Note: Descriptions are shown in the official language in which they were submitted.
The instant invention provides a hybrid internal combustion and
steam engine system yielding good fuel economy over the load and rpm ranges
encountered in vehicle propulsion systems, while minimizing pollutant
emissions. These usually mutually-exclusive goals of high efficiency an~
low pollution cannot be obtained by conventional non-hybrid systems.
The hybrid propulsion system according to the instant invention
provides, in general, for the conversion oE the heat energy lost in the
internal combustion cylinders to mechanical energy by use oE a Rankine cycle
engine such as a steam engine. The steam engine operates both on the heat
content of the cooling fluid in the conventional cooling system used to
remove a portion of the heat of combustion from the internal combustion
cylinder chambers and also on the heat content of the internal combustion
engine exhaust gases.
The invention provides a vehicle propulsion system comprising an
internal combustion engine combined with a steam engine, means for directing
exhaust gas from the internal combustion engine to a steam generator coupled
to provide steam to a steam engine, a transmission for mechanically coupling
the internal combustion engine and the steam engine to propel the vehicle,
means for providing the combustion chamber of the internal combustion engine
with a fuel-air mixture in which the fuel-air ratio is substantially greater
than the stoichiometric fuel-air ratio in order to produce a combusted
exhaust gas from the internal combustion engine which is low in oxides of
nitrogen content and rich in combustibles content, means for introducing air
downstream of the engine for mixing with said exhaust gas to support further
combustion thereof, a combustion device coupled to receive the exhaust gas
to complete the combustion of said exhaust gas, and means for controlling
the relative contributions of the internal combustion engine and the steam
engine to the propulsion system by adjusting the respective inputs of the
engines in accordance with load demand and the pressure of generated steam.
From another aspect, the invention provides the method of reducing
the output of polluting emissions while improving the economy of a vehicle
,~,,i1
propulsion system having an internal combustion engine in combination with a
steam engine by using the heat oF combusted exhaust gas from the internal
combustion engine to generate steam and applying the steam to the steam
engine to develop mechanical work therefrom, comprising the steps of provid
ing the combustion chamber of an internal combustion engine with a com-
bustible mixture having a fuel-alr ratio substantially greater than
stoichiometric in order to produce a combusted exhaust gas from the internal
combustion engine which is low in oxides of nitrogen content and rich in
combustibles content; introducing air downstream of the engine for mixing
with the combustibles-rich exhaust gas to support further combustion thereof;
completing the combustion of the exhaust-air mixture; directing the further-
combusted gas to a steam generator; and controlling the relative contri-
butions of the two engines to the propulsion system by adjusting the respec-
tive inputs of the engines in accordance with load demand and the pressure
of generated steam.
The internal combustion (I.C.) engine of the system of this inven-
tion is operated at an air-fuel mixture providing minimized unburnable
pollutants (N0 ), and an afterburner is provided to recover the chemical
energy in the exhaust gases while eliminating substantially all the com-
bustible pollutants. The afterburner serves as a second heat source to
increase the temperature of the internal combustion engine exhaust gases.
These gases are then directed to a steam generator where they are used to
boil and to superheat the already-heated cooling fluid in a high-pressure
boiler for subsequent use in a high-pressure expander section of a steam
engine to develop mechanical power.
The fluid discharge from the high-pressure expander section is
combined with the vapor formed in the cooling system and reheated by heat
exchange with the exhaust gases. These combined fluids are then used to
operate a lower-pressure expander section of a steam engine to develop
additional propulsion. The discharge from the lower-pressure expander
section is returned to a condenser similar to a conventional radiator for
condensation before return to the cooling jackets surrounding the engine
~;~' cylinders, and to the steam generator unit (boiler) in the exhaust gas
_~ .
2~
stream.
Figure 1 is a combination block and schematic diagram illustrating
the particulars of the present invention;
Figure 2 is a diagram showing the throttle control mechanism for
the arrangement of Figure l;
Figure 3 i9 a graph showing N0 production as a function of air-
fuel ratio in an automoti.ve engine; and
Figure 4 is a graph showing the performance map of a typical
passenger car engine in operation.
