Abstract:
The desired performance of a spark ignition engine is highly related to the position of the spark advance, and consequently to the beginning of the stable combustion inside cylinder. The magnitude of the generated ion current signal, measured by a sensor inside cylinder, is closely correlated to the cylinder pressure magnitude. In this research an improved mathematical model of a four stroke spark ignition engines is presented. In this simulation the geometrical parameters of the engine, valves and spark timing, air to fuel ratio, specific fuel consumption and engine operational conditions are considered during all four strokes of the engines. The engine is divided into some related subsystems namely; throttle body, intake manifold, fuel delivery system, intake and exhaust valves, E.G.R., torque production system, rotational dynamics and emission system. Each subsystem is modeled and the inter-relation between them has been considered. The model is derived based on a combination of thermodynamically relations and dynamical characteristics of engines. A new computer code is developed in Visual C++6 based on derived relations. This code may be considered as an appropriate means to investigate the performance of a given SI engine and to derive the emission results. The computer code is able to evaluate twelve combustion production species in a full thermodynamic equilibrium. Other engine performance quantities such as power, torque, thermal efficiency, work done by piston, pressure and temperature time histories are also evaluated in this simulation. Also, the computer code is able to simulate the ion current during the post flame period as a function of in cylinder pressure and temperature. It is shown that there is a strong correlation between the peak pressure position and the maximum current position. It is also shown that among all combustion products, the NO has the most contribution in generating electrical current and the contribution of the other species are negligible. In this work the contribution of different parameters in ion current generation is considered. By attention to the correlation between spark advance, peak pressure and the maximum ion current position for determining the optimal spark advance, a fuzzy logic controller is developed. The simulation results present a quite satisfactory performance of the closed loop system and robustness of the controller at the presence of the disturbance.