RO2 and QOOH Chemistry in Dimethylether Combustion

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Dimethylether (DME, CH3OCH3) has considerable potential as an alternative clean fuel. It has energy densities similar to current biofuels such as ethanol, is compatible with existing engine technologies, burns with low NOx and soot emissions and can be distributed via available LPG networks. However, relatively little is known about the 'low temperature' (500 - 900 K) combustion of DME; combustion in this temperature range is particularly important in newer engine technologies such as HCCI (homogeneously charged compression ignition). This proposal seeks to characterise the mechanisms of DME combustion providing useful information to the academic combustion community and industrial collaborators. The proposal is matched to EPSRC priorities in energy research.There have been a number of previous studies on low temperature DME oxidation, but no previous study has been able to observe radical intermediates directly or to be free from potential complications of reactions on surfaces. In the current proposal we will use a novel high temperature (up to 900 K), high pressure (up to 5 atm) turbulent flow tube providing a wall-less reactor suitable for studying radical reactions on time scales of up to several hundred milliseconds. The flow tube will be directly interfaced to a low pressure fluorescence cell for radical detection and a time-of-flight mass spectrometer for detection of the proposed products from chain propagation and chain branching reactions (e.g. CO and formaldehyde).Our experiments will probe the competition between chain propagation (controlled oxidation) and chain branching (explosive oxidation) as a function of temperature and pressure. Observation of radicals and stable products, in conjunction with the use of isotopically labelled precursors, will allow us to determine the molecular mechanism of DME oxidation. The experimental results will be combined with theoretical calculations carried both at the University of Leeds and Argonne National Laboratory (Drs Klippenstein and Harding) to give a full picture of the mechanism and allow us to extrapolate our results to wider ranges of temperature and pressure. The impact of the work will be assessed in conjunction with Dr Henry Curran (Director, Centre for Combustion Chemistry, University of Galway) via updated kinetic models of DME combustion and comparison with end-product studies from shock tubes or engine simulations.The work has obvious practical and commercial implications and we are working with Ford and the International DME Association (IDA, and through to IDA to organisations such as Volvo Technologies and Rolls Royce) to enhance the impact of EPSRC investment.