U.S. patent application number 09/752684 was filed with the patent office on 2001-05-24 for high efficiency, air bottoming engine.
Invention is credited to Gray, Charles L. JR..
Application Number | 20010001362 09/752684 |
Document ID | / |
Family ID | 23401070 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001362 |
Kind Code |
A1 |
Gray, Charles L. JR. |
May 24, 2001 |
High efficiency, air bottoming engine
Abstract
An air bottoming powertrain, suitable for use in automobiles
includes an internal combustion engine, a compressor which receives
gaseous working fluid and compresses it to an elevated pressure, a
cooler for operating the compressor isothermally, an expander for
deriving work from the compressed gas and a heat exchanger located
in the compressed gas line for indirect heat exchange between the
compressed working fluid and exhaust gas from the internal
combustion engine. The expander may have a cylindrical barrel with
a plurality of cylinders arranged in the circle and open at one end
face of the cylinder barrel, which end face is sealed closed by a
valve plate. The cylinder barrel and valve plate allow relative
rotation therebetween to drive an output shaft, driven by
compressed gas from the compressor. An alternative expander is a
Scotch Yoke piston motor which includes plural paired and axially
aligned cylinders on opposing sides of an output shaft. In the
Scotch Yoke-type piston motor each cylinder is axially divided by a
thermal brake into a thermally insulated outer portion and cooled
inner portion. Likewise, each piston is axially divided by a
thermal brake into a cooled inner section and a thermally insulated
outer section.
Inventors: |
Gray, Charles L. JR.;
(Pinckney, MI) |
Correspondence
Address: |
LORUSSO & LOUD
3137 Mount Vernon Avenue
Alexandria
VA
22305
US
|
Family ID: |
23401070 |
Appl. No.: |
09/752684 |
Filed: |
January 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09752684 |
Jan 3, 2001 |
|
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09356338 |
Jul 19, 1999 |
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Current U.S.
Class: |
60/616 ;
123/563 |
Current CPC
Class: |
F02B 75/02 20130101;
Y02T 10/166 20130101; Y02T 10/12 20130101; Y02T 10/14 20130101;
F02G 5/02 20130101; F02B 41/00 20130101 |
Class at
Publication: |
60/616 ;
123/563 |
International
Class: |
F02B 033/00; F02G
003/00 |
Claims
What is claimed:
1. An air bottoming power train comprising: a source of combustion
exhaust gas; a compressor which receives a gaseous working fluid
and compresses it to an elevated pressure; a cooler for cooling
said compressor to provide near isothermal compression; an expander
having a plurality of cylinders, each cylinder having a piston
reciprocally mounted therein and operating in a two stroke cycle
including an expansion stroke and an exhaust stroke, said pistons
driving an output shaft; a compressed gas line for feeding the
compressed gaseous working fluid from the compressor to the
expander; expander valve means for successively admitting the
compressed gaseous working fluid from said compressed gas line to
individual cylinders of said expander in succession and for
continuously admitting the compressed gaseous working fluid to an
individual cylinder through a first portion of the expansion stroke
to maintain constant pressure; a heat exchanger located in said
compressed gas line for indirect heat exchange between the
compressed gaseous working fluid and the exhaust gas; and an
exhaust gas line for feeding the exhaust gas from the source
through said heat exchanger.
2. The power train of claim 1 wherein said source of exhaust gas is
an automotive internal combustion engine.
3. The power train or claim 1 further comprising a surge tank
located in said compressed air line between said compressor and
said heat exchanger.
4. The power train of claim 1 wherein at least one of said
compressor and said expander is a bent-axis piston machine.
5. The power train of claim 1 wherein said expander comprises a
cylinder barrel, said plurality of cylinders being formed in a
circle within said cylinder barrel and open at one endface of said
cylinder barrel and closed at an opposite endface of said cylinder
barrel, and a valve plate sealing closed said one end of said
cylinder barrel, said valve plate having a compressed gas inlet and
an exhaust gas outlet, said cylinder barrel and said valve plate
being mounted for relative rotation therebetween, the relative
rotation driving the output shaft.
