US3760778A

US3760778A - Vapor generators

Info

Publication number: US3760778A
Application number: US00200445A
Authority: US
Inventors: C May
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-12-04
Filing date: 1971-11-19
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25
Also published as: SE366817B; DK137201B; FR2117144A5; ZA717643B; DK137201C; AU3605471A; AT315208B; AR194214A1; BE776217A; DE2159771A1; GB1364456A; AU452911B2; ES397646A1; CA940397A; NL7116595A; CH540460A; IT945215B

Abstract

Apparatus for the generation of liquid vapor under pressure by means of heat from the combustion products of an internal combustion engine comprises a reservoir for the liquid to be vaporized having an inlet duct for the combustion products which communicates with the lower part of the interior of the reservoir. The combustion products pass from the inlet duct into the reservoir by way of a screen formed with a large number of small holes providing free passage for gas or liquid and this screen is preferably formed by an extension of the duct lying within the reservoir and formed with the small holes round its periphery. As a result of this construction the combustion product may bubble upwardly through liquid in the reservoir so as to transfer heat directly to the liquid with a high rate of heat transfer. An outlet from the reservoir is preferably so constructed as to reduce the amount of liquid carried over with the vapor and the outlet line may pass through at least one further closed vessel in order to trap any residual liquid. The internal combustion engine supplying the combustion products is preferably of the free-piston type and includes an arrangement for avoiding excessive heating of a release valve and its seat. For this purpose a duct is provided to supply liquid to a chamber in contact with the heated portion of the cylinder head and this chamber includes a portion adjacent the seat of the release valve which includes narrow outlets opening into the inlet duct in the region of reduced pressure immediately following the valve opening. In this way liquid is drawn into the inlet duct leading to appreciable cooling of the release valve and its seat.

Description

United States Patent [191 May Sept. 25, 1973 VAPOR GENERATORS [76] Inventor: Claude H. May, Beaumont Cambridge Pk., St. Peter Port,

, Guernsey (Channel ls.)

[22] Filed: Nov. 19, 1971 [21] App]. No.: 200,445

[30] Foreign Application Priority Data Dec. 4, 1970 Great Britain 57,809/70 [52] US. Cl 123/41.17, 123/25 D, 60/310, 126/360 A [51] Int. Cl. F0lp 9/02, F01n 3/04 [58] Field of Search 123/41.17, 188 S, 123/25 D, 25 P; 122/31 A, 7 R; 126/360 A;

Primary Examiner-Al Lawrence Smith Assistant Examiner-Dennis Toth Attorney-Joseph F. Brisebois et al.

[5 7] ABSTRACT Apparatus for the generation of liquid vapor under pressure, by means of heat from the combustion products of an internal combustion engine comprises a reservoir for the liquid to be vaporized having an inlet duct for the combustion products which communicates with the lower part of the interior of the reservoir. The combustion products pass from the inlet duct into the reservoir by way of a screen formed with a large number of small holes providing free passage for gas or liq-' uid and this screen is preferably formed by an extension of the duct lying within the reservoir and formed with the small holes round its periphery. As a result of this construction the combustion product may bubble upwardly through liquid in the reservoir so as to transfer heat directly to the liquid with a high rate of heat transfer. An outlet from the reservoir is preferably so constructed as to reduce the amount of liquid carried over with the vapor and the outlet line may pass through at least one further closed vessel in order to trap any residual liquid. The internal combustion engine supplying the combustion products is preferably of the freepiston type and includes an arrangement for avoiding excessive heating of a release valve and its seat. For this purpose a duct is provided to supply liquid to a chamber in contact with the heated portion of the cylinder head and this chamber includes a portion adjacent the seat of the release valve'which includes narrow outlets opening into the inlet duct in the region of reduced pressure immediately following the valve opening. In this way liquid is drawn into the inlet duct leading to appreciable cooling of the release valve and its seat.

