2. Principles of Inteernal Combustion Engine.pptx

PRINCIPLES OF INTERNAL COMBUSTION ENGINE Introduction Heat engine is 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. Heat engine is of two...

PRINCIPLES OF INTERNAL COMBUSTION ENGINE Introduction Heat engine is 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. Heat engine is of two types: i. External combustion engine ii. Internal combustion engine i. External combustion engine: Here the combustion uses heat in the form of steam, which is generated in a boiler, placed entirely separate from the working cylinder. In internal combustion engine, the combustion of fuel takes place inside the cylinder and heat is generated within the cylinder of the engine. ii. Internal combustion engine: It has the engine designed to derive its power from the fuel, burnt within the engine cylinder. It uses the expansive force of gases produced by burning the fuel within the cylinder. The generated heat is converted into useful power by a piston, constrained within the cylinder. The motion of the piston rotates the crankshaft with help of the connecting rod. The heat that supplies the energy for working substance is generated within the cylinder. Hence, the name is given internal combustion engine. There are two ways in which combustion takes place within the cylinder: By rapid explosion of the air-fuel mixture within the cylinder, when it is ignited by a spark, is called constant volume combustion (C.V.C). Combustion takes place by slow burning when the fuel is injected into highly compressed heated air contained in the cylinder. This is called constant pressure combustion (C.P.C), because when the combustion takes place, the pressure in the cylinder is almost constant.  Advantages of I.C.E. over E.C.E.: 1. More mechanical simplicity and lower weight/power ratio. 2. They do not need auxiliary equipment, such as boiler & condenser. 3. They could be started and stopped in a short time. 4. Their thermal efficiency is higher than other heat engines. 5. Their initial cost is low. These advantages make I.C.E. more suitable in the  Principles of I.C Engine A mixture of fuel with correct amount of air is exploded in an engine cylinder which is closed at one end. As a result of the explosion, heat is released and this causes the pressure of the burning gases to increase. This pressure increase, forces a close fitting piston to move down the cylinder. This movement of piston is transmitted to a crankshaft by a connecting rod so that the crankshaft turns a flywheel; to obtain continuous rotation of the crankshaft this explosion has to be repeated. Before this can happen, the used gases have to be expelled from the cylinder, the fresh charges of fuel and air must be admitted and the piston must be moved back to its starting position. This sequence of events is known as the working cycle. Mechanical cycle of internal combustion engine can be completed in two ways: a. When the cycle is completed in two revolutions of the crankshaft, it is called four stroke cycle engines. b.When the cycle is completed in one revolution of the crankshaft, it is called two stroke cycle engines. Cylinder events of four- stroke cycle  CONSTRUCTIONAL FEATURES OF IC ENGINE: The cross section of IC engine is shown in Fig. 1. A brief description of these parts is given below. Cylinder: The cylinder of an IC engine constitutes the basic and supporting portion of the engine power unit. Its major function is to provide space in which the piston can operate to draw in the fuel mixture or air (depending upon spark ignition or compression ignition), compress it, allow it to expand and thus generate power. The cylinder is usually made of high-grade cast iron. In some cases, to give greater strength and wear resistance with less weight, chromium, nickel and molybdenum are added to the cast iron. Fig. 1 Cross-section of a diesel engine  Piston: The piston of an engine is the first part to begin movement and to transmit power to the crankshaft as a result of the pressure and energy generated by the combustion of the fuel. The piston is closed at one end and open on the other end to permit direct attachment of the connecting rod and its free action. The materials used for pistons are grey cast iron, cast steel and aluminium alloy. However, the modern trend is to use only aluminium alloy pistons in the tractor engine.  Piston Rings: These are made of cast iron on account of their ability to retain bearing qualities and elasticity indefinitely. The primary function of the piston rings is to retain compression and at the same time reduce the cylinder wall and piston wall contact area to a minimum, thus reducing friction losses and excessive wear. The other important functions of piston rings are the control of the lubricating oil, cylinder lubrication, and transmission of heat away from the piston and from the cylinder walls. Piston rings are classed as compression rings and oil rings depending on their function and location on the piston.  