US3220393A

US3220393A - Lpg fuel supply systems for internal combustion engines

Info

Publication number: US3220393A
Application number: US325608A
Authority: US
Inventors: Lawrence J Schlink
Original assignee: General American Transportation Corp
Current assignee: General American Transportation Corp
Priority date: 1963-11-22
Filing date: 1963-11-22
Publication date: 1965-11-30
Anticipated expiration: 1982-11-30

Description

Nov. 30, 1965 1 SCHUNK LPG FUEL SUPPLY SYSTEMS FOR INTERNAL coMBusTxoN ENGINES Filed Nov. 22, 1963 ATTYS.

United States Patent O 3,220,393 LPG FUEL SUPPLY SYSTEMS FR INTERNAL COMBUSTION ENGINES Lawrence J. Schlink, Sharon, Pa., assigner to General American Transportation Corporation, Chicago, Ill., a corporation of New York Filed Nov. 22, 1963, Ser. No. 325,608 4 Claims. (Cl. 12S- 120) The present invention relates to LPG fuel supply systems for internal combustion engines, and particularly to such systems employing propane as the LPG fuel, and specifically to such systems incorporated in railway cars utilizing internal combustion engine driven equipment for heating, cooling or similar purposes.

In a conventional railway refrigerator car, the refrigeratin-g equipment is driven by an internal combustion engine operating on propane and supplied from a pressure tank that is subject to the ambient temperature. The refrigerating equipment is capable of direct operation for cooling the lading in warm weather and of heat-pump operation for heating the lading in cold weather; whereby it is equally necessary to operate the refrigerating equipment in extremely cold weather, as it is in extremely hot weather, since a lading will be damaged by freezing in cold weather or by spoiling in hot weather.

In the system, the lower portion of the fuel tank contains a body of liquid propane and the upper portion of the fuel tank contains a quantity of vaporous propane, with these two states Iof the propane in equilibrium under the prevailing pressure-temperature conditions in the fuel tank. Propane has substantial volatility over the ambient temperature ran-ge; however, at temperatures of about 30 F. and below, the vapor pressures are relatively low, and at temperatures of about 100 F. and above, the vapor pressures are relatively high, and at temperatures in the general range of 50 F. to 90 F., the vapor pressures are moderate. It is highly desirable to operate the internal combustion engine on a combustible mixture 'of vaporous propane and air; whereby at temperatures above about 50 F., adequate vaporous propane is ordinarily generated in the fuel tank to supply the requirements of the engine; however, at temperatures below about 50 F., the rate of generation of vaporous propane in the fuel tank is inadequate to supply the requirements of the engine.

In order to overcome this diiculty, it is conventional practice to incorporate in such railway refrigerator car a preheater for vaporizing the liquid propane, so as to supply the vaporous propane requirements of the engine during cold weather, as explained above. However, the preheater is ordinarily of the open-flame type that requires starting with vaporous propane. Hence, in exceedingly cold weather, below about 30 F., substantial difficulty is encountered in startin-g the operation of the preheater. Moreover, such preheaters, although widely used in such railway refrigerator cars, are not only troublesome in exceedingly cold weather, as explained above, but they constitute a major fire hazard, since the openflame burning of propane vapor is altogether unsatisfactory from the standpoint of safety.

While the foregoing discussion has been set forth in terms of propane, as the LPG fuel, the same considerations apply to butane and to the other members of this class of petroleum fuels.

Accordingly, it is a general object of the present invention to provide an improved and simplified system for supplying vaporous LPG fuel to an internal combustion engine that does not require a pheheater of the openflame type.

Another object 'of the invention is to provide an irnvproved LPG fuel supply system for an internal combus- Mice tion engine, wherein facility is provided for starting the engine with the initial quantity of vaporous fuel in the associated fuel tank, and including a vaporizer arranged in good heat-exchange relation with the engine, whereby the heat produced by the initial running of the engine renders operative the vaporizer, so that the liquid fuel in the fuel tank may be converted to vaporous fuel in order to sustain the operation of the engine.

A further object of the invention is to provide a fuel supply system of the character described, wherein the engine may be readily started in the coldest weather, and wherein the running engine then produces its own supply of vaporous fuel from liquid fuel in the fuel tank, whereby continued running of the engine is assured.

