A Comprehensive Experimental and Kinetic Modeling Study of the Combustion Chemistry of Diethoxymethane

The potential biohybrid fuel diethoxymethane (DEM) shows similar efficiency in reducing the peak mole fraction of soot precursors as oxymethylene ethers with having a higher energy density. In the present work, the fundamental combustion chemistry of DEM is studied experimentally and theoretically to obtain a comprehensive description of its combustion characteristics. A detailed kinetic model is developed to describe the pyrolysis and oxidation processes at low and high temperatures. To achieve this, rate coefficients for the unimolecular fuel decomposition and the thermal dissociation of a relevant Q˙OOH radical are predicted from high-level ab initio calculations. In addition, ignition delay times of DEM have been measured in a shock tube and in a laminar flow reactor over a wide range of conditions (p = 1-50 bar, T = 480-1170 K, and equivalence ratios of 0.5, 1.0, and 2.0). Laminar burning velocity experiments of DEM/air mixtures have been performed in a spherical combustion vessel at an initial temperature of 398 K, at pressures from atmospheric pressure to 2.5 bar, and at equivalence ratios from 0.8 to 1.7. In addition, the experimental measurement campaign in this study was complemented with the determination of extinction strain rates for non-premixed DEM flames in a laminar counterflow burner. All of these experiments substantially extend the current database describing DEM oxidation. The validation of the newly developed model is performed with the data sets from this work and available literature. Rate of production and sensitivity analyses were performed to identify critical pathways and to understand the mechanism in more detail. In contrast to other highly reactive fuels, the characteristic of autoignition behavior of DEM is different and does not show negative temperature coefficient (NTC) behavior under the conditions investigated. The chemical reactivity at intermediate temperature of DEM is controlled by two fast β-scission reactions and HȮ2 elimination reactions.