Reactivity controlled compression ignition and conventional diesel combustion: A comparison of methods to meet light-duty NOx and fuel economy targets

This study compares conventional diesel combustion and reactivity controlled compression ignition combustion in a light-duty engine at NOx levels equivalent to US Tier 2 Bin 5 and proposes a simple method to account for the added fluid consumption required to meet NOx constraints using aftertreatment. Reactivity controlled compression ignition and conventional diesel combustion are compared assuming that the conventional diesel combustion mode uses selective catalytic reduction to meet NOx constraints. The results show that reactivity controlled compression ignition is capable of meeting cycle-averaged NOx targets (equivalent to Tier 2 Bin 5) without NOx aftertreatment. In addition, efficiency comparisons show that reactivity controlled compression ignition offers a 4% improvement in fuel consumption and a 7.3% improvement in total fluid consumption (fuel + diesel exhaust fluid) over conventional diesel combustion with selective catalytic reduction. The fuel consumption improvement is due primarily to lower heat transfer losses. Additionally, it was found that the efficiency of reactivity controlled compression ignition can be further improved by careful selection of operating conditions and the combustion chamber configuration. The modeling shows that over 52% gross indicated efficiency can be achieved in the light-duty engine while meeting NOx targets in-cylinder.