Gas Dynamics and Combustion Lab

Gas Dynamics and Combustion Lab at CNR-TEMPE: Supersonic
Combustion Test Facilities

LABORATORY UPDATES

Last update: January 4th, 2001 (G. Riva)
Research Topics (applications):   Experimental Diagnostics:
Supersonic combustion and Rocket Based Combined Cycles or RBCC (hypersonic flight and reusable launchers)

   High speed cinematography (up to 104 frames/second)
High pressure sprays (direct injection diesel engines)

   Single-Bit Digital Image Acquisition System (DIAS) (up to 106 frames/second, 2000 frames)
Hypervelocity (two-stage light-gas guns)
   Schlieren and Shadow visualization
   

Transient pressure detection and recording digital systems (multi-channel, 10 MHz, 12 bit resolution)

Supersonic Combustion

Earth orbits are presently reached by transatmospheric accelerators powered by rockets. Rockets are relatively simple, and provide thrust at all speeds, even in the absence of atmosphere, but their efficiency is low, as they must carry both fuel and oxygen, with penalties in terms of payload. Combined propulsion systems employing airbreathing engines for most of the atmospheric flight and rockets for the rest of the trajectoty (RBCC) may offer better performance, provided hypersonic airbreathing engines (RAMJET - SCRAMJET) are reliable and efficient.

Supersonic combustion has to be used for flight Mach numbers above 5-6 in order to keep the temperature at sustainable levels, and limit dissociation. Laboratory testing of supersonic combustion implies the generation of high enthalpy supersonic flows, in which the fuel can ignite and burn.

The facility at CNR-TEMPE allows combustion tests for flow Mach numbers up to 3 (flight Mach number: 6-7), with test times up to 30 ms. Fuel (hydrogen) pre-heating systems (up to 1000 K) are used to shorten ignition delays and combustion times.

Supersonic combustion (Mach 3): plot of a test analysis, showing the time evolution of equivalence ratio (E), combustion efficiency (h ), and specific heat ratio(g ) upstream and downstream of the combustion chamber.

Photo Gallery

  • Experimental facility: images of the supersonic combustion pulse facility.
  • Wave marks: shock wave patterns drawn by combustion residuals on the tunnel side walls.
  • Vortex marks: vortex images drawn by combustion residuals on the bottom wall.

High Pressure Sprays

High pressure sprays are studied in connection with fuel injection systems of direct injection diesel engines. Actually, high injection pressure (coupled with appropriate timing) has positive effects on some pollutant emissions, namely black smoke and particulate.

Single shot high pressure injectors are developed and used at CNR-TEMPE to explore a pressure range up to 3500 bar. Combustion parameters such as ignition delay, combustion time, and flame propagation dynamics are investigated using pressure sensors and high speed visualization techniques. Spray penetration and vaporization are studied replacing air with nitrogen in the constant volume combustion chamber. High pressure and temperature (60 bar, 1100 K) are obtained in the chamber by the pre-combustion of a H2-O2 stoichiometric mixture, preventively mixed with the initial air (or nitrogen) charge.

 

Spray combustion: ignition and flame spreading in a high-temperature, constant volume bomb (image obtained by integration of a DIAS frame sequence).

Photo Gallery

  • Experimental setup: images of high p-T combustion bomb and related setup.
  • DIAS: Images and description of the Digital Image Acquisition System.

Hypervelocity

Research activities on hypervelocity in the last decade were mainly connected to the development of reliable refuelling systems for nuclear fusion prototype plants. One of the suggested refuelling methods was the injection in the plasma core of high speed (2-4 km/s) cryogenic deuterium pellets, that leave nearly unperturbed the plasma boundaries.

