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RAMJET AND SCRAM-JET

RAMJET

DESIGN

scram-jet

Ramjet performance parameters vs. flight Mach number

Hill and Peterson:

  • Specific thrust has peak value for set Tmax and Ta
  • Specific thrust increases as maximum allowable combustor exit temperature increases
  • Specific fuel consumption decreases with increasing flight Mach number

Ramjet engine cycle

Ramjet performance parameters vs. flight Mach number

An ideal ramjet engine follows the constant pressure or Brayton (Joule) cycle, like an ideal gas turbine engine. In an actual ramjet engine, there will be pressure losses during combustion. Figure shows the variations in temperature, pressure, velocity and Mach number through a representative ideal ramjet engine flying at Mach 2.0.

Basic principle of ramjet

  • Specific thrust has peak value for set Tmax and Ta
  • Specific thrust increases as maximum allowable combustor exit temperature increases
  • Specific fuel consumption decreases with increasing flight Mach number

INLET

Nozzle

The propelling nozzle is a critical part of a ramjet engines, since it accelerates exhaust flow to thrust.

For a ramjet operating at subsonic flight Mach Number, exhaust accelerates through a converging nozzle. For a supersonic flight Mach Number, acceleration is typically achieved via a convergent-divergent nozzle

Features

Ramjets will push out the very high dynamic pressure within the air approaching the intake lip. An efficient intake will recover much of the free stream stagnation pressure, which is used to support the combustion and expansion process in the nozzle.

Most ramjets operate at supersonic flight speeds and use one or more conical (or oblique) shock waves, terminated by a strong normal shock, to slow down the airflow to a subsonic velocity at the exit of the intake. Further diffusion is then required to get the air velocity down to a suitable level for the combustor

History

Burner

Jet engine lacking of compressors and turbines

Diffuser

The amount of thrust or push desired from the ram jet engine at a given speed determines the size of the diffuser entrance area. The larger the diffuser entrance area the greater the thrust. The ratio of diffuser entrance area to diffuser exit area varies from three to four for most subsonic ram jet designs. The most widely used value being three and one-half.

The length of the diffuser depends upon the designer's choice of one of two probable configurations. A hollow cone frustum is the easier of the two configurations to fabricate but is longer in length than the other configuration which consists of a hollow cone frustum with a curved insert. The latter configuration is used in most commercial ram jet designs because its shorter length offers less drag (resistance to movement through the atmosphere).

The combustion chamber is merely a hollow cylinder with a diameter equal to that of the diffuser exit diameter. Its length is usually determined by trial and error. As with other jet engines the combustor's job is to create hot air. It does this by burning a fuel with the air at

essentially constant pressure. The airflow through the jet engine is usually quite high, so sheltered combustion zones are produced by using flame holders that stop the flames from blowing out.

  • The duty cycle is continuous.
  • Subsonic combustion.
  • It has no moving parts, except for the part of fuel.
  • This open-sided u only have fuel nozzles in the Center.
  • a speed of initial impulse should be so that the engine begins to run.
  • Does not need power turbine because that there is no compressor.

Réne Lorin was designed in 1913 by the French inventor

History

During World War II, a tremendous amount of time and effort were put into researching high-speed jet- and rocket-powered aircraft, predominantly by the Germans. After the war, the US and UK took in several German scientists and military technologies through Operation Paperclip to begin putting more emphasis on their own weapons development, including jet engines

The Bell X-1 attained supersonic flight in 1947 and, by the early 1960s, rapid progress towards faster aircraft suggested that operational aircraft would be flying at "hypersonic" speeds within a few years. Except for specialized rocket research vehicles like the North American X-15 and other rocket-powered spacecraft, aircraft top speeds have remained level, generally in the range of Mach 1 to Mach 3.

In the 1950s and 1960s a variety of experimental scramjet engines were built and ground tested in the US and the UK. In 1964, Dr. Frederick S. Billig and Dr. Gordon L. Dugger submitted a patent application for a supersonic combustion ramjet based on Billig’s Ph.D. thesis. This patent was issued in 1981 following the removal of an order of secrecy.

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