Numerical investigation on ignition characterization of high-pressure oxymethylene ether and n-dodecane sprays

This work investigates the ignition behavior of a high-pressure oxymethylene ether (OME_x) spray, applied to the Engine Combustion Network (ECN) Spray D flame, using large-eddy simulations. The results are compared to available experiments. A referential case of traditional n-dodecane spray using the same configuration was simulated. Besides, two different OME_x mechanisms, namely the Cai et al. (2020) and Niu et al. (2021) mechanisms, are evaluated for the prediction of the OME_x spray. It was concluded that the results of both mechanisms are in agreement with the experiments, with the Cai et al. slightly overpredicting the ignition delay time and the flame lift-off length (LOL_HTC) and Niu et al. slightly underpredicting them in comparison to the experiments. Further analysis of the low-temperature combustion (LTC) and high-temperature combustion (HTC) flame was conducted by comparing to the n-dodecane spray. It was found that the OME_x spray forms more CH₂O around the LOL_HTC, and that HTC is present not only in the periphery of the spray as in the n-dodecane spray but also in the spray head. Besides, due to the different thermophysical properties of OME_x components, the variation of enthalpy as a result of preferential evaporation is significant and subsequently affects the ignition. On the other hand, scalar dissipation rate shows reduced effects on ignition as compared to the n-dodecane spray. An evaluation of the equivalence ratio at the LOL_HTC for the currently investigated OME_x spray configuration suggests a value of around 1.3 for all the simulated cases. The oxygen ratio at the LOL_HTC is around 0.1. Thus, the currently studied spray is expected to be a non-sooting spray, aligning with experimental work.