The Laminar Burning Velocity of Mixtures ofHydrogen, Air and Residuals at Spark-Ignition Engine Conditions

摘要

Hydrogen can be used as an alternative fuel in spark-ignition engines. Exhaust emissions arevery clean, CO2 emissions are eliminated and there is an unlimited resource of hydrogen. Theauthors aim to develop a computer model for the combustion of hydrogen in spark-ignitionengines to optimise the performances of these engines, without the need for extensiveexperimental work.A quasi-dimensional simulation programme was chosen as a compromise between accuracyand calculation time. During its development, the lack of a suitable laminar flame speedformula for hydrogen/air mixtures became apparent. A literature survey shows that none ofthe existing correlations covers the entire temperature, pressure and mixture compositionrange as encountered in spark-ignition engines. Moreover, there is ambiguity concerning thepressure dependence of the laminar burning velocity of hydrogen/air mixtures. Finally, nodata exists on the influence of residual gases.This paper looks at several reaction mechanisms found in the literature for the kinetics ofhydrogen/oxygen mixtures. An extensive set of simulations with a one-dimensional chemicalkinetics code is performed to evaluate these mechanisms. Their performance is judged bycomparing with experimental data for varying equivalence ratio, temperature, pressure, andresidual gas content. The calculated effect of residuals on the burning velocity is shown to befairly accurate, and an extension to existing correlations that do not implement residual gaseffect is proposed. The extension is valid for residual gas volume fractions up to 30%. Theperformance of the mechanisms to predict temperature and pressure effects is shown to bequite poor.Finally, attention is given to the appearance of cellular flames. The occurrence of cellularinstability for hydrogen flames at engine conditions is shown and implications for turbulentcombustion models are discussed.