A hydrogen-oxygen fueled internal combustion engine is described, which utilizes an inert gas, such as argon, as a working fluid to increase the efficiency of the engine, eliminate pollution, and facilitate operation of a closed cycle energy system. In a system where sunlight or other intermittent energy source is available to separate hydrogen and oxygen from water, the oxygen and inert gas are taken into a diesel engine into which hydrogen is injected and ignited. The exhaust is cooled so that it contains only water and the inert gas. The inert gas in the exhaust is returned to the engine for use with fresh oxygen, while the water in the exhaust is returned to the intermittent energy source for reconversion to hydrogen and oxygen

Laumann, E. A.

Reynolds, R. K.

English

NASA Technical Reports Server

[111 4,112,875 
1451 Sep. 12, 1978 
United States Patent [191 
Laumann et al. 
[54] HYDROGEN-FUELED ENGINE 
[76] Inventors: James C. Fletcher, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Eugene A. Laurnan, 
Pasadena; Rollin IC. Reynolds, 
Tujunga, both of Calif. 
[21] Appl. No.: 718,268 
[22] Filed: Aug. 27, 1976 
[51] Int. c1.2 ........................ F02B 75/12; F02B 43/08 
123/DIG. 12 
[58] Field of Search .......... 123/1 A, 3, 119 A, 119 E, 
123/DIG. 12; 204/129; 431/2,4 
[561 References Cited 
[52] U.S. c1. ....................................... 123/1 A; 123/3; 
U.S. PATENT DOCUMENTS 
1,905,627 4/1933 Holland ............................ 123/119 E 
2,169,844 8/1939 Marshall .......................... 123/119 E 
2,742,885 4/1956 Thwaites ......................... 123/119 A 
2,937,634 5/1960 Kelseaux ...................... 123DIG. 12 
3,459,953 8/1969 Hughes ............................ 123/119 E 
3,572,297 3/1971 Murray ............................ 123/119 E 
3,672,341 6/1972 Smith ............................... 123/119 E 
3,970,054 7/1976 Henault ....................... 123DIG. 12 
2,183,674 12/1939 Erren ........................... 123DIG. 12 
3,982,878 9/1976 Yamane ................................... 431/4 
4,003,345 1/1977 Bradley ........................ 123/DIG. 12 
FOREIGN PATENT DOCUMENTS 
831,429 12/1937 France ............................. 123DIG. 12 
Primary Examiner-Charles J. Myhre 
Assistant Examiner-Craig R. Feinberg 
Attorney, Agent, or Firm-Wilfred Grifka; John R. 
Manning; Monte F. Mott 
[571 ABSTRACT 
A hydrogen-oxygen fueled internal combustion engine 
is described herein, which utilizes an inert gas, such as 
argon, as a working fluid to increase the efficiency of 
the engine, eliminate pollution, and facilitate operation 
of a closed cycle energy system. In a system where 
sunlight or other intermittent energy source is available 
to separate hydrogen and oxygen from water, the oxy- 
gen and inert gas are taken into a diesel engine into 
which hydrogen is injected and ignited. The exhaust is 
cooled so that it contains only water and the inert gas. 
The inert gas in the exhaust is returned to the engine for 
use with fresh oxygen, while the water in the exhaust is 
returned to the intermittent energy source for reconver- 
sion to hydrogen and oxygen. 
6 Claims, 2 Drawing Figures 
INERT GAS ELECTROLYSIS 36 INTERMITTENT 
APPARATUS CURRENT - 
SUPPLY 
https://ntrs.nasa.gov/search.jsp?R=19780025583 2020-03-20T13:52:38+00:00Z
U.S. Patent Sept. 12,1978 Sheet 1 of 2 4,112,875 
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U.S. Patent Sept. 12, 1978 
FIG. 2 
Sheet 2 of 2 4,112,875 
LOW POWER (J = 1.5) 
0 8 16 24  32 40 
COMPRESSION RATIO(R1  
4,112,875 
3 1 
HYDROGEN-FUELED ENGINE 
ORIGIN OF INVENTION 
The invention described herein was made in the per- 5 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 42 USC 2457). 
