Modeling of Combustion in Stratified Hydrogen-Air Mixtures
Rebecca Owston
Mechanical Engineering Dept.
LWSN 3102AB 4:00 - 5:00 PM
Wednesday, March 25, 2009
This talk will begin by discussing an interesting difference between hydrogen flames and hydrocarbon flames when they interact with walls. Such interactions are important in engines. Results from recent numerical work carried out to address the two questions above will then be presented.
Immediate challenges facing the power-generation and transportation sectors include the need to decrease emission of toxic pollutants and greenhouse gases, while simultaneously reducing dependence on nonrenewable resources. Replacement of hydrocarbon fuels with hydrogen has the potential to address both of these concerns for some applications. While the combustion of hydrogen has been investigated extensively in the past, such investigations do not always provide answers to specific questions which arise in the context of applications. For example, two questions that arise when using hydrogen in direct-injected hydrogen internal combustion engines are: How does the flame propagate from a spark-ignition source in hydrogen-air stratified mixtures? Is there an optimal composition where ignition is preferred in a hydrogen-air stratified mixture? Since a significant number of properties of hydrogen are very different from those of conventional fuels, previous results from the existing body of literature on hydrocarbon-fueled engines do not necessarily hold true for hydrogen-air combustion. This is a strong motivation for continued research in hydrogen-air mixtures. Furthermore, since the detailed chemistry of hydrogen oxidation is fairly well-known, flow-chemistry interactions can be studied with greater confidence relative to hydrocarbon fuels, and fundamental insights gained can be useful in understanding stratified-charge combustion of any fuel.
This talk will begin by discussing an interesting difference between hydrogen flames and hydrocarbon flames when they interact with walls. Such interactions are important in engines. Results from recent numerical work carried out to address the two questions above will then be presented. First, simulations of flame propagation from a spark-ignition source will be examined. It will be shown that the flame propagates through the stratified mixture as a triple flame. Several interesting properties of the triple flame and the dependence of the properties and speed of flame on thermodynamic conditions will be presented. Next, results from simulations where the spark location was varied in the stratified mixture will be presented, and the sensitivity of the subsequent flame speed to the initial location will be examined. In these simulations, the fluid mechanics equations are directly solved and coupled to a detailed chemical mechanism through an interface with CHEMKIN. Finally, the outlines of a model developed for predicting
combustion in stratified mixtures will be discussed. This model can be used in LES, and RANS simulations.
Biography - Rebecca Owston is a doctoral candidate in the Mechanical Engineering Department, specializing in Computational Engineering through the Computational Science and Engineering program at Purdue University. She earned an M.S.M.E. degree at Purdue (2006), and a B.S. at the University of Tennessee, Knoxville (2004). She is a NSF graduate research fellow and a fellow of the National Defense Science and Engineering Graduate Fellowship program. Her research interests lie in the general areas of reacting fluid mechanics, heat transfer, and combustion modeling. She currently has four archival publications, and has participated in various conferences through papers and presentations