= THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47 St., New York, N.Y. 117 84-GT-13 [^^ The Society shall not be responsible for statements or opinions advanced in papers or In S discussion at meetings of the Society or of its Divisions or Sections, or printed in its publications. Discussion is printed only if the paper is published in an ASME Journal, ^^( Released for general publication upon presentation. Full credit should be given to ASME, the Technical Division, and the authoris). Papers are available from ASME for nine months after the meeting. Printed in USA. Copyright 1984 by ASME NOx ABATEMENT VIA WATER INJECTION IN AIRCRAFT-DERIVATIVE TURBINE ENGINES D. W. Bahr and T. F. Lyon Aircraft Engine Business Group General Electric Company Cincinnati, Ohio ABSTRACT The results of analytical and experimental investigations to develop efficient and reliable water injection methods for reducing the nitrogen oxides (NO x ) levels of the LM25 and LM5 engines are presented. These aircraft-derivative turbine engines are equipped with compact annular combustors. In these investigations, various methods of injecting water into the combustor primary zone were evaluated in combustor and engine tests to identify methods with minimal water flow requirements for a given degree of NO x abatement. Primary emphasis was focused on the development of methods of injecting liquid water into the engines when operating with distillate fuels. Methods of injecting both liquid water and steam when operating with natural gas were also investigated. The impacts of water injection on combustor and engine performance and operability were additionally assessed. Satisfactory accommodation of water/fuel weight ratios above unity and associated NO x level reductions as high as 9 percent were demonstrated. INTRODUCTION During the past few years, standards to limit the nitrogen oxides (NO x ) emission levels of stationary gas turbine engines have been established in the United States and in several other nations. In the United States, such standards have been promulgated by both the U.S. Environmental Protection Agency (EPA) and by various state and other local regulatory agencies. The EPA-prescribed NO x emission standards are national standards and set minimum requirements which must be met by all designated engine installations regardless of location [1]. For the most part, the NO x emission standards prescribed by state or other local agencies are even more stringent. The standards proposed by the California Air Resources Board, for example, are appreciably more stringent [2]. In many cases, significant reductions in the uncontrolled NO x levels of the affected engines are required to meet these standards. To date, the basic abatement approach that has been most widely applied to obtain these needed reductions consists of the injection of water into the engine combustion system [3]. The injection of either liquid water or steam directly to the primary zone of an engine combustor results in significant decreases in its local flame temperatures and, therefore, in the resultant NO x levels. Within recent years, an extensive series of analytical and experimental investigations was conducted by the General Electric Aircraft Engine Business Group to develop efficient and reliable water injection methods for reducing the NO x levels of the LM25 and LM5 engines. These engines are aircraft-derivative turbine engines, which are used in a variety of industrial applications. The LM25 engine has a nominal output power rating of 22. megawatts (29,5 horsepower) and cycle pressure ratio of 18.6. The LM5 engine has a nominal output power rating of 33.3 megawatts (44,7 horsepower) and cycle pressure ratio of 26.8. Both engines are equipped with compact annular combustors and are designed to operate with both gaseous and distillate fuels. Because of their high cycle pressure ratios, the uncontrolled NO x levels of these engines are high, relative to those of older technology engines with similar output power ratings. In these investigations, various methods of injecting liquid water into the two engine combustors, when operated with diesel fuel, were evaluated and developed in component tests. The preferred method was subsequently evaluated in engine tests. In less extensive investigations, methods of injecting both liquid water and steam into the two engine combustors, when operated with natural gas, were also evaluated. The important findings of these investigations, including the impacts of water injection on engine performance and operability, are summarized in this paper. TEST ENGINES AND COMBUSTORS The LM25 and LM5 engines are aircraftderivative turbine engines which are used in a variety of industrial applications. The LM25 engine is also
