Engine preheating process and system

A preheater system especially useful for diesel engine cold starts stores waste heat extracted from the engine exhaust flow in the form of chemical potential in a thermal storage material such as lithium bromide. The energy is retrieved during a cold start by direct hydration of that material to preheat engine intake air.

This invention relates to engine preheating. It relates more particularly 
to a system and process for preheating an engine, especially a diesel 
engine, to facilitate starting the engine in cold weather. 
BACKGROUND OF THE INVENTION 
Diesel engines are increasingly being used in automobiles, trucks and heavy 
equipment because they are more rugged and efficient than their gasoline 
counterparts and have longer life expectancies. The diesel engine does, 
however, experience some problems which are not encountered in gasoline 
powered engines. One of these problems is the difficulty of starting a 
diesel engine in cold weather. 
In a diesel engine, combustion takes place when air, compressed in the 
engine cylinders, reaches the ignition temperature of the diesel fuel. In 
warm weather, the intake air can easily reach the fuel ignition 
temperature when it is compressed. However, when a cold engine is started, 
some of the heat generated by the compression of the air in the cylinders 
is dissipated to the engine parts and this heat-sinking effect may result 
in the air not reaching the ignition temperature upon compression. Thus, 
at colder temperatures, especially below freezing, the heat produced by 
compression may not be able to overcome the heat-sinking effects of the 
cold engine. Indeed, it can be quite difficult, even impossible, to start 
a diesel engine in very cold weather conditions. 
Many techniques for alleviating engine cold start problems have been 
proposed and developed. Essentially, in order to counter the heat-sinking 
effects of the cold engine parts, the engine must be supplied with 
additional heat from one source or another. Current engine cold start aids 
make use of three different sources of thermal energy. There are some 
preheater systems which convert electrical energy from the engine battery 
or an external outlet into thermal energy. Some known systems employ small 
fuel burners which draw fuel from the main tank in order to provide heat. 
Some preheaters produce heat by other forms of chemical burning. In all of 
these prior systems, the thermal energy produced is used to heat oil in 
the engine crankcase and/or engine intake air to assist the starting of 
the engine. However, they all have certain drawbacks which militate 
against their being considered the ultimate solution to the cold start 
problem. 
The systems which derive their heat from a battery tend to drain the 
battery, which itself does not operate efficiently in cold weather. Also, 
in many cases, an external electrical source is not available. Those 
systems which produce heat by fuel or the burning of other chemicals can 
present a hazard when operating for long periods in a confined space 
because they generate poisonous or noxious fumes. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an improved 
system to facilitate the starting of an engine in cold weather. 
Another object of the invention is to provide a system of this type which 
does not require an external energy source to assist the starting of the 
engine. 
Yet another object of the invention is to provide an engine cold start 
system which does not release additional noxious fumes into the 
environment when it is in operation. 
A further object of the invention is to provide a system for preheating the 
intake air of an engine, particularly a diesel engine, to facilitate 
engine cold starts. 
Still another object of the invention is to provide an engine preheating 
process which produces one or more of the above advantages. 
Other objects will, in part, be obvious and will, in part, appear 
hereinafter. 
The invention accordingly comprises the several steps and the relation of 
one or more of such steps with respect to each of the others, and the 
apparatus embodying the features of construction, combination of elements 
and arrangement of parts which are adapted to affect such steps, all as 
exemplified in the following detailed description, and the scope of the 
invention will be indicated in the claims. 
Briefly, our preheater system uses waste thermal energy from the engine 
exhaust gases produced when the engine is running as a source of thermal 
energy. This thermal energy is stored in a special thermal storage 
material in the form of chemical potential by a direct 
dehydration/hydration process. The thermal energy is released during a 
cold start and used to warm the engine intake air before it reaches the 
engine cylinders. This thermal energy carried into the cylinders by the 
intake air helps to overcome the heat-sinking effects of the cold engine 
when the engine is cranked. 
