Robert C. Hendricks

Glenn Research Center, Cleveland, Ohio

David L. Daggett

Boeing Commercial Airplane, Seattle, Washington

Dale T. Shouse and William M. Roquemore

Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio

Andreja Brankovic and Robert C. Ryder, Jr.

Flow Parametrics, LLC, Ivoryton, Connecticut

Can Water-Injected Turbomachines Provide CostEffective Emissions and Maintenance Reductions?

NASA/TM—2011-214039

May 2011

141–ISROMAC–11
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Robert C. Hendricks

Glenn Research Center, Cleveland, Ohio

David L. Daggett

Boeing Commercial Airplane, Seattle, Washington

Dale T. Shouse and William M. Roquemore

Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio

Andreja Brankovic and Robert C. Ryder, Jr.

Flow Parametrics, LLC, Ivoryton, Connecticut

Can Water-Injected Turbomachines Provide CostEffective Emissions and Maintenance Reductions?

NASA/TM—2011-214039

May 2011

141–ISROMAC–11

National Aeronautics and

Space Administration

Glenn Research Center

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NASA/TM—2011-214039 1 

Can Water-Injected Turbomachines Provide Cost-Effective Emissions 

and Maintenance Reductions? 

Robert C. Hendricks 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

David L. Daggett 

Boeing Commercial Airplane 

Seattle, Washington 98124 

Dale T. Shouse 

Air Force Research Laboratory 

Wright-Patterson Air Force Base 

Dayton, Ohio 45433 

William M. Roquemore 

Air Force Research Laboratory 

Wright-Patterson Air Force Base 

Dayton, Ohio 45433 

Andreja Brankovic 

Flow Parametrics, LLC 

Ivoryton, Connecticut 06442 

Robert C. Ryder, Jr. 

Flow Parametrics, LLC 

Ivoryton, Connecticut 06442 

Abstract 

An investigation has been performed to evaluate the effect of 

water injection on the performance of the Air Force Research 

Laboratory (AFRL, Wright-Patterson Air Force Base 

(WPAFB)) experimental trapped vortex combustor (TVC) over 

a range of fuel-to-air and water-to-fuel ratios. Performance is 

characterized by combustor exit quantities: temperature and 

emissions measurements using rakes, and overall pressure drop, 

from upstream plenum to combustor exit. Combustor 

visualization is performed using grayscale and color still 

photographs and high-frame-rate videos. 

A parallel investigation evaluated the performance of a 

computational fluid dynamics (CFD) tool for the prediction of 

the reacting flow in a liquid fueled combustor (e.g., TVC) that 

uses water injection for control of pollutant emissions and 

turbine inlet temperature. Generally, reasonable agreement is 

found between data and NOx computations. 

Based on a study assessing the feasibility and performance 

impact of using water injection on a Boeing 747–400 aircraft to 

reduce NOx emissions during takeoff, retrofitting does not 

appear to be cost effective; however, an operator of a newly 

designed engine and airframe might be able to save up to 

1.0 percent in operating costs. Other challenges of water 

injection will be discussed. 

Introduction 

Aviation is anticipated to resume growing at about 5 percent 

per year, and in some sectors twice that rate is anticipated [1]. As 

such, environmental and fuels availability pressures will continue 

to mount and could invoke limits to the growth of commercial 

aviation. Therefore, the aviation community is putting more 

effort towards improving aircraft environmental, aerodynamic, 

and engine performance. Continued reductions in NOx emissions 

are an important part of the solution, yet are difficult to control as 

new engines utilize higher overall pressure ratios (OPRs) to 

enhance fuel efficiency. Without implementing new combustor 

technology, such increases in OPR will result in higher NOx 

emissions. 

A method to control NOx emissions in industrial gas turbines 

is to inject water by misting the inlet air or direct injection into 

the combustor. Water injection has been used for over 60 years in 

aviation for engine cooling, which then enabled an added thrust 

capability. However, during the early years of its use, the side 

benefit of emissions reduction was not considered. 

In the older Boeing 747–100s and 200s aircraft that 

used water injection, wing tanks held between 420 and 

704 gallons of demineralized conditioned water for takeoff 

use. Associated maintenance problems included system 

corrosion, water freezing, increased engine maintenance, and 

occasional improper use of poor quality water (i.e., tap water). 

