Shock Tube Studies Of The Combustion Of Methane Hydrogen Oxygen Mixtures

Shock tubes are as close to an ideal reactor as most modern experiments can attain to examine chemical kinetics. As reaction temperatures drop, homogeneous combustion within a shock tube begins to exhibit inhomogeneous modes, which in a typical Hydrogen-Oxygen system are expressed as deflagration to detonation transition. Experimental results of such a system in the University of Central Florida’s low-pressure shock tube have been collected through end and side-wall imaging to analyze flame structure and chemical kinetics. The purpose of this work is to conduct a baselining of these results using both chemical and computational fluid dynamics modeling. The model will use the Siemens STAR-CCM+ computational fluid dynamics software in order to accurately simulate the system. A seven-step reaction mechanism will be used to accurately capture initialization, propagation, and termination of the combustion within an implicit unsteady, three-dimensional, direct eddy simulation solution on a well-conditioned mesh. The end goal of this study is to create a lightweight model of hydrogen-oxygen combustion with a shock tube for baselining purposes. Both a two- and three- dimensional model were applied in this effort. The simulation results indicate good conditioning and agreement with the experimental results, although some combustion phenomena are not captured as well as a higher fidelity, significantly more computationally expensive model would.

The combustion behavior of methane and ethane is important to the study of natural gas and other alternative fuels that are comprised primarily of these two basic hydrocarbons. Understanding the transition from methane-dominated ignition kinetics to ethane-dominated kinetics for increasing levels of ethane is also of fundamental interest toward the understanding of hydrocarbon chemical kinetics. Much research has been conducted on the two fuels individually, but experimental data of the combustion of blends of methane and ethane is limited to ratios that recreate typical natural gas compositions (up to ~20% ethane molar concentration). The goal of this study was to provide a comprehensive data set of ignition delay times of the combustion of blends of methane and ethane at near atmospheric pressure.