US2745251A - Apparatus for atomization of a liquid fuel - Google Patents

Description

May 15, 1956 R. M. SCHIRMER 2,745,251

APPARATUS FOR ATOMIZATION OF A LIQUID FUEL Filed Dec. 26, 1951 2 Sheets-Sheet 1 FUEL CONTROL DENSITY CONTROL AIR ELOC ITY CONTROL FIG. 2 I F/G.

INVENTOR. R. M. SCHIRMER A T TOPNEYS May 15, 1956 R. M. SCHIRMER APPARATUS FOR ATOMIZATION OF A LIQUID FUEL Filed Dec. 26, 1951 2 Sheets-Sheet 2 A TTORNEKS process.

United States Patent APPARATUS FOR ATOMIZATION on A LIQUID FUEL Robert M. Schirmer, Bartlesville, Okla., assi@or to Phillips Petroleum Company, a corporation of Delaware Application December 26, 1951, Serial No. 263,171

Claims. (Cl. SO-39.74}

This invention relates to a continuous combustion apparatus. In another of its aspects this invention relates to an improved fuel combustion apparatus for a gas turbine power plant. In still another of its aspects this in vention relates to apparatus for controlling fuel atomization and automatically sensing and compensating for changes in combustor inlet air density, linear air velocity and the fuel flow.

In the usual continuous combustion device such as a turbojet engine, the incoming air from the mechanical compressor is divided into two main portions. One portion of the air introduced immediately adjacent to the fuel nozzle is called primary air and is supplied in such manner as to maintain a near stoichiometric mixture with the fuel in the combustion zone (primary combustion zone). The other portion, termed secondary air, is introduced downstream in the direction of air flow from the primary combustion zone into a so-called secondary combustion zone and serves to quench combustion and to dilute and cool the combustion gases to temperatures which the turbine can withstand. The fuel is dispersed in the air of the primary combustion zone in some manher to form a mixture of fuel and air which is neither too rich nor too lean (near stoichiometric) and which also permits stable and efficient propagation of the combustion The flow velocity through the primary combustion zone is maintained low in order not to exceed the effective transformation velocity. It is desirable, to induce a high degree of turbulence in the air supplied. In general it is desirable in the operation of a thermojet engine to obtain complete combustion withinthe primary combustion zone in order to prevent escape of unburned fuel out of the exhaust nozzle.

While the maintenance of a stable and efiicient combustion process cannot be achieved unless the relative proportions of fuel and air supplied to the primary combustion zone form an inflammable mixture, the manner in which the fuel is admitted, the size and distribution of the fuel particles, and other considerations relating to fuel dispersion and atomization all exert a major and often predominant effect upon the operational limits and combustion efiiciency. In the usual operation of a thermojet engine the fuel nozzle receives the fuel from a fuel metering control and delivers it to the combustion chamber in a dispersed state for combustion. Normally the outlet orifice of the fuel nozzle is fixed in size so that the atomization of a particular fuel is dependent upon a rate of flow of fuel therethrough. While it is true that variable area nozzles have been developed in order to obtain good atomization over a Wide range of fuel flow in an attempt to provide a solution of the atomization problem under changing, operating conditions, these devices have not been too successful. They do not provide for optimum stratification of the fuel-air mixture under all operating conditions. There still remains atomization problems encountered with changing conditions of air supplied to the combustion chamber.

The distribution of the fuel droplets dispersed in the 2,745,251 Patented May 15, 19.56

