Unit-1: Farm Mechanisation PDF

Unit-1. SOL-214 FARM MECHANISATION Mechanised agriculture is the process of using agricultural machinery to mechanize the work of agriculture, greatly increasing farm worker productivity. The effective mechanization cont...

Unit-1. SOL-214 FARM MECHANISATION Mechanised agriculture is the process of using agricultural machinery to mechanize the work of agriculture, greatly increasing farm worker productivity. The effective mechanization contributes to increase production in two major ways: firstly, the timeliness of operation and secondly the good quality of work. The requirement of power for certain operations like seedbed preparation, cultivation and harvesting becomes so great that the existing human and animal power in the country appears to be inadequate. As a result, the operations are either partially done or sometimes completely neglected, resulting in low yield due to poor growth or untimely harvesting or both. SCOPE OF MECHANISATION It is quite true that the Indian farmers have the lowest earnings per capita because of the low yield per hectare they get from their holdings. One of the few important means of increasing farm production per hectare is to mechanise it. Mechanisation in India may have to be done at various levels. Broadly, it can be done in three different ways: I. By introducing the improved agricultural implements on small size holdings to be operated by bullocks. II. By using the small tractors, tractor-drawn machines and power tillers on medium holdings to supplement existing sources. III. By using the large size tractors and machines on the remaining holdings to supplement animal power source. But many people are of the opinion that Indian agriculture cannot be fully mechanized. Only the improved animal-drawn implements should be introduced. It is felt that 1. There is a surplus of agricultural labour in India. 2. There are enough draft animals available in the country to do the farm work effectively. 3. The size of farm holdings of the majority of the Indian farmers is too small to justify theuse of a tractor on their farms. 4. The investing capacity, of the farmers is too poor to buy a tractor and tractor-drawn implements. 5. The technical know-how of the people in the country is low. 6. In the absence of suitable farm road system, the tractor and tractor-drawn machines cannot be effectively utilized under the present conditions. 7. It will not be possible to increase the yield by using mechanical power.  8. Mechanization will not result in lowering the cost of production. 9. It will not be possible to mechanize every bit of farm operation. 10. A large labour force will get displaced from agriculture. History indicates that the development in farm mechanization is very closely related to the shortage of human labour and industrial development in the country. Farmers of India like their counterparts in other countries are interested to improve their income, life style and general well- being. They see mechanization as a means for achieving their objectives. In spite of the limitations with which they exist, their performance has been noteworthy. There is a positive correlation between application of improved technologies and the land productivity. The technical know-how of the people in the country is quite satisfactory. It always develops with the opportunities and experience. The repair, maintenance and overhaul facilities for tractors and other machines are expanding, even in the small towns, with the expansion of rural electrification in the country. Drudgery and physical exertion are typical of much Indian agriculture today. It scares away men of intelligence and ability from agriculture. All people would favor minimizing this to a considerable extent. The development of improved riding type animal drawn machines can improve the present condition, but they cannot be a substitute for the tractor- drawn machines. By using mechanical power, man will be able to control larger areas and as such his family members will get more free time. More power is essential in carrying out operations effectively at the right time and for changing the attitudes and uplifting the social status and dignity of those who work in agriculture. There are three ways in which progress can be made towards increased power, all of which must be worked on simultaneously in combination with integrated and matched implements. 