A preferred embodiment of the invention is shown schematically
in block diagram form in Figure 1. Air and fuel are supplied to conven-
tional carburetor 10 having a throttle 11, and a mixture is supplied to the
I.C. engine 12. The mixture provided by the carburetor 10 is purposely made
richer than stoichiometric, in a range oE fuel-air ratios between .075 ancl
.120, preferably about .090. The exhaust gas from the I.C. engine, which
under moderate to heavy loads will be at a temperature in the range of
1000 F and for a fuel-air ratio of .090 input to the engine will contain
about 3.5% hydrogen and 8% carbon monoxide, is mixed with air from air
source 14 (which may typically be a blower driven as an accessory) in either
exhaust pipe 16 or afterburner 17 and the combustible mixture burned in
afterburner 17. This combustion releases sufficient heat to raise the
exhaust gas
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Z~:
temperature to approximately 2300F.
The exhaust gas from the internal combusti.on
engine is sufficiently rich in combustibles that when mixed
with sufficient air a combustion reaction can be initiated by
a spark, and maintained by suitable combustion chamber design.
Back mixing of hot burnt exhaust into the fresh mix-ture by well
known methods such as flameholders, opposing jets, or other
methods of providing recirculation is an efEective and suitable
method of burning this exhaust. The air may be introduced
into the exhaust gas any time after the expansive stroke in
the I.C. engine cylinder has been essentially completedj e.g.,
as extra scavenging air in a two-stroke engine, from ports
opened by exhaust valve opening in a four-stroke engine, in the
piping between the cylinder and the afterburner, or in the
aEterburner itself. A conventional spark plug fired by the
I.C. engine ignition sy~stem is placed in a low velocity region
of the flow for initial ignition of the exhaust gas-air
mixture. It is useful to provide a region of unrecirculated
flow after the main combustion has taken place to finish off
the combustion. Normally the transition from the afterburner
to the associated steam generator unit 18 will provide this.
A combustion chamber volume of between 100 and 200 cubic
inches is a suitable size for the afterburner. The burnt
exhaust gas is conducted to steam generator unit 18, which pre-
ferably consists of approximately 150 feet of steel tubing
approximately 1/~ inches inside diameter and 3/8 inches out-
side diameter within a suitable casing.
A convenient arrangement of the steel tubing is to
wind two adjacent coiIs of approximately ten layers, the
coils having an inside diameter of about 3 inches and an
l~Z~ 2
outside diameter of 10 inches, with a length of 5 inches for
each coil. F.xhaust gas is lntroduced into the space at the
center of the first coil, flows radially outward over the steel
tubing, emerges from the first coil and is then ducted and
directed radially inward through the second coil. It emerges
in the center of the second coil substantially cooled by
virtue of the transfer of-its heat energy to the fluid flowing
within the steel tubing and is ready for discharge to the
atmosphere. Water from a boiler feed pump 20 is introduced
into the tubing at the center of the second coil, flows
spirally outward through the gecond coil and then spirally in-
ward through the first coil until it is discharged as steam
to a throttle valve 22.
The exhaust gas is cooled to about 500F in the pro-
cess of transferring lts heat to the water in steam generator
unit 18. The water and the exhaust gas are preferably in sub-
stantially counter-current flow heat transfer relationship
within the steam generator unit 18. Suitable operating con-
ditions for the steam generator unit 18 are to introduce the
feed water at 1500 psi and 180F from the boiler feed pump
20, and for the ~enerator 18 to produce 900F superheated
steam. The steam generator unit 18 may be conceptually dlvi-
ded into four sections, which are the superheater 18a, the
boiler 18b, the feedwater heater or economizer 18c, and the
optional reheater 18d. Normally the second coil is the
economizer 18c, and the first coil serves the function of
boiler 18b and superheater 18a. The optional reheater 18d
is composed of additional tubing inserted into the ducting
between the first coil and the second coil, or may be
integrated into the casing.
The feedwater first enters the economizer 18c where
it is heated to the boiling temperature, which for a pres~
sure of 1500 psi is 650F. The heated water passes into the
boiler section l~b where the transferred heat converts the
water into steam~ The steam leaves the boiler and proceeds
to the superlleater 18a where additional heat is added to
superheat the steam. Practical designs of steam generator
~mits often utilize the "once through" concept where the
wa~er is p~ped through a tube or tubes countercurrent to the
heat source fluid flow. In such a generator the boundary
between feedwater heater and boiler, and between boiler and
superheater may vary considerably with operating conditions
without material consequence insofar as ~he opera~ion of the
steam generator unit is concerned. The steam generator 1
essentially consists of some relatively small high pressure
steel tubing through which the water flows, climbing in
temperature until it boils, then turning into steam at
constant temperature as it advances further, and eventually
after being fully vaporized, climbing further in temperature
until delivered from the steam generator unit I8. Steam
throttle 22 controls the application of the high pressure steam
B to a steam ~ 24 having high pressure section 24a and
low pressure section 24b.