air stream in the primary combustion zone. is generally directly related to the combustion stability efiiciency achieved in the combustion chamber. Conditions which affect the optimum size and distribution of fuel droplets to the combustion chamber (atomization) include air density, linear air velocity through the combustion zone (primary combustion zone in the case of a turbojet engine) and the rate of flow of fuel to the fuel nozzles. For instance, with comparable rates of mass air flow in a jet engine, changes in air density such as those accompanying changes in altitude of the aircraft necessitate a change in fuel atomization in order to maintain high combustion efiiciency and stability. A decrease in the density of the air at constant linear velocity through the combustion zone requires a greater degree of atomization of the fuel in order to secure complete vaporization and combustion of the liquid fuel before .drop-out'of unburned fuel droplets occurs. Similarly at a comparable air density an increase in linear velocity of the air to the combustion zone requires finer fuel atomization to prevent incomplete vaporization of the fuel and dropout of unburned fuel particles within the combustion zone. However, fuel atomization under any operating condition reaches an optimum, usually dependent on combustor design, beyond which the increased homogeneity of the fuel-air mixture resulting therefrom destroys the stratified nature of the fuel-air mixture. As indicated stratification of the fuel and air within the combustion chamber is often the principal factor controlling the combustion process. At low fuel-air ratios, a rapid fuel vaporization (finer atomization) in a limited portion of the air flO'v is desirable to provide a local zone where near stoichiometric mixtures can be established. A nozzle that provides a fine fuel spray with a small degree of penetration should therefore serve best at low fuel-air ratios. As the fuel flow is increased with constant air mass flow, overenrichment of these local zones would result with the same fuel nozzle. Better results are obtained with a fuel nozzle that provides a coarser fuel spray with greater penetration range in order to involve a larger portion of the air with the fuel and to maintain the local optimum fuel-air ratio. Accordingly as the fuel-air ratio is progressively increased the combustion is served best by coarser and coarser fuel sprays, however, the optimum spray in the last analysis is determined by combustor design. Thus, in order to mainta'm high combustion efficiency during the changes in the conditions surrounding combustion of the fuel in the combustion chamber, such as is experienced in jet engine aircraft operation, it is necessary to atomize the fuel to such a degree in accordance with the conditions as to secure substantially complete vaporization and combustion of the fuel in the primary combustion zone. in the case of a turbojet engine for example, complete vaporization and combustion should take place in the primary combustion zone before the combustion gases are quenched by the on-rushing air in the secondary combustion zone and without loss of unburnt fuel in either the exhaust gases or drop-out of liquid fuel particles.

It is accordingly an object of this invention to provide an improved continuous combustion apparatus. A further object of this invention is to provide apparatus for obtaining stable combustion and high combustion ethciency during changes inair density, rate of fuel how and changes in linear air velocity supplied to the combustion zone. Another object of this invention is to provide apparatus for obtaining optimum fuel atomization under varying operating conditions.

Other objects and advantages of the invention will appear in the following more detailed description of the invention, taken in connection with the accompanying drawings in which:

Fig; l is a schematic representation of one embodiment of this invention as applied'to a turbo-jet engine;

Fig 2 is a schematic representation in cross section of a gas assist fuel nozzle; and

' Figs. 3a, 3b, and 3c areschematic representations of various electrical means for regulating the gas feed to theg as assist nozzle in accordance with the various detected'changes in. air density, linear air'veloeity, and rate. of fuel flow.

Ithas now been discovered that stable and efficient combustion can be maintained in a continuous flow combustion process in which changes in air density, linear air velocity and fuel flow are encountered by maintaining fuel atomization within a range which establishes sufiicient turbulence and vaporization of the fuel so as to maintain substantially all the combustion within the combustion zone.- .Further, it has been discovered that optimum atomization of a liquid fuel can be maintained by the use of a suitable gas-assist fuel nozzle in combi nation with suitable means to sense changes in air density, linear air velocity and fuel flow, and other devices associated therewith to control the assist gassupplied to the gas-assist fuel nozzle. The gas-assist fuel nozzle employed in the practice of this invention may be of any conventional type well known to those skilled in the art. A suitable fuel nozzle is one wherein gas is injected through tangential slots to strike the fuel issuing from the orifice of the nozzle in such a manner as to further break up the fuel into a finer atomized mixture of fuel and air. It is pointed out that in comparison to the amount of air necessary to form an inflammable mixture; 'Wlth the fuel present .in the combustion chamber the amount of gas used in the gas-assist nozzle toootain in air density. A pressure type or orifice flow meter 19 in fuel line 26 is employed to sense and detect "changes in the rate of fuel flow therethrough. In the embodiment of the invention as illustrated in Fig. 1, air supplied to gas-assist nozzle is obtained from an auxiliary compressor 21 via lines 23 and 22 which communicate with the gas-assist nozzle. If desirable, of course, the air for the gas-assist fuel nozzle may be obtainedfrom a suitable high pressure stage of compressor-l2. Asindicated, the

