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

Abstract

The main goal of researches in the field of automotive engineering is to obtain a large-scale implementation of low- or zero-emissions vehicles in order to substantially reduce air pollution in urban areas. A fundamental step toward this green transition is represented by the improvement of current internal 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 direct injection. Gaseous fuels, such as liquefied petroleum gas (LPG) or natural gas (NG), proved to be a valid alternative to gasoline in order to reduce pollutant emissions and increase fuel economy. In previous works the authors investigated the simultaneous combustion, in an SI engine, of gasoline and a gaseous fuel (referred to as Double-Fuel operation, DF) both in the naturally aspirated and supercharged version; a significant increment of engine efficiency and a great reduction of pollutant emissions 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 heat release analysis, performed on the DF supercharged engine fueled with mixtures of gasoline and NG 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 contribute to increase the combustion speed, which, in some cases, produced engine-indicated efficiency increments up to 5%. The wide set of experimental data presented in this article allows us to better understand the combustion behavior of gasoline-NG fuel mixtures and can be also used to calibrate combustion submodels integrated into engine numerical simulations.