Physics-based predictive modeling for ultra-low-emission combustion technology

Prospective technologies for low-emission power and propulsion systems rely on highly dilute, low-temperature combustion. Low-temperature combustion prevents formation of oxides of nitrogen, but it has not been achieved in automotive and aerospace applications due to lack of understanding and predictive models. This study will probe the fundamental fluid dynamic processes which are critical to ensure stable, efficient, and clean conversion of fuel energy under such highly dilute conditions. Two complementary technological applications motivate this study. The first is application of 'split-injection' strategies, which are being investigated by partners in the automotive industry. These strategies employ large numbers of separate fuel-injection events in order precisely to control the timing and rate of heat release and pollutant formation. The second application is the injection of highly dilute reactants into a flow structure that recirculates combustion products. This process underpins low-emission aero-engine development by project partner Rolls-Royce - indeed it is fundamental to the development of combustion systems in general. High-end scientific computing methods will be employed to perform full-resolution numerical experiments, designed to explain the relationship between the fluid-, mixing-, and chemical-dynamics of split-injection. For the first time, the age concept will be used in the analysis of these experiments; the age, or residence time, of a mixture is a natural reference quantity for understanding how kinetically limited combustion processes (e.g. autoignition, highly-dilute combustion, NOx and soot-particle formation) evolve. A novel modelling framework, built on this concept of fluid age will be developed and subsequently its potential for the design of ultra-low-emission combustion systems will be demonstrated in automotive and aerospace applications.

This project develops technical knowledge and design tools needed to accelerate deployment of ultra-low-emission combustion technology. It is nationally important that UK industry leads the exploitation of this technology. Combustion provides more than 90% of UK primary energy and the resulting emissions effect air-quality for, and health of the UK population. The analytical tools developed in this research have potential to guide and influence evidence-based policy on emissions. Pathways for achieving these economic, social and environmental impacts are integrated throughout this project.

Economic impact: The most immediate impact of the proposed research will be to benefit automotive and aerospace propulsion and power generation technology. The computational design tools and physical insight being developed will reduce the need for expensive prototype manufacturing and testing in engine development programmes, leading to reduced development time and costs for new low-emission engines. This impact will be achieved through close collaboration with UK-based aircraft engine manufacturer Rolls-Royce plc and automotive consultant Ricardo UK Ltd.. These companies are ideally placed to contribute to the development of low-emission technologies, to exploit them, and thereby to benefit the UK economy.
The researchers will work with engineers at Ricardo and Rolls-Royce throughout this project to ensure that the academic developments and software tools become part of their design processes. The timescale for these design improvements to feed through to the performance of energy technology is estimated to be 3 to 15 years.

Impact on UK skill-base: The early-career researchers working on this project are developing a rare set of theoretical, computational, and engineering skills which are needed to solve complicated multi-disciplinary problems. The quality of their skills will be enhanced by the opportunity this project gives them to work internationally with world-wide specialists. These skills will be shared with the UK firms collaborating on this project. The researchers will provide training to the company engineers on the use of the design tools being developed, but the impact of this project on the UK skill-base is far wider than that: The researchers are planning to develop a demonstration experiment which illustrates the flame- and fluid-dynamics of a pulsed jet flame. The demonstration experiment and animations of our computer simulations will be used to explain this theoretical and computational research in an exciting and tangible way. The demonstration experiment will feature in the University's public outreach days and on youtube.com.

Impact on air quality and climate policy: Episodes of dangerous concentrations of oxides of nitrogen (NOx) have risen since 2009 in certain UK cities even though ever more stringent EU vehicle emission standards have been introduced. This apparent contradiction is explained not only by the increased uptake of diesel cars, but by the alarming finding that under everyday urban operating conditions modern diesel engine emissions of NOx may be five times higher than the values suggested by their performance under Euro-V test conditions (Carslaw et al. 2011). Therefore it is necessary to address this disparity between regulation and reality, and the analytical tools developed in this project can help this.
Ricardo UK has a standing as an independent authority in the automotive industry and serves in an advisory role, for example helping to shape the US's CAFE fuel economy rules. The proposed research on low-emission combustion technology contributes to the understanding of how little pollution automotive engines can potentially produce - which is an important criterion in how emission targets are set - and, through the on-going collaboration with Ricardo described above, the project's findings will further equip Ricardo to advise in this regard.