| Summary: | 碩士 === 國立中興大學 === 農業機械工程學系 === 88 === A four- stroke gasoline engine was used to study the effects of engine speed and valve clearance on the engine torque, brake horse power, and brake specific fuel consumption of this engine. The exhaust gas such as carbon monoxide, carbon dioxide, hydrocarbon and free oxygen were also investigated. The experimental results could be provided to the users and repairmen of a four-stroke gasoline engine for reference.
The partial load experimental results showed that：
(1) The overall results of engine torque, brake horse power, and brake specific fuel consumption for valve clearance at 0.35mm were better than that valve clearance greater or less than 0.35mm.
(2) The maximum engine torque was happened at 1900 RPM engine speed.
(3) The maximum engine brake horsepower was happened at 3700 RPM∼4000 RPM engine speed.
(4) The engine speed at minimum brake specific fuel consumption was happened between maximum engine torque and maximum brake horsepower.
The full load experimental results showed that：
(1) The overall results of engine performance for engine speeds lower than 3100 RPM had positive relationship with valve clearance. However, the 0.35mm valve clearance had the best engine performance for engine speeds than 3400 RPM.
(2) The engine torque curve was symmetrical and the maximum torque was happened at 3100 RPM engine speed.
(3) The maximum brake horsepower was happened at 4600 RPM∼4900 RPM engine speed.
(4) The minimum brake specific fuel consumption for different valve clearances were located at different engine speed owing to the double-tube carburetor of the experimental engine.
The exhaust gas analytical results showed that：
(1) The valve clearance had negative effects on the carbon monoxide for engine speeds lower than 3400 RPM, but positive effects on the carbon dioxide. The carbon monoxide was lowest and carbon dioxide was highest at 0.35mm valve clearance as engine speeds higher then 3700 RPM.
(2) The percentages of hydrocarbon were lowest and carbon dioxides were highest for 0.35mm valve clearance compared with others.
(3) The lower the valve clearance, the higher the percentages of carbon monoxide and hydrocarbon in the exhaust gas. As valve clearance were larger than 0.35mm, the high percentages carbon monoxide and hydrocarbon were happened at high engine speeds.
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