 
NASA/TM—2011-214039 2 

These factors gave water injection a poor reputation in the 

aviation industry. However, lessons learned from this system, 

coupled with operating experience of industrial engines, and 

good design practices may make water injection again worthy of 

consideration for emissions reduction during takeoff. Based on 

experimental trapped vortex combustor (TVC) data, CFD results, 

and prior studies, a study was completed to assess the feasibility 

and performance impact of using water injection on a Boeing 

747–400 aircraft to reduce NOx emissions during takeoff to 

3000 ft (914 m) altitude. At a 1:1 water-to-fuel injection into the 

combustor, the engine’s turbine inlet temperature (T4) would be 

reduced by over 120 °F (67 K). Engine NOx emissions are 

reduced up to 80 percent with hot section life improvement 

estimates up to a 29-percent increase in turbine life. Performance 

penalties include a 750-lb (340-kg) increase in aircraft empty 

weight due to the system components. This weight increase uses 

an additional 20 U.S. gallons more fuel on a 3000 nmi mission. 

About 400 gallons of conditioned water will be used onboard the 

aircraft during takeoff to 3000 ft altitude.

Trapped Vortex Combustor (TVC) 

The new prototype TVC represents one type of compact, 

high-efficiency, high-turndown-ratio, low-emissions combustor 

that has been developed to control the NOx increases that come 

with higher OPR, more fuel efficient engines. However, it is 

increasingly difficult to constrain the specific NOx increase 

associated with higher OPR designs. 

Water-Injected TVC 

One of the methods used to control NOx emissions in 

industrial gas turbine engines is to inject water directly into the 

combustor. As the water-to-fuel injection ratio is increased to a 

1:1 ratio, T4 decreases as the combustor flame temperature 

decreases, as visualized in Figure 1 [2]. This reduces NOx 

emissions and is also expected to improve turbine life. 

CFD Simulations of Water-Injected TVC 

Computational fluid dynamics (CFD) simulations are being 

performed utilizing a methodology that includes computeraided design (CAD) air-solid modeling of the geometry, 

application of a flow solver with parallel processing capability 

and distributed over networked computers, and graphical and 

quantitative post-processing tools [3]. Physical models include 

liquid fuel droplet dynamics and evaporation, with combustion 

modeled using a hybrid finite-rate chemistry model developed 

for Jet-A fuel. CFD and experimental results with water 

injection are compared for cases with cavity-only fueling 

(Fig. 2) [3], while a numerical study of cavity and main fueling 

was also performed (Fig. 3) [3]. 

Predicted and measured trends in combustor exit 

temperature, CO and NOx are in general agreement at the 

different water-to-fuel loading rates, although quantitative 

differences exist between the predictions and measurements 

(Fig. 3) [3]. 

The NOx–OPR Challenge 

Although excellent progress has been made in reducing 

aircraft engine hydrocarbon and carbon monoxide emissions, 

NOx has been difficult to control. A tradeoff exists between 

engine fuel efficiency and NOx emissions. As engine fuel 

efficiency is improved by increasing the Overall Pressure Ratio 

of the engine’s compressor, the increased compressor exit gas 

temperature (T3) that goes with the higher OPR usually results 

in higher specific NOx emissions. 

Based on experimental TVC data, combustor CFD modeling 

results and prior test data, a study was completed to assess the 

feasibility and performance impact of using water injection on a 

Boeing 747–400 aircraft to reduce NOx emissions during 

takeoff [2 and 4]. 

Earlier studies of Roquemore et al. [5] and Burrus et al. [6] 

compared the combustor performance of the TVC with the 

current aircraft fleet and projected combustor designs. 

Normalizing these results in terms of a current fleet engine fuel 

burn (baseline: 767 airplane), increases in fuel economy are 

gained through increasing OPR, but at the expense of NOx 

increases. NASA’s Ultra Efficient Engine Technology (UEET) 
NASA/TM—2011-214039 3 

 
NASA/TM—2011-214039 4 

new engine cycle and combustor goals have increased OPRs to 

between 50 and 57 and have set NOx emissions goal at 

70 percent ICAO-1996 which translates to EINOx = 36 and 

24 g/kg of fuel at 100 and 85 percent power, respectively, for 

OPR = 55, 85.8 klbf (382 kN), 100 percent class engine. At 

these pressure ratios, the TVC NOx emissions would be 

70 percent of the baseline, but still higher than the more 

aggressive goal of 80 percent reduction. Augmenting the TVC 

with a 1:1 water injection ratio would readily achieve the 

emissions reduction goal. 

Other NOx emissions reduction technologies, such as 

Talon X1

 and TAPS2 combustors offer some degree of 

emissions reduction during takeoff and are a crucial part of the 

solution as they do provide emissions reductions during cruise. 

Potential Benefits and Liabilities 

For the primary Pratt & Whitney PW4062 engine studied for 

the Boeing 747–400 aircraft, injecting water directly into the 

combustor was determined to be less problematic and offer 

greater NOx emissions reduction capability than injection into 

the compressor. Test data from several sources and engine types 

showed that using a 1:1 water-to-fuel injection ratio should 

yield an 80 percent NOx reduction as shown in Figure 4 [2]. 

