Evaluation of Emissions and Performances from Partially Premixed Compression Ignition Combustion using Gasoline and Spark Assistance

Several new combustion concepts have been developed during last decade with the aim of reducing pollutant emissions. Specifically, these strategies allow a simultaneous reduction of NOx and soot emissions by reducing the local combustion temperatures, enhancing the fuel/air mixing (PCCI, HCCI…). In spite of their benefits, these concepts present difficulties controlling the appropriate combustion phasing as well as high knocking levels and therefore, their operating range is reduced to low-medium loads. In this work gasoline is considered as a fuel in order to improve combustion strategies based on fully or partially premixed combustion in CI engines. Its use provides more flexibility to achieve lean and low combustion temperature, however the concept has demonstrated difficulty under light load conditions using gasoline with ON up to 95. For this reason, spark assistance is being investigated as a suitable strategy to provide cycle-to-cycle control by decoupling the thermodynamic conditions and the ignition process for CI engines. Thus, the current paper presents a preliminary investigation of gasoline CI with spark assistance, with the objective of evaluating the performances and emissions without any type of optimization. Parametric variations in injection timing and rail pressure were carried out with single and double injection strategies in a high speed single-cylinder diesel engine with a modified cylinder head that includes a spark plug. A detailed analysis of the air/fuel mixing process has also been developed by means of a 1-D in-house spray model. Results show how the spark discharge is promoting and controlling the start of combustion and providing cycle-to-cycle combustion control.