BACKGROUND OF THE INVENTION 
This invention relates to hydrogen fueled engines. 
Considerable efforts have recently been directed 
towards utilizing intermittent natural power sources, 
such as sunlight, to generate hydrogen for use when 15 
power is not available from the natural source. Hydro- 
gen can be utilized as the fuel in a diesel engine, in 
combination with air. However, if an engine with a high 
compression ratio is utilized to increase the efficiency of 
10 
operation, then nitrous oxide pollution is generated. A 
system which substantially eliminated such pollution, 
while also providing greater efficiency in engine opera- 
tion, would enable the production of mechanical or 
electrical energy at lower cost. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a hydro- 
gen-fueled energy system is provided which is of high 
efficiency and which produces substantially no pollu- 
tion. The system includes an engine powered by hydro- 
gen and oxygen, with an inert gas as a working fluid. 
The inert gas permits operation at very high thermal 
efficiencies for any given volumetric compression ra- 
tios. The exhaust of the engine contains substantially no 
pollutants, and can be cooled to separate liquid water 
from the working fluid. The working fluid can be re- 
turned to the engine, while the water can be utilized in 
the production of hydrogen and oxygen. 
The novel features of the invention are set forth with 
particularity in the appended claims. The invention will 
be best understood from the following description when 
read in conjunction with the accompanying drawings. 
BRIEF DESCRIPTION O F  DRAWINGS 
FIG. 1 is a simplified diagram of a closed cycle, hy- 
drogen-fueled energy system, constructed in accor- 
dance with the present invention; and 
FIG. 2 is a graph showing the theoretical efficiency 
of hydrogen-fueled engines. 
DESCRIPTION OF PREFERRED 
EMBODIMENTS 
FIG. 1 illustrates a closed cycle energy system 10, 
which is based on the use of hydrogen as a fuel. The 
system includes an intermittent current supply 12 in the 
form of a bank of solar cells which receives sunlight 14 
and converts it to current. During sunny days, the sup- 
ply provides current over line 16 which flows through 
a switch 18 to an output line 20 for transmission to 
electricity users. On very cloudy days and at night, 
current is supplied through the switch 18 to the output 
line 20, by a current generator 22 which is driven by a 
diesel engine 24. During sunny days, the intermittent 
supply 12 also supplies current to an electrolysis appara- 
tus 26 which receives water from a water supply 27 and 
separates the water into hydrogen and oxygen. The 
hydrogen is delivered over line 28 to a hydrogen stor- 
age device 30 which can supply pressured hydrogen on 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
L 
its output line 34. An oxygen outlet 36 of the electroly- 
sis apparatus delivers oxygen to an oxygen storage de- 
vice 40 which supplies pressured oxygen. The oxygen 
supply 40 delivers the oxygen through a control valve 
42 to a carburetor 44, and the outlet 46 of the carburetor 
is connected to the engine 24 to supply oxygen thereto. 
At the same time, hydrogen from the hydrogen supply 
outlet 34 is delivered to an injection valve 48 which 
injects the hydrogen into the engine 24. 
In accordance with the present invention, the work- 
ing fluid, an inert gas, is supplied through a pipe 50 to 
the carburetor 44 to mix with the oxygen therein, so 
that a mixture of oxygen and the inert gas is supplied 
from the carburetor outlet 46 to the engine. The inert 
gas is initially supplied from an inert gas storage con- 
tainer 52 through a control valve 54 to a pipe 56 which 
leads to a separator 58, the inert gas in the separator 58 
flowing through the pipe 50 to the carburetor 44. The 
proportion of inert gas, of the oxygen-inert gas mixture, 
is preferably great enough to constitute a majority of 
the mass of the mixture, and in any case should consti- 
tute more than lo%, by weight, of the oxygen-inert gas 
mixture. 
