EP0218505B1 - Energy production installation with several diesel engine cylinders supercharged by reciprocating-piston compressors - Google Patents

Abstract

A power production apparatus comprises a Diesel engine having a plurality of sequentially operating motor cylinders and a plurality of alternating air compressor cylinders. Each motor cylinder has scavenge ports connected to receive scavenging air from that compressor cylinder whose compression stroke occurs while the scavenge ports of the motor cylinder are closed. An intake capacity having a volume equal to about five times the cubic capacity of the motor cylinder is located on the air path. The apparatus may consist of a gas turbine and a multi-tandem free piston gas generator and a gas turbine; the gas generator then has a plurality of Diesel type motor cylinders whose pistons are drivably connected to compression pistons.

Description

The invention relates to energy production installations comprising at least one diesel engine with several cylinders operating sequentially, supercharged by several reciprocating compressors supplying the purge air to the engine.

Diesel engines are generally supercharged by a rotary compressor or an alternating compressor whose cylinders operate in an offset manner. In the second case, all the cylinders emerge in the same manifold. Consequently, the scanning of the engine cylinders is carried out at a substantially constant intake pressure. A thermodynamic study of the phenomena which occur during the sweeping shows that the compression work with transfer depends directly on the difference between the average inlet pressure of the sweeping air and the exhaust pressure. Consequently, the work during transfer is determined by the average pressure in the manifold, and not by the discharge pressure of a particular compressor cylinder. It should however be noted that this is only true in the case of an engine and a compressor having several cylinders. In the case of an installation having a single engine cylinder supplied by a single compressor cylinder (such as that described in the document FR-A-1 238 426), the situation is completely different since there is no manifold for mixture feeding several cylinders.

An installation is known according to the preamble of claim 1. The installation of this type described in FIG. 1 of GB-A-1 116 162 comprises several driving cylinders. Each engine cylinder has a row of intake and sweep lights, powered by a capacity that receives compressed air from two compressor cylinders, each located on one side of a compressor piston. Because of this arrangement, the intake capacity acts as a collector causing the engine cylinder to sweep at substantially constant intake pressure, with the drawbacks exposed above.

The invention aims in particular to provide an installation in which this work is significantly reduced. To this end, it proposes an installation according to the characterizing part of claim 1.

Thanks to this arrangement, the scanning is carried out at a gradually decreasing intake pressure, which reduces the work performed. The gain thus obtained can be further increased by providing the exhaust pipes of the engine cylinder with a constant section close to the lights, then a slowly increasing section, which makes it possible to cause a rapid drop in the pressure in the engine cylinder, first up to a value of the order of 1.5 Pe (Pe being the pressure prevailing in an exhaust capacity), then up to a value lower than the pressure prevailing in the exhaust capacity, from made of creating a depression wave. The vacuum in the cylinder may remain until the piston returns until the intake ports are closed.

The invention finds a particularly important application in installations comprising a gas generator with free pistons of the multi-tandem type, associated with a gas turbine. The generator comprises engine cylinders operating according to a Diesel cycle, belonging to two groups operating in phase opposition, and compressor cylinders also divided into two groups. It has already been proposed (EP-A-7874) to specialize compressors so that certain compressor cylinders provide a primary flow supplying the engines and others a secondary flow supplying a gas turbine at the same time as the exhaust gases of the engine cylinders. This solution has many advantages over those adopted previously when a large fraction of the air flow supplied by the compressors is used for sweeping the motors. However, this interest diminishes as a larger fraction of the flow is used to directly feed the gas turbine. It then becomes more advantageous to adopt the solution according to the invention defined above, which is all the easier as one can assign a compression chamber to each engine cylinder. In particular, it is possible to supply each engine cylinder, delimited by two engine pistons, from a single compressor compartment, chosen so that the delivery stroke coincides with the moment when the lights of the corresponding engine are closed.

The provisions defined above make it possible to significantly reduce the work of the exhaust gases. They can be implemented on a driving cylinder comprising conventional type scanning lights. It is known that, depending on whether the scanning lights are designed so as to provide a radial air jet or an air jet having a tangential component, the flow during the first phase of the scanning takes place according to a different regime . In the first case, the flow of fresh sweeping air is in the form of a central jet, surrounded by an annular wake of hot combustion gases. This solution has the advantage of ensuring efficient scanning. But there is no rotational movement of the fresh gases in the engine. On the contrary, when the lights are tilted, the fresh air is distributed in a stable annular sheet, in rotation, surrounding a core of hot gases: the rotational movement remains at the start of combustion and is favorable to the latter. On the other hand, the scanning no longer concerns the central part of the cylinder and it is not very effective.

