Boiling liquid cooling system for internal combustion engines

A reduction of hot spots in the combustion chambers and the simultaneous elevation of bore temperature in an internal combustion engine are achieved by a boiling liquid cooling process in which a high molecular weight, high saturation temperature organic coolant is supplied to the coolant jacket of the engine head entirely in the liquid state, thereby greatly reducing the ratio of vapor to liquid in the head jacket for more effective heat transfer from the head to the coolant.

DESCRIPTION 
Technical Field 
The present invention relates to a cooling system for internal combustion 
engines that significantly increases the efficiency of and reduces the 
undesired emissions from the engine and is less expensive to make, install 
and maintain than conventional cooling systems. The system also makes it 
possible to improve the aerodynamic efficiency of vehicles by greatly 
reducing or eliminating the drag of a cooling air intake. 
BACKGROUND ART 
Effect of Temperature on Engine Performance 
It is well known that the efficiency of the internal combustion engine is 
greatly affected by temperature. It is for this reason that a major 
modification of the engine cooling system may have a first-order effect on 
engine performance. In general internal combustion engines, whether diesel 
or spark-ignition, are "heat engines" and operate more efficiently when 
hot. Accordingly, current design convention seeks to provide for 
attainment of temperatures of the walls of the cylinder bores at as high a 
level as possible. For this reason present-day liquid-coolant systems are 
operated under pressure. Pressure raises the boiling point of the liquid, 
and accordingly the coolant may be operated at higher temperatures without 
"boiling over." 
In conventional cooling systems, however, there is a penalty for high bore 
temperatures--temperatures at the cylinder head are also increased. This 
tends to cause premature ignition of the fuel charge, which most drivers 
recognize as "knocking", and localized heat damage such as metal cracks. 
Further insight into temperature effect is gained from consideration of 
what happens to the energy of the fuel supplied to the engine of an 
automobile. It is roughly as follows: 
Heat rejection in the exhaust gas--33% 
Heat rejection in engine cooling--29% 
Indicated horsepower--38% 
The indicated horsepower is partly consumed by pumping gases into, through 
and out of the combustion chambers and out the exhaust pipe (6% of total 
energy input), piston ring friction (3%), and other engine friction (4%), 
leaving an engine brake horsepower of 25% of energy in. In the case of 
automobiles, by far the largest field of use of internal combustion 
engines, only about one-half of the brake horsepower is ultimately used to 
move the automobile. The other half is lost in coasting, idling and 
braking, in drive train friction and other losses and in powering 
accessories. About one-half of the energy at the wheels is used to 
overcome aerodynamic drag and the rest tire friction and hysteresis. 
Engine temperature affects cylinder cooling heat rejection and 
thermodynamic cycle efficiency in various ways. Engine temperature also 
affects friction losses. The requirement in conventional vehicles of a 
radiator cooled by ambient air flow increases aerodynamic drag, relative 
to the more efficient body shapes that could be used if the cooling air 
intake for the radiator were eliminated. 
Basic Engine Cooling Requirements 
The primary purpose of an engine cooling system is to keep the engine 
within maximum and minimum temperature limits under varying loads and 
ambient conditions. 
The combustion process in an engine causes excessively high temperatures 
around the mixture ignition areas, normally in the top part of the 
combustion chamber in piston engines, and exhaust valve seat and port 
surfaces. Excessive temperatures in these areas cause surface ignition, 
leading to engine knock, mechanical failures of engine materials, and 
increases in HC (hydrocarbon) and NO.sub.x (oxides of nitrogen) emissions. 
Excessive cooling of the engine adversely affects fuel consumption, 
exhaust emissions of HC and CO, deposits, and vehicle driveability. 
Temperature differences throughout the engine cause thermal distortion and 
stress, which lead to engine wear, leakage, and failure. The ideal cooling 
system, therefore, balances these factors in order to maintain a 
temperature that is high enough to promote fuel economy, minimize 
emissions, maintain driveability, etc., low enough to eliminate 
preignition and mechanical failure and uniform enough to eliminate thermal 
distortion and its resulting problems. 
In addition to the cooling requirements for an engine operating under 
steady state conditions, as described above, a cooling system has further 
complicating requirements. The temperature of the engine has a tendency to 
increase with an increase in engine load. These load increases may be due 
to increased speed, road grade changes, additional weight in the vehicle, 
or many other causes. In addition, the ambient temperature increases have 
an adverse effect on engine temperatures since the temperature 
differential between the engine and the cooling air is reduced. For all of 
the above reasons, a cooling system which can maintain a uniform 
temperature in spite of varying engine loads and ambient conditions is the 
design objective. 
Types of Cooling Systems 
The radiative and convective heat transfer from combustion gases to the 
combustion chamber walls, the conductive heat transfer through the 
combustion chamber walls to other parts of the engine and the heat 
transfer area between the engine metal and the cooling system are all 
variables determined by engine design. As such, these factors are beyond 
the control of the cooling system design, and are assumed to be constant 
for purposes of comparison among various types of cooling systems. 
Air Cooling Systems 
Due to the low order of the heat transfer coefficient of air, a large 
volume of air flowing over the heat transfer area is required to reduce 
the temperature in an engine. This method of cooling is generally 
unsatisfactory in an automotive engine due to the wide variations in 
ambient conditions, e.g., ambient temperature and vehicle speed, and 
engine speeds and the difficulty in maintaining any control over engine 
temperature. As the vehicle speed increases, the volume of air flowing 
over the engine also increases, and as the vehicle speed decreases or the 
vehicle stops, the volume of air, even enhanced by a large fan, decreases; 
consequently, the cooling effect decreases. Additionally, finned areas 
create local hot spots between fin-to-bore contact points. It is difficult 
to maintain the engine temperature within required limits, thus making 
this cooling method ineffective for surface vehicles. Because air 
temperatures at high altitudes are very low, air cooling is generally 
satisfactory for aircraft, though there are advantages to be derived from 
liquid cooling of aircraft engines. 
Liquid Cooling Systems 
The liquid cooling system is the system most commonly used to control the 
temperatures in internal combustion engines. Conventional liquid cooling 
systems are pressurized, with forced circulation of a liquid coolant by 
means of an engine-driven pump. The closed loop system circulates the 
liquid coolant between the engine water jacket, where heat is transferred 
to the coolant from the combustion chambers, and a radiator, where heat 
absorbed by the coolant in the engine is transferred to air flowing 
through the radiator. A pressure relief valve in the radiator fill cap is 
set at a pressure high enough to raise the coolant boiling point, thus 
preventing the liquid coolant from escaping under the normal range of 
engine operating temperatures. 
To reduce engine warm-up time, a thermostatic valve is located at the 
outlet of the engine water jacket. The thermostatic valve opens only when 
the temperature exceeds a predetermined value. At coolant temperatures 
below the preset value of the thermostatic valve, little or no coolant can 
flow to or from the engine, so that the temperature of the relatively 
small portion of the total coolant that is trapped in the engine jacket 
will rise rapidly, and the engine can operate more efficiently sooner 
after a cold start. 
Although conventional pressurized single-phase liquid coolant systems are 
reliable and require relatively little maintenance, they have several 
inherent drawbacks. Surface convective heat transfer coefficients for a 
fluid in the liquid phase are relatively low and vary with flow velocity. 