6. The power train of claim 1 wherein said expander has a
bent-shaft configuration, said expander having a total displacement
which changes as an angle between the cylinder barrel and the
output shaft is changed.
7. The power train of claim 1 wherein said valve plate has an
arcuate groove in a face sealing against said cylinder barrel, said
arcuate groove being in communication with said exhaust gas outlet
and in register with said circle.
8. The power train of claim 5 wherein said cylinder barrel is
rotatable about a central axis and said valve plate is
stationary.
9. The power train of claim 1 wherein said expander is a Scotch
yoke piston motor including plural paired and axially aligned
cylinders on opposing sides of the output shaft and pistons
reciprocally mounted in said cylinders and driveably connected to
said output shaft, wherein: each cylinder is axially divided into a
thermally insulated outer portion and a cooled inner portion, the
insulated outer portion being separated from the cooled inner
portion by a thermal brake; and each piston is axially divided into
a thermally insulated outer section and a cooled inner section,
said cooled inner section having an exterior surface bearing oil
rings sealing with said cooled inner portion of said cylinder, said
thermally insulated outer section being thermally isolated from
said cooled inner section by a thermal brake.
10. An expander for use in an automotive power train, said expander
comprising: a cylinder barrel and a plurality of cylinders formed
in a circle within said cylinder barrel, open at one endface of
said cylinder barrel and closed at an opposite endface of said
cylinder barrel; and a valve plate sealing closed said one end of
said cylinder barrel, said valve plate having a compressed gas
inlet and an exhaust gas outlet, said cylinder barrel and said
valve plate being mounted for relative rotation therebetween, the
relative rotation driving an output shaft.
11. The expander of claim 1 having a bent-shaft configuration and
said expander having a total displacement which changes as an angle
between the cylinder barrel and the output shaft is changed.
12. The expander of claim 10 wherein said valve plate has an
arcuate groove in a face sealing against said cylinder barrel, said
arcuate groove being in communication with said exhaust gas outlet
and in register with said circle.
13. The power train of claim 10 wherein said cylinder barrel is
rotatable about a central axis and said valve plate is
stationary.
14. Expander for use in an automotive power train, said expander
being a Scotch yoke piston motor including plural paired and
axially aligned cylinders at opposing sides of an output shaft and
pistons reciprocally mounted in said cylinders and drivably
connected to said output shaft; wherein: each cylinder is axially
divided into a thermally insulated outer portion and a cooled inner
portion, the insulated outer portion being separated from the
cooled inner portion by a thermal brake; and each piston is axially
divided into a hollow outer section and a cooled inner section,
said cooled inner section having an exterior surface bearing oil
rings, sealing with said cooled inner portion of said cylinder,
said hollow outer section being thermally isolated from said cooled
inner section by a thermal brake.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The field of the present invention is internal combustion
engines for motor vehicles and, in particular, utilization of the
heat energy normally discarded in the exhaust of internal
combustion engines by converting the heat to mechanical work in a
highly efficient manner, thereby increasing the overall efficiency
of fuel utilization.
[0003] 2. Prior Art
[0004] The growing utilization of automobiles greatly adds to the
atmospheric presence of various pollutants including oxides of
nitrogen and greenhouse gases such as carbon dioxide.
[0005] Internal combustion engines create mechanical work from fuel
energy by combusting the fuel over a thermodynamic cycle consisting
typically of compression, ignition, expansion, and exhaust.
Expansion is the process in which high pressures created by
combustion are deployed against a piston, converting part of the
released fuel energy to mechanical work. The efficiency of this
process is determined in part by the thermodynamic efficiency of
the cycle, which is determined in part by the final pressure and
temperature to which the combusted mixture can be expanded while
performing work on the moving piston.
[0006] Generally speaking, the lower the pressure and temperature
reached at the end of the expansion stroke, the greater the amount
of work that has been extracted. In conventional engine designs,
expansion is limited by the fixed maximum volume of the cylinder,
since there is only a finite volume available in which combusting
gases may expand and still perform work on the piston. This makes
it impractical to expand to anywhere near ambient temperature and
pressure, and instead a large amount of energy remains and is
normally discarded with the exhaust. The production of work from
the initial expansion of combustion gases is commonly referred to
as "topping," while the extraction of work from once-expanded gases
is referred to as a "bottoming cycle."
