CA1126520A - Water injection for gas turbine engine emission control - Google Patents
Water injection for gas turbine engine emission controlInfo
- Publication number
- CA1126520A CA1126520A CA309,992A CA309992A CA1126520A CA 1126520 A CA1126520 A CA 1126520A CA 309992 A CA309992 A CA 309992A CA 1126520 A CA1126520 A CA 1126520A
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- fuel
- water
- combustor
- flow
- gas turbine
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Abstract
Abstract Simplified apparatus is provided ? separate pipe flows of fuel and water prior to delivery to the combustor of a gas turbine engine to reduce the temperature to which pressurized air is heated by the combustion of fuel, thereby reducing nitrous o?ide emissions in the products of combustion.
The separate pipe flows of fuel and water are combined in a simple T-section wherein the two flows are generally normal at their point of confluence within the T-section to produce turbulent mixing therein. It has been discovered that the mixture of fuel and water transforms into a homogeneous cream at water-to-fuel ratios slightly in excess of 0.7 for diesel fuel No. 2, and that the rate of separation is greatly reduced, thereby minimizing the var?ance in the percen-tage of fuel within the mixture between a plurality of nozzles fed from a common fuel manifold receiving the mixture.
The separate pipe flows of fuel and water are combined in a simple T-section wherein the two flows are generally normal at their point of confluence within the T-section to produce turbulent mixing therein. It has been discovered that the mixture of fuel and water transforms into a homogeneous cream at water-to-fuel ratios slightly in excess of 0.7 for diesel fuel No. 2, and that the rate of separation is greatly reduced, thereby minimizing the var?ance in the percen-tage of fuel within the mixture between a plurality of nozzles fed from a common fuel manifold receiving the mixture.
Description
~26~
BACKGROIJND C)F THE INVENTION
This invention relates to gas turbine engines an~, more particularly, to a simplified approach for reducing nitrous oxide emissions through the technique of water injection.
In this era of environmental awareness it is anticipated that regulations covering air pollution will become increasingly restrictive and that compliance with industrial emission standards will become more difficult to attain. These environmental considerations will have an impact upon the development of industrial gas turbine engine power plants and may require the reduction of exhaust emission levels consistent with available technology at realistic costs. However, the trend in gas turbine engine development is toward higher temperature engines which, though they are inherently more efficient, also tend to produce higher emission levels of nitrous oxide (NOX).
It is generally accepted that NOX formation increases exponentially with flame temperature, It has also been generally acknowledged that NOX formation can be reduced by introducing water in the form of liquid or steam into the combustion process to reduce the temperature to which the air is heated by the combustion of fuel in the primary zone of combustion.
Because of the exponential increase of NVX formation with flame temperature, relatively large reductions in NOX can be achieved with relatively low water flow rates. Furthermore, the specific method of water injection in gas turbine engines does not appear to be particularly important. Water has been injected separately into the combustor through distinct water nozzles as a liquid and as steam. It has also been injected into the combustor in the upstream, down-stream and "side stream" directions through separate water passages in the fuel injector. It has even been introduced through dual~flow nozzles wherein ~.~
~lZ~
the water and fuel were injected coaxially into the combustor. However, although these methods of injecting water have been successful in controlling NOX, they have, on occasion, produced some problems with hardware life due to local temperature gradients in the region where the water is being injected.
In fact, instrumented sector tests have demonstrated that in using the upstream method of injecting water through the nozzle, combustor metal temperature variations increase from a normal 500 F temperature variation with no water injection to an 800 F variation with the amounts of water injection necessary to achieve significant NOX reductions. While these temperature variations are the measured results of one particular series of engine sector tests, they are representative of the trend in temperature variations to be found in other gas turbine engine combustors.
More recently, a concept for emulsifying the fuel and water together and injecting the mixture through the normal (or enlarged) fuel nozzleshas been used successfully. This has considerable advantages over the systems relying on separate injection of fuel and water since complexity is minimized, separate nozzles may be eliminated, and costs reduced accordingly.
There is an old axiom that fuel and water won't mix. However, they will--but only temporarily. They then separate at a rate that appears to be a function of the specific gravity of the fuel. As the specific gravity approache~ unity (where fuel has the same density as water), the separation rate becomes much slower. To achieve satisfactory fuel-water emulsion, current practice has been to process the two separate liquids through a homo-genizer where each fuel is pressurized to a very high level and then sprayed through extremely small orifice~ into impingement against a hard impact block in a common mixing chamber. The impact breaks each fluid into 5~
extremely fine particles which become intimately mixed, or emulsified, into one homogeneous fluid, The subsequent separation rate is apparently slowed by the intimacy or fineness of the emulsion. This homogenizing equipment is, of course, very bulky and costly.
