Autoignition of DME/DMM Fuel Blends: Part II: Reaction Wave Propagation Modes in the Presence of Temperature Gradients

Detonation development in the presence of hot spots is a challenge for some combustion concepts based on autoignition. When those reactivity gradients are caused by temperature inhomogeneities, the disturbed autoignition process can be affected by fuel blends, which reduce the temperature sensitivity of ignition delay times. In Part I of this study, a fuel blend of dimethyl ether (DME) and dimethoxymethane (DMM) is proposed. The reduction of temperature sensitivities of ignition delay times was experimentally confirmed. In the present Part II of this study, fuel blends of DME and DMM are investigated numerically to classify the effect on the mode of autoignitive wave propagation. Two none-dimensional parameters t and e are usually used to create regime diagrams for autoignitive wave propagation in the presence of hot spots. The parameter t is a measure for coupling between pressure wave and reaction wave, whereas e qualitatively describes the characteristic time scale of heat release. Both parameters are calculated using zero-dimensional simulations. Fuel blending using DME and DMM allows for a reduction of t lower than unity over a wide range of temperatures, which is associated with supersonic autoignitive wave propagation. Comparing calculated t and e values to an existing regime diagram from the literature, fuel blending has a significant impact on the position in the regime diagram and thus helps to inhibit detonation formation in the presence of hot spots.