| Summary: | 碩士 === 國立海洋大學 === 機械與輪機工程學系 === 87 === Liquefied Petroleum gas is an important alternative fuel. The government has practiced the policy of encouraging LPG-fueled vehicles to reduce the air pollution of metropolitan area. Diesel engines are extensively applied on trucks, power plants, and on construction, agricultural machinery. It also possesses a high potential to reduce exhaust emissions if these diesel engines are changed to fuel with LPG.
An LPG-fueled diesel engine must change the ignition method to spark-ignition. The ignition timing can be freely adjusted under different operating conditions. Although LPG has a high octane number, the compression ratio must be reduced for an LPG-fueled diesel engine to avoid the occurrence of knocking. It has been shown that in some study the compression ratio of LPG-fueled gasoline engine is 11.7 or lower. Therefore, this thesis modifies a single-cylinder utility diesel engine to be LPG-fueled with electronically controlled spark-ignition. The compression ratio is changed to between 10 and 14. The air-fuel ratio is controlled to be lean condition. Engine testing are conducted, looking forward to determining appropriate compression ratio and air-fuel ratio for better engine performance, fuel consumption and exhaust emissions.
The results shows larger brake horsepower is achieved at compression ratio of 11 and 12, while knocking occurs at compression ratio of 14. The higher the compression ratio, the more hydrocarbon emission is found at the engine exhaust. As for the relative air-fuel ratio, higher output torque and horsepower are obtained at l=1.1 among lean air-fuel ratios. The CO and HC emissions are also effectively reduced at this air-fuel ratio.
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