FR2688031A1 - Self-igniting engines, which remain hot when stationary, and with a modest compression ratio - Google Patents

Abstract

The invention relates to self-igniting engines kept hot when stationary, by virtue of a jacket or cover made from quality thermal insulation materials and a minimum of heat bridges. Vigorous heating of the fuel before injection (generally direct injection) allows much better combustion than in current diesels. What is more, this heating of the fuel participates, to a very large extent, in the cooling of the cylinder block and of the cylinder head, whence a significant simplification in both systems. The injection of this hot fuel is obtained by pressurizing the fuel before it is heated, and the quantity of fuel injected under pressure varies depending on the lift and opening time of needles or small valves, the opening of which is controlled by any means whatsoever which may be computer-aided. Starting is obtained with the aid of heating of the intake air. The pistons are made of cast iron (or steel) in order to shorten the starting phase requiring heating of the intake air.

Description

 The present invention relates to self-ignition engines, with direct injection of fuel into the combustion chamber, more particularly.

 In the self-ignition engines currently in use, it is the heating, resulting from a strong compression of the fresh air admitted, which is responsible for igniting the fuel (diesel fuel generally) when it is injected, when the piston reaches top dead center, at the end of the compression time. For truck or automobile engines with direct injection, the compression compression ratios, for non-supercharged engines, are not less than 15 (and more often higher), their injection pumps are necessarily very high compression , and despite this, these engines generally emit slightly more unburned particles in the exhaust gases than turbulent turbocharged "combustion engine" diesels. The volumetric compression rates of the latter are around 21 to allow cold starts, despite the use of glow plugs.

 In order to simplify the fuel injection system, as well as the shape of the cylinder head, while having good combustion, manufacturers have formerly produced engines, known as semi-diesels, in which part of the cylinder head does not was not cooled by circulation of water, and which, therefore, was brought to a temperature of up to 700OC to 800OC during operation. The jet of diesel produced by the injector (and a low pressure pump) was directed towards the uncooled part of the cylinder head, to be vaporized and ignited there very quickly. The compression compression ratio of these "semi-diesel" engines was significantly lowered to take account of the embrittlement of the cylinder head brought to high temperature. These semi-diesel engines were, in most cases, two-stroke engines with pistons and crankshafts relatively light.

In 1974, an American imagined a self-ignition engine (patent
US 3,945,352) into which the fuel (not necessarily diesel) was injected in the form of superheated steam and at high pressure at a temperature much higher than the flammability temperature of the fuel considered (flash point or flash point , or flash point, in English), which allows, in theory, to obtain an excellent self-ignition (even if, theoretically, an engine was built whose compression ratio was close to 1) with, in addition, l advantage of an increased combustion temperature for the same quantity of fuel, because, to the chemical energy of the liquid fuel considered, it is necessary to add the quantity of heat corresponding to the product of the mass injected, multiplied by the mass heat of the fuel , then by the difference in temperature added, the quantity of heat to which the latent heat of vaporization of the fuel in question must still be added. This superheated steam was obtained thanks to an external mini-boiler, combined with a temperature exchanger: exhaust gas / fuel, integrated. The boiler was responsible for vaporizing and overheating (under high pressure) the fuel, as was done in the past in steam engines. This new type of engine has a classic spark ignition system and an external carburetor for cold starts, because the rise in high temperature and high pressure of the external mini-boiler requires a long time .

Perhaps the problems linked to the injection of superheated steam at very high pressure with variable and precise flow rates have hindered the development of this new type of engine?
I myself deposited a patent in December 1981, registered under the number 2 517 741, in which one of the claims related to a device of thermal insulation of very good quality of the whole of the engine block, whose purpose was to allow restarts with the engine block at a temperature very close to its operating temperature when cruising, and this several tens of hours (even several days) after the last stop, even in winter. "restarts", such an engine, transformed into a real heat accumulator, can be used to supply a considerable quantity of calories which can be used to heat the passenger compartment of a vehicle from the start assured. Another goal sought, by keeping the engine warm, not indefinitely, but for long periods (which statistically makes cold engine restarts quite rare) is to obtain self-ignition which is still acceptable with an engine equipped with a Compression rate lower than on conventional direct injection diesels, in order to reduce mechanical and thermal stresses on pistons and crankshaft, which allows them to be designed lighter. This allows a direct weight gain on pistons , but also allows increased rotation speeds, therefore the production of brighter motors (increased power-to-mass ratio).