The internal combustion engine 12 is provided with
a water (or comparable liquid) cooling jacket 30 which
is arranged to operate substantially above atmospheric pres-
sure. Water is provided to it by a low pressure output con-
nection on thé boiler feed pump 20, driven as an accessor-y, or
by a separate boiler feed pu~p (not shown). Heat lost to the
cylinder walls and head of the I.C. engine converts some of
æ
the jacket water to stean, which is separated from the water in a steam/water
separator 32. This steam is merged in a junction element 34 with low
pressure steam that is the exl~aust from the intermediate pressure cylinder
which is the second stage of the hlgh pressure section 24a of the steam
engine 24, directed through the reheater section l~d oE the steam generator
unit 18, and expanded in the low pressure cylinders section 24b of the steam
engine 24. A throttle valve 50 is provided for controlling the steam supply
from the I.C. engine jacket 30 and separator 32 to the low pressure cylinders.
A check valve 52 is placed in this line to prevent steam from the inter-
mediate cylinder exhaust back-flowing into the steam/water separator unit 32
and the I.C. engine jacket 30 during warmup of the system. The exhaust from
the low pressure cylinders is directed to a condenser 36 and associated hot
we]l 38 where the steam is condensed to water and the heat of condensation
rejected to the atmosphere with the assistance of a cooling fan 39.
Superheated high pressure steam is delivered at pressures such as
1500 psi, and temperatures such as 900 F to the steam engine 24, where a
portion of the heat energy of the steam is converted into work. The steam
expansion is preferably conducted in several stages. In one embodiment the
steam engine has four cylinders, one high pressure, one intermediate
pressure, and two low pressure. Design center steam pressure values for the
high pressure cylinder are 1500 psia inlet and 400 psia exhaust; values for
the intermediate cylinder are 400 psia inlet and 100 psia exhaust, and for
the two low pressure cylinders, lO0 psia inlet and 20 psia exhaust.
--7--
~'22~
e~ e
The mechanical output of the steam e*~ ~E 24 is
delivered through output shaft 40 via over-running clutch 42
to the I.C. engine shaft 44. The combined power of the two
engines is delivered to transmission 46 which transmits the
power to the drive wheels of the vehicle.
For an intermediate-sized American car of about 3500
lbs. weight, the displacement of the I.C. engine 12 should
be chosen in the range of 80 to L00 cubic inches, and the
er~gJr~e
steam ~æ~eæ 24 should have a displacement of about 126
cubic lnches. The steam ~ displacement is preferably
distributed among the cylinders with 6 cubic inches in the
high pressure cylinder, 20 cubic inches in the intermediate
pressure cylinder, and 50 cubic inches in each of the low
pressure cylinders. The four cylinders may be in-line, or
have any other suitable mechanical arrangement. Each cylinder
is provided with conventional steam inlet exhaust valves,
not shown, preferably càm-operated poppet valves similar to
those used in automotive practice. Power control is pre-
ferably exercised by steam inlet cutoff control 23 on the
high pressure cylinder, and throttling via throttle 50 of the
steam supply from the steam water separator 32 to the low
pressure cylinders which should operate with steam inlet valve
cutoff of about 30% of stroke. For turning over the steam
engine from a full stop, means may be provided to extend cutoff
to 70% of stroke, and small bleeds from the high pressure
steam supply arranged so that intermediate pressure and low
pressure steam is available at the start. The high pressure
steam throttle 22 is also provided to extend the range of
power control when the inlet valve cutoff has been reduced
to a practical minimum, and to cut off the steam supply to the
~ 2~
engine completely when desired. The control of the duration
of admission of steam supply to the high pressure cylinder
may be accomplished by methods well known to those skilled
in the art, such as operating the inlet valve with a three
dimensional cam that is geared to the crankshaft, and is trans-
lated to give the variously desired angles of admlssion.
- - Alternatively a series poppet valve arrangement may be used,
one controlling admission, and the other cutoff. Steam is
admitted to the cylinder only when both valves are open, and
the phase between the two valves is obtained by suitable
differential rotations of their respective camshafts, an
arrangement known in the prior art.