Since water suppression of NOX is simply a function of water concentration, the emulsion concept is only one means employed to assure that each fuel nozzle is supplied with the same quantity of fuel and water as are all the others. Since all nozzles are supplied by a common pressure source (usually a fuel manifold), then all will flow the same rate of fluid, be it fuel, water or a fuel-water emulsion. If separation occurs prior to combus-tion, then some nozzles wiLl flow more fuel (or water) than others and unacceptable temperature distributions will result inside the engine. In fact, it has been found that fuel variations between nozzles in excess of 10 percent are generally undesirable. In short, the fuel and water need be mixed or emulsified only to the extent required to assure uniform distributions through-out the manifolded fuel nozzles. Since state-of-the-art fuel-water emulsifiers or homogenizers are inherently complex, heavy and costly, it would be advan-tageous to develop a simple emulsifier which merely meets requirement of uniform fuel distribution among the manifolded nozzles.
SUMMARY OF THE INVENTION
Accordingly, it is the primary object of the present invention to provide an improved gas turbine engine wherein NOX formation is reduced through a simplified concept of water injection.
It is another object of the present invention to provide a method for reducing NOX emissions from gas turbine engine combustors through a simplified concept of water injection.
6~;20 It is yet another object of the present invention to provide a method of operating a gas turbine engine with water injection which minimizes the variation in fuel percentage between a plurality of nozzles by prolonging the fuel-water separation time.
These, and other objects and advantages, will be more clearly understood from the following detailed descriptions, the drawings and specific examples, all of which are intended to be typical of, rather than in any way limiting on, the scope of the present invention, Briefly stated, the above objectives are attained by introducing separate fuel and water flows through the generally perpendicular inlets of a common plumbing T-section whereh the two flows are generally normal at their point of cor~luence to produce turbulent mixing. The resulting mixture remains homogeneous for the short time required for it to be injected into the combustor, particularly if the flow remains turbulent until injection. It has ~,~15 been discovered that at water-to-fuel ratios slightly in excess of 0. 7 (for diesel fuel No, 2) the mixture begins to transform into a homogeneous cream having a much slower rate of separation. Therefore, the variance in fuel percentage among a plurality of fuel nozzles fed from a common manifold receiving the mixture may be reduced. In~trumented sector tests have demonstrated that instead of an increase in combustor temperature variation as experienced with .~ the separate in~ection of fuel and water, utilization of the pre~ent fuel-water emulsification approach significantly decreases the temperature variation, thereby tending to prolong combustor life.
BRIEF DESCRIPTION OF THE DRAWI~GS
While the ~pecification concludes with claims particularly pointing out and distinctly claiming the sub~ect matter which i~ regarded as , . .
;5Z~
part of the present invention, it is believed that the invention will be more fully understood from the following description of the preferred embodiments which are given by way of example with the accompanying drawings in which:
Figure 1 is a graphical representation of the variation in NOX
S emissions from a gas turbine engine with flame temperature;
Figure 2 is a partial cross-sectional schematic view of a gas turbine engine incorporating the subject invention;
Figure 3 is an enlarged fragmentary view of the fuel-water mixing apparatus of the subject invention showing its relationship to the combustor fuel nozzles;
Figure 4 graphically compares the effect of water injection on NOX emissions for separate injection of fuel and water and an emulsified mixture of fuel and water; and Figure 5 illustrates the phase changes of an emulsified fuel-water mixture as the water-fuel ratio is varied.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings wherein like numerals correspond to like elements throughout, attention is fir~t directed to Figure 1 which is a graphical repre~entation of the exponential relationship of NOX generation (represented by a nondimensional NOX index) with name temperature in a gas turbine engine. Line 10 represents the locus of test data relating to this phenomenon. It is generally recognized that NOX control can be achieved by injecting li~uid water or steam into the combustion process to lower peak Mame temperatures and, since the relationship between NOX generation and flame temperature is exponential, it can be appreciated from Figure l that relatively small amount~ of water injection can produce large reductions in ~Z65Z~:l N0x. The invention soon to be described relates to the reduction of N0x in gas turbine engines and embodies the N0x reduction-through-water-injection concept depicted in Figure 1.