The invention can better be understood by following 
the complete cycle of operation as illustrated in FIG. 1. 
The diesel engine 24 receives a mixture of oxygen and 
inert gas from the carburetor 44, and receives injected 
hydrogen from the injector valve 48. A glow plug 60 
assures combustion of the hydrogen and oxygen to 
produce high pressures that move the pistons of the 
diesel engine. An exhaust 62 of the engine carries away 
the products of combustion, which includes the com- 
bined hydrogen and oxygen, in the form of steam, some 
residual oxygen, and the inert gas. The exhaust moves 
through a cooler 64 which cools the exhaust so that the 
steam condenses to liquid water. The exhaust passes 
through the pipe 56 to the separator 58, where the water 
falls through an outlet 66 into a gathering tank 68 which 
leads back to the water supply 27. The inert gas 69 in 
the separator 58 remains gaseous, and passes through 
the pipe 50 to the carburetor 44 for reuse. The inert gas 
storage container 52 makes up for losses of the inert gas 
by supplying small quantities to the system. The water 
in the water supply 27 is supplied to the electrolysis 
apparatus 26 so that it can be separated into hydrogen 
and oxygen for reuse in the engine. Any uncombusted 
oxygen and/or hydrogen is returned with the argon, 
through the pipe 50 for reuse. If significant amounts of 
carbonates or unreacted hydrocarbons are present in 
the exhaust (due to lubricating oil in the engine) then 
the carbonates and light hydrocarbons can be removed 
with an absorption filter and the heavy hydrocarbons 
can be filtered out of the water. Excessive hydrogen can 
be removed with a catalyst, or less hydrogen can be 
injected into the engine to account for hydrogen in the 
exhaust. Normally, a substantially stoichiometric ratio 
of hydrogen to oxygen is passed into the engine, al- 
though some excess oxygen can be admitted to help 
achieve complete combustion, the excess oxygen not 
being wasted since it is recycled. 
The usefulness of the inert gas arises from the fact 
that the proper selection of the inert gas permits opera- 
tion of the engine at higher thermal efficiencies than 
otherwise possible, and with no pollution of the atmo- 
sphere. 
If it were possible to operate a diesel engine at con- 
ventional compression ratios, utilizing only oxygen and 
hydrogen at complete combustion, then excessive tem- 
' 
4.1 12,875 
3 
peratures would be created that could harm the engine, 
when the engine were operated at close to its maximum 
power output: Actually, complete combustion of hy- 
drogen and oxygen in a stoichiometric ratio (the ratio 
which permits complete combination) does not occur 
because of the quenching effect of the steam created by 
some of the combustion gases. When air, which con- 
tains nitrogen and oxygen, is utilized instead of pure 
oxygen, a lower power output is produced and the 
properties of nitrogen result in the production of nitro- 
gen oxides which pollute the atmosphere. 
There are several thermodynamic properties of gases 
that affect the efficiency of a reciprocating, internal 
combustion engine. Three of these properties are the 
specific heat of the gas at constant pressure (C,), the 
specific heat ratio y of the gas which equals the specific 
heat at constant pressure (CJ divided by the specific 
heat at constant volume (CJ, and the thermal conduc- 
tivity of the gas. An ideal diluent gas has a low specific 
heat at constant pressure (C,), a high ratio of specific 
heats (y), and a low thermal conductivity. 
The desirability of having low thermal conductivity 
arises from the fact that this will cause minimal heat loss 
to the walls of the cylinder in which the combusted 
gases lie. Low thermal conductivity also minimizes the 
amount of engine cooling that is required. 
The desirability of employing a working fluid of low 
specific heat arises from the fact that such a gas will 
achieve a higher pressure when heated, as by the com- 
bustion of hydrogen and oxygen. Thus, for a given 
amount of heat resulting from combustion, the gas will 
rise to a higher pressure than a gas with a high specific 
heat. This raises the specific output of a given size en- 
gine, and as losses are mostly a function of engine size 
and configuration, the ratio of power output to power 
loss increases. 