and 19. Control device 27 regulates the air supply to gas better atomization of the fuel is very low and hardly'sufficient to affect the ratio of the fuel and air in the combustion chamber. When air is used in the gas-assist nozzle it is very suitably supplied from an appropriate auxiliary compressor. Air as the assist gas can also be supplied from a suitable higher pressure stage of the turbo compressor. It is, of course, realizedthat the gas (air) utilized in the gas-assist nozzle may also be supplied from other sources, such as a pressure tank. Gases other than air may be used to assist atomization of the fuel; these gases include the normally gaseous hydrocarbons such as CH4, CzHs, C2H4, CzI-Iz, C3Ha, etc. also the various nitrogen and carbon oxides, oxygen, nitrogen, etc.

Various devices and means are available and may be devised for sensing changes in linear air velocity, air density and rate of fuel flow and various means may be employed in coordinating the responses derived thereplied to spray head 33 via conduit 34. The interior of spray head 33 is fitted with suitable helical vanes 35 to p from and/or the detected changes to control certain op.- I

'erations, such asthe amount of gas supplied as assist to the gas-assist fuel nozzle. All these means and devices which may be employed in carrying out the practice of port combustion of a liquid fuel injected into combustion chamber 13 through fuel nozzlelS wherein it is ignited by a suitable means such as spark plug 16. The impact 1 section of a Pitot tube 17 located in front of combustion chamber 13 is employed to sense and detect changes in linear air velocity of the air issuing from compressor 12. Associated with Pitot tube 17 in close proximity thereto is thermocouple 18 preferably located, as shown, in front of the entrance 14 to combustion chamber 13. Thecombination of the static pressuretap of Pitot tube 17 and thermocouple 18 is employed to senseand detect changes assist nozzle 15 by actuating valve 24 in accordance with changes in linear air velocity detected by the velocity pressure section of Pitot tube 17. Control device 28 translates changes in pressure and temperature as indicated by Pitot tube 17 and thermocouple 18 into changes in. air density and actuates valve25" in accordance with these changes in density so as to regulate the air supply to gas assist nozzle 15.. Control device 29 regulates the .air supply to gas assist nozzle 15 'by actuating valve 26 in accordance with fluctuations in fuel supply as detected by pressure type fluid flow meter19. Control devices which may be used in accordance with one embodiment of this invention are described more in detail hereinafter in thediscussion of Figures 3a, 3b, and 30. Other electrical and/or appropriate mechanical detecting of fuel flow'and controlling means and techniques which are Well known in the art may, also be used or substituted.

Referring now to Fig. 2 wherein is shown schematically in cross-section a typical gas-assist fuel nozzle, liquid fuel. is forced through conduit 30 out throughoriiice 31. The interior of conduit 315 is fitted with helical vanes32 which tend to impart a rotary or gyratory motion to the liquid fuel in conduit 3t). Upon emerging from orifice 311, the liquid fuel is atomized into a fine spray and the degree of fuel atomization is determined by the gas-whichis'supimpart a rotary motion to the assist gas as it enters space 36 around fuel orifice 31 in order to assist in the dispersion and atomization of the fuel. Although some atomization is obtained directly by means of the fuel orifice 31 itself, th'e degree of atomization is primarily governed by the gas-assist and can be considered directly related to the amount of assist gas supplied via conduit 34 for this purpose. a

