Experimental investigation on combustion and emission characteristics of reactivity controlled compression ignition engine powered with iso-propanol/biodiesel blends

Recently, reactivity controlled compression ignition (RCCI) has been proposed in order to achieve a higher thermal efficiency with lower emissions than conventional combustion. In RCCI mode, as the fuel types and their combinations affects the reactivity stratification inside cylinder, thus combustion control, in present study, iso-propanol was evaluated as low-reactivity fuel (LRF) when petroleum diesel, commercial biodiesel and their blends were high-reactivity fuels. It is of great importance that iso-propanol and biodiesel be used together in RCCI mode, as they significantly affect the in-cylinder stratification due to their high octane/cetane number. Therefore, the reactivity controlled compression ignition (RCCI) combustion characteristics was investigated in a diesel research engine using iso-propanol, petroleum diesel, biodiesel and their blends as fuels. Tests were conducted on varying loadings (from 20% to 60% of max torque) and premixed ratios of LRF (Rp = 0, 0.15, 0.30, 0.45, and 0.60) at a constant engine speed of 2400 rpm. Results, which were compared with conventional diesel combustion (CDC), showed that, as the premixed ratio (Rp) of low-reactivity fuel (iso-propanol) increased, ignition delay (ID) period prolonged while combustion duration (CD) and rate of pressure rise (RoPR) reduced assisted to reduce NO emissions and smoke opacity in the exhaust. NO and smoke opacity reduced simultaneously for biodiesel-propanol combinations up to 40% under 20% load and 0.60 premixed ratio of LRF compared to CDC. Propanol premixed ratio of 0.30 at 60% load was found to be optimum concerning lowest emissions. In conventional mode, HC emissions reduced by up to 52% when biodiesel and its blends with diesel fuel are used, whereas they increased significantly in RCCI mode. According to overall results, it is concluded that RCCI performed better than CDC at entire load.