An Experimental Investigation on Air-Fuel Mixture Formation Inside a Low-Pressure Direct Injection Stratified Charge Rotary Engine 930678

Stratified charge engines have been getting attention for the drastic improvement in thermal efficiency at low-load region. There have been researchers on the two types of engines-the high pressure direct injection stratified charge type in which fuel is supplied directly at high pressure into its combustion chamber right before ignition timings, and the low pressure direct injection stratified charge type in which fuel is injected directly into its cylinder while the cylinder pressure is comparatively low[ 1- 3].
Rotary engines have higher freedom than reciprocating engines in terms of equipping direct fuel injection devices, since their combustion chambers rotate along the rotor housing. The fuel supply units, therefore, need not be exposed to high temperature combustion gas. Realization of the low pressure direct injection stratified charge (hereafter “LDISC”) engine is, however, almost impossible without comprehensive understanding of flow fields, because the air-fuel mixing time of this kind of engine is much longer than that of high pressure injection type engines, and hence the flow fields are supposed to give more effect on the mixing process.
There have been several reports on the flow fields of peripheral inlet ported rotary engines from the report made by Yamamoto et al. [ 4] to computational or visualization studies including by the authors[ 5- 8]. Although there have been some computational studies on the flow fields of side ported rotary engines, they focuses on the flow inside a supercharged direct injection stratified charge rotary engine[ 9] at higher intake pressure than that of this study or inside a primixed-charge natural-gas-fueled rotary engine mainly of near top dead center[ 10]. Thus, the flow fields of side ported rotary engines have not been revealed adequately.
The desirable state of stratification in rotary engines is considered to be the stratification of air-fuel mixture in the leading side of combustion chambers. This is because: out of two ignition plugs installed one on the leading side (hereafter “L-side”) and one on the trailing side (hereafter “T-side”) of the combustion chamber, the ignition plug on the L-side has larger opening area and hence better ignitability than the T-side plug, and the poor flame propagation on the T-side of the combustion chamber due to the effects of wall quenching and squish flow.
In this study, to observe the flow-fields and the air-fuel mixing process of a side ported LDISC rotary engine from intake to compression stroke, a transparent single-rotor engine was designed. Not only does the paper provide visualized flow fields, but also shows some results from combustion analysis made on an actual engine with same geometries and timings.


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