THE FOUR-STROKE ENGINE This represents a simple piston engine system, which involves the use of an ignitable gas that does work on the system and drives the engine. Figure 87 is a four-stroke internal combustion engine described visually:
Figure 87.
There are four cycles: intake-exhaust, compression, ignition, and power. The compression stroke involves work being done on the system, increasing the pressure and temperature. There is heat transfer in the next part, causing a pressure increase and temperature increase. This happens so quickly in a combustion engine that volume is nearly (but not completely) constant. The final part, power is is (nearly) adiabatic process so that work is done to a greater degree because the pressure is greater. Exhaust leaves the system and the volume is returned to its initial state. During the first part, air is mixed with fuel during intake. In the second part, compression of the air-fuel mixture occurs in a process that is nearly adiabatic. Work is done on the compressed gas. In the power stroke, there is ignition of the air-fuel mixture, creating thermal energy that increases the pressure, pushing on the piston.
192