The invention also aims to provide an installation whose scanning means allow obtain the favorable effects of the rotary movement while ensuring an interesting sweeping of the entire engine cylinder. To this end, the invention in particular proposes an installation in which each engine cylinder comprises scanning lights distributed regularly around the cylinder at one end of the latter and exhaust means, such as lights, also regularly distributed at the other end of the cylinder delimited by two pistons moving in opposite directions, said scanning lights being distributed in two successively uncovered rows, the lights of the row discovered first being arranged so as to provide a jet having a tangential component while the lights second discoveries are provided to provide a jet directed substantially towards the axis.

The two rows are supplied by the same intake capacity, but means are advantageously provided for delaying the arrival of purge air at the lights of the first row. This result can in particular be achieved by providing a winding path or a secondary capacity between a main intake capacity (which directly feeds the lights of the second set) and the lights of the first set.

Under these conditions, the first row of lights, providing a jet oriented for example at 30 ° with respect to the radial direction, establishes a flow of peripheral annular type animated with a high speed of rotation. The second row causes the appearance of a central jet without rotation ensuring efficient scanning. During the sweeping and the subsequent compression, there is a progressive entrainment of the central core of fresh gas by the rotating peripheral flow, which makes it possible finally to arrive at a mass of air in rotation in block at a higher speed. reduced than in previous engines, but retaining the desired favorable effect on combustion.

Furthermore, when two rows of scanning lights are provided, it is advantageous to have means delaying, and possibly slowing down, the arrival of fresh air by the lights of the first row, it is thus possible to give the air front cool which propagates along the cylinder towards the exhaust lights, a gait closer to a front perpendicular to the axis.

In a multitandem gas generator installation, each compressor cylinder, or at least each compression chamber, has so far been assigned to a determined flow. For example, in the document EP-A-7874 already cited, certain compressor cylinders provide a primary air flow intended for the engine, while others supply the secondary air flow intended for the turbine. However, under these conditions, the sweep ratio (that is to say the ratio between the quantity of air passing through the motors and the displacement of these motors) is fixed or, at least, can only be modified by important steps. The invention also aims to provide means for more precise adaptation of the scanning ratio to the needs of scanning of the kind defined above. To this end, the invention also proposes to assign some of the compressors of the installation to a single flow and other cylinders to two flows, by providing discharge valves opening into two separate manifolds assigned, one to the flow. primary, the other to secondary flow.

• - les Figures 1, 2 et 3 sont des schémas montrant, à divers stades du cycle de fonctionnement, la disposition des composants d'un cylindre moteur et d'un cylindre compresseur d'une installation suivant un mode de réalisation de l'invention,
• - la Figure 4 est un schéma, en coupe suivant un plan passant par l'axe longitudinal d'un cylindre moteur, montrant la modification du front de propagation des gaz de balayage obtenue grâce à l'invention,
• - la Figure 5 est un schéma à grande échelle, en coupe suivant un plan passant par l'axe d'un cylindre moteur, montrant une disposition possible des lumières de balayage,
• - les Figures 6 et 7 montrent l'orientation des lumières de balayage des deux rangées illustrées en Figure 5,
• - la Figure 8 est un schéma montrant la propagation des fronts de balayage dans un cylindre moteur équipé de lumières du type montré en Figures 5 à 7,
• - la Figure 9 est un schéma de principe montrant deux des compresseurs d'une installation à générateur de gaz à pistons libres, l'un des deux cylindres compresseurs étant mixte en ce sens qu'il est affecté, d'une part, au circuit d'air primaire, d'autre part, au circuit d'air secondaire.

