Experimental and numerical study on lean premixed methane–hydrogen–air flames at elevated pressures and temperatures Erjiang Hu, Zuohua Huang*, Jiajia He, Haiyan Miao State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China article info Article history: Received 6 May 2009 Received in revised form 29 June 2009 Accepted 29 June 2009 Available online 17 July 2009 Keywords: Methane Hydrogen Lean premixed flame Experimental study Numerical analysis abstract Experimental and numerical study on the lean methane–hydrogen–air flames at elevated pressures and temperatures was conducted. The unstretched laminar burning velocities and Markstein lengths were obtained over a wide range of hydrogen fractions at elevated pres- sures and temperatures. The sensitivity analysis and flame structure were also analyzed. The results show good agreement between the computed results and experimental data. The unstretched laminar burning velocities are increased with the increase of initial temperature and hydrogen fraction, and they are decreased with the increase of initial pressure. With the increase of initial pressure and hydrogen fraction, Markstein lengths are decreased, indi- cating the increase of flame instability. Laminar burning velocity is depended on the competition between the main chain branching reaction and chain recombination reaction. The chain branching reaction is a temperature-sensitive reaction, while the recombination reaction is a temperature-insensitive reaction. Numerical study shows that the suppression (or enhancement) of overall chemical reaction with the increase of initial pressure (or temperature) is closely linking to the decrease (or increase) of H, O and OH mole fractions in the flames. Strong correlation is existed between burning velocity and maximum radical concentrations of H and OH radicals in the reaction zone of premixed flames. ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction With the shortage of crude oil reserves and the strengthening of automotive emission legislations, the development of alternative fuel engines has attracted more and more atten- tion in engine community. Natural gas, in which methane is its major component, is considered to be one of the favorable fuels in engines, and the utilization of natural gas has been realized in the spark-ignition engines. However, due to the slow burning velocity of natural gas and its poor lean-burn capability, the natural gas spark-ignition engine still remains its disadvantages like low thermal efficiency, large cycle-by- cycle variation, and poor lean-burn capability, and these will decrease the engine power output and increase the fuel consumption [1,2]. One of the effective methods to solve the problem of slow burning velocity of natural gas is to mix natural gas with a fuel that possesses high burning velocity. Hydrogen is regarded as the best gaseous candidate due to its high burning velocity, and the combination of natural gas with hydrogen is expected to improve the lean-burn characteristics and decrease the engine emissions [3–6]. In order to understand the effect of hydrogen addition into natural gas on engine combustion, the understanding of fundamental combustion behavior with hydrogen enriched * Corresponding author. Tel.: þ86 29 82665075; fax: þ86 29 82668789. E-mail address: zhhuang@mail.xjtu.edu.cn (Z. Huang). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.06.072 international journal of hydrogen energy 34 (2009) 6951–6960