Hypervelocity studies at CNR-TEMPE led to the extensive use of gas dynamic systems called Two-Stage Light-Gas Guns, that can accelerate projectiles to velocities of many kilometers per second. The essential component of these devices is a free piston compression tube, driven by a high pressure reservoir, in which hydrogen or helium can be used as propellant gas. The projectile accelerates in a barrel mounted on the head of the free piston tube, where sharp pressure pulses are produced by the piston stroke. The peak pressure and temperature reached in the piston tube may be of the order of 2000-3000 bar and 3000 K. The two stage gun built at CNR-TEMPE was optimized for 4 mm diameter, 30 mg weight projectiles. Its limit speed is about 6 km/s, with 5 km/s as a routine performance. A three-stage gun is currently under development for the acceleration of smaller projectiles (about 6 mg weight) to higher velocities (8.9 km/s, up to now).

Nanolamp image of a 4 mm diameter moplen sphere (speed 3 km/s, direction: from right to left) impacting a 2 mm thick aluminum target.

Photo gallery

  • Impact : a sequence of 6 frames showing the impact dynamics of a high speed projectile.
  • Waves: shadowgraph images of the unsteady shock wave pattern produced by a supersonic projectile in air.
  • Two-stage gun: a picture of the smallest prototype of two-stage gun ever built at CNR-TeMPE.

 
Contracts and Cooperation
- Italian Space Agency (ASI)
- Università di Roma "La Sapienza", Roma, Italy
- European Economic Community (EEC)
- Daimler-Benz AG, Stuttgart, Germany
- Harwell Laboratories, Combustion Centre, Oxfordshire, UK
- Progetto Finalizzato Trasporti 2 (PFT2)
- Ente Nazionale Energie Alternative (ENEA), Frascati, Italy
- Oak Ridge National Laboratories, Oak Ridge, Tennessee, USA
- Istituto Gas Ionizzati, Padova, Italy

Selection of Published Papers

 
Riva G. and Reggiori A. "Modeling of Pellet Acceleration by Two-Stage Guns", Fusion Technology, Vol. 15, p. 143-153, March 1989.
 
Daminelli G.B., Reggiori A., and Riva G., "Visualization of Unsteady Sprays by Digitized Image Acquisition", SAE Paper 890323, SAE 1989 Transactions, Journal of Engines, p. 469-474, 1989.
 
Riva G. and Reggiori A., "Modeling of Low-Acceleration Two-stage Guns for Tokamak Refueling", Fusion Technology, Vol. 21, p. 31-40, January 1992.
 
Riva G., Reggiori A., and Daminelli G.B., "Diesel Spray Combustion Rate Enhancement by Increasing Injection Pressure", SAE Paper 930926, SAE 1993 Transactions, Journal of Engines, p. 1417-1429, 1993.
 
Riva G., Daminelli G.B., and Reggiori A., "Hydrogen Autoignition and Combustion in Supersonic Flow at Low Equivalence Ratio", AIAA Journal of Propulsion and Power, Vol. 13, N. 4, P. 532-537, August 1997.
 
Riva G., Reggiori A., and Daminelli G.B., "High Temperature Hydrogen Supply Technique for Supersonic Combustion Pulse Facility", Proceedings of the XIII ISABE, Chattanooga, Tennessee, USA, Vol. 1, p. 357-365, September 1997.
 
Reggiori A., Riva G., and Daminelli G.B., "A Method for Evaluating the Combustion Efficiency in Direct Connect Supersonic Combustion Test Facilities", 22nd International Symposium on Shock Waves, Imperial College, London, UK, paper 3860, July 1999. Proceedings, p. 291-296. (PDF, 315 KB)
 
 
 
CNR-TEMPE, Gas Dynamics and Combustion Lab, Via Cozzi 53, 20125 Milano, Italy.
- Laboratory, phone: (++39)-02-66173.298, fax: (++39)-02-66173.294.
- Prof. Adolfo Reggiori, phone: (++39)-02-66173.292, E-mail: adolfo.reggiori@ieni.cnr.it
- Dr. Giulio Riva: phone: (++39)-02-66173.291, E-mail: giulio.riva@ieni.cnr.it
- Mr. Giambattista Daminelli: phone: (++39)-02-66173.290, E-mail: giambattista.daminelli@ieni.cnr.it