Experimental and chemical kinetic modeling study of trimethoxy methane combustion

Abstract

The use of oxymethylene ethers (OMEs) as alternative fuels or fuel-additives has motivated the present study on the combustion behavior of trimethoxy methane (TMM), which is a branched version of OMEs. A detailed chemical kinetic model for TMM combustion is provided, which is based on a recent model for the structurally similar dimethoxy methane (DMM) and recent elementary reaction kinetics studies. This model is validated against TMM ignition delay times measured in a shock tube at 20 and 40 bar, under fuel lean, stoichiometric, and fuel rich conditions. Further, the TMM model is validated against laminar burning velocities, which were measured in a heat flux setup for a variation of fuel/air ratios. A good agreement between the TMM model predictions and the measured ignition delay times and laminar burning velocities is observed. At fuel rich conditions in the shock tube, however, the model underestimates the reactivity of TMM by up to 60%, which could not be compensated by physically meaningful modifications of the TMM model. The analysis of the TMM model shows that at low temperatures, TMM is primarily consumed via H-atom abstraction by ȮH radicals, followed by classical β-scission and low-temperature chemistry. At higher temperatures, a significant fraction of TMM is consumed via unimolecular decomposition, leading to a higher reactivity compared to OME2. The present model and experiments lay the foundation for future kinetic modeling of TMM and other branched OME-like compounds.