A shock tube study of the ignition delay time of DME/ammonia mixtures: Effect of fuel blending from high temperatures to the NTC regime

An experimental and chemical kinetic investigation has been conducted to understand the effect of dimethyl ether (DME) blending on the ignition delay time of ammonia (NH₃) from high temperatures to the negative temperature coefficient (NTC) regime in a shock tube with the DME fractions of 0 %, 5 %, 25 %, 50 %, and 100 %, temperatures of 690–1810 K, pressures of 1.2 and 10 atm, and equivalence ratio of 1.0. Four representative literature chemical kinetic models were validated against our measurements, however none of the above models can provide reasonable predictions of the experimental data in the NTC regime. A chemical kinetic model was developed in this study, the model was also been validated by the ignition delay times, laminar flame speeds and specie profiles data of DME/ammonia mixtures in the literature. Experimental results show that the ignition delay times of NH₃ can be obviously shorten by 5 % DME addition in both high temperature and the NTC region. Chemical kinetic analyses reveal that the addition of 5 % DME can rapidly generate OH radical through the reaction pathway of HO₂ → H₂O₂ → OH at 1250 K. At 800 K, the blended DME can be rapidly consumed via the reaction pathway of R → RO₂ → QOOH → OOQOOH to promote the production of OH radical in the early stage, thus lead to the reduced ignition delay time of DME/NH₃ mixture.