Abstract:
The engine ( 10 ) includes at least one firing tube ( 12 ) wherein an exhaust stream ( 32 ) from the firing tube ( 12 ) drives a turbine ( 30 ). A scroll ejector attenuator ( 40 ) is secured between and in fluid communication with an outlet end ( 28 ) of the firing tube ( 12 ) and an inlet ( 76 ) of the turbine ( 30 ). The attenuator ( 40 ) defines a turning, narrowing passageway ( 72 ) that extends a distance the exhaust stream ( 32 ) travels before entering the turbine ( 30 ) to attenuate shockwaves and mix the pulsed exhaust stream ( 32 ) into an even stream with minimal temperature differences to thereby enhance efficient operation of the turbine ( 30 ) without any significant pressure decline of exhaust stream ( 32 ) pressure and without any backpressure from the attenuator ( 40 ) on the firing tube ( 12 ).

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This disclosure was made with Government support under contract number HR 0011-09-C-0052 awarded by DARPA. The Government has certain rights in this disclosure. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to pulse detonation engines and more specifically relates to a scroll ejector attenuator for directing flow of an exhaust stream leaving firing tubes of the engine. 
     BACKGROUND ART 
     In the field of pulse detonation engines (“PDEs”) it is generally known that such engines operate by producing a series of pulsed detonations within one or more firing tubes of the engine. An oxidant such as atmospheric air and fuel are directed into an inlet of the firing tube and then combusted within the tube. This results in a dramatic pressure rise as a pressure wave of combusted oxidant and fuel moves along the firing tube increasing in velocity to produce a detonation wave that results in very substantial thrust as an exhaust stream passes out of an outlet of the firing tube. 
     It is also known that PDEs are integrated with traditional turbine engines, wherein the exhaust stream from the pulse detonation engine (“PDE”) is directed to flow into the turbine to drive the turbine. In such turbine hybrid PDEs, it is common that the turbine typically drives a compressor to force air into one or more of the firing tubes within the PDE. 
     While such PDEs have tremendous potential for efficient use of fuel and production of enormous thrust per unit mass of the PDE, they nonetheless also have many challenges that have hindered development of an efficient, long-running PDE for an aircraft or a hybrid turbine PDE for production of electrical power. For example, firing PDE tubes directly into a turbine provides a very efficient system layout or architecture. However, in a typical PDE, firing tubes pulse at different times producing a very unsteady flow of the exhaust stream out of the firing tubes. Additionally, the resulting exhaust stream has an extremely high and uneven temperature with localized temperature spikes, etc. This results in significant structural, thermal and performance duress on the turbine. 
     Firing directly into the turbine also creates a partial-admission turbine effect, wherein a full force of the exhaust stream from the firing tubes only impacts a partial section of the turbine. Even if the firing tubes discharge around a full annulus of the turbine, the unsteady flow of the pulsed and turbulent exhaust stream has the effect of changing incidence angles with each cycle or pulse. This has the same effect on the turbine as the partial-admission turbine effect resulting from a varying number of firing tubes firing at different times and impacting the turbine. For example, it is known that many PDEs utilize a bundle of firing tubes and activate one, several or all of the tubes to meet varying thrust requirements. Studies of PDEs have shown that unsteady, high-temperature exhaust, while manageable on the basis of an average thermal load, nonetheless has the potential to cause deleterious thermal erosion of turbine air foil surfaces due to high-temperature peaks. It is known that, efficient, long-term operation of turbines requires minimizing vibratory stress. Unfortunately, combining PDEs with turbines imposes great vibratory stress upon the turbine, primarily because of the unsteady, turbulent flow of the exhaust stream at supersonic speeds combined with the fluctuating and extremely high temperatures of the exhaust stream. 
     Therefore, there is a need for a pulse detonation engine that minimizes structural, thermal and long-term, operational duress upon a turbine driven by an exhaust stream from firing tubes of the pulse detonation engine. 
