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Combustion properties of hydrogen with N₂ dilution were investigated. The laminar and turbulent burning velocities were examined for outwardly propagating stoichiometric H₂/O₂/N₂ flames varying the amount of diluent N₂. The unstretched laminar burning velocity, ul decreased with the increase in the amount of N₂. Markstein number, Ma, the sensitivity of the flame to the stretch due to the thermo-diffusive effects decreased with the increase in the amount of N₂.

EGR (Exhaust Gas Recirculation) is adopted to reduce NOx emission in spark ignition engines. The effects of dilution with CO₂ and N₂, the main components of EGR, on laminar flame were investigated. It had been found that CO₂ and N₂ dilutions affected not only laminar burning velocity but also the response of flame to the flame stretch due to the change in the thermo-diffusive properties of the mixtures by the dilutions. Thus, turbulent flames were also investigated at fixed flame stretch factors to examine solely the thermo-diffusive effects on turbulent flame.

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.