While it is recognized that gas turbine engines are, by now, 5 well understood in the art, a brief description of a representative engine will enhance appreciation of the interrelationship of various components in light of the invention soon to be described. To that end, attention is now directed to Figure 2 wherein a gas turbine engine of the marine or industrial variety, depicted generally at 12 and embodying the present invention, is diagrammati-10 cally shown. This engine may be considered as comprising a core engine 14and an independent power turbine 16. The core engine includes an axial flow compre6sor 18 having a bladed rotor 20. Air enters inlet 22, is compressed by compre6sor 18 and is then discharged to a combustor 24 where it is normally mixed with fuel and combusted to provide high energy combustion gases to drive the core engine turbine 26. Turbine 26, in turn, drives rotor 20 through shaft 28. The hot gases of combustion then pass through and drive the power turbine 16 which, in turn, drives an energy-absorbing device (not shown) through power shaft 30. Power is thus obtained by the action of the hot gases of combustion driving power turbine 16. The products of combustion are then 20 collected and exh~stedthrough discharge nozzle 32 which, in some applications, may be a propulsive nozzle. The above description is typical of many present-day gas turbine engines of the industrial power generation or marine propulsion variety and is not meant to be limiting on the present invention since it will 600n become readily apparent from the following description that the present 25 invention is capable of application to any gas turbomachine, whether of the turbojet, turboprop or turbo6haft variety. The foregoing description of the -l~Z6520 operation of the engine of Figure 2 is, therefore, merely meant to be illustrative of one type of application.
The present invention provides a simplified means for emulsifying fuel and water to reduce gas turbine engine NOX emissions and to achieve a more uniform fuel-water distribution within the combustor of the gas turbine engine. Directing attention now to Figure 3, there is depicted schematically an apparatus which embodies the present inventive concept.
Surprisingly, it was discovered that when water was added to a gas turbine engine fuel delivery system through a simple plumbing "T" 34, sufficient homogenization occurred. In particular, T-section 34 is provided with a first inlet 36 for receiving a flow of fuel and a second inlet 38 for receiving a flowof water. Pipes or tubes 40, 42 are connected to inlets 36, 38, respectively, and comprise portions of the respective fuel and water delivery systems. The water and fuel flows are pipe flows, not sprays or mists, and are generaUy normal to each other at their point of confluence within the "T" to produce turbulent mixing therein. A single outlet 44 discharges the mixture into a pipe 46 by which the mixture is carried to a flow splitter 48. Each splitter leg 50 communicates with a generally semicircular fuel manifold 52 feeding a plurality of nozzles 54 disposed within the upstream end of combustor 24 (see Figure 2) in the usual manner of a gas turbine engine.
When the fuel and water are introduced into the "T" at conditions sufficient to produce turbulent mixing (i. e., at a turbulent Reynolds number), sufficient homogenization occurs such that the proportions of fuel and water delivered to each nozzle 54 are sufficiently uniform. In tests performed using a mixing "T" having a, 375" diameter water inlet, a . 625" diameter fuel inlet and die~el No, Z as the fuel, a 1% variation in fuel content was measured at ~lZ6~
the discharge of splitter legs 50. In one manifold section 54 having fifteen nozzles, a 3. 5% fuel variation ~maximum minus minimum, divided by average) was recorded at the nozzle discharge. With JP4 fuel, the fuel variation at the nozzles was 10%. For yet unexplained reasons, when the water inlet diameter 5 was reduced to . 31", the percent fuel variation (for diesel No. 2) between splitter legs 50 increased from 1% to as high as 7. 8%, yet still within accept-able limits. Experimental accuracy may account for much of this difference.
The flow velocity rates in a gas turbine engine are such that the elapsed time that it takes to travel from the "T" element (which, practically 10 speaking, is located just upstream of the fuel manifolds) to the most distant nozzle 54 is only a few sec~nds, well within the "stay" time of the emulsion (the time before significant separation occurs). Additionally, the turbulence level in the manifolds tends to complement the stay time because the inherently high fluid velocities promote mixing rather than settling. Furthermore, while 15 Figure 3 depicts a right angle "T", some angle other than 90 at the point of confluence would be acqeptable providing that the mixing and the flow at the point of confluence wa~ turbulent so as to homogenize the two dissimilar liquids.
Test8 conducted utilizing the present invention showed that N0x 20 reductions attained with the use of the emulsified fuel-water mixtures were eomewhat greater than those obtained with separately injected water. Figure 4 shows a comparison of the N0x emissions measured during these tests. For example, a N0x reduction of 50% would require a water-to-fuel ratio of 0. 6 when the water is injected separately. The same N0x reduction could be 25 obtained with a ratio of 0. 4 when the mixture is emulsified in accordance with the present invention.
~1265~0 The present invention could be incorporated into a gas turbine engine, such as the representative industrial-type gas turbine engine of Figure
BACKGROIJND C)F THE INVENTION
This invention relates to gas turbine engines an~, more particularly, to a simplified approach for reducing nitrous oxide emissions through the technique of water injection.
In this era of environmental awareness it is anticipated that regulations covering air pollution will become increasingly restrictive and that compliance with industrial emission standards will become more difficult to attain. These environmental considerations will have an impact upon the development of industrial gas turbine engine power plants and may require the reduction of exhaust emission levels consistent with available technology at realistic costs. However, the trend in gas turbine engine development is toward higher temperature engines which, though they are inherently more efficient, also tend to produce higher emission levels of nitrous oxide (NOX).
