Effects of Ethanol–Diesel on the Combustion and Emissions from a Diesel Engine at a Low Idle Speed

In this study, detailed experiments were conducted on the combustion and exhaust characteristics of ethanol–diesel blended fuels. The four-stroke four-cylinder common-rail direct injection diesel engine was used. The experiment was carried out at 750 rpm at a low speed idle, and a 40 Nm engine load was applied to simulate the operation of the accessories during the low idle operation of the actual vehicles. The test fuels were four types of ethanol-blended fuel. The ethanol blending ratios were 0% (DE_0) for pure diesel, and 3% (DE_3), 5% (DE_5) and 10% (DE_10) for 3%, 5% and 10% ethanol mixtures (by vol.%). Blending ethanol with diesel fuel increased the maximum combustion pressure by up to 4.1% compared with that of pure diesel fuel, and the maximum heat release rate increased by 13.5%. The brake specific fuel consumption (BSFC) increased, up to 5.9%, as the ethanol blending ratio increased, while the brake thermal efficiency (BTE) for diesel-ethanol blended fuels remained low, and was maintained at 23.8%. The coefficient of variation (COV) of the indicated mean effective pressure (IMEP) was consistently lower than 1% when ethanol was blended. The blending of ethanol increased the ignition delay from a 12.0 degree crank angle (°CA) at DE_0 to 13.7 °CA at DE_10, and the combustion duration was reduced from 21.5 °CA at DE_0 to 20.8 °CA at DE_10. When ethanol blending was applied, nitrogen oxides (NOx) reduced to 93.5% of the level of pure diesel fuel, the soot opacity decreased from 5.3% to 3% at DE_0, and carbon monoxide increased (CO) by 27.4% at DE_10 compared with DE_0. The presence of hydrocarbon (HC) decreased to 50% of the level of pure diesel fuel, but increased with a further increase in the ethanol blending ratio. The mean size of the soot particulates was reduced by 26.7%, from 33.9 nm for pure diesel fuel, DE_0, to 24.8 nm for DE_10.