Compression rings are usually plain one-piece rings and are always placed in the grooves nearest the piston head. Oil rings are grooved or slotted and are located either in the lowest groove above the piston pin or in a groove near the piston skirt. Their function is to control the distribution of the lubricating oil to the cylinder and piston surface in order to prevent unnecessary or excessive oil consumption. Figure 2. Components of the diesel engine  Piston Pin: The connecting rod is connected to the piston through the piston pin. It is made of case hardened alloy steel with precision finish. There are three different methods to connect the piston to the connecting rod. Connecting Rod: This is the connection between the piston and crankshaft. The end connecting the piston is known as small end and the other end is known as big end. The big end has two halves of a bearing bolted together. The connecting rod is made of drop forged steel and the section is of the I-beam type.  Crankshaft: This is connected to the piston through the connecting rod and converts the linear motion of the piston into the rotational motion of the flywheel. The journals of the crankshaft are supported on main bearings, housed in the crankcase. Counter- weights and the flywheel bolted to the crankshaft help in the smooth running of the engine. Engine Bearings: The crankshaft and camshaft are supported on anti-friction bearings. These bearings must be capable of withstanding high speed, heavy load and high temperatures. Normally, cadmium, silver or copper lead is coated on a steel back to give the above characteristics. For single cylinder vertical/horizontal engines, the present trend is to use ball bearings in place of main bearings of the thin shell type.  Valves: To allow the air to enter into the cylinder or the exhaust, gases to escape from the cylinder, valves are provided, known as inlet and exhaust valves respectively. The valves are mounted either on the cylinder head or on the cylinder block. Camshaft: The valves are operated by the action of the camshaft, which has separate cams for the inlet, and exhaust valves. The cam lifts the valve against the pressure of the spring and as soon as it changes position the spring closes the valve. The cam gets drive through either the gear or sprocket and chain system from the crankshaft. It rotates at half the speed of the camshaft.  Flywheel This is usually made of cast iron and its primary function is to maintain uniform engine speed by carrying the crankshaft through the intervals when it is not receiving power from a piston. The size of the flywheel varies with the number of cylinders and the type and size of the engine. It also helps in balancing rotating masses.  FARM TRACTOR Tractor is a self-propelled power unit having wheels or tracks for operating agricultural implements and machines including trailers. Tractor engine is used as a prime mover for active tools and stationary farm machinery through power take-off shaft (PTO) or belt pulley.  CLASSIFICATION OF TRACTORS Tractors can be classified into three classes on the basis of structural-design: i. Wheel tractor: Tractors, having three or four pneumatic wheels are called wheel tractors. Four- wheel tractors are most popular everywhere. ii. Crawler tractor. iii. Walking tractor (Power tiller): Power tiller is a walking type tractor. This tractor is usually fitted with two wheels only. The direction of travel and its control for field operation is performed by the operator, walking behind the tractor.  On the basis of purpose, wheeled tractor is classified into three groups: (a) General purpose tractor: It is used for major farm operations; such as ploughing, harrowing, sowing, harvesting and transporting work. Such tractors have (i) low ground clearance (ii) increased engine power (iii) good adhesion and (iv) wide tyres. (b) Row crop tractor: It is used for crop cultivation. Such tractor is provided with replaceable driving wheels of different tread widths. It has high ground clearance to save damage of crops. Wide wheel track can be adjusted to suit inter row distance. (c) Special purpose tractor: It is used for definite jobs like cotton fields, marshy land, hillsides, garden etc. Special designs are there for special purpose tractor.  