extensively used in marine applications. The LM25 engine is a derivative of the TF39 and CF6-6 aircraft turbine engines and the LM5 engine is a derivative of the CF6-5 aircraft turbine engine. Both are lightweight, compact and high performance engines, with high cycle pressure ratios and turbine inlet temperatures. As a result, both have high thermal efficiencies. Also, both engines are designed to operate with both gaseous and distillate fuels. The key performance characteristics of these two engines, when operated with natural gas, are summarized in Table I. TABLE I. Estimated Average Engine Performance Ch a racte ristics Fuel: Natural Gas ISO Operating Conditions No Inlet Or Exit Installation Pressure Losses Output Shaft Speed: 36 RPM No Water Injection LM25 LM5 Model 7LM25-PE 7LM5-PA Base Rating - Shaft Power 22. 33.33 (Megawatts) - Heat Rate 6885 6743 (kilojoules/watt-hr) - Heat Rate 9.741 9.54 (BTU/Horsepower-hr) Both engines are equipped with compact annular combustors. Cross-sectional illustrations of the two combustors are presented in Figures 1 and 2. The two designs have several similar features. Both configurations employ 3 fuel injectors and high airflow swirl cups around each fuel injector. The LM5 is, however, a shorter and more compact configuration. Fig. 2. Cross-Sectional Drawing of LM5 Combustor controlled NO x levels of the LM25 and LM5 engines are presented in Figure 3. For reference purposes, the applicable EPA-prescribed standards for stationary gas turbines used in electric utility'applications are included in this figure. In both cases, the standard includes the allowable heat rate adjustment, which increases the allowable NO x level from the base level of 75 ppm by volume at 15 percent oxygen. C No Installation Losses ol^^ese T o, 4 ^ x,5 o T x E - i t has p a ea "C i _ / Applicable EPA Stan da rds o d O y 1 i /,5 Foe\ (tor Electric Utility Installations) an 3 C^ v 2 C) CC ISO Conditions Sep ^^ool^^e ^ Je^ MSCUOINa ^M25^^INa` Ga n 1 2 3 4 Shaft Power, Megawatts Fig. 3. Average Engine Status - Uncontrolled NO x Levels of LM25 and LM5 Engines Fig. 1. Cross-Sectional Drawing of LM25 Combustor These two combustors were developed to meet stringent smoke emission limitations. Accordingly, with either gaseous or distillate fuels, both engines operate with non-visible smoke levels. With gaseous fuels, the engine smoke levels are extremely low. Because of the high cycle pressure ratios of the two engines, their uncontrolled NO x levels are comparatively high, relative to those of older technology engines with similar output power ratings. The un- Consistent with calculations of the stoichiometric flame temperatures attainable in the primary zones of the two engine combustors, the NO x levels of both engines with natural gas fuel are in the range of 5 to 6 percent of those with diesel fuel. Because of its higher cycle pressure ratio, the NO x levels of the LM5 engine are higher with either fuel type than those of the LM25 engine. As a consequence of this higher pressure ratio, the LM5 combustor inlet air temperatures are higher. As a result, the peak combustion gas temperatures in its primary zone are higher. These higher primary zone temperatures, along with the higher combustor operating pressure, result in increased nitric oxide formation rates. ANALYTICAL ASSESSMENTS As the initial step in the development of suitable water injection provisions for these engines, analytical
studies were conducted to define the water flow/no x abatement relationships for an idealized model of the combustion and water injection processes. These relationships were defined for both liquid water injection and steam injection and for operation with either gaseous or distillate fuels. A simple, one-dimensional combustor model was used in conducting these analyses. In this model, a uniform mixture of stoichiometric combustion gases was assumed to be contained in a zone at the forward end of the combustor. The NO x emissions were assumed to be entirely generated in this zone. The zone was assumed to be continuously supplied with all of the fuel flow and the total combustor airflow fraction needed for a stoichiometric mixture. This fraction is, therefore, a variable and is dependent on the overall combustor temperature rise. Any injected water was assumed to be uniformly distributed in this zone. At any selected combustor operating condition, the reductions in the bulk temperature of the stoichiometric mixture resulting from the injection of water were then calculated by means of an enthalpy balance. Based on known temperature/reaction rate relationships for the thermal production of nitric oxide, these temperature reductions were, in turn, used to calculate the percentage reductions in the generated quantities of nitric oxide. The resulting idealized water flow/n x abatement relationships for the LM25 and LM5 engines, when operated at high power conditions with distillate fuel having a heating value of 42.8 x 1 6 joule per kilogram (18,4 BTU per pound), are presented in Figure 4. As is shown, the required steam flows for any selected degree of NO x abatement are approximately 55 percent greater than those with liquid water. This relationship is consistent with the enthalpy difference between the two fluids and the resulting difference in their combustion gas cooling capabilities. 