The invention will be better understood on reading the following description of particular embodiments, given by way of nonlimiting examples. The description refers to the accompanying drawings, in which:

• FIGS. 1, 2 and 3 are diagrams showing, at various stages of the operating cycle, the arrangement of the components of a driving cylinder and of a compressor cylinder of an installation according to an embodiment of the invention,
• FIG. 4 is a diagram, in section along a plane passing through the longitudinal axis of a driving cylinder, showing the modification of the propagation front of the sweeping gases obtained thanks to the invention,
• FIG. 5 is a large-scale diagram, in section along a plane passing through the axis of a driving cylinder, showing a possible arrangement of the scanning lights,
• FIGS. 6 and 7 show the orientation of the scanning lights of the two rows illustrated in FIG. 5,
• FIG. 8 is a diagram showing the propagation of the scanning fronts in an engine cylinder fitted with lights of the type shown in FIGS. 5 to 7,
• - Figure 9 is a block diagram showing two of the compressors of an installation with a gas generator with free pistons, one of the two compressor cylinders being mixed in the sense that it is assigned, on the one hand, to the circuit primary air, on the other hand, to the secondary air circuit.

Firstly, with reference to FIGS. 1 to 3, there will be described an operating cycle of an assembly comprising only an engine cylinder 10 and a compressor cylinder 12 of a gas generator with free pistons which may have the general constitution described. in the aforementioned document EP-A-7874. The compressor cylinder 12 contains a piston 14 separating a compression compartment 16 assigned to the primary flow and a compartment 18 assigned to the secondary flow and directly supplying a gas turbine not shown. The compartment 16 is provided with valves 20 for intake of fresh air and with valves 22 for delivery to an intake capacity 24. The piston 14 is mechanically coupled to a driving piston 26 delimiting, with a symmetrical piston 28, a compartment motor 30 which, in the position of maximum separation of the pistons 26 and 28, has a volume equal to about one fifth of the volume of the capacity 24. The piston 26 cooperates with scanning lights 32 while the piston 28 cooperates with exhaust lights 34 opening into a pipe 36 supplying an exhaust capacity 38 connected to a high turbine pressure (not shown).

Figure 1 shows in solid lines the position of the movable assembly comprising the pistons 14, 26 and 28 at the time of opening of the exhaust lights 34, that is to say when the puff occurs exhaust. Due to the difference in location of lights 32 and 34, the scanning lights are still closed. The engine pistons move away from each other. The compression chamber 16 is in suction, the piston 14 moving away from the plate which carries the valves 20 and 22. In the intake capacity there prevails a pressure Pc, while the pressure in the compressor compartment 16 is substantially equal to the inlet pressure Pa. The pressure prevailing in the engine cylinder 30 is substantially equal to 3Pi.

By means of an appropriate design of the exhaust lights 34 and of their connection with the pipe 36, the total pressure at the inlet of the pipes then increases rapidly and reaches a value of approximately 1.5 Pe.

The engine pistons then uncover the scanning lights 32, as indicated in dashes in FIG. 1. The intake capacity 24 is then in connection with the engine cylinder 30. As soon as the exhaust puff has released the pressure which prevails in the engine below Pc, the intake capacity 24 begins to discharge into the engine to sweep it (dashed arrow in Figure 1).

This scanning process continues until the moving parts have reached their maximum travel, that is to say the external dead center, as indicated in solid lines in Figure 2. The movement of the moving parts reverse, as indicated by the arrows f. The engine scanning continues as indicated by the arrows F. The intake capacity 24 is always in communication with the engine and isolated from the compressor.

The compression phase in the engine and the discharge from the compressor 12 to the intake capacity 24 then begins. During the movement of the engine pistons 26 and 28 (in dashes in Figure 2), the pistons 26 and 28 successively close the scanning lights 32 then the exhaust lights 34, isolating the engine from the intake capacity . The compressor 12 during this time charges the intake capacity whose pressure rises.

When the engine pistons come to internal dead center, their movement begins to reverse, the fuel is injected into the engine and combustion begins.

Finally, the expansion of the engine takes place at the same time as that of the dead space of the compressor while the intake capacity 24 is awaiting discharge (Figure 3) and the cycle resumes.

Whether the sweeping is carried out at constant inlet pressure or at variable pressure, the use of a traditional arrangement of lights allows the drawbacks already mentioned to remain, namely the incomplete nature of the sweeping in the event of a jet injection. tangential, the absence of rotary movement favorable to combustion in the event of radial jets.

One might think that it is possible to avoid the difficulty by giving the scanning lights a twisted shape, so that the injection takes place with a tangential component in the part of the lights closest to the median plane, radially in the part furthest from the median plane. However, regardless of the difficulties in producing such lights, an additional problem remains, due to the difference in the course of the different air streams. This difference in path means that, when the fresh air front reaches the scanning lights, it presents a shape of the kind shown in solid lines in FIG. 4, leaving a core of burnt gases which may be trapped in the cylinder.

