Computational Fluid-Dynamics Analysis of the Effect of Ethanol-Air Mixture Supply in a Heavy-Duty Engine

As part of a research project aiming to propose a solution for off-grid charging stations based on the adoption of an alternative engine, this study investigated the combustion development and pollutant emissions of a heavy-duty PFI internal combustion engine fueled by ethanol. With minor modification of the current ICE technology, an attempt is made to adapt it to alternative fuels. Some critical issues represent the major challenges to be dealt with in order to optimize the engine performance, say: - The control of the air-fuel mixture quality, which undergoes problems related to the slow evaporation rate of the alcohol fuel so inclining non-uniform distribution of the reactants inside the cylinders. - The control of the flame speed governed combustion that could attain detonation regimes, depending on the fuel-air ratio and the spark timing. - The NOx and CO formation as results of either uncontrolled temperature peaks or ineffective combustion. For this purpose, an in-depth analysis of the in-cylinder phenomena is performed by using a CFD solver for the reacting flow. A geometry of the cylinder system complete with intake and exhaust ducts was created for calculations with the three-dimensional Ansys FORTE code. Experimental data allowed a preliminary validation of the CFD based predictions under a large variety of operating conditions. After a model calibration, alternative solutions are proposed to optimize the engine performance and reduce fuel consumption and polluting emissions at medium-high load. In particular, the effect of the mixture formation process on the in-cylinder phenomena is investigated by experiencing several solutions for the fuel injection as to identify the most appropriate one for supplying cylinders with a uniform mixture and achieving an efficient combustion process as well.