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| United States Patent |
3,552,370 |
|
Briggs
|
January 5, 1971
|
INTERNAL COMBUSTION ENGINE
Abstract
An internal combustion engine having combustion chamber wall surfaces
coated with a heat insulating base layer including nickel and aluminum for
retarding heat transfer by conduction and an outer layer including copper
for reflecting infrared radiation, and a method for applying said coating
to the combustion chamber wall surfaces of the engine.
| Inventors: |
Briggs; Southwick W. (Chevy Chase, MD) |
| Appl. No.:
|
04/801,124 |
| Filed:
|
February 20, 1969 |
| Current U.S. Class: |
123/669 ; 92/223 |
| Current International Class: |
F02B 77/02 (20060101); F02b 023/00 (); F16j 001/04 (); C23c 007/00 () |
| Field of Search: |
123/191A 92/223 308/4 117/105
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Burns; Wendell E.
Claims
I claim:
1. An internal combustion engine including a combustion chamber having a wall surface, the improvement comprising a multilayer coating on at least a portion of said wall surface, said
coating including an insulating base layer applied to said wall surface composed of nickel and aluminum for retarding heat transfer through said wall surface by conduction and an outer layer including copper applied to said base layer for reflecting
infrared heat radiation.
2. The internal combustion engine of claim 1 wherein said inner base layer is applied by flame spraying of powdered aluminum and nickel and wherein said outer layer of copper is applied by flame spraying.
3. The internal combustion engine of claim 1 wherein said inner base layer has a thickness in a range between 3 to 20 mils and said outer layer is approximately 5 mils in thickness.
4. The internal combustion engine of claim 1 wherein said base layer comprises approximately 5 to 20 percent aluminum and 95 to 80 percent nickel.
5. The internal combustion engine of claim 1 wherein said coating has a porosity of 3 to 5 percent by volume.
6. The internal combustion engine of claim 2 wherein said aluminum and nickel are sprayed onto said wall surface in an acetylene flame and said copper is sprayed in a hydrogen flame.
7. The internal combustion engine of claim 2 wherein said inner base coating comprises a mixture of 95 percent nickel and 5 percent aluminum applied to a thickness of up to 20 mils on said wall surface.
8. The internal combustion engine of claim 7 wherein said outer layer comprises cuprous material approximately 5 mils in thickness.
9. The internal combustion engine of claim 1 wherein said inner and outer layers are applied in nonuniform thicknesses on different areas on said wall surface.
10. A method of coating a combustion chamber wall surface of an internal combustion engine comprising the steps of applying a base coating on said surface up to 20 mils in thickness composed of nickel and aluminum and applying an outer coating
on said base coating of cuprous material approximately 5 mils in thickness.
11. The method of claim 10 wherein said base coating is applied by flame spraying a mixture of powdered nickel and aluminum in an acetylene-rich flame.
12. The method of claim 11 wherein separate flames are used for simultaneously applying aluminum and nickel in a ratio of approximately 5 percent aluminum and 95 percent nickel.
Description
The
present invention relates to internal combustion engines and is concerned with the coating of combustion chamber wall surfaces to reduce heat losses and to reduce air pollution in the exhaust gases by providing for more complete burning of the fuel in
the combustion chamber.
The present invention is an improvement over the copending Pat. application Ser. No. 699,568, filed Jan. 22, 1968, U.S. Pat. No. 3,459,167, issued Aug. 5, 1969.
In the past, various types of coating materials have been applied to combustion chamber wall surfaces in internal combustion engines to improve engine efficiency and performance by reducing the heat losses from the gases in the combustion
chamber. In some instances such coating materials were effective to reduce a portion of the heat losses radiated in the form of infrared energy but were relatively inefficient in reducing the heat losses through the walls via direct heat conduction.