1.o.7 - \\\\\ 3=.5 \\\\ Fuel Heating Value (joule/kg) \\\\ Distillate 42.8 x 1 6 \\\ Gaseous 5. x 1 6..4- \\ \\ vo \ \.3 \^ O o \ z \ o ci,2 \ \ With Steam Injection ' \ /\ =r \ \ 3 v \ \ o `.1 \ With Liquid \ _ Water Injection y \.7 \ \.5 1..4.8 1.2 1.6 2. 2.4 In Figure 4, the NO levels are expressed in terms of a ratio (RNOx) of the NO level with water injection to the uncontrolled NO x level. Also, the water and fuel flows are expressed as ratios. In this normalized format, the water flow/nox abatement relationships are largely independent of the absolute NO x levels, fuel flows and water flows. As such, the observed relationships of different engines, as well as those of a given engine at various different power settings, can be directly compared when expressed in this format. In this normalized format, the idealized water flow/no x abatement relationships of the LM25 and LM5 engines are the same, as is shown in Figure 4. Using the same simple combustor model, idealized water flow/no x abatement relationships for the LM25 and LM5 engines; when operated at high power conditions with natural gas having a heating value of 5. x 1 6 joule per kilogram (21,5 BTU per pound), were also calculated. These results are presented in Figure 4, along with the calculated distillate fuel relationships. As is shown in Figure 4, a higher water/fuel weight ratio, at any selected RNOx value, is required with natural gas than with distillate fuel. This result stems from the fact that, for any given overall combustor temperature rise, less fuel flow is needed with natural gas because of its higher heating value. However, with a constant overall temperature rise, the quantity of heat released in the primary zone is essentially the same with either fuel type and, to a first approximation, the quantity of primary zone gases heated to stoichiometric flame temperatures is the same. Therefore, the required water flow quantity is virtually the same with either fuel type, for any selected RNOx value, and the resulting water/ fuel ratio is higher with natural gas than with distillate fuel. For any engine, both idealized and observed water flow/no x abatement relationships can be generalized for any fuel type by a simple adjustment of the water/ fuel weight ratio to account for heating value differences. If a fuel with a heating value of 42.8 x 1 6 joules per kilogram (18,4 BTU per pound) is selected as the reference fuel, generalized relationships are provided by the following reference water/ fuel weight ratio parameter: / Water Flow Rate \ = Fuel Flow Rate /Reference Water Flow Rate (42.8 x 1 6 \ \ Fuel Flow Rate /Observed \Fuel Heating Value*) * Expressed in joules per kilogram With this adjusted (reference) parameter, RNOx becomes a function of the injected water flow per joule of heat release in the combustor, rather than of only water/fuel weight ratio. As such, the idealized water flow/no x abatement relationships are then identical with both gaseous and distillate fuels. It should be noted that these idealized relationships are the same even in instances where the absolute NO x levels are significantly different because of differences in the stoichiometric flame temperatures of the fuels. Fig. 4. Idealized Water Flow/NO x Relationships For LM25 and LM5 Engines, At High Load Conditions
Fuel In Water/Fuel In P Water In Water Fuel In In Water Out -* Fuel Out Water Out Fuel Out Water Out Water/Fuel Out Fig. 5. Liquid Water Injection Methods Evaluated In LM25 Combustor Component Tests With Diesel Fuel EXPERIMENTAL EVALUATIONS - WITH LIQUID FUEL OPERATION The initial experimental efforts were primarily focused on the development of methods of injecting liquid water into the LM25 and LM5 combustors, when operating with distillate fuels. As the first step of these development efforts, three candidate water injection methods were screened and compared in LM25 combustor component tests with diesel fuel. The methods that were evaluated are illustrated in Figure 5. The NO x abatement results obtained in these tests are presented in Figure 6. As is shown, the best water effectiveness levels (lowest required water flows for a given degree of NO x abatement) were obtained with water/ fuel premixing and with primary zone injection. For reference purposes, the idealized liquid water flow/nox relationship, which was evolved in the analytical assessments and is shown in Figure 4, is included in Figure 6. in Figure 7. In these tests, two slightly different nozzle configurations for injecting the water/fuel mixtures were evaluated. The results were found to be very similar to those obtained with water/fuel premixing in the LM25 combustor component tests. O z cc 1..8.6.4.2 - With Baseline Water/Fuel Nozzles With Alternate Water/Fuel Nozzles 1.