It is generally accepted that NOX formation increases exponentially with flame temperature, It has also been generally acknowledged that NOX formation can be reduced by introducing water in the form of liquid or steam into the combustion process to reduce the temperature to which the air is heated by the combustion of fuel in the primary zone of combustion.
Because of the exponential increase of NVX formation with flame temperature, relatively large reductions in NOX can be achieved with relatively low water flow rates. Furthermore, the specific method of water injection in gas turbine engines does not appear to be particularly important. Water has been injected separately into the combustor through distinct water nozzles as a liquid and as steam. It has also been injected into the combustor in the upstream, down-stream and "side stream" directions through separate water passages in the fuel injector. It has even been introduced through dual~flow nozzles wherein ~.~
~lZ~
the water and fuel were injected coaxially into the combustor. However, although these methods of injecting water have been successful in controlling NOX, they have, on occasion, produced some problems with hardware life due to local temperature gradients in the region where the water is being injected.
In fact, instrumented sector tests have demonstrated that in using the upstream method of injecting water through the nozzle, combustor metal temperature variations increase from a normal 500 F temperature variation with no water injection to an 800 F variation with the amounts of water injection necessary to achieve significant NOX reductions. While these temperature variations are the measured results of one particular series of engine sector tests, they are representative of the trend in temperature variations to be found in other gas turbine engine combustors.
More recently, a concept for emulsifying the fuel and water together and injecting the mixture through the normal (or enlarged) fuel nozzleshas been used successfully. This has considerable advantages over the systems relying on separate injection of fuel and water since complexity is minimized, separate nozzles may be eliminated, and costs reduced accordingly.
There is an old axiom that fuel and water won't mix. However, they will--but only temporarily. They then separate at a rate that appears to be a function of the specific gravity of the fuel. As the specific gravity approache~ unity (where fuel has the same density as water), the separation rate becomes much slower. To achieve satisfactory fuel-water emulsion, current practice has been to process the two separate liquids through a homo-genizer where each fuel is pressurized to a very high level and then sprayed through extremely small orifice~ into impingement against a hard impact block in a common mixing chamber. The impact breaks each fluid into 5~
extremely fine particles which become intimately mixed, or emulsified, into one homogeneous fluid, The subsequent separation rate is apparently slowed by the intimacy or fineness of the emulsion. This homogenizing equipment is, of course, very bulky and costly.
Since water suppression of NOX is simply a function of water concentration, the emulsion concept is only one means employed to assure that each fuel nozzle is supplied with the same quantity of fuel and water as are all the others. Since all nozzles are supplied by a common pressure source (usually a fuel manifold), then all will flow the same rate of fluid, be it fuel, water or a fuel-water emulsion. If separation occurs prior to combus-tion, then some nozzles wiLl flow more fuel (or water) than others and unacceptable temperature distributions will result inside the engine. In fact, it has been found that fuel variations between nozzles in excess of 10 percent are generally undesirable. In short, the fuel and water need be mixed or emulsified only to the extent required to assure uniform distributions through-out the manifolded fuel nozzles. Since state-of-the-art fuel-water emulsifiers or homogenizers are inherently complex, heavy and costly, it would be advan-tageous to develop a simple emulsifier which merely meets requirement of uniform fuel distribution among the manifolded nozzles.
SUMMARY OF THE INVENTION
Accordingly, it is the primary object of the present invention to provide an improved gas turbine engine wherein NOX formation is reduced through a simplified concept of water injection.
It is another object of the present invention to provide a method for reducing NOX emissions from gas turbine engine combustors through a simplified concept of water injection.
6~;20 It is yet another object of the present invention to provide a method of operating a gas turbine engine with water injection which minimizes the variation in fuel percentage between a plurality of nozzles by prolonging the fuel-water separation time.
These, and other objects and advantages, will be more clearly understood from the following detailed descriptions, the drawings and specific examples, all of which are intended to be typical of, rather than in any way limiting on, the scope of the present invention, Briefly stated, the above objectives are attained by introducing separate fuel and water flows through the generally perpendicular inlets of a common plumbing T-section whereh the two flows are generally normal at their point of cor~luence to produce turbulent mixing. The resulting mixture remains homogeneous for the short time required for it to be injected into the combustor, particularly if the flow remains turbulent until injection. It has ~,~15 been discovered that at water-to-fuel ratios slightly in excess of 0. 7 (for diesel fuel No, 2) the mixture begins to transform into a homogeneous cream having a much slower rate of separation. Therefore, the variance in fuel percentage among a plurality of fuel nozzles fed from a common manifold receiving the mixture may be reduced. In~trumented sector tests have demonstrated that instead of an increase in combustor temperature variation as experienced with .~ the separate in~ection of fuel and water, utilization of the pre~ent fuel-water emulsification approach significantly decreases the temperature variation, thereby tending to prolong combustor life.
