Study on the Influence of Different Internal Exhaust Gas Recirculation Formation Modes on the Combustion Performance of Gasoline, Methanol, and Ethanol SI Engine

To promote the efficient and clean application of low-carbon alcohol fuels in internal combustion engines, this article compares and studies the effects of three internal EGR strategies, including exhaust valve lift strategy (EVVL), exhaust timing advance strategy (EVT), and intake valve timing advance strategy (IVT), on the combustion, performance, and emissions of gasoline, methanol, and ethanol. Under the same internal EGR rate, the internal EGR temperature generated by the three valve strategies is, from highest to lowest, as follows: EVT, EVVL, and IVT. With an increase in internal EGR in the cylinder, the ignition delay and combustion duration under the EVVL and IVT strategies increase progressively, whereas the ignition delay under the EVT strategy tends to first shorten and then lengthen. Methanol has the shortest combustion duration. Furthermore, methanol and ethanol have lower heat transfer and exhaust losses than gasoline. The thermal efficiency of methanol, ethanol, and gasoline can be raised by 7.7%, 7.5%, and 7.2%, respectively, using the IVT strategy; 3.1%, 3.9%, and 4.6% using the EVVL strategy; and 6.82%, 6.85%, and 7% using the EVT strategy. The combination of methanol and ethanol with internal EGR technology greatly reduces NOx emissions, with an 84.5% reduction under the EVVL strategy.