Development of Efficient and Clean Turbulent Stratied Mixture Combustion Technologies for Future Combustors using High-Fidelity Simulations

According to the U.S. Department of Energy, the combustion of fossil fuels accounts for 80% of the worlds energy usage, and their projections show this gure reducing to only 68% in 2050. The emissions resulting from combustion lead to climate change and poor air quality in densely populated cities. Consequently, pollution control regulations are becoming ever stricter, posing a major challenge for engineers to design an environmentally friendly combustion engine with
acceptable engine efficiency.

In some engineering applications, combustion takes place in a conguration where the fuel and oxidiser are neither homogeneously mixed nor completely separated from each other prior to combustion. This kind of combustion is often referred to as stratified charge combustion or partially premixed combustion. This inhomogeneous mixture allows a leaner overall fuel-air ratio to be used, which has the potential to signicantly reduce pollutant emissions while increasing
engine efficiency. The technology is currently being used in direct injection and homogeneous charge compression ignition engines in modern vehicles, and in lean premixed prevapourised gas turbine engines in aircraft as well as many other applications. Such engines are still in their infancy in most cases. Uncertainties regarding combustion behaviour, when compared with premixed and non-premixed counterparts, is impeding their widespread adoption. Taking automotive engines as an example, improper mixture preparation and can lead to pre-ignition caused by excessive pressure, or engine knocking due to the flame not consuming all of the available reactants. Both of these drastically reduce engine efficiency. Thus, further research is required into proper mixture preparation for reliable, clean and efficient stratified mixture combustion.

In this research project, Direct Numerical Simulations of turbulent stratied mixture combustion will be performed on national high-performance computing facilities. The number of such studies of stratified mixture combustion is scarce when compared with premixed and non-premixed cases. Direct Numerical Simulations resolve the turbulent reacting flow entirely, without the need for turbulence models (i.e. approximations). The simulation data can be treated as experimental data with a very high resolution. As the first step of this project, three-dimensional Direct Numerical Simulations will be performed with simplied chemistry to improve the fundamental understanding of the thermal aspect of the stratified charge combustion process. Simplified chemistry reduces the number of equations to be solved resulting in much quicker simulation times. Based on this understanding, detailed chemistry 3D simulations will be carried out. These simulations will provide important physical insight into the not-well-understood physics of turbulent mixing and will further knowledge regarding optimal mixture and turbulence properties for clean, efficient combustion. As these simulations are of such high computational cost, they cannot be afforded for routine engineering calculations. Therefore, the physical insight obtained from this simulation database will be transferred into accurate turbulence models for industrial solvers based on the Reynolds Averaged Navier-Stokes and Large Eddy Simulation frameworks.

The major beneciaries of this work are the industrial sectors engaged in developing new concepts for designing low-pollution high-efficiency automotive engines and gas turbines. The design process in these applications depends on the predictive capability of engineering calculations.