Detailed Combustion Analysis of a Supercharged Double-Fueled Spark Ignition Engine

The main goal of researches in the field of automotive engineering is to obtain a large-scale implementationof low- or zero-emissions vehicles in order to substantially reduce air pollution in urbanareas. A fundamental step toward this green transition is represented by the improvement of currentinternal combustion (IC) engines in terms of fuel economy and pollutant emissions. The spark ignition(SI) engines of modern light-duty vehicles are supercharged, down-sized, and equipped with directinjection. Gaseous fuels, such as liquefied petroleum gas (LPG) or natural gas (NG), proved to be avalid alternative to gasoline in order to reduce pollutant emissions and increase fuel economy. Inprevious works the authors investigated the simultaneous combustion, in an SI engine, of gasolineand a gaseous fuel (referred to as Double-Fuel operation, DF) both in the naturally aspirated andsupercharged version; a significant increment of engine efficiency and a great reduction of pollutantemissions were obtained with respect to pure gasoline operation, with almost unchanged performance.This article is a development of the previous work and shows the results of a detailed heatrelease analysis, performed on the DF supercharged engine fueled with mixtures of gasoline andNG in order to highlight the effects of engine speed, charging pressure, and fuel mixture composition(the proportion between gasoline and NG) on the combustion speed.It was found that both gasoline content in the DF mixture and supercharging pressure contributeto increase the combustion speed, which, in some cases, produced engine-indicated efficiencyincrements up to 5%. The wide set of experimental data presented in this article allows us to betterunderstand the combustion behavior of gasoline-NG fuel mixtures and can be also used to calibratecombustion submodels integrated into engine numerical simulations.