The storing of thermal energy in the form of a chemical potential produces 
many beneficial side effects. The system is completely self-contained and 
does not require an external energy source. Moreover, the energy can be 
stored in the thermal storage material at ambient temperature. Therefore, 
the preheater can be maintained in a ready-to-start condition for an 
indefinite period of time. For the same reason, no insulation is required 
to contain the thermal energy so that the preheater system can be quite 
compact. Further, as will be seen, the preheater is a completely closed 
system. Therefore, the operation of the system releases no fumes or 
noxious gases into the atmosphere that could present a hazard to personnel 
working in the vicinity of the associated engine. Finally, the system 
comprises, for the most part, standard sheet metal parts. Therefore, it is 
relatively inexpensive to make and to incorporate into present day 
vehicles and other heavy equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Since the present system relies on the dehydration/hydration cycle to store 
thermal energy in the form of a chemical potential, a brief description of 
that phenomenon is in order. When hydrating certain materials, i.e. adding 
liquid water, considerable heat is released. In some cases, water 
molecules are adsorbed by the material and the heat of adsorption is 
released. In other cases, the water dissolves the material which, in turn, 
evolves heat in the form of heat of solution. The direct 
dehydration/hydration processes are reversible in that they form a cycle 
in which energy is alternately stored and released. 
The full cycle of steps for thermal energy storage in this fashion is 
illustrated in FIG. 3. As shown there, the hydrated thermal storage 
material is present at stage A in the cycle. At stage B, the thermal 
energy to be stored is applied to that material to heat the material and 
drive off the water therein. This thermal energy is used to break the 
bonds between the molecules of the storage material and the wetting agent, 
i.e. the liquid water. In stage C, after the thermal storage material has 
been dehydrated and is still at an elevated temperature, it is sealed off 
from all water or moisture. The material eventually cools to ambient 
temperature giving up its sensible heat to the environment and may be 
stored indefinitely in stage D. 
When it is desired to recover the stored thermal energy, it can be released 
from the thermal storage material in stage E simply by adding liquid water 
to the material to rehydrate the material. As soon as the water contacts 
the thermal storage material, the bonds between the water molecules and 
the molecules of the storage material are recreated. The formation of 
these bonds results in the conversion of chemical potential energy to 
thermal energy. The rehydrated storage material is now at stage A again 
and in condition to repeat the cycle. The storage material can be 
dehydrated and rehydrated repeatedly, each time storing and then releasing 
thermal energy. 
One class of materials which will undergo a hydration-dehydration reaction, 
is adsorbents, including zeolites, silica gels, charcoals and activated 
aluminas. Each of these materials has a large internal surface area and 
the ability to trap and hold water by capillary action and physical 
adsorption. Physical adsorption or physiosorption is reversible adsorption 
by weak interaction only; no covalent bonds occur between the adsorbent, 
the thermal storage material in this case, and the adsorbate, i.e. the 
water. When water contacts any dehydrated adsorbant material, a bond forms 
due to a discontinuity in intramolecular or interatomic forces. The amount 
of heat evolved in the adsorption reaction depends upon the adsorbant and 
adsorbate and the strength of the bond formed. The weak bond between the 
adsorbant and the adsorbate can be broken only by the input of thermal 
energy. 
A second class of materials that will undergo a reversible hydration 
process is salts. When a salt such as lithium chloride (LiCl) or lithium 
bromide (LiBr) is dissolved in water, it disassociates into its component 
ions. The polar water molecules are attracted to the salt's ions and form 
weak bonds with them. As a result of the formation of these bonds, heat is 
involved as heat of solution. The strength of these bonds and thus the 
amount of heat evolved by their formation depends upon the salt used. When 
the salt in solution is heated to a sufficiently high temperature, the 
water can be boiled off of the solution leaving the dehydrated salt. 
The zeolites, salts, aluminas, charcoals and silica gels all have the 
ability to form a weak bond with water molecules which releases heat. In 
each case, the weak bond formed does not involve any rearrangement of 
atoms between molecules. The water can be extracted from each of these 
materials simply by heating them. Both of these classes of materials can 
undergo repeated FIG. 3 cycles of hydration and dehydration, and therefore 
are potential candidates for the thermal storage material in a preheater 
system that relies on reversible hydration. 
We have found, however, that of all of these materials, only a very few 
have the requirements necessary for proper operation in this environment. 
These requirements include the following: 
reversibility--material should be able to be recycled repeatedly without 
changing its structure and experience a consistent temperature rise upon 
successive rehydrations; 
time/temperature profile for dehydration--material should be dehydrated 
completely at temperatures of 200.degree. to 350.degree. C. by the heat 
evolved by the engine exhaust gases in a reasonably short time, e.g. under 
2 hours; 
thermal energy storage density--material should evolve sufficient thermal 
energy when rehydrated to raise engine intake temperature at least 
30.degree. to 45.degree. C.; 
water penetration--to evolve thermal energy quickly during rehydration, 
there should be quick penetration of water into the material. 
