Session: 01-02 Conceptual Design and Optimization I

Paper Number: 121997

121997 - Assessment of a Liquid Hydrogen Conditioning System for Retrofitting on Kerosene Designed Turbofan 

Over the past few years, the use of cryogenic liquid hydrogen (LH_­2) in aviation is being considered as a potential long-term solution towards emissions reduction. However, the handling and integration of the cryogenic fuel introduce major challenges on engine and fuel system level associated with the energy required to adequately condition it before combustion. Future clean sheet concepts may be designed to optimally address the fuel system heat management, but in the short term LH_­2­ is likely to be implemented on existing kerosene-based platforms to minimise the risk related to the integration of the new technology.

This study described a comprehensive performance assessment and analysis of an LH2 preheating system for the case of retrofit to a kerosene–designed engine. The fuel treatment system utilises bleed flows from either the high-pressure compressor or the by-pass duct to feed a secondary combustion chamber. The exhaust gasses are then directed to a heat exchanger, where heat is transferred to the hydrogen to adequately raise its temperature before combustion. The preheater preliminary sizing is discussed considering the effect of different preheating solutions, such as air bleed sources, on engine operation and performance for critical operating points.

A two-spool turbofan kerosene model is used as a baseline and developed using PROOSIS simulation environment. The model is extended to accommodate the fuel system components, hydrogen properties for the fuel system flows and combustion products, utilizing suitable map correction factors. For pre-sizing and assessing the integrated preheater-engine system a suitable modelling methodology considering on and off-design simulation at specific operating points is developed and suitable control logic is defined. In the context of retrofitting, a case where turbine capacities and core nozzle are altered to minimise changes on the compressor working lines and avoid shaft over-speeding is analysed.

The two-spool turbofan kerosene model is assessed on key operating conditions with predetermined thrust requirements. Retrofitting hydrogen fuel without considering the fuel treatment presents a reduction in the turbine operating temperatures, while a decrease in energy consumption of approximately 1.5% is calculated across the operating points. When the preheater is integrated, the energy consumption is increased by more than 8%, due to the higher bleed flows extracted from the core, the pump power requirement to compress the hydrogen and the additional fuel consumed in the secondary combustion. Sourcing air from the high-pressure (HP) compressor results in higher turbine temperatures and deviations from the baseline kerosene HP compressor working lines and spool speeds. Sourcing air from the by-pass duct provides the most energy-efficient solution, although it introduces integration issues due to the preheater size and operability challenges at low power conditions.

Presenting Author: Pavlos Rompokos Cranfield University

Presenting Author Biography: Pavlos Rompokos is a research fellow in the power and propulsion centre of Cranfield University School of Aerospace, Transport and Manufacture. He received an integrated master’s degree in mechanical engineering from National Technical University of Athens and an MSc and PhD in aerospace propulsion from Cranfield University. His current field of research is the implementation of hydrogen on propulsion systems for civil aviation and is contributing to the tasks of EU and ATI funded projects.

Authors:

Pavlos Rompokos Cranfield University
Vasileios Kyritsis Rolls-Royce plc
Christos Mourouzidis Cranfield University
Ioannis Roumeliotis Cranfield University