FR2500002A1 - - Google Patents

Abstract

THE INVENTION CONCERNS A SYNTACTIC FOAM AND ITS APPLICATION AS A COATING ON CERTAIN SURFACES OF AN INTERNAL COMBUSTION ENGINE. THIS RESINOUS FOAM HAS A THERMAL CONDUCTANCE AND A THERMAL PENETRATION WHICH ALLOWS THE TEMPERATURE OF THE SURFACES OF AN ENGINE COATED WITH THIS FOAM TO EXCEED, DURING THE COMBUSTION PROCESS, THE TEMPERATURE OF THE FORMATION OF THESE DEPOTASIN, WITHOUT EXCEEDING CHANGE WITHOUT CHANGE. TO SIGNIFICANTLY RAISE THE TEMPERATURE OF THE AIR AND FUEL INTAKE CHARGE DURING THE INTAKE AND COMPRESSION TIMES OF THE ENGINE CYCLE. FIELD OF APPLICATION: INTERNAL COMBUSTION ENGINES.

Description

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  The invention relates to internal combustion engines

  dull, both spark-ignition internal combustion engines and internal combustion ignition engines

  by compression such as engines of the Diesel type.

  The invention also relates to the application of a

  coating on the internal surfaces of combustion engines

  tion, and in particular the application of a protective coating

  on the non-swept surface of a combustor combustion chamber, on the intake valves, on the surface of the intake manifold exposed to the mixture

  air and fuel, and on the surface of the exhaust manifold.

  exposed to exhaust fumes.

  It is known that the thermal efficiency of the combustion engine

  internal bustion can be improved by the application, on

  the aforementioned surfaces of the combustion chambers, a

  thermal insulation garment for reducing heat loss to the coolant during compression and working time (at least 30-40% of the total heat produced in an internal combustion engine is lost in the coolant ). Licences

  United States of America N04 074 671 and N03 820 523 describing

  the application, for this purpose, of a thin layer of ceramics

  on the surface of the combustion chamber. Licences

  United States of America Nos. 3,911,891 and 3,552,370 disclose

  wind the application of layers of certain materials in the

same purpose.

  U.S. Patent Nos. 3,066,663 and 3,019,277 disclose the coating of certain surfaces.

  combustion chambers with thick ceramic insulation

  and thermal conductivity, to prevent the formation of deposits causing incandescent ignition and the occurrence of muffled noise when a fuel or lubricant containing phosphorus is used

  in a high compression engine.

  Deposition of substances on combustion chamber surfaces appears to be increasing the octane requirement of new spark ignition engines when operating on non-leaded fuels due to the increased compression ratio. and recycled heat to the fuel and fresh air charge. The increase in the octane requirement, in this case, may correspond to six octane numbers

  or more. The octane requirement is the minimum amount of

  tane necessary to avoid any noticeable knock. By avoiding the increase of the octane requirement, it is possible to use higher compression ratios with better efficiency and / or the use of a fuel without

lead, containing less octane.

  A thermal insulation coating applied to the top surface of a piston also tends to reduce the heat load of the piston. This causes a decrease in the rate of formation of the deposit in the zone of the segments,

  which attenuates the exfoliation of the segments.

  The use of intake manifolds and

  Isolated intake weights decreases heating of the mixture

  of air and fuel from the intake

  spark-ignition devices, which reduces their octane requirement, and decreases the temperature rise of the intake air in compression-ignition engines, thereby improving their efficiency.

volumetric efficiency.

  Isolated exhaust manifolds increase the heat that can be used for overfilling

  spark-ignition and spark-ignition engines

  and raise the temperature of the exhaust gases to the level

  catalysts in spark ignition engines.

  An insulating, low heat capacity coating formed on the top surface of a piston and on the surfaces of a combustion chamber reduces the thickness of the non-brittle extinguishing layer close to these surfaces. improves volatilization during the combustion of all hydrocarbon liquids on the surfaces. These two

  processes promote the combustion of hydrocarbons and

  the emission of hydrocarbons5 the exhaust.

