Combustion Characteristics of Spark Ignition Engine Fuelled by Compressed Natural Gas in a Direct Injection Compressed Natural Gas Engine

摘要

New alternative fuel is needed due to the increasing energy price of the conventional fuel (gasoline and diesel) couple with the environmental protection and fuel shortage which is a non-renewable fuel source. Research on improving the fuel economy and combustion characteristics of the internal combustion engine has become imperative. Compressed natural gas is the most promising alternative fuel to be utilized in the internal combustion engine. The reason being that the combustion characteristics of compressed natural gas generate a lower emission relative to conventional fuel. Thus, the purpose of this research was to study the combustion characteristics of a compressed natural gas in a direct injection compressed natural gas engine at stoichiometric and lean mixtures and quantitatively analyzed Cylinder pressure, Heat release rate and Mass fraction burned. The research was conducted experimentally under various engine conditions which were at stoichiometric and lean mixtures, wide open throttle and at various engine speeds so as to analyze the combustion characteristics of the engine. The result showed that, increasing the engine speed will increase the cylinder pressure due to the increase in burning velocity. While mass fraction burned also increase as the engine speed increase. This is due to the enhance turbulence within the engine combustion chamber. Heat release rate increase as the engine speed increases. This might largely be due to the increase in flame development duration within the combustion chamber. More so, the results also reveal that the maximum cylinder and heat release rate occurred at stoichiometric mixture. In addition, the maximum cylinder pressure for stoichiometric mixture peak at 61 kPa while for lean mixture was at 56 kPa which showed approximately 9% increment in cylinder pressure was achieved. While the heat release rate at 4000 rpm for both mixtures (stoichiometric and lean mixtures) under consideration respectively are 0.0219 kJ/°C A and 0.0184 kJ/°C A. This showed approximately 20% increment in heat release rate at that operating condition. More efficient and stable the combustion capable of enhancing the performance and drastically reduce the emission characteristics of the internal combustion engine were obtained.