     SUMMARY OF THE INVENTION 
     The disclosure includes a pulse detonation engine including at least one firing tube configured to direct an exhaust stream through an outlet end of the firing tube; a turbine secured in fluid communication with the outlet end of the at least, one firing tube so that the exhaust stream passes into and drives the turbine; and, a scroll ejector attenuator secured in fluid communication with and between the outlet end of the at least one firing tube and the turbine. The scroll ejector attenuator defines a turning, narrowing passageway for directing flow of the exhaust stream from the outlet end of the at least one firing tube through the turning, narrowing passage and out of a discharge end of the scroll ejector attenuator adjacent an inlet of the turbine. 
     The pulse detonation engine may also be constructed so that a cross-sectional area or a radius of an entry end of the turning, narrowing passage is greater than one of a corresponding cross-sectional area or a radius of the discharge end of the scroll ejector attenuator. Also, cross-sectional areas or radii within the turning, narrowing passageway decrease between the entry end and the discharge end of the scroll ejector attenuator. 
     The pulse detonation engine may be configured so that a flow length of the turning, narrowing passage is greater than an axial length of the scroll ejector attenuator. For purposes herein, the “axial length” of the scroll ejector attenuator is a shortest distance between the entry passage and the discharge end of the scroll ejector attenuator. Moreover, the “flow length” as used herein means an average distance the exhaust stream passes in transiting from the entry passage to the discharge end of the scroll ejector attenuator. 
     The scroll ejector attenuator may also include an impact well for re-directing flow of the exhaust stream. The impact wall is configured to be tangential to a flow direction axis parallel to flow of the exhaust stream passing out of the outlet end of the firing tube. 
     The pulse detonation engine may also include at least a first firing tube and a second firing tube. An ejector portion of the scroll ejector attenuator would be secured between the outlet ends of the first and second firing tubes and the turning, narrowing passageway, and the ejector portion defines an undivided entry passage configured to receive and mix exhaust streams from the at least first and second firing tubes. 
     Additionally, the ejector portion of the scroll ejector attenuator may define a divided entry passage that defines at least a first entry manifold and second entry manifold configured so that the first entry manifold receives and mixes an exhaust stream from at least the first firing tube and the second entry manifold receives and mixes an exhaust stream from at least the second firing tube. 
     The scroll ejector attenuator may also define a common passage in fluid communication with a first entry manifold and a second entry manifold defined within a divided entry passage. The common passage would be configured for receiving and mixing the exhaust streams from the first and second entry manifolds and for directing the mixed exhaust streams into the turning, narrowing passageway. 
     The pulse detonation engine may also be configured so that the turning passageway of the scroll ejector attenuator results in the exhaust stream exiting the discharge end of the scroll ejector attenuator in a swirling orientation relative to a plane defined to be parallel to the discharge end of the scroll ejector attenuator. 
     The present disclosure also includes a method of directing flow of an exhaust stream from at least one firing tube into an inlet of a turbine of a pulse detonation engine. The method includes receiving and mixing the exhaust stream within an entry passage of a scroll ejector attenuator; turning the flow of the exhaust stream from a direction of the flow of the exhaust stream exiting the at least one firing tube to follow a flow path within a turning, narrowing passageway defined within the scroll ejector attenuator, wherein the flow path within the passageway is greater than an axial length between the entry passage and a discharge end of the scroll ejector attenuator; and, directing flow of the exhaust stream through the discharge end of the scroll ejector attenuator and into the inlet of the turbine. 
     The aforesaid method of directing flow of the exhaust stream may also include directing the exhaust stream from at least a first firing tube into a first entry manifold of a divided entry passage of the scroll ejector attenuator; directing an exhaust stream from at least a second entry manifold of a divided entry passage of the attenuator; mixing the exhaust stream from the first firing tube within the first entry manifold; mixing the exhaust stream from the second firing tube within the second entry manifold; directing flow of the first exhaust stream from the first entry manifold into a common passage; directing flow of the second entry manifold into the common passage; mixing the first-exhaust stream and the second exhaust stream within the common passage; and then directing flow of the mixed first and second exhaust streams through the turning, narrowing passageway of the scroll ejector attenuator. 