The thermal storage material which most satisfies the above requirements is 
lithium bromide (LiBr), although certain zeolites may be useful to a 
lesser extent in certain specific applications. These zeolites include the 
following: 
PQ-3A--molecular sieve, type 3A, potassium cation powder from PQ Corp.; 
pQ-13X--molecular sieve, type 13X cation 8-12 mesh bead from PQ Corp.; 
M-564--molecular sieve, type 3A, potassium cation, 8-12 mesh bead from 
Davidson, brand material distributed by Fisher Scientific Co., Fairlawn, 
N.J.; 
ZLD-4000--molecular sieve, type X, powder, from Union Carbide Corporation, 
Danbury, Conn. 
Refer now to FIG. 1 of the drawings which shows our preheater system as it 
would be incorporated into a truck, bus or other piece of equipment 
powered by a diesel engine. It should be understood, however, that the 
preheater system could be used in other types of engines or, indeed, in 
other different applications to preheat a fluid of one kind or another. 
As shown in FIG. 1, the system includes a preheater unit 10 which contains 
an exhaust stage heat exchanger shown generally at 12, which transfers 
thermal energy from the engine exhaust gases to the thermal storage 
material M in unit 10 for dehydrating that material, and an intake stage 
heat exchanger shown generally at 14 which transfers heat from the 
rehydrated storage material M to the engine intake air. There is also a 
water collection and storage section indicated generally at 16 which 
directs water from the thermal storage material to an elevated storage 
tank 18 during dehydration, stores the water and then subsequently 
releases the water back into the storage material M during rehydration and 
preheating. 
As best seen in FIGS. 1 and 2, the exhaust stage heat exchanger 12 in 
preheater unit 10 includes a pipe 22 made of a corrosion-resistant, 
thermally conductive metal such as stainless steel which is connected to 
receive the exhaust gases of the engine being served by this system. That 
is, it is connected at its entrance end, i.e. the left end in FIG. 1, to 
the engines exhaust manifold. Hot engine exhaust gases enter the entrance 
end of the pipe 22 and leave through the opposite end thereof which is 
presumably connected to a standard muffler. Mounted on edge to an 
intermediate segment of pipe 22 is an array of longitudinal stainless 
steel fins 24. The illustrated system has four such fins spaced 90.degree. 
apart around the pipe. Preferably, the fins are welded to pipe 22 so that 
the pipe and fins are in intimate heat exchange relationship. These fins 
are in the order of 13 inches long and 1 inch wide and have a thickness in 
the order of 1/8 inch. 
A relatively short segment of pipe 22 spaced just beyond the left ends of 
fins 24 is provided with exterior threads 26. Also, a circular flange 28 
is brazed coaxially to pipe 22 just beyond the right ends of those fins. 
The finned segment of pipe 22 is received in an elongated 32 tube also made 
of a corrosion-resistant, thermally conductive metal such as stainless 
steel. The left or entrance end of tube 32 is provided with an end cap 34 
which is press-fit into that end of the tube. End cap 34 has an axial 
passage 36 which is threaded to receive the threaded segment 26 of pipe 
22. These parts are arranged so that when the pipe is threaded into 
passage 36 as shown in FIG. 1, the flange 28 abuts the exit or righthand 
end of tube 32 and constitutes an end cap that closes that end of the 
tube. If needed, a suitable heat-resistant gasket (not shown) may be 
provided between the tube end and flange 28 to provide a fluid-tight seal 
there. 
Pipe 22, tube 32, flange 28 and end cap 34 define a chamber or compartment 
38 which is fluid-tight an filled with thermal storage material M of the 
type described above, preferably lithium bromide (LiBr) in crystal powder 
form. Chamber 38 is able to accommodate approximately one kilogram of 
storage material M, with the fins 24 maximizing the thermal contact with 
the storage material. 
A tubular baffle 42 having the same maximum diameter as tube 32 is welded 
or brazed to the entrance end of tube 32 The entrance end segment 42a of 
baffle 42 is conical in shape, tapering toward tube 22, with the tube 
passing snugly through an axial opening 42b in that member. 
Still referring to FIGS. 1 and 2, tube 32 and its contents are received in 
a tubular housing 44 made of a corrosion-resistant material such as 
stainless steel. Housing 44 is longer and larger in diameter than tube 32 
so that an annular passageway 46 exists between the tube and the housing. 
Housing 44 has an entrance end segment 44a which is conical or tapered at 
more or less the same angle as the baffle 42a. The left or entrance end of 
housing segment 44a is butt-welded or brazed to an adjacent end of a 
relatively large diameter pipe 48 arranged coaxially on pipe 22 with the 
annular space between the two pipes providing a path for intake air into 
passage 46. The baffle 42a and the housing segment 44a help to change the 
cross section of the intake air entering preheater unit 10 from circular 
to annular to minimize eddies in the air flow at the entrance end of 
preheater unit 10. 
