The combination of three-way catalytic converter and stoichiometric mixture in Spark Ignition engines is world-wide used. However, another relevant solution to reduce fuel consumption and pollutant emissions is the lean burn working. Global lean mixtures can be obtained by diluting stoechiometric one with an excess of intake air or with massive exhaust gas re-circulation (EGR). One of the main advantages is a gain of efficiency due to less pumping losses. Unhappily, engine torque fluctuations arise and consequently the engine efficiency gain is not as high as we can theoretically expect. Moreover, incomplete combustion or misfire can occur, providing unacceptable hydrocarbons emissions. One cause is the difficulty to ignite lean mixture flames.Therefore, the objective of our work is to understand as well as possible, the main cause of initiation failures, with extensive use of optical diagnostics.In this paper we present some experimental investigations on the behaviour of the flame kernel submitted to an aerodynamic flow around the electrodes in an engine environment. The flow is investigated by Particle Imaging Velocimetry (PIV) which provides an instantaneous 2-D velocity field at a fixed time in each engine cycle. The originality of this study is that we get the simultaneous information of the flame kernel surface with an intensified CCD camera, to correlate flame shape with aerodynamical field within each individual cycle.We clearly show flame kernel is convected in the combustion chamber as the main flow field.
Effects of instantaneous flow field near the spark plug on the flame kernel behavior in a s.i. engine
1999
Conference paper
English
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