     The method of directing flow of an exhaust stream may also include directing flow of the exhaust stream through the discharge end of the stroll ejector attenuator so that the flow of the exhaust stream swirls relative to a plane defined to be parallel to the discharge end of the scroll ejector attenuator. 
     It is a general object of the present disclosure to provide a pulse detonation engine having a scroll ejector attenuator that, overcomes deficiencies of the prior art. 
     It is a more specific object of the present disclosure to provide a pulse detonation engine having a scroll ejector attenuator that enables efficient operation of a turbine that receives an exhaust stream of firing tubes of the engine to drive the turbine. These and other objects and values of the present disclosure will become apparent in the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified schematic drawing of a pulse detonation engine having a scroll ejector attenuator constructed in accordance with the present disclosure. 
         FIG. 2  is a perspective, fragmentary drawing of a first embodiment of a scroll ejector attenuator. 
         FIG. 3  is perspective, fragmentary drawing of a second embodiment of a scroll ejector attenuator. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in detail,  FIG. 1  shows a simplified, schematic representation of a pulse detonation engine having a scroll ejector attenuator and is generally designated by reference numeral  10 . The pulse detonation engine  10  includes at least one or more firing tubes  12 . In  FIG. 1  the engine  10  depicts five identical firing tubes  12 . The firing tubes  12  are secured within a tube enclosure  14  which may include bypass passages  16  for permitting passage of coolant air to flow adjacent the tubes  12  to cool them during operation of the engine  10 . The engine  10  may include a compressor  18  upstream of the tube enclosure  14  for compressing air and directing it into the tube enclosure  14 . The engine  10  may also include an engine housing  20  surrounding all of the components of the engine  10 . As shown in  FIG. 1  atmospheric air passes into the engine housing  20  in s direction designated by arrow  22 , through the compressor  18  and in a direction designated by arrow  24  into the tube enclosure  14 . 
     Each of the firing tubes  12  is configured to receive an oxidant and a fuel at an inlet end  26  of the firing tube  12 , and each tube  12  is configured to direct an oxidant and fuel combustion exhaust stream through an outlet end  28  of the firing tube  12 . A turbine  30  is secured in fluid communication with the firing tubes  12  and is also secured downstream from the outlet ends  28  of the firing tubes  12  so that the exhaust streams  32  pass through and thereby drive the turbine  30 . The turbine  30  also includes a turbine shaft  34  for directing rotational power to the compressor IS or to an electrical generator (not shown). 
     A scroll ejector attenuator  40  is secured in fluid communication with and between the outlet ends  28  of the firing tubes  12  and the turbine  30 . The scroll ejector attenuator  40  includes an ejector portion  42  defining an entry passage  44  that is positioned adjacent the outlet ends  28  of the firing tubes  12 . The entry passage  44  has a cross-sectional area greater than a cross-section area of the outlet ends  28  of the firing tubes  12 . As described above, this permits expansion of the exhaust streams  32  as they enter the entry passage  44  of the attenuator  40 . The entry passage  44  also defines an impact wall  46  (shown in hatched lines in  FIG. 1 ) for re-directing flow of the exhaust streams  32  and for merging the exhaust streams into one mixed stream  48 . 
     The impact wall  46  is configured to be tangential to a flow direction axis  50  of the exhaust streams  32  passing out of the outlet ends  28  of the firing tubes  12 . Because the impact wall  46  within the entry passage  44  of the ejector portion  42  is structured to be aligned tangentially to the flow axis  50  of the exhaust stream, the impact wall  46  directs the exhaust stream to flow radially inward through the scroll ejector attenuator  40  to the turbine  30 . This preserves a tangential momentum of the exhaust stream leaving the firing tubes  12 , while providing for mixing of the stream. 
     A scroll attenuator portion  70  of the scroll ejector attenuator  40  is integral with the ejector portion  42  and includes an exhaust stream flow tunnel that defines a turning, narrowing passageway  72  (shown in the hatched lines  72  with the hatched lines  48  of the mixed exhaust stream in  FIG. 1 ). The turning passageway  72  directs flow of the exhaust stream  48  from the entry passage  44  of the ejector portion  42  through the turning passageway  72  and out of a discharge end  74  of the scroll ejector attenuator  40  adjacent an inlet  76  of the turbine  30 . A cross-sectional area or a radius of the entry passage  44  or entry end  44  of the turning passage  72  is greater than a corresponding cress-sectional area or a radius of the discharge end  74  of the scroll ejector attenuator  40 . 