  It is possible to increase the efficiency of internal combustion engines in general, and to operate, in particular, spark ignition engines with unleaded fuel, containing less octane, without cognemnwt, if, in an engine internal combustion chamber

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  of combustion having a surface exposed to combustion} at least a part of this surface has, in combination,

  thermal conductance and thermal penetration allow

  the temperature of this surface, during the combustion process, to exceed the temperature at which

  deposits are formed, and said part of the surface stores insufficiently

  heat to substantially raise the temperature of the intake air-fuel charge during the times

  intake and compression of the engine.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which: FIG. 1 is a partial vertical section of a

  detail of an engine some parts of which are covered with

  according to the invention; and FIG. 2 is a partial and schematic cross-section, on an enlarged scale, of the coating according to the invention, this figure being made from a scanning electron micrograph, after cutting of the coating perpendicular to the surface and observation of said coating in a parallel direction

to said surface.

  The present invention can be applied to any internal combustion engine, and in particular to the combustion engine.

  common internal combustion, reciprocating pistons

  tive. FIG. 1 represents an embodiment of the invention in which a coating of material, having

  thermal penetration and thermal conductance require

  Dees, is applied to the surfaces of a conventional combustion chamber 1 and intake manifold 2 of a four-stroke engine. The piston 3 and the intake valve 4 are shown in approximate relative positions that they occupy at the beginning of the intake time and the piston downstroke. The mixture of fuel and air (not shown) arrives through the intake manifold 2, passes through the open intake valve 4 and enters the combustion chamber 1 where it is finally ignited by the spark plug 5 ignition. According to the invention, at least a portion of one or more of the surfaces of the combustion chamber, the intake valve and the exhaust and intake manifolds are coated with a material having the indicated thermal parameters. for example, a heat-stable closed cell structure resin foam of about 0.02 to 1 mm thick, this thick

  it is preferably between 0.04 and 0.2 mm.

  In the embodiment shown in Figure 1, at least a portion of the unswept surface of the combustion chamber 6-8 is coated, particularly

  not scanned from the cylinder head 6, the face of the valve 7 of ad-

  the upper surface 8 of the piston (ie the part exposed to combustion), and at least a portion of the surface of the intake manifold 9-10 is also

  particularly the chamber 9 of the intake manifold

  the tulip-shaped part of the valve 10 of

  mission which, for convenience, is considered

  forming part of the surface of the intake manifold.

  FIG. 2 diagrammatically shows in section and on an enlarged scale a particular embodiment of the coated surface according to the invention. FIG. 2 is taken from a real electron micrograph using a scanning electron microscope and covering a resinous foam covering with closed cellular structure, according to the invention, presenting the thermal parameters required. The coating is cut perpendicular to the surface and is observed parallel to this surface. As shown in Figure 2,

  hollow microspheres 11 form, in a resinous matrix,

  12, a coating 13 of closed-cell foam applied to the surface 14. The dimension indicated at 15 corresponds to

  100 Nm. The microspheres 11 contain a gas (not shown in FIG.

té) which can be air.

  The closed cell material according to the invention is a particular material because of its low heat capacity. This material may be used as an integral part of the combustion chamber surface, in which case it is produced during the construction of the engine, or it may be applied in the form of a coating recessing the surface of finished parts of the chamber combustion, as shown in Figure 1; Closed cell materials according to the invention,

  thermal conductivity and heat capacity

  Specifically, they can be defined by mathematical models of oscillating thermal systems such as the surface of a combustion chamber of internal combustion engines. The criteria required for materials suitable for the implementation of the invention are expressed in the form

  thermal penetration and thermal conductance.

  An internal combustion engine having a low thermal penetration and high thermal conductance coating recycles less heat to the fuel and fresh air charge than an engine with conventional deposits formed from unleaded gasoline or leaded gasoline,

  and, therefore, it has a lower octane requirement

  than a chamber with these conventional deposits.