A further object of the invention is to provide a fuel supply system of the character described, wherein the running engine renders effective the vaporizer to produce vaporous fuel in a quantity greatly in excess of the requirements of the engine, so that the excess vaporous fuel may be supplied to other devices or auxiliaries that are 'operated by vaporous fuel.

A still further object of the invention is to provide a fuel supply system of the character described that incorporates safety devices rendering it altogether safe in operation and simple to control.

Further features of the invention pertain to the particular connection and arrangement of the elements of the fuel supply system, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specication, taken in connection with the accompanying drawing, in which:

The single figure is a diagrammatic illustration of an LPG fuel supply system for an internal combustion engine and embodying the present invention.

Referring now to the drawing, the fuel supply system there illustrated and embodying the features of the present invention, comprises a fuel storage tank 10' of the pressure type adapted to contain a LPG fuel, such as propane. As illustrated, the tank 10 is arranged in a substantially horizontal position, whereby the lower portion thereof contains a body 11a of the fuel in the liquid state and the upper portion thereof contains a quantity 11b of the fuel in the vaporous state, with the body 11a and the quantity 11b in the respective liquid and vaporous states in equilibrium with each other under the prevailing pressure-temperature conditions in the tank 10, in a well-known manner. Thus, it will be appreciated, that should the pressure of the quantity 11b be reduced, some of the fuel in the body 11a would boil off to produce or generate some additional vaporous fuel, so as simultaneously to' increase the pressure of the quantity 11b and to cool both the body 11a and the quantity 11b, thereby to establish the equilibrium mentioned under the new conditions of pressure-temperature in the fuel in the tank 10. Since propane is characterized by high volatility over the ambient temperature range, there is always some of the fuel in the vaporous st-ate, as long as there is a supply thereof in the liquid state at a temperature above the boiling point. However, the tank 10 is under relatively low pressure at temperatures of about 30 F. and below, and is under relatively high pressure at temperatures of F. and above, as is well understood.

Also, the system comprises an internal combustion engine 12 of any suitable type that is operative upon a combustible mixture of vaporous propane and air; which engine 12 includes a vaporous fuel supply pipe 13 and an exhaust gases pipe 14, as well as a carburetor device 15 that is connected to'the vaporous fuel supply pipe 13 and that is operative to mix air with the vaporous fuel and to inject the resulting combustible mixture into the cylinders of the engine 12 in proper timed sequence in the cycle of operation thereof, all in a conventional manner. Also, a blower 16 is operated by the engine 12; which blower 16 is provided with a casing 17 having an inlet 18 and an outlet 19. The blower 16 is operative to draw cooling air into the outlet 18, to circulate the cooling air through the casing 17 and into good heatexchange relation with the block of the engine 12, and then to discharge the resulting hot air from the casing 17 through the outlet 19 for a purpose more fully explained hereinafter.

A first fuel outlet pipe 20 is connected to the top of the tank in communicating relation with the quantity 11b of vaporous fuel in the upper portion of the tank 10; and a second fuel outlet pipe 21 is secured in place in an opening provided in the top of the tank 10 and projects downwardly thereinto and provided With an open bottom end disposed adjacent to the bottom of the tank 10 and in communicating relation with the body 11a of liquid fuel in the lower portion of the tank 10. The first fuel outlet pipe 20 is connected by a manually operable service valve 22 to supply a pipe 23; and the second fuel outlet pipe 21 is connected by a manually operable service valve 24 to a supply pipe 25. The supply pipe 23 is protected against over pressure by a connected high pres" sure relief valve 26; and, similarly, the supply pipe 25 is protected against over pressure by a connected high pressure relief valve 27.

Also, the system comprises a manifold 28, and a main vapor feed pipe 29. A single stage pressure regulator 30 is provided that includes a high-pressure inlet connected to the manifold 28 and a low-pressure outlet connected to the main vapor feed pipe 29. The vaporous feed supply pipe 13 extending to the carburetor 15 is connected to the manifold 28; while the main vapor feed pipe 29 extends to supply other devices or auxiliaries, not shown, that require the supply thereto of vaporous fuel at modest pressure. A back pressure valve 31 is provided that includes an inlet connected to the manifold 28 and an outlet connected to the supply pipe 23.