In the typical automotive cooling system, cooled liquid from the radiator 
enters the engine water jacket at the lower front part of the engine, and 
heated liquid leaves from the top of the engine. Therefore, the front 
cylinders will run cooler than the rear cylinders. Also, it is difficult 
to maintain uniform flow velocity of the liquid coolant through the 
complex flow passages inside the cooling jacket, so local hot spots 
develop throughout the engine. These hot spots are believed to contribute 
to the production of oxides of nitrogen in the engine exhaust gases. 
Since the highest temperatures are generated in the combustion chambers at 
the tops of the cylinders, and since the coolant flow is generally upward 
through the engine, the upper part of each cylinder is much hotter than 
the lower part. This temperature differential from top to bottom of the 
cylinder causes thermal distortion of the engine block and cylinder head 
with consequent increased blow-by and oil consumption. Another problem 
caused by top-to-bottom temperature differentials is that of wall 
quenching, which produces an unburned layer of gases on the relatively 
cooler lower cylinder walls. This is a source of excessive carbon monoxide 
and unburned hydrocarbons in the exhaust gases. It also results in poorer 
fuel efficiency. Additionally, liquid systems are highly sensitive to 
ambiant temperature changes on a directly proportionate scale. 
Evaporative Cooling Systems 
Evaporative cooling (known also as boiling liquid or ebullient cooling) of 
internal combustion engines has been known for at least seventy years and 
has been the subject of numerous efforts over those years to develop a 
system that fulfills the many functional requirements for engine cooling 
systems in a reliable, effective, low-cost, practical way. Despite those 
efforts boiling liquid cooling has had virtually no commercial 
application. Some automobiles with boiling liquid cooling systems were 
built in the 1920's, and boiling liquid cooling has been applied to some 
extent to stationary engines, such as those used in the drilling industry, 
within the last twenty-five years. Nonetheless, there are some generally 
recognized advantages to boiling liquid cooling. 
One of the advantages of a boiling liquid cooling system is that the 
convective heat transfer coefficients for vaporizing and condensing the 
coolant are an order of magnitude greater than the coefficient for raising 
the temperature of a circulating liquid coolant without boiling. 
Therefore, the temperature of the coolant in an evaporative system tends 
to be virtually the same in all parts of the engine. 
In typical boiling coolant systems, liquid coolant is boiled within the 
cooling jacket of the engine, and the vaporized coolant is withdrawn from 
the upper part of the cooling jacket and conducted to an air-cooled 
radiator or condenser, either directly or through a vapor-liquid separator 
tank. The condensate collects in a sump connected to the bottom of the 
condenser and is returned to the inlet of the engine cooling jacket or to 
a supply tank for gravity flow to the engine. 
Since boiling occurs at a constant temperature (assuming constant 
pressure), and since surface convective heat transfer coefficients for 
fluids being converted to the vapor state are much higher than those for 
the same fluids kept in the liquid state, boiling liquid cooling systems 
can maintain cylinder wall temperatures more nearly constant from top to 
bottom. In addition, the entire cylinder wall will usually be hotter, 
thereby reducing the production of carbon monoxide and unburned 
hydrocarbons in the exhaust gases, reducing friction, and improving fuel 
economy. 
There are, however, several disadvantages to conventional pressurized 
evaporative cooling systems. An inherent major problem is loss of coolant 
supply in those systems due to vapor loss through vents or pressure relief 
valves and greater risk of high pressure leaks in the system. Many vapor 
cooling system produce an excessive volume of vapor in order to maintain 
the engine at the desired temperature level (100.degree.-116.degree. C., 
212.degree.-240.degree. F.). In a high pressure system, the condenser, 
where the vapor is condensed back to a liquid state, may restrict fluid 
flow, thereby causing back pressure and vapor build-up in the engine 
cooling jacket. This back pressure displaces the liquid coolant in the 
engine cooling jacket with vapor, and contributes to engine failure 
through loss of cooling in the region where vapor has displaced liquid 
phase coolant. A further problem with most previous systems is the need 
for condenser fans and circulating pumps, either mechanical or electrical. 
It is because of these and other problems that previous vapor cooling 
systems have not, since the early days of the automobile, been 
commercially used in automotive engine cooling systems and little used in 
other fields. 
Particular Prior Art References 
There is, of course, a substantial body of patent, technical and lay 
literature on the subject of boiling liquid cooling for internal 
combustion engines. A few of these documents warrant a brief discussion 
here, because certain of the embodiments of the present invention may 
utilize some of the concepts found in them. 
One such concept is the use of a condenser, the condensing surface of which 
is constituted by an external skin panel of a vehicle. This idea is 
proposed for use in automobiles in Barlow U.S. Pat. No. 1,806,382, May 19, 
1931 and for use in aircraft in Lynn et al., U.S. Pat. No. 1,860,258. The 
Barlow patent also describes the advantage of such a condenser of 
eliminating the need for a fan to blow cooling air through a tube 
condenser and of being able to provide a hood over the engine compartment 
that will reduce intrusion of dust and lessen release of fumes back toward 
the passenger compartment. 
Another feature that is useful in the present invention is that the 
condenser be located at a level above the engine coolant jacket and that 
condensed coolant be returned to the jacket by gravity. This eliminates 
the need for a pump. Elevated condensers with gravity return of condensate 
to the engine are proposed in the Barlow patent and in Bullard U.S. Pat. 
No. 3,082,753. 
The Basic Defect of Prior Art Systems 
It is believed that a basic and fatal defect has existed in all previously 
proposed boiling liquid systems, namely that a major fraction of the 
coolant in the coolant jacket of the engine head is in the vapor phase 
during most operating conditions of the engine other than during warm-up. 
Universally, the coolant in the jacket of the engine head receives the 
vapor evolved from the coolant in the block. When vapor from the block is 
combined with the large amount of vapor evolved in the head, especially 
around the exhaust ports and near the dome of the combustion chamber, the 
total vapor content of the head coolant jacket is so high that there is 
insufficient liquid coolant available in places where it is most needed to 
extract heat by vaporizing, and hot spots develop and persist in the 
combustion chamber dome. The vapor in the head has little capacity to 
accept more heat, and vapor pockets tend to form near the hottest regions 
where they are the most damaging to effective heat transfer. 
The problem of the presence of excessive coolant vapor in the head coolant 
jacket can be especially harmful in narrow portions of the jacket, such as 
above the exhaust ports and at the openings where the block jacket 
communicates with the head jacket. Even small projections on the walls of 
the jacket in these narrow passages can deflect the flow of liquid coolant 
and provide a site for a vapor pocket where a hot spot can develop and 
persist. These vapor pockets tend themselves to block or divert the flow 
of liquid coolant. Hence, the engine runs much of the time with a 
substantial fraction of vapor in the head coolant jacket and with 
insufficient coolant in the liquid phase for adequate heat transfer. 
The fact that most boiling liquid cooling systems proposed and used in the 
past have produced a violently boiling effluent from the head, such that a 
lot of liquid coolant is expelled with the vapor and a vapor-liquid 
separation is needed, strongly suggest the presence of excessive vapor. 
More importantly, preignition (knocking), which is undoubtedly due to hot 
spots, has been a chronic problem in vapor-cooled engines--pre-ignition 
reduces efficiency and can cause severe engine damage and ultimate 
failure. This ultimately requires a retarding of the ignition spark lead 
(advance) for correction, which results in a loss of fuel economy. The hot 
spots also cause high thermal stresses that lead to cracking of the head. 
DISCLOSURE OF INVENTION 
There is provided, in accordance with the present invention, a solution to 
the problem of excessive coolant vapor in the engine head, which solution 
involves various aspects and is applicable to numerous embodiments. The 
invention, moreover, makes it possible to achieve not only the recognized 
advantages of boiling liquid cooling but additional advantages and 
unexpected results as well. 