5 Claims, 6 Drawing Figures United States Patent [1 1 1 3,760,778 May Sept. 25, 1973 r. 55 l 40 i5 l 42 A 39 I 4 0/ I as PATENTEDSEPZSIHTS SHEET 1 OF 4 Inventor Attorney PATENTEUSEPZSIHIS SHEET 2 BF 4 I nvenlor Attorney PATENTED8EP25|975 5.760.778

SHEET 3 (IF 4 Inventor Attorney PATENTED SEPZS I973 SHEET 0F 4 I rwenlor A Home y VAPOR GENERATORS This invention relates to apparatus for the generation of liquid vapour at high temperature and pressure for utilisation in driving prime movers. It is particularly applicable to the generation of steam for such purposes although in'sorn'e circumstances other liquids may be used. Aparticularly suitable source of heat for the generation of 'liquidvapour is'the combustion'products of an internal combustion engine which are fed to a reservoir partly filled with liquid to be vaporised.

According to the present invention the reservoir has an inlet duct for the combustion products which communicates with the lower part of the interior ofthe'reservoir by way of a'screenfo'rmed with a large number of smallholes providing free passage for gas or liquid whereby the combustion product may bubble upwardly through liquid in the reservoir so'as to transfer heat'directly to the liquid. In this way, the heat and pressure of the combustion product may be transmittedtothe liquid with high efficiency. The screen is preferably constituted by an extension of the inlet duct lying within the reservoir and formed with the small'holes round its periphery. With such an arrangement it is possible to create a large number of small bubbles so that the ratio of surface area to volume'isvery high and consequently a high rate of heat transfer is achieved.

By selecting the size of hole so that the gas bubbles are above a certain critical size, the temperature of the trapped gas within the bubble will still be above that of the liquid when it breaks through the surface. This will provide super heat to the vapour and in this way an ext'remely efficient vapour generator is provided.

If the apparatus is to be fitted to a vehicle, for which purpose it is particularly suitable, the reservoir is'prefe'rably cylindrical and is divided into axial compartments by circular baffle plates formed with openings for the passage of liquid and pressure fluid. The provision of these baffles avoids splashing and liquid surging during movement of the equipment while the presence of the openings permits free but controlled flow of both liquid and pressure fluid. The baffle plates may for example divide the reservoir along its length into compartments having a length of about 65 percent of the diameter.

In use it is important to keep the vapour dry and it is thus desirable to arrange the outlet pipe from the reservoir so as to avoid as far as possible liquid being carried over with the pressure fluid. For this purpose the outlet may comprise a pipe which extends upwardly towards the top of the reservoir where its end is obstructed, the walls of the pipe close to the end being formed with openings for the passage of pressure fluid and the upper portion of the pipe, including the openings, being surrounded by a cup-shaped shield formed with drainage openings at the bottom. Pressure fluid can pass freely over the top of the shield and out through the openings in the pipe, but any liquid which tends to be splashed over the top of the shield is unlikely to enter the pipe and merely flows outwardly through the drainage openings. As an additional protection, the drainage openings in the cup may themselves be protected from splash by a down-turned skirt.

Apart from the construction of the reservoir itself, problems may arise in the internal combustion engine supplying the combustion products owing to the very high temperature and back-pressure in the outlet duct of the engine and subsequent build-up of heat in the area of the release valve which leads to erosion of the valve and its seat. This excessive heating may be at least partly counteracted by use of an engine which is specifically designed for this purpose. In a preferred construction of engine for this purpose an outlet from the, or each, release valve is connected to the duct for the combustion products and a second duct is provided to supplyliquid either from the reservoir or from a separate tank to a chamber or chambers in contact with the heated portion or portions of the, or each, cylinder head. Each chamber includes a portion adjacent the seatof the respective release valve and also includes narrow outlets opening into the inlet duct in the region of reduced pressure immediately following the valve opening. In this way liquid is drawn into the inlet duct, thus leading to a circulation of liquid from the reservoir, through the chamber, into contact with the metal adjacent the seat of the release valve and then through.

the narrow openings into the inlet duct where the liquid is immediately vaporised by contact with the hot released gases. This leads to appreciable cooling of the, or each, release valve and the respective seat or seats.

