US3690100A

US3690100A - Method of operating a reaction propulsion engine and fuels therefor

Info

Publication number: US3690100A
Application number: US554597A
Authority: US
Inventors: Robert L Wolf; Christopher J Cowlin
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1961-11-13
Filing date: 1966-06-01
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12

Abstract

1. The method of operating a ram air reaction propulsion system comprising: directing a fuel capable of endothermically dissociating at temperatures between about 200* to 2,000* F. into indirect heat exchange between the inlet ram air of the system and said fuel to bring about the endothermic dissociation of at least a portion of the fuel by the transfer, prior to mechanical compression of the ram air, of a portion of the heat energy from the ram air of the system to the fuel prior to combustion of the fuel in the ram air; utilizing a portion of the ram air heated fuel to mechanically compress the fuel cooled ram air; burning the fuel exhausting from said further air compressing step in the said further compressed air; and thereafter expanding the combustion products through an outlet nozzle of the system.

Description

llnited States Patent Wolf at al.

[54] METHOD OF OPERATING A REACTION PROPULSION ENGINE AND FUELS THEREFOR Inventors: Robert L. Wolf, Chesterfield County; Christopher J. Cowlin, Richmond, both of Va.

Assignee: Texaco Inc., New York, NY.

Filed: June 1, 1966 Appl. No.: 554,597

Related US. Application Data Continuation of Ser. No. 325,352, Nov. 20, 1963, abandoned, which is a continuation-inpart ofSer. No. 152,097,Nov. 13,1961.

References Cited UNITED STATES PATENTS 12/1952 Phanery ..60/5.6

TURBINE BY- PASS VA LVE AIR r me rueuqet TURBINE TEMPERATURE SPEED SENSING MEANS 1 Sept. 12, 1972 3,067,594 12/1962 Bland ..60/35.6

Primary ExaminerSamuel Feinberg Attorney-Stowell and Stowell EXEMPLARY CLAIM 1. The method of operating a ram air reaction propulsion system comprising: directing a fuel capable of endothermically dissociating at temperatures between about 200 to 2,000 F. into indirect heat exchange between the inlet ram air of the system and said fuel to bring about the endothermic dissociation of at least a portion of the fuel by the transfer, prior to mechanical compression of the ram air, of a portion of the heat energy from the ram air of the system to the fuel prior to combustion of the fuel in the ram air; utilizing a portion of the ram air heated fuel to mechanically compress the fuel cooled ram air; burning the fuel exhausting from said further air compressing step in the said further compressed air; and thereafter expanding the combustion products through an outlet nozzle of the system.

3 Claims, 2 Drawing Figures o znp sso JFfiZUMP TURBINE COMBUSTOR NOZZLE -I COMPRESSOR SEQkT JRE F SENSING MEANS TANK METHOD OF OPERATING A REACTION PROPULSION ENGINE AND FUELS THEREFOR This application is a continuation application of my application, Ser. No. 325,352, filed Nov. 20, 1963 now abandoned, and application, Ser. No. 325,352 is a continuation-in-part of our co-pending application, Ser. No. 152,097, R. L. Wolfet al., filed Nov. 13, 1961.

This invention relates to reaction propulsion engines and to method of operating such engines. In one particular aspect, the present invention relates to fuels suitable for use in air-breathing reaction propulsion engines capable of operation at hypersonic speeds.

The use of rocket propulsion is generally inefficient because of the inherently low fuel impulse value of chemical rocket systems. The usual ram jet cycles are unattractive at hypersonic speeds because at speeds above about Mach 8 the amount of energy at the air inlet is so great that the additional heat liberated by combustion of the fuel in the ram air is mainly expended in dissociating the components of the combustion gases. The energy absorbed by such fuel or combustion product dissociation is only partially recovered on recombination when the gases are expanded through the exit nozzle to the atmosphere.

These difficulties, in the ram jet cycles, can be avoided by transferring a portion of the energy of the inlet air to the fuel by heat exchange between the inlet air and the fuel. The energy thus transferred is utilized at least in part by expanding the fuel in an impulse reaction nozzle and/or a turbine driving an air compressor.

In general, the invention comprises the method of operating an air-breathing propulsion system comprising transferring a portion of energy from the inlet air of the system to the fuel supply by indirect heat exchange between the inlet air and a fuel capable of endothermically dissociating at temperatures between about 200 to 2,000 E, converting the useful work at least a portion of the heat transferred to the said fuel by direct expansion of at least a portion of the fuel, burning at least a portion of the said fuel in the inlet air, and expanding the combustion products through an impulse expansion nozzle.

The invention will be more particularly described with reference to the drawings wherein:

FIG. 1 is a schematic representation of the operation of such a system at high Mach numbers; and

FIG. 2 is a schematic representation of a system of the invention at lower Mach numbers.

Referring to FIG. 1 of the drawings, fuel is pumped from the fuel tank through an indirect heat exchanger wherein its temperature is raised by heat exchange with the hot incoming ram air.

