RO2 and QOOH Chemistry in Dimethylether Combustion

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.

Impact is fully integrated into this project. Dimethyl ether (DME) has good potential for use as a future fuel. The objective of the project is to better understand the very poorly characterised, but vitally important issues around DME autoignition. For coventional engines an understanding of the combination of fluid mechanics and heat release has been sufficient to drive the development of engine design, however, for newer technologies such as homogeneous charge compression ignition (HCCI), the chemistry of autoignition is central to our understanding of processes such as engine knock and performance under a range of conditions. Understanding the chemistry of DME chain branching will therefore have significant impact to engine design and the viability of DME as a fuel of the future.

Impact is classified by EPSRC under four major headings: Knowledge, People, Economy and Society (http://www.epsrc.ac.uk/funding/apprev/preparing/Pages/economicimpact.aspx).
Knowledge - Knowledge generation is a major component of this project and in addition to dissemination through appropriate conferences and journal publications, we will be running workshops with industrial collaborators to facilitate direct transfer into industry. Collaborators include Ford and the International DME Association, and through the IDA links to companies such as Volvo Technologies and Total; Curran has collaborations with Rolls Royce turbines. The updating of chemical models of DME combustion ensures that the detailed chemical understanding developed through experiments, ab initio and master equation calculations is presented in a format that will be useful for applications. It is important to note that knowledge transfer is a two way process and workshops run during the early part of the project will be a way for collaborators to provide input and help shape all aspects of the project.
People - ROQOCO will provide multidisciplinary training to the PDRA and encourage them to interact with other academics in the programme and external collaborators, providing well trained and motivated researchers equipped for careers in research and/or industry.
Economy - ROQOCO will contribute significantly to our understanding of DME combustion and hence there is the potential for significant impact on the uptake of DME as a viable fuel. As DME can be efficiently synthesised from natural gas (or biomass), the UK could benefit significantly in the medium to long term.
Society - Energy provision and security is a major societal issue. Having DME is a viable transportation or electricity generating fuel that can be produced from either renewable sources (biomass, hence with potential to reduce CO2 emissions) or relatively stable supplies of natural gas, widens the spectrum of fuels available in the future and this can only enhance stability of supply.