Experimental Study on HCCI Combustion in a Small Engine with Various Fuels and EGR

ABSTRACT

Because Asian countries have a large number of motorcycles, motorcycle engine exhaust emission poses a major problem in the region. Homogeneous charge compression ignition (HCCI) is a promising combustion technology with high efficiency and low nitrogen oxide emission. This study investigated the combustion characteristics of HCCI in a 150 cc motorcycle engine with three types of dual fuel. The main fuels consisted of dimethyl ether (DME), kerosene, and n-heptane, and gasoline was the additive fuel. External exhaust gas recirculation (EGR) was used to expand the operating range of the engine. All test points were executed under stable HCCI operation with a coefficient of variation < 5%. A total of 107 data sets were obtained by adjusting the amount of main fuel, additive fuel, and EGR. Two-stage ignition was observed because of the diesel-like main fuels. The results revealed that the temperature at the start of combustion was approximately 500–700 K, and the temperature of the first-stage maximum heat release rate (MHRR1) was approximately 600–800 K. The relationship between the crank angle (CA) at which the mass fraction burnt is 50% (CA50) and the CAs of the maximum cylinder pressure, maximum cylinder gas temperature, and MHRR were linear. The R square for the curve fitting of each relationship was > 0.9. The findings suggest that adjusting the CA50 to a value greater than 5° after top dead center, or limiting the maximum cylinder pressure to < 50 bar is crucial to preventing excessive pressure rising. Overall, kerosene was deemed unsuitable for engines because of its high sulfur content, whereas DME is considered an excellent option.