Power plants – Combustion products used as motive fluid – External-combustion engine type
Reexamination Certificate
2001-06-15
2003-04-08
Nguyen, Hoang (Department: 3748)
Power plants
Combustion products used as motive fluid
External-combustion engine type
C060S521000, C060S522000
Reexamination Certificate
active
06543215
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to components of an external combustion engine and, more particularly, to thermal improvements relating to the heater head assembly of an external combustion engine, such as a Stirling cycle engine, which contribute to increased engine operating efficiency and lifetime.
BACKGROUND OF THE INVENTION
External combustion engines, such as, for example, Stirling cycle engines, have traditionally used tube heater heads to achieve high power.
FIG. 1
is a cross-sectional view of an expansion cylinder and tube heater head of an illustrative Stirling cycle engine. A typical configuration of a tube heater head
108
, as shown in
FIG. 1
, uses a cage of U-shaped heater tubes
118
surrounding a combustion chamber
110
. An expansion cylinder
102
contains a working fluid, such as, for example, helium. The working fluid is displaced by the expansion piston
104
and driven through the heater tubes
118
. A burner
116
combusts a combination of fuel and air to produce hot combustion gases that are used to heat the working fluid through the heater tubes
118
by conduction. The heater tubes
118
connect a regenerator
106
with the expansion cylinder
102
. The regenerator
106
may be a matrix of material having a large ratio of surface to area volume which serves to absorb heat from the working fluid or to heat the working fluid during the cycles of the engine. Heater tubes
118
provide a high surface area and a high heat transfer coefficient for the flow of the combustion gases past the heater tubes
118
. However, several problems may occur with prior art tube heater head designs such as inefficient heat transfer, localized overheating of the heater tubes and cracked tubes.
As mentioned above, one type of external combustion engine is a Stirling cycle engine. 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 that approximates the ideal Stirling thermodynamic cycle. Additional background regarding aspects of Stirling cycle machines and improvements thereto are discussed in Hargreaves,
The Phillips Stirling Engine
(Elsevier, Amsterdam, 1991).
The principle of operation of a Stirling engine is readily described with reference to
FIGS. 2
a-
2
e,
wherein identical numerals are used to identify the same or similar parts. Many mechanical layouts of Stirling cycle machines are known in the art, and the particular Stirling engine designated by numeral
200
is shown merely for illustrative purposes. In
FIGS. 2
a
to
2
d
, piston
202
and displacer
206
move in phased reciprocating motion within cylinders
210
that, in some embodiments of the Stirling engine, may be a single cylinder. A working fluid contained within cylinders
200
is constrained by seals from escaping around piston
202
and displacer
206
. 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 position of displacer
206
governs whether the working fluid is in contact with hot interface
208
or cold interface
212
, corresponding, respectively, to the interfaces at which heat is supplied to and extracted from the working fluid. The supply and extraction of heat is discussed in further detail below. The volume of working fluid governed by the position of the piston
202
is referred to as compression space
214
.
During the first phase of the engine cycle, the starting condition of which is depicted in
FIG. 2
a
, piston
202
compresses the fluid in compression space
214
. The compression occurs at a substantially constant temperature because heat is extracted from the fluid to the ambient environment. The condition of engine
200
after compression is depicted in
FIG. 2
b
. During the second phase of the cycle, displacer
206
moves in the direction of cold interface
212
, with the working fluid displaced from the region cold interface
212
to the region of hot interface
208
. The phase may be referred to as the transfer phase. At the end of the transfer phase, the fluid is at a higher pressure since the working fluid has been heated at a constant volume. The increased pressure is depicted symbolically in
FIG. 2
c
by the reading of pressure gauge
204
.
During the third phase (the expansion stroke) of the engine cycle, the volume of compression space
214
increases as heat is drawn in from outside engine
200
, thereby converting heat to work. In practice, heat is provided to the fluid by means of a heater head
108
(shown in
FIG. 1
) which is discussed in greater detail in the description below. At the end of the expansion phase, compression space
214
is full of cold fluid, as depicted in
FIG. 2
d
. During the fourth phase of the engine cycle, fluid is transferred from the region of hot interface
208
to the region of cold interface
212
by motion of displacer
206
in the opposing sense. At the end of this second transfer phase, the fluid fills compression space
214
and cold interface
212
, as depicted in
FIG. 2
a
, and is ready for a repetition of the compression phase. The Stirling cycle is depicted in a P-V (pressure-volume) diagram shown in
FIG. 2
e.
The principle of operation of a Stirling cycle refrigerator can also be described with reference to
FIG. 2
a
-
2
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
214
is typically in thermal communication with ambient temperature and the expansion volume 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 due to several daunting challenges to their development. These involve practical considerations such as efficiency and lifetime. The instant invention addresses these considerations.
SUMMARY OF THE INVENTION
In accordance with preferred embodiments of the present invention, there is provided an external combustion engine of the type having a piston undergoing reciprocating linear motion within an expansion cylinder containing a working fluid heated by heat from an external source that is conducted through a heater head having a plurality of heater tubes. The external combustion engine has an exhaust flow diverter for directing the flow of an exhaust gas past the plurality of heater tubes. The exhaust flow diverter comprises a cylinder disposed around the outside of the plurality of heater tubes, the cylinder having a plurality of openings through which the flow of exhaust gas may pass. In one embodiment, the exhaust flow diverter directs the flow of the exhaust gas in a flow path characterized by a direction past a downstream side of each outer heater tube in the plurality of heater tubes. Each opening in the plurality of openings may be positioned in line with a heater tube in the plurality of heater tubes. At least one opening in the plurality of openings may have a width equal to the diameter of a heater tube in the plurality of heater tubes.
In another embodiment, the exhaust flow diverter further includes a set of heat transfer fins thermally connected to the exhaust flow diverter. Each heat transfer fin is placed outboard of an opening and directs the flow of the exhaust gas along the exhaust flow diverter. In another embodiment, the exhaust flow diverter directs the radial flow of the exhaust gas in a flow path characterized by a directio
Langenfeld Christopher C.
LaRocque Ryan Keith
Norris Michael
Smith III Stanley B.
Strimling Jonathan
Bromberg & Sunstein LLP
New Power Concepts LLC
Nguyen Hoang
LandOfFree
Thermal improvements for an external combustion engine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermal improvements for an external combustion engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermal improvements for an external combustion engine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3086671