1. By improving bullock harness and hitches; 2. By developing and introducing small tractors; 3. By increasing the number of large horsepower tractors. These machines will be helpful in providing power efficiently for good seedbed preparation, which is quite essential for maximizing the germination of the seed and seedling growth. In addition to this, the mechanization of the following fields of agriculture- is equally essential. I. Shaping and levelling of farm fields for getting even distribution and depth of irrigation water; II. Development of planting and fertilizing machines to place the seed more precisely in rows and to place the fertilizer correctly with respect to seed or plant;  III. Spraying and dusting machinery to apply chemicals for weed and pest control; IV. After production operations such as harvesting, threshing, winnowing and drying. State of Mechanization: Agricultural system all over the world has undergone changes in terms of cropping system, type of power sources used and application of inputs to achieve high level of productivities. Even in India, mechanization of agriculture has advanced considerably. In certain region, the level of mechanization has gone far ahead of the average level in the country. Human and animal power sources are no longer the predominant sources on Indian farms. The annual addition of tractor population is more than one hundred thousand tractors. Similarly, about the hundred thousand pump sets are being installed on Indian farms annually. On the basis of annually critical review of the mechanization position, one observes that the shortage of labour and high labour wages are the factors which strongly propel mechanization. Consequently, the more labor-intensive operations, such as pumping of irrigation water, land preparation and threshing are the first operations, which are mechanized. Large amount labour or draft power, which can be replaced through machines, provides a strong incentive to mechanize. The farm operations, which can be categorized as: I. Highly power intensive operations, II. Intermediate power and control intensive operations, III. Highly control intensive operations. SOCIAL CONSIDERATION TO FARM MECHANIZATION The steps towards development of an appropriate agricultural technique in India are not working with the motto of saving labour but of improving and increasing agricultural production. Most people believe that India is burdened with surplus labour and that there are far too many draft animals for the cultivation of available farmland. Above all, there is an unfounded fear that farm mechanization will precipitate widespread rural unemployment as agriculture contributes over two- thirds of all jobs in India. The fact is however, that India 's increased food requirements must be met through increased productivity of the land from higher yields and more multiple cropping which would require additional labour for carrying out different farm operations. From the energy application point of view, the Indian agriculture is in the transition from stage 1 (human power) and stage 2 (animal power) to stage 3 and 4 (power tiller or four-wheel tractor). However, animal power will co-exist with mechanical power in the country. Animal drawn machines must be provided with tiding arrangements so that walking behind the machine can be avoided. The following can help in increasing the agricultural production in the country: I. Agriculture must continue to productively employ as many or more labourers per cultivated hectare in the foreseeable future. II. The small & scattered land holdings and the poor economic conditions of the average farmer restrict the use of units designed for large-scale mechanization. The power tillers and related equipment, therefore, find a greater scope to be used on such farms. Power tillers attached with rotavator are better suited for puddling operations in rice growing regions. III. Cropping intensity should be increased to 200 to 250 per cent level from the present levelof 100 to I80 per cent. IV. Due to the fragmentation of lands, the number of holdings has gone up and therefore, appropriate size of farm machines has to the introduced for the tillage, planting transplanting and harvesting of crops. Custom hiring of machines will have large scope in future. V. An economical multi-crop thresher may be developed to suit farmers’ need. High-capacity threshers capable of threshing wheat and paddy crop at 15 to 20 per cent moisture content need immediate attention. VI. Custom hiring of farm equipment should be encouraged as it has resulted to the increased power availability on the farms and in turn increased land productivity.  