Other deficiencies in prior coating materials are the fact that many of the coatings are not able, physically, to withstand the relatively high temperatures encountered and the high pressures involved. Moreover, many combustion chamber surface coating
materials are unsuitable because of low resistance to chemical corrosion and oxidation, and low wear resistance, and many such coatings do not stand up under operating conditions long enough to prove economically feasible. Because of high mechanical
stresses developed in combustion chambers, due to high temperatures and rapid changes in temperature high frequency, repetitious intervals, physical failure of coatings by spalling off, cracking and chipping are severe problems.
The present invention has for an object the provision of a new and improved internal combustion engine having combustion chamber wall surfaces covered with a new and improved coating material, highly effective in reflecting infrared heat
radiation and having excellent insulating qualities to resist direct conductive heat transfer from the combustion gases through the combustion chamber wall surfaces.
Another object of the present invention is to provide a new and improved method for applying a heat flow retarding coating to the combustion chamber wall surfaces of an internal combustion engine.
Another object of the present invention is to provide a new and improved internal combustion engine having a coating material applied to the combustion chamber wall surfaces comprising a base layer for retarding heat flow by conduction and having
high mechanical strength, and an outer layer for reflecting infrared radiation securely bonded to said base layer and also having high mechanical strength and good wear resistance characteristics.
Still another object of the present invention is to provide a new and improved coating of the type described for application onto combustion chamber wall surfaces of an internal combustion engine, said coating having high mechanical strength and
being able to withstand high temperatures and pressures, and having good wear resistance characteristics.
It has been found that particular portions or locations on the wall surfaces in a combustion chamber are hotter than others, and these portions generally have less carbon accumulating thereon, and it is an object of the present invention to
provide an internal combustion engine wherein the hotter portions or locations in the combustion chamber are provided with different thicknesses of coating material than other portions.
Another object of the present invention is to provide a new and improved internal combustion engine having a combustion chamber surface coated with heat reflective material, which material can be easily and rapidly applied, is low in cost, and
has a long and useful life under high wear conditions of high pressure and temperature.
Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and
forming a part of this specification.
For a better understanding of the present invention, reference should be had to the accompanying drawings in which:
FIG. 1 is a fragmentary, sectional, elevational view depicting the invention as applied to the combustion chamber of a diesel-type, internal combustion engine;
FIG. 2 is a greatly enlarged, fragmentary, sectional view taken on line 2-2 of FIG. 1 and illustrating a coating applied to the piston head of the engine with the thickness of the coating being exaggerated to better illustrate a feature of the
invention;
FIG. 3 is a graphical representation illustrating comparative test results between a standard engine having no combustion chamber surface coating and the same engine having coated combustion chamber wall surfaces in accordance with the present
invention;
FIG. 4 is a graphical representation illustrating comparative test results between a standard engine having no combustion chamber surface coating and the same engine having coated combustion chamber wall surfaces in accordance with the present
invention; and
FIG. 5 is a bar graph illustrating comparative test results between a standard engine having no combustion chamber surface coating and the same engine with several different types and/or thicknesses of coating applied and showing the effect of
the different coatings on engine performance.
Briefly, the present invention is concerned with a coating material applied to combustion chamber surfaces, such, for example, as a piston head, cylinder wall, engine head, etc., of an internal
combustion engine. The coating is highly reflective of infrared heat radiation and also provides a heat insulating barrier resisting the transfer of heat by conduction from the gases in the combustion chamber through the chamber walls. In the
illustrated embodiment, a multilayer coating for combustion chamber wall surfaces of a diesel-type engine comprises a lower or insulating base layer for retarding conductive heat transfer through the engine walls, which base layer includes nickel and
aluminum and an outer layer including copper which is effective to reflect a high percentage of the infrared heat radiation that is generated by the burning gases in the combustion chamber. By providing an efficient reflective surface for infrared heat
radiation and also providing an insulating layer for resisting heat transfer by conduction through the cylinder walls, the multilayer coating of the present invention greatly reduces heat losses from the hot gases in the combustion chamber and,
accordingly, the temperature of the gases in the combustion chamber is elevated above the temperatures developed in a similar engine without coated combustion chamber surfaces. The coating and higher temperature results in a much higher percentage of
hydrocarbons being completely oxidized, thereby producing higher engine efficiency, reduced fuel consumption, and a reduced amount of unburned hydrocarbons in the exhaust gases, the latter factor being of considerable importance in view of the present
stress on means for reducing air pollution from internal combustion engines.
