CI/PCCI Combustion Mode Switching of Diesohol Fuelled Production Engine 2017-01-0738
Premixed charge compression ignition (PCCI) combustion is an advanced combustion technique, which has the potential to be operated by alternative fuels such as alcohols. PCCI combustion emits lower oxides of nitrogen (NOx) and particulate matter (PM) and results thermal efficiency similar to conventional compression ignition (CI) engines. Due to extremely high heat release rate (HRR), PCCI combustion cannot be used at higher engine loads, which make it difficult to be employed in production grade engines. This study focused on development of an advanced combustion engine, which can operate in both combustion modes such as CI combustion as well as PCCI combustion mode. This Hybrid combustion system was controlled by an open engine control unit (ECU), which varied the fuel injection parameters for mode switching between CI and PCCI combustion modes. At low-to-medium engine loads, engine was operated in PCCI combustion mode and at higher engine loads ECU automatically switched the engine operation in CI combustion mode. Experiments were carried out using diesohol (10% v/v ethanol in mineral diesel,) at constant engine speed (1500 rpm) and load was varied from idling to full load (6 bar BMEP). To explore the emission behavior in different combustion modes and mode transition periods, continuous sampling of exhaust gas was carried out, which included regulated emission, unregulated gaseous species and particulate measurements. Results showed lower NOx and PM emissions from PCCI combustion mode however performance of PCCI combustion was slightly inferior compared to CI combustion mode. Diesohol showed slightly lower BTE and EGT compared to mineral diesel. During mode transition from PCCI to CI combustion mode, sudden increase in exhaust gas temperature (~75°C) was the main reason for improved CI combustion. Slightly higher concentration of unregulated species such as sulphur dioxide (SO2), formaldehyde (HCHO), etc. in PCCI combustion was an important observation of this study. Particulate number-size distribution showed the presence of nano-particles in CI combustion however in PCCI combustion, most of the particulates lied in accumulation size range. Diesohol resulted in slightly lower particulate emissions compared to mineral diesel.