Bi-fuel SI Engine Model for Analysis and Optimization

Abstract

The natural gas as an alternative fuel has economical and environmental benefits. Bi-fuel engines powered by gasoline and compressed natural gas (CNG) are an intermediate and alternative step to dedicated CNG engines. The conversion to bi-fuel CNG engine could be a short-term solution to air pollution problem in many developing countries. In this paper a mathematical model of a bi-fuel four-stroke spark ignition (SI) engine is presented for comparative studies and analysis. It is based on the two-zone combustion model, and it has the ability to simulate turbulent combustion. The model is capable of predicting the cylinder temperature and pressure, heat transfer, brake work , brake thermal and volumetric efficiency, brake torque, brake specific fuel consumption (BSFC), brake mean effective pressure (BMEP), concentration of CO2, brake specific CO (BSCO) and brake specific NOx (BSNOx). The effect of engine speed, equivalence ratio and performance parameters using gasoline and CNG fuels are analysed. The model has been validated by experimental data using the results obtained from a bi-fuel engine. The results show the capability of the model in terms of engine performance optimization and minimization of the emissions. The engine used in this study is a typical example of a modified bi-fuel engine conversion, which could benefit the researchers in the field. 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 opportunities. With regard to the climatic situation of some countries, and considering the existence of broad networks of gas distribution natural gas can be a suitable alternative to conventional fuels. The growth of bi-fuel vehicle usage in some countries is dependent on local strategies for the gasification of vehicles, which can be categorized in different levels, for example: workshop conversion of vehicles (short-term approach), factory production of bi-fuel engines (mid-term approach) designing and producing base CNG engine (long-term approach) (2).Developing bi-fuel engines (gasoline and CNG) in the short and mid-term is a strategy for achieving the emission targets in some countries. Therefore, it is necessary to understand the engine performance in these cases. 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 specifically for simulation of turbulent combustion. Furthermore, a thermodynamics model of a bi-fuel SI engine in Matlab environment has been developed based on mathematical model that it described in section 2, and validated by experimental data. This model modified for CNG and gasoline and it has ability for evaluating of the engine performance and the emissions characteristic.