In particular the present invention is an engine cooling process that is 
characterized in that coolant is supplied in a liquid state substantially 
free of vapor to the coolant jacket of the head such that the major part 
of the head coolant jacket is kept filled with coolant in liquid state 
under all operating conditions of the engine. The process can be carried 
out in the following ways: 
(1) The coolant used in the process has a saturation temperature above the 
highest temperature attained by the walls of the coolant jacket of the 
engine block. In this mode the process is carried out by the inherent 
physical property of the coolant. The coolant cannot vaporize except in 
the head; hence it can be supplied to the head coolant jacket from the 
block coolant jacket and will enter the head coolant jacket in liquid 
state. Suitable coolants are high molecular weight, non-aqueous organic 
liquids having a saturation temperature of greater than about 132.degree. 
C. (270.degree. F.) at the operating pressure of the process, some 
examples being ethylene glycol, propylene glycol, tetrahydrofurfuryl 
alcohol, dipropylene glycol and 2,2,4-trimethyl-1,3-pentanediol 
monoisobutyrate. 
(2) The coolant is supplied to the head coolant jacket exclusively and 
directly from a vapor condenser that receives and condenses coolant 
discharged in the vapor state from the engine. In this mode the head 
coolant jacket is either separate from (does not communicate with) the 
block coolant jacket or the engine does not have a block coolant jacket. 
(3) As in case (2) above, a liquid coolant is supplied directly to the head 
jacket exclusively from a condenser chamber. The block coolant jacket 
separately receives liquid coolant condensed in the same condenser chamber 
from coolant vapor evolved in the block and head jackets. 
(4) Again as in cases (2) and (3) above, make-up coolant is supplied 
directly to the head jacket, but in this case as coolant condensate from a 
condenser chamber that receives vapor solely from the head coolant jacket. 
Vapor from the block coolant jacket is conducted to a second condenser 
chamber, and the condensate is returned from the second condenser chamber 
to the block coolant jacket. In short there are two vapor cooling 
circuits, one for the block and one for the head. 
In all modes of practicing the present invention the saturation temperature 
should, in general, be as high as practicable, taking into account the 
avoidance of undesirable conditions having to do with, for example, the 
durability of the engine and components of the vehicle near the engine, 
the effectiveness and life of the engine lubricant, and engine 
performance, such as instability of the flame front and ignition delay, 
unreasonable ignition settings, pre-ignition and detonation ("knock"), 
excessive emissions and reduced efficiency. In general, the higher the 
saturation temperature of the coolant up to the limit established by the 
aforementioned factors, and probably other factors as well, the higher 
will be the bulk temperature of the engine, and the lower will be the 
level of heat rejection. Hence, the efficiency of the engine will be 
greater. It will be recognized, of course, that different engine designs 
may respond in different ways to different coolants, and various tradeoffs 
are certainly possible, if not probable, in selecting a coolant. Diesel 
engines, for example, do not pre-ignite as can spark ignition engines; 
therefore, a diesel engine equipped with a cooling system according to the 
process of this invention can utilize a coolant having a saturation 
temperature higher than coolants suitable for spark ignition engines. 
As discussed briefly above, it is believed that there is a heretofore 
unrecognized basic and fatal defect in boiling liquid cooling systems for 
internal combustion engines, namely, too much coolant vapor and not enough 
coolant liquid in the head coolant jacket. The coolant universally 
proposed and used in the prior art systems is water. Even when a high 
boiling temperature antifreeze is mixed with the water coolant, the 
saturation temperature of the coolant is in the range of 104.degree. C. to 
116.degree. C. (220.degree. F. to 240.degree. F.), depending upon the 
pressure of the system. It has been observed that block coolant 
temperatures would be 16.degree. C. to 28.degree. C. (30.degree. F. to 
50.degree. F.) higher than this range were it not for the heat rejected by 
the block into the coolant jacket water. The heat rejected in this area 
causes the continuous conversion of liquid coolant into vapor. The vapor 
thus formed rises within the jacketed volume around the block and then 
enters the head coolant jacket, continuing to rise until finally it 
evolves from the top of the head jacket. To the extent that this vapor 
continuously occupies volume within the head jacket, liquid coolant is 
displaced. Under some operating conditions the head jacket contains an 
insufficient ratio of liquid to vapor in important areas, and cooling in 
these areas is inadequate. 
In the first mode of the present invention described briefly above, the 
coolant supplied to the head coolant jacket is in the liquid state because 
the saturation temperature is higher than the maximum temperature of the 
block coolant jacket walls. Prototype cooling systems according to this 
invention have shown that the temperatures close to a cylinder wall at 
full load are 121.degree. C. (250.degree. F.) at the mid-stroke point and 
about 132.degree. C. (270.degree. F.) at the top-stroke point when the 
engine is run with the liquid phase coolant at 149.degree. C. (300.degree. 
F.). Thus, the coolant leaves the block jacket and enters the head jacket 
substantially in the liquid state. 
In addition to mitigating the problem of excessive vapor in the head simply 
because no vapor enters the head from the block, there are other important 
beneficial effects of using a coolant having a saturation temperature that 
is higher than the coolant jacket temperature in the block. First, the 
cylinder walls are hotter than with water cooling (either liquid or 
boiling water), thereby providing more complete combustion of the fuel by 
reducing quenching (extinguishing of the flame near the cool walls of the 
cylinder during the power stroke). The hotter walls also mean there is 
less heat rejection and greater thermal efficiency and a reduction in 
friction due to reduced oil viscosity. The bore is of more uniform 
diameter from top to bottom and more uniform roundness, thereby reducing 
blow-by and wear of the ring grooves, the cylinder walls and the rings. 
The wall temperature stays well above the dew point of water vapor in the 
combustion gases, so there is no water condensation on the cylinder walls 
that can get into the oil and form sludge and acids. 
The result of raising the cylinder wall surface temperature has several 
interrelated effects on ignition timing, flame speed, and octane 
requirement. Normally, elevated engine temperatures in the conventional 
pumped liquid-cooled engine require using high octane fuel. However, the 
reverse is true with the invention. The hotter cylinder wall surfaces tend 
to decrease ignition delay (as well as the cyclic variability of ignition 
delay), which markedly reduces the time required for peak combustion 
pressure to be achieved after ignition. The cooler cylinder head surfaces 
complement this by reducing "hot spots." For this reason, engines having 
cooling systems according to the invention tolerate considerably more low 
end spark advance but require significantly less total high end spark 
advance than conventionally cooled engines. 
When the ignition timing is adjusted appropriately, the octane requirement 
of an engine cooled according to the invention is actually reduced. 
Although the cylinder-end gas is at a higher temperature, the higher flame 
speed combined with the elimination of hot spots on the combustion dome 
surface causing detonation causes the flame front to completely traverse 
the combustion chamber before the end gas has a chance to auto ignite. In 
addition, the markedly reduced cyclic variability of ignition delay allows 
engine operation much closer to the knock limit without occasional 
slow-burn or ignition-delay induced knock. 
Liquid fuel will not burn. It is evident, therefore, that since fuel is 
introduced into the engine in liquid-droplet form, the fuel must be 
atomized on its way through the venturi intake manifold, intake ports, 
valves, during the intake stroke, compression stroke and even during 
combustion. It is common for a large fraction of the fuel to remain in 
liquid form at the time of ignition. 
This causes three problems: First, the combustible mixture which is in the 
gaseous phase is leaner than the bulk ratio of air to fuel which was 
supplied by the fuel system, lowering flame speed and temperature. 