BRIEF DESCRIPTION OF THE DRAWI~GS
While the ~pecification concludes with claims particularly pointing out and distinctly claiming the sub~ect matter which i~ regarded as , . .
;5Z~
part of the present invention, it is believed that the invention will be more fully understood from the following description of the preferred embodiments which are given by way of example with the accompanying drawings in which:
Figure 1 is a graphical representation of the variation in NOX
S emissions from a gas turbine engine with flame temperature;
Figure 2 is a partial cross-sectional schematic view of a gas turbine engine incorporating the subject invention;
Figure 3 is an enlarged fragmentary view of the fuel-water mixing apparatus of the subject invention showing its relationship to the combustor fuel nozzles;
Figure 4 graphically compares the effect of water injection on NOX emissions for separate injection of fuel and water and an emulsified mixture of fuel and water; and Figure 5 illustrates the phase changes of an emulsified fuel-water mixture as the water-fuel ratio is varied.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings wherein like numerals correspond to like elements throughout, attention is fir~t directed to Figure 1 which is a graphical repre~entation of the exponential relationship of NOX generation (represented by a nondimensional NOX index) with name temperature in a gas turbine engine. Line 10 represents the locus of test data relating to this phenomenon. It is generally recognized that NOX control can be achieved by injecting li~uid water or steam into the combustion process to lower peak Mame temperatures and, since the relationship between NOX generation and flame temperature is exponential, it can be appreciated from Figure l that relatively small amount~ of water injection can produce large reductions in ~Z65Z~:l N0x. The invention soon to be described relates to the reduction of N0x in gas turbine engines and embodies the N0x reduction-through-water-injection concept depicted in Figure 1.
While it is recognized that gas turbine engines are, by now, 5 well understood in the art, a brief description of a representative engine will enhance appreciation of the interrelationship of various components in light of the invention soon to be described. To that end, attention is now directed to Figure 2 wherein a gas turbine engine of the marine or industrial variety, depicted generally at 12 and embodying the present invention, is diagrammati-10 cally shown. This engine may be considered as comprising a core engine 14and an independent power turbine 16. The core engine includes an axial flow compre6sor 18 having a bladed rotor 20. Air enters inlet 22, is compressed by compre6sor 18 and is then discharged to a combustor 24 where it is normally mixed with fuel and combusted to provide high energy combustion gases to drive the core engine turbine 26. Turbine 26, in turn, drives rotor 20 through shaft 28. The hot gases of combustion then pass through and drive the power turbine 16 which, in turn, drives an energy-absorbing device (not shown) through power shaft 30. Power is thus obtained by the action of the hot gases of combustion driving power turbine 16. The products of combustion are then 20 collected and exh~stedthrough discharge nozzle 32 which, in some applications, may be a propulsive nozzle. The above description is typical of many present-day gas turbine engines of the industrial power generation or marine propulsion variety and is not meant to be limiting on the present invention since it will 600n become readily apparent from the following description that the present 25 invention is capable of application to any gas turbomachine, whether of the turbojet, turboprop or turbo6haft variety. The foregoing description of the -l~Z6520 operation of the engine of Figure 2 is, therefore, merely meant to be illustrative of one type of application.
The present invention provides a simplified means for emulsifying fuel and water to reduce gas turbine engine NOX emissions and to achieve a more uniform fuel-water distribution within the combustor of the gas turbine engine. Directing attention now to Figure 3, there is depicted schematically an apparatus which embodies the present inventive concept.
Surprisingly, it was discovered that when water was added to a gas turbine engine fuel delivery system through a simple plumbing "T" 34, sufficient homogenization occurred. In particular, T-section 34 is provided with a first inlet 36 for receiving a flow of fuel and a second inlet 38 for receiving a flowof water. Pipes or tubes 40, 42 are connected to inlets 36, 38, respectively, and comprise portions of the respective fuel and water delivery systems. The water and fuel flows are pipe flows, not sprays or mists, and are generaUy normal to each other at their point of confluence within the "T" to produce turbulent mixing therein. A single outlet 44 discharges the mixture into a pipe 46 by which the mixture is carried to a flow splitter 48. Each splitter leg 50 communicates with a generally semicircular fuel manifold 52 feeding a plurality of nozzles 54 disposed within the upstream end of combustor 24 (see Figure 2) in the usual manner of a gas turbine engine.
