Combining mass spectrometry, i2PEPICO, and FTIR spectroscopy: Comprehensive speciation in DMM/NO oxidation

Abstract

Oxymethylene ethers (OMEs) are potential alternative fuels that can be produced in a sustainable way based on CO2 and electricity. Additionally, they exhibit low tendencies to emit NOx or soot during practical combustion. Dimethoxy methane (DMM, CH3OCH2OCH3) has received increasing attention as the smallest OME with a O-CH2-O moiety. In the face of a possible application in exhaust gas recirculation (EGR) scenarios, understanding the influence of NOx on DMM oxidation is of importance. In this work, eleven mixtures of DMM/NO/O2/Ar were investigated in an atmospheric laminar flow reactor employing an extensive set of diagnostics. Molecular-beam mass spectrometry (MBMS), Fourier-transform infrared (FTIR) spectroscopy, NOx chemiluminescence detection, and double imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy were combined to obtain a reliable speciation. All in all, species concentrations from different instruments showed a good agreement and one technique could counterbalance the physical limitations of another technique in many cases. In this manner, accurate mole fraction profiles of intermediates like e.g. CH4, C2H4, NO2, and methyl formate (C2H4O2) were gained. Based on i2PEPICO results, nitromethane (CH3NO2) and trans-HONO could additionally be identified as crucial intermediates in the NO-assisted oxidation of DMM. The present data set therefore provides an excellent basis to enhance future model development.