ABSTRACT
Figure 2.1 shows a schematic representation of a spark ignited (SI) engine. For four-stroke engines that consist of the intake stroke, compression stroke, combustion stroke, and exhaust stroke, thermal energy is generated by the combustion of the compressed air-fuel mixture, and the thermal energy is transferred as the force acting on the piston. The force depends on the efficiency of the released energy conversion, which is called heat release, the air charge during the intake stroke, and the fuel injection. When the combustion finishes, the gas is pushed out through the exhaust valve. The opening-closing timing of the intake valve determines the amount of air charge, and the intake air mass flow rate depends also on the pressure and temperature of the intake manifold and the pressure and temperature of the cylinder. Hence, the variations of the pressure and temperature in the intake manifold cause the variation of the intake air mass flow rate. Furthermore, the produced thermal energy and the variations of the air mass flow rate passing the throttle valve and the intake valve follow the mass and energy conservation laws.
