Laminar Burning Velocities for Hydrogen-, Methane-, Acetylene-, and Propane-Nitrous Oxide Flames

Abstract

Mixtures of four fuels (hydrogen, methane, acetylene and propane) with nitrous oxide were studied to experimentally and numerically determine the laminar flame speeds at near atmospheric pressure (0.8 atm). Using the flat flame method, laminar flame speeds for these nitrous oxide flames were determined for different levels of dilution with nitrogen. A comprehensive hydrocarbon oxidation mechanism in the literature was integrated with a hydrogen-nitrous oxide sub-mechanism, and computational flame speed results using this mechanism were compared to experimental data. For all four fuel systems (hydrogen-, methane-, acetylene-, and propane-nitrous oxide), the compiled chemical mechanism under-predicted the measured laminar flame speeds over the whole range of equivalence ratio investigated. Flame speed sensitivity analyses for the hydrogen-, acetylene-, and propane-nitrous oxide systems have shown that the most sensitive reactions are within the hydrogen-nitrous oxide sub-mechanism. A revision to the reaction rate constant expression for the N₂O + H ⇌ N₂ + OH pathway, one of the most sensitive reaction steps, within the reported uncertainty has improved computational predictions of experimental flame speed data, although further optimization and validation of the kinetic mechanism are required.

Keywords:

• Nitrous oxide chemical kinetics
• Nitrous oxide flame speeds

Acknowledgments

The authors would like to acknowledge financial support from the US Air Force (AFRL/RZA) and from Firestar Engineering, LLC under the DARPA/SBIR program. The authors also would like to thank Prof. Anthony Dean for his insights and suggestions.

Notes

Units: cm³, cal, mol, and sec..

*Rate represented as sum of two Arrhenius expressions.

*The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government.