Experimental and kinetic modeling study on laminar burning velocities and ignition delay times of NH3/PODE3 blends

Ammonia–polyoxymethylene dimethyl ether 3 (PODE₃) dual fuel mode shows great potential in enhancing ammonia combustion performance, reducing carbon-related and pollutant emissions, and promoting the widespread application of ammonia-fueled engines. In this study, the ignition delay times (IDTs) of NH₃/PODE₃ blends were measured using a rapid compression machine (RCM) within a wide temperature (T_eff) range at elevated pressures (P_eff). Moreover, the laminar burning velocities (LBVs) of NH₃/PODE₃ blends were determined employing a constant-volume combustion vessel at wide initial pressures, temperatures, and ammonia molar ratios (AMRs). The outcomes demonstrate that the incorporation of PODE₃ conspicuously shortens the IDTs and augments the LBVs of NH₃. Based on these data, a detailed chemical reaction mechanism for NH₃/PODE₃ blends has been developed, encompassing 319 species and 2015 reactions. This proposed mechanism was meticulously validated against IDTs, LBVs, and major species mole fraction profile data over an extensive spectrum of experimental conditions, covering not only pure NH₃ and pure PODE₃ but also NH₃/PODE₃ blends with diverse ammonia fractions. The results evince a high degree of prediction accuracy when applying this mechanism, thereby corroborating the efficacy and appropriateness of the mechanism for CFD simulations in NH₃–PODE₃ dual fuel engines. Pathway analysis and sensitivity analysis were also conducted. The results demonstrate that the H-abstraction reactions of PODE₃ by NH₂ radical, R9: PODE₃ + NH₂=PODE₃B + NH₃ and R10: PODE₃ + NH₂=PODE₃A + NH₃, are sensitive only under the condition of AMR = 92.5 % and 1.5 MPa with respect to IDTs. The chain branching reactions, R#1: O₂ + H = O + OH, exhibits the highest sensitivity coefficients for LBV. The NNH radical plays a crucial role in both IDTs and LBVs of NH₃/PODE₃ blends, whereas the CH₃ radical is more prominent at rich regime for LBVs. The results further indicate that increasing AMR can enhance the flame stability of NH₃/PODE₃ blends.