The outer surface of the thermally conductive tube 32 comprises the intake 
stage heat exchanger 14 which transfers heat between the storage material 
M inside chamber 38 and the cold intake air conducted into passage 46 via 
pipe 48. To increase the heat exchange efficiency between the storage 
material and the intake air, axial fins 52 of stainless steel are brazed 
or welded on edge to the outside surface of the stainless steel tube 32, 
with the fins extending substantially the entire length of that tube. 
Preferably, the fins are divided lengthwise into a plurality of lengthwise 
segments or sections with the fin segments or sections being staggered as 
shown in FIG. 2 to promote turbulence in the intake air flowing along 
passage 46. 
The exit or right end of housing 44 is closed by an end cap 48 pressfit 
into that end of the housing, an axial clearance hole 52 being provided 
for pipe 22 in end cap 48. The space inside housing 44 between flange 28 
and housing end cap 48 forms a plenum 54 for collecting and mixing the 
heated intake air leaving annular passageway 46. This hot air is conducted 
out of plenum 54 by a pipe 56 having one end brazed or welded to an open 
port 58 in end cap 48. The opposite end of pipe 56 is connected to the air 
intake port of the engine being served by this system. If desired, the 
outer surface of housing 44, including its entrance segment 44a, may be 
covered by a thermally insulating sheath 60 as shown in phantom in FIGS. 1 
and 2. Sheath 60 not only protects heat exchanger apparatus 10 from 
corrosion and damage due to external sources, it also helps to maximize 
the heat exchange efficiency of the apparatus. 
Still referring to FIGS. 1 and 2, the water collection and storage section 
16 of the present system includes, in addition to water tank 18 elevated 
above preheater unit 10, a plurality of, herein four, perforated pipes 62 
which extend substantially the entire length of chamber 38 between the 
fins 24 therein, the pipes exiting that chamber through flange 28 as shown 
in FIG. 1. The exit ends of pipes 62 connect via a circular manifold 64 in 
plenum 54 to a pipe 66 which extends out through a hole 68 in the wall of 
housing 44. The outer end of pipe 66 is connected by way of an on/off 
valve 72 to a pipe 74 leading from the bottom of tank 18. Although valve 
72 could be a manual valve, in most applications it is an electrically 
operated solenoid valve controllable automatically or by the operator of 
the vehicle or other piece of equipment in which this system is installed. 
Water collection and storage section 16 also includes a pipe 76 having one 
end connected to the top of chamber 38 through a hole 78 in flange 28. 
Pipe 76 extends out of housing 44 through a hole 80 in the wall thereof 
and is connected by way of a second solenoid operated on/off valve 82 a to 
pipe 83 leading to the top of tank 18. 
Chamber 38 in tube 32 and the components of the water collection system 16 
including pipes 62 and 76, water tank 18 and all of the pipes and fittings 
connecting those parts comprise a completely closed fluid-tight system for 
the circulation of fluid either as a liquid or as a gas or vapor between 
the storage material M in chamber 38 and tank 18. A pressure relief valve 
18a is provided on tank 18 to prevent excessive pressure build up in that 
closed system 
We will now describe the operation of this system with reference to FIGS. 1 
and 4. For purposes of this description, we will assume that the diesel 
engine served by the system has just been started so that hot engine 
exhaust gases are flowing through pipe 22 and cold intake air is flowing 
into pipe 48 leading to passageway 46 in unit 10. We will also assume that 
the storage material M is already wetted with water from tank 18 and that 
valves 72 and 82 are in their open positions. 
To start the dehydration reaction, valve 72 is closed. This may be done by 
the operator or automatically by a timer after the engine has been running 
for a few minutes. This marks the beginning of Step 1 in FIG. 4. During 
continued operation of the engine during Step 1, the thermal energy from 
the engine exhaust gases is transferred by the exhaust stage heat 
exchanger 12 to chamber 38 and it vaporizes the moisture content of the 
storage material M, the vapor collecting at the top of chamber 38. There 
is a pressure buildup in chamber 38 which drives off the water vapor 
through pipe 76 to the elevated tank 18 where it eventually condenses to 
liquid water W which remains in the tank. 
