Effects of biofuel blends on transient reactivity-controlled compression ignition engine combustion

Abstract

Reactivity-controlled compression ignition is a low-temperature engine combustion strategy that utilizes in-cylinder blending of fuels with different autoignition characteristics to produce low NO_x (oxides of nitrogen) and particulate matter emissions while maintaining high thermal efficiency. This study investigates reactivity-controlled compression ignition combustion in a light-duty, multi-cylinder, compression ignition engine over steady-state and transient operating conditions with both petroleum and bio-derived fuels. The engine experiments consisted of in-cylinder fuel blending with port fuel injection of gasoline or E20 and early-cycle, direct injection of ultra-low sulfur diesel or B20. Performance and emissions results were compared at steady-state and over an up-load change between 1 and 4 bar brake mean effective pressure at 1500 r/min. The results under steady-state operation showed that E20 offered reduced hydrocarbon emissions from the lower port fuel injection mass fraction. Port fuel injection mass fraction is defined as the mass fraction of the port fuel injection injected fuel compared to the total fuel injected, as calculated by $PF{I}_{fraction}=({\stackrel{.}{M}}_{PFI})/({\stackrel{.}{M}}_{PFI}+{\stackrel{.}{M}}_{DI})$ . E20 also was shown to offer higher peak load capability and thermal efficiency than gasoline. Conversely, B20 was found to require a higher port fuel injection mass fraction with resulting higher hydrocarbon emissions. Peak load and efficiency were not affected by the use of B20. Steady-state NO and particulate matter emissions were unaffected by either of the biofuels. During the transient tests, E20 reduced hydrocarbon emissions while B20 increased hydrocarbon emissions. Both biofuels offered faster transient response to recover the CA50 to the steady-state CA50 value than gasoline or ultra-low sulfur diesel.