  During at least a portion of the combustion process, the temperature of the combustion chamber surface becomes high enough to prevent the formation of conventional deposits. Computer models suggest that thin coatings or a surface area with volumes

  high voids, with closed cells, on combustion chambers.

  allow a heat recycle almost as low as that achieved with a metal combustion chamber

  while achieving a sufficient surface temperature

  during combustion, to prevent the formation of

  classic pots. We observe, on computer models,

  a reduction in the heat recycled as a result of a reduction in

  thermal penetration and an increase in

  thermal conduction. A reduction in the thermal penetration

  and a simultaneous increase in thermal conduction

  that are more beneficial than any modifications made separately to one or the other of these properties. The effect

  beneficial thermal penetration has no limit

  férieure. The upper limit to the utility of conductance

  thermal equation corresponds to the points at which the surface does not

  more heat, during combustion, to prevent

  expensive accumulation of deposits, which eliminates the benefit,

  presented by the coating, the limitation of the

  the octane requirement. This upper limit is even lower than the thermal penetration values are higher. The thermal penetration is defined as gKQC, where K is the thermal conductivity, Q-is the density and C is the heat capacity. Thermal conductance is defined as K / d, where d is the thickness. The subjects to

  closed cell structure according to the invention have a penetration

  thermal energy, indicated in units of the international system,

  less than about 600 J / m2oKs1 / 2 and a thermal conductance

  at least about 2000 J / m2 0Ks. The product of thermal penetration by thermal conductance of suitable materials is less than about 3x10 J2 / m4oK2s3 / 2. Of

  Moreover, the heat retention of the surface must be insuf-

  to raise the temperature of the fuel load

  and intake air of more than about 330C above the ac-

  temperature increase of the clean engine. Preferred coatings, such as closed-cell polyimide resin foam, containing carbon black and microspheres, have a thermal penetration of about 380 J / m2 Ks1 / 2 and

  a thermal conductance of 3000 J / m20Ks.

  The material may be any mineral or organic material

  solid, modified or unmodified, having an internal void volume sufficient to-satisfy the parameters indicated. The

  Suitable organic materials include poly-

  imide at high temperature and resinous foams contain

  mantle microspheres. Suitable inorganic or inorganic materials include materials such as oxides, nitrides and carbides of Si, Ti, Cr, Ta, Nb, Zn and others modified by the introduction of a sufficient void volume, that is, -describing microspheres, foaming agents or gases, etc., in order to meet the parameters indicated for the

  thermal conductance and thermal penetration. Professionals-

  Thermal properties of a foam with a given non-void volume (NV) can be evaluated from the following relationships:

K, K * NV / (2 - NV)

ç = * NV

C = Cs s

  o the index s denotes the thermal property of the solid.

  A desired tanner for NV can be quickly determined by substituting the expressions of K, and C for the foam in the formula for thermal penetration and adjusting the NV value until the desired thermal penetration value is reached. . The thickness d of the coating can be adjusted so that the thermal conductance is placed between the desired limits. For example, for silicon nitride, K is 18 W / m², g is 3240 kg / m3 and C is 1060 J / kg K. Silicon nitride foam

  having a non empty volume NV of 0.08 has an estimated value of

  k-value of 0.75 W / mOK and an estimated thermal penetration of 454 J / m 2 Ks 1/2. A 0.2 mm thick coating of this foam has a thermal conductance of 3750

W / M20K.

  Modified inorganic composites can be

  formed by mixing organic or inorganic microspheres

  with the inorganic material and hot pressing or sintering the material to give a solid, or by

  any other method known to those skilled in the art.