We will now describe a scanning system with two rows of lights, allowing in any case to combine the advantages of radial scanning with rotary scanning and also allowing, at the cost of simple arrangements, to modify the flow front so to give it a look like the one shown in dashes in Figure 4.

Figure 5, on which the elements corresponding to those of Figure 1 are designated by the same reference number, shows an intake capacity 24 formed in the cylinder housing 30 and communicating directly with a row of intake lights 32 ₂ which open radially into the cylinder (Figure 6). Another row of lights 32 "placed so as to be discovered first by the piston 26 during the rebound stroke, are, on the contrary, oriented obliquely, with an angle relative to the radial plane which will generally be approximately 30 ° (Figure 7).

To reduce the relative advance of the fluid threads coming from the 32 "lights, the arrangement shown in FIG. 5 acts on two factors. On the one hand, it tends to decrease the total pressure of the peripheral fluid threads, supplied by the lights 32" by decreasing their speed. On the other hand, it delays the appearance of the effective flow through these lights 32 ₁ . These two results are achieved by having, between the intake capacity 24 and the lights 32 "a pipe 40 in baffles, of small volume but of length much greater than the axial interval between the rows 32, and 32 ₂ , This pipe phase out the flow and cause a pressure drop which reduces the total supply pressure.

Thanks to this arrangement, there is a slight backflow from the engine towards the intake when the lights 32 _{1 are} opened. Mixtures between cold sweeping air and burnt gases are limited during this discharge by the large relative elongation of the pipe 40.

• - la longueur de la conduite 40 est déterminée pour que la différence entre la pression dans la capacité d'admission 24 et la pression dans le moteur ait changé de signe quand l'onde de détente due à la réflexion de l'onde de compression à l'extrémité de la conduite 40 arrive aux lumières 32₁, ce qui limite le débit refoulé,
• - la durée d'aller-retour des ondes doit être telle que le piston 26 ait découvert toute la longueur des lumières 32₁ à l'instant de retour,
• - le début d'ouverture des lumières 32₂ doit intervenir lorsque la masse de gaz admise dans le moteur par les lumières 32₁ est du même ordre de grandeur que la masse initialement refoulée du moteur vers la conduite 40.

The dimensions of the pipe 40 will depend on the parameters of each particular installation. But they will obey the following rules:

• the length of the pipe 40 is determined so that the difference between the pressure in the intake capacity 24 and the pressure in the engine has changed sign when the expansion wave due to the reflection of the compression wave at the end of the pipe 40 arrives at the lights 32 ₁ , which limits the delivery rate,
• the duration of the round trip of the waves must be such that the piston 26 has discovered the entire length of the lights 32 ₁ at the instant of return,
• the start of opening of the lights 32 ₂ must occur when the mass of gas admitted into the engine through the lights 32 ₁ is of the same order of magnitude as the mass initially discharged from the engine to the pipe 40.

The presence of the two rows of lights and of the pipe 40 brings other favorable results. In particular, by accepting an initial discharge of the gases, the total length of the scanning and intake lights 32 ₁ - 32 ₂ can be increased by approximately 30% for the same useful displacement. The phase shift of the flow by the lights 32 ₁ flattens the tip of the peripheral fresh air front.

To slow down this peripheral front, the pressure drops in the pipe 40 are used. In practice, a pressure drop of the same order as that caused by the lights 32 _{1 will be used} , which reduces the speed at which the lights pass through. a ratio which corresponds approximately to that of the distances traveled by the peripheral air streams and close to the axis.

Figure 8 shows the results of a simulation carried out to determine the fronts of invasion of the cylinder 30 by the fresh air when the lights are of the kind shown in Figure 5. The curves identified by the references 1, 2, 3, 4 and 5 show the edges respectively 2 ms, 6 ms, 10 ms, 16 ms and 20 ms after the start of opening of the second row of lights.

To delay the supply of lights 32 ₁ , other solutions are possible, in particular the use of valves with delayed controlled opening or calibrated valves with automatic opening interposed between the intake capacity and the lights 321 of the first set.

