Session: 04-21 Combustion Emissions I

Submission Number: 174470

Low Nox Hydrogen Combustion Testing in High Steam Environment for Future Aeroengine Concept 

This paper reports high-pressure combustion tests of hydrogen in a steam-air mixture that represents the hot-section working fluid of the Hydrogen Steam-Injected Intercooled Turbine Engine (HySIITE) concept. This novel propulsion concept is being studied by Pratt & Whitney, an RTX business (P&W), with a portion of the studies sponsored by the Department of Energy (DoE), Advanced Research Projects Agency-Energy (ARPA-e).

The HySIITE concept targets 35% efficiency improvement in comparison with kerosene-powered turbofan engines in service today, making the HySIITE concept a promising candidate to defray the costs of using expensive alternative, zero-carbon fuels. The efficiency improvement is primarily achieved by implementing i) onboard liquid hydrogen storage, ii) a condenser for condensing water out of the exhaust, iii) pumping the recovered water into the compressor for intercooling, iv) an evaporator to generate steam from the remainder of the recovered water using waste heat in the engine exhaust, and v) injection of the steam into a combustor that can maintain stable hydrogen combustion at high steam/air ratios, virtually eliminating NO_x emissions and enabling high liner longevity.

As part of the validation of this concept, we carried out a combustor design, manufacture, and test activity. A Rich-Quench-Lean (RQL) combustor was selected as a burner architecture in this study due to the low risk of flashback and good turndown performance. A fuel injector and air swirler were designed and implemented at the forward end of the combustor aiming for good mixing and secure flame anchoring in the presence of high steam content, but simultaneously without having flame attachment or flashback risk at the nozzle face due to vigorous hydrogen combustion.  Throughout the test activity, the combustor rig was operated at a scaled pressure (150 psia) and steam/air mixture temperatures (typically 650°F – 850°F) with a variable amount of high-pressure saturated steam mixing to the air.  The top and bottom walls of the combustor, representing an annular combustor’s inner and outer walls, were effusion-cooled by the steam/air mixture. The side walls of rig, where adjacent sectors would be located in an annular combustor, were water-cooled.  Air and steam flow to the combustor’s forward end, feeding the swirler and bulkhead, was supplied separately from air and steam flows to the combustor’s aft end where quench holes and effusion liners were located. This configuration enabled separate control of the forward versus aft airflows regardless of pressure drop and also allowed steam to be supplied and mixed separately into the forward versus aft airflows without impacting air splits.  Combustion was achieved with Steam-to-Air Ratio (SAR) over 0.8, which exceeds all operating points of the HySIITE concept. Stable hydrogen combustion up to about 0.5 SAR was achieved with steam mixed uniformly into the combustor airflow, but this approach resulted in reduced flame stability when higher SAR was attempted. Stable combustion at higher SAR was achieved by shifting steam injection to the aft-end. NO_x emissions were measured at the scaled cruise and takeoff conditions, including with sweeps across SAR and Fuel-to-Air Ratio (FAR) for both conditions. The resulting NO_x emission levels were lower than 2.5 ppm for all conditions investigated due to low combustion temperature with the high steam content, as enabled by the wide flammability limits of hydrogen. Combustor pressure fluctuations and steam-mixture-cooled wall temperatures were also continuously monitored, and no significant fluctuations or excessive temperatures were observed over the entire test activity.

Presenting Author: Wookyung Kim RTX Technology Research Center

Presenting Author Biography: Dr. Wookyung Kim is a Senior Manager of Combustion and Propulsion Team at RTX Technology Research Center (RTRC). The areas of his interest span overall advanced combustor research specializing in combustor stability, spray physics, plasma applications and sustainable combustion. Prior to joining the RTRC, Dr. Kim was Post Doctoral fellow/Research Associate at Jet and Flame lab. and Plasma Physics Lab. of Stanford University where he received his M.S. and Ph.D.

Authors:

Wookyung Kim RTX Technology Research Center
Lance Smith RTX Technology Research Center
Zhongtao Dai RTX Technology Research Center
Neil Terwilliger Pratt & Whitney