TRACTOR COMPONENTS A tractor is made of following main components: (1) I. C. engine, (2) Clutch (3) Transmission gears (4) Differential unit (5) Final drive (6) Rear wheels (7) Front wheels (8) Steering mechanism (9) Hydraulic control and hitch system (10) Brakes (11) Power take-off unit (12) Tractor pulley and (13) Control panel. Every tractor is fitted with an I. C. engine, the engine may be carburetor type or diesel type but nowadays almost all the tractors are diesel tractors.  SELECTION OF TRACTOR Selection of tractor depends upon following factors: (1) Land holding: Under a single cropping pattern, it is normally recommended to consider 1 hp for every 1 hectare of land. In other words, one tractor of 20-25 hp is suitable for 20 hectares farm. (2) Cropping pattern: Generally less than 1.0 hectare/hp have been recommended where adequate irrigation facilities are available and more than one crop is taken. So a 30-35 hp tractor is suitable for 25 hectares farm. (3) Soil condition: A tractor with less wheel base, higher ground clearance and low overall weight may work successfully in lighter soil but it will not be able to give sufficient depth in black cotton soil.  (4) Climatic condition: For very hot zone and desert area, air cooled engines are preferred over water-cooled engines. Similarly for higher altitude, air cooled engines are preferred because water is liable to be frozen at higher altitude. (5) Repairing facilities: It should be ensured that the tractor to be purchased has a dealer at near by place with all the technical skills for repair and maintenance of machine. (6) Running cost: Tractors with less specific fuel consumption should be preferred over others so that running cost may be less. (7) Initial cost and resale value: While keeping the resale value in mind, the initial cost should not be very high; otherwise higher amount of interest will have to be paid. (8) Test report: Test report of tractors released from farm machinery testing stations should be consulted for guidance.  CONTROL BOARD OR DASH BOARD OF A TRACTOR The control board of a tractor generally consists of: (1) Main switch (2) Throttle lever (3) Decompression lever (4) Hour meter (5) Light switch (6) Horn button (7) Battery charging indicator (8) Oil pressure indicator and (9) Water temperature gauge.  TRACTOR TYRES AND FRONT AXLE TYRES: The tyres are available in many sizes with the ply ratings as 4, 6 or 8. The ply rating of tyres indicates the comparative strength of tyres. The higher the rating, the stronger are the tyres. The tyre size 12—38 means, that the sectional diameter of the tyre is 12" and it is mounted on a rim of 38“ diameter. The inflation pressure in the rear wheels of the tractor varies between 0.8 to 1.5 kg/cm2. The inflation pressure of the front wheel varies from 1.5to2.5kg/ cm2. Useful life of the pneumatic tyres under normal operating condition may be about 6000 working hours for drawbar work.  FRONT AXLE: Front axle is the unit on which fronts wheel are mounted. These wheels are idler wheels by which tractor is steered in various directions. The axle is a rigid tubular or I-section steel construction pivoted at the centre. There are various adjustments of front wheel. Hitching system of Tractor Drawn Implements Tractor drawn implements possess higher working capacity and are operated at higher speeds. These implements need more technical knowledge for operations and maintenance work. Tractor drawn implements may be a) Trailed type b) Semi-mounted type and c) Mounted type.  a) Trailed type implement: It is one that is pulled and guided from single hitch point but its weight is not supported by the tractor. b) Semi-mounted type implement: This type of implement is one which is attached to the tractor along a hinge axis and not at a single hitch point. It is controlled directly by tractor steering unit but its weight is partly supported by the tractor. c) Mounted type implement: A mounted implement is one which is attached to the tractor, such that it can be controlled directly by the tractor steering unit. The implement is carried fully by the tractor when out of work. SOME IMPORTANT TERMS CONNECTED WITH TRACTORS Wheelbase: Wheel base is the horizontal distance between the front and rear wheels of a tractor, measured at the ground contact. Ground clearance: It is the height of the lowest point of the tractor from the ground surface, the tractor being loaded to its maximum permissible weight. Track: Track is the distance between the two wheels of the tractor on the same axle, measured at the point of ground contact. 28/5/24  Turning space: It is the diameter of the smallest circle, described by the outermost point of the tractor, while moving at a speed, not exceeding 2 km/hr with the steering wheels in full lock. Cage wheel: It is a wheel or an attachment to a wheel with spaced cross bars for improving the traction of the tractor in a wet field. It is generally used in paddy fields.  