Scramjet ok for flight test

The SJX61-2 scramjet engine, part of the X-51A Scramjet Engine Demonstrator-WaveRider (SED-WR), has successfully cleared ground tests and is being readied for a flight test.

This engine is unique because it is liquid hydrocarbon fuelled and will operate in the Mach 4.5-6 flight envelope.  This makes it a so-called “dual-mode” scramjet, with regions of both subsonic and supersonic combustion occurring in its combustion chamber.  The successful development of dual mode engines that run on liquid hydrocrabons (like kerosene or Jet fuel) is a vital part of the overall development of the scramjet.  It will enable acceleration from the low Mach number turbojet flight regime (Mach 3) through to pure hypersonic (Mach 6+).

Most scramjet designs hydrogen fuel (e.g. X-41A and HyShot). Practical designs (especially military) need to run on liquid fuels, due to their ease of use and high energy density.  Hydrogen has high energy per unit mass (J/kg), but very low energy density (J/cu.m), thereby requiring the use of expensive and awkward cryogenic fuel systems.  Liquid fuels are as convenient to use as petrol from your local fuel supplier, but there is a performance penalty due to lower energy per unit mass and difficulties in mixing and ignition (and probably total pressure loss).

Read the Press Release.

Excerpt from spaceref.com:  ”The X-51 Flight Test Program plans to demonstrate the operation of a scramjet engine within the Mach 4.5 to 6.0-plus range during four flight tests beginning in 2009. The program will set the foundation for several hypersonic applications, including access to space, reconnaissance-strike and global reach. The SJX61-2 duplicates the flight configuration propulsion design, including a Full Authority Digital Engine Control (FADEC), flight fuel pump and ethylene start system to orchestrate the closed-loop thermal management and combustion systems that use JP-7 fuel.”