Further, the system comprises manually operable valve mechanism 40, including a first valve casing 41 housing a rotatable ported block 42, a second valve casing 43 housing a rotatable ported block 44, and a manually operable handle lever 45 mounted for pivotal movements between start and run positions and commonly operatively connected to the two ported blocks 42 and'44, as indicated at 46. The casing 41 has first and second inlets respectively connected to the

supply pipes

23 and 25, and an outlet connected to a transfer pipe 47; while the casing 43 has an inlet connected to the transfer pipe 47, and first and second outlets respectively connected to the manifold 28 and to a pipe 51. Also, a check valve 52 is provided that has an inlet connected to the pipe 51 and an outlet connected to a pipe 53. In the valve mechanism 40, when the manual lever 45 occupies its start position, the block 42 is actuated to the position illus` trated, so that the supply pipe 23 is connected by the block 42 to communicate with the transfer pipe 47, and so that the block 42 closes the supply pipe 25, and the block 44 is actuated to the position illustrated, so that the transfer pipe 47 is connected by the block 44 to the manifold 28 and so that the block 44 closes the pipe 51. On the other hand, when the manual lever 45 occupies its run position, the block 42 is actuated to connect the supply pipe 25 to the transfer pipe 47 and to close the connection between the supply pipe 23 and the casing 41, and the block 44 is actuated to connect the transfer pipe 47 to the pipe 51 and to close the connection between the manifold 28 and the casing 41.

Further, the system -comprises a vaporizer 62 having an inlet connected to the pipe 53 and an Qutlet connected to the manifold 23. The exhaust gases pipe 14 from the engine 12 includes a heat'exchanger 61 operatively associated in good heat-exchange relation with the vaporizer 60. Specifically, a casing 62 is provided that encloses the vaporizer 60 and the heat exchanger 61; which casing 62 is provided with an inlet connected to the outlet 19 from the blower 16, and an outlet communicating with the atmosphere.

Considering now the mode of operation of the system, and assuming that the engine 12 is to be started, when it is cold, and that the weather is cold, so that only a relatively loW pressure is present in the storage tank lil, the manual lever 45 is operated into its start position, and the service valves 22 and 24 are operated into their open positions. With the manually operable valve mechanism 40 in its start position, the vaporous fuel from the quantity 11b proceeds from the upper portion of the tank 10 via the

elements

20, 22, 23, 41, 47 and 43 into the manifold 28; from the manifold 28 the vaporous fuel is throttled by the regulator 30 into the main vapor feed pipe 29 at a predetermined modest pressure; and from the manifold 28 the vaporous fuel proceeds directly into the carburetor 15. In the carburetor 15, a combustible mixture is produced by the addition of air into the vaporous fuel; and this combustible mixture is supplied to the cylinders of the engine 12. It may be assumed that the engine 12 is cranked or started promptly in a conventional manner; whereby heat is developed in the block of the engine 12 and heat is rejected from the engine 12 via the exhaust gases passing therefrom through the exhaust gases pipe 14. The blower 16 is operated by the operating engine 12, so that heat is removed from the engine block by the cooling air circulated by the blower 16 causing hot air to pass via the outlet 19 into the casing 62; and, of course, the heat exchanger 61 is heated by the hot exhaust gases passing therethrough, since the element 61 is arranged in the exhaust gases pipe 14, as previously noted. The hot air passing into the casing 62 is directed into heat-exchange relation with the heat exchanger 61, so that the temperature of the hot air mentioned is substantially elevated. The exceedingly hot air then passes into heat-exchange relation with the vaporizer 60 and thence to the atmosphere; whereby the temperature of the vaporizer 60 is elevated in an obvious manner.

After the operator cranks or starts the engine 12, and determines that it is operating satisfactorily at steady state, he shifts the lever 45 from its start position to its run position. With the manually operable valve mechanism 40 in the run position, the liquid fuel from the body 11a proceeds from the lower portion of the tank 10 Via the

elements

21, 24, 25, 41, 47, 43, 51, 52 and 53 into the vaporizer 60. In the hot vaporizer 60, the liquid fuel is immediately flashed into vaporous fuel and proceeds into the manifold 28 from which it is throttled into the main vapor feed pipe 29. Also, from the manifold 28 the vaporous fuel is supplied via the vaporous fuel supply pipe 13 to the carburetor 15; whereby the operation of the engine 12 is sustained, in an obvious manner.