Referring now, more particularly, to the drawings, and specifically to FIG. 1, the present invention is, by way of example, illustrated as applied to a diesel-type internal combustion engine, and it is to be understood that the invention is
applicable to other types of internal combustion engines as well as to internal combustion chambers generally, wherein it is desired to minimize heat losses between the burning gases and the combustion chamber wall surfaces. In FIG. 1, the engine block
is referred to generally by the reference numeral 10, and includes one or more cylinders 12, each having an upper end closed by the cylinder head structure 14. A piston 16, having a plurality of rings 18 thereon, is disposed for sliding movement in the
cylinder 12 for travel toward and away from the cylinder head 14 in the conventional manner. The cylinder head structure 14 is provided with a pair of valve openings or valve seats for each cylinder, and an exhaust and intake valve is associated with
each pair of seats, one of which is shown as the valve 20. Each cylinder is provided with a fuel nozzle 22 for introducing fuel into the combustion chamber for burning.
A combustion chamber 24 is defined within the cylinder 12 between the upper surface or head of the piston 16, the lower or undersurface of the head structure 14 and the lower surfaces of the valves 20. In accordance with the present invention,
all or part of the wall surfaces defining the combustion chamber 24 are coated with heat-reflective material and the coating is generally designated by the numeral 26 and is described in greater detail hereinafter. The coating 26 is shown in exaggerated
thickness on the piston head in FIG. 2, and is especially adapted to withstand the high operating temperatures and pressures encountered in the combustion chamber 24 and is well suited to resist the corrosive activity of high temperature burning gases.
In addition to the above purposes, the coating 26 is especially adapted to reflect infrared heat radiation generated by the burning gases and is particularly effective in reflecting radiation having a wave length in the range between .7 and 10.0
microns. Besides being effective to reflect a high percentage (approximately 75 percent or more) of the infrared heat radiation generated by the burning gases in the combustion chamber 24, the coating 26 is also effective as an insulating barrier and
resists the flow of heat by conduction through the wall structures. The coating 26 is effective to reduce heat losses in two ways; one way, by reflecting infrared heat radiation generated in the gases in the chamber and, secondly, by providing an
insulating barrier around the wall surfaces of the combustion chamber 24 to retard the flow of heat by conduction through the wall structure defining the combustion chamber.
Referring now, more particularly, to FIG. 2, it has been established that combustion chamber wall surfaces of internal combustion engines have some portions, hot spots, etc. that are hotter than others. In accordance with the present invention,
the heat reflective coating 27 may be applied in several different thicknesses on a combustion chamber wall surface and may be applied in a greater thickness at the higher temperature locations than in the colder areas. For example, as shown in FIG. 2,
the region designated as T.sub.2 represents a portion of the combustion chamber wall surface that normally runs hotter than an adjacent region on the piston head surface designated T.sub.1. The coating 26 is applied in greater thickness in the hotter
region T.sub.2 than in the lower temperature region T.sub.1, so that the greater temperature differential will be resisted by a greater thickness of coating material 26. Temperature studies on high speed, internal combustion engines have indicated that
the central portion of the piston head is generally higher in temperature than the peripheral portions thereof and, accordingly, the coating 26 is applied in greater thickness in the center of the piston head surface than around the outer edges.
