Development of tools for the numerical simulation of turbulent combustion

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Combustion of hydrocarbons is an important phenomenon in many engineering applications. The chemical kinetic mechanisms required to completely describe these systems are usually extremely large, often comprising thousands of reactions involving hundreds of chemical species. In virtually all practical applications of combustion processes, the flow in which the combustion takes place is turbulent and there is a complex, non-linear interaction between the chemical and flow processes. New developments in the use of stochastic processes to simulate combustion processes have begun to offer new insight into the discrete nature of processes like chemical reactions. A recent stochastic particle model (SPM) has been used to study the effects of discrete reactions on the shot-to-shot variations in ignition delay times. Understanding these variations is critical to the design and operation of advanced new engine concepts such as HCCI engines. We will use the SPM to study ignition in two contexts: 1 - ignition homogeneity, where it is often assumed that the entire homogeneous mixture ignites simultaneously, but evidence suggests that there may be a regime in which ignition occurs in spots that lead to propagating flames; and 2 - ignition of turbulent jets using Large Eddy Simulation with the stochastic particle model will be used to generate independent reduced chemistry manifolds that will allow us to study the independent effects of turbulence and chemical reaction variations. We will also use the Linear Eddy Model, a model that approximates the impact of turbulent mixing in one-dimensional simulations of reacting flows, to generate improved predictions of the probability density function of reaction progress variable in turbulent premixed combustion, with a view to improving our predictions of turbulent premixed flames.