POWER TILLER It is a prime mover in which the direction of travel and its control for field operation is performed by the operator walking behind it. It is also known as hand tractor or walking type tractor. The concept of power tiller came in the world in the year 1920. Japan is the first country to use power tiller on large scale. In Japan, the first successful model of power tiller was designed in the year 1947. Production of power tiller rapidly increased during the year 1950 to 1965.  Power tiller is a walking type tractor. The operator walks behind the power tiller, holding the two handles of the power tiller in his own hands. Power tiller may be called a single axle walking type tractor, though a riding seat is provided in certain designs. Power tiller  Components of power tiller: A power tiller consists of the following main parts: (1) Engine (2) Transmission gears (3) Clutch (4) Brakes (5) Rotary unit. All the power tillers are fitted with an I. C. engine. At present, most of the power tillers are fitted with diesel engines. The makes like Kubota, Mitsubishi, and Sarachi all use diesel engines  Operation: The main clutch is a lever on the handle. The lever can be shifted to on or off position while operating in the field. When the lever is shifted to on position, the power from the engine is transmitted through the main clutch to the various parts of the power tiller. When the lever is shifted to off position the power from the engine is cut-off from the rest of the transmission.  Power transmission in power tiller: For operation of power tiller, the power is obtained from the IC Engine, fitted on the power tiller. The engine power goes to the main clutch with the help of belt or chain. From main clutch, the power is divided in two routes, one goes to transmission gears, steering clutch and then to the wheel. The other component goes to the tilling clutch and then to the tilling attachment.  The flow diagram for transmission of power is given below: Transmission gear Steering clutch Wheels Engine Main clutch Tilling clutch Tilling attachment  V-belt is usually used to transmit power from the engine to the main clutch, because V-belt has very high efficiency and it works as a shock absorber also. Main clutch: Power goes from the engine to the main clutch. Clutch may be: (i) Friction clutch or (ii) V-belt tension clutch. Friction clutch is generally used for bigger power tillers. Usually it is a dry type multiple disc clutch. V-belt tension clutch is used for small power tillers. The main functions of clutch in a power tiller are: (i) to transmit engine power to transmission gears and (ii) to make power transmission gradual and smooth.  Transmission gears: Transmission box consists of gears, shafts and bearings. The speed change device may be; (a) gear type or (b) belt type. Brakes: All power tillers have some braking arrangement for stopping the movement. Most of the power tillers use inner side expansion type brake. Wheels: Usually 2 to 4 ply pneumatic tyres are used in power tillers. The pressure of the tyre ranges from 1.1 to 1.4 kg/cm2. Rotary unit: Power tiller has a rotary unit for field operation. Rotary unit is of two types: (a) Centre drive type and (b) Side drive type.  Centre drive type has got transmission at the centre and the side drive type has transmission at one side. Centre drive type has the following characteristics: (a) Tilling width can be widened (b) Rotary unit is light in weight (c) Fixing of attachment is easy (d) The tine shaft can be detached easily (e) Mounting and dismounting of rotary unit is very easy (f) It may leave some portion of the field untilled (g) It has one point support on the ground. In side drive type;- (i) Deeper tilling is possible (ii) The arrangement is useful for hard soil (iii) It  Rotary tines: Rotary tines are used in rotary unit for soil cutting and pulverization purpose. Rotary tines are of three types: (i) Straight tines (ii) Curved tines and (iii) Sliding tines. In case of straight tines : (a) Power consumption is less (b) Fine pulverization of soil is possible (c) Poor soil turning (d) Grass entangles in the tines very easily (e) It is suitable for hard soil. In case of curved tines: (a) Good soil turning is possible (b) It is suitable for avoiding grasses (c) Pulverization of soil is coarse and (d) Power consumption is high.  Sliding tines have the characteristics of sliding on their positions according to the requirement. Steering cutch lever: Steering clutch is provided on the grip of the right and left handles. When (he left side is gripped, power is cut-off on left side of the wheel and the power tiller turns to the left. Similarly when the right side is gripped, the power tiller turns to the right.