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SIMULATION ANALYSIS ON ENGINE PERFORMANCE FOR SPARK IGNITION ENGINE
Rosli Abu Bakar, Azhar Abdul Aziz, Low Cheng Yee & Chong Chin Lee Automotive Development Centre Fakulti Kejuruteraan Mekanikal Universiti Teknologi Malaysia (UTM) 81310 UTM Skudai Tel: 607 5534752 Fax: 607-5566159 E-mail: rosliab@fkm.utm.my Abstract
The simulation on the performance of a spark ignition engine using differenttypes of fuel i.e. compressed natural gas, hydrogen and gasoline has been developed. Compressed natural gas and hydrogen were studied due to their ability to produce low exhaust emission compared to the conventional fuel. The simulation was written in computer language using the stage-by-stage approach, which divided into Ideal Cycle Simulation, Fuel-air Cycle Simulation, Progressive Combustion, andActual Cycle Simulation. From this simulation results, the full load engine performance has been compared over a range of different engine speed, compression ratio and equivalence ratio. It is found that qualitative trend of the engine performance is similar while quantitative characteristics are different from those of gasoline engines. The limits and trends of the performance enable one to seewhat one could expect from an engine working with such system variables. To confirm predictions of thermodynamics modelling and to define engine performance, comparisons between simulation results and experimental result are also included.

Keywords: Computer simulation, Spark ignition engine, Compressed natural gas, Hydrogen, Gasoline, Ideal cycle simulation, Progressive combustion simulation,and Actual Cycle Simulation, Engine performance. 1. Introduction
Simulation is the process of formulating a model of a physical system using a mathematical model representing the actual processes through a set of algebraic, differential or integral equations and the analysis, which is made using a computer. In recent years, the availability of fast digital personal computers has revolutionizedthe simulation techniques, which before were not amenable under the purview of simulation studies. One such area is the computer simulation of spark ignition engines. The technology of simulation can make major contributions to engine engineering at different levels of generality or detail, corresponding to different stages of model development. Designs of an internal combustion engine rely heavilyon previous experience and know-how. Extensive testing of the prototype is necessary and selecting the best design from such testing is a difficult task. A simulation on engine performance is extremely necessary because: (i) It is economical compared to experimental study. (ii) It serves as a tool for a better understanding of the variables involved and their effect on engine performance. (iii) Itsystematizes knowledge obtained through expensive engine testing. (iv) It reduces time-consuming tests by narrow down the variables involved and thus saves time.

(v) It helps in optimising the engine design for a particular application. The engine converts heat energy from chemical reaction of fuel and oxygen, into mechanical energy. Since the heat energy is derived from the fuel, thecharacteristics of the fuel used have considerable influence on the efficiency and performance of the engines. Internal combustion engine can be operated on different types of fuels such as liquid, gaseous and solid fuels. Among them, gaseous fuels are ideal fuels and pose very few problems in using them in internal combustion engines. Being gaseous, they mix more homogeneously with air and eliminate thedistribution and starting problems that are encountered with liquid fuels. Even though the gaseous fuels are the most ideal for internal combustion engines, storage and handling problems restrict their use in automobiles. Being a viable alternative to gasoline for vehicular application, compressed natural gas (CNG) is the most common form of on-board storage for gaseous fuels nowadays. Due to...