Fuel effects on reactivity controlled compression ignition (RCCI) combustion at low load

Reactivity Controlled Compression Ignition combustion (RCCI) has been demonstrated at mid to high loads [1, 2, 3, 4, 5, 6] as a method to operate an internal combustion engine that produces low NOx and low PM emissions with high thermal efficiency. The current study investigates RCCI engine operation at loads of 2 and 4.5 bar gross IMEP at engine speeds between 800 and 1700 rev/min. This load range was selected to cover the range from the previous work of 6 bar gIMEP down to an off-idle load at 2 bar. The fueling strategy for the low load investigation consisted of in-cylinder fuel blending using port-fuel-injection of gasoline and early cycle, direct-injection of either diesel fuel or gasoline doped with 3.5% by volume 2-EHN (2-ethylhexyl nitrate). At these loads, engine operating conditions such as inlet air temperature, port fuel percentage, and engine speed were varied to investigate their effect on combustion. Results show that at the 4.5 bar gIMEP operating condition it was possible to maintain 54% gross indicated thermal efficiency with NOx and PM emissions below US EPA 2010 limits. The results also show that it is possible to operate at a near idle load of 2 bar gross IMEP load with a gross indicated thermal efficiency of 49% at 1300 rev/min and 44% at 800 rev/min.