 Next session on the performance of IC engines, we are going to discuss air standard cycle and especially auto cycle. I am Professor Vivek Satay from Mechanical Engineering Department, Valchand Institute of Technology, Sohlapur. Now, let us see what is the outcome of this particular session. You will be able to evaluate and analyze auto cycle. What is expected under this? You must know how to draw the cycle on PV diagram on the TS diagram and possibly you will be able to analyze the expression for efficiency of the auto cycle. Now, before going into the discussion, I will make one say concept clear of air standard efficiency. Now, this is the question that why we require air standard efficiency for analysis. The thing is clear, Karnot cycle is the ideal cycle and very important thing about Karnot is that Karnot never assumes any working medium means Karnot cycle is supposed to be the ideal cycle in which heat supplied and heat rejection say took place with the reservoirs and you know that concept of reservoir is a thought, an idea means we cannot have such reservoir as such in practical cases. In practical cases, either we have to burn air, we have to burn fuel or burn something which can produce motive power. Now, one limitation of Karnot cycle. Now, first thing is limitation I will talk about. If I ask you what is the limitation of Karnot cycle? Can you tell me, I will ask you the question, what are the processes in the Karnot cycle? Yes, they are two isentropics and two isotherms that is true, but how they are connected whether adiabatic is connected to adiabatic or isentropic is connected to isentropic or isentropic connected to isothermal. Yes, if you have a doubt that I can have a isentropic process connected to an isentropic process, can you answer me? I ask a simple question, forget about it, this is the PV diagram, this is the PV diagram in which this is my isentropic, this is my isentropic process that is PV raise to gamma is equal to constant and suppose this is my another isentropic process, say 2 to 3, 2 to 3. Now this may be up or down, it does not it makes no difference because I can have any process which is isentropic and any process which is 1, 2, 3 and isentropic. So what has happened? This process is also PV raise to gamma and this is also PV raise to gamma. Now the salient question is what has happened? Two isentropics have crossed each other, two isentropics have crossed each other. Now when we think of a Karnot engine where there is a isentropic process and isothermal process, isentropic process and isothermal process, this cycle is important means isentropic is connected to isothermal, isothermal is connected to isentropic because if you see the TS diagram that will be picture will be more clear to you, when I draw the TS diagram it looks like this 1, 2, 3 and 4. So what has happened now? This is isentropic followed by isothermal, isentropic followed by isothermal and what is very important? This is compression, this is compression followed by expansion, compression followed by sorry this is expansion followed by compression means this is a compression, this is expansion, this is the compression, this is the expansion. So what is wonderful thing is this is compression, compression, expansion, expansion, this is very important expansion, expansion and this is compression and this is compression. Now many students wonder how we can have a process which is compression, compression followed by expansion, expansion, this is the question that I am asking you, that whenever we have two processes isothermal and isentropic, they follow each other, theoretically it may have practical problems that we are going to see in detail right now. But if I ask you is this possible, my question is is this system possible, yes, can we have two isentropics meeting each other, yes, it is not possible, it is not possible, now let us see what it means. See this is 1 to 2, this is 3 to 1, if I connect one process here, if I connect one process here by some process and suppose this process is isothermal, this process is isothermal, have you got an idea, so I have this one adiabatic, this is an adiabatic and this is isothermal, it is reversible adiabatic, it is adiabatic, it is adiabatic and reversible, this is adiabatic and reversible, so I can call this as isentropic process. If I connect these two points by an isothermal process, then what has happened, I have got area under the curve, I have got area under the curve, now what is area under the curve, it is work done, it is work done. Now you will say that yes sir, we can calculate area under the curve, we can take the area under this curve, area under this curve, minus area under this curve and I can get the answer, it means that you have not understood these statements of second law of thermodynamics. Now let us see, actually in adiabatic do we have heat transfer or heat interaction, no, so heat transfer in this process and in this process is 0, so q is equal to 0 in this process and in this process. Then this is an