 The devices presented below, objects of the invention, are intended, mainly, to improve the cold start (and in very cold weather) of diesel engines, to improve the combustion of fuel in engines of this type (injection direct in particular), because the latter generally tend to emit more fine unburned carbon particles than the indirect injection engines with turbulent chamber, auxiliary. To counter this trend, direct injection engines require the use of very high pressure injection pumps, which spray diesel better, but which have a high price.

 These devices, according to the invention, can be used to simply improve conventional self-ignition engines (indirect or direct 4-stroke or 2-stroke injection), or be used to create a truly new category of engines with self-ignition, brighter than their predecessors, in the areas of power, relative to their mass, energy efficiency, reduction of the emission of unburnt particles in exhaust gases with, in addition, the particularity to store large amounts of heat for very long periods following their shutdown, lowering the compression compression rate to values as low as 10, with an optimum depending on the desired use, which may be in a range of lo to 15 (15 is a compression ratio value close to that of current direct injection engines). In the case of supercharged engines, the compression ratio volumetric ique (in the alternative part) can be further lowered slightly.

 The first device that is the subject of the invention consists of a significant improvement in the thermal insulation system of the engine block (subject of my patent no. 2517 741, device in which the entire engine block is contained in a high-quality isothermal enclosure This improvement consists in using thermal insulators resistant to high temperatures, in order to be placed close to the exhaust manifold, so as to protect in this zone the high quality thermal insulation materials of the enclosure. high-quality thermal insulation could, on the one hand, consist of multi-layer thermal super-insulators, derived from those used by the space industry. In addition, to increase the mass of materials, kept warm, contained in the insulating enclosure (the cooling time constant of the isolated engine block is almost directly proportional to the mass of materials contained inside the enclosure), we will include the gearbox, equipped with a specific cooling system (connected to an external radiator), if necessary, the clutch, the injection pump, the filter fuel, alternator, starter.

 The second device which is the subject of the invention is a system which, in particular, combines the cylinder head cooling system and a fuel heating system, just before the fuel is injected.  In this system, the fuel therefore plays the role of water in a conventional cooling system.  It is the "cold" fuel coming from the tank to replace (in the cooling cavities of the cylinder head) the consumed fuel, which absorbs the heat.  Such a combination benefits both the cooling system (which it simplifies), and the efficiency of the engine, by recovering calories which would otherwise be lost.  This fuel heating system will preferably be pressurized so that no fraction of the various hydrocarbons constituting the fuel is brought to the boil. In order to ensure sufficient cooling of the cylinder head in all circumstances, the flow of fuel circulating inside the cylinder head will be increased when necessary, thanks to an auxiliary circuit which leaves the cylinder head and returns to it, passing through a cooler (heat exchanger) outside the enclosure.  This annex circuit is, of course, also pressurized and fitted with a pump to circulate the fuel inside. The main objective of this system is not to find extremely high temperatures (ie above 200OC or 473 "K).  What is sought after in priority is an improvement in self-ignition and combustion, which would allow, for example, the production of an engine having a compression compression rate of only 12 and a rotational speed close to 5000 rpm.  for an automobile engine with conventional medium pressure injection pumps (or only slightly modified).  The thermal energy thus added to the potential chemical energy of the fuel brings about an improvement in efficiency, but the improvement in the quality of combustion is greater. We can progress in obtaining a high injection temperature if this does not create too expensive technological problems to solve for the medium pressure injection pump, by making a double walled exhaust manifold, between which will circulate the fuel already warmed in the cells contained in the cylinder head.  The double walled collector system can be replaced for more solidity by a pipe (in the thickness of the wall of the exhaust manifold) in the form of a spiral with the turns more or less contiguous (the internal shape of the wall of the collector could thus be completely smooth as in a conventional collector).

The injection of the heated fuel may be carried out by an injection pump of a type and technology similar to those of current conventional injection pumps, but there is another solution for injecting the heated fuel, which could be better in terms of production cost and reliability. This solution consists in having, upstream of the fuel heating system, a very high pressure pump driven by the engine itself (proportional rotation speeds) with a flow rate intended to be slightly greater than what is necessary to obtain the maximum power. . A pressure regulator will permanently adjust the flow rate to the strictly necessary value. The injectors are, in this system, replaced by valves similar to the valves called "needles" in the old diesel engines with compressed air injection. The variations of power and torque will be obtained by controlling the lifting height of "the needle "and its opening time using a microprocessor.