Since the operator may shift the manual lever 45 from its start position into its run position very shortly after operation of the engine 12 is started, there is always enough vaporous fuel in the quantity 11b, even in subzero weather, for the present purpose; however, in cold weather, the operator should so shift the manual lever 45 promptly, as it is apparent that the accumulated quantity 11b of vaporous fuel is consumed faster by the engine 12 than it is being automatically generated in the tank 10. In moderate and warm weather, the operator can take his time about shifting the manual level 45, as explained above, without danger of consuming all of the available vaporous fuel by the running engine 12; however, it is contemplated that the operator will always shift the manual lever 45 promptly, after he starts the engine 12 and determines that it is running satisfactorily. Thus, the

manual lever 45 always occupies its run position, during the normal running of the engine 12.

In the normal running of the engine 12, the check valve 52 prevents high pressure in the manifold 28 and in the vaporizer 60 from causing blow-back through the pipe 53 and into the pipe 51, so as to prevent liquid fuel from moving backwards from the pipe 51 through the

elements

43, 47, 41, 25, 24 and 21 back into the body 11a contained in the tank 10. On the other hand, in the event of an abnormally high pressure of the vaporous fuel in the manifold 28, the back pressure valve 31 opens to throttle the vaporous fuel from the manifold 28 back into 'the supply pipe 23; whereby the same may pass through the elements 22 and 20 back into the quantity 11b contained in the upper portion of the tank 10. Of course, the

relief valves

26 and 27 serve the usual high pressure relief functions with respect to the

respective supply pipes

23 and 25, effecting the escape of the high pressure vaporo us fuel to the atmosphere in the event of abnormally high and dangerous pressures in the

respective supply pipes

23 and 25.

When operation of the engine 12 is to be arrested, the service valves 22 and 24 are closed to cut-off the supply of vaporous fuel from the fuel outlet pipe to the supply pipe 23 and to cut-off the supply of liquid fuel from the fuel outlet pipe 21 to the supply pipe 25. Also, at this time, the manual lever 45 is ordinarily returned back into its start position, so as again to condition the system for subsequent restarting of the engine. Of course, closure of the services valves 22 and 24 insures that no fuel is supplied 'into the manifold 28 whereby operation of the engine 12 and the other devices or auxiliaries connected to the main vapor supply pipe 29 are arrested.

As previously explained, the engine 12 may drive an associated refrigeratng machine capable of both direct operation to effect cooling of a lading chamber and heatpump operation to effect heating of the lading chamber, such, for example, as disclosed in U.S. Patent No. 2,887,853, granted on May 26, 1959 to Paul Talmey; whereby, as disclosed in the Talmey Patent, the refrigerating machine, the engine 12, the fuel storage tank 10, and the other elements of the fuel supply system would then be incorporated in the associated railway refrigerator car, not shown.

While the present fuel supply system is ideally suited for use in a railway refrigerator car, as explained above, the same is of general utility; whereby in the interest of brevity no showing of the details of this particular application is considered necessary. Furthermore, other applications of the fuel supply system to internal combustion engines driving other types of loads are equally obvious and well understood. The system also has the advantage that it employs heat in the vaporizer 62 that is rejected by the engine 12, thereby increasing the overall efiiciency of the system, as compared to conventional systems employing fuel burners for the purpose of vaporizing the liquid fuel, as previously explained.

In view of the foregoing, it is apparent that there has been provided a fuel supplysystern for an internal combustion engine operating on LPG fuel in the vapor phase, with admixed air, that insures easy starting of the engine, even in the coldest weather, and that insures proper running of the engine after starting thereof. Also, the system incorporates the necessary safety devices and arrangements so that safe and proper operation of the engine is assured, even though the engine is unattended for long time intervals.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications that fall within the true spirit and scope of the invention.

What is claimed is:

1. In combination, a tank adapted to contain liquefied petroleum fuel that is characterized by high volatility so that it is under relatively low vapor pressure at 30 F. and under relatively high vapor pressure at F., whereby within this pressure range the lower portion of said tank may contain a body of the fuel in the liquid state and the upper portion of said tank may contain a quantity of the fuel in the vapor state with the two states of the fuel in equilibrium under the prevailing pressuretemperature conditions thereof in said tank, a first fuel outlet pipe connected to the upper portion of said tank above the operative range of liquid fuel levels therein and communicating with the quantity of vaporous fuel in said tank, a second fuel outlet pipe connected to the lower portion of said tank below the operative range of liquid fuel levels therein and communicating with the body of liquid fuel in said tank, a manifold, an internal combustion engine provided with a vaporous fuel supply pipe connected to said manifold, a liquid fuel vaporizer having an inlet and an outlet and arranged in good heat-exchange relation 4with said engine, the outlet of said vaporizer being connected to said manifold, valve mechanism connected to said first and second fuel outlet pipes and to said manifold and to the inlet of said vaporizer, said valve mechanism having a start position and a run position, said valve mechanism in its start position opening said first fuel outlet pipe to said manifold and closing said second fuel outlet pipe from the inlet of said vaporizer, said valve mechanism in its run position closing said first fuel outlet pipe from said manifold and opening said second fuel outlet pipe to the inlet of said vaporizer, and means for selectively operating said valve mechanism between its start position and its run position. p

