Water injection technology has historically been used in aviation to increase jet engine thrust and is presently used for ground power applications to increase gas turbine power and life, and to reduce the emissions of oxides of nitrogen (NOx). Analytical systems studies were performed at the NASA Glenn Research Center to estimate the effects of water injection on a commercial turbofan engine to reduce specific fuel consumption (SFC), NOx emissions, and engine hot-section temperatures while maintaining constant thrust. The subsequent reduction in hot-section temperatures could increase engine life and reduce maintenance costs. In-house efforts included engine cycle modeling and mission analysis. Contracted efforts repeated and verified the in-house results. The researchers also developed preliminary schematics with the hardware required to implement this technology and estimated the changes to engine life and maintenance cost.

The baseline vehicle was a 300- passenger aircraft using two high bypass turbofan engines. Water injection before the low-pressure compressor (LPC) yielded greater reductions in maximum temperature and fuel consumption than combustor water injection, but it required almost twice as much water during the takeoff cycle. Water could be used through top-of-climb for continued reduction of the maximum cycle temperature and emissions, but this would require large amounts of water.

Estimates of hot-section life improvement from the lower temperatures with water injection would vary depending on engine type (for engines that experience higher removal or maintenance rates because of turbine blade temperature distress, water injection would be of more value). However, a breakdown of waterinjection costs with average estimated engine maintenance savings suggests that savings could well offset the added costs of water injection.

Even though water injection is quite successful in reducing NOx emissions during takeoff, low-emission combustors are still needed for the cruise and climb portions of the flight. Although the NOx emission rate is high during takeoff and initial climbout, most NOx is generated during the long cruise and climb periods where water injection is impractical because of the large quantity of water that would be required. Other considerations are potentially reduced smoke emissions but potentially increased hydrocarbon and carbon monoxide emissions, depending on the engine cycle. This will require further investigation if water injection is to be incorporated in new or existing engines.

Bibliography:
Daggett, D.L., et al.: Water Injection: Disruptive Technology to Reduce Airline Emissions and Maintenance Costs. SAE Paper 2004-01-3108, 2004.
Daggett, David L.; and Hendricks, Robert C.: Water Misting and Injection of Commercial Aircraft Engines to Reduce Airport NOx. NASA/CR-2004-212957, 2004.

Special Recognition:
Runner-up, Society of Automotive Engineers (SAE) 2004 Environmental Excellence in Transportation Award

Glenn Authors and Contacts:
Christopher A. Snyder, 216-977-7018, Christopher.A.Snyder@nasa.gov
Jeffrey J. Berton, 216-977-7031, Jeff.Berton@grc.nasa.gov
Robert C. Hendricks, 216-977-7507, Robert.C.Hendricks@nasa.gov

Programs/Projects:
Propulsion and Power Project