In accordance with this invention, and as illustrated by Fig. 1, the system therein detects changes in air density, air velocity, and fuel flow by the indicated sensing elements so that whenever the values of these variables change, more or less air is supplied to gas-assist nozzle 15 in order to bring about optimum atomization of the fuel under the conditions of operation. The degree of opening of air supply valves 24, 25 and 26 depends on the amount of change of each of these variables. In most cases, of course, the relationship between the magnitude of the detected variables and the valve opening is not linear and accordingly as the variablechangesit would be desirable for the air-assist to change at an accelerating rate or decelerating'rate dependent upon the, particular engine design. Also for certain engine designs these variables may have very little or a controlling influence upon the combustion efliciency and stability. For

example in some engines depending upon the design, thelinear air velocity through the combustion zone may entirely govern the kind of atomization required for optimum combustion whereas in other engines it may have very little if any influence.

In accordance with one embodiment of this invention I and inorder to obtain the desired control, the changes.

in the values of the variables as detected by the respective sensing means may be converted into electrical voltages proportional to these changes in the variable. After amplification, these detected non-linear voltages will cause the air which is supplied to the gas-assist nozzle to be controlled at the proper rate for optimum operation for the engine under these conditions. The exponential power to which these voltages must be raised to obtain the non-linear function may be less than, equal to, or greater than one depending upon combustion chamber design, fuel nozzle characteristics, the degree of control desired, etc.

Referring now to Figs. 3a, 3b and 30, therein are shown schematic representations for various electrical methods for regulating the gas to the gas-assist nozzle in accordance with the various sensed or detected changes in air density, linear air velocity and rate of fuel flow. It is obvious that other electrical and/or appropriate mechanical detecting of fuel flow and controlling means and techniques may also be used or substituted. Figure 3a, in particular, schematically shows a control system for regulating the air to the gas-assist nozzle in accordance with changes in air density. From a consideration of the simplified, general gas equation pv=nRT and in view of the definition of density, it is readily apparent that the density of a gas is proportional to a constant times the ratio of the pressure of the gas divided by its absolute temperature. Accordingly, therefore, changes in density may be detected by determining changes in pressure and temperature in the air. Accordingly, and as illustrated by Fig. 3a, a voltage er is generated by the thermocouple 4t and is proportional to the temperature of the air. This voltage es is amplified in a D. C. amplifier 41 to some value ken which is applied to servomechanism 42 which controls variable resistance 43 in bridge network 44. Similarly, the change in pressure detected by the static opening of Pitot tube 45 is converted to a voltage e by means of a pressure transducer 46 and amplified by D. C. amplifier 47 to voltage ke The voltage ke is applied to servomechanism 48 which controls variable resistance 49, also a part of bridge network 44. The bridge network 44 also contains variable resistance 50 and a fixed resistance 51, and a source of potential 52 and servomechanism 53, all as indicated and shown in Fig. 3a. Bridge network 44 is balanced by servomechanism 53 by varying the resistance of variable resistance 50. When balance is achieved, the resistance of variable resistance 50 and, therefore, the rotation of servomechanism 53 is proportional to the change in density of the air.

The mechanical output of bridge servomechanism 53 is connected to the movable arm 54 of the non-linear, continuously-variable potential divider 55. A voltage drop is developed across divider 55 by the current flowing from the source of supply 56 so that the voltage drop ke d, developed between the end of the winding of potential divider 55 and the contact point of arm 54 is non-linearly related to the variation in density of the air. The nature of this non-linear voltage depends, of course, upon the value of the exponential which depends upon the way the potentiometer is wound which in turn depends upon the particular jet engine design.

