Prevention of Contrail Formation in Hydrogen Fuel Cell Aircraft

Contrail emissions are aviation's largest non-CO2 contribution to global climate change. According to the Schmidt-Appleman criterion, low-temperature fuel cell propulsion systems can promote contrail formation in three ways compared to conventional turbofan engines: 1) through hydrogen as fuel, 2) through increased efficiency and, most importantly, 3) through external cooling. This paper covers theoretical background, system design, control strategies and practical considerations to avoid contrail formation for fuel cell propulsion systems. It is derived how contrails can be avoided by the combination of firstly condensing water vapor in the fuel cell exhaust and secondly mixing the still moist fuel cell exhaust with dry cooling air. Since the additional condenser cooling air flow will create additional drag, a control scheme is presented to condense as little water as necessary, thus minimizing additional drag. Potentially avoiding contrails completely may represent a major environmental opportunity for fuel cells compared to conventional turbofan engines.