Development of Laminar Burning Velocity Correlation for the Simulation of Methanol Fueled SI Engines Operated with Onboard Fuel Reformer

Abstract

Methanol fueled spark ignition (SI) engines have the potential for very high efficiency using an advanced heat recovery system for fuel reforming. In order to allow simulation of such an engine system, several sub-models are needed. This paper reports the development of two laminar burning velocity correlations, corresponding to two reforming concepts, one in which the reformer uses water from an extra tank to produce hydrogen rich gas (syngas) and another that employs the water vapor in the exhaust gas recirculation (EGR) stream to produce reformed-EGR (R-EGR). This work uses a one-dimensional (1D) flame simulation tool with a comprehensive chemical kinetic mechanism to predict the laminar burning velocities of methanol/syngas blends and correlate it. The syngas is a mixture of H2/CO/CO2 with a CO selectivity of 6.5% to simulate the methanol steam reforming products over a Cu-Mn/Al catalyst. The simulation was exercised over syngas contents in the blend, fuel-air equivalence ratios, pressures, unburned gas temperatures and EGR ratios ranging respectively from 0% to 50%, 0.5 to 1.5, 10 to 85 bar, 550 to 800 K and 0% to 30% (by mass). The developed correlations are ready to be implemented into engine simulation tools as well as computational fluid dynamic codes. Based on the developed correlations, optimal control strategies and dilution methods have been studied. The engine is able to work with the same mass burning rate at leaner mixtures or lower intake charge temperatures with an onboard fuel reformer. If the engine is operated at stoichiometric condition, at the same mass fraction of methanol to the catalyst and the same EGR, the R-EGR concept is recommended because it provides a faster laminar burning velocity and does not require an extra tank of water for fuel reforming.