Numerical study of combustion mode and diffusive transport underlying fuel ignitions in lean stratified dimethyl ether-air premixture at various turbulence intensities

Abstract

This paper presents a systematic numerical investigation of the auto-ignition phenomenon in stratified dimethyl ether (DME)/air turbulent mixtures. The study was conducted at an initial pressure of 30 atm, mean temperature of 650 K, and equivalence ratio of 0.45, with varying Damköhler numbers (Da) ranging from 0.01 to 1.1. The simulations indicated that the transition point between two combustion modes, deflagration wave and spontaneous ignition, occurred at a Da value of 0.06. The chemical explosive mode analysis identified the leading role of diffusive transport in both modes. A diffusion index (DI) was defined to quantify contributions of each diffusive sub-process. The DI results revealed that heat conduction and oxygen diffusion are the most important processes for the low-temperature ignition, followed by DME, CH2O, and HOCH2OCO with decreasing importance. Further DI analysis of the detailed local flame structure demonstrated that heat, DME, O2, and H2O2 diffusive transports have moderate importance for depressing turbulent propagation at local extinction modes. In conclusion, the proposed DI method has the potential to be a more efficient and rigorous substitution for sensitivity analysis and transport budget analysis.