Ideally, the surface temperature of the combustion chamber walls should be uniform to prevent hot and cold spots which can cause preignition in the engine. Practically, the surface temperature should be maintained as high as is possible without
causing the relatively thin coating 26 to melt or to lose appreciable mechanical strength or wear resistance. Cold spots in a combustion chamber are believed to cause carbon accumulations to develop on the wall surfaces of the chamber, and these carbon
deposits are thought to cause an increase in the amount of unburned hydrocarbons moving out of the combustion chamber in the exhaust gases. Accordingly, it has been found that by regulating the thickness of the coating 26, a more uniform combustion
chamber wall surface temperature can be obtained, and the formation of carbon deposits can be greatly reduced or eliminated entirely. In addition, by reducing the heat losses from the combustion gases, the gases are maintained at higher temperatures,
which results in a smaller amount of carbon condensing out on the adjacent wall surfaces and also results in a lower percentage of unburned hydrocarbons in the exhaust.
The coating layer 26 comprises an inner or base layer 28 which functions as an insulating heat barrier because of its comparatively low heat-conductive characteristic in comparison to the base metal of the engine, normally aluminum, iron, or
alloy. In accordance with the present invention, it has been found that a base layer 28, comprising a mixture of nickel and aluminum, provides an excellent insulating barrier for resisting the conductive flow of heat from the combustion chamber gases
through the combustion chamber wall structure. The coating 26 also includes an outer layer 30 applied onto the base layer 28, and the primary function of the outer layer 30 is to reflect the infrared heat radiation received directly back into the
burning gases. Copper and cuprous oxide material has been found to make an excellent outer coating 30 for reflecting infrared heat radiation and these materials have good mechanical strength and wear resistance and can be readily bonded or fused with a
base layer 28 formed of a mixture of nickel and aluminum.
FIGS. 3 and 4 represent graphically comparative test results performed on a single cylinder, Wisconsin Model PHD internal combustion engine driven generator power plant having a nominal full load capacity of 7500 watts at 115/230 volts. Tests on
specific fuel consumption, air-to-fuel ratio, exhaust gas temperature, and unburned hydrocarbon content in the exhaust gases were run over a representative load range with a standard engine having no coating applied to the combustion chamber wall
surfaces, and the curves relating thereto are marked as STANDARD on the diagrams shown in FIGS. 3 and 4. Tests for unburned hydrocarbons in the exhaust measurements were made with a flame-ionization exhaust gas analyzer rather than an infrared analyzer,
and it should be noted that in the higher load range, the amounts of unburned hydrocarbons in the exhaust gases were well in excess of the maximum of 275 parts per million allowed under present State of California and Federal standards.
After the above tests were completed, the engine was disassembled and the surfaces of the combustion chamber, including the piston head surface, the cylinder head surface, the valve heads, and the upper portion of the cylinder wall not contacted
by the piston were coated in accordance with the present invention with a base layer about 10 mils thick formed of a mixture of 95 percent nickel and 5 percent aluminum applied in powdered form by flame spraying with an acetylene-rich flame. After the
base coating was applied, an outer layer 30 of copper approximately 5 mils in thickness was applied onto the insulating layer 28 by flame spraying in a hydrogen-rich flame. Comparable tests on the engine with the coated combustion chamber were then run,
and the curves labeled TEST indicate the test results obtained in FIGS. 3 and 4.
In comparing the test results on specific fuel consumption in pounds per kilowatt hour between the STANDARD engine and the TEST engine coated in accordance with the present invention, as described, it will be seen that the fuel consumption for
the TEST engine is considerably lower throughout the entire load range, indicating a much higher efficiency obtained because of the coating applied to the combustion chamber wall surfaces. Comparing the test results on unburned hydrocarbons in the
exhaust gases, it will be seen that in the high load range (for example, 6 1/2 KW), there is almost eight times as much unburned hydrocarbon in the exhaust gases of the STANDARD engine as in the TEST engine, and the maximum value for the TEST engine is
less than 100 parts per million. This low figure is well within the maximum permissible, as presently set by the California State Vehicle Testing Standards, and is even below the 100 mark which is the proposed standard for the future. The coated TEST
engine also registers a great improvement in air-fuel ratio, as indicated in FIG. 4, and a much leaner mixture can be used in the coated TEST engine, resulting in higher fuel economy, lower specific fuel consumption, and a hotter burning mixture. It
should also be noted that the coated TEST engine results in a somewhat higher exhaust temperature than does the STANDARD untreated engine, and this is believed to be one of the reasons for the reduction in the unburned hydrocarbons in the exhaust gases.