The voltage ke d and the constant voltage es from the source of voltage 57 are bucked through fixed resistances S and the voltage Ae taken off across resistance 53 is applied to the contacts of normally open relay 62. The resulting voltage Ae is also applied to selenium rectifier 60 and the coil section 61 of relay 62 connected in series. The state of the contacts of relay 62 is normally in the open position; however, whenever voltage ke d becomes smaller than the predetermined value of voltages es, the polarity of the voltage es in accordance with the relationshipe Ae=eske a is such that current passes through rectifier 60 and coil 61 of relay 62 so that the contacts of the relay are closed and Ae is applied to a suitable electrically controlled or electric pneumatic control valve such as valve 25 of Fig. 1 in the gas supply system. The predetermined value of voltage es is equal to voltage ke d when the density of the air is such that additional gas-assist is just necessary to maintain suitable'atomization of the fuel which is supplied to the combustion zone of the engine. Whenever the voltage k2 d is in excess of the voltage the resultant voltage Ae is such that current will not pass through rectifier 60 and relay 62 remains open and as a result the above-indicated control valve 25 is not actuated.

Referring now to Fig. 3b there is shown a schematic representation of a similar control system for regulating the gas supply to the gas assist nozzle in accordance with fluctuations in the linear velocity of the air supplied for combustion of the fuel. According to this method for sensing and detecting and utilizing changes in linear air velocity, changes in linear air velocity are detected by the velocity-pressure section of a suitable Pitot tube 70. The pressure registered is proportional to the linear air velocity and is converted by pressure transducer 71 to a voltage ev which is amplified in D. C. amplifier 72 to form value ke'v and supplied to servomechanism 73. The mechanical output of servomechanism 73 is connected to the movable arm 74 of non-linear continuously variable potential divider 75 in the same manner that the mechanical output of bridge-servomechanism 53 of Fig. 3a is applied to the movable arm of non-linear, continuously variable potential divider 55 of Fig. 3.2, so as to generate voltage ke' v. The remainder of the control system of Figure 3b is substantially the same as that used for controlling the gas-assist in accordance with changes in air density as set forth and explained with reference to Fig. 3a and a control voltage M is obtained. It is, of course, realized that the values of some or all of the components of the system may or may not be diiferent, however, the operation is similar.

The schematic representation shown in Fig. 3c is very similar to that shown in Fig. 3b and provides a control system for regulating the air to the gas-assist nozzle in accordance with changes in the rate of fuel flow to the combustion chamber. According to Fig. 3c fluctuations in fuel flow are detected by pressure-type fiuid flow meter 3% and converted by means of pressure transducer 81 to a voltage er which is proportional to the rate of fuel flow. The voltage er is amplified in D. C. amplifier 82 to form voltage k"er and supplied to servomechanism 83. The mechanical output of servomechanism 83 is connected to the movable arm 84- of non-linear continuously variable potential divider 35 in the same manner that the mechanical output of bridge-servomechanism 53 of Fig. 3a is applied to the movable arm of nonlinear, continuously variable potential divider 55 of Fig. 3:! so as to generate voltage k"e r. Voltage ke r is generated and bucked against a predetermined voltage e"s from voltage source 86 in the same manner as described and set forth with relation to Fig. 3a to yield a control voltage Ae".

Accordingly, and in accordance with this embodiment of the invention, three voltages ke d, ke v and k"e r are generated in accordance with changes in air density. linear air velocity and rate of fuel flow respectively, and bucked against three determined voltages 6s, e's, e"s. The resultant voltages Ae, Ae' and Ae" are applied to three control valves in the gas-assist system (see Fig. l) to regulate the supply of gas to the gas assist fuel nozzle so as to maintain optimum atomization of the fuel under the operating conditions.

According to another embodiment of this invention it is conceivable that the characteristics of certain combustion chambers may be such that instead of requiring separate variations of gas to the gas assist nozzle in accordance with the individual values of the above-indicated three variables, the regulations of gas to the gasassist nozzle may be made through a single valve or control means actuated by. the sum of the individual voltages, Accordingly, in this manner, the voltages ke d, ke v and k' 'e rdeveloped across the non-linear continuou'sly variable potential divider 55, '75 and 85 are all bucked against only one predetermined voltage 85. It is realized, of course, that in this embodiment that it Will be necessary for at least some of the values of the constants k, k, and k and x, y and z to be arranged so that the effect exercised by each element of each control system'will be suificient and appropriate for the particular jet engine design.