Recent test results, as well as historical data, showed that 

there could be a large potential reduction in smoke emissions 

when using water injection during takeoff. For noise 

considerations, water injection adds mass to the engine exhaust. 

When keeping thrust constant, a corresponding decrease in jet 

velocity was calculated to result in a small reduction in noise. 

 1

Pratt & Whitney, East Hartford, CT, and MTU Aero Engines GmbH, 

Munich, Germany. 2

General Electric Company, Fairfield, CT, and CFM International. 
NASA/TM—2011-214039 5 

The engine’s turbine inlet temperature was calculated to be 

reduced by over 120 °F (67 K). Engine operation at reduced 

temperatures also holds the potential for hot-section life 

improvement. According to the estimates obtained from one 

engine company, up to a 29 percent increase in turbine life may 

be expected. 

Performance penalties include approximately a 750-lb 

(340-kg) increase in aircraft weight that could reduce range 

by 60 nmi. Carrying this additional weight requires about 

20 U.S. gallons more fuel on a 3000 nmi mission. Another 

challenge of water injection is its increased propensity to cause 

the compressor to stall (i.e., reduces the stall margin). 

Addressing this issue may result in redesign issues and fuel 

efficiency penalties on older engines. Active compressor stall 

control systems could address these concerns on newly 

designed engines (e.g., [7]). These engine operability issues 

need to be addressed along with the requirements of significant 

testing and certification. 

The resulting high development costs, coupled with engine 

performance penalties on older engine designs, will make the 

system unattractive as a retrofit option. However, for a newly 

designed engine and airframe, some of these costs and penalties 

may be reduced. If one considers the full impact of reduced 

landing fees and potential of the longer lived turbine’s positive 

impact on engine maintenance costs, the system was estimated 

to have potential savings for an operator of a newly designed 

airplane of up to 1.0 percent in operating costs (Fig. 5) [2]. 

Conclusions 

If the engine operational uncertainties can be overcome, 

water injection may become an attractive option to consider for 

future aircraft in dramatically reducing takeoff NOx and 

possibly smoke emissions. Although water injection is an old 

technology, further study and tests are required in order to 

validate the potential for this technology to be used on newer, 

higher performing engines. A change of this magnitude in 

engine and airplane systems architecture can only be made with 

well-understood technology. 

References 

[1] Broichhausen, Klaus: Engine Technology Prepared in 

Europe⎯Innovation by Successful Partnerships. 

ISABE−2005−1001, 2005. 

[2] Daggett, D.L.; Hendricks, R.C.; and Mahashabde, A.: Water 

Injection⎯Could It Reduce Airplane Maintenance Costs and 

Airport Emissions. ISABE−2005−1249, 2005. 

[3] Brankovic, A.; and Ryder, R.: Emissions Prediction and 

Measurement for Liquid Fueled TVC Combustor With and 

Without Water Injection. AIAA−2005−0215, 2005. 

[4] Daggett, D.L.: Water Injection Feasibility for Boeing 747 

Aircraft. NASA/CR⎯2005-213656, 2005. 

[5] Roquemore, W.M., et al.: Vortex Combustor Concept for 

Gas Turbine Engines. AIAA−2001−0483, 2001. 

[6] Burrus, D.L., et al.: Performance Assessment of a Prototype 

Trapped Vortex Combustor Concept for Gas Turbine 

Application. ASME 2001−GT−0087, 2001. 

[7] Scheidler, S.G.; and Fottner, L.: Active Stabilization of the 

Compression System in a Twin-Spool Turbofan Engine at Inlet 

Distortions. ISABE 2003−1083, 2003. 
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14. ABSTRACT

An investigation has been performed to evaluate the effect of water injection on the performance of the Air Force Research Laboratory 

(AFRL, Wright-Patterson Air Force Base (WPAFB)) experimental trapped vortex combustor (TVC) over a range of fuel-to-air and water-tofuel ratios. Performance is characterized by combustor exit quantities: temperature and emissions measurements using rakes, and overall 

pressure drop, from upstream plenum to combustor exit. Combustor visualization is performed using grayscale and color still photographs 

and high-frame-rate videos. A parallel investigation evaluated the performance of a computational fluid dynamics (CFD) tool for the 

prediction of the reacting flow in a liquid fueled combustor (e.g., TVC) that uses water injection for control of pollutant emissions and 

turbine inlet temperature. Generally, reasonable agreement is found between data and NOx computations. Based on a study assessing the 

feasibility and performance impact of using water injection on a Boeing 747-400 aircraft to reduce NOx emissions during takeoff, 

retrofitting does not appear to be cost effective; however, an operator of a newly designed engine and airframe might be able to save up to 

1.0 percent in operating costs. Other challenges of water injection will be discussed.

15. SUBJECT TERMS

Seals; Coatings; Thin films; Turbomachines; Life 

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