  The function of the surface coating in the combustion chamber is to prevent heat loss,

  to prevent the permanent deposit of substances with

  higher than that of the coating, and

  burn the hydrocarbons in the choking zone adjacent to the free surface of the liner. Its function, in the intake manifold, including the shaped part

  tulip of the intake valve, is to prevent overheating

  excessively high fuel and air (ie

  overheating than that required for volatilization

  tion). In the combustion chamber, the precursors of the deposit are volatilized by the high temperature present at the free surface of the coating during the work cycle. High temperatures are obtained at the surface of the coating

  choosing a low heat capacity coating.

  The coating according to the invention is suitable for

  Spark ignition type and compression ignition type internal combustion engines, for example two-cycle or four-stroke engines, as well as rotary piston engines, commonly referred to as "Wankel" engines. The surfaces which can be coated in the internal combustion engine comprise at least a portion of the surface of the combustion chamber, namely the unswept surface which is in contact with the combustion gases and which comprises

  the upper surface of the piston (ie the outer part of the

  placed on combustion), the face of the valve and the cylinder head and / or the surface of the intake manifold, i.e.

  surface which is in contact with the load of

  air and air, between the carburettor and the

  and that includes the tulip-shaped portion of the intake valve. The coating is applied by all

  suitable method for forming a sensitive layer

  uniformly adhering to the surface, or to a suitably prepared surface, and this coating has a thickness of about 0.02 to 1 mm, preferably about 0.2 to 0.04 mm, and even more preferably, from about 0.03 to

  0.15 mm, in the case of surfaces exposed to combustion.

  The thermal properties of the coating are such that

  has a long life and low heat capacity

  that it is harmless to the engine, and that it is

  also feels good thermal stability.

  At least a portion of some of the surfaces

  is coated with organic or inorganic foam.

  It is preferable that a part of the combustion chamber and in particular the cylinder head, which is in contact with the combustion gases, be coated. The upper surface of the piston (i.e., the combustion face of the piston) is also a surface which is preferable to coat. The faces of the valves exposed to combustion can be coated, in particular the intake valve. The surface of the intake manifold that is in contact with the mixture of fuel and intake air, between the carburettor and the combustion chamber, can be coated with resinous foam, especially the parts of the surface of the collector. inlet reaching the highest temperature due to their proximity to the combustion chamber, and more particularly the tulip-shaped portion of the intake valve. The surfaces of the combustion chamber or intake manifold or

  two are covered, at least in part, in the manner

  written above, but for different reasons. While the combustion chamber is coated to operate the engine in a more adiabatic manner, i.e. to reduce heat loss to the coolant

  at the end of the compression time and during the

  and to reduce heat deposition and recycling, the intake manifold is coated to prevent overheating of the fuel and air load, ie any heating exceeding that required for

  the volatilization of the mixture, and to reduce also the

  accumulation of deposits around the tulip-shaped part

  of the intake valve. The coating of the collector

  more to the carburetor engine than to the

direct injection.

  In another embodiment of the invention, at least a portion of the surface of the exhaust port is coated with said organic or inorganic foam to isolate the exhaust gas, which tends to

  higher temperature the exhaust gas when

  be used by a turbocharger, or when they are subject to a catalytic limitation of

polluting substances.

  Closed cellular structure coating

  the invention, which is thermally stable, resists oxidation

  and at decomposition even at the high surface temperatures at which it is intermittently exposed in internal combustion engines (e.g., about 400 ° C and higher). This coating derives its properties from both

  materials of which it is constituted and of its mode of realization.

  The coating comprises a large number of vacuum embedded in

  a resinous matrix or in an inorganic material mentioned

  previously born. In particular, the voids constitute about 40% or more, by volume, of the coating. The latter is called precisely "foam" because of the large number of voids (in fact, gas-containing cells) it contains. The voids are substantially closed, i.e. the foam has a closed cell structure, so that the pressure in a given closed cell does not vary with the 10 engine pressure cycles. A relatively simple method of producing closed cell foam coating according to the invention is to drown a large number of spheres.

  preformed hollow sections, previously referred to and hereinafter

  spheres "in a resinous matrix, such foam being called" syntactic foam "(Modern Plastics Encyclopedia

1978-79, McGraw-Hill, page 145).