^ `Noter Injection Mode..2.4.6.8 1. 1.2 1.4 1.6.8 -( X.6 I z.4 -.2 L.. v ^ O O Upstream Injection n Primary one Injection V Premixed Water/Fuel Idealized Relationship A- ^O (from Fig_ 4) ^ L^^7.2.4.6.8 1. 1.2 1.4 Fig. 6. NO x Abatement Pesults of LM25 Combustor Component Tests With Diesel Fuel, At Simulated Base Load Conditions Based on these encouraging results and its inherent simplicity, the use of water/fuel premixing was then further evaluated in LM5 combustor component tests. The NO x abatement results of these tests are presented Fig. 7. NO x Abatement Results of LM5 Combustor Component Tests With Diesel Fuel and Premixed Water/Fuel, At Simulated Base Load Conditions Based on these combustor component test results, the use of water/fuel premixing was selected for further evaluations in both LM25 and LM5 engine tests. In both engines, the water/fuel premixing was accomplished by simply injecting the water via a teeconnection located at the fuel manifold inlet. A photograph of the installation used in the LM25 engine is shown in Figure 8. No other water/fuel mixing provisions were used. Previously conducted flow tests of this simple arrangement showed that reasonably uniform water/fuel ratios were obtained around the entire length of the engine fuel manifold. Additional descriptive information on this water injection method is contained in Reference 4. The key results of these engine tests are presented in Figure 9. Satisfactory accommodation of water/fuel ratios as high as 1.6 was demonstrated in these tests. With a water/fuel ratio of about 1., the NOx levels of 4
4 Fuel Inlet - - Water Inlet flows for a given degree of NO abatement). As an illustration of the agreement between combustor component and engine test results, the LM25 component and engine NO abatement results are compared in Figure 1. As is shown, generally good agreement between the component and engine data was obtained. 1. - n.8 U w" 4-.6.4 - Component Test (from Fig. 6).2 Engine Test (from Fig. 9) ( ri..2.4.6.8 1. 1.2 1.4 Fig. 1. Comparison of NO x Abatement Results Obtained In LM25 Combustor Component and Engine Tests With Diesel Fuel and Premixed Water/ Fuel, At high Load Conditions Fig. 8. Engine Fuel Manifold With Water Injection Connection At Manifold Inlet 1. Engine.8 O LM25 x.6 LM5 The impacts on the other emissions of concern -- smoke, carbon monoxide (CO) and unburned hydrocarbons (HC) -- were also monitored in these component and engine tests. A key purpose of the CO and HC measurements was to detect any impact of water injection on combustion efficiency. The measured HC levels of both engines were very low, both without and with water injection. The impacts on the CO levels of both engines, as measured in the engine tests, are presented in Figure 11. As is shown, the measured CO levels of both engines without water injection were very low. Using these data, the calculated combustion efficiency of each engine is greater than 99.9 percent. The effects of water injection on the CO levels of the two engines were found to be different -- of the two, the LM25 engine was found to be more sensitive. However, K.4.2..2.4.6.8 1. 1.2 1.4 1.6 LL C, 4 O3 a Cc Engine O LM25 LM5 Fig. 9. NO Abatement Results of LM25 and LM5 Engine Tests With Diesel Fuel and Premixed Water/Fuel, At High Load Conditions C 2 a N E 1 w ' v- both engines were reduced to about 1 percent of the uncontrolled levels. As was found in the abovedescribed analytical assessments, the normalized water flow/no x relationships of the two engines were found to be generally similar. However, with high water/fuel weight ratios, the LM5 engine was found to have better water effectiveness levels (lower water..2.4.6.8 1. 1.2 1.4 1.6 Fig. 11. CO Results of LM25 and LM5 Engine Tests With Diesel Fuel and Premixed Water/Fuel, At High Load Conditions 5
