Conceptual design of the hydrogen-enhanced intercooler

Licentiate thesis, 2024

Previous research has shown that intercooling is a key enabler for allowing the
introduction of future engine concepts with high thermal management demands.
One such engine concept is the composite cycle engine (CCE), which combines the
high power density of the turbomachinery with the increased thermal efficiency of an
internal combustion engine (ICE). Implementing intercooling, where fan discharge
air is used as coolant, into the CCE has shown a potential reduction of 20% in the
weight of the ICE! Further, using hydrogen as an aircraft fuel, stored in cryogenic
state, improves the benefits from intercooling when used as a coolant. Although the
low fuel mass flow, hydrogen can facilitate substantial cooling of the core-air stream
because of the very low storage temperatures and outstanding thermal properties.
The EU project MINIMAL was formed to further develop the intercooled CCE
fuelled by hydrogen. The required cooling is expected to exceed the possible values
if using only the fan discharge air or the fuel. Hence, the aim of this thesis will be
to investigate the hydrogen-enhanced intercooling concept, where the idea is to use
both the fan discharge air and hydrogen for intercooling.
The first phase in developing the hydrogen-enhanced intercooler is to facilitate easy
heat exchanger design space exploration. A novel method (GenHEX) is developed
which generalizes the heat exchanger matrix geometry down to three geometrical
generalization parameters (GGPs). This enables a design approach that reduces
the demands on designer intuition, luck, and access to extensive databases. Instead,
it uses correlations for estimating the aerothermal performance and an application
specific objective function to decide the best combination of GGPs, which then guides
the designer in designing the heat exchanger. This novel method is the basis for
Paper 1, where it was validated against state-of-the-art heat exchanger performance.
The second phase discusses the down-selection of various hydrogen-enhanced
intercooler arrangements and important design considerations such as the risk of
freezing, hydrogen leakage, and structural integrity. Semi-idealized heat exchangers
were used for the down-selection, and one arrangement was selected for further
investigation using the GenHEX method to estimate the performance with and
without design constraints for risk mitigation. The findings during the second phase
are the basis for Paper 2.