Secondly, the heat required to atomize that liquid fuel is stolen from the 
flame, lowering its speed and temperature. Thirdly, some of this liquid 
fuel finds its way into the quench layer, increasing the quantity of fuel 
which is not burned. With the cooling process of this invention the bulk 
engine bore (swept volume) and intake runners temperature is raised, 
thereby promoting more complete fuel atomization before the flame is 
initiated. This leaves more combustion energy available for conversion to 
work and less fuel in the quench layer. More complete fuel atomization in 
the intake manifold leads to better uniformity of fuel-air ratio between 
cylinders. This feature, in turn, allows more efficient fuel-air mixture 
calibrations, more satisfactory performance with alternate fuels or both. 
More effective fuel atomization allows for more efficient fossil fuel 
efficiency and is an absolute necessity when using alcohol fuels or 
wide-cut distillate fuels. 
Enhanced mixture preparation leads to improved driveability, which allows 
the driver to use the throttle less aggressively and results in reduced 
fuel consumption. Engines equipped with the invention show a 10% to 13% 
improvement in fuel economy in controlled laboratory tests. 
Boiling liquid cooling effects a marked decrease in unburned hydro-carbon 
and carbon monoxide emissions due to both the lower concentration of fuel 
in the quench layer and reduced thickness of that quench layer. The quench 
layer is well known in engine technology and is described as a layer of 
unburned liquid fuel approximately 0.18 mm to 0.38 mm (0.007" to 0.015") 
thick at the surface of the cylinder wall. Its concentration and thickness 
are inversely proportional to wall temperature heat level and are 
drastically reduced as the wall temperature rises. This occurs because at 
lower temperatures, about 82.degree. C. to 93.degree. C. 
(180.degree.-200.degree. F.), the cylinder wall is a parasite to the 
combustion flame, extracting (absorbing) enough heat from the flame to 
keep it from burning to the wall surface. The high levels of wall 
temperature in this invention minimize this parasitic nature of the 
cylinder wall by allowing the flame to burn closer to the wall and reduce 
the quench layer. Additionally, a decrease in carbon monoxide emissions is 
observed due to more complete combustion and increased flame burn time. 
Normally, as cylinder head surface temperatures rise to excessive levels in 
an engine equipped with a conventional liquid cooling system, emissions of 
oxides of nitrogen tend to increase slightly with increased engine 
temperatures, all other variables being held constant. However, with the 
present invention and the increased cooling rate (capacity) of the 
cylinder head cooling jacket behind the combustion chamber surface allows 
for a lowering of cylinder head combustion chamber surface temperatures, 
even though the bulk engine operating temperature has been raised 
considerably, e.g., 38.degree. C. (100.degree. F.) or more. This is 
accomplished in that the vapor saturation of the coolant in the cylinder 
head jackets has been lowered to a point where there is a sufficient 
amount of liquid coolant free of vapor available to the critical heat 
areas of the head to allow the increased capabilities of heat transfer 
unique to boiling liquid cooling (its high coefficient of heat transfer) 
to keep those critical areas sufficiently cool to avoid the occurrence of 
hot spots on the combustion chamber surfaces of the cylinder head. 
In order to minimize the amount of vapor in the head coolant jacket it is 
important to provide a vapor outlet conduit (or conduits) from the head 
coolant jacket of sufficiently large size to keep the pressure 
differential between the jacket and the condenser chamber low, preferably 
less than about 7 kPa (1 psi). Moreover, attention must be given to 
avoiding the possible trapping of vapor in an elevated region of the 
jacket in any operating position of the engine; in vehicles this means 
taking into account uphill and downhill operation. Two or more vapor 
outlet conduits or a manifold may be required in some designs. 
Once these surface hot spots (which can glow red at times) are minimized or 
eliminated, the higher flame speed, higher combustion temperatures and 
pressures can be easily tolerated by the engine without causing auto 
ignition (detonation) and higher levels of NO.sub.x, and creating a need 
for less high end distributor advance. 
Additionally, because the thickness of the quench layer and its inherent 
content of raw fuel have been minimized and cylinder temperatures are 
higher, a greater portion of the fuel fraction of the intake change is 
burned, and there are less residual fuel particles left to form deposits. 
Typically, engines equipped with this invention show no carbon deposits 
after 40,000 km (25,000 miles) of operation. The elimination of carbon 
deposits (which also glow) minimizes early ignition (pre-ignition) and 
allows for more optimum ignition settings, typically an increased low end 
advance. 
By optimization of ignition timing, air-fuel ratio, and exhaust-gas 
recirculation quantity, a simultaneous reduction in all three exhaust 
emissions and in fuel consumption is achieved. 
In diesel engines ignition is timed by the injection of fuel into the 
combustion chambers. Hot spots on surfaces of combustion chambers, 
although they exist in a conventionally cooled diesel engine, will not 
cause pre-ignition as they will in a spark ignition engine. Nonetheless, 
thermal stresses in diesel engine cylinder heads due to the presence of 
hot spots can cause damage due to working, cracking and the erosion of 
material. Those thermal stresses are relieved by eliminating hot spots by 
application of the process of this invention. 
Higher bore temperatures in diesel engines reduce the formation of exhaust 
particulates while simultaneously increasing the efficiency of the 
conversion of fuel energy to usable power. With both spark ignition and 
diesel engines, the increased bore temperatures which result from the 
application of the process of this invention yield greater engine power 
while at the same time the engines run cleaner. 
The high boiling point coolants used in accordance with this invention have 
a higher molar heat of vaporization than does water. Accordingly, the 
quantity of vapor produced in the head is lower than with water, 
everything else being equal. This means fewer moles of vapor in the head 
jacket for a given rate of heat removal. Moreover, vapor releases from the 
hot walls of the jacket more readily with high molecular weight organic 
coolants than with water. These preferred coolants have a much lower 
surface tension. Thus the vapor bubbles break away from the wall more 
easily, making way for liquid state coolant to close quickly behind the 
escaping bubbles and wetting the wall. Moreover, the heat transfer from a 
surface being cooled to liquid being converted to vapor is several times 
greater when vaporization takes place directly at the heating surface 
(nucleate boiling) than when it takes place through a blanketing film of 
gas (film boiling). Observations suggest that as compared to water the use 
of higher saturation temperature organic coolants promote the condition of 
nucleate boiling rather than film boiling. 
The above points add up to more effective cooling of the head due to the 
existance of a considerably higher ratio of liquid to vapor in the head 
jacket than with prior art boiling liquid cooling processes. 
In a desirable mode of a system according to the invention, the condenser 
chamber is designed to provide for unobstructed entry and flow of the 
coolant vapor, to promote rapid and efficient condensation and to be 
located above the engine to permit gravity flow of the condensate to the 
engine. In this practice of the method and in embodiments of the 
apparatus, in which an elevated condenser provides favorable conditions 
for convective flow of vapor and gravity return of condensate, the cooling 
system has no moving parts. The elimination of a coolant pump, a fan to 
cool the condenser, belts with drives, all thermostats and a higher cost 
tube heat exchanger makes the system less costly than present pumped 
liquid systems and most previously known boiling coolant systems. 
