 Hello everybody, myself P. V. Ekhande working as an assistant professor in Department of Mechanical Engineering at Valchin Institute of Technology, Solapur. Today we will see the comparison between two-stroke and four-stroke IC engines that is a two-stroke and four-stroke internal combustion engines. At the end of these sessions, students will be able to explain the difference between two-stroke and four-stroke internal combustion engines. Now the basic working of two-stroke and four-stroke engines that is known to you. In two-stroke engines, the operations suction, compression, expansion and exhaust, these are there, whereas the same are there in case of the four-stroke engines, but how that is performed or what is the difference by considering the engine design or engine size. So all those points will cover in this discussion. So first point of the differentiation or comparison is the cycle, the cycle which is used that is different for the different types of the fuel. So for petrol engine, the auto cycle is there and for diesel engine, there is a diesel cycle. So this cycle is completed in two-stroke in case of the two-stroke engines and for completion of this cycle, the two-strokes are completed by one revolution of the crankshaft whereas in case of the four-stroke engine, for completion of the cycle, whether it is a diesel engine or the auto cycle, there we require the four different strokes for completion of the cycle. Means we have the four different strokes in case of the four-stroke engine and for completion of this four-stroke engine cycle, we require the two revolutions of the crankshaft. So this is the first point of the comparison. Now second point of the comparison is related to the operations which are carried out during the completion of the one-cycle. So in case of the two-stroke engine, the overlapping of the operation is there. So the operations suction, compression, exhaust, expansion, these are completed in combination in case of the two-stroke engine. So that's why we can say that there is a overlapping of the operations in case of the two-stroke engine whereas in case of the four-stroke engine, these each operations are completed separately or distinctly. The first stroke will be the suction stroke, second will be the compression stroke, third will be the expansion of the gases and fourth will be exhausting or expelling of the gases from the cylinder to the atmosphere. So these all operations are performed separately in case of the four-stroke engine. Now the next point of the comparison is the size and weight which is required for this two-stroke or the four-stroke engine. The size and weight is less for the two-stroke engine whereas the size or the weight will increase in case of the four-stroke engine. That's why the engine is bulky in case of the four-stroke engine because of the number of parts which are required over there are increased. So there we need the valves, whirling system etc. So the engine becomes bulky in case of the four-stroke engine. Have you understood these three comparison points that is cycle completion in two different strokes or four strokes required for that four-stroke engine overlapping of the operations in case of the two-stroke and the distinct operations are there and size and weight which is less and heavy in case of the four-stroke engine. Now you think how to recognize the two-stroke engine and four-stroke engine if that is kept in front of you. Can you tell? Absolutely right. We can recognize the engine with the help of the whirling system if that is available we can say that as a four-stroke engine if whirling system is not available we can consider that as a two-stroke engine. Now the next points of the comparison those are fourth point is thermal efficiency which is less in case of the two-stroke engine whereas thermal efficiency is higher in case of the four-stroke engine. Now here for this comparison point we must think of the operations or the working of the two-stroke engine why the thermal efficiency is the less in case of the two-stroke engine because there is the wastage of the fuel during the exhausting of the gases as there is the entry of the fresh fuel charge from the transfer port in the cylinder at the same time the exhaust is going on and that is why the some amount of fuel is getting wasted along with the exhaust gases that is why the thermal efficiency is less in case of the two-stroke engine. But that is not the case in case of the four-stroke engines where the thermal efficiency is higher why this is higher because the suction of the charge or the suction of petrol air mixture in case of the petrol engine or thus in case of the diesel engine there will be the ignition of the diesel during the third stroke where the diesel is injected. So that charge ignition is taking place in separate stroke and that is why there is no wastage of the diesel or the petrol in case of the four-stroke engine and that is why the thermal efficiency is high in case of the four-stroke engine. Now the next point of the comparison that is related to the cost of the engine now as we have seen in the earlier slide there is a light weight for the two-stroke engine and simple in design so that is why the simple construction leads to the lesser cost in case of the two-stroke engine whereas the heavy weight and the complicated valve mechanism that increases the cost in case of the four-stroke engine. So engine design as well as the manufacturing of those volume 16 valve parts that increases the cost of the four-stroke engine. Now the next point of the comparison that is related to the cooling required for the engine in case of the two-stroke engine the cooling system required is a that way or that needs the higher area or the better system because the consumption the ignition of the fuel takes place in one revolution for one time whereas the ignition of the fuel or the combustion of the fuel takes place in two revolutions of the engine for the four-stroke engine. So in case of the two-stroke engine there is a higher temperature developed in the engine parts and that's why we require the proper and the best cooling system or greater cooling system in case of the two-stroke engine to cool the engine at the faster rate whereas in case of the four-stroke engine the lesser cooling system is required as there is only one time combustion of the fuel takes place in two revolutions of the engine. So that is the main point where we are providing the cooling system to the greater extent in case of the two-stroke engine. Now the next point of the comparison that is related to the wear and tear of the engine we have seen that in case of the two-stroke engine the wear and tear of the engine will be more because there is the combustion taking place in each revolution for the engine in case of the two-stroke engine whereas the combustion of the fuel is once and there is the separate system wall system is provided for the four-stroke engine that's why the lesser wear and tear will be there in case of the four-stroke engine whereas here greater wear and tear is there because of the high speed of the engine the speed of this engine will be also greater as compared to the two-stroke four-stroke engine so that is one more point of the comparison where wear and tear is higher in case of the two-stroke engine and the next point of the comparison is the power produced for the same size of the engine that is more in case of the two-stroke engine and that is but natural because in case of the two-stroke engine in each revolution one power is generated one ignition takes place in each revolution and that ignition of the fuel leads to the generation of the power in each stroke and that's why engine is more power producing in case of the two-stroke whereas the power produced for the same size it will be lesser because in two revolutions it leads to one combustion then next points which are there those two points are related to the turning moment so in each stroke each revolution we are getting the one power stroke that's why it requires the more turning moment it generates the more uniform turning moment that's why the lighter flywheel will be sufficient for the two-stroke engine whereas for four-stroke engine we require the heavier flywheel because we have to store the power during one idle revolution of the cycle because in one revolution the power is generated and in other revolution the power is not generated so we must provide the heavier engine in case of the four-stroke engine and last this application the application of the two-stroke engine is for the mainly two wheelers that is scooters motorcycles and the cars buses or the four wheelers those are mainly provided with the four-stroke engine secondly in the ship propulsion also we can go for the two-stroke engine because there we need the heavy engine high power so that's why we can we have to provide the two-stroke engines for the ship propulsion