Refer for a moment to FIG. 5A. The curve A therein represents the average 
temperature of the storage material (LiBr) in chamber 38 during this 
dehydration Step 1 in an actual system. As shown by that curve there, at 
the beginning of Step 1, there is a rapid rise in the temperature of the 
storage material M. Then, as the water in chamber 38 begins to boil, the 
temperature of the storage material and water mixture rises more slowly 
until a steady state temperature is reached after about 2 hours. The curve 
in FIG. 5B shows that dehydration progresses rapidly at first but slows as 
the process proceeds over the 2 hour time period. The dashed line in FIG. 
5B represents the total amount of water contained in the storage material 
M at the beginning of Step 1. It is estimated that under actual operating 
conditions, the storage material 42M in chamber 38 would be completely 
dehydrated in less than two hours. 
After the prescribed period during which material M will have been 
dehydrated completely, valve 82 is closed by an engine operation timer or 
other suitable means so that no moisture can enter or leave chamber 38, 
i.e. valve 72 is still closed. The engine can now be turned off commencing 
Step 2 in FIG. 4 with chamber 38 and the storage material 42 therein 
allowed to cool to ambient temperature. For the entire duration of Step 2, 
the thermal energy from the engine exhaust gases is stored as a chemical 
potential in material 42. The system can remain substantially indefinitely 
at room temperature in this condition so long as moisture is excluded from 
chamber 38. 
When it is desired to start the associated engine from a cold start, prior 
to cranking the engine, valves 72 and 82 are opened by an operator 
actuated control to commence Step 3 in FIG. 4. As soon as the valve 72 
opens, water W flows by gravity from tank 18 into the perforated pipes 62 
of preheater unit 10 whereupon the water quickly and completely permeates 
the thermal storage material 42M in chamber 38. Valve 82 is opened, as 
well as valve 72, to prevent vacuum buildup in tank 18 due to the draining 
water W. As soon as the storage material is wetted by the water, hydration 
of the storage material results in the immediate conversion of the 
potential energy in the storage material to thermal energy. This heat is 
transferred by the intake air heat exchanger 14 to the intake air flowing 
along passageway 46. That heated air is then conveyed by pipe 56 to the 
air intake port of the associated engine. 
There is an optimum amount of water that should be used to rehydrate a 
specific amount of storage material M. Less water than the optimum would 
not sufficiently hydrate the material, and more than the optimum amount 
would result in heat loss to raise the temperature of the excess water. We 
have found that the optimum amount of water that should be added to a 
lithium bromide storage material 42M is in the order of 47% by weight of 
the rehydrated mixture. The above-described zeolites, on the other hand, 
should be rehydrated to about 25-30% by weight of the rehydrated mixture. 
FIG. 6 shows the temperature of the air in plenum 54 at the exit end of the 
preheater unit 10 during Step 3. As seen there, using lithium bromide 
storage material, the air temperature rises steadily from the ambient air 
temperature (20.degree. C.) at the entrance end of unit 10 to about 
70.degree. C. in about 5 minutes and after cranking commences, the 
temperature tails off in about 10 minutes. Thus, FIG. 6 shows that lithium 
bromide storage material, when rehydrated, can quickly raise the 
temperature of engine intake air by a significant amount for a length of 
time sufficient to cold start a diesel engine. 
During the rehydration and preheating Step 3, the associated engine 
presumably did start so that hot engine exhaust gases again flow in pipe 
22. At the end of Step 3 whose duration can be set by a suitable timer, 
the storage material 42 in chamber 38 is completely rehydrated. At this 
point then, valve 72 can be closed to ready the system for another cycle 
of operation at Step 1 in FIG. 4. 
As is apparent from the foregoing, then, our engine preheater system which 
employs the hydration-dehydration cycle of lithium bromide or other 
similar material to store thermal energy derived from engine exhaust flow 
as a chemical potential in the material has many advantages over the prior 
preheating systems discussed at the outset. Our system is small and 
compact. It is completely self-contained. It emits no noxious fumes or 
reaction products and it is quite compact and easy to install on existing 
vehicles and equipment. Furthermore, the system requires no external 
energy source and it can store potential energy at ambient temperatures 
without insulation substantially indefinitely. 
It will thus be seen that the objects set forth above, among those made 
apparent from the preceding description, are efficiently attained and, 
since certain changes may be made in carrying out the above process and in 
the construction set forth without departing from the scope of the 
invention, it is intended that all matter contained in the above 
description or shown in the accompanying drawings shall be interpreted as 
illustrative and not in a limiting sense. 
It is also to be understood that the following claims are intended to cover 
all of the generic and specific features of the invention herein 
described.