Study of combustion and emission characteristics of a diesel engine fueled with diesel, butanol-diesel and hexanol-diesel mixtures under low intake pressure conditions

Abstract

A significant number of landmasses on earth are above sea level where the ambient pressure is below 1 atm. With economy and population growth, the rapid expansion of human activities at these high-altitude regions is expected. However, the research on diesel engine combustion and emissions under low intake pressure conditions are limited, especially when alcohol-diesel mixtures are used as fuel. In this work, the combustion and emission characteristics of a common-rail diesel engine fueled with diesel, butanol-diesel and hexanol-diesel mixtures under low intake pressure conditions were investigated. Mixtures were prepared with two blend ratios, which were 20% and 40% by volume. Experiments were conducted under five different intake pressures (1.2, 1.0, 0.8, 0.7, and 0.6 atm) and two engine loads (0.45 MPa and 0.55 MPa IMEP). The combustion characteristics and engine performance were analyzed using measurements of in-cylinder pressure, HRR, ignition delay, combustion duration, ISFC and ITE. NOx, soot, CO, and HC emissions under different operating conditions were also measured and discussed. Results revealed lower intake pressure led to higher ISFC and lower ITE. Soot and CO emissions increased significantly once intake pressure dropped below 0.8 atm, while NOx emissions decreased with intake pressure reduction. Under the same conditions, adding renewable alcohol extended the ignition delay and reduced the combustion duration. These effects were more pronounced for combustion of butanol-diesel mixtures than combustion of hexanol-diesel mixtures. Combustion of hexanol-diesel mixture with 20% blend ratio (H20) had similar or lower ISFC and higher ITE than diesel combustion when intake pressure was lower than 1 atm due to its fuel oxygen content and similar fuel properties as diesel. The engine fueled with H20 could still operate under intake pressure of 0.6 atm and engine load of 0.45 MPa IMEP, but the engine misfired when other fuels were used. In terms of emission characteristics, adding alcohol significantly reduced soot and CO emissions, especially when intake pressure was below 1 atm. However, combustion of alcohol-diesel mixtures produced more NOx emissions than diesel combustion under the same conditions.