13-03-2012, 02:49 PM
Pulse Detonation Engine
[attachment=18262]
1 Introduction
1.1 General
This project investigated the ability to split and utilize a propagating detonation wave as both an ignition source and a thrust producer. The resulting hardware could be directly employed in ignition system design. The research is aimed toward practical application, and therefore investigates using commercially available components rather than design optimization. Though system level effects were addressed in this work, the focus was on successful proof of concept.
The Air Force Research Laboratory Propulsion Directorate, Turbine Engine Division, Combustion Sciences Branch at Wright-Patterson AFB, Ohio, sponsored this research. All testing was conducted in the D-Bay test cell of Building 71 at Wright-Patterson AFB.
1.2 Background
A Pulse Detonation Engine, PDE, is a tube, filled with a combustible mixture, closed at one end, and ignited. The high pressure behind the detonation wave against the closed end of the tube and the rapid expulsion of products out the open end produces thrust. Fig. 1.1 shows the test PDE located in Building 71 at Wright-Patterson AFB. Although the photographed configuration has four thrust tubes, testing for this project used one or two thrust tubes. The expelled flames visible in Fig. 1.1 are a result of detonation combustion
Problem statement
Due to the high temperatures and harsh vibrations, the integration of components and systems into a PDE has posed new challenges. One example is the ignition system. Using spark plugs for ignition was convenient for small scale testing at low frequencies. Larger scale testing and practical systems could require frequencies on the order of 100 Hertz for long durations. These requirements and the relative complexity of a multi-tube engine required a sophisticated ignition system that could endure this punishing environment.
Zeldovich, von Neumann, Döring (ZND) wave model
The 1-D control volume analysis only incorporated part of the physical structure of a detonation wave. In the 1940’s Zeldovich, von Neumann, and Döring independently proposed modeling a detonation wave as a shock wave followed by combustion (Turns 2000:613). This simple structure was named the ZND detonation wave after these three individuals. Though this simplified the actual structure, it closely modeled the observed pressure trace produced as a detonation wave passed a pressure transducer.
Dimensional detonation wave structure
As noted throughout this discussion, the actual detonation mechanism and structure is quite complicated. A realistic understanding of results can only be discussed after considering detonation development and fully dimensioned structure. The actual structure involved a fully dimensioned process that included thermo-chemistry and multiple shock interaction. “According to Strehlow, the first evidence of multidimensional wave structure was obtained in 1926 by Campbell and Woodhead” (Kuo, 1986:263). They noted the non-steady and 3-dimensional nature of detonations. Denisov and Troshin in 1959 were the first to capture the visible cell pattern that defined detonation passage. They coated the interior wall with soot that collected the record of the passing detonation. Example photos of smoked-foil records are available in Kuo (Kuo 1986:264-265) The physics of this pattern is the intersection of Mach-stem, reflected, and incident shock waves. At this intersection, called the triple point, the heightened energy level prompts ignition.
[attachment=18262]
1 Introduction
1.1 General
This project investigated the ability to split and utilize a propagating detonation wave as both an ignition source and a thrust producer. The resulting hardware could be directly employed in ignition system design. The research is aimed toward practical application, and therefore investigates using commercially available components rather than design optimization. Though system level effects were addressed in this work, the focus was on successful proof of concept.
The Air Force Research Laboratory Propulsion Directorate, Turbine Engine Division, Combustion Sciences Branch at Wright-Patterson AFB, Ohio, sponsored this research. All testing was conducted in the D-Bay test cell of Building 71 at Wright-Patterson AFB.
1.2 Background
A Pulse Detonation Engine, PDE, is a tube, filled with a combustible mixture, closed at one end, and ignited. The high pressure behind the detonation wave against the closed end of the tube and the rapid expulsion of products out the open end produces thrust. Fig. 1.1 shows the test PDE located in Building 71 at Wright-Patterson AFB. Although the photographed configuration has four thrust tubes, testing for this project used one or two thrust tubes. The expelled flames visible in Fig. 1.1 are a result of detonation combustion
Problem statement
Due to the high temperatures and harsh vibrations, the integration of components and systems into a PDE has posed new challenges. One example is the ignition system. Using spark plugs for ignition was convenient for small scale testing at low frequencies. Larger scale testing and practical systems could require frequencies on the order of 100 Hertz for long durations. These requirements and the relative complexity of a multi-tube engine required a sophisticated ignition system that could endure this punishing environment.
Zeldovich, von Neumann, Döring (ZND) wave model
The 1-D control volume analysis only incorporated part of the physical structure of a detonation wave. In the 1940’s Zeldovich, von Neumann, and Döring independently proposed modeling a detonation wave as a shock wave followed by combustion (Turns 2000:613). This simple structure was named the ZND detonation wave after these three individuals. Though this simplified the actual structure, it closely modeled the observed pressure trace produced as a detonation wave passed a pressure transducer.
Dimensional detonation wave structure
As noted throughout this discussion, the actual detonation mechanism and structure is quite complicated. A realistic understanding of results can only be discussed after considering detonation development and fully dimensioned structure. The actual structure involved a fully dimensioned process that included thermo-chemistry and multiple shock interaction. “According to Strehlow, the first evidence of multidimensional wave structure was obtained in 1926 by Campbell and Woodhead” (Kuo, 1986:263). They noted the non-steady and 3-dimensional nature of detonations. Denisov and Troshin in 1959 were the first to capture the visible cell pattern that defined detonation passage. They coated the interior wall with soot that collected the record of the passing detonation. Example photos of smoked-foil records are available in Kuo (Kuo 1986:264-265) The physics of this pattern is the intersection of Mach-stem, reflected, and incident shock waves. At this intersection, called the triple point, the heightened energy level prompts ignition.