In accordance with the present invention, the base layer 28 of the coating 26 is applied to the wall surfaces of the combustion chamber 24 by flame spraying a mixture of powdered aluminum and nickel. The percentages of the components in the
mixture may vary between about 5 percent aluminum and 95 percent nickel to about 20 percent aluminum and 80 percent nickel. One source of material suitable for use is produced by the METCO CORPORATION, and this company markets a suitable powdered
mixture which is sold under the trademarks "Nickel-Aluminae" and "METCO -450." A conventional flame spraying apparatus may be used for applying the aluminum-nickel mixture onto the combustion chamber wall surfaces, and after application of the base layer
28, an outer layer 30 of copper is applied by flame spraying powdered copper in a hydrogen-rich flame until the desired thickness is obtained.
It has been found that a base layer 28 of nickel aluminum mixture, flame sprayed onto the base metal of the engine to a thickness within the range of 3 to 20 mils, provides an excellent heat insulating barrier for resisting heat flow by
conduction. An outer layer 30 applied onto the base layer 28 with a thickness in the range of 4 to 6 mils provides excellent infrared heat reflectivity and bonds well to the base layer. When the base layer 28 and outer layer 30 are applied by flame
spraying, as described herein, the resulting coating 26 has a porosity of about 3 to 5 percent by volume and it is believed that this permits higher combustion chamber surface temperatures (up to about 1475.degree.) to be accommodated without physical
failure, such as cracking, melting, or spalling of the coating from the base metal.
It is believed that the coating 26 applied in a flame spraying operation as described provides the necessary porosity in the coating, so that high temperatures and pressures and uneven heating do not cause excessive internal stresses to develop
in the coating material, and consequently the coating has a long and useful life. It is believed that the copper and cuprous oxides forming the outer layer 30 of the coating 26 should be about 5 mils in thickness, and a layer of this thickness is able
to withstand temperature of approximately 1600.degree. without melting away, excessive corrosion, or wear. The base layer 28 beneath the outer layer 30 is thick enough to provide just enough insulation so that the outer surface of the outer layer is
maintained at temperatures below but within a 100.degree. F. of the melting temperature of the material. It is believed that a nickel-aluminum base layer 28 can be applied up to a maximum thickness of approximately 20 mils and in various lesser
thicknesses so that an outer layer 30 of copper of approximately 6 mils thickness does not reach a temperature above its melting point. However, it is believed that for best advantage the outer layer 30 of copper and cuprous oxides may vary in thickness
from approximately 4 to 6 mils; for example, in FIG. 2, the area T.sub.1 might be 4 mils in thickness and in the ares T.sub.2 it may be about 5 or 5 1/2 mils in the region of higher temperature.
