Comparison of four butanol isomers blended with diesel on particulate matter emissions in a common rail diesel engine

As a renewable fuel, butanol has a higher energy density than short-chain alcohols, and can be mixed with diesel in any proportion. To analyze the particulate matter emissions of butanol isomer in compression ignition engines, in this paper, the four butanol isomers were blended with diesel (25 vol%) named as n-butanol/diesel, s-butanol/diesel, i-butanol/diesel and t-butanol/diesel. The characteristics of particulate matter emissions were studied under a wide range of engine loads (3bar-9bar) and exhaust gas recirculation (EGR) rates (0%-60%). The results revealed that for all tested fuels as indicated mean effective pressure (IMEP) increased, particulate matter emissions first decreased and then increased. Compared to diesel under low load condition (IMEP = 3bar), the blending of butanol isomers had limited effect on particulate matter emissions. Among them, t-butanol increased the peak of particulate size distribution. When the engine load is higher than IMEP of 6 bar, the blending of butanol isomer significantly improved the particulate matter emissions. For IMEP fixed at 8bar, increasing the EGR rate made the particulate matter increase, especially for direct injection diesel. Butanol isomer/diesel blends can achieve low NOx and significantly improves particulate matter emissions in low temperature combustion mode (EGR = 60%). When EGR rates higher than 30%, the butanol isomer/diesel blends had a much smaller GMD than neat diesel. A comprehensive investigation of the four butanol isomer/diesel blends showed that t-butanol always had the highest particles than other butanol isomers under different EGR rates.