  The microspheres are mixed in the resin solution which is then matured to form a rigid matrix on the surface. Commercially available microspheres can be obtained from materials

  inorganic and organic substances and their mixtures.

  Suitable organic microspheres are selected from

  glass, ceramics and quartz and their mixtures.

  Suitable inorganic microspheres include phenol-formaldehyde plastic microspheres and the like. The inorganic microspheres have an average diameter of about 0.01 to 0.2 mm and are preferably present in amounts of about 40 to 80%, by volume, of the cured foam and preferably

  between about 50 and 65% by volume. These microspheres

  They preferably have an average diameter of about 0.01 to 0.1 mm and are preferably present in amounts of about 50 to 70% by volume of the cured foam. The plastic microspheres are classified according to their pressure tolerance, by applying to these spheres a pressure of about 2750 kPa in a liquid, this application of pressure being followed by a flotation of the desired fraction. Inorganic microspheres are used to increase, in addition to void volume, the resistance of the closed cell foam. Inorganic microspheres are present in amounts between

  about 40 and 70% by volume of the ripe foam. The micro-

  spheres are subjected to a pressure of about 12000 kPa

- before the waterline.

  The organic resinous matrix used in the context of the present invention comprises any resin that hardens to form a rigid matrix having the properties

  longevity and thermal stability indicated previously.

  Resinous composites containing resin, carbon and / or silica are preferred. Many of these resins are high temperature polymers containing

  aromatic rings ("Advances in Macromolecular Chemis-

  try, Vol. 2, Academic Press, New York, 1970, pp. 175-236, M.M.Koton), fluoropolymers or polymers of

  organic silicon compounds, for example poly-

  aromatic, and polyphenylene oxides, polyesters, polyamides, polyanhydrides and aromatic polyureas having melting points above 300 C

  are known. Preferably, the resin is a poly-

  imide or thermosetting or thermoplastic polyamide such as aromatic polymers which ripen to form

  poly (amide-imides) as described in US Pat.

  United States No. 3,190,856, for example polymers of trimellitic anhydride and aromatic diamines described in U.S. Patent Nos. 4,136,085 and 3,347,808. Polyimide resins are widely available (Modern Plastics Encyclopedia 1979-80, McGraw Hill, pp. 76-78). Thermosetting polyimides do not exhibit distinct softening points below their normal degradation temperature of up to 260 C or more. A thermoplastic polyimide has a melting point of about 310 ° -365 ° C. Polyimides are generally produced by the reaction of anhydrides or dianhydrides with di (primary) amines ("Polyimides a new Class of Thermally-stable Polymers"). Technomic Publ.Co., Stamford, Conn., 1970, NA Adrova et al.), For example the reaction of

O

C o oo C, or .O

0

O O

  ili -Ni2 avea H.a <- n, OR i ') Z t "F 1 lt, I> u lo-@--.t

O O

  o X and Y are selected from -C (CF3) 2, t -O- -C-, etc. In a preferred embodiment, the resinous matrix is a composite of polyimide and carbon black or graphite, preferably containing. also other fillers such as the powdery forms of boron, ZnO,

  Al and amorphous silica fume. It is advantageous to use

  a dense carbon black, having a low surface area / volume ratio. Such composites are more

  rigid, from the point of view of structure, and more refractory

  because they retain their shape and longevity, even

  above the softening point of the resin. A matrix

  this preferred composite resinous material comprises from about 30 to 85% by weight of polyimide resin, from 70 to 15% by weight of carbon black, and from 0 to 7% by weight of silica fumes. On the one

  even more preferable, when using micro-

  spheres of plastic material, the composite resinous matrix comprises from about 35 to 50% by weight of polyimide, from about 65 to 50% by weight of carbon black, and from 0 to 4% by weight of silica fumes. A preferred closed cell structure foam composition comprising inorganic microspheres comprises from about 60 to 80% by weight of resin

  polyimide and about 40 to 20% by weight of carbon black.