FIG. 5 is a bar graph representing comparative test results performed on the same engine with several different types and thicknesses of coating 26 on the wall surfaces. When a STANDARD engine with no combustion chamber surface coating was
tested, a fuel consumption in pounds per hour of approximately 9.2 was obtained, and the exhaust gases contained about 800 parts per million of unburned hydrocarbons when run at a medium load and constant power setting. It is significant that at the
same load and power setting, the same engine, having different types and thicknesses of coatings, as designated in the graph, performed better than the uncoated or STANDARD engine. With an insulating base layer 28 of nickel and aluminum 3 mils thick and
an outer layer 30 of copper oxide 4 1/2 mils thick, a fuel consumption of 8.2 pounds per hour was obtained, and the amount of unburned hydrocarbons in the exhaust was reduced to 480 parts per million. It is believed that the heat insulating
characteristics and heat reflectivity of the various different types and thicknesses of coatings tested are responsible for the large reduction in the amount of unburned hydrocarbon in the exhaust gases, generally because of the higher temperatures in
the gases attained in the combustion chamber 24. As the base or insulating layer 28 is increased to about 9 mils in thickness, and with the same thickness and type of outer layer 30, the fuel consumption in pounds per hour is further reduced to about
7.0, and the unburned carbon in the exhaust is reduced significantly down to about 300 parts per million. When the engine was provided with a base layer 28 of nickel and aluminum 10 mils in thickness and a 5 mil outer layer 30 of aluminum oxide rather
than copper or cuprous oxides, a slight increase in the fuel consumption is observed and a slight increase in the amount of unburned hydrocarbons in the exhaust gases of approximately 460 parts per million is observed. This result is believed to be due
to the fact that an outer coating 30 of aluminum is not as heat reflective as a copper/cuprous oxide coating of the same thickness. With a base layer 28 of aluminum and nickel 20 mils in thickness and an outer layer 30 formed of copper oxide 5 mils in
thickness, it should be noted that the fuel consumption is reduced to 6.5 pounds per hour and the amount of unburned hydrocarbons in the exhaust gas is reduced to 60 parts per million, which is well within the proposed future standards of the State of
California.
From the foregoing, it should be noted that the thickness of the insulating or base layer 28 appreciably affects the fuel consumption and the amount of unburned hydrocarbons in the exhaust gases. Also, it should be mentioned that the copper
oxide used for the outer layer 30 approximately 4 to 6 mils in thickness appears to be slightly more effective than a coating of aluminum oxide of approximately the same thickness.
A base layer 28 comprising a mixture of aluminum and nickel and applied as described by flame spraying in an acetylene-rich flame has been found to provide good mechanical strength and wear resistance. Mixtures ranging from 5 percent to 20
percent aluminum and from 95 percent to 80 percent nickel have been used, and slightly better characteristics are obtained when the mixture has a higher percentage of nickel.
Tests indicate that an outer coating comprising 100 percent copper/cuprous oxides approximately 4 to 6 mils in thickness is extremely effective when applied onto a base layer 28 comprising a mixture of nickel and aluminum (from 5 to 20 percent
aluminum and from 95 to 80 percent nickel) between 3 and 20 mils in thickness. The hotter spots on the walls of the combustion chamber 24 are preferably coated with a thicker insulating layer 28, as indicated in FIG. 2; for example, the region T.sub.2
and the outer layer 30 may vary between 4 and 6 mils in thickness between the areas T.sub.1 and T.sub.2. It is believed that a thicker base layer 28 provides a better barrier against conductive heat flow and that a base layer up to 20 mils in thickness
comprising a mixture of nickel and aluminum can be used effectively when applied in a flame spraying operation, as mentioned hereinbefore.
The aforementioned system of coating the wall surfaces provides a combustion chamber with fewer hot spots and evens out the temperature gradient along the wall surfaces which tends to reduce internal stresses in the engine structure and coating
material. When a nickel and aluminum base layer 28, applied by flame spraying in an acetylene-rich flame, and an outer coating 30 of copper/cuprous oxides, applied by flame spraying in a hydrogen-rich flame are used, the resultant coating improves
engine performance and reduces air pollution caused by unburned hydrocarbons in the exhaust gases of the engine.
From the foregoing, it will be seen that the present invention provides a means of improving fuel economy, reducing unburned hydrocarbons in the exhaust gases, and increasing the horsepower available from a given size engine. It is believed that
the coating 26 applied to the wall surfaces of the combustion chamber 24 of an engine works in a twofold manner, the outer layer 30 being effective to reflect a majority of the infrared heat developed in the combustion process back into the gases, and
the base layer 28 serving as an insulation barrier which reduces heat losses through the combustion chamber wall surfaces by conduction heat transfer. The coating 26, in accordance with the invention, is mechanically strong and wear resistant, and can
be economically applied to combustion chamber wall surfaces of internal combustion engines and combustion chambers generally.
* * * * *
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