WP6: Propulsion


Involved partners: ESA-ESTEC, NLR, JAXA

Progress beyond the State of the Art

Subsonic combustion ramjets (operating up to Mach 5) have been largely studied since decades and several countries have developed and operated operational military systems (USA, Russia, France, Germany). Regarding dual mode ramjets or scramjet technology, there have been ground firing tests (for example France already demonstrated a dual mode ramjet operating from Mach 2 to Mach 7+), and even flight tests of scale models equipped with an engine launched from a rocket or an airplane to test the behaviour at specific Mach numbers.

HIKARI at this time has to address two topics: propulsion architectures and tanks storing cryogenic fluids (minus 160°C at least). For engines, two very different options have to be investigated: one relying on single engine class (special attention will be given to noise at take-off), the other relying on three engine classes (turbofan, rocket and ramjet technology), focusing on rocket engine only, one option combining liquid oxygen (LOX) and liquid methane (LCH4 or LNG), the other featuring liquid hydrogen (LH2) as fuel.

For tanks, two kinds of activities need to be conducted: one which is system design oriented, aiming at providing parameters driving efficiency of storing capability of cryogenic tanks, and the other one being more technology oriented, focusing on technology of tank wall.

Main Activities

6.1.1 Single engine class (JAXA): A single engine class is a turbojet running from Mach 0 to supersonic speeds and burning hydrogen fuel. The objective of this task is to conduct performance analysis of a pre-cooled turbojet engine for high-speed transport:

  • Analyze the propulsive performance of pre-cooled turbojet (PCTJ) for high-speed transport application.
  • Analyze overall mass of the PCTJ.
  • Support the systems analysis of high-speed transport.

6.1.2 Assessment of noise from a single engine class at take-off (NLR): The objective is to evaluate the propulsive and noise performance of a pre-cooled turbojet engine for high-speed transport for the ICAO LTO cycle:

  • Develop model framework for a pre-cooled turbojet engine in the NLR gasturbine simulation program GSP 11 for the low Mach number range.
  • Analyze the propulsive performance of the pre-cooled turbojet engine for the ICAO LTO cycle.
  • Perform noise analysis (jet noise) of the JAXA pre-cooled turbojet engine at ICAO Annex 16 (chapter 3) certification points:
    • lateral full-power reference noise measurement point.
    • flyover reference noise measurement point.

A comparison will be carried out with maximum allowable noise levels as provided by ICAO Annex 16, and certification noise levels of relevant aircraft that are available in open literature.

6.1.3 Innovative LOX/LH2 engine (AST): Two main axes will be covered by the work package.

First solutions to be considered will be identified, such as pressure level, powerpack architecture, nozzle concepts. It will be done thanks to bibliography and internal studies. After the choice of the configuration and architecture, preliminary design will be performed with advanced project tools and comparison with conventional on performed. Required technological improvements will be also identified.

6.2.1 LOX/LH2 Tank Design: Two main axis will be covered by the work package:

  • Review of past studies on metallic tanks for reusable launchers performed in the frame of FLPP and FLTP and identification of the points/technology/architecture to be available and interesting for a plane like ZEHST.
  • Identification of the main topics from a functional point of view, linked with cryogenic propellant use in term of propellant management (impact of safety, evaporation, center of mass control, heat fluxes) and technological means to be used for that: PMD (Propellant Management Device), Feeding systems, Residuals.

6.2.2 Passive and Active Pressurization Control of Cryogenic Reservoirs (ESTEC): The heat flux penetration into on-board cryogenic tanks and hence the corresponding fuel boil off will be at first order passively tuned by carefully designing the insulation system. A generic study will be performed assessing the heat flux control, the amount of fuel boil-off and the potential of self-pressurization by a parametric study. The studied parameters will be aeroframe temperatures, fuel types (LH2, LCH4, LOX), insulation types (micro-fibers, blankets, sandwich…), volume/surface ratios and fuel fill levels. The study will provide an estimation of the extent to which active control is needed to maintain the correct pressurization level. A more specific evaluation will be worked out along an ATLLAS and/or LAPCAT vehicle.

Expected Results

HIKARI is expected to focus on two different topics that require very specialized knowledge possessed only by a few entities in the world, among which members of HIKARI consortium. HIKARI collects this knowledge in a single consortium which will perform a step forward in two different but interconnected domains:

  • The first one relates to propulsive architectures. HIKARI will contribute to further comprehension of two options that are being investigated in other projects: single engine (such as the one under development in Japan), and rocket engine as being part of a multiple engines concept such as the ZEHST one in Europe. In both cases, HIKARI proposes to get a step further the work already on-going with the existing projects. In the case of single engine, an assessment of noise at take-off will also be performed. As for rocket engine, this technology is very mature for space applications, but deserves to be revisited when addressing point-to-point transport of paying passengers. Indeed embedded safety and reusability / ease of operations become a must, and impact to rocket engine design has to be carefully crafted as such.
  • The second topic relates to tanks storing cryogenic fluids (minus 160°C at least). One task will aim at providing the driving parameters for optimizing the storing efficiency of storing capability of cryogenic tanks. The other one will focus on technologies needed for cryogenic tank pressurization.