March 19, 2021, ©. Leeham News: This week we look deeper into the gains we can have for a hydrogen gas turbine-propelled airliner.
The ideas stem from the work of Chalmers Professor T. Grönstedt’s team in different EU research projects.
When we have discussed a hydrogen-fueled version of a gas turbine to drive our propulsors (fan/propfan/propeller), we have assumed an equal efficiency conversion of the gas turbine between Jet-A1 and hydrogen. We also mentioned there is potential to increase the efficiency of a hydrogen gas turbine.
The team around Professor Tomas Grönstedt at the Chalmers technical university in Gothenburg, Sweden, has worked on such improvement for five years in different research projects.
One of the projects is EU’s ENABLEH2 where Figure 1 shows the principle possibilities for use of the huge heat sink liquid hydrogen (LH2) represents. One can cool different parts of the gas turbine but also cryogenic electric motors (blue circuit in Figure 1) used in the aircraft.
If we focus on the possible improvements in a gas turbine, Figure 2 shows a more detailed view of what is researched in ENABLEH2.
The LH2 in the tank is stored at 22K. As it passes the pre-cooler ahead of the IPC/Booster (Intermediate Pressure/Booster Compressor), the H2 goes from 24K to 228K. Gradually it’s used to intercool the compressors and through a heat exchanger, cool the turbine cooling air tapped from the last stage of the high-pressure compressor. Finally, it’s heated to 700K with pressure about double that of the combustor before it enters the fuel nozzles in the combustor.
The heating of the LH2 from 22K to 700K has two positive effects:
I discussed what the practical result could be on the specific fuel consumption of a hydrogen gas turbine with Professor Grönstedt. “You can expect an improvement of 5% or more when you use the LH2’s heat sink capacity intelligently” was his answer. “There is also a lot of potential in lower emissions for NOx in the combustor process. All this needs research. We started early with heat management research and this enables us to now test the concepts from ENALBEH2 in test rigs.”
The carbon-fueled turbofan core is entering a phase of diminishing returns from higher pressure ratios and increased turbine entry temperatures. A switch to LH2 as fuel opens a smorgasbord of new possibilities around heat management and clean combustion as hydrogen burns cleaner than carbon fuels (no soot and less NOx).