The Indian Space Research Organization (ISRO) has recently accomplished a significant milestone in space technology by successfully completing the hot test of a Scramjet Engine. This positions India as one of the four countries worldwide to demonstrate the flight testing of a Scramjet Engine.
Air-Breathing Engines: An Introduction
Air-breathing engines are powerful, advanced propulsion systems that harness atmospheric air to fuel combustion. Instead of carrying both fuel and oxidizer on board, these internal combustion engines utilize air from the environment, which is directly heated by burning fuel before being expelled through a propulsive nozzle.
A continuous flow of air is essential to the operation of air-breathing engines. The intake air is compressed, mixed with fuel, ignited, and then ejected as exhaust gas. A typical air-breathing engine can produce thrust around eight times its own weight. This thrust is derived from the expulsion of working gases through the exhaust nozzle.
Types of Air Breathing Engines
The operational efficiency of air-breathing engines varies depending on their type, Mach range, and speed. Three main types include Ramjets, Scramjets, and Dual Mode Ramjets (DMRJ).
A Ramjet uses the vehicle’s forward motion to compress incoming air for combustion, requiring no rotating compressor. It operates most efficiently at supersonic speeds but falters when reaching hypersonic velocities.
On the other hand, a Scramjet engine stands as an improvement over the Ramjet, as it can operate effectively at hypersonic speeds and allows for supersonic combustion.
A DMRJ is another variation, where a Ramjet transforms into a Scramjet over the Mach 4-8 range. This transformation empowers the engine to operate efficiently in both subsonic and supersonic combustion modes.
Speed Ranges: Mach Numbers and Their Corresponding Velocities
Speed ranges for these engines are categorized into five main ranges: Subsonic (<0.8 Mach, <274m/s), Transonic (0.8-1.2 Mach, 274-412m/s), Supersonic (1.2-5 Mach, 412-1715m/s), Hypersonic (5-10 Mach, 1715-3430m/s), and High-Hypersonic (10-25 Mach, 3430-8507m/s).
The Significance of Air Breathing Engines
The successful development and use of air-breathing engines highlight a significant breakthrough in space technology, mainly by offering an avenue for affordable space transportation systems.
Most importantly, they contribute to developing reusable launch vehicles, as they significantly reduce the propellant mass needed for the launch vehicle. To provide some context, approximately 86% of the total launch vehicle mass comprises propellant mass, out of which around 70% is oxidizer.
Air-breathing engines slash nearly 70% of the propellant bulk by leveraging atmospheric oxygen available up to a height of 50km from the earth’s surface. Thus, with this innovation, countries can look forward to more sustainable and economical space exploration endeavors.