Each chamber into which the liquid flows may include an' annular portion separatedfrom the region of reduced pressure by an annular diaphragm having a free inner edge bearing against the wall of the annular portion of the chamber adjacent the valve seat, the narrow openings being formed between this edge of the diaphragm and the wall. The diaphragm thus divides the chamber from the duct by which the combustion products are supplied to the reservoir and additionally forms a sealing gasket against the high pressure of the pressure fluid.

Apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a vertical section through the end of a reservoir and of an internal combustion engine supplying products of combustion to the reservoir;

FIG. 2 is a sectional view of the reservoir as seen from the right hand side of FIG. 1;

FIG. 3 is an end view, partly in section, of the internal combustion engine seen from the left in FIG. 1;

FIG. 4 is a sectional view to a reduced scale corresponding to FIG. 2 and showing subsequent details of an outlet line;

FIG. 5 is a detailed view showing part of a diaphragm seen in FIG. 1; and,

FIG. 6 is a sectional view to an enlarged scale showing part of a release valve and seat seen in FIG. 1 and also including the edge of the diaphragm seen in FIG. 5.

. Turning first to FIG. 1, the release or outlet end of an internal combustion engine is indicated generally as l and from it the products of combustion pass along a line 2 and thence via an inlet duct 3 to the interior of a cylindrical reservoir indicated generally as 4 and of which only the left hand end is shown in FIG. 1. The inlet duct 3 continues downwardly at 5 towards the bottom of the reservoir 4 where it turns through a right angle at 6 and leads to a perforated horizontal extension 7 formed with a large number of small holes 8 through which the products of combustion bubble upwardly through liquid in the reservoir 4. The level of the liquid is indicated by two horizontal lines 9 which represent the upper and lower levels which may be assumed by the liquid during operation. For most purposes the liquid in the reservoir will be water and will be described as such, but under some circumstances other liquids may be used.

The perforated extension 7 forms a screen through which passage of the combustion products transfers heat directly to the water within the reservoir. The arrangement of holes 8 around the extension 7 is best seen from FIG. 2, but this arrangement is by no means critical. The arrangement is such that a large number of small bubbles is created so that the ratio of surface area to volume is very high and consequently a high rate of heat transfer is achieved. When the liquid in the reservoir is water, it is found that a suitable size of hole is of approximately 0.75 mm diameter which causes the gas bubbles to be above a critical size in which the temperature of the trapped gas is still above that of the water when each bubble breaks through thesurface. This provides super heat to the steam and in this way an extremely efficient vapour generator is provided.

If the apparatus is fitted to a vehicle there is a risk of the water surging from one end to the other of the reservoir and to reduce this, baffle plates 12 of which only one is seen in FIG. 2 are provided at intervals along the length of the reservoir. Each plate 12 is formed with openings 13 seen in FIG. 2 which permits free but con trolled flow of both liquid and steam while avoiding splashing and the surging movement of the water. The baffle plates 12 are arranged to divide the reservoir 4 into compartments each having a length of about 65 percent of the diameter.

Outlet of pressure fluid from the reservoir 4 is controlled by the requirements of the motor to be driven or other apparatus to be supplied with the pressure fluid. An outlet pipe 15 extends from the top of the reservoir 4 and passes outwardly through the wall at 16 in the lower half of the reservoir. It is important to avoid liquid being carried over with the pressure fluid into the pipe 15 and for this purpose the pipe is formed close to its end (which is obstructed by the presence of the wall of the reservoir) with small openings 17, and the upper end of the pipe is surrounded by a cup-shaped shield 20 formed with drainage openings 21 close to its bottom and lying on a line at right angles to that of the openings 17. Although pressure fluid can flow freely through the entrance to the pipe 15, little water can get over the top of the cup 20 and such as does passes over in a direction at right angles to the line of the openings 17 and then drains away through the openings 21 rather than into the pipe 15. As an additional protection the drainage openings 21 are themselves protected by a downturned skirt 22.