The condenser chamber can be also located below the vapor outlet, but this 
will necessitate the use of a condensate return pump. This configuration 
will allow placement of the condenser to the best advantage in a 
particular vehicle design, for example, behind the bumper of a motor 
vehicle or beside the engine oil pan. In such applications, the 
disadvantage of using a condensate return pump can be more than 
compensated for, as a trade-off, by, for example, optimum use of available 
space in the vehicle or improvement in the aerodynamics of the vehicle. No 
problem is presented in the process of condensing high molecular weight 
coolant vapor in a condenser located at a lower elevation than the area 
where the vapor is created, inasmuch as low molecular weight gaseous 
impurities, such as air or water vapor, are displaced to a level above the 
heavier coolant vapor while the vapor readily flows downwardly by gravity. 
Prior art vapor cooling systems, in contrast, have the problem that air 
existing within a condenser chamber located below the vapor outlet will 
resist being displaced by water vapor by virtue of its having a greater 
molecular weight than the water vapor. 
The operation of the invention at ambient pressure or low pressures above 
ambient, say 35 kPa (5 psi), as is preferred, allows less costly and more 
easily installed hoses and hose fittings. The chance of coolant leakage is 
greatly reduced in an atmospheric or low pressure system, and if a leak 
does occur, the rate of coolant loss should be low enough to permit the 
vehicle to travel many miles for repair without an elevation in engine 
temperature or damage. Leaks in the hoses and condensers can easily and 
effectively be temporarily repaired at roadside or a service station with 
tape and permanent repairs deferred to a time more convenient to the 
vehicle owner. Field repairs to the condenser, due to its low operating 
pressure, may be made with a simple epoxy patch or high strength tape. 
The invention is useful to great advantage in Otto cycle carburetor and 
fuel-injected piston engines, in Diesel engines, and Wankel engines. All 
of the engine types may be used in all types of vehicles, including 
automobiles, trucks, airplanes, self-propelled rail cars, railroad 
locomotives, and water craft, and in stationary applications. Stationary 
engines could require fan-cooling of the condenser if space is limited or 
a large non-forced air condenser if space is not a premium. 
Vehicles embodying the present invention can be designed with reduced 
aerodynamic drag, because the conventional radiator cooled by air flow 
entering some part of the vehicle can be replaced by an external body 
panel. For example, the nose of an automobile or the cowling of an 
aircraft engine can be closed up for reduced drag, hence providing better 
performance with the same engine or the same performance with a smaller 
engine. The condenser chamber in an airplane can be built into the surface 
of the wing, in which case it can perform all or part of the de-icing 
function. 
There is frequently an overheating problem with liquid-cooled airplane 
engines when the airplane is waiting for take-off--the radiator does not 
have the cooling capacity for the comparatively high ground temperature 
and comparatively low propeller air flow during standing and taxiing. The 
surface condenser can readily be designed to handle ground conditions with 
virtually no weight increase, and a constant engine temperature can be 
maintained as the aircraft climbs into cold ambients. In fact, the 
invention provides a weight advantage, not only in aircraft but all 
vehicles, because the fill of coolant is much lower than that required in 
a liquid cooling system of comparable capacity. 
There are preferred ways of carrying out each mode of the process according 
to the invention. As mentioned above, there are advantages to returning 
condensed coolant to the head coolant jacket by gravity return from a 
vapor condenser chamber that has an outlet above the top of the head 
coolant jacket. In addition to eliminating a pump, a gravity system 
ensures that no vapor will be returned to the coolant jacket, provided, of 
course, that the condenser has sufficient capacity to condense all vapor 
supplied to it. In many previously proposed systems it was possible for 
vapor to be returned to the coolant jacket with condensate. 
According to another aspect of the present invention, there is provided an 
improvement in vehicles powered by internal combustion engines that are 
boiling-liquid cooled and that, as known in the prior art, have a surface 
condenser chamber, one condensing surface of which is a substantially 
horizontally oriented upwardly facing external skin panel of the vehicle 
that is located at a level above the engine at all normal attitudes of the 
vehicle in operation. The invention is characterized in that the coolant 
is a high molecular weight organic liquid having a saturation temperature 
at atmospheric pressure of not less than about 132.degree. C. (270.degree. 
F.), and a surface tension at a temperature of 15.degree. C. (59.degree. 
F.) of less than about 70 dynes per centimeter. Examples of such coolants 
are referred to above. 
In one embodiment the invention is further characterized in that there are 
separate coolant jackets for the engine block and the engine head and in 
that there are two coolant circulation circuits, one between the block 
coolant jacket and the condenser chamber and one between the head coolant 
jacket and the condenser chamber. 
In another embodiment the invention is characterized in that there is a 
second surface condenser chamber having condensing surfaces that include 
an external skin panel of a vehicle that is located at a level above the 
engine at all normal attitudes of the vehicle in operation. There are 
separate coolant jackets for the block and the head of the engine, and 
there are separate coolant circulation circuits, one between the first 
condenser chamber and the block coolant jacket and one between the second 
condenser chamber and the head coolant jacket. 
A further embodiment is characterized in that there is no coolant jacket in 
the engine block and in that the inlet and outlet conduits are both 
connected between the condenser chamber and the head coolant jacket.

MODES FOR CARRYING OUT THE INVENTION 
The schematic depictions in FIGS. 1 through 4 of piston engines are 
intended to be representative of any state-of-the-art piston engine, 
whether it be an Otto cycle gasoline engine or a Diesel engine. In FIGS. 1 
to 4, the corresponding major components of the engine are identified with 
the same reference numerals. Those basic components include an oil pan 10, 
a block 12 formed with one or more cylinders 14 in which pistons 16 
reciprocate along a stroke length controlled by a crankshaft (not shown) 
and a connecting rod 18. Each cylinder 14 is surrounded by a block coolant 
jacket 20. A head 22 is bolted to the block 12 and is sealed to the block 
by a head gasket 24. The engine head 22 has a head coolant jacket 26. For 
the sake of simplicity, the intake and exhaust valves and the induction 
and exhaust ports constructed into the head are not shown. The reference 
numeral 28 represents the valve cover. 
In the embodiment of the invention shown in FIG. 1 the block coolant jacket 
20 communicates with the head coolant jacket 26 through passages 30. A 
conduit 32 is connected to the top of the head coolant jacket 26 and to a 
condenser chamber 34, the upper wall of which is a panel 36 of a material 
that has a comparatively high thermal conductivity. Any metal is entirely 
satisfactory, and plastics impregnated with metal powder to impart thermal 
conductivity can also be used. This form of heat exchanger chamber has 
advantages for use in vehicles such as automobiles, trucks, aircraft, 
locomotives and the like, because the panel 36 may be an external skin 
panel of the vehicle and thus be exposed to an air flow as the vehicle 
moves for enhanced removal of heat. The chamber 34 is further defined by a 
pan-like member 38 that is suitably joined and sealed to the panel 36. The 
pan-like member 38 can, for example, be strongly fastened to the panel 36 
by an adhesive and a rolled crimped edge. The member 38 should have a high 
thermal conductivity in order to promote condensation of the vapor. The 
pan 38 of the chamber 34 includes a collector portion 40, and a condensate 
return conduit 42 leads from the collector portion back to the lower 
portion of the block coolant jacket 20. 
Instead of having a vapor outlet conduit and a separate condensate return 
conduit, a single conduit leading from the top of the head to a low point 
in a condenser located above the head can serve both the vapor discharge 
and condensate return functions. Such an arrangement is shown in FIG. 6 
and described below. 
