Analysis of the Effects of Injection Pressure Variation in Gasoline Partially Premixed Combustion 2021-01-0517

Compression-ignited engines are still considered the most efficient and reliable technology for automotive applications. However, current and future emission regulations, which severely limit the production of NOx, particulate matter and CO₂, hinder the use of diesel-like fuels. As a matter of fact, the spontaneous ignition of directly-injected Diesel leads to a combustion process that is heterogeneous by nature, therefore characterized by the simultaneous production of particulate matter and NOx. In this scenario, several innovative combustion techniques have been investigated over the past years, the goal being to benefit from the high thermal efficiency of compression-ignited engines, which results primarily from high Compression Ratio and lean and unthrottled operation, while simultaneously mitigating the amount of pollutant emissions. To achieve these goals, gasoline Partially Premixed Combustion, an innovative combustion methodology mainly characterized by the high-pressure direct injection of gasoline in a CI engine, proved to be very promising. This work analyzes the combustion process produced by a multi-jet pattern which introduces gasoline in a light-duty compression-ignited engine installed in a test cell. The engine has been modified to operate in stable operating conditions over its whole operating range. Since this combustion methodology is very sensitive to cylinder thermal conditions, the stability of the optimized multi-jet pattern has been guaranteed directly by controlling the intake conditions, i.e. intake temperature and pressure. Experimental tests have been carried out at very different loads to highlight how the control parameters of interest affect the combustion process. Several tests, run in stable conditions (optimized injection pattern), have been compared to quantify the impact of injection pressure variations on combustion efficiency and emissions. The obtained results demonstrate that the optimal management of the injection pressure is a key parameter for combustion optimization and for the limitation of combustion impulsiveness, necessary to comply with the reliability limitations over the whole engine operating range.