Evaluation of comparative engine combustion, performance and emission characteristics of low temperature combustion (PCCI and RCCI) modes

Abstract

In this study, a comparative investigation of engine combustion, performance and emission characteristics of low temperature combustion modes namely premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) with conventional compression ignition (CI) combustion mode was performed. Experiments were performed in a single cylinder research engine at constant engine speed (1500 rpm) and at four different engine loads (1, 2, 3 and 4 bar brake mean effective pressure (BMEP)). Baseline CI and PCCI mode combustion experiments were performed using mineral diesel as test fuel; while mineral diesel-methanol fuel pair was used as high-reactivity fuel (HRF) and low-reactivity fuel (LRF) respectively in RCCI mode combustion. Results showed that RCCI mode combustion was relatively more stable compared to baseline CI and PCCI combustion modes. At higher engine loads, RCCI mode combustion exhibited relatively lower knocking and combustion noise than other combustion modes. Performance characteristics showed that brake thermal efficiency (BTE) of RCCI mode combustion was comparable to baseline CI mode combustion, however, at higher engine loads, RCCI mode combustion resulted in relatively higher BTE compared to both baseline CI and PCCI combustion modes. Significantly lower EGT of RCCI mode combustion compared to baseline CI as well as PCCI combustion modes was another important finding of this study. Emission results showed that RCCI mode combustion emitted relatively lower oxides of nitrogen (NOx), but significantly higher hydrocarbons (HC) compared to baseline CI and PCCI combustion modes. A NOx-BTE trade-off analysis was also carried out, which demonstrated the suitability of RCCI mode combustion at all engine loads. Finally, a parametric analysis was carried out to compare the critical parameters of baseline CI, PCCI, and RCCI combustion modes at low and high engine loads, which exhibited improved engine performance and emission characteristics of low temperature combustion (LTC) modes, especially the RCCI mode combustion.