The coolant jackets 20 and 26 and the conduits 32 and 42 are filled with 
coolant to a level a short distance above the top of the head coolant 
jacket 26, as represented by the dashed line A in FIG. 1. As the engine 
warms up, the coolant expands, generally about 2 to 4 percent, so that the 
coolant level in the warmed-up engine rises to about the level represented 
by the dashed line B. The amount of coolant required for a cooling system 
embodying the present invention is much less than the amount required in a 
pumped liquid cooling system, inasmuch as very little coolant is ever 
present in the condenser. In a typical four cylinder engine, for example, 
the coolant fill is approximately three and one-half quarts. Because of 
the reduced amount of coolant, there is a reduced mass of coolant present 
to take heat from the engine during warm-up, and the engine warms up 
rapidly. Moreover, the warm-up is smoother than with a pumped liquid phase 
coolant system, inasmuch as there is no thermostat or equivalent element 
that causes variations in the flow rate, and thus the temperature of 
coolant being returned to the engine from the radiator, and hence tends to 
change the warm-up rate as the thermostat opens during the warm-up phase 
of operation. It is well known that the warm-up time in the operation of 
internal combustion engines is a period of low operating efficiency and is 
mechanically hard on the engine. The quick and smooth warm-up of the 
engine made possible with the cooling process of the present invention 
enhances engine efficiency, particularly in cold weather, and reduces 
wear. 
From a cold start, the coolant in the head jacket 26 warms very quickly, 
say about one or two minutes, depending on ambient conditions. As heat is 
rejected by the engine into the cooling system, the temperature of the 
coolant can continue to rise until its boiling point is reached. At this 
level, the temperature of the engine stabilizes, as the temperature of the 
coolant can rise no further. Additional engine heat that is rejected into 
the cooling system causes liquid coolant to vaporize. The vapor is removed 
by convection from the area of its creation enabling liquid coolant to 
occupy its previous location. The heat contained in the coolant vapor is 
rejected through the exposed walls 36 and 38 of the condenser chamber as 
the vapor is condensed back to a liquid. 
With the high saturation temperature, high molecular weight, low surface 
tension coolants used in the process of the present invention there are 
several benefits that ensure effective cooling of the engine head. For one 
thing, the low surface tension of the coolant ensures that only small 
vapor bubbles form and facilitates release of small vapor bubbles from the 
internal walls of the coolant jacket 26. The lower the surface tension of 
the coolant, the better. With a high saturation temperature coolant which 
has a surface tension lower than that of water when measured at 15.degree. 
C. (59.degree. F.) and recognizing that surface tension decreases as a 
function of increasing temperature and that the saturation temperature of 
the preferred coolant will be substiantially greater than the saturation 
temperature of water, the surface tension of the coolant is assured to be 
well below that of water at the saturation temperature. Due to the 
significantly reduced surface tension, more of the metal surface is wetted 
by coolant in the liquid phase, and there is more efficient heat transfer 
from the walls to the coolant. 
A second advantage of these coolants is the low temperature difference 
between the saturation temperature of the coolant and the temperature of 
the metal of the engine head, which results in a greater level of nucleate 
boiling and a reduced level of film boiling of the coolant. The rate of 
heat transfer in a nucleate boiling situation is considerably greater than 
the rate of heat transfer in a film boiling situation. Accordingly, the 
rate of heat rejection by vaporization of the coolant is higher with the 
high boiling point, high molecular weight, low surface tension coolant 
than it is with water. 
Tests have shown that the temperatures measured at external surfaces near 
critical heat areas of the cylinder head cooled with ethylene glycol or 
propylene glycol in the system depicted in FIG. 1 are about 17.degree. C. 
(30.degree. F.) lower than the temperature at the same location in the 
head for the same engine cooled with conventional water-antifreeze liquid 
coolant in a conventional pumped liquid cooling system. It is possible 
that there is a much greater difference between the temperatures at the 
internal head surfaces in the practice of the present invention and in the 
conventional system. It is believed that the reduced temperature results 
from a considerably more effective heat exchange between the metal of the 
head and the coolant with the present invention. 
There is probably a considerable amount of boiling going on in the head 
coolant jacket of conventionally liquid-cooled engines at some interfaces 
between the metal and the liquid coolant. In some of these locations, the 
vapor thus formed becomes trapped, and the heat transfer rate from the 
metal to the liquid is thereby made very inefficient due to the presence 
of a vapor barrier between the metal and the liquid. Hence, the average 
temperature conditions throughout the head are somewhat higher than they 
are with the present invention. Such boiling in the head is particularly 
prevalent around the exhaust passages and near the exhaust valve seat 
areas of a conventionally liquid-cooled engine. With the coolants used in 
the present invention the vapor more readily leaves the wall and is more 
easily replaced by liquid for better heat transfer. 
A third benefit of a high saturation temperature, high molecular weight 
coolant in the process of the invention is that the moles of vapor emitted 
for a given level of heat rejection can be substantially less than the 
moles of water vapor involved for the same heat rejection in a boiling 
water cooled engine. A reduction in the quantity of vapor produced is 
beneficial as it means a reduction in the ratio of vapor to liquid present 
throughout the system, i.e., the coolant jacket, the conduits and the 
condenser. Many organic liquids exhibit molar heats of vaporization which 
exceed that of water. Propylene glycol, for example, has a molar heat of 
vaporization about 20 percent greater than that of water. Thus, propylene 
glycol produces only about 80 percent as many moles of vapor as water 
would in removing the same amount of heat. 
The coolants used according to this invention have saturation temperatures 
which exceed the temperatures seen over most of the internal surfaces of 
the block coolant jacket 20. This means that little or no vapor is 
produced in the block jacket, that any vapor produced recondenses rapidly 
and that the coolant conducted from the block jacket to the head jacket is 
substantially free of vapor and is therefore in the greatly preferred 
state for effective heat transfer. In short, the head coolant jacket does 
not have to serve as a conduit for the conduction of coolant vapor from 
the block as well as a temporary repository for vapor created in the head 
jacket itself, and therefore the vapor level in the head is believed to be 
substantially lower than in a boiling liquid coolant system using an 
aqueous coolant. 
Coolant vapor produced in the head jacket 26 rises to the top of the jacket 
and passes out through one or more of the vapor discharge conduits 32, is 
released into the condenser 38 and rises by convection and momentum in the 
condenser up to the thermally conductive upper wall 36. At relatively low 
levels of vapor evolution from the coolant jacket 26 only a small fraction 
of the total surface area of the condenser appears to be contacted by 
vapor. Vehicles equipped with a cooling system in which the condenser is 
the entire vehicle hood exhibit significant heating of the surface area of 
the hood only to the extent of from about one quarter to half of the total 
surface area. From these observations it is concluded that a condenser 
chamber in which the entire surfaces of the hood panel 36 and the bottom 
pan 38 are available as condensing surfaces for the vapor has the 
capability of condensing as much vapor as the engine can generate under 
all temperature conditions and operating loads, with the possible 
exception in extreme circumstances of prolonged full load operation of the 
engine at low vehicle speeds in bright direct sun where solar heating of 
the hood surface can considerably reduce the condensing capacity of the 
vehicle hood. Even this extreme condition should be accommodated by 
applying a solar type clear reflective mono-directional coating to the 
hood or avoiding the use of heat-absorbing, dark colors for the hood of a 
vehicle operated in severe conditions. 
Upon contact with the walls of the condenser, coolant vapor is condensed. 
The configuration and orientation of the pan 38 should be designed to 
promote reasonably rapid flow of the condensed coolant to the collector 
portion 40 and gravity return of the coolant through the return conduit 42 
to the coolant jacket. Rapid return of the coolant to the engine is 
particularly desirable in cold ambient temperatures, in order to avoid 
substantial cooling of the condensate before it reaches the engine jacket. 