Fuel In Liquid Water Liquid Water N. In ' Fuel In Fuel Out Fuel Out Liquid Water' Out y ` Fuel Out Fuel Out Liquid Water Out Fig. 12. Water Injection Methods Evaluated In LM25 and LM5 Combustor Component Tests With Natural Gas Fuel even with a water/fuel ratio of 1., its combustion efficiency was only decreased to 99.8 percent. In the case of the LM5 engine, no sensitivity was observed even with a water/fuel weight ratio as high as 1.2. This sensitivity difference appears to be primarily due to the cycle pressure ratio difference between the two engines. The much higher pressure ratio of the LM5 engine results in both higher combustor inlet air temperatures and pressures at the high power operating conditions and, thus, more favorable combustion operating conditions. No other adverse impacts on combustor performance or operability were observed in these tests. Both the smoke emission and the exit temperature distribution characteristics of the two combustors were found to be virtually unchanged over the range of tested water/fuel ratios. Also, no adverse effects on combustion stability or on combustor dome and liner metal temperature gradients were observed. EXPERIMENTAL EVALUATIONS - WITH GASEOUS FUEL OPERATION Liquid Water Injection In parallel with the development efforts with distillate fuels, more limited investigations were conducted to develop liquid water injection methods compatible with gaseous fuel operation. These efforts consisted of both LM25 and LM5 combustor component tests with natural gas as the fuel. In these tests, two water injection methods were investigated. One injection method involved the use of dual fuel nozzle configurations like that shown in Figure 12. These LM25 and LM5 nozzle configurations are used in engine applications which require the accommodation of both gaseous and distillate fuels. In this basic design, liquids are injected and pressure-atomized by a conventional dual-orifice fuel nozzle which is located within a separately supplied ring of gas injection ports. This nozzle type was evaluated in both LM25 and LM5 combustor component tests. The other injection method involved the use of a nozzle configuration in which the water was injected via six simple orifices. The natural gas was injected via a ring of ports positioned around these six liquid injection orifices. This configuration, which is also illustrated in Figure 12, was evaluated in only the LM5 combustor component tests. The NO x abatement results of these tests are presented in Figure 13. As is shown, similar water effectiveness levels were obtained, although the LM5 dual fuel nozzle was less effective at high water/fuel weight ratios. Also included in Figure 13 for reference purposes is the idealized liquid water flow/no x relationship, which was evolved in the analytical assessments and is shown in Figure 4. 1..8.6 cc.4.2 ^ G Idealized Relationship (from Fg. 4) Combustor W ate r Injection Mode LM5 Standard LM5 Dual Fuel Nozzle n LM25 Standard LM25 Dual Fuel Nozzle v LM5 Special LM5 Fuel Nozzle..2.4.6.8 1. 1.2 1.4 1.6 Fig. 13. NOx Abatement Results of LM25 and LM5 Combustor Component Tests With Natural Gas, At Simulated Base Load Conditions The deviations of these measured water effectiveness levels with natural gas operation from the idealized values were found to be generally greater than those observed with diesel fuel operation and water/ fuel premixing -- as can be seen by the direct comparison of the results presented in Figure 14. In Figure 14, the water/fuel ratios for natural gas operation are adjusted values, using the fuel heating value adjustment described above as a part of the analytical assessments discussion. With this adjustment, the idealized and measured water flow/no x relationships shown in Figure 13 are shifted somewhat to the left.
1. No adverse impacts on combustor performance, stability, smoke emission or metal temperature.8 characteristics were observed in these LM25 and LM5 combustor component tests with natural gas. x.6 cc.4.2 \ - Nat. Gas Fuel with \ \ Std. Dual Fuel Nozzle ^^ (from Fig 13) Diesel Fuel with \ \ Premixed Water and Fuel (from Fig. 6)-^ Idealized \ ^ Relationship \ (from Fig. 4)...2.4.6.8 1. 1.2 1.4 x 42.8 x 1 6 Fuel Heating Value (J/kg) Fig. 14. Comparison of Liquid Water Effectiveness Levels Measured In LM25 Combustor Component Tests With Diesel and Natural Gas Fuels, At Simulated Base Load Conditions These comparisons suggest that more effective methods of introducing the liquid water and mixing it with natural gas should be obtainable. In any case, significant NO x level reductions and satisfactory accommodation of high water/fuel ratios were demonstrated in these tests with natural gas. With a water/fuel ratio of about 1., the NO x levels of both engines were reduced to about 2 percent of the uncontrolled levels. The estimated impacts of water injection on the CO levels of the two engines are shown in Figure 15. As a starting point for these estimates, CO emission data obtained in LM25 and LM5 engine tests with natural gas, but with no water injection, were used. The effects of water injection on these observed CO levels were then estimated by applying the same percentage increases to these CO levels as those obtained with water injection in the engine tests with diesel fuel. These effects with diesel fuel are shown in Figure 11. Similarly obtained estimates of the effects of water injection on the HC levels of the two engines, when operated with natural gas, indicate a negligible sensitivity. Steam