Six-Stroke, High-Efficiency Quasiturbine Concept Engine With Distinct, Thermally-Insu
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18-10-2010, 12:36 PM

Six-Stroke, High-Efficiency Quasiturbine Concept Engine
With Distinct, Thermally-Insulated
Compression and Expansion Components

George Marchetti and Gilles Saint-Hilaire

Need to increase engine thermal efficiency. This paper presents a Quasiturbine thermal management strategy in the development of high-efficiency engines for the 21st century. In the concept engine, high-octane fuels are preferred because higher engine efficiencies can be attained with these fuels. Higher efficiencies mean less fuel consumption and lower atmospheric emissions per unit of work produced by the engine. While the concept engine only takes a step closer to the efficiency principles of Beau de Rochas (Otto), it is readily feasible and constitutes the most efficient alternative to the ideal efficiencies awaiting the development of the Quasiturbine photo-detonation engine, in which compression pressure and rapidity of ignition are maximized. One of the most difficult challenges in engine technology today is the urgent need to increase engine thermal efficiency. Thermal management strategies and the choice of fuels will play crucial roles in the development of high-efficiency engines for the 21st century. However, it was during the 19th century that the fundamental principles governing the efficiency of internal combustion engines were first posited. In 1862, Alphonse Beau de Rochas published his theory regarding the ideal operating cycle of the internal combustion engine. He stated that the conditions necessary for maximum efficiency were: (1) maximum cylinder volume with minimum cooling surface; (2) maximum rapidity of expansion; (3) maximum pressure of the ignited charge and (4) maximum ratio of expansion. Beau de Rochas' engine theory was first applied by Nikolaus Otto in 1876 to a four-stroke engine of Otto's own design. The four-stroke combustion cycle later became known as the "Otto cycle". In the Otto cycle, the piston descends on the intake stroke, during which the inlet valve is held open. The valves in the cylinder head are usually of the poppet type. The fresh fuel/air charge is inducted into the cylinder by the partial vacuum created by the descent of the piston. The piston then ascends on the compression stroke with both valves closed and the charge is ignited by an electric spark as the end of the stroke is approached. The power stroke follows, with both valves still closed and gas pressure acting on the piston crown because of the expansion of the burned charge. The exhaust stroke then completes the cycle with the ascending piston forcing the spent products of combustion past the open exhaust valve. The cycle then repeats itself. Each Otto cycle thereby requires four strokes of the piston- intake, compression, power and exhaust- and two revolutions of the crankshaft. The disadvantage of the four-stroke cycle is that only half as many power strokes arecompleted per revolution of the crankshaft as in the two-stroke cycle and only half as much power would be expected from an engine of given size at a given operating speed. The four-stroke cycle, however, provides more positive scavenging and charging of the cylinders with less loss of fresh charge to the exhaust than the two-stroke cycle. Modern Otto cycle engines, such as the standard gasoline engine, deviate from the Beau de Rochas principles in many respects, based in large part upon practical considerations related to engine materials and the low-octane fuel used by the engine. The six-stroke Quasiturbine concept engine described in this monograph is designed to overcome many of the limitations inherent in the Otto cycle and bring the engine's operating cycle closer to Beau de Rochas' ideal efficiency conditions. The preferred fuel for the concept engine is methanol because of its high-octane rating and its ability to cool the fuel/air charge during the intake stroke.

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