     It is important to stress that, in addition, the cross-sectional areas or the radii within the turning, narrowing passageway  72  decrease between the entry end  44  and the discharge end  74  of the scroll ejector attenuator  40 . In other words, the differing cross-sectional areas or differing radii described above are not to foe seen as a large opening followed by a generally, constant cross-section area passageway ending with a small outlet. Instead, the turning passageway  72  has a decreasing diameter to progressively attenuate the exhaust stream  32  passing through the passageway  72 . This is referred to as the cross-sectional areas or the radii of the passageway  72  decreasing between the entry end  44  and the discharge end  74  of the scroll ejector attenuator  40 . 
     A flow length of the turning passageway  72  is greater than an axial length of the scroll ejector attenuator. The phrase “axial length” means a shortest distance between the entry passage and the discharge end of the scroll ejector attenuator. The phrase “flow length” means an average distance the mixed exhaust stream  48  passes in transiting from the entry passage  44  to the discharge end  74  of the scroll ejector attenuator  40 . (For purposes herein, the word “about” means plus or minus ten percent.) 
       FIG. 2  shows a fragmentary view of a first alternative scroll ejector attenuator  80  showing an ejector portion  82  that defines an undivided entry passage  84  for receiving exhaust streams (not shown) from a first firing tube  86  and from a second firing tube  88  of a pulse detonation engine not shown in  FIG. 2 ). The undivided entry passage  84  of the  FIG. 2  embodiment is similar to the entry passage  44  of the ejector portion  42  of the  FIG. 1  embodiment and could be located adjacent outlet ends  28  of the firing tubes  12  of the  FIG. 1  pulse detonation engine  10 . The undivided entry passage  84  that is configured to receive and mix the exhaust streams from a plurality of firing tubes  86 ,  88 . The inventors herein have determined that mixing of the exhaust streams within the scroll ejector attenuator  10 ,  80  must be controlled to minimize pressure losses within the exhaust streams. For particular arrangements of firing tubes  12 ,  86 ,  88 , it has been found that an undivided entry passage  84  promotes effective mixing with minimal pressure loss within the exhaust stream. 
       FIG. 3  shows a fragmentary view of a second alternative scroll ejector attenuator  90  showing an ejector portion  92  that defines a divided entry passage  94  for receiving exhaust streams (not shown) from firing tubes of a pulse detonation engine (not shown in  FIG. 3 ). The divided entry passage  94  of the  FIG. 3  embodiment is similar to the entry passage  44  of the ejector portion  42  of the  FIG. 1  embodiment and could be located adjacent outlet ends  28  of the firing tubes  12  of the  FIG. 1  pulse detonation engine  10 . The divided entry passage  94  defines a first entry manifold  96  adjacent and divided from a second entry manifold  98 . The manifolds  96 ,  98  may be constructed to each receive one or a plurality of exhaust streams from a plurality of firing tubes  12 . For example, a pulse detonation engine may include an even number of firing tubes, such as six firing tubes (not shown). The divided entry passage  94  would be configured to have exhaust streams of three firing tubes pass into the first entry manifold  96  and exhaust streams of the other three firing tubes pass into the second entry manifold. 
     For particular pulse detonation engines  10 , depending upon the number and arrangement of firing tubes, it may be appropriate to utilize a divided entry passage  94  to minimize mixing losses within the ejector portion  92  of the scroll ejector attenuator  90 . A first mixing of a portion of a total number of firing tubes occurs within the manifolds  96 ,  98 . The scroll attenuator portion  100  of the attenuator  90  may also define a common passage  102  wherein the divided exhaust streams from the first and second manifolds  96 ,  98  are mixed a second time. The double mixing of the second alternative embodiment of the scroll ejector attenuator  90  results in effective mixing while minimizing pressure losses within the exhaust stream. 