 In the versions of self-ignition engines, where the application of the new systems described above will have been used to produce an engine with a moderate compression ratio (12, as in the example of application proposed above ), it will be necessary, despite the very high thermal insulation of the engine block (block associated with the gearbox, preferably), and despite the fuel brought to much more than 1000C in the heating system (during a previous operating period), to provide a preheating system for starts after long periods of stoppage. It is necessary to consider separately the law of cooling of the engine block as a whole, and the law of cooling of the fuel heating system described above. Indeed, just after stopping the engine, this system is much more high temperature than the block, but this high temperature affects a low mass of materials which, moreover, is not thermally isolated from the rest of the engine block.

 Preheating can be carried out simply by conventional glow plugs in the combustion chambers, but I suggest using a powerful electrical resistance placed in the air intake manifold (as close as possible to the intake valves) . Such a system will certainly require more electrical energy to ensure start-up than with conventional spark plugs, but it makes it possible to produce a cylinder head of simpler and more solid form, the resistance (s) not being subjected to the shock. thermal from internal combustion, this equipment will have a longer life.

 Finally, a strong heating of the air, before and during the starting phase, will certainly require equipping vehicles with a larger electrical installation, but the engine efficiency will be better during the first minutes of operation, and especially the greatly reduced pollution. In addition, the energy required to heat the intake resistor can be supplied at 220 V outside when possible, and on vehicles with mixed propulsion: internal combustion engine, electric propulsion, plus buffer battery, the fraction of energy reserved for starting compared to the stored electrical energy will become negligible.

In addition to the systems described above, I propose to make the pistons, variants of engines with moderate compression ratio, entirely in cast iron. In fact, with a compression ratio of only 12, as already taken as an example above, the mechanical and thermal stresses will be closer to those of a petrol engine than to that of a conventional diesel. However, it is necessary to take into account the worst diffusion of the temperature from the upper part of the piston to the whole mass of the latter, in calculating its resistance. The use of cast iron for the manufacture of pistons will present as an advantage of keeping more calories inside the combustion chamber, of reducing their expansion, of being more robust, of allowing better lubrication, of staying hot longer after the engine has stopped, of heating up quickly on the surface during start-ups. For supercharged engines, operating at high torque and low rotational speed (relative to their "atmospheric" version),
The disadvantage of a cast iron piston, with a mass slightly greater than that of its aluminum alloy equivalent, is even less appreciable than for "atmospheric" engines.

 The use of cast iron or steel to produce cylinder head, cylinder liner, engine block (used today on certain diesel engines of road vehicles) would be particularly advantageous in the case of variants of engines with moderate compression ratio, with preheating. external (starting air), at medium injection pressure, and with the fuel not yet correctly preheated. In the "2-stroke" variants of the engines according to the invention, the cylinder head and the cast iron cylinder block could be in one piece, which would further add to the simplicity of construction, and to the rapid reduction of fine unburnt carbon particles during the rare Cold starts. For variants, the injection of preheated fuel is ensured by the high pressure prevailing inside the heat exchanger system (cylinder head and tube winding the exhaust manifold), it is, of course, necessary that 'there is upstream a high pressure fuel pump drawing cold fuel from the tank; this pump must be in action before an engine is restarted if the pressure inside the "hot" fuel circuit has dropped below a preset threshold.

 To improve the rare cold starts of an engine according to the invention, provided with a thermally insulating jacket, and also to limit the fuel reheating temperature, for better lubrication, and better sealing of the injectors, it would be possible -be advantageous to use a diesel (or other fuel) having a cetane number higher than current products. Vegetable oils with a high natural viscosity should be particularly suitable for use on engines of this type.

 The experience acquired in the production and use of the engines according to the invention may show that it would be possible to heat the fuel less before injecting it while retaining very good self-ignitions and combustion, despite a low compression ratio. Also, I propose a variant of the fuel heating system integrated into the cooling system, which consists in associating the cylinder head (and / or complete engine block) with the manifold, so that they form only one and same part, by casting the metal constituting them in a single operation. A short section (a few centimeters to a few tens of centimeters) of the exhaust gas evacuation tube, in the shape adapted to the particular configuration of the engine compartment and of the vehicle that the engine fitted, can be associated with the cylinder head (and / or the engine block) and the exhaust manifold, in one piece.

