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Using CNG (compressed natural gas) as a fuel for diesel engines certainly results in the reduction of pollutant emissions. Having several merits in the viewpoints of the wide driving range due to the running possibility by using only diesel fuel, and no major modification on the engine, dual fuel engine is much effective and adequate than other CNG types to improve air quality in urban areas. In order to convert existing diesel engine for truck to CNG-diesel operation, it is necessary to compromise engine power with emissions. In this study, we have developed a CNG-diesel dual fuel supply system through the modification of mechanism in injection pump, the supplement of gas mixer, and mechanical control system and measured power, fuel consumption rate, and emissions.

Natural gas possesses several characteristics that make it desirable as an engine fuel; 1)lower production cost, 2)abundant commodity and 3)leaner energy source than gasoline. Due to the physical characteristics of natural gas, the volumetric efficiency and flame speed of a natural gas engine are lower than those of a gasoline engine, which results in a power loss of 10-20% when compared to a normal gasoline engine. This paper describes the results of a research to improve the performance of a natural gas engine through the modification and controls of compression ratio, air/fuel ratio, spark advance and supercharging. It emphasizes how to improve the power characteristics of a natural gas engine. Combustion characteristics are also studied using an ion probe. The ion probe is applied to measure flame speed of gasoline and methane fuels.