Improvement of Combustion in a Diesel-Natural Gas DF-PCCI Engine by Diesel Two-stage Injection

Abstract

A two-stage diesel injection strategy in a diesel-natural gas dual-fuel premixed charge compression ignition (DF-PCCI) engine was investigated under a low load condition. Under this condition, the combustion efficiency becomes low because of the low equivalent ratio. This problem can be solved by supplying more diesel with low natural gas substitution rate(NGSR); however, thermal efficiency deteriorates as a result. As such, the two-stage diesel injection strategy was applied in order to delay the combustion phase at low NGSR of DF-PCCI. The two-stage injection timing was selected based on the thermal efficiency and combustion efficiency of single diesel injection at DF-PCCI combustion. By applying the two-stage diesel injection strategy, despite a slight decline of thermal efficiency, unburned hydrocarbon(UHC) and carbon monoxide(CO) were significantly reduced as compared with the single diesel injection strategy DF-PCCI.