When the fuel and water are introduced into the "T" at conditions sufficient to produce turbulent mixing (i. e., at a turbulent Reynolds number), sufficient homogenization occurs such that the proportions of fuel and water delivered to each nozzle 54 are sufficiently uniform. In tests performed using a mixing "T" having a, 375" diameter water inlet, a . 625" diameter fuel inlet and die~el No, Z as the fuel, a 1% variation in fuel content was measured at ~lZ6~
the discharge of splitter legs 50. In one manifold section 54 having fifteen nozzles, a 3. 5% fuel variation ~maximum minus minimum, divided by average) was recorded at the nozzle discharge. With JP4 fuel, the fuel variation at the nozzles was 10%. For yet unexplained reasons, when the water inlet diameter 5 was reduced to . 31", the percent fuel variation (for diesel No. 2) between splitter legs 50 increased from 1% to as high as 7. 8%, yet still within accept-able limits. Experimental accuracy may account for much of this difference.
The flow velocity rates in a gas turbine engine are such that the elapsed time that it takes to travel from the "T" element (which, practically 10 speaking, is located just upstream of the fuel manifolds) to the most distant nozzle 54 is only a few sec~nds, well within the "stay" time of the emulsion (the time before significant separation occurs). Additionally, the turbulence level in the manifolds tends to complement the stay time because the inherently high fluid velocities promote mixing rather than settling. Furthermore, while 15 Figure 3 depicts a right angle "T", some angle other than 90 at the point of confluence would be acqeptable providing that the mixing and the flow at the point of confluence wa~ turbulent so as to homogenize the two dissimilar liquids.
Test8 conducted utilizing the present invention showed that N0x 20 reductions attained with the use of the emulsified fuel-water mixtures were eomewhat greater than those obtained with separately injected water. Figure 4 shows a comparison of the N0x emissions measured during these tests. For example, a N0x reduction of 50% would require a water-to-fuel ratio of 0. 6 when the water is injected separately. The same N0x reduction could be 25 obtained with a ratio of 0. 4 when the mixture is emulsified in accordance with the present invention.
~1265~0 The present invention could be incorporated into a gas turbine engine, such as the representative industrial-type gas turbine engine of Figure
2, having a fuel flow delivery system 56 comprising, in part, a tank 58 from which fuel is pumped and routed through a fuel control 60 of a known variety which is responsive to operator throttle input and which senses and compen-sates for measured engine parameters. Fuel from such a control is routed to the inlet side 36 of "T" 34. Water is pumped to T-inlet 38 from a tank 62 and through a valve 64 which is interlocked with the output of the fuel control to maintain the desired water-fuel mixture ratio. Such a control apparatus is within the skill of those familiar with such control art and is beyond the scopeof the present invention.
It was also discovered that when the water-fuel ratio for diesel No. 2 exceeds 0. 7, the consistency of the emulsion begins to change from suspended water drops in fuel to a homogeneous cream, and the cream is fully formed as the ratio approaches 1. 0. This is shown schematically by the solid line path 64 of Figure 5. Whereas the normal mixture of suspended water drops in fuel required less than several minutes to separate, the creamy homogeneous mixtures required two to eight hours to ~eparate. Clearly, this reduced tendency to separate means that a more uniform fuel distribution may be obtained between the plurality of nozzles and that the mixing "T" can be locatedfurther from the nozzles. Tests performed with JP4 fuel showed that the creamy mixture forms at a water-fuel ratio of 1. 4.
Interestingly, after the cream has been formed and the water flow reduced slightly, there is no significant apparent change in consistency until the water-fuel ratio is reduced from 0. 9 to 0. 65, as shown by the dottedline path 66 of Figure 5. As this point is approached, the creamy mixture .. g_ .
llZ6S;~
becomes heavy, changing from the consistency of whipping cream to that of paint, Decreasing the water-fuel ratio further returned the mixture to its normal suspended state. Tests indicate that there is no significant increase in manifold fuel pressure for the creamy emulsion at similar operating conditions.
5 While the water-fuel ratio at which conversion to the creamy mixture occurs may be above the normal operating range for some engines, it may be advanta-geous to initially run to high water-fuel ratios to get the cream to "start" and then to reduce the ratio, staying on the dotted curve 66 of Figure 5 to take advantage of the hysteresis-like phenomenon whereby a creamy texture can be 10 maintained at lower water-fuel ratios than on the solid line path of Figure 5, The phenomenon causing the cream to form can probably be explained by the large difference in surface tension of the two fluids. Applica-tion of high shear stress to the two-phase mixture results in more subdivision of the fuel pha~e than the water phase Initially, the fuel is a continuous phase 15 while the water is in relatively large drops that settle rapidly. As water addition continues, a point is reached where a phase reversal occurs and the water becomes the continuous phase having the fuel suspended therein as relatively small drops with little opportunity to coalesce and separate. This is the emulsion described herein as "cream, " probably a pseudoplastic fluid 20 rather than a Newtonian fluid ~such as the ~uel or water alone). The process can be reversed by adding larg~ quantities of fuel to the mixture while the shearing action continues.