We will now describe, with reference to FIG. 9, an arrangement making it possible to better adjust the flow of sweeping air sent to the driving cylinders, in a gas generator which may have the general constitution shown in document EP-A-7874 already. mentionned. Figure 9 shows only two compressors among the eight that include such a generator. The compressor 42 is intended to supply only air to the secondary circuit, via a heat exchanger 44 intended to heat it. The air having passed through the exchanger 44 is sent to a high pressure gas turbine 46.

At least one other compressor cylinder 12, or at least the other compartment delimited by the compressor piston 14 in the cylinder 12, is mixed in the sense that it supplies air to the primary circuit, which includes a cooler 48 and opens out. in an engine cylinder 30, and in the secondary circuit. For this, the delivery manifold 50 of the cylinder 12 is separated by a partition 52 into two chambers. In each chamber, several discharge valves 22 of the compressor open. Since the number of these valves is high, often between ten and twenty, there is thus an extremely flexible adjustment mode.

The solution shown in Figure 9 also provides a much greater freedom of choice between the ratio of primary and secondary air flow rates provided by all of the compressors.

Claims (11)

1. Power production apparatus comprising at least one Diesel engine having a plurality of sequentially operating motor cylinders (10), supercharged by a plurality of alternating compressor cylinders (12, 16) delivering scavenging air to the engine, each motor cylinder (10) being fed with scavenging air through an intake capacity (24) which is dedicated to it and whose volume is equal to several times the cubic capacity of the respective motor cylinder (10),
characterized in that a compressor cylinder (12, 16) associated to each motor cylinder (10)-capacity (24) pair feeds only said capacity (24) and the cylinder is that of the compressor cylinders (12, 16) whose compression stroke occurs and ends while the scavenging ports (32) of the respective motor cylinder (10) are closed.

2. Apparatus according to claim 1,
characterized in that the volume of said capacity is about five times the cubic capacity of the cylinder.

3. Apparatus according to claim 1 or 2,
characterized in that the exhaust pipes (36) of the motor cylinder (10), located opposite to the intake ports (32) of the motor cylinder (10) have a cross-sectional area which is constant in the vicinity of the exhaust ports (34), then a cross-sectional area which slowly increases for causing a fast drop of the pressure in the motor cylinder (10) as soon as the exhaust ports open.

4. Apparatus according to claim 1, 2 or 3, of the type comprising a multi-tandem free piston gas generator provided with said motor cylinders and a gas turbine which receives the exhaust gases of the motor cylinders,
characterized in that each motor cylinder (10), defined by two motor pistons (26, 28), is fed from a single compressor chamber (16) defined by a double action compressor cylinder (10) and by a piston (14) which is driven by one of the pistons (26) of the cylinder, so selected that the compression stroke of the compressor occurs while the ports (32, 34) of the respective motor are closed.

5. Apparatus according to claim 4, wherein each motor cylinder has scavenging ports (32) or valves regularly distributed around the cylinder at an end thereof and exhaust means, such as ports (34), which are also regularly distributed at the other end of the cylinder defined by two pistons (26, 28) which move in opposite directions,
characterized in that the scavenging ports are distributed in two rows (32, and 32₂) which are successively uncovered.

6. Apparatus according to claim 5, characterized in that the ports (32₁) of the row which is uncovered first are so located as to deliver a jet which has a tangential component while the ports (32₂) uncovered thereafter are arranged for delivering a jet which is directed substantially toward the axis.

7. Apparatus according to claim 6,
characterized in that the ports (32₁) of the first row deliver a jet which is at an angle of about 30° with the radial direction.

8. Apparatus according to claims 6 or 7,
characterized in that both rows (32₁, 32₂) are fed by a same intake capacity (24), means being provided for delaying delivery of scavenging air to the ports (32₁) of the first row.

9. Apparatus according to claim 8,
characterized in that said means consist of the sinuous passage (40) between the intake capacity (24) and the ports (32₁) of the first set.

10. Apparatus according to claim 8,
characterized in that said means comprise valves with delayed controlled opening or automatically opening loaded valves located between the intake capacity (24) and the ports (32₁) of the first set.

11. Apparatus according to any one of the preceding claims,
characterized in that one at least of the compressor cylinders (10) has a compression manifold (50) separated in two chambers each connected to the cylinder by compression check valves (22) and in that one of the chambers feeds the motor cylinders (30) while the other chamber feeds a high pressure gas turbine (46).

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