The Effect of Diluent on Flame Structure and Laminar Burning Speeds of H2/CO/oxidizer/diluent

Askari, O., Vien, K., Wang, Z., & Metghalchi, H. (2016). The Effect of Diluent on Flame Structure and Laminar Burning Speeds of H2/CO/oxidizer/diluent. Spring Technical Meeting Eastern States Section of the Combustion Institute. Princeton, NJ.

Experimental studies have been performed in conjunction with a novel differential based multi-shell model to investigate the flame structure and laminar burning speed of H2/CO/oxidizer/diluent premixed flames at high pressures. The laminar burning speed of the combustion process is extracted from the pressure rise during flame propagation. This paper focuses on synthetic gas (syngas) as the fuel, which is a mixture of H2 and CO, and investigates the effect of dilution with helium and EDG (Extra diluent gases), with a composition of 14% CO2 and 86% N2. In this experiment three different EDG concentration (0%, 5% and 10%) has been used. The experiments were performed in two constant volume spherical and cylindrical chambers. The cylindrical chamber was set up in a Z-shaped Schlieren shadowgraph system equipped with a high speed CMOS camera, capable of taking pictures up to 40,000 frames per second, that was used to study the stability of the flame. Laminar burning speeds were measured by a novel thermodynamic model using pressure rise during flame propagation in the spherical chamber. The experiments have been done for laminar burning speeds of smooth H2/CO/O2/He and H2/CO/air/EDG flames over a wide range of temperatures (298K up to 500K), pressures (from sub-atmospheric up to 6atm), equivalence ratios (0.6-3) and three different hydrogen concentration of 5%, 10% and 25% respectively. Extra diluent gases (EDG) lower the laminar burning speeds but do not have significant effect on the stability compared to syngas/air in the stoichiometric case. Substitution of nitrogen in the air with helium, exactly with the same percentage, increases the range of temperature and pressure of stable flame as well as the laminar burning speed.