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EGR (Exhaust gas recirculation) can reduce the pumping loss and improve the thermal efficiency of spark ignition engines. The techniques for combustion enhancement under high EGR rate condition has been required for further improvement of the thermal efficiency. In order to develop the technique of combustion enhancement by turbulence, the influences of turbulence scale on combustion properties, such as probability of flame propagation, EGR limit of flame propagation, flame quenching and combustion duration were investigated under the condition of same turbulence intensity. Experiments were carried out for stoichiometric spherically propagating turbulent i-C8H18/Air/N2 flames using a constant volume vessel. It was clarified that all of these combustion properties were affected by the turbulence scale. The development of spherically propagating turbulent flame during flame propagation was affected by the turbulence scale.

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.

Outwardly propagating stoichiometric flames of H2/CH4/air were studied in a constant volume fan-stirred combustion chamber in order to investigate the effects of hydrogen concentration on the turbulent burning velocities. The experiments were conducted at mixture temperature of 350 K and mixture pressure of 0.10 MPa. The mole fraction of hydrogen in the binary fuel was varied from 0 to 1.0 for turbulence intensities equal to 1.23, 1.64 and 2.46 m/s. Laminar flames of the mixtures were first investigated to obtain the unstretched laminar burning velocities and the associated Markstein numbers. The unstretched laminar burning velocity increased non-linearly with increase in hydrogen fraction. The Markstein number and the effective Lewis number of the mixtures varied non-monotonically with hydrogen mole fraction. The Markstein number was used to investigate the influence of thermo-diffusive effects on the turbulent burning velocity.