Otherwise, there will be a tendency for part of the coolant jacket 
receiving the condensate to be excessively cooled, thereby increasing the 
temperature gradient in the cylinder walls and somewhat reducing the 
advantages of the present invention that result from having more even 
temperatures throughout the full height of the cylinder walls. 
A cooling system constructed to operate according to the process of this 
invention by utilizing a nonaqueous, high molecular weight, high 
temperature boiling point coolant may be designed to operate either with 
the condenser chamber vented to the atmosphere or with the system entirely 
closed. For a closed system, the pressure difference between the inside of 
the condenser and the outside of the condenser is a function of the 
average temperature of the enclosed volume at any given ambient pressure. 
The average temperature of the enclosed volume depends upon the quantity 
and temperature of the entering vapor, the effectiveness of the heat 
transfer of the condenser and the total volume enclosed by the condenser. 
Pressure and vacuum relief valves will be incorporated into a closed 
system in order to compensate for altitude changes or to protect the 
system in the event that volatile impurities such as water are present in 
or introduced into the coolant. 
If the system is operated with the condenser vented to the atmosphere, the 
vent should be located at a cool location remote from the vapor inlet or 
inlets and in an upper part of the condenser chamber. As the preferred 
coolants for use in the process of this invention are of high molecular 
weight (molecular weight greater than 60), and the vapor is heavy relative 
to air (mw=28) and relative to water vapor (mw=18), the primary impurities 
(air and water vapor) are displaced by the heavier coolant vapor and are 
pushed out of the vent. 
Engines equipped with the system depicted in FIG. 1 and operated with high 
molecular weight, high boiling point coolants have exhibited a reduction 
in hot spots, detonation and pre-ignition and a considerable reduction in 
the temperature gradient from top to bottom in the engine, improved fuel 
mileage and lower levels of emissions. Because of elevated, more even bore 
temperature distribution, engine lubrication is more efficient, wear is 
thus reduced and fuel economy improved. Because of the hotter bore 
temperatures in the block, water contamination, sludge, and acid formation 
in the lubricating oil are lower. The engines have been free of audible 
knock. 
The condenser chamber itself can be constructed in various ways to provide 
rigidity. The pan will include stiffening ribs, certainly with myriad 
openings to allow vapor and liquid to move freely throughout the chamber. 
The pan can be joined in any suitable manner to the external body panel 
that forms the condensing surface. Modern adhesives are ideally suited for 
joining and sealing the pan to the body surface with rolled and crimped 
edges. 
Systems designed for vehicles will have to include vapor and condensate 
conduit systems and a condenser that provide for taking vapor from the 
highest point in the head coolant jacket and for return of the condensate 
from the lowest point in the condenser for all normal operating attitudes 
of the vehicle. In some cases this will require providing two or more 
vapor discharge conduits 32 leading to the condenser and two or more 
return conduits leading from the condenser back to the engine, thus 
accommodating the system for good vapor and condensate flow paths in the 
circulating system for both uphill and downhill operation. In other cases 
it may suffice to use the same conduit or conduits for conducting vapor 
from the engine to the condenser chamber and for returning the condensate 
from the condenser to the engine. For example, a single conduit conducting 
vapor from the top of the head coolant jacket to the collector in the 
front lower portion of a condenser built into a sloped automobile hood can 
also conduct condensate in the opposite direction. 
The geometry of the system should also be such to ensure that the fill 
level, which corresponds substantially to the horizontal regardless of the 
attitude of the vehicle, in the head coolant jacket is never allowed to 
drop below the top of the jacket 26 or at least maintains a liquid fill 
level throughout the head jacket that covers the exhaust ports and fills 
the major portion of the head jacket. Obviously, uncovering of the exhaust 
ports would lead to a very undesirable temperature build-up in the exhaust 
port or ports involved. 
It is well known that the heat rejection into the coolant of an internal 
combustion engine occurs primarily in the head. Accordingly, as shown in 
FIG. 2, the present invention is applicable to an engine in which the 
engine block 12' is cooled by heat rejection through the metal walls of 
the cylinders to the outside air, and there are no coolant jackets around 
the cylinders. Indeed, the cylinders may have ceramic liners, and the 
block may be designed to retain heat in the cylinder walls, thereby to 
improve the thermodynamic efficiency of the engine cycle by minimizing 
heat rejection from the swept volume. In such an engine the high boiling 
temperature coolant fills only the head coolant jacket 26, and the engine 
head 22 is sealed to the block by a solid head gasket 44. One or more 
vapor discharge conduits 32 lead from the uppermost portion or portions of 
the head coolant jacket 26 to the condenser chamber 34, and one or more 
condensate return conduits 42 lead from the condenser chamber back to the 
coolant jacket 26. 
With the embodiment of FIG. 2 the conduit 32 connecting the head coolant 
jacket 26 to the condenser chamber 34 may serve the dual functions of 
conducting vapor from the engine head to the condenser chamber and 
returning the condensate from the chamber to the coolant jacket. In all 
embodiments of the invention the conduit(s) used to conduct vapor from the 
head coolant jacket to the condenser chamber should be of relatively large 
diameter to ensure maximum freedom of evolution of the vapor phase coolant 
from the engine to the condenser chamber. Vapor conduction hoses or pipes 
of about one to two inches in diameter are typical for small displacement 
automotive engines. Obviously, systems for larger engines will benefit 
from larger conduits. Typically, condensate return hoses are 1/2" to 3/4". 
The operation of the system shown in FIG. 2 is essentially the same as the 
operation of the system shown in FIG. 1, in that all make-up coolant 
entering the head is in the liquid state. However, in the case of the 
embodiment of FIG. 2, condensed coolant is returned directly to the head 
coolant jacket 26 from the condenser chamber rather than returning via the 
block. The same advantages of a reduced level of vapor in the head and 
consequent better heat transfer conditions in the head coolant jacket are 
obtained with the embodiment of FIG. 2 as those obtained with the 
embodiment of FIG. 1. 
With some engine designs and some coolants, it may happen that the coolant 
in the block coolant jacket reaches the saturation temperature. Instead of 
having coolant vapor flow from the block into the head coolant jacket, the 
vapor may be withdrawn separately from the block jacket and conducted to 
the condenser. An embodiment of such a system is shown in FIG. 3. Vapor 
from the block coolant jacket 20 passes through one or more branch 
conduits 46 connected to the uppermost portion or portions of the block 
coolant jacket. The branch conduits join the main vapor discharge conduit 
32. A second branch conduit (or conduits) 48 connects the head coolant 
jacket 26 to the conduit 32. Accordingly, vapor is conducted separately 
from the block coolant jacket 20 and the head coolant jacket 26 to the 
condenser chamber 34. The condensate condensed in the condenser 34 is 
returned from the collector portion 40 through the main return conduit 42 
which feeds a branch conduit 50 connected to the head coolant jacket 26 
and a branch conduit 52 connected to the block coolant jacket 20. In the 
method as practiced in the system shown in FIG. 3, the condensate supplied 
to the head coolant jacket 26 via the branch conduit 50 is free of vapor, 
hence minimizing the amount of vapor in the head coolant jacket at all 
times, especially by reason of not supplying any vapor-laden coolant to 
the head jacket. The system shown in FIG. 3 is capable of operating with a 
coolant having a relatively low saturation temperature. 
