Simulation and Experimental study on Swirling and Tumbling Motions of SI engine

Gas motion within the cylinder is one of the major factors that control the combustion process in spark-ignition engine. It also has significant impact on heat transfer. Both the bulk gas motion and the turbulence characteristics of the flow are important and governing the overall behavior of the flow. Intense turbulence is required to realize stable combustion with low laminar burning flame velocity for lean burn. Generally speaking, kinetic energy to produce turbulence is given by air flow during the intake process. The energy preserved in the large scale eddies and converted into turbulence at the end of compression stroke. Mitsubishi [1,2] and Subaru adopt tumble as the large scale eddy to preserve the energy. Honda [3] adopts swirl, and Toyota [4,5] , Nissan [6] and Mazda[7] adopt so-called inclined swirl, that is the flow combined tumble and swirl. The aim of the paper is to find out which is more adequate for lean burn, tumble or swirl? For finding the answer, two flow control baffles are made and installed in the cylinder head of engine. The behavior of the combustion with these control baffles are simulated and tested. With the first flow control baffle, the part of the intake port entrance is blocked so the flow during entering the cylinder rotates and produces different bulk motion, swirl. (Figure 1) And with another flow control baffle the entire of one of the intake valve (from two intake valves) is covered. (Figure 1)