleaned properly. 5. All the joints from the air cleaner to the carburettor should be properly sealed. 6. Precleaner should be kept clean. Fuel system The fuel is a substance consumed by the engine to produce energy. The common fuels for IC engines are; 1. Petrol 2. Power kerosene 3. High speed diesel oil 4. Light diesel oil Quality of fuel The quality of the fuel mainly depends upon the following properties: 1. Volatility of fuel 2. Calorific value of fuel 3. Ignition quality of fuel Volatility: Volatility of fuel has considerable effect on the performance of the engine by affecting the following; a. Ease of starting the engine b. Degree of crankcase oil dilution c. Formation of vapour lock in the fuel system d. Accelerating characteristics of the engine e. Distribution of fuel in multi cylinder engine In I.C. engine, all the liquid fuel must be converted into vapour fuel before burning. High speed diesel oil is most difficult to vaporise. Vaporising temperature of high speed diesel oil is higher than that of the petrol, hence the petrol vaporises quicker than diesel oil in the engine cylinder. This helps in easy starting of petrol engines. If all the liquid fuel is not well vaporised, it would do crankcase oil dilution. A fuel having more volatility has got more ignition chances, so there is chances of vapour lock in the fuel system. Quickness in vaporising the fuel helps in producing more power swiftly which accelerates the engine. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 29 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) The oil that vaporises quickly can be distributed well in different cylinders of the engine hence distribution of fuel in different cylinder is better in petrol engine than that of diesel engine. Calorific value: The heat liberated by combustion of a fuel is known as Caloric value or Heat value of the fuel. It is expressed in kcal/kg or kcal/m3 or kJ/kg or kJ/m3. The heat value of a fuel is an important measure of its worth, since this is the heat which enables the engine to do the work. The Calorific value of the common IC engine fuel are listed below. Sl. No. Fuel Calorific value (kg/kcal) 1 Light diesel oil 10300 2 High speed diesel oil 10550 3 Power kerosene 10850 4 Petrol 11100 Ignition quality: Ignition quality refers to ease of burning the oil in the combustion chamber. Octane number and Cetane number are the measures of ignition quality of the fuel. (a) Octane number: It is a measure of knock characteristics of a fuel. The percentage of iso- octane (C8H18) in the reference fuel consisting of a mixture of iso-octane and normal heptane (C7H16), when it produces the same knocking effect as the fuel under test, is called Octane number of the fuel. Iso-octane has excellent antiknock qualities and is given a rating of 100. Normal heptane would knock excessively and hence it is assigned a value of zero. (b) Cetane number: The percentage of cetane in a mixture of cetane (C 16H34) and alpha- methyl naphthalene (C11H16) that produces the same knocking effect as the fuel under test is called Cetane number of the fuel. Diesel fuels are rated according to cetane number which is the indication of ignition quality of the fuel. The higher the cetane number the better the ignition quality of the diesel fuel. The commercial diesel fuels have got cetane rating varying from 30 to 60. Fuel test A few important tests are recommended to determine the suitability of fuels for an IC engine. The following are the important tests; 1. Gravity or specific gravity test 2. Distillation test (measure of volatility of a fuel) 3. Vapour pressure test (measure of starting ability as well as vapour lock tendencies of the fuel) Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 30 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 4. Sulphur test 5. Carbon residue 6. Gum test 7. Flash test Fuel supply system in Spark Ignition engine The fuel supply system of spark ignition engine consists of 1. Fuel tank 2. Sediment bowl 3. Fuel lift pump 4. Fuel filters 5. Carburettor and 6. Fuel pipes In some spark ignition engine, the fuel tank is placed above the level of the carburettor (Fig. below). The fuel flows from the fuel tank to the carburettor under the action of gravity. There are one or two filters between the fuel tank and the carburettor. A transparent sediment bowl is also provided to hold the dust and dirt of the fuel. If the tank is below the level of the carburettor, a lift pump is provided in between the tank and the carburettor for forcing fuel from the tank to the carburettor of the engine. The fuel comes from the fuel tank to the sediment bowl and then to the lift pump. From there the fuel goes to the carburettor through suitable pipe. From the carburettor, the fuel goes to the engine cylinder through the inlet manifold of the engine. Method of supplying fuel to the jet of the carburettor Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 31 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) If the fuel tank is above the carburettor, the fuel flows by gravity force to a float chamber which maintains constant head at the jet of the carburettor (Fig. below). If the tank is below the carburettor, there are three methods of supplying fuel to the jet of the carburettor: (a) Suction method (b) Overflow method (e) Float