Oxymethylene ether – n-dodecane blend spray combustion: Experimental study and large-eddy simulations

Abstract

E-fuels, made from renewable electricity and a CO2 source, have been proposed as a renewable alternative for the mobility sector. In this work, the ignition process and soot formation of the e-fuel oxymethylene ether 1 (OME1) and its blends with n-dodecane are investigated. Experiments of the spray ignition of both neat fuels and a promising fuel blend are conducted under the Engine Combustion Network Spray A conditions in a high-pressure spray chamber and it is found that the fuel blend ignites very similar to n-dodecane. To investigate this behavior in more detail, first a kinetic reaction mechanism for blends of OME1 and n-dodecane is developed and validated using new shock tube measurements. Large-eddy simulations are then performed for the experimental conditions, and spray characteristics as well as ignition delay and flame structure agree well with the experimental results. A super-linear reduction in common soot precursors in the gas phase is found for the fuel blend, which is mainly attributed to a shift of soot precursor production towards higher mixture fractions due to the oxygen content in the fuel. The ignition behavior of OME1 and the fuel blend is investigated in mixture fraction space using one-dimensional unsteady flamelets. It is found that the slow ignition behavior of OME1 is rooted in its high stoichiometric mixture fraction, shifting the most reactive mixture for second stage ignition to very fuel-rich regions, which have a low temperature in a spray case with a cold fuel side. The ignition process of the fuel blend is dominated by its n-dodecane fraction up to 60 mol% OME1 in the blend, and the low increase of ignition delay in this range can be explained by dilution of n-dodecane with OME1.