Week 2 Air standard Cycle

AIM

We are currently working on developing code for the air standard Otto cycle to extract the pressure versus volume diagram and calculate the thermal efficiency of the cycle.

_{The ideal Otto cycle is a thermodynamic cycle that describes how a spark-ignition internal combustion engine works. It consists of four processes:}

• _{Adiabatic compression: Process 1 → 2}
• _{Isochoric heat addition: Process 2 → 3}
• _{Adiabatic expansion: Process 3 → 4}
• _{Isochoric heat removal: Process 4 → 1}
  

_{The ideal Otto cycle has the following characteristics:}

_{There is no heat entering or leaving the gas during the compression and power strokes}

• _{There are no friction losses}
• _{Burning occurs instaneously at constant volume}

_{In reality, the ideal cycle doesn't occur and there are many losses associated with each process. The shape of the p-V diagram for a real cycle is similar to the ideal, but the area (work) is always less than the ideal value.}

_{Otto cycle}

_{The Otto cycle is the ideal cycle for spark-ignition engines. It is named after Nikolaus A. Otto. He built a successful four-stroke engine in 1876 in Germany using the cycle proposed by Frenchman Beau de Rochas in 1862. The main processes occurring in an Otto cycle are as follows:}

_•

_{Isentropic compression}

_•

_{Constant volume heat addition}

_•

_{Isentropic expansion}

_•

_{Constant volume heat rejection}

_{Both the intake and the exhaust valves are closed, and the piston is at its lowest position. During the compression stroke, the piston moves upward, compressing the air–fuel mixture. Shortly before the piston arrives at the highest position, the spark plug fires and the mixture ignites, raising the pressure and temperature of the system. The high-pressure gases force the piston down, which sequentially forces the crankshaft to rotate, creating a useful work output through the expansion or power stroke. Close to the end of the expansion stroke, the exhaust valve opens and the combustion gases that are above atmospheric pressure rush out of the cylinder through the open exhaust valve. This process is called exhaust blowdown, and most combustion gases exit the cylinder by the time the piston reaches the lowest position. The cylinder is still filled by the exhaust gases at a lower pressure at the lowest position. The piston moves upward one more time, purging the exhaust gases through the exhaust valve, and down a second time, drawing in fresh air-fuel mixture through the intake valve. It is noted that the pressure in the cylinder is slightly above the atmospheric value during the exhaust stroke and slightly below during the intake stroke.}

_{A four-stroke cycle means that there is 1 cycle, 4 stroke and 2 revolutions, whereas a two-stroke cycle means that there is 1 cycle, 2 stroke and 1 revolution. The two-stroke engines are generally less efficient than their four-stroke counterparts but they are relatively simple and inexpensive, and they have high power-to-weight and power-to-volume ratios.}

_{Similar to other cycles, the actual cycle deviates from the ideal cycle. The ideal Otto cycle contains two strokes equivalent to one mechanical cycle or one crankshaft rotation. On the other hand, the actual engine operation contains four strokes equivalent to two mechanical cycles or two crankshaft rotations. This can be corrected by including intake and exhaust strokes in the ideal Otto cycle.}

Conclusion