Power plants – Motor operated by expansion and/or contraction of a unit of... – Unit of mass is a gas which is heated or cooled in one of a...
Reexamination Certificate
2000-03-02
2001-06-19
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Unit of mass is a gas which is heated or cooled in one of a...
C060S522000, C060S526000
Reexamination Certificate
active
06247310
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to improvements to a Stirling cycle heat engine or refrigerator and more particularly to improvements relating to mechanical and thermal components of a Stirling cycle heat engine or refrigerator which contribute to increased engine operating efficiency and lifetime, and to reduced size, complexity and cost.
BACKGROUND OF THE INVENTION
Stirling cycle machines, including engines and refrigerators, have a long technological heritage, described in detail in Walker,
Stirling Engines,
Oxford University Press (1980), incorporated herein by reference. The principle underlying the Stirling cycle engine is the mechanical realization of the Stirling thermodynamic cycle: isovolumetric heating of a gas within a cylinder, isothermal expansion of the gas (during which work is performed by driving a piston), isovolumetric cooling, and isothermal compression. The Stirling cycle refrigerator is also the mechanical realization of a thermodynamic cycle which approximates the ideal Stirling thermodynamic cycle. In an ideal Stirling thermodynamic cycle, the working fluid undergoes successive cycles of isovolumetric heating, isothermal expansion, isovolumetric cooling and isothermal compression. Practical realizations of the cycle, wherein the stages are neither isovolumetric nor isothermal, are within the scope of the present invention and may be referred to within the present description in the language of the ideal case without limitation of the scope of the invention as claimed.
Various aspects of the present invention apply to both Stirling cycle engines and Stirling cycle refrigerators, which are referred to collectively as Stirling cycle machines in the present description and in any appended claims. Additional aspects of Stirling cycle machines and improvements thereto are discussed in a co-pending U.S. patent application entitled “Stirling Cycle Machine Improvements,” filed Jul. 14, 1998, and incorporated herein by reference.
The principle of operation of a Stirling cycle engine is readily described with reference to
FIGS. 1
a
-
1
f
, wherein identical numerals are used to identify the same or similar parts. Many mechanical layouts of Stirling cycle engines are known in the art, and the particular Stirling engine designated generally by numeral
10
is shown merely for illustrative purposes. In
FIGS. 1
a
to
1
d
, a piston
12
(otherwise referred to herein as a “compression piston”) and a second piston (also known as an “expansion piston”)
14
move in phased reciprocating motion within cylinder
16
. Compression piston
12
and expansion piston
14
may also move within separate, interconnected, cylinders. Piston seals
18
prevents the flow of a working fluid contained within cylinder
16
between piston
12
and piston
14
from escaping around either piston
12
. The working fluid is chosen for its thermodynamic properties, as discussed in the description below, and is typically helium at a pressure of several atmospheres. The volume of fluid governed by the position of expansion piston
14
is referred to as expansion space
22
. The volume of fluid governed by the position of compression piston
12
is referred to as compression space
24
. In order for fluid to flow between expansion space
22
and compression space
24
, whether in the configuration shown or in another configuration of Stirling engine
10
, the fluid passes through regenerator
26
. Regenerator
26
is a matrix of material having a large ratio of surface area to volume which serves to absorb heat from the working fluid when the fluid enters hot from expansion space
22
and to heat the fluid when it passes from compression space
24
returning to expansion space
22
.
During the first phase of the engine cycle, the starting condition of which is depicted in
FIG. 1
a
, piston
12
compresses the fluid in compression space
24
. The compression occurs at a constant temperature because heat is extracted from the fluid to the ambient environment. In practice, a cooler
68
(shown in
FIG. 2
) is provided, as will be discussed in the description below. The condition of engine
10
after compression is depicted in
FIG. 1
b
. During the second phase of the cycle, expansion piston
14
moves in synchrony with compression piston
12
to maintain a constant volume of fluid. As the fluid is transferred to expansion space
22
, it flows through regenerator
26
and acquires heat from regenerator
26
such that the pressure of the fluid increases. At the end of the transfer phase, the fluid is at a higher pressure and is contained within expansion space
22
, as depicted in
FIG. 1
c.
During the third (expansion) phase of the engine cycle, the volume of expansion space
22
increases as heat is drawn in from outside engine
10
, thereby converting heat to work. In practice, heat is provided to the fluid in expansion space
22
by means of a heater
64
(shown in
FIG. 2
) which is discussed in greater detail in the description below. At the end of the expansion phase, the hot fluid fills the full expansion space
22
as depicted in
FIG. 1
d
. During the fourth phase of the engine cycle, the fluid is transferred from expansion space
22
to compression space
24
, heating regenerator
26
as the fluid passes through it. At the end of the second transfer phase, the fluid is in compression space
24
, as depicted in
FIG. 1
a
, and is ready for a repetition of the compression phase. The Stirling cycle is depicted in a P-V (pressure-volume) diagram as shown in
FIG. 1
e
and in a T-S (temperature -entropy) diagram as shown in
FIG. 1
f
. The Stirling cycle is a closed cycle in that the working fluid is typically not replaced during the course of the cycle.
The principle of operation of a Stirling cycle refrigerator can also be described with reference to
FIGS. 1
a
-
1
e
, wherein identical numerals are used to identify the same or similar parts. The differences between the engine described above and a Stirling machine employed as a refrigerator are that compression volume
22
is typically in thermal communication with ambient temperature and expansion volume
24
is connected to an external cooling load (not shown). Refrigerator operation requires net work input.
Stirling cycle engines have not generally been used in practical applications, and Stirling cycle refrigerators have been limited to the specialty field of cryogenics, due to several daunting engineering challenges to their development. These involve such practical considerations as efficiency, vibration, lifetime, and cost. The instant invention addresses these considerations.
SUMMARY OF THE INVENTION
A method of combusting a fuel and air in a burner of an external combustion engine, the fuel and air combined to form a fuel-air mixture having a variable fuel-air ratio, the fuel-air mixture when combusted producing an exhaust gas product includes igniting the fuel-air mixture to form a flame at a first fuel-air ratio produced by a first air flow rate and a fuel flow rate, increasing the air flow rate to produce a second fuel-air ratio, controlling the fuel flow rate based at least on a temperature of the heater head, and maintaining the flame at the second fuel-air ratio by adjusting the air flow rate based at least on a temperature of the air and an oxygen concentration in the exhaust gas product. Igniting the fuel and air where the fuel having an auto-ignition temperature and a flame speed includes propelling the air at a speed above the flame speed into an inlet of a throat, the throat also having an outlet and a constant cross sectional area from inlet to outlet and mixing fuel into the air forming the fuel-air mixture, the fuel-air mixture exiting the outlet, such that a flame is created in the air fuel mixture outside the outlet of the throat.
In accordance with another embodiment of the invention, the second fuel-air ratio is maintained by adjusting the air flow rate based on an oxygen concentration in the exhaust gas. In a further embodiment, the second fuel-air ratio may be maintained by adjusting the air
Kamen Dean L.
Langenfeld Christopher C.
Norris Michael
Bromberg & Sunstein LLP
New Power Concepts LLC
Nguyen Hoang
LandOfFree
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