It was established previously that the powering baseline for high-speed ships above 36 MW can be met with external combustion machinery, i.e. gas turbines. Hydrogen fuelling of gas a turbine has a long research track starting in 1943 with LH2 fuelling experiments of jet engines at Ohio state university in the US. These experiments formed the early basis of the NASA42 LH2 and LO2 rocket program according to Seaworthy Systems Inc. (2001). Experiments performed in 1956, described by Peschka (1992), under the auspices of the NACA43 Lewis Research Centre used a B- 57 Canberra airplane with one modified jet engine operating on hydrogen. Concurrently, a research program initiated by Pratt and Whitney and supported by the US Air Force aimed to develop a hydrogen jet engine for the CL400 reconnaissance plane (Mach 2.5, 30km altitude, 4000 km range). This aircraft design program was suspended in 1958 primarily due to a limited supply of LH2 at that time and the development of the U2 high-altitude plane. The program however proved successful in operating an 8,950 kW, 18 stage, and 25,000 rpm jet engine on LH2. This research programme established that, due to the superior mixing ability of hydrogen with air better combustion than with existing hydrocarbons could be achieved. Subsequently, the hydrogen combustion chamber of the turbine could be shortened considerably, producing a shorter and lighter jet engine, see Figure 1.11.
The early seventies saw continued research efforts in hydrogen turbine aviation applications; the research driven by the oil crisis according to Peschka. The hydrogen aviation research continued into the early nineties culminating in a successful joint Russian/German research project. This
42 National Aeronautics and Space Administration 43 National Advisory Committee for Aeronautics
project involved a three-engine Tupolev 155 and an Airbus A320 plane converted for LH2 use. American hydrogen aviation research efforts from this period (1970 – 1990) are described by Brewer (1991). This in-depth reference describes the hydrogen research program by Lockheed Martin involving both LH2 fuelled supersonic and subsonic passenger aircraft designs. Brewer focuses on the technical, economical, operational and infrastructural aspects of LH2 aviation design. His research indicates important advantages of LH2 for aviation:
Figure 1.11: Schematic of the Pratt & Whitney 304-Jet engine for LH2 [from: Peschka (1992)]
Improved safety: In case of a survivable airplane crash, the LH2 tanks used are less likely to rupture causing no fuel spillage. In case of tank rupture, the LH2 will vaporize quickly, become buoyant and dissipate into the atmosphere, minimizing fire risks. Finally, in case of fire, the heat affected zone will be shorter in duration, reducing the time occupants are exposed.
Improved performance: Due to the higher specific heat of LH2, compared to current aviation fuel, the engine performance is superior using this fuel. Secondly, the low density of LH2 reduces the airplane gross takeoff weight, thus reducing required wing surface area and powering re- quirements. A 16.4% gain is achieved in the LH2 aircraft’s energy contents required for its design mission, i.e. block fuel.
Lower direct operating costs: Brewer identified a 40% DOC reduction by using a combination of advantages created by the hydrogen utilization. These advantages are an aerial frictional resistance reduction using cryogenic wall cooling on the surface of the wings and magnetic refrigeration techniques in LH2 production.
The Cryoplane research is described by Pohl and Malychev (1997), indicating that DOC of a LH2 converted Airbus A310-300 design is 57% higher than its current kerosene version. This cost differential is essentially driven by LH2 fuel cost. LH2 fuel cost represented 47% of DOC for the hydrogen fuelled Airbus A310 compared to 15% of DOC for the kerosene A310 design. It should be noted that the DOC profiles of the kerosene and LH2 A310 planes were established with a unit LH2 price of 3.07 €/kg and a unit kerosene price of 0.23 €/kg. Pohl and Malychev stipulate that the LH2 fuel for the A310 plane is obtained from electrolysis utilizing electricity generated by hydro-power, i.e. carbon neutral LH2. This would explain the relatively high LH2
fuel price. The research work by Pohl and Malychev indicates that economic analysis of a hydro- gen transportation system is essential and that the production method influences the economic viability of such a system.
Published research describing hydrogen usage in gas turbines for marine propulsion is limited. Noteworthy research is described by Ford (1977), detailing the conversion of a small 260 kW gas turbine inside a 36 feet, 30 knot, US Navy landing craft using pressurised hydrogen gas. This research, performed by the David W. Taylor Naval Research and Development Centre describes the required modifications to a SR6B-68 turbine for hydrogen fuel operation. The paper by Ford concludes that minimal modifications were required to the existing turbine and that such modifi- cations involved the fuel rate control systems and the combustion chamber design. These modifications then allowed the correct air flow patterns inside the combustion chamber avoiding excessive operating temperatures. The landing craft performed a run with the modified turbine operating at 260 kW driving the landing craft at 30 knots. Lower operating temperatures were measured in the modified turbine with hydrogen than measured with diesel fuel.