Experimental study of butanol/biodiesel dual-fuel combustion in intelligent charge compression ignition (ICCI) mode: A systematic analysis at low load

Abstract The direct injection dual-fuel intelligent charge compression ignition (ICCI) is demonstrated as an advanced combustion mode with high efficiency and low emissions at medium to high engine loads, owing to the flexible in-cylinder concentration control of two fuels with different reactivity. Due to the incomplete combustion of part fuels, the improvement of efficiency and emissions under low load is always very difficult for most of new combustion modes. To deal with this problem, this paper systematically analyzed the combined effect of intake temperature, intake pressure, direct injection timings and the corresponding energy ratio of the two fuels on ICCI combustion strategy fueled with biofuels of butanol and biodiesel at indicated mean effective pressure of 4 bar. Results show that the high efficiency, low hydrocarbons (HC), carbon monoxide (CO) and particulate matter (PM) emissions are obtained at relative high intake temperature and low intake pressure condition. Sufficiently advance direct injection timing (SOI1) of the butanol could shorten the combustion duration and improve indicated thermal efficiency (ITE), along with the reduction of nitrogen oxides (NOx) and PM emissions, while the ignition delay is insensitive to SOI1. MPRR is significantly reduced with the advance of direct injection timing of biodiesel (SOI2), which improves the combustion process and reduces pollutant emissions, especially for NOx emissions. CO and HC emissions increase at first and then decrease with the advance of SOI2. Based on the optimized intake boundary conditions, as the butanol energy ratio is upgraded, the ITE shows slightly decrease at first and then increase, but the NOx emissions are close to zero.