The Downsizing Spark-Ignition Engine (DSIE) is one of the most promising solutions to reduce the CO2 emissions. In order to optimise all operating modes, the dilution of fresh gases by exhaust gases (EGR) is the main planned way to decrease the pumping losses, to limit abnormal combustions and NOx emissions. However, the dilution obtained by recirculation of exhaust gases requires a cooler to control the temperature of fresh gases and can involve a certain number of technological problems such as those related on the vapour condensation and the clogging of EGR circuit. Moreover, the control of the composition of recirculated gases and the time response of EGR loop can disturb the management of the automotive control.
The research project MACDOC (DSIE at Controlled Oxygen rate) aimed to evaluate, in experiments then by a simulation system, the potential of controlling oxygen quantity in the inlet of DSIE.
A different way was explored within the framework of MACDOC: to control the concentration of oxygen in-situ thanks to the technology of the polymer membranes. That could make it possible to simplify the loop of dilution of air-fuel mixtures, by avoiding and partly answering the various technological issues such as efficiency increase, the control of abnormal combustions and of the strong fluctuation cycles, the adequacy between DSIE and alternative fuels (Natural Gases, alcohols, etc.) and hybridisation of the vehicles which require an optimisation to limit regulated or non-regulated pollutant emissions, due to the more frequent stops of the IC engine.
The study of the impact of controlling the oxygen concentration on the combustion characteristics and emissions was performed at 1 400 rpm, at several loads (Indicated Mean Effective Pressure (IMEP) from 400 to 1 000 kPa). For each operation point, the spark advance and the intake pressure were adjusted simultaneously in order to maintain the load and obtain a minimum value of the indicated Specific Fuel Consumption (SFC). The effect of the oxygen concentration on the engine combustion characteristics was simulated by using the commercial software AMESim, with the combustion model developed by IFP Energies nouvelles, and an adapted algorithm was used to avoid residual gas calibration. By implementing a correlation for the laminar burning velocity, the in-cylinder pressures were perfectly predicted with a maximum pressure relative error of less than 2% for almost all the operating points. The classification of engine combustion according to the Peters-Borghi diagram, gives a deeper insight into the interaction between turbulence and the flame front.
More details at https://ogst.ifpenergiesnouvelles.fr/articles/ogst/abs/2016/04/ogst150049/ogst150049.html