Numerical Studies of H2 and H2/CO Autoignition in Turbulent Jets

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Title: Numerical Studies of H2 and H2/CO Autoignition in Turbulent Jets
Author: Gupta, Kamlesh Govindram
Advisors: Dr. William Roberts, Committee Member
Dr. Tiegang Fang, Committee Member
Dr. Tarek Echekki, Committee Chair
Abstract: The present study is carried out in two parts. In the first part, the autoignition of hydrogen in a turbulent jet with preheated air is studied computationally using the stand-alone one-dimensional turbulence (ODT) model. The simulations are based on varying the jet Reynolds number and the mixture pressure. Also, computations are carried out for homogeneous autoignition at different mixture fractions and the same two pressure conditions considered for the jet simulations. The simulations show that autoignition is delayed in the jet configuration relative to the earliest autoignition events in homogeneous mixtures. This delay is primarily due to the presence of scalar dissipation associated with the scalar mixing layer in the jet configuration as well as with the presence of turbulent stirring. Turbulence plays additional roles in the subsequent stages of the autoignition process. Pressure effects also are present during the autoignition process and the subsequent high-temperature combustion stages. These effects may be attributed primarily to the autoignition delay time sensitivity to the mixture conditions and the role of pressure and air preheating on molecular transport properties. The overall trends are such that turbulence increases autoignition delay times and accordingly the ignition length and pressure further contributes to this delay. In the second part of this study, similar autoignition study of mixture of hydrogen and carbon monoxide is conducted. Two different mixture compositions are considered. They correspond to H2:CO:N2 ratios by volume of 15:35:50 and 20:30:50. Each composition is simulated for two oxidizer preheat temperatures and two fuel jet Reynolds numbers at atmospheric pressure. Homogeneous autoignition is carried out for same preheat mixture conditions for comparison with the turbulent jet results. The autoignition delay time recorded for jet cases is lower than the homogeneous autoignition delay time. This is attributed to the differential diffusion of hydrogen, which plays an important and enhancing role of the diffusion of hydrogen into the oxidizer.
Date: 2010-03-03
Degree: MS
Discipline: Mechanical Engineering

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