Despite these various precautions, there is still a risk that a small quantity. of water may be carried over down the pipe 15 and this needs to be trapped and allowed to be vaporised by the higher temperature of the superheated steam which follows it. For this purpose, reservoirs 24 and 34 (shown in FIG. 4) similar to the reservoir 4 are provided in series with the outlet from the reservoir 4. In other words, pressure fluid from the reservoir 4 together with any entrained liquid passes firstly to the reservoir 24, the outlet from which is arranged in a similar way to that from the reservoir 4 and the components of which are indicated by the same reference numerals. The outlet from the reservoir 24 then passes to the reservoir 34 where again the outlet arrangement is similar, in any convenient direction and from there the pressure fluid passes onwardly to its point of application. By the time the pressure fluid leaves the reservoir 34 any entrained liquid is quite negligible.

By means of the arrangements just described, the heat from and with the products of combustion of the engine 1 is converted with high efficiency into a pressure fluid which can be withdrawn as required. As the pressure in the reservoir 4 builds up, it applies back pressure to the engine 1 and this, in combination with the high temperatures involved tends to cause the release valve of the engine to overheat, leading to erosion of the valve and its seat. Although any form of internal combustion engine can be used for the supply of combustion products, a free-piston engine is particularly suitable for this purpose and it is an engine of this type which is shown in the drawings.

The piston and cylinder are shown as 35 and 36 respectively and the release valve and its seat as 38 and 39 respectively. The release valve carries a sparking plug 40 at its center and is controlled by four loading springs 41 of the leaf pack type. Two of these are seen at the right hand side of FIG. 3, the left hand half of this Figure being in section. The valve 38 opens automatically when the pressure in the combustion chamber shown as 42 exceeds that exerted by the springs 41 and the combustion products then pass to the reservoir 4. The free-piston engine illustrated will, of course, have two opposed cylinders, but in principle an engine having any number of cylinders may be used. These will all have similar release valve arrangements so that a description of the single cylinder shown in the drawing will suffice.

In the illustrated arrangement, the line 2,

inlet duct

3,5 and right angle piece 6, are repeated in mirror fashion at the opposite end of the reservoir 4, where the products of combustion enter the horizontal extension 7 from the opposite end. With any other number of cylinders these may either be arranged to manifold into the existing

lines

2, 3 or may use an additional reservoir 4a shown in dotted lines in FIG. 4 which, in turn, feeds into the reservoir 24.

In order to reduce erosion of the release valve 38 and its seat 39 a cooling arrangement is provided which (as illustrated) is supplied with liquid from the reservoir 4 by a further line not shown in detail but indicated diagrammatically by the dotted line 45. Alternatively this line may be supplied from a separate source to replace lost water. Before passing to a detailed description of the cooling system, it is important to understand the sequence of events immediately prior to and following the instant of ignition in the combustion chamber 42 of the free-piston engine. For purposes of description it can be assumed that the cylinder is freshly and fully charged with a stoichiometric air/fuel mixture and that the piston 35 is approaching the peak of compression and ignition. At this stage, clue to the logarithmic characteristics of compression, the change in the rate of rise of pressure in the combustion chamber 42 is quite rapid. As the kinetic energy previously imparted to the piston 35 is being expended equally rapidly, deceleration is correspondingly high. Just as the piston reaches the limit of its outward stroke ignition occurs and almost immediately thereafter several other events follow on virtually simultaneously. The actual order of these events may not be that described because of certain operational variables, but in any case only a few microseconds will separate the events and their interaction.

