Influences of Turbulence Scale on Development of Spherically Propagating Flame under High EGR Conditions

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. As the size of flame becomes larger, the scales of turbulent eddies effective to turbulent burning velocity may vary.