Six Stroke Engine - Compression and Expansion Components

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 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 are

2

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 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.

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

engine's power because the pressure of the combustion event is not properly

synchronized with the engine's power stroke. Knock can also seriously damage engine

parts. A cooling system also serves to maximize volumetric charge efficiency by

reducing