expansion, in this situation it is expansion, if I reverse the cycle it may be compression, but as this is expansion there is a heat interaction, so q is there, so whenever there is a heat interaction and that is a heat supplied, why heat supplied? Because it is expansion, so when isothermal expansion is there and there is a heat supplied to the system, what has happened as a system for three processes 1, 2, 3, 1, this is cycle, this is what? A cycle, in the cycle I have supplied heat q s and I have applied and I have obtained the work w, so what I am doing, I am interacting with a single reservoir, I am getting a work done from the system, so I am getting this work done from the system, so this is nothing but it is 1 T engine, 1 T engine is thermodynamically not allowed and that is why what has happened, that cannot cycle if you see, it is always a process, this process turns out to be heat rejection, supply, this turns out to be heat supplied, so we have here heat supplied to the system, this is heat rejection because of the nature of the isothermal process, now the question is, is this cycle practically feasible? Because isentropic process is a very fast process, isothermal process is a slow process, again isentropic is a fast process and again it is a slow process, so what has happened, we have got a fast process followed by a slow process, fast process followed by a slow process, it is not possible to have mechanical linkage which can handle this particular process in detail, so what happened, though it is a ideal cycle, though it gives you the maximum value of the efficiency that is possible, it is a guideline, then actually in the engine we burn fuel, that may be petrol, that may be diesel, that may be LPG, that may be CNG, that may be mixed fuel, that may be any other thing, we are discussing that part in detail afterwards, but right now if you burn fuel what will happen, there is a process which is completely different than the ideal one, but still we require some ideal process, so that we can compare our actual process with that particular process and that ideal process instead of your Carnot engine, we assume that it is an air standard cycle, so what is air standard cycle, in air standard cycle we assume that air is a working medium, so very important things that we must know about this air standard efficiency is that, there are various assumptions that we make and these are very important assumptions that we have, the first important assumption is we assume that it is an ideal gas, it is an ideal gas, see there is a difference, Carnot engine is ideal engine, but the air standard efficiency we evaluate using ideal gas as a working fluid, now when we have got an ideal gas it uses, it obeys PV is equal to MRT, there is no change in CP, CP and CV they are constant, so these are the basic two assumptions, there is no, there is a mass conservation that is M is equal to constant, so with this basic three assumptions we go for the analysis of cycles, so there are some standard cycles for which we are evaluating the efficiencies, one is the auto cycle, second is a diesel cycle and third is a dual cycle, so auto cycle is used for petrol engines, diesel cycle is used for diesel engines and dual is also used for diesel engines, so that part we will see in the next session, so in the next session we will go for auto cycle analysis in which we will draw the PV diagram and TS diagram, we will derive the expression for efficiency of auto cycle and the same procedure we will be adopting for finding out the efficiencies for diesel and dual, I think that part you can do as an assignment afterwards, now those who are interested in studying the further part about the subject, they can go for internal combustion engine Heavood or internal combustion engine by Gupta, so now your picture is clear, we started with our thermodynamics, thermodynamic analysis of Carnot cycle, then we studied that Carnot cycle is valid only for 2T engine, if there are multiple resource reservoirs, sources and sinks, we have to go for classes in equality, then after that we have seen that though it is a Carnot engine is ideal engine, the practical engine will not work on that because it is a fast process followed by a slow process, mechanical linkage is not possible, so we have using the actual cycles are using fuels, but for that we are again some ideal that is called as an air standard cycle and for that air standard cycles, say we are studying in detail about auto, diesel and dual cycle, once we study that then we can go further for the actual cycles, so what is the difference between the ideal cycle that is air standard cycle and the actual cycle and then we can do the comparison, but remember always Carnot efficiency is going to be the guiding limit for maximum efficiency of an engine operating between the highest temperature in a cycle and the lowest temperature in a cycle, so thank you for this particular session, in the next session we will meet and discuss the auto cycle in detail, thank you once again.