Essay About Stroke Engine And High-Efficiency Quasiturbine Concept Engine

Six Stroke Engine – Compression and Expansion Components
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A Six-Stroke, High-Efficiency Quasiturbine Concept Engine
With Distinct, Thermally-Insulated
Compression and Expansion Components
Abstract: One of the most difficult challenges in engine technology today is the urgent
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 Ottos 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 are
completed 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 engines
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.
Maximum Volume / Minimum Cooling Surface
The first Beau de Rochas principle teaches that the engine should have a
minimum cooling surface area while still allowing for maximum charge volume during
intake (“volumetric charge efficiency”). Otto cycle engines generally have cooling
systems.1 The cooling system represents an engineering compromise. Without a cooling
system, the pre-mixed fuel/air charge could prematurely ignite (or “knock”) during the
compression stroke, especially with low-octane fuels like gasoline. Knock reduces the
engines power because the pressure of the combustion event is not properly
synchronized with the engines power stroke. Knock can also seriously damage engine
parts. A cooling system also serves to maximize volumetric charge efficiency by
reducing