Insight into the combustion and emission performance of reactivity-controlled compression ignition (RCCI) fueled with hydrogen (H2) and polyoxymethylene dimethyl ethers (PODEn)

The reactivity -controlled compression ignition (RCCI) engines fueled with polyoxymethylene dimethyl ethers (PODEn) and hydrogen (H2) demonstrate great potential in enhancing engine performance because of the beneficial fuel properties of PODEn. This study comprehensively investigates the performance of H2/PODEn RCCI at medium load with the gross indicated mean effective pressure of roughly 6 bar in a single -cylinder light -duty compression -ignition engine. The results showed that H2/PODEn RCCI has a more retarded ignition timing than that of H2/diesel RCCI under the same premixed energy ratio because the higher heat of absorption of PODEn reduces the bulk -gas temperature during the evaporation process owing to its higher latent heat of vaporization and lower heating value. Moreover, the combustion of H2 shifts from flame propagation in H2/diesel RCCI to spontaneous auto -ignition dominated by the reactivity stratification in H2/PODEn RCCI, because the higher fuel reactivity and greater volatility of PODEn enhance the mixing of direct -injection PODEn and premixed H2, and promote the auto -ignition reactivity of the H2/air mixture. Overall, H2/PODEn RCCI exhibits a greater advantage in the ignition control than H2/diesel RCCI to achieve successive ignition and reduce heat release rate due to its higher sensitivity of combustion to fuel reactivity gradient. Based on this benefit, H2/PODEn RCCI considerably improves engine thermal efficiency and simultaneously reduces peak pressure rise rate and soot emissions, in particular realizing an order of magnitude decrease in nitrogen oxides emissions compared to H2/diesel RCCI.