valve method Fig: simple carburettor with gravity feed float chamber (a) Suction method: In this method there is a check valve, provided in the fuel tank. The check valve is connected to the needle valve through a pipe. It is mainly used on single cylinder engine operating at constant load or speed (below in Fig. a). Any change in engine load or speed, requires adjustment of the needle valve. The fuel is drawn from the tank through a tube and the amount of fuel is controlled by a needle valve. (b) Overflow method: A pump supplies fuel to a chamber equipped with an overflow pipe. It is used on stationary single cylinder engine. A fuel pump is used to maintain regular supply of fuel oil. Excess fuel is sent back to the fuel tank by a return pipe (below in Fig. b). (c) Float valve method: A diaphragm pump is use to lift the fuel from the tank to the float chamber. This method is common on multicylinder engines. The amount of fuel is controlled by a float operated needle valve in the pressure line (Fig. c). Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 32 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Fig. a: Carburettor with suction feed and check valve; Fig. b: Carburettor with feed pump to fuel reservoir Fig. c: Diaphragm type fuel pump Carburettor: The process of preparing an air-fuel mixture away from the cylinders of an engine is called carburetion and the device in which this process takes place is called carburettor. Functions of carburettor The main functions of the carburettor are: 1. To mix the air and fuel thoroughly 2. To atomise the fuel 3. To regulate the air-fuel ratio at different speeds and loads and 4. To supply correct amount of mixture at different speeds and loads. Components of Carburettor A carburettor consists of the following components: 1. Venturi tube: It is provided to produce low pressure in the throat of the carburettor. The suction force causes the fuel to rise in the jet. The fuel is discharged at a rate proportional to the air velocity, available at that point. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 33 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 2. Float chamber: Float chamber is a reservoir to maintain a constant level of fuel in the carburettor. Fuel comes from the tank to the float chamber. There is a hollow float provided with a needle. With the level of the fuel going down, the float with the needle also goes down allowing the fuel to come into the float chamber from the fuel tank. As the fuel level goes up, the needle closes the passage and the fuel does not come in the float chamber. Thus a constant level in float chamber is always maintained. 3. Throttle: It is a butterfly valve between the mixing chamber of the carburettor and the inlet manifold of the engine to regulate the quantity of charge. It may be operated by a hand lever, a foot lever or a governor. 4. Choke: It is a device for restricting the air supply in the carburettor. With restriction of air supply, the mixture becomes richer which helps in starting the engine easily. It is a type of butterfly valve fitted in the air passage of the carburettor unit, 5. Main jet: It is a small opening of exact size through which fuel passes from the float chamber to the throat of the carburettor in form of spray. The jet may be of fixed type or adjustable type. Small stationary single or multi cylinder engines are usually equipped with fixed type of jet, whereas large size tractor engines are equipped with adjustable type of jet. 6. Idling jet: It is a special type of jet which supplies fuel at idling speed or low speed of the engine. It usually consists of a passage which goes to the air stream at the end of the butterfly. The opening is on the manifold side of the butterfly. When the butterfly valve is closed, the sucking force in the manifold pulls the necessary idling fuel from the idling jet. 7. Compensating jet: When main jet supplies richer mixture at higher speed the compensating jet supplies leaner mixture at that speed. This helps the mixture to maintain correct proportion of air-fuel at different loads and speeds. There is an accelerating well through which the jet gets the fuel. 8. Economiser: It is a device for regulating the fuel supply in the main jet. The difference of air pressure at the air intake and above the throttle, affects the movement of the piston. Fuel system of Diesel engine Fuel system of diesel engine consists of the following components (shown in Fig below): 1. Fuel tank 2. Fuel lift pump or feed pump 3. Fuel filter 4. Fuel injection pump 5. High pressure pipe 6. Over flow valve Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 34 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 7. Fuel Injector (Injection nozzles) Fig. Flow diagram of Fuel in diesel engine Fuel is drawn from the fuel tank by the Feed pump (as shown in Fig. below) and forced to the Injection pump through Fuel filter. The Injection pump supplies high pressure fuel to injection nozzles through delivery valves and high pressure pipes. Fuel is injected into the Combustion chamber through Injection nozzles. The fuel that leaks out from the injection nozzles passes out through leakage pipe and returns to the fuel tank through the over flow pipe. Overflow valve installed at the top of the filter, keeps the feed pressure under specified limit. If the feed pressure exceeds the specified limit, the overflow valve opens and then the excessive fuel returns to fuel tank through overflow pipe. Fig. General layout of fuel supply in diesel engine 1. Fuel Tank: It is a storage tank of suitable size and shape, usually made of mild steel sheet. Atmospheric pressure is maintained in the tank with the help of a pin hole on the cap. Usually a wire gauge strainer is provided under the cap to prevent foreign particles. Usually a drain plug is provided at the bottom for flow of fuel. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 35 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 2. Fuel Lift Pump (Feed pump or Transfer pump): Fuel lift pump may be (i) Plunger type, (ii) Diaphragm type. Plunger Type may be single acting or double acting pump usually mounted on the side of the Injection pump housing. It is driven by Injection pump camshaft. It transfers fuel from the fuel tank to the inlet gallery of the Injection pump through fuel filter. The fuel pressure at the feed pump must be in the range of 1.5 to 2.5 kg/cm2. It delivers adequate amount of fuel to the injection pump. 3. Fuel filter: It is a device to remove dirt from fuel Oil. Solid particles and dust in diesel fuel are very harmful for giving a fine degree of filtration. Fuel injection equipment in diesel engines are extremely sensitive to dirt and solid particles present in fuel. A filter (in Fig. below) is used to remove the dirt and solid particles from the fuel to ensure trouble free fuel supply. It consists of a hollow cylindrical element contained in a shell, an annular space being left between the shell and the element. The filtering element consists of metal gauge in conjunction with various media such as packed fibres, woven cloth, felt, paper etc. These filters are replaced at certain intervals, specified by the manufacturer. Fig: Fuel Filter for Diesel Engine Preliminary filter (Sediment bowl assembly) This filter is mostly fitted below the fuel tank or in between fuel tank and the fuel lift pump. It prevents dust and foreign materials from reaching inside the fuel line. It usually consists of a glass cap with gasket. Heavy dust particles settle at the bottom and clean fuel flows ahead. Main fuel filters Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 36 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Mostly two stage filters are used in diesel engines: 1. Primary: This filter removes coarse material, water and dust. 2. Secondary: This filter removes fine dust particles. Filters are made of different materials like: (a) Metal element: Metal element consists of porous metal filter elements. (b) Felt and cloth element: Felt & cloth element is a cloth of special weaving, which facilitates easy filtration. (c) Paper disc: Paper disc type filtering element is enclosed in a metal case, which can be replaced easily after being clogged. 4. Fuel injection pump: It is a high pressure pump, which supplies fuel to the injectors according to the firing order of the engine. It is used to create pressure varying from 120 kg/cm2 to 300 kg/cm2. It supplies metered quantity of fuel to each cylinder at appropriate time. Fuel injection pump is usually of two types. (a) Multi element pump and (b) Distributor (Rotary) type pump Each fuel pump unit (Multi element pump) consists of the plunger & barrel, camshaft, delivery valve and fuel control valve. In distributor (rotary) type of pump, one plunger and one barrel assembly deliver fuel not to one cylinder but to several cylinders. Plunger not only reciprocates, but rotates also in a close fitting barrel. This helps in distributing fuel to a number of cylinders in turn. Numericals 1. An I.C. engine consumes high speed diesel (HSD) oil at the rate of 0.5 kg/h. calculate the power of the engine. Assume calorific value of HSD as 10550 kcal/kg and 1 cal = 4.2 J and 1 J/s = 1 Watt. Solution: Heat value = 0.5 × 10550 = 5275 kcal/h Power of the engine = 5275 kcal/h = 5275 × 4.2 kJ/h = = = Power of engine = 6.15 kW Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 37 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 2. A four stroke diesel engine operating at 800 rpm uses 0.11 kg of fuel in 4 minute while developing a torque of 75 Nm. Calculate brake specific fuel consumption. Solution: Brake power (kW) = = = 6.28 kW Brake specific fuel consumption = = 0.262 kg/kw-h 3. A diesel engine has the following specification: Cylinders = 4; stroke = 4; hp = 45; speed = 1200 rpm; fuel consumption = 0.25 kg/hp-h. Find the weight of fuel required for single power impulse in any cylinder. Solution: Fuel consumption for 4 cylinder per hour = 0.25 × 45 kg Fuel consumption per cylinder per hour = Time taken in 2 revolutions = = minutes In 60 minutes, fuel consumption in single cylinder = 2.81 kg and in minutes, fuel consumption = = 0.078 g. Required fuel for single power impulse = 0.078 g. Governor in engine system Governor is a mechanical device, designed to control the speed of an engine within specified limit, used on tractor, other automobiles or stationary engines for (i) maintaining a nearly constant speed of engine under different load conditions, (ii) protecting the engine and the attached equipment against high speeds, when the load is reduced or removed. Tractor engines are always fitted with governor. There is an important difference in principle between the controls of a tractor engine and that of a motor car. In case of motor car, the fuel supply is under direct control of the accelerator pedal, but in tractor engine, the fuel supply is controlled by the governor. The operator changes the engine speed by moving the governor control lever. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 38 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Ignition system Fuel mixture of I.C. engine must be ignited in the cylinder at proper time for useful work. Arrangement of different components for providing such ignition at proper time in the engine cylinder is called Ignition system. There are four different system of igniting fuel: (a) Ignition by electric spark i.e. spark ignition (b) Ignition by heat of compression i.e. compression ignition (c) Ignition by hot tube or bulb and (d) Ignition by open flame. Only the first two are important methods for modern engines. Spark ignition The purpose of spark ignition is to deliver a perfectly timed surge of electricity across an open spark plug gap in each cylinder at the exact moment so that the charge may start burning with maximum efficiency. There are two methods in spark ignition: (a) Battery ignition and (b) Magneto ignition Battery ignition system Principle of working: Battery ignition system includes two circuits: 1. Low voltage (Primary circuit) and 2. High voltage (Secondary circuit) The low-voltage circuit consists of battery, ignition switch, a series of register, primary winding and contact breaker. All are connected in series. The high-voltage circuit consists of secondary winding, distributor rotor, high voltage wiring and spark plugs. They are also connected in series. Fig. Battery Ignition System When the ignition switch is closed, current flows from the battery through the primary winding of the Ignition coils provided contact breaker points are closed. They produce magnetic field around the winding (Fig. above). When the piston is at the end of compression stroke, the contact breaker point opens. Thus the flow of current in primary winding causes the magnetic field to collapse. As the field collapse, its lines of force cut the wire turnings of the secondary winding. This increases the voltage across the secondary winding terminals to Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 39 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) a value of 20 to 24 thousand volts. The high-voltage surge is delivered to the centre terminal of the distributor cap where it is picked up by the rotor and directed to the proper spark plug. A spark jumps the plug gap and ignites the compressed air-fuel mixture. Components of Battery Ignition System This system consists of a number of components such as: 1. Spark plug; 2. Distributor; 3. Ignition coil; 4. Condenser; 5. Ignitions switch 6. Dynamo and 7. Storage battery. Spark plug: Spark plug ignites the fuel-air mixture in combustion chamber. It is a device for the high voltage current to jump and ignite the charge (Fig. below). It provides insulated and grounded electrode within the cylinder of the engine to form a gap across which the spark jumps and ignites the charge. Each spark plug consists of a threaded outer shell with an outside electrode, insulator and a copper gasket. Usually spark gap settings are kept between 0.50 and 0.85 mm. If the clearance is too wide, it does not give satisfactory results. Spark plugs are of two types: (a) Cold plug and (b) Hot plug. Cold plug ha a short insulator, extending into the cylinder. It conducts the heat away from the point rapidly allowing it to be cooled by the cylinder jacket. The short path dissipates heat quickly, so it is named as Cold plug. Hot plug has comparatively longer insulator, so the heat has to pass through a longer path to reach the cooling water and hence the heat is not dissipated quickly. Fig. Spark plug Distributor: It is a device for interrupting the low voltage primary current and distributing the resulting high voltage current to the engine cylinder in proper sequence and in proper time. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 40 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) The main functions of distributor are: (a) It closes and opens the primary circuit. (b) It distributes the resulting high voltage current from the secondary circuit to the spark plugs. The distributor consists of: (a) housing (b) drive shaft (c) cam (d) breaker point (e) condenser (f) rotor and (g) cap. It is a rotary switch that connects the high tension terminal from the ignition coil to the proper spark plug wires at the instant the breaker point opens (as shown in above Fig. of battery ignition system). Ignition coil: Ignition coil serves the purpose of a small transformer. It steps up low voltage to a very high voltage (may be 20,000 volts) necessary to jump the gap of the spark plug. The coil consists of primary winding and secondary winding, wound round a soft iron core. Primary winding is made of copper wire of about 8 mm diameter having less number of turns. Secondary winding consists of thousands of turn of very fine insulated copper wire as about 0.1 mm diameter. The voltage varies as the ratio of turns of wire of the primary