The rate of flow of fuel to the ram air heat exchanger may be controlled within wide limits by varying the output from the fuel pump or by providing a control valve in the outlet line from the fuel pump to the heat exchanger. The pump output volume or the control valve may be manually controlled and/or as indicated in the drawing, the control of the pump output or control for an output control valve may be provided by the compressor outlet temperature sensing means which would insure that sufficient fuel is passed to the heat exchanger to maintain limits on the turbine inlet temperature and the compressor discharge temperature.

The heated fuel passes through a turbine bypass valve where only the amount of heated fuel necessary to operate the turbine is actually passed through the turbine. The turbine operates the pump which passes the fuel from the fuel storage tank to the heat exchanger and also the turbine drives the air compressor which compresses the air after it has left the heat exchanger prior to passage of the air to the combustor. The heated fuel not required for turbine operation may be passed directly to the combustor where it is burned, along with the fuel exhausting from the turbine, with the air from the air compressor. The combustion gases are passed to the atmosphere through the expansion nozzle as indicated in the drawing.

It will also be appreciated that the fuel passing directly from the turbine bypass valve to the combustor may be expanded through a thrust nozzle positioned within the combustor or all or a portion of this fuel may be expanded through a thrust nozzle external of the combustor. The use of such a thrust nozzle has particular utility where the amount of fuel needed to cool the ram air is greater than the amount which could be burned stoichiometrically with the available air supply.

The turbine bypass valve may be preset for the particular mission of the vehicle to be driven by the reaction engine or, as shown in FIG. '1, the bypass valve may be provided with a controller 10. The controller 10 may regulate the turbine bypass valve in accordance with the temperature of the fuel passing to the turbine or by sensing the speed of the turbine, thereby preventing overheating and/or overspeeding of the turbine or overspeeding of the air compressor driven thereby. Further, the controller for the turbine bypass valve may be fuel or compressor temperature responsive, vehicle altitude or speed responsive, or a combination of two or more of these factors.

Operation of the system of the invention at low Mach numbers is schematically represented in Flg. 2. Operation is similar to that shown in FIG. 1 except that a regenerative heat exchanger is included in the fuel heating cycle to provide additional heat for the fuel for operation of the turbine. As in thesystem illustrated in FIG. 1, the fuel is pumped to the heat exchanger and its temperature raised by heat exchange with the incoming ram air. The heated fuel is then passed to the turbine bypass valve and sufficient fuel is diverted for use in operation of the turbine. Interposed between the turbine bypass valve and the turbine is a temperature modulating valve and a mixer. A portion of the fuel heated by means of the incoming air is further heated by the regenerative heat exchange in the combustion zone and passed to the mixer wherein it is returned to the body of heated fuel to be expanded through the turbine. It is the function of the turbine temperature modulating valve to pass sufiicient fuel to the regenerative heat exchanger to provide that the fuel mixture finally expanded through the turbine has a high enough energy value to satisfy the requirements of the turbine in operating the fuel pump and the air compressor. The heated fuel, together with the fuel exhausting from the turbine, may be combined with the compressed air and are burned in the combustor and passed through a nozzle to the atmosphere as before.

As discussed with reference to the embodiment shown in FIG. 1, the rate of flow of fuel to the ram air heat exchanger may be controlled within wide limits by varying the output from the fuel pump or by providing a control valve in the outlet line from the fuel pump to the heat exchanger. The pump output volume or the control valve may be manually controlled and/or as indicated in the drawing, the control of the pump output or control for an output control valve may be provided by the compressor outlet temperature sensing means which would insure that sufficient fuel is passed to the heat exchanger to maintain limits on the turbine inlet temperature and the compressor discharge temperature.

For high cooling efficiency and to provide a high absorption of energy per pound of fuel, it is desirable that the fuel selected have a high heat capacity within the expected operating temperature range of 200 F. to about 2,000 F. At the same time, for efficient conversion of energy into thrust in the expansion process, the fuel should be one which provides low average molecular weight components in the exhaust gases. It has been discovered that fuels which undergo endothermic decomposition or dissociation at temperatures which will provide maximum cooling of the inlet air are particularly suited for use in such a system. The most suitable fuels will dissociate at these temperatures to hydrogen and other relatively low molecular weight compounds without the formation of free carbon particles. Preferred examples of such fuels are ammonia, methyl alcohol, ethylene glycol, and cyclohexane.

The preferred high heat capacity fuels, ammonia, methyl alcohol, ethylene glycol and cyclohexane, dissociate into hydrogen and nitrogen, hydrogen and carbon monoxide, hydrogen and carbon monoxide, and hydrogen and benzene, respectively. The dissociation is endothermic and the resulting gaseous products are of low average molecular weight and are exceptionally clean; that is, they and their combustion products have little or no tendency to foul the engine as they contain no free carbon.

