Abstract
Opposed-piston two-stroke engines (OP2S) have demonstrated high thermodynamic efficiencies due to reduced heat losses and high volume-to-surface area ratios. This leads to remarkable advantages over four-stroke conventional diesel engines, as well as superior combustion characteristics. Therefore, combining this concept with renewable fuels and advanced technologies, such as pre-chamber, can be a route to high-efficiency, carbon-neutral powertrains. The narrow-throat KAUST pre-chamber was chosen for initial assessment, due to its advantage of being a drop-in concept, which lowers the technological barriers for deployment. Key engine design aspects contributing to methanol evaporation and mixture formation in a passive pre-chamber methanol OP2S engine were numerically investigated. CONVERGE™ was selected as the solver to explore the sensitivity of the evaporation and the mixture formation to the variation of injection direction, port swirl angle, and piston bowl shape. Previous studies of the port swirl angle in OP2S engines report that its design can lead to a concentration of hot residual gases around the cylinder axis in the main chamber. Specifically for methanol, these unscavenged residuals could thermally contribute to an increase in evaporation. However, the current study reveals that the sensitivity of methanol to evaporation and mixing are mainly related to the flow dynamics, while the effect of the remaining hot gases is secondary. Lastly, a modified piston was used to demonstrate the sensitivity of fuel evaporation and mixing due to flow patterns associated with the piston design.