Injection More recently, a test series was conducted to evaluate the effectiveness levels obtainable with steam injection. These development efforts involved LM5 combustor component tests, in which the steam and natural gas were premixed. The steam/fuel mixture was introduced into the combustor via sample gas injectors. This configuration is shown in Figure 12. The NO x abatement results of these tests are presented in Figure 16. Also included in Figure 16 for reference purposes is the idealized steam flow/no x relationship which was evolved in the analytical assessments and is shown in Figure 4. The steam effectiveness levels were found to be somewhat closer to the idealized values than was observed with liquid water injection and natural gas -- as can be seen by comparing these results with those contained in Figure 13. As expected, this finding demonstrated that premixing is a useful and effective injection method, confirming the results obtained with liquid water and distillate fuel. 1..8 x.6 z.4 -.2.. \o Idealized Relationship (from Fig. 4) v ^^.5 1. 1.5 2. 2.5 3. Steam/Fuel Weight Ratio Fig. 16. NO x Abatement Results of LM5 Combustor Component Test With Natural Gas and Premixed Steam/Fuel, At Simulated Base Load Conditions ADDITIONAL EVALUATIONS v U- U- 6 m a 4 C y 2 E w..2.4.6.8 1. 1.2 1.4 Fig. 15. Estimated CO Levels of LM25 and LM5 Engines With Natural Gas Fuel and Water Injection Via Dual Fuel Nozzles, At High Load Conditions In addition to determining the effects of water injection on combustion efficiency, the thermodynamic effects of liquid water on engine thermal efficiency were also assessed. The later impacts were analytically determined in engine thermodynamic cycle studies. The key results of these studies are presented in Figure 17. In these studies, output power was held constant. As is shown in Figure 17, water injection was found to result in substantial heat rate penalties (increases) in both engines. As an alternative to maintaining constant output power, it is possible to operate either engine with a constant firing temperature (constant turbine inlet temperature), by increasing the fuel flow as the water flow is increased. In this case, additional output power is obtained. However, the adverse impacts of water injection on engine thermal efficiency is still essentially the same as those shown in Figure 17.
v d a U y Lx C dc '-C W a G 2.4 6.8 1 12 t4 Fig. 17. Calculated Impact of Liquid Water Injection on Thermal Efficiency of LM25 and LM5 Engines With Either Diesel Or Natural Gas Fuel, At Base Load Conditions The effects of steam injection were not quantified in these studies. These effects on engine performance are generally favorable and, if the steam is generated by an exhaust gas heat recovery method, can have a very beneficial impact on engine thermal efficiency as well as on output power. The effects of water injection on combustor and turbine section life and durability were also not quantified as a part of these investigations. However, based on the results of the various experimental evaluations, no adverse impacts are expected. With premixed water/fuel, no significant changes in metal temperature gradients due to water injection were observed in the combustor section. Similar findings were obtained with the various liquid water injection methods used with natural gas. Also, because no significant changes in combustor exit temperature distribution due to water injection were observed with either fuel type, no effects on the turbine section are anticipated. RELATED CONSIDERATIONS Fuel nozzle operational life effects were not evaluated as a part of these investigations. However, the subsequent introduction of the water injection methods evolved in these investigations into LM25 and LM5 engines did necessitate some fuel system design changes to prevent adverse life impacts. Specifically, to accommodate the delivery of water -- especially liquid water -- via the fuel nozzles, some changes were required in the materials used in their fabrication. These material changes primarily involved the spin chamber and exit orifice elements of these fuel nozzle assemblies and were needed to eliminate corrosion and erosion problems. With liquid water injection, some changes in the flow dividing elements of the fuel system were also found to be needed to eliminate fuel nozzle erosion problems. With the introduction of these fuel system design modifications, the water injection methods developed in these investigations have been successfully incorporated into operational LM25 and LM5 engines. These water injection methods are currently being used in both distillate and natural gas-fueled engines. Another key consideration is that, with any of these NO x abatement systems, a high degree of water purity is required. Consistent with previously-defined fuel purity