to the secondary winding. If the battery is connected in the primary circuit, current flows and forms an electromagnet. When the electrical circuit is suddenly broken, the electromagnetism dies out very quickly and thereby induces very high voltage in secondary winding. Condenser: A condenser consists of a pair of flat metal plates, separated by air. The most common type of condenser is of metal foil strips, separated by wax impregnated paper. The condenser in the distributor is connected across the contact breaker points (as shown in above Fig. of battery ignition system). It is used to produce a quick collapse of the magnetic field in the coil to obtain extremely high voltage. In doing so, the condenser prevents sparking across the contact breaker points, thus preventing the points from burning. Ignition switch: A switch provided in the primary circuit for starting and stopping the engine is called ignition switch. It Push-pull type or Key type. Dynamo: The purpose of the dynamo is to keep the battery charged and to supply current for ignition, light and other accessories. The dynamo supplies direct current to the battery and keeps it fully charged. It consists of a frame, soft iron pole shoes, field winding, armature winding, commutator, brushes, brush holder, spring, terminals and drive pulley. Storage battery: Storage battery is a device for converting chemical energy into electrical energy. There are several types of battery; but lead-acid battery is most common for I.C. engines, used for automobiles. Magneto ignition system A magneto is used to generate an electric current for producing spark in I.C. engine. A high tension magneto generates very high voltage, needed for spark plug (Fig. below). Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 41 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) The electrical principle involved in magneto ignition is similar to battery ignition, the chief difference being that the primary current is produced by magneto and not by battery. Magneto may be considered as combination of a generator for producing low voltage current and an ignition coil for producing high voltage current. Fig. Magneto ignition The main components of magneto ignition system are: (a) Frame (b) Permanent magnet (c) Armature (d) Soft iron field (e) Rotor (f) Primary and Secondary winding (g) Breaker points and (h) Condenser. The armature consists of an iron core on which there are two sets of winding: 1. Primary and 2. Secondary The armature is driven by the engine. As the armature rotates, primary windings cut the lines of force of the magnetic field and an induced current flow in the primary circuit. As the primary current reaches its maximum value in each direction, the primary circuit is suddenly opened by a contact breaker and the current collapses. This action induces a very high voltage in the secondary winding which causes a momentary spark to jump at the spark plug gap. A distributor is provided which carries current to the spark plug through high tension wires. The condenser is used to eliminate the arching at the breaker points and intensifying the current in the secondary circuit. For multi-cylinder engines, a distributor and a rotor are required to distribute the current to the different spark plugs. Some high speed engines have magneto built into the flywheel. Ignition by Heat of Compression Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 42 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Process of igniting fuel by heat of compression is known as Compression ignition method. Diesel engine is a compression ignition engine. In this method, no electrical accessory is needed for ignition purpose. When air is compressed in an engine cylinder, the volume of air is reduced and heat is generated in the cylinder and consequently the fuel is ignited in the cylinder. This causes a rapid rise of temperature in the cylinder. There is no external agency to produce a spark in the cylinder. The ignition temperature of the common internal combustion engine varies from 5000 to 900°F. A compression pressure at 35 to 45 kg/cm2 easily ignites the fuel. Compression ignition engine has a compression ratio ranging from 14:1 to 22:1. Other Methods of Ignition Ignition by hot tube or hot bulb: It consists of a tube like projection on the end of the side of the cylinder. The outer end of the tube is closed and the other end opened into the combustion space. It is heated by a flame or some other external source. As the charge is compressed, a certain portion enters the tube and is ignited by a contact with the hot inner surface. In hot bulb method, there is a bulb in place of a tube. In some heavy duty stationary oil engines, a bolt or a pin is provided in the cylinder head that projects into the combustion space. When this bolt is heated by some external source, it causes ignition of fuel in the engine cylinder. It is not a common method used in modern days. Open flame method: This method consists of two gas jets, one burning continuously on the outside of the engine and the other jet coming in contact with first jet and the combustion chamber alternately. The second jet is extinguished each time by the explosion and so it requires relighting. It is not a common method used for ignition purpose. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 43 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Cooling system Fuel is burnt inside the cylinder of an internal combustion engine to produce power. The temperature produced on the power stroke of an engine can be as high as 1600°C and this is greater than melting point of engine parts. The cylinder and cylinder head are usually made of cast iron and piston in most cases is made of aluminium alloy. It is estimated that about 40% of total heat produced is passed to the atmosphere via the exhaust, 30% is removed by cooling system and only about 30% is used to produce useful power. Bad effect of high temperature in the engine 1. Cylinder and piston may expand to such an extent that the piston would seize in the cylinder and stop the engine. 2. Lubricating quality of the oil inside the cylinder would be destroyed due to high temperature and there may not be sucking of air in the cylinder. 3. Pre-ignition of fuel mixture would take place and would cause engine knocking as well as loss of power. For satisfactory performance of the engine, neither overheating nor overcoo1ing is desirable. Experiments have shown that best operating temperature of I.C. engine lies between 140°F to 200°F, depending upon types of engines and load conditions. Purpose of cooling 1. To maintain optimum temperature of engine for efficient operation under all conditions. 2. To dissipate surplus heat for protection of engine components like cylinder, cylinder head, piston, piston rings and valves. 3. To maintain the 1ubricating property of the oil inside the engine cylinder for normal functioning of the engine. There are two different methods of cooling: 1. Air cooling and 2. Water cooling Air cooling Air cooled engines are those engines, in which heat is conducted from the working components of the engine to the atmosphere directly. In such engines, cy1inders are generally not grouped in a block. Principle of air cooling Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 44 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) The cylinder of an air cooled engine has fins to increase the area of contact of air for speedy cooling. The cylinder is normally enclosed in a sheet metal casing called Cowling. The flywheel has blades projecting from its face, so that it acts like a fan drawing air through a hole in the cowling and directing it around the finned cylinder. For maintenance of air cooling system, passage of air is kept clean. This is done by removing the cowling and cleaning out the dirt etc. by a stiff brush or compressed air. When, separate fan is provided, the belt tension is to be checked and adjusted if necessary. Advantages of air cooled engine 1. It is more simple in design and construction. 2. Water jackets, radiators, water pump, thermostat, pipes, hoses etc. are not needed. 3. It is more compact. 4. It is comparatively lighter in weight. Disadvantages 1. There is uneven cooling of the engine parts. 2. Engine temperature is generally high during working period. Water cooling Engines, using water as cooling medium is called “water cooled engines”. The liquid is circulated round the cylinders to absorb heat from the cylinder walls. In general, water is used as cooling liquid. The heated water is conducted through a radiator which helps in cooling the water. There are three common methods of water cooling: 1. Open jacket or hopper method. 2. Thermo-siphon method 3. Forced circulation method Open jacket or hopper method: There is a hopper or a jacket containing water, which surrounds the engine cylinder. So long as the hopper contains water, the engine continues to operate satisfactorily. As soon as the water starts boiling, it is replaced by cold water. The hopper is large enough to run for several hours without refilling. A drain plug is provided in a low accessible position for draining water as and when required. This system is not common in present days. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 45 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Fig. Open jacket or hopper system Thermo-siphon method: It consists of radiator, water jacket, fan, temperature gauge and hose connections. The system is based on the principle that heated water which surrounds the cylinder becomes lighter in weight and it rises upwards in liquid column. Hot water goes to the radiator, where it passes through tubes surrounded by air. Circulation of water takes place due to the reason that water jacket and the radiator are connected at both sides i.e. at the top and the bottom. A fan is driven with the help of a V-belt to suck air through tubes of the radiator unit, cooling radiator water. The disadvantage of the system is that circulation of water is greatly reduced by accumulation of scale or foreign matter in the passage and consequently it causes overheating of the engine. Forced Circulation method: In this method, a Water pump is used to force water from the radiator to the water jacket of the engine. After circulating the entire run of water jacket, water comes back to the radiator where it loses its heat by the process of radiation. To maintain the correct engine temperature, a thermostat valve is placed at the outer end of cylinder head. Cooling liquid is by-passed through the water jacket of the engine until the engine attains the desired temperature. Then thermostat valve opens and the by-pass is closed, allowing the water to go to the radiator. The system consists of Water pump, Radiator, Fan, Fan-belt, Water jacket, Thermostat valve, Temperature gauge and Hose pipe. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 46 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Fig. Forced circulation system 1. Water pump: It is a centrifugal type pump. It has a casing and an impeller, mounted on a shaft. The casing is usually made of cast iron. Pump shaft is made of some noncorrosive material. At the end of the shaft, a small pulley is fitted which is driven by a V-belt. Water pump is mounted at the front end of the cylinder block between block and the radiator. When the impeller rotates, the water between the impeller blades is thrown outward by centrifugal force and thus water goes to the cylinder under pressure. The pump outlet is connected by a hose pipe to the bottom of the radiator. The impeller shaft is supported on one or more bearings. There is a seal which prevents leakage of water. 2. Radiator: Radiator is a device for cooling the circulating water in the engine. It holds a large volume of water in close contact with a large volume of air so that heat is transferred from the water to the air easily (Fig. below). Hot water flows into the radiator at the top and cold water flows out from the bottom. Tubes or passages carry the water from top of the radiator to the bottom, passing it over a large metal surface. Air flows between the tubes or through the cells at right angles to the downward flowing water. This helps in transferring the heat from the water to the atmosphere. On the basis of fabrication, the radiator is of two types: (a) Tubular type and (b) Cellular type or Honey Comb type. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 47 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Fig. Radiator in cooling system 3. Thermostat valve: It is a control valve, used in the cooling system to control the flow of water when activated by a temperature signal. It is a special type of valve, which closes the inlet passage of the water connected to the radiator (Fig. below). The thermostat is placed in the water passage between the cylinder head and the top bf radiator. Its purpose is to close this passage when the engine is cold, so that water circulation is restricted, causing the engine to reach operating temperature more quickly. Thermostats are designed to start opening at 700C to 750C and then fully open at 820C for petrol engine and 88-900C for diesel engine. The thermostat valves are of two types: (a) Bel1ows and (b) Bimetallic Fig. Position of Thermostat valve in cooling system 4. Water jackets: Water jackets are cored out around the engine cylinder so that water can circulate freely around the cylinder as well as around the valve opening. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 48 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) 5. Fan: The fan is usually mounted on the water pump shaft. It is driven by the same belt that drives the pump and the dynamo. The purpose of the fan is to provide strong draft of air through the radiator to improve engine cooling. Assignment: Care and Maintenance of Cooling system for cooling system trouble. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 49 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Lubrication system IC engine is made of many moving parts. Due to continuous movement of two metallic surfaces over each other, there is wearing of moving parts, generation of heat and loss of power in the engine. Lubrication of moving parts is essential to prevent all these harmful effects. Purpose of lubrication Lubrication produces the following effects: 1. Reducing frictional effect. 2. Cooling effect 3. Sealing effect and 4. Cleaning effect Reducing frictional effect: The primary purpose of the lubrication is to reduce friction and wear between to rubbing surfaces. Two rubbing surfaces always produce friction. The continuous friction produces heat which causes wearing of parts and loss of power. In order to avoid friction, the contact of two sliding surfaces must be reduced as far as possible. This can be done by proper lubrication only. Lubrication forms an oil film between two moving surfaces. Lubrication also reduces noise, produced by movement of two metal surfaces over each other. Cooling effect: The heat, generated by piston, cylinder and bearings is removed by lubrication to a great extent. Lubrication creates cooling effect on the engine parts. Sealing effect: The lubricant enters into the gap between the cylinder liner, piston and piston rings. Thus, it prevents leakage of gases from the engine cylinder. Cleaning effect: Lubrication keeps the engine clean by removing dirt or carbon from inside of the engine along with the oil. Lubrication theory There are two theories in existence regarding the application lubricants on a surface: (a) Fluid film theory: According to this theory, the lubricant is supposed to act like mass of globules, rolling in between two surfaces. It produces a rolling effect which reduces friction. (b) Boundary layer theory: According to this theory, the lubricant is soaked in rubbing surfaces and forms oily surface over it. Thus the sliding surfaces are kept apart from each other, thereby reducing friction. Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 50 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Types of lubricant: Lubricants are obtained from animal fat, vegetable and minerals. Lubricants made of animal fat, does not stand much heat. It becomes waxy and gummy which is not very suitable for machines. Vegetable lubricants are obtained from seeds, fruits and plants. Cotton seed oil, olive oil, linseed oil and castor oil are used as lubricant in small simple machines. Mineral lubricants are most popular for engines and machines. It is obtained from crude petroleum found in nature. Petroleum lubricants are less expensive and suitable for Internal combustion engines. A good lubricant should have the following qualities: i. It should have sufficient viscosity to keep the rubbing surfaces apart. ii. It should remain stable under changing temperatures. iii. It should keep lubricated parts clean. iv. It should not corrode metallic surfaces. Assignment Question: Lubricating oil tests Engine lubricating system The lubricating system of an engine is an arrangement of mechanism and devices which maintains supply of lubricating oil to the rubbing surface of an engine at correct pressure and temperature. The parts which require lubrication are: 1. Cylinder walls and piston 2. Piston pin 3. Crankshaft and connecting rod bearings 4. Camshaft bearings 5. Valve operating mechanism 6. Cooling fan 7. Water pump and 7. Ignition mechanism The below two are common systems of lubrication used on stationary engines, tractor engines and automobiles: 1. Splash system: In this system, there is an oil trough, provided below the connecting rod. Oil is maintained at an uniform level in the oil trough. This is obtained by maintaining a continuous flow of oil from the oil sump or reservoir into a splash pan which has a depression or a trough like arrangement under each Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 51 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) connecting rod [as shown in Fig. below Fig (a) and (b)]. This pan receives its oil supply from the oil sump either by means of a gear pump or by gravity. A dipper is provided at the lower end of the connecting rod. This dapper dips into the oil trough and splashes oil out of the pan. The splashing action of oil maintains a fog or mist of oil that drenches the inner parts of the engine such as bearings, cylinder walls, pistons, piston pins, timing gears etc. This system is usually used on single cylinder engine with closed crankcase. For effective functioning of the engine, proper level of oil is maintained in the oil pan. Lubrication depends largely upon the size of oil holes and clearances. This system is very effective if the oil is clean and undiluted. Its disadvantages are that lubrication is not very uniform and when the rings are worn, the oil passes the piston into combustion chamber, causing carbon deposition, blue smoke and spoiling the plugs. There is every possibility that oil may become very thin through crankcase dilution. The worn metal, dust and carbon may be collected in the oil chamber and be carried to different parts of the engine, causing wear and tear. Fig. (a) Splash lubrication system, (b) splash unit 2. Forced feed System: In this system, the oil is pumped directly to the crankshaft, connecting rod, piston pin, timing gears and camshaft of the engine through suitable paths of oil [as shown in Fig. below]. Usually the oil first enters the main gallery, which may be a pipe or a channel in the crankcase casting. From this pipe, it goes to each of the main bearings through holes. From main bearings, it goes to big end bearings of Connecting rod through drilled holes in the crankshaft. From there, it goes to lubricate the walls, pistons and rings (Fig. below). There is Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 52 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) separate oil gallery to lubricate timing gears. Lubricating oil pump is a Positive displacement pump, usually gear type or vane type. The oil also goes to valve stem and rocker arm shaft under pressure through an oil gallery. The excess oil comes back from the cylinder head to the crankcase. The pump discharges oil into oil pipes, oil galleries or ducts, leading to different parts of the engine. This system is commonly used on high speed multicylinder engine in tractors, trucks and automobiles. Fig. Forced feed lubrication system Dr. Shrinivasa D J, Dept. of Agricultural Engineering, Institute of Agricultural Sciences, BHU, Varanasi Page 53 Study material for Subject ‘Farm Machinery and Power’ - ENG 212 (1+1) Classification of tractor Tractors can be classified into three classes on the basis of structural design, 1. Wheel tractor 2. Crawler tractor (track type or chain type) 3. Walking tractor Wheel tractor: Tractors having three or four pneumatic wheels are called wheel tractors. Four wheel tractors are most popular everywhere. Crawler tractor: This is also called tract type tractor or chain type tractor. In such tractor, there is endless chain or track in place of pneumatic wheel. Walking tractor: Power

ENG 212 Farm Machinery and Power Notes PDF

Document Details

Tags

Related

Summary

Full Transcript

Upgrade to continue