SOURCES OF FARM POWER A farm power for various agricultural operations can be broadly classified as: (1) Tractive work such as seed bed preparation, cultivation, harvesting and transportation. (2) Stationary work like silage cutting, feed grinding, threshing, winnowing and lifting ofirrigation water. These operations are done by different sources of power, namely human, animal, oil engine, tractor, power tiller, electricity and renewable energy (biogas, solar and wind). HUMAN POWER Human beings are the main source of power for operating small tools and implements. They are also employed for doing stationary work like threshing, winnowing, chaff cutting and lifting irrigation Water. It is generally believed that there is surplus human power available for agricultural operations in India. According to 2001 census figures, the total Indian rural population is about 74 crores. Of the total rural population only 30 per cent is available for doing farm work. Hence the total number of persons available would be about 74 x 0.30 = 22.2 crores. This figure includes both the landless labourers as well as the owners of farms in the country. On the average a man develops nearly 0.I horsepower (hp.). Therefore, the total poweravailable through human source may be about 2.2 crore hp. But there is a steady decline in the number of landless labourers available for doing farm work in rural areas. ANIMAL POWER The most important source of power on the farm all over the world and particularly in India is animal. It is estimated that nearly 80 per cent of the total draft power used in agriculture throughout the world is still provided by animals, although the number of agricultural tractors has become double after every ten years since 1930. India with its 22.68 crore cattle possesses the largest number of cattle in the world. Among them the bullocks and buffaloes happen to be the principal sources of animal power on Indian farms. However, camels, horses, donkeys, mules and elephants are also used for the farm work. The average force a bullock can exert is nearly equal to one tenth of its body weight. But for a very short period, it can exert many more times the average force. Generally, a medium size bullock can develop between 0.50 to 0.75 hp.Thus, the variation in power developed by animals is considerable. Actually, small size bullocks are not able to develop even 0.50 hp and most of them are not fit for heavy work. Animals Can be a very cheap source of farm power if raised by the farmer himself. It becomes the costliest source if the animal has to be bought from outside. Considering the overall situation of the draft animals available in the country, it is estimated that the total work animals may be about 7.56 crores in number, that is 33 per cent ofthe total horse power output from the animals would be about 7.56 x 0.50 = 3.78 crore hp. Advantages: Easily available, Used for all types of work, Low initial investment, Supplies manure to the field and fuels to farmers and Live on farm produce. Disadvantages: Not very efficient, Seasons and weather affect the efficiency, cannot work at a stretch, require full maintenance when there is no farm work, creates unhealthy and dirty atmosphere near the residence and very slow in doing work. MECHANICAL POWER The third important source of farm power is mechanical power that is available through tractors and oil engines. The oil engine is a highly efficient device for converting fuel into useful work. The efficiency of diesel engine varies between 32 and 38 per cent, whereas that ofthe carburetor engine is in the range of 25 and 32 per cent. In recent years, diesel engines and tractors have gained considerable popularity in agricultural operations. Small pumping sets within 3 to 10 hp range are very much in demand. Likewise, oil engines of low to medium speed developing about 14 to 20 hp are successfully used for flourmills, oil ghanis, cotton gins, etc. Diesel engines of the larger size are used on tractors. It is estimated that about one million tractors of about 25 bhp range are in use for agricultural operations in India. Similarly, the total number of oil engines for stationary work may be taken as about 60 lakhs of 5 hp each. Thus, the total power available from mechanical source would work out to be 55 million hp (Oil engines = 0.60 x 5 = 3.0 crore hp, tractors = 0.1 × 25 = 2.50 crore hp. Advantages: Efficiency is high; not affected by weather; can run at a stretch; requires less space and cheaper form of power Disadvantages: Initial capital investment is high; fuel is costly and repairs and maintenance needs technical knowledge. ELECTRICAL POWER Now-a-days electricity has become a very important source of power on farms in various states of the country. It is steadily becoming more and more available with the increase of various river valley projects and thermal stations. On an average about 1/10th of the total electrical power generated in India, is consumed for the farm work. The largest use of electric power in the rural areas is for irrigation and domestic water supply. Besides this, the use of electric power in dairy industry, cold storage, fruit processing and cattle feed grinding has tremendously increased. Advantages: Very cheap form of power; high efficiency; can work at a stretch; maintenance and operating cost is very low and not affected by weather conditions. Disadvantages: Initial capital investment is high; require good amount of technical knowledge and it causes