[0007] Bottoming cycles are commonly employed as part of the
combined cycle operation of steam power plants. "Performance
Analysis or Gas Turbine Air-Bottoming Combined System," Energy
Conversion Management, vol. 37, no. 4, pp. 399-403, 1996; and "Air
Bottoming Cycle: Use of Gas Turbine Waste Heat for Power
Generation," ASME Journal of Engineering for Gas Turbines and
Power, vol. 118, pp. 359-368, April 1996 are representative of the
state of the art in this field. Exhaust heat rejected from a
primary gas turbine (the topping cycle) is used to heat water to
produce steam that is expanded in a secondary steam turbine (the
bottoming cycle). Although in this case the working fluid of the
bottoming cycle is steam, other fluids having more favorable
physical or thermodynamic properties may be used, for instance
ammonia-water mixtures or even a gas.
[0008] Bottoming cycles that employ water/steam or any other
recirculating medium as she working fluid must provide additional
hardware for recirculation and purification. For instance,
steam-based plants require a boiler, a sophisticated steam turbine,
condenser, purification system to prevent mineral deposits and
scaling, pumps, etc. For this reason, they are practically limited
to stationary applications such as public power utilities and
industrial plant use and are precluded from mobile applications
such as motor vehicles.
[0009] Motor vehicles represent a large portion of total energy use
in the world today. There are, of course, differences between
stationary power plants and power plants of motor vehicles. First,
motor vehicles usually do not employ a turbine in the topping phase
and so produce a less uniform flow rate of gases in the exhaust.
Second, for a motor vehicle the equipment devoted to the bottoming
cycle should be low cost, relatively simple to operate and
maintain, and lightweight. Third, in a motor vehicle the working
fluid of the bottoming cycle should be safe and not require
extensive recirculation hardware.
[0010] The use of air as a working fluid for stationary power
generating applications has been investigated. In U.S. Pat. No.
4,751,814, "Air Cycle Thermodynamic Conversion System," a gas
turbine topping cycle is combined with an air turbine bottoming
cycle. Air is compressed in an intercooled multi-stage compression
system that maintains air temperature as low as possible. Heat from
the turbine exhaust is transferred to the compressed air via a
counter flow heat exchanger, and the heated compressed air is
expanded through an air turbine to provide at least sufficient work
to run the compressors and preferably enough to use for other
purposes. This system obviates sophisticated purification and
processing of the working fluid (atmospheric air) if it is
recirculated at all, and dispenses with bulky steam handling
equipment. However, the system depends on turbine-based topping and
bottoming apparatus which is not well suited to conventional motor
vehicle applications.
[0011] Piston (or other means with sealed moving surfaces)
compressors and expanders provide high efficiency for the processes
of compression and expansion, out exhibit friction that is
generally higher than a gas turbine of the same size (i.e.,
operating at similar gas flow rates). However, gas turbines
(especially for the smaller sizes that would be needed for road
vehicles) do not provide process efficiency as high as desired
because of gas leakage around the edges of the turbine blades (the
moving surfaces), which are not sealed.
[0012] Further, gas turbines operate at extremely high speed (often
greater than 100,000 RPM), and the speed reduction gearing
necessary to provide mechanical power at speeds usable in a mobile
vehicle (e.g., less than 6,000 RPM) is costly and inefficient.
SUMMARY OF THE INVENTION
[0013] Therefore, an object of this invention is to provide a power
train inclusive of a bottoming cycle which is suitable for use in
automobiles.
[0014] Another object of the present invention is to provide such a
power train using air as a working fluid in the bottoming
cycle.
[0015] Yet another object of this invention is to provide a sealed
moving surface compressor and expander design that performs
compression and expansion with minimal friction, so that the net
efficiency is significantly greater than that achievable with gas
turbines.
[0016] A further object of this invention is to provide compressor
and expander designs that operate efficiently at speeds below 6,000
RPM.