The desirability of utilizing a working fluid of large 
specific heat ratio y, arises from its ability to produce 
high peak cylinder pressures under adiabatic compres- 
sion, and maximum energy extraction during the expan- 
sion phase of the engine cycle. The theoretical effi- 
ciency of an engine operating at various compression 
ratios R, combustion intervals J, and specific heat ratios 
y are shown in the graph of FIG. 2. The combustion 
interval J, with gaseous nitrogen as a fuel, is essentially 
the interval during which hydrogen is injected and 
combusted. Specifically, J equals the cylinder volume at 
the end of combustion (which normally occurs a short 
time after injection of fuel ceases), divided by the mini- 
mum cylinder volume (when the piston is at top dead 
center). The injection of gaseous hydrogen normally 
occurs between the time a piston reaches top dead cen- 
ter and the time it reaches a point less than 30" past top 
dead center. A long injection schedule sustains the pres- 
sure to increase the power output of the engine, but 
reduces the theoretical efficiency of the engine since 
much of the pressure is lost at the end of the piston 
stroke. The compression ratio R is the ratio between the 
volume within the cylinder at the beginning of com- 
pression by the piston, to the volume at top dead center 
when the volume within the cylinder is a minimum. 
Although the theoretical efficiency can be maximized 
by 'using a large compression ratio, physical limitations 
exist and increased mechanical losses are produced at 
higher compression ratios. Thus, a major factor which 
is available to increase efficiency is the specific heat 
ratio y. 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
4 
A formula for indicated (theoretical) engine eff- 
ciency N, as a function of the compression ratio R, the 
combustion duration interval J, and the ratio of specific 
heats y is given below: 
FIG. 2 provides graphs of the theoretical efficiencies at 
different compression ratios R, combustion intervals J, 
and specific heat ratios y. It can be seen that the use of 
a gas of high specific heat ratio y, such as 1.6, can pro- 
duce a considerably higher efficiency than can be pro- 
duced with gases of lower specific heat ratio. For exam- 
ple, at a combustion interval of 1.5 and a compression 
ratio of 16, a gas of a specific heat ratio y of 1.6 provides 
a theoretical efficiency of approximately 78%, while a 
gas with a specific heat ratio y of 1.4 (equal to that of 
air) provides a theoretical efficiency of about 63%, or in 
other words about 19% less. 
The following table provides a comparison of the 
above-described properties of different gases which can 
be utilized in an engine: 
Specific Heat 
Ca&-gm-'--' K-' 
Sub- (Consffnt) (Constant) E{- 
stance Pressue Volume cal-cm-'-sec-'-K-' 
Air ,2404 .I715 1.401 7.197 X 
.2 187 .I563 1.399 7.427 X 
- - 8.88 X 
Thermal 
Conductivity 
C C" Y 
3.428 2.442 1.404 49.94 x 10-5 
2064 .I626 1.281 5.06 x lo-' 
H2 
0 2  
COZ 
NO, 
He 1.248 ,752 1.660 
Ar .1252 .07531 1.668 
Kr .04 .0238 1.68 
39.85 X lo-' 
4.238 X 
2.26 X 
Ne 2 5  ,152 1.64 11.75 X 
Xe .04 ,024 1.66 
Steam 
,248 ,177 1.40 7.18 x 10-5 
.4801 ,3657 1.310 5.510 x IO-' N2 
It can be seen that the noble gases (He, Ar, Kr, Ne, 
and Xe), which are monatomic, all have a high specific 
heat ratio y of more than 1.6, which is considerably 
more than the specific heat ratio of 1.4 for air which is 
composed primarily of diatomic gases. As described 
above, it is desirable to provide a gas of large y, low C, 
and low thermal conductivity. The optimal gas would 
be krypton, with argon being a close second choice. 