The normal steam admission duration to the high
pressure cylinder under full torque load con~itions wlll be;
in thè range of 20 to 30% of strokej and for various cruise
conditions be in the range of 5% to 20% of s-troke. Under
surge conditions the admission will be increased to a maximum
of about 70% - 80% of stro~e. The steam consumption and the
B e~g~'ne
consequent power of the steam ~p2~eæ 24 is controlled ~y
the coordinated operation of the high pressure throttle 22,
the low pressure throttle 50, and the high pressure cylinder
inlet valve-steam admission cutoff control (not shown). As
more power is demanded of the steam engine, the two throttles
are opened further, and the steam admission time lengthened.
The cranks of the high and the intermediate pressure cylinders
of section 24a may be disposed at an angle of 180 to each
other, in which case the high pressure cylinder exhaust valve
can also serve as the intermedlate cylinder inlet valve, i.e.,
a transfer valve. The exhaust steam from the lntermedlate
pressure cyllnder is merged ln junction element 34 with the
_g_
Z~22
steam from the steamjwater separator 15 and conducted through
the reheater section 18c of the steam generator unit 18. Under
various low power conditions the exhaust from the intermediate
cylinder can be at a lower pressure than the steam supply from
the engine jacket, so a check valve 33 is placed between the
exhaust of the intermediate pressure cylinder and steam line
junction element 34.
The condenser 36 is about the same size, and may
go in the same place, as the standard automobile radiator.
The heat transfer requirements are somewhat greater, but not
substantially so, than those of the standard automobile
radiator. The condenser 36 is preferably constructed of
externally finned vertical steel tubes, ~or the strength ~o
resist internal pressure, and the geometry to avoid damage
when the water freezes. The vertical condenser tubes are
connected between headers at the top and bottom, and the-sides
of the bottom plenum are mad~ sufficiently flexible to ac-
commodate expansion of the accumulated water during feeezing.
This bottom plenum is made sufficiently large so that it can
contain all the water that could accu~ulate in the condenser
during shutdown without the water level rising into the vertical
tubes. The bottom plenum of the condenser may serve as the
hot well 38, or a separate flexlble-walled container may be
provided. Water from the hot well 38 is pumped by the boiler
feed pump(s) such as 20 to the I.C. engine cooling jacket 30
and to the steam generator unit 18. A vacuum line 54 is con-
nected from the condenser 36 and hot well 38 via check valve
56 to the I.C. en~ine intake manifold to collect and dispose
of the non-condensibles that may accumulate in the steam system
due to decomposition of steam cylinder lubricating oil, and
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' ~ ~ 2'~ ~2 ~
in-leakage of air through imperfect seals. The flow is suit-
ably restricted to prevent excessive quan~ities of steam from
being admitted to the I.C. engine. Thus the check valve 56
may be provided with a restricted orifice to permit limited
flow in a one-way direction only without disrupting the mix-
ture at the I.C. engine inlet under any operating conditions.
Coordinated control of the power of the I.C. engine
E~ etl~qin~
12 and the steam e~Fa~6~ 24 may be achieved by a control unit
~ such as is illustrated in Fig. 2. In the unit ~3 of Fig.2
a link rod 61 is connected to the standard foot control pedal
that is operated by the driver of the car. Slotted arms 62
and 64 connected together by shafts 65a, 65b are caused to
rotate about the axis of shaft 65b mounted in base 63 by the
motion o'f link rod 61. Control rods 67 and 69 connected to
the various throttles and cutoff control at the points desig-
nated "C" in Fig. 1 have pins 66 and 68 riding in the slots
- in the control arms 62, 64. The linkage consisting of links
70 and 72 joined by link 71 is actuated by rod 73 to control
the relative demand made upon the I.C. engine and the steam
en~ / ~e
e~a~e~ to provide the power call'ed for by the driver's ac-
tuation of the power control pedal and consequently the link
rod 61. Rod 73 is moved upward with increase of steam pres-
sure i.n line 81 applled to piston 80 in cylinde:r 82'against
spring 84. This upward motîon moves the pin on steam
power control rod 69 higher in the slot in arm 64) and the
pin'on I.C. engine throttle control rod 67 lower in the slot
in arm 62, with the effect that as the steam pressure in-
creases, the operation of the'linkage arranges that more power
will be called for from the steam engine, and less from the
I.C. engine. Thus, when steam pressure is larger than the
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1 ~ ~f~ ~2Z
desired predetermined value, steam will be drawn from the
boiler and cooling jacket at a greater rate, and the I.C.
engine will operate at a lower Fuel and air throughput to make
less exhaust gas, and less heat for the steam generator 18
and englne jacket 30. Accordingly, the two eEfects cooperate
to bring the steam pressure to the desired predetermined value.