[0017] Accordingly, the present invention provides an air bottoming
power train which includes a source of combustion exhaust gas, e.g.
the internal combustion engine (ICE) of an automobile; a compressor
which receives a gaseous working fluid and compresses to an
elevated pressure; a cooler for cooling the compressor to provide
near isothermal compression; an expander having a plurality of
cylinders, each cylinder having a piston reciprocally mounted
therein and operating in a two stroke cycle including an expansion
stroke and an exhaust stroke, the pistons driving an output shaft;
a compressed gas line for feeding the compressed gaseous working
fluid from the compressor to the expander; and an expander valve
for successively admitting the compressed gaseous working fluid
from the compressed gas line into individual cylinders of said
expander in succession and for continuously admitting the
compressed gaseous working fluid to an individual cylinder through
a first portion of the expansion stroke to maintain constant
pressure. A heat exchanger is located in the compressed gas line
for indirect heat exchange between the compressed gaseous working
fluid and the exhaust gas, and is fed the exhaust gas by an exhaust
gas line running through the heat exchanger.
[0018] A preferred expander includes a cylinder barrel with a
plurality of cylinders formed in a circle within the cylinder
barrel, open at one end face of the cylinder barrel and closed at
an opposite endface of the cylinder barrel. A valve plate seals
closed the one end of the cylinder barrel. The valve plate has a
compressed gas inlet and an exhaust gas outlet. The cylinder barrel
and the valve plate are mounted for relative rotation therebetween,
the relative rotation serving to drive an output shaft. The
expander preferably has a bent-shaft configuration, and has a total
displacement which changes as an angle between the cylinder barrel
and the output shaft is changed. The valve plate my have an arcuate
groove in a face sealing against said cylinder barrel, the arcuate
groove being in communication with the exhaust gas outlet and in
register with the circle.
[0019] A second preferred embodiment of the expander is a Scotch
yoke piston motor including plural paired and axially aligned
cylinders on opposing sides of an output shaft and pistons
reciprocally mounted in the cylinders and drivably connected to the
output shaft. Each cylinder is axially divided into a thermally
insulated is outer portion and a cooled inner portion, the
insulated outer portion being separated from the cooled inner
portion by a thermal brake; and further, each piston is axially
divided into a hollow outer and a cooled inner section, the cooled
inner section having an exterior surface bearing oil rings sealing
with the cooled inner portion of the cylinder, the hollow outer
section being thermally isolated from the cooled inner section by a
thermal brake.
[0020] The present invention utilizes an air bottoming cycle in
conjunction with unique multi-cylinder piston compressor and
expander designs that are well suited for use with the conventional
automotive exhaust gas stream.
[0021] An ideal representation of the desired air bottoming
thermodynamic cycle is shown in FIG. 1. The line ab represents
intake of working fluid to the compressor. Line bc represents
isothermal compression of the working fluid. Line cd represents
absorption of heat by the working fluid at constant pressure during
constant pressure expansion. Line db represents adiabatic expansion
of the heated compressed gas to ambient conditions, producing the
maximum possible work. Line ba represents the exhaust of the
expanded air before the beginning of the next cycle.
[0022] The present invention effects an air bottoming cycle
consisting of five distinct phases: (1) Compression, made
relatively isothermal by cooling, of a gaseous working fluid such
as air in a compressor, and optional buffering of the compressed
air stream in an optional surge tank to reduce fluctuations in the
heat exchanger inlet stream, (2) Addition of heat to the compressed
working fluid at relatively constant pressure through a device such
as a counter flow heat exchanger recovering heat from the internal
combustion engine exhaust; (3) An initial, near constant pressure,
expansion of the heated, compressed working fluid; (4) A final
relatively adiabatic expansion of the partially expanded working
fluid to as close to ambient conditions as possible, producing the
maximum amount of work and; (5) Exhaust of the expanded working
fluid from the expander or its conveyance to an appropriate
destination such as the air intake of the internal combustion
engine.