The rise of pressure in the combustion chamber 42 will absorb the remaining kinetic energy in the assembly including the piston 35 which will thus complete its outward stroke and instantaneously start accelerating in the opposite direction, thus starting to increase the volume of the combustion chamber 42. As it is virtually impossible for all the heat in the fuel to be yielded to the charge at constant volume, there is a time-lag between the generation of the flame nucleus at the ignition point and flame propagation throughout the charge. Pressure then rises rapidly and soon exceeds that exerted by the springs 41 so that the release valve 38 starts to open. The products of combustion start to escape at acoustic velocity which is modified by a coefficient of efflux due to the narrow orifice 46 between the valve 38 and the seat 39. As the valve 38 opens to the full the coefficient will improve and the orifice 46 will enlarge. Whereas in a conventional engine, ignition in the closed chamber would cause a pressure rise of some five times the compression pressure, this does not occur in a free-piston engine as illustrated in which the pressure rise is limited to about half that which would otherwise be expected. Nevertheless, by the time the release valve 38 is again seated which is about 1 millisecond later, some 80 percent of the combustion products will have escaped and most of the energy necessary for cycling will have been imparted to the piston assembly. At this stage the inward movement of the piston will have led to an increase of volume of the combustion space 42 of about 60 percent. This space is of course filled with gas still at a fairly high temperature but at a pressure only a little above the compression pressure. As a result, the weight of the gas will be only about 10 percent that of the initial charge. During the subsequent expansion and rapid cooling the remainder of the energy necessary for the cycling is imparted to the piston assembly and completion of the inward stroke then drops the pressure in the cylinder below ambient atmospheric pressure. The result of the above further improves the overall thermal efficiency of the unit quite apart from the high efficiency of the operation of the reservoir 4, as already described.

The improvement results from three main factors. Since the free-piston engine operates substantially at one set load and frequency, it is possible to adjust both the air/fuel ratio and the ignition timing to their optimum settings. The total amount of heat for subsequent transfer to the working fluid in the reservoir 4 is removed from the combustion space 42 at the outer end of the working stroke of the piston and, as already described, only the small proportion of burned gas required for cycling loses heat to the cylinder walls. Moreover, the relatively much lower pressure of gas during this stroke results in less friction due to inflation of the piston rings. Finally, as a result of thecooling system about to be described, the unavoidable heat transfer through the walls of the combustion chamber 42 is absorbed by the cooling liquid and passes with it and the products of combustion into the pressure fluid in the reservoir 4.

Returning to the details of the cooling system supplied by the line 45, the liquid from the reservoir 4 passes through a fitting (not shown in the drawings) screwed into the outer head 51 at 52. From there the liquid passes to a substantially annular chamber 53.

From there the liquid flows circumferentially around the chamber 53 in both directions as indicated by the arrow in the half-section of FIG. 3, most of this liquid passing through a pair of holes 54, one of which is seen in both FIGS. 1 and 3. The remainder passes through a hole 55, which reduces the risk of vapour lock. These holes all extend through into an annular chamber 60 surrounding the inner head 61. The chamber 60 is separated by a diaphragm 62 from a chamber 63 into which the products of combustion pass immediately after flowing through the orifice 46 when leaving the combustion chamber 42 after the release valve 38 has opened. The

holes

54 and 55 thus pass through an outer portion of the diaphragm 62 which is annular in shape and has a free inner edge 65 which bears against the inner head 61 which constitutes the wall of the chamber 60. The inner edge 65 of the diaphragm 62 is shown to an enlarged scale in FIG. 6 for which it can be seen that the edge locates in an annular recess indicated generally as 67 in the inner head 61. This recess 67 has a square-cut corner 68 and the edge 65 is chamfered at 70-so as to leave an annular passage 71 of triangular section between the edge of the diaphragm 62 and the recess 67. In addition, the edge 65 of the diaphragm 62 is shaped as shown in FIG. 5. Thus the right hand side of the diaphragm as seen in FIG 6, that is to say the side in communication with the chamber 60, is formed with a series of approximately radial slots 73, which decrease in depth from the edge 65 so as to form a triangular configuration as seen in FIG. 5. These slots are equally spaced and alternate with a series of generally axial slots 74 best seen in FIG. 5.1m one of whichcan be seen in FIG. 6.

Thus it will be understood that the combination of the slots 73, the annular passage 71 and the axial slots 74 provides a series of narrow openings connecting the liquid in the chamber 60 to the chamber 63. In other words, liquid is able to pass in a generally radial direction along one of the slots 73, from there in a circumferential direction along the passage 71 and thence in an axial direction along one of the slots 74 into the chamber 63. The diaphragm 62 effectively forms a sealing gasket between the liquid in the chamber 60 and the high pressure of the combustion products in the chamber 63 against leakage to the exterior of the head. Nevertheless, the presence of the narrow openings just described allows a small proportion of the liquid to pass gradually through to the chamber 63 where it is swept up and vaporised by the products of combustion as a result of the venturi or extractor effect created by the high velocity flow through the orifice 46 and into the widely expanding passage following it. The overall effect is that liquid entering from line 45 firstly has a cooling effect in passing through the chamber 53, being itself further heated in the process, and then, in passing into the chamber 60 absorbs conducted heat from the chamber walls and serves to scour excess heat from the vicinity of the valve seat 39.

