Turbulent Burning Velocities of Stoichiometric Hydrogen-Carbon Monoxide-Air Flames at Elevated Pressures

Syngas, is an alternative fuel consisting mainly of hydrogen and carbon monoxide in various proportions. An understanding of the effects of the varying constituents on the combustion characteristics is important for improvement of the thermal efficiency of syngas-fueled engines. The effects of hydrogen concentration and mixture pressure on the turbulent burning velocity of outwardly propagating stoichiometric flames of hydrogen-carbon monoxide-air were studied in a constant volume fan-stirred combustion chamber at a constant mixture temperature of 350 K. The mole fraction of hydrogen in the binary fuel was varied from 0 to 1.0, at mixture pressures of 0.10, 0.25 and 0.50 MPa. The turbulence intensity was kept constant at 3.27 m/s. For fixed mixture pressures, it was found that the turbulent burning velocity increased with an increase in hydrogen fraction primarily due to increase in the unstretched laminar burning velocity. The ratio of the turbulence intensity to the unstretched laminar burning velocity decreased with an increase in hydrogen fraction. This led to a decrease in the ratio of the turbulent burning velocity to the unstretched laminar burning velocity. For fixed hydrogen fractions, the turbulent burning velocity and the ratio of turbulent burning velocity to the unstretched laminar burning velocity increased with an increase in mixture pressure even though the unstretched laminar burning velocity decreased. This observation was due to an increase in the ratio of the turbulence intensity to the unstretched laminar burning velocity, a decrease in the Markstein number, and an increase in the turbulence Reynolds number.