Ideal Engine Cycles

Ideal Engine Cycles

 Ideal Engine Cycles Otto Cycle The Otto cycle is a model of the real cycle that assumes heat addition at top dead center. The Otto cycle consists of four internally reversible cycles, that describe the process of an engine.


Process 1-2 is an isentropic compression of air and fuel, which occcurs when the piston moves from bottom dead center (BDC) to TDC. In this process air and fuel are compressed and ready for the second process.

Process 2-3 is a constant volume heat addition process where the air to fuel mixture is ignited.

Process 3-4 is an isentropic expansion, where work is done on the piston, but no heat is added. This process is referred to as the power stroke. The nal

 process, 4-1, is a constant volume heat removal that ends at BDC. Work and heat are important aspects of engines, that can be  . On the T -s diagram the area 1-4-a-b-1 corresponds to the heat rejected per unit of mass. corresponds to the heat added per unit of mass. The enclosed area shown represents the net heat added during the process. The area 1-2-a-b-1 in the p-v diagram corresponds to the work input per unit mass and area 3-4-b-a-3 corresponds to work output per unit mass. The net work done is interpreted by the enclosed , in the T -s diagram. In the Otto cycle there are therefore two processes that involve work but no heat transfer and two di erent processes that involve heat transfer but no work. The thermal e ciency of the otto cycle increases with increasing compression ratio. When the Otto cycle is analyzed on a cold air standard basis an expression relating the compression ratio, r, temperature and pressure is obtained from isentrropic properties.