When such fuels are used at relatively low flight speeds below about Mach 1.5 in a system where the incoming air and a regenerative heat exchanger are used to heat the fuel prior to combustion, there will be very little heating of the fuel by the incoming air. Most of the heat required to decompose and/or evaporate the fuel and heat the fuel to the turbine inlet temperature required to operate the air compressor will come from the regenerative heat exchanger. As the flight speed and the temperature of the inlet air increase, there will be more cooling of the air ahead of the compressor and hence more heating of the fuel prior to its passage to the turbine and/or combustion zone. Thus, less heat will be required from the combustion zone via the regenerative heat exchanger and less fuel will be programmed through the regenerative heat exchanger located in the combustion area prior to its expansion across the turbine. At still higher flight speeds, all of the required heat will come from the cooling of the inlet air and no heat will be taken from the combustion zone via the regenerative heat exchanger.

The air to fuel indirect heat exchanger located ahead of the air compressor serves three main purposes. The first is to increase the available turbine work of the fuel by heat addition without combustion while lowering the work required to compress the air thereby making the cycle more efficient. The second is to cool the incoming air to acceptable temperature levels, preferably below 1,200 F., to avoid overheating the compressor. The third is to increase the density of the air through cooling to give a higher mass flow per unit compressor frontal area and a resultant higher level of thrust.

At higher flight Mach numbers, it becomes increasingly important to cool the incoming air, down to acceptable levels for the compressor. It then becomes necessary to run the heat exchanger richer than at lower Mach numbers, i.e., using an amount of fuel in excess of that which can be expanded across the turbine without overspeeding the rotating assembly. The excess fuel is passed either directly to the combustor or to a thrust nozzle mounted in the combustor for combustion along with the fuel that has been expanded across the turbine. A portion of the fuel used in cooling the inlet air may be burned stoichiometrically with the air in the combustor while the remainder may be expanded directly to the atmosphere through a separate thrust nozzle, not shown in the drawings. The proportion separately expanded is determined by the maximum exhaust gas temperature and the maximum degree of dissociation to be maintained. The use of endothermically dissociating fuels according to the process of our invention minimizes the expenditure of uncombusted fuel.

EXAMPLE I An engine of the type illustrated in FIG. 1 can be operated efficiently through the velocity range from about Mach 4 to about Mach 10 at altitudes up to 150,000 feet using the endothermically dissociating fuels of the invention while holding the compressor inlet temperature below l,200 F. by heat exchange between the inlet air and the fuel.

EXAMPLE II An engine of the type illustrated in FIG. 2 can be operated efficiently through the velocity range from static launch to Mach l0 and at altitudes up to 150,000 feet using the endothermically dissociating fuels of the invention. Below about Mach 4 heat is added to the fuel in the regenerative heat exchanger to provide enough energy to drive the turbine without the use of auxiliary fuel combustion ahead of the turbine. Above about Mach 6 none of the fuel is passed to the regenerative heat exchanger as inlet air heating of the fuel provides all of the energy requirement of the turbine.

We claim:

1. The method of operating a ram air reaction propulsion system comprising: directing a fuel capable of endothermically dissociating at temperatures between about 200 to 2,000 F. into indirect heat exchange between the inlet ram air of the system and said fuel to bring about the endothermic dissociation of at least a portion of the fuel by the transfer, prior to mechanical compression of the ram air of a portion of the heat energy from the ram air of the system to the fuel prior to combustion of the fuel in the ram air; utilizing a portion of the ram air heated fuel to mechanically compress the fuel cooled ram air; burning the fuel exhausting from said further air compressing step in the said further compressed air; and thereafter expanding the combustion products through an outlet nozzle of the system.

2. The method defined in claim 1 wherein the ram air is further compressed by expanding the ram air heated fuel across a turbine of a turbocompressor. 5 3. The inyention defined in claim 2 wherein the fuel is selected from the group consisting of ammonia, methyl alcohol, ethylene glycol and cyclohexane.

Claims

1. The method of operating a ram air reaction propulsion system comprising: directing a fuel capable of endothermically dissociating at temperatures between about 200* to 2,000* F. into indirect heat exchange between the inlet ram air of the system and said fuel to bring about the endothermic dissociation of at least a portion of the fuel by the transfer, prior to mechanical compression of the ram air of a portion of the heat energy from the ram air of the system to the fuel prior to combustion of the fuel in the ram air; utilizing a portion of the ram air heated fuel to mechanically compress the fuel cooled ram air; burning the fuel exhausting from said further air compressing step in the said further compressed air; and thereafter expanding the combustion products through an outlet nozzle of the system.

2. The method defined in claim 1 wherein the ram air is further compressed by expanding the ram air heated fuel across a turbine of a turbocompressor.

3. The invention defined in claim 2 wherein the fuel is selected from the group consisting of ammonia, methyl alcohol, ethylene glycol and cyclohexane.