From a practical standpoint, argon is the best choice 
because of its availability, since argon constitutes ap- 
proximately 1% of air while krypton constitutes only 
about one-ten thousandth of one percent of air. Argon 
can be obtained from air by liquifying the air. 
A closed cycle energy system of the type illustrated 
in FIG. 1 can be used to produce energy in a variety of 
locations, such as in desert-like environments where 
large amounts of sunlight are available but water is not 
readily available. This is because substantially all of the 
water used to generate the fuel and oxidizer can be 
recovered, and the inert gas used as the working fluid 
can be easily separated from the rest of the exhaust and 
reused. Of course, inert gas can be effectively utilized in 
a hydrogen-powered engine for other applications, be- 
cause of the higher efficiency of engine operation. 
Thus, the invention provides a hydrogen-fueled en- 
gine of high efficiency and which produces substan- 
tially no pollution. This is accomplished by utilizing a 
mixture of oxygen and an inert gas, as the atmosphere 
5 
within the engine in which the hydrogen is combusted. 
The inert gas is chosen so it has a large specific heat 
ratio of about 1.6 or more, and is inert in the presence of 
oxygen and hydrogen at a typical combustion tempera- 
ture on the order of 3000" C to avoid the generation of 
pollutants. An especially appropriate inert gas is argon. 
This fueling arrangement enables the provision of a 
relatively simple closed cycle energy system, wherein 
the exhaust can be cooled to produce water and the 
inert gas, which are easily separated and which each 
can be recycled for reuse in the engine. 
Although particular embodiments of the invention 
have been described and illustrated herein, it is recog- 
nized that modifications and variations may readily 
occur to those skilled in the art and consequently it is 
intended that the claims be interpreted to cover such 
modifications and equivalents. 
What is claimed is: 
1. A method for operating a hydrogen-fueled internal 
6 
delivering oxygen and a monatomic inert gas to the 
combustion chamber of an engine; 
compressing the oxygen and inert gas in said cham- 
ber; 
injecting hydrogen into said chamber when the oxy- 
gen and inert gas therein are compressed, to raise 
the gas pressure, and then produce work while 
lowering the pressure; 
cooling the exhaust gas from said engine to produce 
water and said inert gas, for reuse in engine opera- 
tion. 
4. A method for operating a hydrogen-fueled engine 
introducing into a combustion chamber oxygen and 
an inert monatomic gas that is inert in the presence 
of oxygen and hydrogen at a temperature of 3000" 
C.; 
compressing the oxygen and inert gas in said combus- 
tion chamber; 
5 
10 
comprising: 
15 
combustion engine comprising: 20 injecting hydrogen into said combustion chamber at a 
time when the oxygen and inert gas therein are 
compressed, and allowing said hydrogen to ignite; 
exhausting the gas in said combustion chamber; and 
extracting inert gas from the exhaust gas. 
5. The method described in claim 4 wherein: said 
inert gas comprises primarily argon. 
6. The method described in claim 4 wherein: said 
oxygen and hydrogen are introduced into said combus- 
tion chamber in a substantially stoichiometric ratio; so 
steam to water, and returning the gas in the cooled 30 that the exhaust consisrs substantially of water and inert 
exhaust to the cylinder of said engine. gas; and including 
separating the water and inert gas in said exhaust and 
separating the water into oxygen and hydrogen. 
introducing a mixture of oxygen and a working fluid 
compressing said mixture; and 
injecting hydrogen into the cylinder, to combust the 
a majority of said working fluid consisting of a noble 
2. The method described in claim 1 including: 
cooling the exhaust of said engine to convert the 
into the cylinder of said engine; 
oxygen and hydrogen; 
gas. 
25 
3. A method for operating a closed cycle energy 
system comprising: 
separating hydrogen and oxygen out of water; * * * * *  
35 
40 
45 
50 
55 
60 
65 


Hydrogen-fueled engine

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