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
2001-05-11
2004-03-16
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, C060S524000, C060S039600
Reexamination Certificate
active
06705081
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to improvements to a burner as for a Stirling cycle heat engine and more particularly to improvements relating to control of the fuel and air input provided to the burner.
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. 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.
Additional aspects of Stirling cycle machines and improvements thereto are discussed in a co-pending U.S. patent application Ser. No. 09/517,245, filed Mar. 2, 2000, 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
prevent 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.
Stirling cycle engines have not generally been used in practical applications, 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
In accordance with preferred embodiments of the invention, a method is provided for controlling the fuel-air ratio of a burner of an external combustion engine having a heater head, where the burner uses a blower responsive to a blower drive signal for injecting air into the burner. The method is based at least on the concentration of a gas in an exhaust gas product of a combustion chamber of the burner and includes measuring the gas concentration in the exhaust gas product, deriving a gas concentration signal from the measured gas concentration, determining the fuel-air ratio from the gas concentration signal and the sign of the derivative of the gas concentration signal with respect to the blower drive signal, and controlling the fuel-air ratio by adjusting an air flow rate into the burner.
In accordance with another embodiment of the invention, the gas concentration in the exhaust gas product of the burner is measured using a gas composition sensor. The gas composition sensor may be an oxygen sensor or a carbon monoxide sensor. The air flow rate may be adjusted to obtain a predetermined optimal fuel-air ratio, where the optimal fuel-air ratio is based on at least a temperature of the air injected into the combustion chamber of the burner. In one embodiment, the temperature of the air may be measured using a temperature sensor. In another embodiment, the temperature of the air is determined based at least on a temperature of the heater head.
In a further embodiment, the gas composition sensor is a carbon monoxide sensor and the air flow rate into the burner is adjusted to minimize the gas concentration signal produced by the carbon monoxide sensor. Alternatively, the air flow rate may be adjusted to obtain a gas concentration signal from the carbon monoxide sensor that is below a predetermined value.
In accordance with another aspect of the present invention, a system is taught for controlling the fuel-air ratio of a burner of an external combustion engine having a heater head. The system is based at least on the concentration of a gas in an exhaust gas product of a combustion chamber of the burner, and includes a sensor for measuring the gas concentration in the exhaust gas product of the combustion chamber of the burner and for generating a sensor signal. The system also includes a blower governed by a blower signal for injecting air into the burner. The system further includes a controller for receiving the sensor signal from the sensor. The controller adjusts the blower based at least on the sign of the derivative of the sensor signal with res
Kamen Dean L.
Langenfeld Christopher C.
Norris Michael
Ormerod, III William W.
Schnellinger Andrew
Bromberg & Sunstein LLP
New Power Concepts LLC
Nguyen Hoang
LandOfFree
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