great danger, if handled without care. WIND POWER The availability of wind power for farm work is quite limited. Where the wind velocity is more than 32 kmph, wind mills can be used for lifting water. Even today in India the wind power has not been fully harnessed. The most important reason is its uncertainty. Experimental results show that a wind mill having 3.6 diameter wheel mounted on 12.0 m tower is able to produce from 0.1 to 0.9 hp with the wind velocity varying from 6.4 to 37 km/h. Thus, the average capacity of a wind mill would be about 0.50 hp. There are about 2540 mills installed in India. Hence the total output may be about 1250 hp only, but it is one of the cheapest sources of farm power available in the country. Some limitations are as follows- Initial investment is high, Repair facilities are not available in rural areas, Even the matching pump sets and electric generators are not readily available in thecountry, It not suitable for all situations in the country. For the present, the wind mills havelimited scope of the use in the country.  IC ENGINE & IT’S WORKING PRINCIPLES A heat engine is a machine, which converts heat energy into mechanical energy. The combustion of fuel such as coal, petrol, diesel generates heat. This heat is supplied to a working substance at high temperature. By the expansion of this substance in suitable machines, heat energy is converted into useful work. Heat engines can be further divided into two types: (i) External combustion and (ii) Internal combustion. In a steam engine the combustion of fuel takes place outside the engine and the steam thus formed is used to run the engine. Thus, it is known as external combustion engine. In the case of internal combustion engine, the combustion of fuel takes place inside the engine cylinder itself. The IC engine can be further classified as: (i) stationary or mobile, (ii) horizontal or vertical and (iii) low, medium or high speed. The two distinct types of IC engines used for either mobile or stationary operations are: (i) diesel and (ii) carburetor. Heat Engine External Combustion Internal Combustion Steam Engine Reciprocating Wankel Rotary G a s Turbine CI Engine SI Engine Two Stroke Four Stroke Two Stroke Four Stroke Flow Diagram 1. Types of Heat Engines Spark Ignition (Carburetor Type) IC Engine In this engine liquid fuel is atomized, vaporized and mixed with air in correct proportion before being taken to the engine cylinder through the intake manifolds. The ignition of the mixture is caused by an electric spark and is known as spark ignition. Compression Ignition (Diesel Type) IC Engine In this only the liquid fuel is injected in the cylinder under high pressure. COMPONENTS OF INTERNAL COMBUSTION 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. 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 aluminum alloy. However, the modern trend is to use only aluminum 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 ion. Fig. 1 Cross-section of a 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. 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. 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. Figure 2. Components of the diesel engine  Materials used for engine parts: S. Name of the Parts Materials of Construction No. 1. Cylinder head Cast iron, Cast Aluminium 2. Cylinder liner Cast steel, Cast iron 3. Engine block Cast iron, Cast aluminum, Welded steel 4. Piston Cast iron, Aluminium alloy 5. Piston pin Forged steel, Casehardened steel. 6. Connecting rod Forged steel. Aluminium alloy. 7. Piston rings Cast iron, Pressed steel alloy. 8. Connecting rod bearings Bronze, White metal. 9. Main bearings White metal, Steel backed Babbitt base. 10. Crankshaft Forged steel, Cast steel 11. Camshaft Forged steel, cast iron, cast steel, 12. Timing gears Cast iron, Fiber, Steel forging. 13. Push rods Forged steel. 14. Engine valves Forged steel, Steel, alloy. 15. Valve springs Carbon spring steel. 16. Manifolds Cast iron, Cast aluminum. 17. Crankcase Cast iron, Welded steel 18. Flywheel Cast iron. 19. Studs and bolts Carbon steel. 20. Gaskets Cork, Copper, Asbestos. PRINCIPLES OF OPERATION OF IC ENGINES: FOUR-STROKE CYCLE DIESEL ENGINE In four-stroke cycle engines there are four strokes completing two revolutions of the crankshaft. These are respectively, the suction, compression, power and exhaust strokes. In Fig. 3, the piston is shown descending on its suction stroke. Only pure air is drawn into the cylinder during this stroke through the inlet valve, whereas, the exhaust valve is closed. These valves can be operated by the cam, push rod and rocker arm. The next stroke is the compression stroke in which the piston moves up with both the valves remaining closed. The air, which has been drawn into the cylinder during the suction stroke, is progressively com- pressed as the piston ascends. The