Alcohol-Fueled Reactivity-Controlled Compression Ignition Combustion for Partial Replacement of Mineral Diesel in Internal Combustion Engines

In this experimental study, a novel combustion technique, “reactivity-controlled compression ignition” (RCCI), has been investigated using alcohols acting as low-reactivity fuel (LRF) and mineral diesel acting as high-reactivity fuel (HRF). Combustion experiments were performed in a single-cylinder research engine at a constant engine speed of 1500 rpm and a low engine load of 3 bar brake mean effective pressure (BMEP). RCCI combustion is a practical low-temperature combustion (LTC) concept, which was achieved using three primary alcohols: Methanol, Ethanol, and Butanol in different premixed ratios (r_p = 0.25, 0.50, and 0.75) with mineral diesel. Results showed a relatively superior performance and emissions characteristics of RCCI combustion than the conventional compression ignition (CI) combustion. The influence of LRF was visible in the RCCI combustion, which exhibited a more stable combustion than the baseline CI combustion. Retarded start of combustion (SoC) with increasing r_p was exhibited by all alcohols; however, this trend was more dominant for Methanol/diesel- and Ethanol/diesel-fueled RCCI combustion. The presence of moisture traces in Ethanol was clearly observed in Ethanol/diesel-fueled RCCI combustion. Butanol/diesel-fueled RCCI combustion showed more significant similarity with conventional CI combustion at the lower r_p. RCCI combustion-fueled with different alcohols produced relatively lower emissions of oxides of nitrogen (NOx); however, hydrocarbon (HC) and carbon monoxide (CO) emissions were higher than that of baseline CI combustion. Among different alcohols, Methanol/diesel and Ethanol/diesel showed a higher reduction in particulate matter (PM) emissions than the Butanol/diesel-fueled RCCI combustion. At higher r_p, particulate characteristics of RCCI combustion were similar to that of spark ignition (SI) engines. Correlation between the total particulate mass (TPM) and the NOx emissions showed a strong possibility of significant emission reduction by employing RCCI combustion in the engines while ensuring energy diversification and use of biofuels in an efficient manner.