requirements of the LM25 and LM5 engines, water purity requirements have been defined and are included in the engine operating manuals. Important liquid water purity requirements of both engines include a maximum limit of 2.64 milligrams of solid contaminants per liter of water and a maximum limit of.5 parts per million (by weight) of metallic contaminants (total of sodium, potassium, lithium, lead and vanadium). In any installation, therefore, some water treatment provisions to provide acceptably pure water must be an integral part of the NO x abatement system. CONCLUDING REMARKS Based on these collective findings, it is concluded that very large NO x level reductions and efficient water utilization can be obtained in the LM25 and LM5 aircraft-derivative engines with the use of suitable techniques of injecting water into the combustor primary zone. In these engines, water/fuel weight ratios well above 1. can be satisfactorily accommodated with either distillate or natural gas fuels. Other than somewhat higher CO levels in the case of the LM25 engine, no adverse impacts on combustor TABLE II. LM25 Engine - Incremental NO x Level Reductions With Liquid Water Injection Engine Rating Baseload Fuel Natural Gas Uncontrolled NO x Level 185 ppm, Referenced to 15% 2 Water Injection Absolute NO x Reduction Percentage NO x Reduction Range (Water/Fuel (ppm, Referenced to 15% 2) (% Uncontrolled NO xlevel) Ratio, By Weight) Increment Cumulative Increment Cumulative. to.1 45 45 24.3 24.3.1 to.2 34 79 18.4 42.7.2 to.3 22 11 11.9 54.6.3 to.4 16 117 8.6 63.2.4 to.5 11 128 5.9 69.2.5 to.6 7 135 3.8 73..6 to.7 7 142 3.8 76.8.7 to.8 6 148 3.2 8..8 to.9 6 154 3.2 83.2.9 to 1. 5 159 2.7 85.9
performance or operability were found, even with water/ fuel ratios in excess of 1.. Also, no adverse impacts on engine hot section life or durability were uncovered. Some fuel system modifications were, however, found to be needed to prevent losses in the operational life of the fuel nozzle assemblies. Also, engine thermodynamic cycle studies showed, as expected, that the use of high liquid water/fuel ratios results in significant losses in engine thermal efficiency. It is further concluded that, while liquid water/ fuel ratios well above 1. can be satisfactorily accommodated, the use of such high ratios is generally not advantageous. As is illustrated by the LM25 engine NO x abatement results contained in Table II, much of the potentially obtainable reductions are realized with liquid water/fuel ratios in the range of.6 to.8. With ratios above this range, the incremental reductions per unit of injected water are relatively small. Thus, large amounts of treated water -- a valuable and, in many cases, an expensive resource -- are needed to obtain relatively small additional ambient air quality benefits. In addition, the small incremental NO x level reductions associated with high liquid water/fuel ratios are accompanied by substantial fuel cost penalties, as is illustrated in Figure 17. Other important considerations are that the use of high liquid water/fuel ratios can result in increased CO emission levels and can be expected to aggravate any possible fuel nozzle life problems which are associated with the use of water injection. Based on these various operational and economic considerations, a water/fuel ratio of about.8 is concluded to be an appropriate upper limit for liquid water injection in the LM25 and LM5 engines. With this upper limit, the uncontrolled NO x levels of both engines, with either distillate or natural gas fuels, are reduced by 8 percent or more. With steam injection, significantly higher water/ fuel ratios than.8 can be economically advantageous, depending on how the steam is generated. For example, with an exhaust gas heat recovery system to generate the steam, very favorable engine thermal efficiency and output power benefits can be realized with high steam injection rates. Based on the limited steam injection data obtained as a part of this program, it is concluded, from the standpoints of combustor performance and operation, that steam/fuel ratios as high as 2.5 can be satisfactorily accommodated. REFERENCES 1. Standards of Performance for New Stationary Sources; Stationary Gas Turbines, U.S. Environmental Protection Agency, Title 4 - Code of Federal Regulations - Part 6, Federal Register, Volume 44, Page 52792, September 1979. 2. Proposed Rule 1134 - Control of Oxides of Nitrogen Emissions From Electric Utility Gas Turbines, State of California Air Resources Board, March 1981. 3. Bahr, D. W., Gas Turbine Engine Emissions Abatement - Status and Needed Advancements, Project Squid Workshop on Gas Turbine Design Problems, Pages 25-223, Hemisphere Publishing Corporation, 198. 4. Campbell, T. C., Method for Reducing Nitrous Oxide Emissions From A Gas Turbine Engine, U.S. Patent 4,214,435, July 198.