Light-Duty Reactivity Controlled Compression Ignition Combustion Using a Cetane Improver

Premixed compression ignition (PCI) strategies offer the potential for simultaneously low NO_x and soot emissions and diesel-like efficiency. However, these strategies are generally confined to low loads due to difficulties controlling the combustion phasing and heat release rate. Recent experiments have demonstrated that dual-fuel reactivity-controlled compression ignition (RCCI) combustion can improve PCI combustion control and expand the PCI load range. Previous studies have explored RCCI operation using port-fuel injection (PFI) of gasoline and direct-injection (DI) of diesel fuel. In this study, experiments are performed using a light-duty, single-cylinder research engine to investigate RCCI combustion using a single fuel with the addition of a cetane improver 2-ethylhexyl nitrate (EHN). The fuel delivery strategy consists of port-fuel injection of E10 (i.e., 10% ethanol in gasoline) and direct-injection of E10 mixed with 3% EHN. The results using the E10+EHN strategy are compared to an E10+diesel dual-fuel strategy.

It was found that the additized E10 blend performed similar to diesel fuel and was capable of achieving controlled PCI operation over a range of conditions. In contrast to previous low-temperature combustion studies using EHN, the present work shows that, since the EHN quantity is very low (~0.3% of the total fuel), the nitrogen in the fuel only results in a small increase in NO_x emissions. Although NO_x emissions of E10-EHN RCCI are slightly higher than E10-diesel RCCI, NO_x levels are below 1 g/kW-hr over a range of loads. Similar to previous light-duty dual-fuel RCCI operation, the single-fuel E10-EHN RCCI strategy demonstrated a peak-indicated efficiency of near 50% at a mid-load (9 bar gross IMEP) operating condition.