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2 OTTO CYCLE This is the cycle of many automobile engines and other four-stroke SI engines.In a real engine, the beginning of the stroke is affected by the intake valve not being fully closed until slightly after BDC.The intake stroke of the Otto cycle starts with the piston at TDC and is a constant- pressure process at an inlet pressure of one atmosphere (process 6-1 in Fig.This ideal cycle is called an Otto cycle, named after one of the early developers of this type of en- gine.The second stroke of the cycle is the compression stroke, which in the Otto cycle is an isentropic compression from BDC to TDC (process 1-2).to 35?C hotter than the surrounding air temperature.1.1).

2 OTTO CYCLE
This is the cycle of many automobile engines and other four-stroke SI engines. For
analysis, this cycle is approximated by the air-standard cycle shown in Fig. 1. This ideal
cycle is called an Otto cycle, named after one of the early developers of this type of en-
gine. The Otto cycle is the air-standard model of most four-stroke SI engines of the last
140 years, including many of today’s automobile engines.
The intake stroke of the Otto cycle starts with the piston at TDC and is a constant-
pressure process at an inlet pressure of one atmosphere (process 6-1 in Fig. 1). This is a
good approximation to the inlet process of a real engine at WOT, which will actually be
at a pressure slightly less than atmospheric due to pressure losses in the inlet air flow.
The temperature of the air during the inlet stroke is increased as the air passes through
the hot intake manifold.The temperature at point 1 will generally be on the order of 25°
to 35°C hotter than the surrounding air temperature.
The second stroke of the cycle is the compression stroke, which in the Otto cycle is
an isentropic compression from BDC to TDC (process 1-2). This is a good approxima-
tion to compression in a real engine, except for the very beginning and the very end of
the stroke. In a real engine, the beginning of the stroke is affected by the intake valve
not being fully closed until slightly after BDC.