Investigating the trend of hydrogen’s flame velocity profile in relation to pressure and temperature above and below the adiabatic point

Abstract

This document discusses the hydrogen combustion flame with a special focus on the flame velocity profile in relationship to combustion pressure and temperature. First, the chemistry associated with hydrogen combustion is discussed along with the important factors that affect the hydrogen flame. Then some of the models for hydrogen flame velocity are discussed. Computational analysis is performed to determine the trend of the flame velocity profile in relation to pressure and temperature above and below the adiabatic temperature point. Twelve test cases, made of combinations of pressure and temperature variations, are used to monitor the trend of the velocity profile when the temperature was under the adiabatic temperature point and when it was above the adiabatic temperature point. It is shown that increasing pressure or temperature, or both, always increased the flame velocity, which is consistent with the physics law. However, this study demonstrated that below the hydrogen adiabatic point, the hydrogen flame average velocity was much more responsive; it increased more than 9 times than when the temperature was above the adiabatic point; it only increased about 5 times. This was observed over the same range of applied pressure and the same range of applied temperature. A physics-based explanation is presented for this trend by considering the kinetic energies associated with the hydrogen species above and below the adiabatic point and the completeness of the combustion. It is also found that the peak velocity profile took place at around 40% of hydrogen concentration.