Abstract
Research has been conducted on an extended expansion engine, using a multiple-linkage system to increase thermal efficiency of internal combustion engines. A four-jointed linkage was attached between the connecting rod and the crank pin of a conventional piston-crank system. The end of the linkage rotates at half the speed of the crankshaft, resulting in piston strokes unequal length in each revolution. The length of the expansion stroke is greater than that of the compression stroke, thereby providing an extended expansion cycle, so called Atkinson cycle. An air-cooled single-cylinder engine equipped with this mechanism was constructed and its thermal efficiency was compared in tests against a conventional engine which has same maxmum power. The brake performance of both engines was measured, displaying 2.7 to 3.5% increase of brake efficiency under high-load operation. Measurements of drive loss during motoring operation showed that the friction of this engine is approximately the same as that of a conventional engine, due to the reduction of the piston skirt friction during expansion stroke. The maximum inclination angle of connecting rod of this linkage system during expansion stroke is small, so the side force of piston skirt is smaller than that of the conventional piston-crank system.
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