compression ratio usually varies from 14:1 to 22:1. The pressure at the end of the compression stroke ranges from 30 to 45 kg/cm2. As the air is progressively compressed in the cylinder, its temperature increases, until when near the end of the compression stroke, it becomes sufficiently high (650-80O oC) to instantly ignite any fuel that is injected into the cylinder. When the piston is near the top of its compression stroke, a liquid hydrocarbon fuel, such as diesel oil, is sprayed into the combustion chamber under high pressure (140-160 kg/cm2), higher than that existing in the cylinder itself. This fuel then ignites, being burnt with the oxygen of the highly compressed air. During the fuel injection period, the piston reaches the end of its compression stroke and commences to return on its third consecutive stroke, viz., power stroke. During this stroke the hot products of combustion consisting chiefly of carbon dioxide, together with the nitrogen left from the compressed air expand, thus forcing the piston downward. This is only the working stroke of the cylinder. During the power stroke the pressure falls from its maximum combustion value (47-55 kg/ cm2), which is usually higher than the greater value of the compression pressure (45 kg/cm2), to about 3.5-5 kg/cm2 near the end of the stroke. The exhaust valve then opens, usually a little earlier than when the piston reaches its lowest point of travel. The exhaust gases are swept out on the following upward stroke of the piston. The exhaust valve remains open throughout the whole stroke and closes at the top of the stroke. The reciprocating motion of the piston is converted into the rotary motion of the crankshaft by means of a connecting rod and crankshaft. The crankshaft rotates in the main bearings, Fig. 3. Principle of four-stroke engine which are set in the crankcase. The flywheel is fitted on the crankshaft in order to smoothen out the uneven torque that is generated in the reciprocating engine. TWO-STROKE CYCLE DIESEL ENGINE: The cycle of the four kind of stroke of the piston (the suction, compression, power and exhaust strokes) is completed only in two strokes in the case of a two-stroke engine. The air is drawn into the crankcase due to the suction created by the upward stroke of the piston. On the down stroke of the piston, it is compressed in the crankcase, The compression pressure is usually very low, being just sufficient to enable the air to flow into the cylinder through the transfer port when the piston reaches near the bottom of its down stroke. The air thus flows into the cylinder, where the piston compresses it as it ascends, till the piston is nearly at the top of its stroke. The compression pressure is increased sufficiently high to raise the temperature of the air above the self-ignition point of the fuel used. The fuel is injected into the cylinder head just before the completion of the compression stroke and only for a short period. The burnt gases expand during the next downward stroke of the piston. These gases escape into the exhaust pipe to the atmosphere through the piston uncovering the exhaust port.  Modern Two-Stroke Cycle Diesel Engine The crankcase method of air compression is unsatisfactory, as the exhaust gases do not escape the cylinder during port opening. Also, there is a loss of air through the exhaust ports during the cylinder charging process. To overcome these disadvantages blowers are used to pre- compress the air. This pre-compressed air enters the cylinder through the port. An exhaust valve is also provided which opens mechanically just before the opening of the inlet ports Fig. 4 Principle of two-stroke cycle diesel engine (Fig. 4). FOUR-STROKE SPARK IGNITION OR PETROL ENGINE In this gasoline is mixed with air, broken up into a mist and partially vaporized in a carburetor. The mixture is then sucked into the cylinder. There it is compressed by the upward movement of the piston and is ignited by an electric spark. When the mixture is burned, the resulting heat causes the gases to expand. The expanding gases exert a pressure on the piston (power stroke). The exhaust gases escape in the next upward movement of the piston. The strokes are similar to those discussed under four-stroke diesel engines. The compression ratio varies from 4:1 to 8:1 and the air-fuel mixture from 10:1 to 20:1. TWO-STROKE CYCLE PETROL ENGINE The two-cycle carburetor type engine makes use of an airtight crankcase for partially compressing the air-fuel mixture (Fig. 5). As the piston travels down, the mixture previously drawn into the crankcase is partially compressed. As the piston nears the bottom of the stroke, it uncovers the exhaust and intake ports. The exhaust flows out, reducing the pressure in the cylinder. When the pressure in the combustion chamber is lower than the pressure in the crankcase through the port openings to the combustion chamber, the incoming mixture is deflected upward by a baffle on the piston. As the piston moves up, it compresses the mixture above and draws into the crankcase below a new air-fuel mixture. The, two-stroke cycle engine can be easily identified by the air-fuel mixture valve attached to the crankcase and the exhaust Port located at the bottom of the cylinder.  