EFFICIENCY AND FUEL ECONOMY BENEFITS OF DOUBLE INJECTION STRATEGIES IN A GASOLINE COMPRESSION IGNITION (GCI) ENGINE

摘要

The present study aims to evaluate fuel injection strategies and their effects on the efficiency and fuel consumption of gasoline compression ignition (GCI) engines. Specifically, single-injection-based GCI combustion is compared to the double injection strategy implementing early, near-BDC first injection for the formation of a premixed charge followed by late near-TDC second injection for the combustion phasing control. The GCI combustion was investigated in a single-cylinder automotive-size diesel engine connected to an EC dynamometer running at fixed speed of 1600 rpm. The engine performance and emissions testing has been conducted in a single-cylinder light-duty diesel engine equipped with a common-rail injection system and fuelled with a conventional gasoline with 91 RON. For each injection condition, the in-cylinder pressure traces were recorded using a piezo-electric pressure transducer, which was used to calculate the indicated mean effective pressure (IMEP), apparent heat release rate, burn duration, and combustion phasing. The net indicated engine efficiency and indicated specific fuel consumption was also calculated. Moreover, both microphone-based noise measurement and in-cylinder pressure-based combustion noise estimation were conducted. Results show that, compared to the single injection strategy, the double injection method shows a smoother in-cylinder pressure trace and lower combustion noise. For fixed IMEP, the fuel consumption of the double injection strategy is significantly lower than that of the single injection. Detailed analysis suggested that the initial reaction of the double injection strategy is driven by the premixed charge formed from the early first injection regardless of the second injection occurring either before or after the start of combustion. The burn duration of the double injection strategy is longer due to the locally lean mixtures formed in the premixed charge of the early first injection.