[0023] The cooled compressor performs a relatively isothermal
compression of a working fluid such as air, which should be at the
lowest practical temperature before entry to the heat exchanger in
order to maximize the potential for recovery of heat. Near
isothermal compression is achieved by one or more of the following
means: cooling the compressor chamber walls using a water-based
coolant, air or other fluid coolant; increasing the turbulence of
the intake working fluid to increase the heat transfer coefficient
and in-chamber mixing; increasing the roughness of the chamber
walls to increase boundary layer turbulence and thus heat transfer
coefficient and to increase heat transfer area; an oil jet spray to
the bottom of each piston; and injecting a liquid into the of
compressing working fluid to extract heat from compression through
phase change (evaporation) of the injected liquid. One unique
feature of the present invention is the option of injecting the
liquid fuel (to assist in cooling the compressing air) that, being
mixed with the exhausted air at the end of the bottoming cycle,
will subsequently be routed to the combustion engine which supplies
the hot exhaust gas to "fuel" this bottoming engine. Methanol or
ethanol are particularly good fuels for this use since they both
can be easily mixed with water to provide an optimum mixture.
[0024] The compressed working fluid is passed through the optional
surge tank and into the counter flow heat exchanger. The working
fluid experiences a temperature increase, adding energy to the
already compressed gas. Relatively constant pressure is assured
because the heated, compressed working fluid enters the expansion
chamber at a rate equal to the propensity for the heat to raise the
pressure of the gas, and thus an initial constant pressure
expansion phase is achieved. After the intake valve is closed,
expansion continues to the end of the expansion stroke, producing
mechanical work as it expands. The near-ambient pressure air
exhausted by the expander could be released to the atmosphere or
optionally fed to the air intake of the internal combustion engine.
Optionally, the exhausted gas from the expander can be fed to the
intake of the internal combustion engine (at any boost pressure)
through the "Phase Change Heat Engine" which increases the
efficiency of the overall cycle and serves as an intercooler for
the charge air of the internal combustion engine. The exhaust gas
could also be the source of heat energy for a "Phase Change Heat
Engine" incorporated into yet another integrated configuration. The
"Phase Change Heat Engine" is disclosed in my copending application
filed on even date herewith, the teachings of which are
incorporated herein by reference.
[0025] Use of a surge tank allows the use of fewer pistons in the
compressor by moderating fluctuations in the compressor outlet
stream and tends to reduce temperature increase during each
compression stroke.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In the drawings:
[0027] FIG. 1 is a graph illustrating an ideal air-bottoming
thermodynamic cycle utilized in the present invention;
[0028] FIG. 2 is a schematic view of a first embodiment of a
powertrain in accordance with the present invention;
[0029] FIG. 3 is an end view of a preferred embodiment of the
compressor and/or expander of the first embodiment depicted in FIG.
2;
[0030] FIG. 4A is a schematic end view of the compressor and/or
expander of the preferred embodiment illustrating the different
phases of operation in one cycle and FIG. 4B is a side view of the
embodiment shown in FIGS. 3 and 4A;
[0031] FIG. 5 is an illustration of the drive shaft connection for
the compressor and the expander in the drive train of the
embodiment of FIG. 2;
[0032] FIG. 6 is a schematic view of a second embodiment of the
powertrain in accordance with the present invention incorporating a
second preferred embodiment for the compressor and the expander;
and
[0033] FIG. 7 is a schematic view of one air of opposing pistons in
the preferred embodiment for the expander shown in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] FIG. 2 shows a preferred embodiment of the invention as
including a cooled, fixed or variable displacement multi-cylinder
piston type compressor 1 of bent-axis design, an optional surge
tank 2, a counter flow heat exchanger 3, and a fixed or variable
displacement multi-cylinder piston type expander 4 of bent axis
design. Constant pressure during the constant pressure heat
addition stage of the cycle is achieved by a unique design of
expander 4.