Similarly if the steam pressure is less than the desired
predetermined value, the mechanism will operate in the reverse
8 manner to increase the I.C, engine throughput and exhaust
eng I r~e.
gas flow, and reduce the steam e*~ e~ steam consumption.
Fig. 3 shows the general trend of oxidesof nitrogen
prod~lction in standard American au~omobile engines for two dif-
ferent cities, Cincinnati and Los Angeles, as a function of
the fuel--air ratio in the rnixture fed to the engine. It is
apparent from this data that changing the fuel-air ratio of the
gasoline-air mixture fed to the internal combustion engine
from the standard value of .0714 to the preferred value of .090
for this invention wlll effect an overall reduction of NOX
emission from .020 lbs~/vehicle mile to about .0025 lbs./
vehicle mile, before crediting the system with the propulsive
effort delivered by the steam engine; including this credit
demonstrates an overall reduction in oxides of nitrogen
emission by a factor of about sixteen.
Fig. 4 is a graph of a performance map of the
conventional I.C. engine installed in an average Americarl car.
The broken line 90 on the map represents level road load. It
is readily apparent that the road load condition is far from
the region of best efficiency. The best efficiency is at a
brake mean effective pressure (bmep) of ab'out 100 psi, and a
piston speed of 1000 ft/min. (approximately the point 92).
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~ 2 ~
With a conventional engine in a standard automobile, fifty
milesan hour cruise in hlgh gear corresponds to a piston speed
of about 1500 ftlminute, and one can see from Fig. 3 ~hat the
road load bmep is about 22 psi, and the brake specific fuel
consumption (bsfc) is 0.8 lbs/hp-hr. ~hen the conventional
engine is replaced with the new engine system of this inven-
tion, the I.C. engine of the new engine system under the
comparable condition is loaded to a bmep of ~4 psi, and lts
bsfc would be 0.6 lb/hp-hr if it were conventionally
carbureted. For the preferred carburetion 1.4 times as much
fuel is fed to the I.C. engine for a total fuel consumption
of 0.82 lb. per I.C. engine horsepower hour. Since the
steam engine part of the system provides an amount of power about
equal to that provided by the I.C. engine of the system, the
overall bsfc of the combined system is half the above value--
. about .42 lb/hp-hr. This i5 about half the fuel consumption
of the conventional I.C. engine.
Overall the new engine is twice as fuel-efficient
in automotive service as the conventional powerplant.
Furthermore combustible pollutants have been reduced to ex-
tremely low values in the afterburner, far below any levels
presently set by any air pollution control agency. In
addition ~he N0x emissions have been reduced by a factor be-
tween lO and 16 below the levels emit-ted by-presently produced
engines. This has been done without compromlse of fuel
economy but instead a dramatic improvement therein has been
achieved.
In this preferred application of the engine to~the
propulsion task, the peak steady state power available from the
`30 system is less than that available from the conventional
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~ 2 ~'2Z
internal combustion engine. However, by taking advantage of
the fact that energy storage in the hot water and hot metal of
the steam generator unit 18 provides a reservoir from which
energy may be drawn for surge power capability, this~engine
will provide acceleration capability in city traffic, freeway
on-ramp accPleration, and passing maneuvers on the open
highway. What will be given up in performance in the
previously discussed sizing of the engine system to the load
is the ability to tow a heavy load up a 10% grade at 60 mph,
or to operate the vehicle on the level at speeds above 100
mph. If this performance were necessary in special cases,
such as for law enforcement vehicles, the displacement of the
I.C. engine and steam engine in the system need only be chosen
somewhat larger, at some cost in fuel economy.
The engine system as shown in Fig. 1 of the drawing
and described in conjunction therewith is essentially a sche-
matic representation of the preferred embodiment of my
invention. Numerous variations may be Pmployed as a matter of
design choice. For example, engine accessories such as the
pumps, fan, blower and the like may be shaft-driven from -the
Sz'~ en.~/ne
B ~c~e~ or the I.C. engine J or -they may be driven by motors
from the electrical system. Other arrangements than that shown
in Fig. 2 may be employed to coordinat.e the operation of ~he
steam and gas engine throttles and other controls.
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