11. Development of a Bi-fuel SI Engine Model

Natural gas is a promising alternative fuel, with the potential to meet strict engine emission regulation, and is cheaper than other fuels in many countries. Use of natural gas as an automotive fuel may bring a reduction of environmental pollutants and reduce the economic costs of the transportation sector. As an intermediate step, and an alternative to dedicated CNG engines bi-fuel engines, powered by gasoline and compressed natural gas (CNG), provide many an opportunity. In support of the development of such engines and to aid analysis and improvement in this study, a four-stroke bi-fuel spark ignition (SI) engine model is developed. The engine model is based on the two-zone combustion model, and it has the ability to simulate turbulent combustion and compared to computational fluid dynamic (CFD) models it is computationally faster and efficient. The selective outputs are cylinder temperature and pressure, heat transfer, brake work, brake thermal and volumetric efficiency, brake torque, brake power (BP), brake-specific fuel consumption (BSFC), brake mean effective pressure (BMEP), concentration of CO₂, brake-specific CO (BSCO) and brake-specific NO _x (BSNO _x ). In this research, the effect of engine speed, equivalence ratio and performance parameters using gasoline and CNG fuels are analysed. In addition, the model has been validated by experimental data using the results obtained from bi-fuel engine tests. Therefore, this engine model is capable for prediction, analysis and useful for optimisation of the engine performance parameters and minimisation of the emissions. In addition, in this chapter, a specific bi-fuel engine is studied and discussed that is used in the vast majority (almost are taxi). Therefore, the model and its results are significant.