[0035] Referring to FIG. 2, fresh air or other gaseous working
fluid flows through the compressor intake 5 into the compressor 1
at either ambient pressure and temperature or at a boosted pressure
level. A boosted pressure allows reduction of the size of the
compressor and potentially the expander. A "plug" of compressed gas
exits the compressor 1 at each compression stroke, through the
compressor exhaust port 6 into the surge tank 2, thereby
maintaining a designated tank pressure. A cooling apparatus 16 may
operate on the compressor 1. The cooling apparatus of the preferred
embodiment includes a water-based coolant which is circulated
through a space around each cylinder and through the head and
includes a means (not shown) of injecting a liquid into the
compressing gas to extract heat from compression through phase
change of the injected liquid. Meanwhile, hot exhaust gases from an
internal combustion engine or similar device 18 flow through the
heat exchanger exhaust gas intake 9 into the heat exchanger 3 and
out the heat exchanger exhaust 8. In so doing, much of the heat
contained in the exhaust gas is imparted to the working fluid that
has concurrently entered the heat exchanger intake 7 and is making
its way to the heat exchanger working fluid exhaust port 10.
Periodically, an intake port 13 to the expander 4 opens, and the
expander chamber 14 expands in volume as it enters an expansion
stroke. As the expander chamber expands, working fluid flows into
the increasing volume chamber (cylinder) 14 at near constant
pressure until the intake port closes. The intake port closes and
the gas continues expansion in the expander chamber 14, producing
mechanical work on a piston 15 transmitted to an output shaft 12.
After expansion, the near-ambient pressure air is exhausted through
the expander exhaust port 11, releasing it to the atmosphere or
optionally feeding it to the air intake of the internal combustion
engine.
[0036] FIGS. 3 and 4 show one embodiment of an expander of the
present invention having a bent-axis motor design. The expander 4
is a cylinder barrel 401 with multiple cylinders formed therein,
here 8 in number shown as 402-409. Each of cylinders 402-409
receives a piston and the pistons drive an output shaft. For
variable displacement configurations, the total displacement of the
expander motor can be varied by tilting the angle of the cylinder
barrel with respect to the plane of the output shaft. Minimum or
zero displacement is achieved when the barrel and output shaft
plane are parallel, while displacement increases as the angle
becomes greater, up to some maximum displacement at some maximum
angle.
[0037] An intake port 410 and exhaust port 412 communicate with
piston/expansion chambers 402-409 at certain critical portions of
each cycle, making possible the constant pressure method of
operation described above. As the cylinder barrel 401 rotates, for
example counter clockwise as indicated by the arrow, the pistons
are also cycling between TDC and BDC and the intake and exhaust
ports present themselves to each piston at the appropriate
times.
[0038] The operation of the expander of the first embodiment will
now be explained with reference to FIGS. 4A and 4B, which follow
the progress of a representative piston/expansion chamber 402
through several critical points of one cycle. In this illustration,
the cylinder barrel 401 is shown rotating counter clockwise with
the valve plate 20 stationary. At position a, the piston is nearing
TDC and has just cleared exhaust port 412, sealing the chamber 402.
At this point the chamber 402 contains trapped residual working
fluid at the near ambient pressure and temperature of the expander
exhaust. As point b approaches, the chamber continues to shrink in
volume, thereby compressing the trapped working fluid. At position
b, the piston has reached TDC and the working fluid in the sealed
chamber 402 has reached maximum compression. Because the chamber
402 seals just prior to TDC, the volume of gas trapped and
compressed, and hence the work and crank angle required, is
minimal. The crank angle between positions a and b is calculated to
achieve good sealing from exhaust port 412. At TDC the unswept
volume is minimized to minimize the quantity of incoming gas from
the heat exchanger required to pressurize the chamber 402. Also at
point b, the intake port 410 is about to be exposed, providing
passage for the heated compressed working fluid to enter the
chamber 402. Past point b, the chamber begins increasing in volume
as it travels toward BDC, accepting working fluid as work is
produced. Position b' represents a typical position in this stage
where the chamber is expanding in volume and the intake port
supplies heated compressed working fluid to fill it. Although the
chamber 402 is increasing in volume, pressure is relatively
constant because the intake port 40 is supplying pressurized
working fluid. Heated compressed working fluid continues to enter
until position c, when the intake port loses contact with the
chamber. From position c to position d, adiabatic expansion of the
plug of heated, compressed working fluid that entered between b and
c (as well as the initial residual compressed gas) takes place,
producing additional work. At position d, the piston reaches BDC
and the gas has been reduced to near ambient pressure. At this
point the exhaust port 412 makes contact with the chamber 402,
allowing the spent fluid to be exhausted as the piston begins
rising again toward TDC and volume decreases. Positions d' and d"
show example positions of the chamber near the beginning and end of
the exhaust cycle. Finally, the cycle repeats itself as the piston
reaches position a, once again sealing the chamber 402 and
beginning the compression of the working fluid remaining in the
chamber. Position a could extend as far as position b without
changing the function of the expander. In an eight cylinder
expander, for example, all eight pistons would perform this cycle
in staged succession, producing a smooth flow of work on the
expander shaft 12.