2. In combination, a tank adapted to contain liquefied petroleum fuel that is characterized by high volatility so that it is under relatively low vapor pressure at 30 F. and under relatively high vapor pressure at 100 F., whereby Within this pressure range the lower portion of said tank may contain a body of the fuel in the liquid state and the upper portion of said tank may contain a quantity of the fuel in the vapor state with the two states of the fuel in equilibrium under the prevailing pressure-temperature conditions thereof in said tank, a first fuel outlet pipe connected to the upper portion of said tank above the operative range of liquid fuel levels therein and communicating with the quantity of vaporous fuel in said tank, a second fuel outlet pipe connected to the lower portion of said tank below the operative range of liquid fuel levels therein and communicating with the body of liquid fuel in said tank, a manifold, a back-pressure valve having a high-presure inlet connected to said manifold and a low-pressure outlet connected to said first fuel outlet pipe, an internal combustion engine provided with a vaporous fuel supply pipe connected to said manifold, a liquid fuel vaporizer having an inlet and an outlet and arranged in good heat-exchange relation with said engine, the outlet of said vaporizer being connected to said manifold, valve mechanism connected to said first and second fuel outlet pipes and to said manifold and to the inlet of said vaporizer, said valve mechanism having a start position and a run position, said valve mechanism in its start position opening said first fuel outlet pipe to said manifold and closing said second fuel outlet pipe from the inlet of said vaporizer, said valve mechanism in its run position closing said first fuel outlet pipe from said manifold and opening said second fuel outlet pipe to the inlet of said vaporizer, and means for selectively operating said valve mechanism between its start position and its run position.

3. In combination, a tank adapted to contain liquefied petroleum fuel that is characterized by high volatility so that it is under relatively low vapor pressure at 30 F. and under relatively high vapor pressure at 100 F.,

whereby within this pressure range the lower portion of said tank may contain a body of the fuel in the liquid state and the upper portion of said tank may contain a quantity of the fuel in the vapor state with the two states of the fuel in equilibrium under the prevailing pressuretemperature conditions thereof in said tank, a first fuel outlet pipe connected to the upper portion of said tank above the operative range of liquid fuel levels therein and communicating with the quantity of vaporous fuel in said tank, a second fuel outlet pipe connected to the lower portion of said tank below the operative range of liquid fuel levels therein and communicating with the body of liquid fuel in said tank, a manifold, an internal combustion engine provided with a vaporous fuel supply pipe connected to said manifold, a liquid fuel vaporizer having an inlet and an outlet and arranged in good heatexchange relation with said engine, the outlet of said vaporizer being connected to said manifold, a check valve having an inlet and an outlet, the outlet of said check valve being connected to the inlet of said vaporizer, valve mechanism connected to said first and second fuel outlet pipes and to said manifold and to the inlet of said check valve, said valve mechanism having a start position and a run position, said valve mechanism in its start position opening said first fuel outlet pipe to said manifold and closing said second fuel outlet pipe from the inlet of said check valve, said valve mechanism in its run position closing said first fuel outlet pipe from said manifold and opening said second fuel outlet pipe to the inlet of said check valve, and means for selectively operating said valve mechanism between its start position and its run position.