  The foam coating can be formed on the surface

  metal face (it being understood that plastic surfaces may be substituted, in some cases, for metal surfaces if the internal combustion engine is partly made of plastic parts) by mixing the polyamide with a solvent (ie i.e., 1-methyl-2-pyrrolidone) and, optionally, a diluent such as p-xylene, a filler such as carbon black, graphite and / or silica fumes and / or powdered boron, and microspheres. This liquid mixture is

  applied by coating or spraying on the surface

  pre, to the desired thickness. The surface can be heated

  before spraying. The diluent and the solvent are removed

  born with care of the coating to limit or prevent

  the appearance of solvent gradients in the coating.

  The latter is matured by heating about 80 ° C to about 370 ° C, during a maturing process of 8-24 hours. The maximum practical temperature of ripening can be limited by the nature of

  spheres because the phenolic microspheres are weakened at the highest temperature. The coating is generally applied to the surface at the desired thickness for continuous use in the engine. However, although it is not essential that the coating be ablative in the case where it is too thick, it can be reduced to a more advantageous thickness, between about 0.04 and

  0.2 mm, for surfaces exposed to combustion.

  The invention will be further described in the following examples, the details of which are in no way limiting.

within the scope of the invention.

Example 1

  The surface of a combustion chamber is coated with a "CFR" engine with side valves (single-cylinder internal combustion engine, 611 cc displacement and a compression ratio of 7.0: 1). a preparation obtained

  by mixing one part by volume of amide polymer

  imide of the "Amoco AI-10" type (a condensation polymer containing aromatic imide linkages and obtained from trimellitic anhydride and diamine), three parts by volume of N-methyl-2-pyrrolidone (NMP) and a portion of volume of "Cabot Sterling MT" carbon black having a mean degree of dispersion) in a high speed mixer until a homogeneous preparation is obtained; three dry volumes of phenolic resin microspheres of the type "Union Carbide BJO-0930" are added and shaken

  until an honmogenic preparation is obtained. The sur-

  The combustion face is painted with this mixture, which is then heated with a hot air gun until it hardens, then oven dried for 16 hours at 60 ° C. and matured at 200 ° C., 230 ° C. , 260 C, 290 C and 315 C, for two hours at each temperature. This finished coating, the engine was subjected to a 65-hour CFR test, with unleaded petrol (alkylate) at 1200 rpm, under an intake vacuum of 13.5 kPa, CO being 1.5 ppm and the ignition advance of 20 degrees,

  without deterioration appearing.

Example 2

  In this example, another combustion chamber

  CFR engine with side valves is equipped with a prepa-

  ration obtained by mixing 24 g of polyimide "Monsanto Skybond 700", which is a heat-reactive aromatic resin, giving by thermal maturation a cross-linked polyimide, 24 g of "Cities Service Columbian Raven MT" carbon black, 12 n-methyl-2-pyrrolidone, and p-xylene in a high speed mixer. 70 cm 3 of "Union Carbide BJO-0840" phenolic resin microspheres are added to 62 g of the above mixture, as well as 5 g of p-x-ylene diluent. The microspheres are prepared by applying a pressure of 2100 kPa in isooctane and then flotation removing the unmilled fraction. The diluted coating is applied by spraying onto a cylinder head preheated to 50 ° C by means of an air-spray nozzle and then allowed to air-dry for 16 hours.

  in order to remove most of the solvent, the coating

  The mixture is then oven-dried at 50 ° C., 75 ° C., 100 ° C. and C, for two hours at each temperature, and cured at 200 ° C., 220 ° C., 240 ° C. and 260 ° C., also at the rate of two hours. at each temperature. This coating completed, the engine is subjected to a test CFR of one hundred hours, under the conditions of Example 1, without it appears

traces of damage.

