A detailed experimental and kinetic modeling study on pyrolysis and oxidation of oxymethylene ether-2 (OME-2)

Abstract

The application of oxymethylene ethers as an alternative fuel (additive) produced via carbon capture and utilization can lead to lower CO2 and particulate matter emissions compared to fossil fuels. To improve the understanding of the pyrolysis and oxidation chemistry of oxymethylene ether-2 (OME-2), a combined experimental and kinetic modeling study has been carried out. Pyrolysis experiments were performed using a quartz reactor over a broad temperature range, from 373 to 1150 K, to elucidate both the primary and secondary pyrolysis chemistry. The thermal decomposition of OME-2 is initiated via a dominant formaldehyde elimination reaction. Radical chemistry becomes only significant at higher temperatures (>800 K) and competes with unimolecular decomposition. Radicals originate mainly from the decomposition of carbenes. Important intermediate products formed during pyrolysis are dimethoxymethane, formaldehyde, methane and methyl formate. The formation of products with carbon-carbon bonds is minor since only carbon-oxygen bonds are present in OME-2. The oxidation chemistry was investigated between 600 and 715 K by ignition delay time measurements in a rapid compression machine for OME-2/air mixtures with an equivalence ratio ϕ of 0.5. No negative temperature coefficient region is observed. An elementary step kinetic model is constructed with the automatic kinetic model generator Genesys starting from the base mechanism AramcoMech 1.3. Important thermodynamic parameters and reaction rate coefficients to describe the low- and high-temperature decomposition chemistry are obtained from quantum chemical calculations. The new kinetic model satisfactorily reproduces the measured ignition delay times, as well as major product mole fractions from the pyrolysis experiments within the experimental error margin of 10% on average, without fitting thermodynamic or kinetic parameters. Finally, rate of production analyses reveal the important decomposition pathways to methyl formate, formaldehyde and others under pyrolysis and low-temperature oxidation conditions.