Fig. 5 Principle of operation of two stroke petrol engine COMPARISON OF CI AND SI ENGINES The CI engine has the following advantages over the SI engine. 1. Reliability of the CI engine is much higher than that of the SI engine. This is because in case of the failure of the battery, ignition or carburetor system, the SI engine cannot operate, whereas the CI engine, with a separate fuel injector for each cylinder, has less risk of failure. 2. The distribution of fuel to each cylinder is uniform as each of them has a separate injector, whereas in the SI engine the distribution of fuel mixture is not uniform, owing to the design of the single carburetor and the intake manifold. 3. Since the servicing period of the fuel injection system of CI engine is longer, its maintenance cost is less than that of the SI engine. 4. The expansion ratio of the CI engine is higher than that of the SI engine; therefore, the heat loss to the cylinder walls is less in the CI engine than that of the SI engine. Consequently, the cooling system of the CI engine can be of smaller dimensions. 5. The torque characteristics of the CI engine are more uniform which results in better top gear performance. 6. The CI engine can be switched over from part load to full load soon after starting from cold, whereas the SI engine requires warming up. 7. The fuel (diesel) for the CI engine is cheaper than the fuel (petrol) for SI engine. 8. The fire risk in the CI engine is minimized due to the absence of the ignition system. 9. On part load, the specific fuel consumption of the CI engine is low. ADVANTAGES AND DISADVANTAGES OF TWO-STROKE CYCLE OVER FOUR- STROKE CYCLE ENGINES Advantages: 1) The two-stroke cycle engine gives one working stroke for each revolution of the crankshaft. Hence theoretically the power developed for the same engine speed and cylinder  volume is twice that of the four-stroke cycle engine, which gives only one working stroke for every two revolutions of the crankshaft. However, in practice, because of poor scavenging, only 50-60% extra power is developed. 2) Due to one working stroke for each revolution of the crankshaft, the turning moment on the crankshaft is more uniform. Therefore, a two-stroke engine requires a lighter flywheel. 3) The two-stroke engine is simpler in construction. The design of its ports is much simpler and their maintenance easier than that of the valve mechanism. 4) The power required to overcome frictional resistance of the suction and exhaust strokes is saved, resulting in some economy of fuel. 5) Owing to the absence of the cam, camshaft, rockers, etc. of the valve mechanism, the mechanical efficiency is higher. 6) The two-stroke engine gives fewer oscillations. 7) For the same power, a two-stroke engine is more compact and requires less space than a four- stroke cycle engine. This makes it more suitable for use in small machines and motorcycles. 8) A two-stroke engine is lighter in weight for the same power and speed especially when the crankcase compression is used. 9) Due to its simpler design, it requires fewer spare parts. 10) A two-stroke cycle engine can be easily reversed if it is of the valve less type. Disadvantages: 2. The scavenging being not very efficient in a two-stroke engine, the dilution of the charges takes place which results in poor thermal efficiency. 3. The two-stroke spark ignition engines do not have a separate lubrication system and normally, lubricating oil is mixed with the fuel. This is not as effective as the lubrication of a four-stroke engine. Therefore, the parts of the two-stroke engine are subjected to greater wear and tear. 4. In a spark ignition two-stroke engine, some of the fuel passes directly to the exhaust. Hence, the fuel consumption per horsepower is comparatively higher. 5. With heavy loads a two-stroke engine gets heated up due to the excessive heat produced.At the same time the running of the engine is riot very smooth at light loads. 6. It consumes more lubricating oil because of the greater amount of heat generated. 7. Since the ports remain open during the upward stroke, the actual compression starts only after both the inlet and exhaust ports have been closed. Hence, the compression ratio of this engine is lower than that of a four-stroke engine of the same dimensions. As the efficiency of an engine is directly proportional to its compression ratio, the efficiency of a two-stroke cycle engine is lower than that of a four-stroke cycle engine of the same size.