The above description of the invention made with reference'to Figs. 1, 2 and 3a, 3b and 3c are, of course, illustrative ofthe invention and are not to be considered as limitative thereof; It is, of course, realized that various sensing, detecting and responsing means and methods may be employed in the practice of this invention. Furthermore, it is, of course, realized that suitable mechanical analogues equivalent to and serving the purposes of the electrical detecting and controlling systems set forth and illustrated in Figs. 3a, 3b and 3c may also be used and in some cases may even be more desirable. It is realized that many modifications, improvements and substitutions may be made by those skilled in the art upon reading this disclosure Without departing from the spirit or scope of this invention.

I claim:

1. An apparatus for atomization of a liquid fuel which comprises in combination a gas assist fuel atomizer comprising a liquid fuel conduit and an air conduit; a fluid flow measuring device in communication with said fuel conduit, said device being adapted to vary the supply of air to said air conduit in response to changes in fuel flow; a linear air velocity measuring device associated with said atomizer, said device being so constructed and arranged that the supply of air to said air conduit is varied in response to changes in linear air velocity; and an air density measuring device associated with said atomizer, said device being so constructed and arranged that the 8 supply of air to said air conduit is varied in response to changes in air density.

2. A fuel atomizer for a power plant including atleast one combustion zone comprising a gas-assist fuel nozzle to supply atomized fuel to said combustion zone and comprising a fuel conduit and an air conduit; means for measuring the rate of flow of fuel through said fuel conduit to said nozzle, said means being connected to a pressure detecting device and said device being so constructed and arranged that the supply of air to said air conduit is varied in response to changes in said rate of fuel flow;

means for measuring the-density of air supplied to said combustion zone, said means being connected to a pressure and temperature detecting device and said device being so constructed and arranged that the supply of air to said air conduit is varied in response to changes in said air density; and means for measuring the linear velocity of air supplied to said combustion zone, said means being connected to a pressure detecting device and said device being so constructed and arranged that the supply of air to said air conduit is varied in response to change in said linear air velocity. V

3. A fuel atomizer according to claim 2 wherein the means for measuringair density comprises in combination a thermocouple and a static pressure measuring device.

4. A fuel atomizer accordingto claim 2 wherein the means for measuring the rate of fuel flow comprises an orifice.

5. A fuel atomizer according to claim 2 wherein the means for measuring linear velocity comprises a static pressure measuring device.

References Cited in the file of this patent UNITED STATES PATENTS Mock Jan. 1, 1952

Claims (1)

1. AN APPARATUS FOR ATOMIZATION OF A LIQUID FUEL WHICH COMPRISES IN COMBINATION A GAS ASSIST FUEL ATOMIZER COMPRISING A LIQUID FUEL CONDUIT AND AN AIR CONDUIT; A FLUID FLOW MEASURING DEVICE IN COMMUNICATIONS WITH SAID FUEL CONDUIT, SAID DEVICE BEING ADAPTED TO VARY THE SUPPLY OF AIR TO SAID AIR CONDUIT IN RESPONSE TO CHANGES IN FUEL FLOW; A LINEAR AIR VELOCITY MEASURING DEVICE ASSOCIATED WITH SAID ATOMIZER, SAID DEVICE BEING SO CONSTRUCTED AND ARRANGED THAT THE SUPPLY OF AIR TO SAID AIR CONDUIT IS VARIED IN RESPONSE TO CHANGES IN LINEAR AIR VELOCITY; AND AN AIR DENSITY MEASURING DEVICE ASSOCIATED WITH SAID ATOMIZER, SAID DEVICE BEING SO CONSTRUCTED AND ARRANGED THAT THE SUPPLY OF AIR TO SAID AIR CONDUIT IS VARIED IN RESPONSE TO CHANGES IN AIR DENSITY.

Images