A (Partially) Steam Engine in the Sky? Pratt & Whitney announces that it, “Has been selected by the U.S. Department of Energy (DoE) to develop novel, high-efficiency hydrogen-fueled propulsion technology for commercial aviation, as part of DoE’s Advanced Research Projects Agency-Energy (ARPA-E).” Their press release continues, “The Hydrogen Steam Injected, Inter‐Cooled Turbine Engine (HySIITE) project will use liquid hydrogen combustion and water vapor recovery to achieve zero in-flight CO2 emissions, while reducing nitrogen-oxide (NOx) emissions by up to 80 percent and reducing fuel consumption by up to 35 percent for next generation single-aisle aircraft.” P&W claims their HySIITE engine’s steam injection will “dramatically reduce” nitrogen oxide emissions, a greenhouse gas. “The semi-closed system architecture is claimed to have thermal efficiency “greater than fuel cells,” and have lower operating costs compared to “drop-in” sustainable aviation fuels (SAF). Steam Aircraft Engines Are Not New The Besler Brothers of Oakland, California demonstrated a Travel Air 2000 biplane powered by their steam engine. The …