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Tests were performed in an actual engine with swirl and without to understand charge swirl effect for an 1.5l, 4-cyl and 4-stroke SI engine. Swirling inlet flow resulted in the improvement of the engine performance at engine speed of up to 4,000rpm, however, it was reversed at higher engine speed, compared with that of ordinary non-swirling case. Additionally, a single shot visualized engine driven by a rapid compression expansion machine was built separately to inspect the swirl effect on combustion process. In the visualization study, stoichiometric LPG -air mixture was used at three different levels of swirl strength, where the equivalent engine speed was set at 1500, 2500 and 3500 rpm and taken by shadowgraph technique with a high speed camera. A visualized tests supported the combustion rate increasing phenomena excited by swirl by observations on equivalent flame radii and, also, by energy release fractions and cyclic variations.

In order to find the dynamic TDC a microwave sensor was installed on the head and a proximity probe on the wall of 4-cyl SI engines. The dynamic TDC determined by the microwave system exhibited fairly consistent results having less than 0.05 degrees in standard deviation and remaining nearly constant throughout the speed range of 1,000-2,500 rpm. There was 0.1-0.2 degrees difference between the dynamic TDC measured by the microwave sensor and that measured by the proximity probe; the microwave result was believed to be more reliable. The difference seemed to originate from the built-in system errors on the part of proximity apparatus caused by insufficient sensitivity and availability of data points and piston tilting motion. Both flush mounted and spark plug type pressure transducers were used to measure the motoring peak pressure.