It should become obvious to one skilled in the art that certain changes can be made to the above-described invention without departing from 25 the broad inventive concepts thereof. For example, the present invention is meant to embrace any arrangement whereby two pipe flows, one of fuel and ~lZ6S~:~
one of water, are combined turbulently without necessity of complex homogenizers. While a simple plumbing "T" section has been demonstrated to be effective, this is merely one example of a means for directly combining the two fluids through turbulent mixing to produce a homogeneous mixture. Injecting the flows at an angle other than 90 at the point of confluence would also be acceptable providing that the mixing which occurred was turbulent (i.e., occurred at a Reynolds number consistent with turbulent flow for the direct combining means employed).
It is intended that the appended claims cover these and all other such variations in the present invention's broader inventive concepts.
SUPPLEMENTARY DISCLOSURE
It has been found that the distance of location of the mixing zone from the combustor is not critical, due to the extended "stay" times that suitable mixtures can achieve, in excess of one minute. However, insofar as nozzle fuel percentage variation is concerned, the best results for the subject system are achieved if the transit time between mixing zone and com-bustor nozzle does not exceed 30 seconds.
In the operation of the system, using a mixing device such as the disclosed "T" arrangement, the homogeneous mixing requires no emulsifying agents intentionally added to fuel or - water, and the provision of turbulent mixing with a Reynolds number of at least 1500 in the resulting mixture produces the desired result. The ratio of water to fuel can operate in the range 0.6 to 1.4 by weight.
What is provided is, in a simplified method for reducing NO emissions from a gas turbine engine having a combustor in which a flow of pressurized air is mixed with fuel and combusted the steps of:
~llZ65~
a) providing a flow of fuel under pressure;
b) providing a flow of water under pressure;
c) mixing directly, the fuel flow and the water flow in a water: fuel ratio in the range 0.6 and l.~ by weight and wherein the conditions are sufficient to produce turbulent mixing with a Reynolds number of at least 1500 in the resulting mixture; and d) delivering the resulting mixture to a plurality of combustor nozzles for combustion,the combustion occurring within thirty seconds from the time the fuel and water flows are mixed.
In the case where the fuel is Dlesel Fuel No. 2 the water: fuel ratio is in the range of 0.7 and 1.0 by weight.
It was also discovered that when the water-fuel ratio for diesel No. 2 exceeds 0. 7, the consistency of the emulsion begins to change from suspended water drops in fuel to a homogeneous cream, and the cream is fully formed as the ratio approaches 1. 0. This is shown schematically by the solid line path 64 of Figure 5. Whereas the normal mixture of suspended water drops in fuel required less than several minutes to separate, the creamy homogeneous mixtures required two to eight hours to ~eparate. Clearly, this reduced tendency to separate means that a more uniform fuel distribution may be obtained between the plurality of nozzles and that the mixing "T" can be locatedfurther from the nozzles. Tests performed with JP4 fuel showed that the creamy mixture forms at a water-fuel ratio of 1. 4.
Interestingly, after the cream has been formed and the water flow reduced slightly, there is no significant apparent change in consistency until the water-fuel ratio is reduced from 0. 9 to 0. 65, as shown by the dottedline path 66 of Figure 5. As this point is approached, the creamy mixture .. g_ .
llZ6S;~
becomes heavy, changing from the consistency of whipping cream to that of paint, Decreasing the water-fuel ratio further returned the mixture to its normal suspended state. Tests indicate that there is no significant increase in manifold fuel pressure for the creamy emulsion at similar operating conditions.
5 While the water-fuel ratio at which conversion to the creamy mixture occurs may be above the normal operating range for some engines, it may be advanta-geous to initially run to high water-fuel ratios to get the cream to "start" and then to reduce the ratio, staying on the dotted curve 66 of Figure 5 to take advantage of the hysteresis-like phenomenon whereby a creamy texture can be 10 maintained at lower water-fuel ratios than on the solid line path of Figure 5, The phenomenon causing the cream to form can probably be explained by the large difference in surface tension of the two fluids. Applica-tion of high shear stress to the two-phase mixture results in more subdivision of the fuel pha~e than the water phase Initially, the fuel is a continuous phase 15 while the water is in relatively large drops that settle rapidly. As water addition continues, a point is reached where a phase reversal occurs and the water becomes the continuous phase having the fuel suspended therein as relatively small drops with little opportunity to coalesce and separate. This is the emulsion described herein as "cream, " probably a pseudoplastic fluid 20 rather than a Newtonian fluid ~such as the ~uel or water alone). The process can be reversed by adding larg~ quantities of fuel to the mixture while the shearing action continues.
