Premixed compression ignition (PCI) strategies offer the
potential for simultaneously low NOx 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
NOx emissions. Although NOx emissions of
E10-EHN RCCI are slightly higher than E10-diesel RCCI,
NOx 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.