The system shown in FIG. 4 provides for the use of different coolants in 
the block coolant jacket and head coolant jacket. One or more vapor 
discharge conduits 54 are connected to the upper portion of the block 
coolant jacket 20 and provide for conduction of coolant vapor from the 
block jacket 20 into a first condenser 56. Condensed coolant is returned 
to the block through a conduit(s) 58. Coolant vapor produced in the engine 
head coolant jacket 26 is conducted into a second condenser 60 through a 
discharge conduit(s) 62, and the condensate in the chamber 60 is returned 
to the head coolant jacket 26 through a conduit(s) 64. The system shown in 
FIG. 4 is intended for use in an engine which is designed to have 
different operating temperatures in the block and the head. For example, 
for improved thermodynamic efficiency it may be desirable for the block to 
run at a higher temperature than the head, the head being kept at a lower 
temperature to prevent detonation, preignition or other undesirable 
effects of an excessively high temperature in the head portion of the 
engine. The higher temperature in the block ensures more complete 
combustion of the fuel as well as greater efficiency of the heat cycle of 
the engine because of reduced heat rejection. The cylinder walls may be 
lined with ceramic or other temperature-resistant liners, and the block 
may have insulated external walls. As this system would most likely be 
employed where the head and the block are to be maintained at two 
different temperatures, separate coolants would be chosen, each having the 
desired respective saturation temperature. 
The two condenser chambers will, of course, be designed to provide the 
necessary condensing capacity for the respective coolant loops, namely the 
coolant loop for the head and the coolant loop for the block. As in the 
embodiments described above, the embodiment of FIG. 4 provides for supply 
of coolant in the liquid state to the head coolant jacket 26, thereby 
minimizing the ratio of vapor to liquid in the head jacket and ensuring 
efficient cooling under all environmental conditions and operating 
conditions. 
In addition to using the method of the invention in piston internal 
combustion engines, the invention also can be used with other internal 
combustion engines. For example, FIG. 5 illustrates schematically a Wankel 
engine having a casing 60 that includes three separate coolant jackets 62, 
64 and 66. The combustable mixture that powers the engine is taken in 
through an intake port 68, is compressed in the internal chamber 70 as the 
volume in the right portion of the chamber (with reference to FIG. 5) is 
swept by one of the surfaces of the rotor 72. The region near the spark 
plug or similar igniter 74 constitutes the head portion of the Wankel 
engine where the combustible fluid supplied to the engine is ignited and 
burned. A second swept volume of the chamber generally inwardly of the 
coolant jacket 66 is the expansion chamber where the working stroke of the 
engine occurs, the exhaust products of the combustion being discharged 
through an exhaust port 75 at the conclusion of the working stroke of each 
face of the rotor. 
The highest point in each of the coolant jackets 62, 64 and 66 is connected 
by a vapor discharge conduit 76, 78 and 80, respectively, to a condenser 
chamber 82 mounted in a suitable location at a level above the engine. 
Vapor produced in each of the coolant jackets is conducted through the 
associated discharge conduit(s), is released into the condenser chamber, 
rises by convection and momentum up into contact with the thermally 
conductive upper wall 84 of the chamber and is condensed by heat exchange 
with the wall 84. The condensate falls onto the pan 86 of the condenser 
chamber, flows to the collector portion 88 and is returned through a 
common return conduit 90 to each of the respective coolant jackets 62, 64 
and 66 through branch return conduits 92, 94 and 96. 
In the general descriptions of this invention reference has always been 
made to the block coolant jacket and head coolant jacket of the engine. 
Inasmuch as the configuration of a Wankel engine differs from that of a 
piston engine, reference is made above to the swept volumes of the chamber 
70. Portions of the casing 60 of the Wankel engine lying generally 
outwardly of the swept volumes are functionally equivalent to the cylinder 
block of a piston engine. It is intended that all references herein to the 
block coolant jacket be applicable to the coolant jackets 62 and 66 that 
are associated with the swept volumes of the Wankel engine. Similarly, it 
is intended that the coolant jacket 64 adjacent the combustion zone of the 
chamber 70 be understood to be the head coolant jacket of the Wankel 
engine. Hence the method of the present invention is practiced in the 
Wankel engine shown in FIG. 5 by virtue of the fact that liquid coolant is 
supplied from the condenser 82 in the liquid state to head jacket 64 
adjacent the combustion zone, thereby establishing a favorable ratio of 
vapor phase coolant to liquid phase coolant in the head coolant jacket 64. 
A modification of the embodiment of FIG. 5 that will be readily apparent to 
one skilled in the art in the light of the foregoing involves the 
provision of separate condenser chambers for each jacket in a manner 
analagous to the embodiment of FIG. 4. With such modification, each 
coolant jacket of the engine can be supplied with a different coolant, 
thereby enabling optimization of temperatures in the various zones of the 
engine for maximum thermodynamic efficiency and for attainment of other 
desirable mechanical characteristics such as reduced thermal stresses in 
the casing, good lubrication, more effective heat transfer rates and other 
objectives. 
In a Wankel engine the exhaust port is at a location in the engine that is 
remote from the combustion zone, unlike Otto cycle and Diesel piston 
engines where the combustion zone and exhaust port are both in the head. 
Effective cooling of the exhaust port region of the Wankel engine casing 
is ensured by the fact that liquid coolant is supplied to both the jacket 
66 and the jacket 62, either one of which may be joined to the jacket 
portion 98 that lies between the intake and exhaust ports 68 and 74. 
Accordingly, a low level of vapor is present in the region surrounding the 
exhaust port, thereby providing effective cooling for the exhaust port. 
FIG. 6 illustrates the use of the invention in an automobile having a 
transverse mounted engine 102 located in an engine compartment that is 
covered by a hood 104. The hood 104 and a pan 110 define a condenser 
chamber 106 that receives vapor conducted from the top of the head coolant 
jacket through conduit 108. The vapor condenses in the chamber, and the 
condensate returns through the same conduit 108 to the head coolant 
jacket. The conduit 108 is a flexible hose that is suitably installed to 
allow the hood to be raised for access to the engine compartment. The nose 
114 of the vehicle can be completely or largely closed, thus reducing 
drag. A small air intake may be provided to cool the engine compartment 
and oil pan. 
In a system for an aircraft powered by a piston or Wankel engine(s), the 
condenser chamber may be in the roof of the fuselage or the top of the 
wing of an airplane or in the top of the body of a helicopter. FIG. 7 
illustrates an airplane 120 having engines 122 installed in pods 124 under 
the wings 126. The condenser chambers 128 are built into the upper wing 
surfaces generally above the engine so that the propeller wash will 
provide a cooling air flow over the external cooling panel when the plane 
is on the ground. Generally, aircraft cooling systems embodying the 
present invention will have small pumps for returning condensate to the 
engine from condensate collectors at the four corners of the condenser 
chambers, inasmuch as the system must accommodate considerable pitch and 
roll motions. A by-product function of wing surface condensers is 
de-icing. 
In the general description of this invention reference has often been made 
to "the saturation temperature" and to "the boiling point". These 
designations are correctly used with reference to properties of pure 
coolant substances or azeotropic mixtures since for non-azeotropic 
mixtures boiling occurs over a range of temperatures with the lowest 
temperature, called the bubble point, and the highest temperature, called 
the dew point. In practice liquids used for coolants according to this 
invention may not be entirely pure substances or azeotropic mixtures 
inasmuch as they may contain additives such as stabilizers, inhibitors, 
and coloring agents, and they may contain impurities such as water or 
other unintended ingredients. Further, a coolant formulated for use with 
this system may consist of a mixture of substances which might cause the 
liquid to exhibit a boiling range and hence a range of saturation 
temperatures.