 Furthermore, the walls of the "exhaust" pipes integrated into the block described above will be very thick, with cooling cells formed inside, communicating with the cooling cells of the cylinder head, and / or all of the engine block. These common cooling cells will, of course, be filled with fuel intended to be injected, heated, in the combustion chamber.

 By thus building the engine, there is the possibility of recovering sufficient calories for heating the fuel, while avoiding a delicate seal between the fuel heating circuits "engine" and fuel heating "exhaust manifold". This translates into a gain in simplicity of construction and reliability.

 Additional advantages can be considered, such as the increase in the hot mass of the engine block contained in the isothermal enclosure with, as a consequence, the increase in the cooling time constant after shutdown. Cooling the exhaust gases will slightly reduce the noise emitted.

 The devices described above are applicable both simultaneously to constitute a new and very efficient type of motor, or individually to improve already existing motors. However, their application on a two-stroke engine would be clearly preferable, since it is desirable to have an engine of great mechanical simplicity (and compact) inside a thermally insulating enclosure such as that already described.

 It is also desirable to have an engine which rises in temperature as quickly as possible (the two times have a combustion per revolution) to heat the fuel intended to be injected. The heating time of the air admitted during the start-up phase (engine completely cold) will therefore be shorter.

 NOTE 1 - It is useful to remember that a two-stroke direct injection engine eliminates the major drawback of the two-stroke carburetor, which is to let part of the fuel escape through the exhaust lights before it has even been used. .

NOTE 2 - The use of cast iron to make the piston, and the
cylinder head and cylinders, allows rapid reheating of the internal face of
walls of the combustion chamber.

Claims (7)

 1) Internal combustion engines, with self-ignition, supercharged or not, with fuel preheating, kept warm as long as possible after they are stopped thanks to a thermally insulating envelope, which almost entirely surrounds them, at moderate compression ratio ( 12 to 15 approximately), characterized in that, in order to obtain the greatest possible cooling time constant of the engine block (at a standstill), the maximum of mechanical elements generally associated with vehicle engines, such as clutch, alternator, starter, gearbox, injection pump, filter, exhaust manifold and even part of the exhaust pipe. For these last two elements, insulation thermal capable of withstanding high temperatures, placed directly around it, will protect the high quality insulating jacket placed on top. The gearbox will itself, if necessary, have its own thermal control system (by circulation of heat transfer fluid).  2) Internal combustion engines according to claim 1, characterized in that the preheating of the fuel results both from thermal insulation, but especially from its passage in cells or pipes, formed in the cylinder head or in the cylinder head engine block assembly (instead of water in a conventional cooling system). The engine cooling and fuel preheating systems thus constitute a single system. Heating the fuel can be completed by running the fuel through a spiral line wound around the exhaust pipe for the burnt gases (or the exhaust manifold); this pipe will be formed in the wall of the exhaust tube.  3) Internal combustion engines, according to claims 1 and 2, characterized in that the exhaust gas collector is associated with the cylinder head and / or the complete cylinder block to form a single piece, the walls of or the exhaust manifold tubes are thick enough to provide cells and pipes (to circulate the fuel to be heated) and for better heat distribution between the different parts of the engine. A part of the gas exhaust tube, of a shape adapted to the arrangement of the engine and of the rest of the vehicle, may be associated with the cylinder head manifold block described above so as to form only one piece.  4) Internal combustion engines according to claim 1, characterized in that the injection of the preheated fuel will be carried out by a pump mounted upstream of the fuel preheating system (therefore acting with fuel at room temperature) and by valve injectors (or needles) controlled by any means, but itself controlled, to vary the power and the torque of the engine, with the help of a computer.  5) Internal combustion engines, according to claim 1, characterized in that there is no conventional glow plug in the combustion chamber, but a system for reheating the admitted air, by an electrical resistance ( of suitable power) in the intake manifold, the operation of this electrical resistance must be triggered before running the engine and be extended during the start-up phase (especially for the rare engine starts completely cold).  6) Internal combustion engines, according to claim 1 and characterized in that the pistons are made of cast iron (in one piece) to accelerate the heating of the internal face of the pistons and therefore shorten the operating time of the pre plugs heating, or electric heating of the admitted air.  7) Internal combustion engines according to claim 1, characterized in that the thermal insulation surrounding the engines is carried out with multilayer materials, derived from thermal insulation materials used in the space industry.