[0039] In FIG. 4 (A), the angle (i) is the compression phase, angle
(ii) is the constant Pressure intake and expansion phase, angle
(iii) is the adiabatic expansion phase, and angle (iv) is the
exhaust phase.
[0040] Angles (ii) and (iii) together total 180.degree.,
corresponding to the expansion stroke. Angle (ii) may vary from
about 18.degree. to about 45.degree.. In other words the constant
pressure intake and expansion phase will usually be 10% to 25% of
the total expansion stroke.
[0041] Because of their bent-axis design, the expander 4 and the
compressor 1 are both capable of variable displacement, allowing,
in addition to independently varying the speed of the expander and
compressor, ability to precisely control mass flow rate and
pressure through the system, thus ensuring stable and
thermodynamically efficient operation.
[0042] Variations of foregoing design of the first embodiment will
be apparent to one skilled in the art and include: (1) a fixed
cylinder barrel and rotating valve plate, (2) a fixed cylinder
barrel and individually timed valves, (3) a swash plate or wobble
plate design where the pistons act on an inclined surface through a
sliding pad at the base of the piston producing torque to the plate
which drives an output shaft.
[0043] FIG. 5 illustrates the integration of the bottoming cycle
engine with the internal combustion engine (ICE) 18 and the drive
wheels 60 of a vehicle. Ambient air is inducted into compressor 1
through port 5. Shaft 19 from expander 4 drives compressor 1.
Compressed air is discharged from compressor 1 through port 6 to
heat exchanger 3 and heated compressed air exits heat exchanger 3
and enters expander 4 through port 10. Expander 4 expands the hot
compressed air which produces power which drives compressor 1 and
provides net power which is combined with the power output from ICE
18 by expander gear 62 driving ICE gear 64. The expanded air exits
the expander through port 11. The combined power from the ICE and
bottoming cycle engine flows through transmission 66 to wheels
60.
[0044] FIGS. 6 and 7 illustrate a second preferred embodiment which
uses a crank-loop or "Scotch yoke" crank mechanism design with
guide bearings as the compressor and/or expander, instead of the
bent axis design of the first preferred embodiment. This second
embodiment allows for constant pressure operation approximated
through sizing the volumes of the chambers, the number of
cylinders, and valve timing to ensure sufficiently constant
thruflow.
[0045] In this second embodiment, the crank-loop or "Scotch yoke"
design, with guide bearings which reduce piston side forces and
prevent piston "cocking," is employed in the compressor and
expander instead of a bent axis design. This design reduces side
forces on the pistons by arranging the pistons in rigidly
connected, 180.degree. opposed pairs and driving crankshaft 36, 45
through a linear bearing at the center of the pair. "Scotch Yoke"
type engines are known for very low friction, which makes the
"crank mechanism" well suited, in combination with added guide
bearings, as the piston compressor and/or expander of the
invention. In the prior art, some side forces remain but this
embodiment of the invention utilizes guide bearings/bushings to
eliminate side forces and piston "cocking" and to further improve
performance and reduce friction. Constant pressure operation is
approximated through sizing the volumes of the chambers, the number
of cylinders, and valve timing to ensure sufficiently constant
thruflow.
[0046] Referring to FIG. 6, fresh air or other gas working fluid
flows through the compressor intake 25 into the compressor 30 at
either ambient pressure and temperature or at a boosted pressure
level. As in the first embodiment, a boosted pressure allows a
reduction in the size of the compressor and potentially the
expander. For the two-stroke cycle of compressor 30, working fluid
is received in the stroke from TDC to EDC and is compressed and
exhausted in the stroke from BDC to TDC. Intake and exhaust valves
of various designs (not shown) can be utilized to control the
timing of the intake flow to and the exhaust flow from compressor
30.