  Example 3 A "CFR" engine combustion chamber with side valves is coated with a mixture preparation

  25 g of an aromatic resin composition reacting to the

  their, of the "Monsanto Skybond 700" type, which can give, by thermal maturation, a crosslinked polyimide, 13 g of NMP, and 15 g of heat-treating carbon black beads of the "Cities Service Columbian Raven MT" type, up to to obtain a homogeneous substance in a high speed mixer. 2.6 g of "Union Carbide BJO 0930" microspheres, classified by removal of the floating fraction in a downflow ethanol column, at 41 g are added.

  mixture of polyimide and carbon black forming a

  trice. This coating is dried and matured as described in Example 2. A 65 hour CFR test of the engine, fueled with unleaded gasoline, is then carried out.

  using the test conditions of Example 1, practically

* unchanged. The engine having this coating exhibits an increase in the octane requirement of only 2.3 octane numbers with a spark advance of 300, while the same engine, without cylinder head liner, exhibits

  an increase in the octane requirement of 6.3 indices.

Example 4

  A combustion chamber of a "CFR" engine at

  side valves is spray-coated with a pre-

  paration obtained by mixing 24 g of material of the "Monsanto Skybond 700" type, 24 g of thermal carbon black N-907 of the "Cancarb" type, 24 g of a mixture of 26.5% of

  NMP and 73.5% p-xylene in a high speed mixer.

  70 cm 3 of "Union Carbide BJO0840" treated microspheres are added to 64 g of the above mixture, as well as 6 g of the above mixture of NMP-p-xylene. The microspheres are treated by heating them at 170 ° C. for two hours.

  under a depression of 85 kPa, with a slow nitrogen purge

  and then by subjecting them to a pressure of 2800 kPa, under isooctane, by flotation removal of the unmilled fraction and drying out the residual isooctane. The final mixture is sprayed with an air atomizer to a thickness of 0.127 mm in the cured state. The coating is air-dried for 16 hours, then oven dried and cured at 500C, 800C, 1200C, 1500C, 1800C, 2000C, 2200C and 2400C, two hours at each temperature. . The coating remains unchanged after hours of engine testing with unleaded fuel

  and under the conditions of the test of Example 1.

Example 5

  For this example, a "CFR" engine with side valves is machined so that its compression ratio is 9.5 before the coating is applied. The coating mixture is prepared in a ball mill into which 31 g of Monsanto Skybond 700 material, 23 g of "Monsanto Skybond 705" material, 21 g of N-methyl-2-pyrrolidone are introduced. , 1.2 g of amorphous boron powder,

  95% pure and having a particle size of 0.3-

  1.5 gm, this powder from the firm Atomergic Cheme-

  tals, and 10 g of stainless carbon black with degree of

  medium persion, from Cancarb Limited, under

  the reference "N 907". When the grinding is completed, add

  9.7 g of insoluble glass microspheres of the type "FTD 202"

  Emerson and Cumings. The microspheres are classi

  by application of a pressure of 14000 kPa, in water,

  and retention of the floating fraction. We preheat the culas-

  at 70 ° C before spraying. The sputtered yoke is cured in a programmed oven which is heated from 90 to 155 C in twelve minutes, from 155 to

   C in two hours, and 200 C to 370D C in thirteen hours.

  The engine whose cylinder head is thus coated is tested for hours with a fuel of the alkalate type and with an intake depression of 6.75 kPa. At the end of the test, the coating is practically intact, except in a small area where high velocity gas flows between the cylinder and the valves. In addition, microspheres

  occasional exposures show signs of

  heat treatment on their exposed side. The average thickness of the coating at the start of the test was 84.8 μm and that measured at the end of the test was 77.2 μm.