The large scale view of FIG. 6, in addition to showing the relationship between the diaphragm 62 and the inner head 61, also shows further details of the release valve 38 and the seat 39. Both these parts are subject to erosion due to the high temperatures involved since excess heat absorbed by the valve 38 will tend to flow to the seat 39 during the considerable portion of each cycle when the valve is seated. In order to reduce the efiects of erosion on the engaging faces of these two components, each is shown as provided with an

insert

80 and 81 respectively of metal resistant to high temperature gas erosion and thermal shock. A particularly suitable metal for this purpose is a cobalt base alloy such as that available under the Trade Mark Stellite 6. The valve 38 slides in a guide bore indicated as 83 and the provision of an adequate pressure seal between the valve 38 and the bore 83 is of considerable importance. For this purpose, the wall of the bore is extended at 85 to form a relatively thin, sharp-angled lip which, during the initial manufacture is deformed inwardly as shown in dotted lines at 86 so as to form an interference fit with the valve 38. During initial running, this interference fit maintains an adequate seal, but even after long periods of running when both the surface of the valve 38 and of the lip 85 have been subjected to wear, the seal is maintained since the pressure in the chamber 63 develops a hoop-stress in the lip 85 which will keep the lip in close contact with the sides of the valve 38, thus providing an efficient seal with little friction and negligible wear.

I claim:

1. Apparatus for the generation of liquid vapour under pressure by means of heat from the combustion products of an internal combustion engine, said apparatus comprising an internal combustion engine having at least one release valve having a seat and an outlet, a reservoir for the liquid to be vapourised, an inlet duct to said reservoir for said combustion products, and a connection between said outlet of said release valve and said inlet duct for the combustion products, said duct communicating with the lower part of the interior of the reservoir, and a screen formed with a large number of small holes providing free passage for gas or liquid, said screen being arranged between said duct and the interior of said reservoir whereby the combustion products may bubble upwardly through liquid in the reservoir so as to transfer heat directly to the liquid, and said engine including at least one cylinder head and structure defining at least one chamber in contact with said cylinder head, and a second duct connected to supply liquid from said reservoir to said chamber, said chamber including a portion adjacent said seat of said release valve, said portion including narrow outlets opening into a region in said inlet duct immediately following said valve, whereby liquid is drawn from said chamber into said inlet duct due to reduced pressure in said region.

2. Apparatus according to claim 1, in which said chamber includes an annular diaphragm mounted to separate said annular portion from said region in said inlet duct, said annular diaphragm having a free inner edge bearing against said cylinder head adjacent said valve seat, said narrow openings being formed between said inner edge of said diaphragm and said cylinder head.

3. Apparatus according to claim 2, in which said edge of said diaphragm locates in an annular recess in said cylinder head, said recess being formed with a relatively sharp corner when seen in section, said edge of said diaphragm having a chamfered corner registering with said sharp corner in said recess to leave an annular passage, the side of said diaphragm adjacent said annular portion of said chamber being formed with a plurality of approximately radial slots connecting said portion of said chamber to said passage and said edge of said diaphragm being formed with a plurality of approximately axial slots connecting said annular passage to said region in said inlet duct, whereby the combination of said radial slots, said annular passage and said axial slots together constitute said narrow openings.

4. Apparatus according to claim 1, in which engaging surfaces of said release valve and said seat are provided with inserts of metal resistant to high-temperature gas erosion and thermal shock.

5. Apparatus according to claim 1, including a guide bore in which said release valve works, said bore having a wall which is extended to form a relatively thin, narrow-angled lip bearing against the side of said release valve to maintain an effective seal.