Fuel Injection Strategies for Optimized Combustion and Emissions in a Gasoline Direct Injection Engine

Abstract With gasoline direct injection, fuel injection parameters should be optimally tuned since they are critical in determining the fuel–air mixing and the charge quality during combustion. Fuel injection timing and pressure are two critical parameters examined in this study to investigate their combined impact on fuel–air mixture characteristics. The study aims to investigate the effect of these fuel injection parameters on varying spark timings and engine speeds. The results were analyzed for the engine's combustion, performance, and emissions characteristics. The experiments were conducted on a 500-cc, single-cylinder, wall-guided gasoline direct injection engine. All the tests were performed with a fixed fuel injection quantity of ∼22 mg. Three fuel injection pressures of 100, 150, and 200 bar, and three fuel injection timings, indicating different stages of the intake stroke, were considered for the experiments, namely early intake (315 deg bTDC), mid-intake (270 deg bTDC), and late-intake (225 deg bTDC) injection timing. For an early fuel injection timing (315 deg bTDC), the degree of complete combustion was maximized, resulting in the shortest combustion duration. A fuel injection pressure of 100 bar was found to be suitable for early injection at all engine speeds. Mid-intake injection timing (270 deg bTDC) showed deteriorated combustion at all engine speeds and injection pressures. Late injection timing (225 deg bTDC) resulted in the lowest ignition delay and early pressure rise due to spray-generated turbulence. Higher engine speeds of 1500 and 2000 rpm, along with higher fuel injection pressure, enhanced the combustion for late injection; however, cyclic variations increased. Hydrocarbons and carbon monoxide emissions also increased with late fuel injection timing. Spark advance of ∼28 deg bTDC showed the maximum indicated mean effective pressure with superior combustion stability. Overall, a fuel injection timing of 315 deg bTDC with 100 bar fuel injection pressure resulted in the highest thermal efficiency and lower carbon monoxide and hydrocarbon emissions at all engine speeds. However, nitric oxide emissions were significantly higher for these parameters.