Example 6

  In this example, the same engine and the same test conditions as those of Example 5 are used. The matrix holding the microspheres is prepared by ball milling by mixing 21.3 g of material of the "Monsanto Skybond 705" type. , 31.2 g of "Monsanto Skybond 700" material, 10.9 g of "No.907" stainless steel carbon black produced by Cancarb Limited, and 21.3 g of N-methyl -2-pyrrolidone. 60 g of this matrix are mixed with 13.8 g of ceramic microspheres of the "FA-A" type from Emerson and Cumings, these microspheres having been sieved to remove microspheres larger than 0.08 mm. , then subjected to pressure, in the water,

  15,000 kPa to eliminate the weakest spheres.

  The coating is applied by spraying and matured

  ration as described in Example 5. The coating remains intact

  after 20 hours of testing with an alkalate type fuel, with some coating damage occurring between the valve area and the spark plug. In this test, the average thickness increases from 102 Dam at the beginning of the test to 89 gm at the end of the test. The coating used is subjected to a further 20 hour test with a deposit-forming mixture of unleaded gasoline to which 25% of a heavy component from cracking is added.

  fluid catalytic. The coating maintains the cylinder head practically

  free of deposits. Substantially half of the over-

  face retains a white appearance due to the presence of zinc in the lubricating oil. The totality of the remaining area

  of the breech, with the exception of a small area

  above the intake valve, has a tanned appearance

  due to light deposits (the microspheres are still clearly

  visible below this deposit). Normally, such fuel leaves black and thick deposits on the largest

part of the breech.

Example 7

  Two cylinder heads of a four cylinder, overhead cam and 2.3 liter displacement production engine are spray-coated with a preparation obtained by mixing 32.4 g of material of the "Monsanto Skybond 700" type, 17.5 g of material of the "Monsanto Skybond 705" type, 9.5 g of material of the "Cancarb No907" type, namely thermal carbon black produced by Cancarb Limited, and 22.2 g of N-methyl -2-pyrrolidone, NMP, in a ball mill. 8.2 g of glass microspheres of the "FTF 15" type from Emerson and Cumings, selected under pressure in water at 21,000, are then added to 70.4 g of this mixture.

  kPa. The cylinder head is preheated to 100 ° C. before spraying.

  The culms are then matured.

  using the cycle of Example 5. The engine is subjected to a 230 hour test including a mixed road / city cycle at an average speed of 46.5 km / h. At the end of this test, the two coated rolls have an average increase in the octane requirement of 3.4, whereas it is 4.6 for the uncoated rolls, which corresponds to a decrease

  of the increase in the octane requirement for the cy-

coated linders.

  Two samples of the coating of this example presented

  thermal conductivities of 0.171 and 0.118 J / m Ks, densities of 948 kg / m3 and heat capacities

  estimated at 1130 J / kg K. Thus, their values are

  of 428 and 356 J / m2 Ks1 / 2 The thicknesses of the samples

-6 -6

  lons are respectively 40x106 m and 50x10 6m, which gives K / d values of 4275 and 2360 J / m2 Ks. The product of the thermal penetration by the thermal conductance gives respectively 1.83x106 J2 / m4 K2s3 / 2 and 8 , 4x105 J2 / m40K2s3 / 2 By way of comparison, an unleaded fuel depot, taken from a combustion chamber, presents a

  thermal conductivity of 0.25 J / m Ks, a mass density

  1520 kg / m3 and a heat capacity of 1670,

  which gives a value of 797 J / m2 Ks 1/2 The thickness

  This deposit is 35x10 m (although deposits of more than 100xO10-6m are more common), so

  that its K / d value is 7143 J / m2 0Ks.

  It goes without saying that many modifications can be made to the motor described and represented without leaving

of the scope of the invention.

Claims (1)

CLAIM   Syntactic foam suitable for coating the surfaces of a combustion chamber (1) of an internal combustion engine, characterized in that it comprises a matrix (12) composed of approximately 30 to 60% by weight of polyimide resin, from about 70 to 40% by weight of carbon black, and from 0 to 7% by weight of silica fumes, these substances being blended at about 68% by volume, based on   on the hardened foam, microspheres (11) of   Phenol-formaldehyde type tick, having an average diameter from about 0.03 to 0.08 mm. e