     As is shown in  FIG. 1 , the turning passageway  72  of the scroll ejector attenuator  40  results in the exhaust stream exiting the discharge end  74  of the scroll ejector attenuator  40  in a swirling orientation relative to a plane defined to be parallel to the discharge end  74  of the attenuator  40 . Therefore, the scroll ejector attenuator  40  may be disposed relative to the turbine  30  so that the swirling exhaust stream enters the inlet  76  of the turbine  30  at a particular orientation that may be matched to maximize efficient impact of the swirling exhaust stream upon turbine blades  104 . Because the scroll ejector attenuator  40  produces a swirling exhaust stream, the pulse detonation engine  10  may further benefit by eliminating any need for guide vanes (not shown) that are normally utilized within the turbine inlet  76  to orient a working fluid stream to maximize impact upon turbine blades  104 . 
     The scroll ejector attenuator  40  achieves directing flow of the exhaust stream  32  from the firing tubes  12  along a significantly long length through the turning, narrowing passageway  72  in a very short axial span or overall axial length of the attenuator  40 . As the exhaust stream  32  travels this flow distance within the passageway  72 , streams of more than one firing tube  12  are mixed together. Additionally, the long flow distance provides sufficient time for any remaining shock waves to be attenuated while the exhaust stream  32  is mixed within itself to provide a steady uniform flow to the turbine  30 . Because the impact wall  46  within the entry of the ejector portion  42  and turning passageway  72  is structured to foe aligned tangentially to the flow axis of the exhaust stream  32 , the impact wall  46  directs the exhaust stream  32  to flow radially inward through the turning passage of the scroll to the turbine  30 . This preserves the tangential momentum of the exhaust stream  32  leaving the firing tubes  12 , while providing for mixing of the stream. 
     Because the cross-sectional area or the radius of the entry end  44  of the turning, narrowing passageway  72  is greater than the corresponding cross-sectional area or the radius of the discharge end  74  of the attenuator portion  70 , and because the cross-sectional, areas of the passageway  72  between the entry and discharge end  74  decreases, a flow rate of the exhaust stream.  32  through the passageway  72  must accelerate, which reduces a static pressure of outlets of the firing tubes  12 . This in turn increases a dynamic head of the exhaust stream  32  within the attenuator  40  which reduces a pressure gradient between the exhaust stream  32  within the attenuator  40  and the oxidant and fuel within the firing tubes  12 . This facilitates a required firing tube  12  fill rate and will also prevent any back flow of the exhaust stream  32  within the attenuator  40  into or adjacent the outlet ends  28  of the firing tubes  12 . 
     Therefore, the present PDE with the scroll ejector attenuator  40  collects the highly unsteady combined flow of exhaust streams  32  passing out of the firing tubes  12  along with any bypass cooling air and delivers this flow to the turbine  30  in a state that will allow the turbine  30  to operate effectively. The scroll ejector attenuator  40  mixes the flow of the exhaust streams  32  with a low total pressure loss, while attenuating the unsteadiness of any Shockwaves within the streams  32 , while maintaining a low static pressure at the firing tube  12  outlets to facilitate a high rate of pulsed filling of the tubes  12 , while operating in a high-temperature environment; and it does so without increasing an overall length of the PDE  10 . 
     While the above disclosure has been presented with respect to the described and illustrated embodiments of a pulse detonation engine  10  having the described scroll ejector attenuator  40 , it is to be understood that the disclosure is not to be limited to those alternatives and described embodiments. For example, while the disclosure describes a plurality of firing tubes  12  within the engine  10 , it is to be understood that the disclosure includes a pulse detonation engine  10  having as few as one firing tube  12 , or any reasonable number of firing tubes  12 . Additionally, the above disclosure describes a compressor  18  upstream of the firing tube enclosure  14 . However, it is to be understood that the present pulse detonation engine  10  having a scroll ejector attenuator  40  may not have a compressor. Accordingly, reference should be made primarily to the following claims rather than the foregoing description to determine the scope of the disclosure.