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

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

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.

Planned Impact

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.

Publications

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Shin D, Aspden AJ, Aparece-Scutariu V, Richardson ES (2023) Unsteady self-similarity of jet fluid age and mass fraction

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Shin D.-H. (2017) Self-similarity of passive scalars in a decelerating jet in 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017

 
Description The project has successfully delivered several new results, as well as new computational methods. Controlling the mixing of fuel, air and burned gases is key to achieving efficient low-emission combustion. The mixing dynamics of pulsed fuel injection, also known as split-injection, have been characterised at a fundamental level in order to understand how to tailor the emissions performance of combustion systems, especially future advanced diesel engines. This has been achieved through high-resolution numerical simulations of turbulent mixing in pulsed jets, using the UK's national super computer. The data from these simulations has been analysed in a variety of ways. First, it has been found that the turbulent fuel flow exhibits statistical patterns, remarkably even when the flow is pulsed, enabling theoretical development of simple mathematical models that can be used by design engineers to understand and optimise the effects of different pulsed fuel injection schedules. Second, it has been discovered that the fuel residence time, which is the primary factor controlling the timing of ignition in diesel engines, also exhibits statistical properties that make it possible to predict how residence time varies during a pulsed injection event, and thereby infer how the injection schedule affects ignition and pollutant formation. Due to its physical importance, the fuel residence time has then been used as the basis for deriving new combustion modelling techniques, based on an advanced approach known as double conditional moment closure. This residence time methodology has been tested for its ability to predict split-injection diesel engine performance. The simple properties of residence time statistics obtained in this project make the residence time-based methodology a relatively attractive approach compared to other advanced approaches.
Exploitation Route The key findings of this project relating to the mixing dynamics in unsteady flows are valid for many applications, not just in combustion engines. The properties of unsteady mixing discovered and the modelling methods developed in this work can be applied to situations as diverse as characterising the development of wakes behind submarines, and enhancement of pollution dispersion in the atmosphere.
Sectors Aerospace, Defence and Marine,Energy,Transport

 
Description The project outcomes have been used in analysis of alternative engine concepts, especially for pilot-ignited dual fuel engines, that allow combustion of less-ignitable low-carbon fuels. The theory and modelling of ignition and flame propagation in complex mixtures has been used as a basis for legal evidence in fire and explosion cases.
First Year Of Impact 2019
Sector Aerospace, Defence and Marine,Chemicals,Energy,Transport
Impact Types Economic,Policy & public services

 
Title Pulsed jet DNS data 
Description The data set contains results from full-resolution simulations of turbulent jets involving starting, stopping or continuous flow. 
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
Impact Generation of simple models that predict the relationship between injection rate and entrainment for use in direct injection engine design. 
 
Description Ricardo automotive engineering 
Organisation Ricardo UK Ltd
Country United Kingdom 
Sector Private 
PI Contribution 1) Development of modelling tools 2) Validation and testing of modelling tools 3) Creation of new technology
Collaborator Contribution 1) Access to relevant engine test data 2) Use of Ricardo's design software 3) Use of the Ricardo technical library 4) Joint supervision of PGR student
Impact 1) Simulation tools for automotive applications of cryogenic energy vectors 2) Simulation methodology for split-injection diesel engines 3) Patent application for use of cryogenic energy vectors
Start Year 2010
 
Description Rolls-Royce combustion research 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution 1) Development of simulation tools for engineering design 2) Testing and validation of engineering design tools 3) Invention of new technology
Collaborator Contribution 1) Guidance on appropriate test cases 2) Provision of Rolls-Royce owned software 3) Leadership on the patenting and commercialisation of the combustor-turbine invention.
Impact 1) New design method and simulation tool for predicting altitude relight in gas turbine combustors. 2) Development of a presumed joint-pdf based evaporation model for simulation of turbulent spray combustion. 3) Development of modelling methodology for design of split injection diesel engines. 4) Invention of an integrated combustor-turbine unit.
Start Year 2010
 
Description Sandia Combustion DNS 
Organisation Sandia Laboratories
Country United States 
Sector Private 
PI Contribution Development of models and analysis approaches for simulation and investigation of turbulent combustion
Collaborator Contribution Support on high performance computing and access to research software
Impact Several publications involving Jacqueline H. Chen as co-author
Start Year 2007