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 (PODE n) and hydrogen (H 2) demonstrate great potential in enhancing engine performance because of the beneficial fuel properties of PODE n. This study comprehensively investigates the performance of H 2 /PODE n 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 H 2 /PODE n RCCI has a more retarded ignition timing than that of H 2 /diesel RCCI under the same premixed energy ratio because the higher heat of absorption of PODE n 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 H 2 shifts from flame propagation in H 2 /diesel RCCI to spontaneous auto-ignition dominated by the reactivity stratification in H 2 /PODE n RCCI, because the higher fuel reactivity and greater volatility of PODE n enhance the mixing of direct-injection PODE n and premixed H 2 , and promote the auto-ignition reactivity of the H 2 /air mixture. Overall, H 2 /PODE n RCCI exhibits a greater advantage in the ignition control than H 2 /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, H 2 /PODE n 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 H 2 /diesel RCCI. [Display omitted] • The combustion characteristics of H 2 /PODE n RCCI were extensively investigated. • The auto-ignition/flame propagation mechanism for H 2 combustion was identified. • The H 2 combustion in H 2 /PODE n RCCI is governed by multi-point auto-ignition. • H 2 /PODE n RCCI is able to significantly enhance thermal efficiency. • H 2 /PODE n RCCI can substantially reduce NO x emissions. [ABSTRACT FROM AUTHOR]