Ramjet/Scramjet propulsion has been a major research subject for over two decades. The emphasis has been on solid fuel ramjet (SFRJ) and scramjet combustors. Research on ducted rockets (ram-rockets) has been conducted as well.
Static test facilities include:
- Installation and supply of high pressure air (up to 1 kg/s, 200 atm), oxygen and hydrogen.
- Vitiated air heater burning hydrogen with oxygen makeup (up to 1 kg/s of vitiated air at 1500K and 50 atm), simulating total combustor inlet air conditions corresponding to flight Mach number up to 5+ at high altitude.
The objective of this project was the development and flight testing of Ramtech, a two-stage ramjet rocket vehicle. Ramtech was designed by student teams and their supervisors of the Faculty of Aerospace Engineering, Technion—I.I.T. The 91.5 kg, 3.7 m long vehicle consisted of a solid rocket booster as the first stage and a solid fuel ramjet motor (SFRJ) as the second stage. Its launch on May 9th, 2006 was a major achievement for the Technion students.
The launch has also been a significant technological milestone, being the first launch of an SFRJ ramjet rocket in Israel. It revealed a smooth launching phase and precise and timely operation of most of the designed systems and sequences: booster ignition and combustion, separation phase, and ramjet motor ignition.
The ramjet motor itself demonstrated early extinction, operating for about 3 seconds instead of the designed burning time of about 8 seconds. The reason was an unstable operation of the air inlet caused by a flight Mach number below the minimum required at ramjet takeover (Mach 2.2 instead of 2.5) resulting from an unexpectedly high drag coefficient. Details on the ground testing and the analysis of flight test results deduced from tracking cameras and radar devices reveal the actual performance of the motor and external ballistic characteristics vs. the pre-flight prediction.
Combustion chamber pressure vs. time in one of the initial free-jet engine tests
A comprehensive experimental investigation aimed at the examination of a solid fuel ramjet (SFRJ) regulation concept using an air-division valve was conducted. By controlling the ratio between port and bypass flows, it is possible to maintain a desirable working state over a wide range of flight conditions.
A general regulation law based on maintaining a constant fuel-to-air ratio has been tested. The experimental strategy was to isolate key parameters influencing the fuel regression rate and testing them one at a time, keeping the other parameters constant. Experiments aimed at airflow rate, total air temperature and pressure, as well as port diameter effects simulated a broad flight envelope, from Mach 1.5 to Mach 4.7 and from sea level to 13 km altitude. The test results showed very good agreement with the theory, demonstrating the feasibility, effectiveness, and characteristics of the air-division valve regulation technique in SFRJ motors.
- Pelosi-Pinhas, D. and Gany, A., Solid Fuel Ramjet Regulation by Means of an Air Division Valve, J. of Propulsion and Power, Vol. 16, No. 6, Nov.-Dec. 2000, pp. 1069-1074.
- Pelosi-Pinhas, D. and Gany, A., Analysis and Testing of Fuel Regression Rate Control in Solid Fuel Ramjets, inCombustion of Energetic Materials, K.K. Kuo and L.T. de Luca, eds., Begell House, NY, 2002, pp. 340-353.
- Pelosi-Pinhas, D. and Gany, A., Bypass-Regulated Solid Fuel Ramjet Combustor in Variable Flight Conditions,Journal of Propulsion and Power, Vol. 19, No. 1, Jan.-Feb. 2003, pp. 73-80.
The conventional (subsonic combustion) ramjet cycle provides good performance in the flight speed range of approximately Mach 2-5. However, in the hypersonic flight speed range (Mach 5 and above), the static temperatures resulting from slowing down the incoming airflow become so high that almost no fuel chemical energy can be converted to sensible (thermal) enthalpy due to severe dissociation of the gas molecules. In addition, the resulting high static pressures cause excessive construction loads.
It has been demonstrated that in the hypersonic flight range, the supersonic combustion ramjet (Scramjet) cycle yields superior performance to the conventional (subsonic) cycle. Scramjet research in the world has been focused on liquid fuels, usually liquid hydrogen because of its extremely high combustion energy and excellent cooling properties. Solid fuel scramjets may present the same advantages as other solid fuel motors: simplicity (no need for fuel tanks and feeding systems), high reliability (no moving parts), high energy density, and more.
The objective of the present research is to investigate the characteristics of scramjet combustor employing metallized solid fuel in comparison with non-metallized fuels. The research is motivated by previous theoretical studies which show that metals such as magnesium, aluminum and zirconium can provide much higher heat release per unit mass of air than hydrocarbon fuels, hence, substantially increasing the specific thrust of the engine. The current investigation has been focused on aluminum powder incorporated in a hydroxyl-terminated polybutadiene (HTPB) fuel matrix.
The experiments are conducted using a hydrogen fueled air heater to simulate flight conditions of up to Mach 5.5. Self ignition and stable combustion of both metallized and non metallized fuels has been achieved. Results show that the regression rate of metallized fuel is slightly higher, generating a higher fuel mass flow rate. The addition of aluminum particles improved the specific thrust (thrust per air mass flow rate), while decreasing the specific impulse, as was predicted by theoretical calculations.