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In general, metal-based detergents are used in engine oil to prevent the adhesion and accumulation of deposits and sludge. Because metal-based detergents are additives composed of fatty acid metal salts and carbonates, such as calcium, they are known to be easily affected by water. In particular, over-based metal-based detergents containing a large number of carbonates, which are excellent in terms of detergency, have been used often in recent years. Following the increasing use of biofuels and the diffusion of hybrid vehicles, the risk of water being mixed into engine oil has increased. For example, in hybrid vehicles, it is assumed that the engine oil temperature decreases and it becomes difficult for water to volatilize. Also, the E100 fuel contains several percent of water.

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.