[0047] In this second embodiment both the compressor 30 and the
expander 40 employ a crank mechanism 31, 41 of the crank-loop or
"Scotch yoke" design. These crank mechanisms 31, 41 are further
illustrated with an end view on FIG. 7. Further description can be
found in the journal article The Scotch Yoke Engine as a Compact
and Smooth Running Motor for Passenger Vehicles, MTZ
Motortechnische Zeitschrift 58(1997)6, the teachings of which are
incorporated herein by reference.
[0048] Referring again to FIG. 6, both the compressor 30 and
expander 40 utilize guide bushings/bearings 32, A2 to insure
against piston cocking or side force. Also shown is the oil supply
34 for the guide bushings/bearings 32. Oil is also utilized to cool
the pistons 33 of the compressor 30 to help approach isothermal
compression, and flows from ports 35.
[0049] A "plug" of compressed gas exits compressor 30 at each
compression stroke, through the compressor exhaust port 26 into
surge tank 21. A cooling apparatus 16 may operate on compressor 30
to assist in maintaining near isothermal compression. Hot exhaust
gases from an internal combustion engine or similar device 50 flow
through the heat exchanger exhaust gas intake 29 into heat
exchanger 23 and out the heat exchanger exhaust 28. In so doing,
much of the heat contained in the exhaust gas is imparted to the
working fluid that has concurrently entered the heat exchanger
intake 27 and is making its way to the heat exchanger working fluid
exhaust port 22. Periodically, an intake port 23 to the expander 40
opens, and expander chamber 44 expands in volume as it enters an
expansion stroke. As the expander chamber expands, working fluid
flows into the increasing volume at near approximately constant
pressure until the intake port 23 closes. The intake port 23 closes
and the gas continues expansion in an expander chamber 44,
producing mechanical work on a piston 43 transmitted to an output
shaft 45. After expansion, the near-ambient pressure gas is
exhausted by the expander exhaust port 24, releasing it to the
atmosphere or optionally feeding it to the air intake of internal
combustion engine 50.
[0050] It is especially important to operate expander 40 as near
adiabatically as possible, to maximize efficiency. Toward this end,
the expander expansion chambers 44 are thermally insulated, with
thermal brakes 46 separating the insulated chambers 44 from the
cooled cylinders 47 where the rings of piston 43 must travel on a
cooled and oil lubricated surface. Unique pistons 43 each have an
upper, hot portion 48 which travels through the hot expander
chamber 44, insuring the hot expansion gases do not significantly
access the cooled cylinders 47. The piston hot portions 48 are
hollow to the maximum extent feasible to minimize piston mass and
reduce heat transfer to the lower, cooled portion of piston 43. A
final thermal brake 49 separates the hot, upper portion 48 from the
cooled, lower portion of piston 43. The upper portion 48 is a high
temperature metal alloy, preferably with an insulating ceramic
outer coating; or it may be an all ceramic component, all
carbon-carbon component, or other suitable high temperature
material with low heat transfer characteristics.
[0051] The thermal brakes are gaskets which may be an insulating
ceramic or other conventional thermal insulator.
[0052] One modification eliminates the surge tank, and the speed of
the expander is fixed at a multiple of the speed of the compressor.
An alternate embodiment could include a surge tank, in which case
the speed of the compressor could vary.
[0053] In another modification expanded air would be recirculated,
or fed to the air intake of the ICE, rather than exhausted,
optionally at a pressure providing boost to the internal combustion
engine.
[0054] Other modifications using other types of sealed moving
surfaces for the compressor and expander will be apparent to those
skilled in the art from the foregoing description of two preferred
embodiments.
[0055] The invention may be embodied in other specific forms
without departing from its spirit or essential characteristics. The
present embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the claims rather than by the
foregoing description, and all changes which come within the
meaning and range of the equivalents of the claims are therefore
intended to be embraced therein.
* * * * *