Investigation of butanol-fuelled HCCI combustion on a high efficiency diesel engine

Abstract Highly-diluted diesel homogeneous charge compression ignition (HCCI) combustion can achieve ultra-low NOx and soot emissions but its implementation is impeded by the lack of control on the ignition timing and excessively early combustion phasing (before TDC) that limit the achievable engine load and result in a reduced energy efficiency. The low volatility and high reactivity of common diesel fuels make it non-conducive for HCCI combustion; hence in this work, n-butanol that has a low reactivity and high volatility is studied for HCCI combustion on a single-cylinder high compression ratio (18.2:1) diesel engine without any modifications to the air-path system. The results indicate that n-butanol-fuelled HCCI combustion offers the benefit of ultra-low NOx and smoke emissions with minimal requirements for intake dilution through exhaust gas recirculation (EGR). The low reactivity helps in realizing an optimal combustion phasing, and thermal efficiency levels comparable to that of conventional diesel combustion are consistently achieved. At low-to-mid engine loads (4–7 bar IMEP), the emissions are largely insensitive to the boost pressure, and the boost selection is primarily governed by the trade-off between the combustion instability and the thermal efficiency. At higher engine loads, both boost and EGR are required to limit the high pressure rise rates and to modulate the combustion phasing for high thermal efficiency. The load range is extended up to 10 bar IMEP in n-butanol HCCI mode while maintaining ultra-low NOx and soot emissions with improved performance characteristics compared to diesel HCCI.