 Good morning everybody, myself Prasanna Ekhande, working as an assistant professor in Department of Mechanical Engineering at Walch instead of Technology, Solapur, Maharashtra. Today we will discuss regarding Introduction to Autocycle. At the end of this session you will be able to describe the Otto cycle means it is working you can describe very well with the help of the PV diagram at the end of this session. Now, what is Otto cycle? Otto cycle is one of the thermodynamic cycle which is used for the different applications in the engineering field especially in the thermodynamics or the heat transfer field. Now Otto cycle here Otto stands for the name of the scientist remember that this Otto is not AUTO this Otto is O double TO that is a scientist name on which this cycle has been denoted. Now this is an idealized thermodynamic cycle so whatever the idealized thermodynamic cycles are there amongst that this is one of the cycle there is a Rankine cycle there is a Carnot cycle, Otto cycle, Diesel cycle these are the idealized thermodynamic cycles out of that Otto is one. Now it describes the function of the typical spark ignition piston engine what is meant by the spark ignition? The ignition of the fuel air mixture takes place because of generating the spark either it is with the spark plug or with other modes we can have the generation of the spark and due to that there will be combustion of the fuel or combustion of air fuel mixture so it describes the functioning of typical spark ignition piston engine. So spark ignition for that we can use the short form as a SI spark ignition SI engine. Now third point is the Otto cycle consists of four processes first is isentropic compression second is the heat addition at constant volume third is again isentropic expansion fourth is rejection of heat at the constant volume. Now here isentropic for that we can have the another word as adiabatic and for constant volume we can have the another word as a isochoric process. So isentropic means the entropy remains constant adiabatic or the isentropic that is the name for this alternate names are there. So here the entropy remains constant means there is no heat transfer takes place between the wall of the engine and constant volume means the volume remains constant during the process which can be also called as a isochoric. So first is adiabatic compression second heat addition takes place at constant volume third is the adiabatic or the isentropic expansion and the last fourth is the rejection of heat at constant volume and the one more point which is important in view of the Otto cycle is the system is defined to be the mass of air that is taken in from the atmosphere into the cylinder which is compressed by the piston then it is heated by the spark ignition of the added fuel then allowed to expand and the finally exhausted back to the atmosphere. So these are the few important things with the Otto cycle. Now with respect to this PV diagram we will have the discussion over the Otto cycle it is functioning it is working. Now P stands for pressure V stands for volume TDC means top dead center and BDC means bottom dead center. You know that this is a PV diagram P is on the x axis V is on the y axis sorry P is on the y axis V is on the x axis and when we consider this origin point with respect to this there will be volume in the say x direction positive side. So here up to TDC whatever the volume of the cylinder is that is called as a clearance volume then between TDC and BDC that is called as a swept volume and up to BDC from original point origin point that is called as a total volume and the distance between TDC and BDC is called as a stroke length that length is called as a stroke length. Now the different colors are shown over here for the different processes. The first process if we if we consider from starting at point O means the cylinder piston in the cylinder piston is at the extreme top side. So top dead center and it starts moving in the downward direction. So here from TDC to BDC the movement of the piston is there in the cylinder during which there is a suction of the air fuel mixture or if you have the latest technology in that case the air will be sucked inside the cylinder during the say first process that is the suction stroke from point number 0 to point number 1. So process 0 to 1 is the air is drawn into the cylinder at constant pressure. Earlier there was a say mixture of the air and fuel which was taken from the carburetor but nowadays we have the direct fuel injection system that is why here only air is drawn during the first process that is the 0 to 1. Now the second point is the point number 1 first or the starting is 0 from 1 point to 2 then second process will execute. So 1 to 2 is the adiabatic or isentropic compression whatever the air is taken inside the cylinder now that is compressed because of the movement of the piston from bottom dead center to the top dead center. So whatever the volume is inside the cylinder that will be compressed till top dead center is reached by the piston. Now the whatever the volume of the air is left in the clearance area that is at very high pressure means the pressure increases from point 1 to point 2 means from atmospheric pressure to certain higher pressure there will be compression of the air. Now at point 2 or when the piston reaches the top dead center at that time spark is ignited and there will be injection of the fuel also. So injection of the petrol will be there because auto cycle is mainly used for the petrol as a fuel. So here due to the say spark ignition injection of the fuel the heat addition is there to the cycle. So process 2 to 3 is the constant volume heat transfer to the working gas. So the pressure rises from point number to the point number 3 which is the maximum pressure in the cylinder, maximum pressure in the cycle which is reached because of say combustion of the fuel, composition of the petrol air mixture. So after reaching the point number 3 means here there is a no piston movement from point number 2 to 3 because there is a constant volume. Now after say completion of this process 2 to 3 the 4th process that is 3 to 4 is executed which is a adiabatic or isentropic expansion which is called as a power stroke. This is a stroke in which we will get the power from the engine means when the piston moves from TDC to BDC we get the power from the engine whereas the other strokes are the idle whereas we have to incur the some amount of the energy to that and that is with the help of the flywheel. So third point from that when the process is executed expansion will be there and volume increases from V3 to V4 means from top dead center to bottom dead center the expansion takes place. Now the because of expansion of the gas the volume decreases volume increases and the pressure decreases. So pressure comes down from the point number 3 to point number 4 means P3 to P4 P4 is the maximum highest whereas P4 is the pressure which is more than atmospheric but less than but it is not equivalent to that although the piston reaches the bottom dead center. Now what happens at this position the exhaust valve opens exhaust valve opens and whatever the gases are inside the cylinder are exhausted in the atmosphere because of opening of the exhaust gas and the gases burnt gases passes to the atmosphere through the silencer. But still what happens because of the opening the maximum gases passes to the atmosphere pressure drops from 4 to 1. So this is 4 to 1 is the heat rejection to the atmosphere. So here what happens the pressure drops to the atmospheric pressure once the gases are exhausted from the cylinder at point number 1 or say reaching the piston through the bottom dead center and opening of the exhaust valve. Now still there are the burnt gases inside the cylinder which are to be expelled in the atmosphere and that process takes place from 1 to 0 the mass of air is released or expelled to the atmosphere in the constant pressure condition. So piston moves from bottom dead to the top dead center means process 1 to 0 will executed and whatever the gases are there those are exhausted into the atmosphere and the piston reaches the top dead center position at this time then exhaust valve closes and there will be opening of the suction valve and the cycle repeats means again there will be suction of the air from 0 to 1. So air is drawn into the cylinder at constant pressure compression of that takes place when the suction valve closes at point number 1 because during 0 to 1 process there is a suction of the air because of open condition of the suction valve or the intake valve and then when the piston reaches the bottom dead center position that intake or the suction valve closes. Now both the valves are in the closed condition compression takes place then heat addition takes place during the 2-3 process which can be indicated as a Q supplied then the expansion takes place from 3 to 4 again the opening of the exhaust valve is over here at point number 4 and the pressure drops and then the remaining gases burn gases are expelled to the atmosphere due to the opening of the suction exhaust valve or the outlet valve and the cycle completes or the repeated. So this is the working of auto cycle I think you have understood this how the process are executed what are the different processes is it yes nice thank you the reference books the list is in front of you.