It should become obvious to one skilled in the art that certain changes can be made to the above-described invention without departing from 25 the broad inventive concepts thereof. For example, the present invention is meant to embrace any arrangement whereby two pipe flows, one of fuel and ~lZ6S~:~
one of water, are combined turbulently without necessity of complex homogenizers. While a simple plumbing "T" section has been demonstrated to be effective, this is merely one example of a means for directly combining the two fluids through turbulent mixing to produce a homogeneous mixture. Injecting the flows at an angle other than 90 at the point of confluence would also be acceptable providing that the mixing which occurred was turbulent (i.e., occurred at a Reynolds number consistent with turbulent flow for the direct combining means employed).
It is intended that the appended claims cover these and all other such variations in the present invention's broader inventive concepts.
SUPPLEMENTARY DISCLOSURE
It has been found that the distance of location of the mixing zone from the combustor is not critical, due to the extended "stay" times that suitable mixtures can achieve, in excess of one minute. However, insofar as nozzle fuel percentage variation is concerned, the best results for the subject system are achieved if the transit time between mixing zone and com-bustor nozzle does not exceed 30 seconds.
In the operation of the system, using a mixing device such as the disclosed "T" arrangement, the homogeneous mixing requires no emulsifying agents intentionally added to fuel or - water, and the provision of turbulent mixing with a Reynolds number of at least 1500 in the resulting mixture produces the desired result. The ratio of water to fuel can operate in the range 0.6 to 1.4 by weight.
What is provided is, in a simplified method for reducing NO emissions from a gas turbine engine having a combustor in which a flow of pressurized air is mixed with fuel and combusted the steps of:
~llZ65~
a) providing a flow of fuel under pressure;
b) providing a flow of water under pressure;
c) mixing directly, the fuel flow and the water flow in a water: fuel ratio in the range 0.6 and l.~ by weight and wherein the conditions are sufficient to produce turbulent mixing with a Reynolds number of at least 1500 in the resulting mixture; and d) delivering the resulting mixture to a plurality of combustor nozzles for combustion,the combustion occurring within thirty seconds from the time the fuel and water flows are mixed.
In the case where the fuel is Dlesel Fuel No. 2 the water: fuel ratio is in the range of 0.7 and 1.0 by weight.
Claims (6)
1. In a gas turbine comprising a combustor in which a flow of pressurized air is mixed with fuel and combusted, a fuel delivery system for delivering fuel to said combustor, and a "T" section within said fuel delivery system for directly combining the flow of fuel with a flow of water for direct delivery to said combustor, said "T" section having a first inlet for receiving the flow of fuel and a second inlet for receiving a flow of water, and wherein the two flows are generally normal to each other at their point of confluence within the "T" section to produce turbulent mixing therein.
2. In a method of reducing NOx emissions in a gas turbine engine having a combustor in which a flow of pressurized air is mixed with fuel and combusted, a system for delivering fuel to said combustor, including a "T" section for directly combining the fuel with water within said fuel delivery system for direct delivery to said combustor, wherein the step of combining separate pipe flows of fuel and water is such that the two flows are generally normal at their point of confluence within the combining means and produce turbulent mixing therein.
3. The method as claimed in claim 2 in which a flow of pressurized air is mixed with said fuel and said water and combusted, including the step of increasing the water-to-fuel ratio until a consistency of a homogeneous cream is formed; and delivering the homogeneous cream to the combustor.
4. In a method of operation as recited in claim 3, the further step of reducing the water-to-fuel ratio after the cream has been formed, but to a value greater than that at which the mixture loses its consistency of a homogeneous cream.
Claims Supported by the Supplementary Disclosure
Claims Supported by the Supplementary Disclosure
5. The method as claimed in claim 2 in which the water:fuel ratio ranges from 0.6 to 1.4 by weight and wherein the conditions are sufficient to produce turbulent mixing with a Reynolds number of at least 1500 in the water:fuel mixture.
6. The method as recited in claim 5 wherein when the fuel is Diesel Fuel No. 2, the water:fuel ratio is in the range of 0.7 and 1.0 by weight.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA309,992A CA1126520A (en) | 1978-08-24 | 1978-08-24 | Water injection for gas turbine engine emission control |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA309,992A CA1126520A (en) | 1978-08-24 | 1978-08-24 | Water injection for gas turbine engine emission control |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1126520A true CA1126520A (en) | 1982-06-29 |
Family
ID=4112204
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA309,992A Expired CA1126520A (en) | 1978-08-24 | 1978-08-24 | Water injection for gas turbine engine emission control |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1126520A (en) |
-
1978
- 1978-08-24 CA CA309,992A patent/CA1126520A/en not_active Expired
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