4. In combination, a tank adapted to contain liquefied petroleum fuel that is characterized by high volatility so that it is under relatively low vapor pressure at 30 F. and under relatively high vapor pressure at 100 F., whereby within this pressure range the lower portion of said tank may contain a body of the fuel in the liquid state and the upper portion of said tank may contain a quantity of the fuel in the vapor state with the two states of the fuel in equilibrium under the prevailing pressure-temperature conditions thereof in said tank, a first fuel outlet pipe connected to the upper portion of said tank above the operative range of liquid fuel levels therein and com-v municating with the quantity of vaporous fuel in said tank,

a second fuel outlet pipe connected to the lower portion of said tank below the operative range of liquid fuel levels therein and communicating with the body of liquid fuel in said tank, a manifold, an internal combustion engine provided with a vaporous fuel supply pipe and an exhaust gases pipe, said vaporous fuel supply pipe being connected to said manifold, a liquid fuel vaporizer having an inlet and an outlet, a casing enclosing said vaporizer, said exhaust gases pipe extending through said casing, means including a blower for circulating cooling air over said engine and thence through said casing, wherein the hot circulated air introduced into said casing is first circulated over said exhaust gases pipe extending therethrough and then into heat-exchange relation with said vaporizer enclosed therein, the outlet of said vaporizer being connected to said manifold, valve mechanism connected to said rst and second fuel outlet pipes and to said manifold and to the inlet of said vaporizer, said valve mechanism having a start position and a run position, said valve mechanism in its start position opening said rst fuel outlet pipe to said manifold and closing said second fuel outlet pipe from the inlet of said vaporizer, said valve mechanism in its run position closing said first fuel outlet pipe from said manifold and opening said second fuel outlet pipe to the inlet of said vaporizer, and means for selectively operating said valve mechanism between its start position and its run position.

References Cited bythe Examiner UNITED STATES PATENTS mercial Car Journal; January 1934; pages 2O and 21.

MARK NEWMAN, Primary Examiner.

RICHARD B. llILKINSON, Examiner.

Claims

1. IN COMBINATION, A TANK ADAPTED TO CONTAIN LIQUEFIED PETROLEUM FUEL THAT IS CHARACTERIZED BY HIGH VOLATILITY SO THAT IT IS UNDER RELATIVELY LOW VAPOR PRESSURE AT 30*F. AND UNDER RELATIVELY HIGH VAPOR PRESSURE AT 100*F., WHEREBY WITHIN THIS PRESSURE RANGE THE LOWER PORTION OF SAID TANK MAY CONTAIN A BODY OF THE FUEL IN THE LIQUID STATE AND THE UPPER PORTION OF SAID TANK MAY CONTAIN A QUANTITY OF THE FUEL IN THE VAPOR STATE WITH THE TWO STATES OF THE FUEL IN EQUILIBRIUM UNDER THE PREVAILING PRESSURETEMPERATURE CONDITIONS THEREOF IN SAID TANK, A FIRST FUEL OUTLET PIPE CONNECTED TO THE UPPER PORTION OF SAID TANK ABOVE THE OPERATIVE RANGE OF LUQID FUEL LEVELS THEREIN AND COMMUNICATING WITH THE QUANTITY OF VAPOROUS FUEL IN SAID TANK, A SECOND FUEL OUTLET PIPE CONNECTED TO THE LOWER PORTION OF SAID TANK BELOW THE OPERATIVE RANGE OF LIQUID FUEL LEVELS THEREIN AND COMMUNICATING WITH THE BODY OF LIQUID FUEL IN SAID TANK, A MANIFOLD, AN INTERNAL COMBUSTION ENGINE PROVIDED WITH A VAPOROUS FUEL SUPPLY PIPE CONNECTED TO SAID MANIFOLD, A LIQUID FUEL VAPORIZER HAVING AN INLET AND AN OUTLET AND ARRANGED IN GOOD HEAT-EXCHANGE RELATION WITH SAID ENGINE, THE OUTLET OF SAID VAPORIZER BEING CONNECTED TO SAID MANIFOLD, VALVE MECHANISM CONNECTED TO SAID FIRST AND SECOND FUEL OUTLET PIPES AND TO SAID MANIFOLD AND TO THE INLET OF SAID VAPORIZER, SAID VALVE MECHANISM HAVING A START POSITION AND A RUN POSITION, SAID VALVE MECHANISM IN ITS START POSITION OPENING SAID FIRST FUEL OUTLET PIPE TO SAID MANIFOLD AND CLOSING SAID SECOND FUEL OUTLET PIPE FROM THE INLET OF SAID VAPORIZER, SAID VALVE MECHANISM IN ITS RUN POSITION CLOSING SAID FIRST FUEL OUTLET PIPE FROM SAID MANIFOLD AND OPENING SAID SECOND FUEL OUTLET PIPE TO THE INLET OF SAID VAPORIZER, AND MEANS FOR SELECTIVELY OPERATING SAID VALVE MECHANISM BETWEEN ITS START POSITION AND ITS RUN POSITION.