Patent Grant
10060618
The invention described relates generally to pressure gain combustion and in particular to a pressure gain combustion apparatus such as a pulse detonation engine and a method for operating same.
Pressure-gain combustion increases pressure across a combustion chamber thereby thermodynamically approximating a constant volume process, resulting in higher efficiency engines than conventional constant-pressure combustion engines. One method to achieve pressure-gain combustion is with an oscillatory combustion apparatus such as pulse jets or a pulse detonation engine (otherwise known as “pulse detonation combustor”) that carry out pulse detonation combustion.
Pulse detonation combustion is a type of pressure gain combustion process wherein an engine is pulsed to allow a combustible mixture in the combustion chamber to be purged and renewed in between detonations triggered by an ignition source. The detonation is a supersonic combustion event wherein a flame front becomes coupled to a shock wave and propagates through a reactive mixture at sonic velocities. As a consequence, its thermodynamic behaviour effectively approaches that of a constant-volume combustion process which provides higher pressure, higher thermal efficiency and lower specific fuel consumption compared with constant-pressure or steady deflagration processes. Pulse detonation combustors are potentially thermodynamically more efficient because they rely on a pressure rise from a supersonic, shock-induced combustion wave, rather than the constant pressure deflagration process in a standard constant-pressure combustor. The flame speed in a pulse detonation can travel at 6000 fps., compared to 20-70 fps in a conventional constant pressure combustor.
The operational cycle of a single detonation cycle is comprised of filling a detonation tube with a combustible mixture of fuel and oxidant, igniting the mixture, propagating a detonation wave towards the discharge end of the tube, and expelling the combustion products. In an open ended combustion tube, the products are expelled from the tube by rarefaction waves created by a sudden expansion to atmospheric pressure as the detonation wave exits the open end. The cycle can be repeated several times a second.
Rapid transitioning to detonation is desirable to achieve high operating frequencies resulting in higher power output. The deflagration-to-detonation transition (DDT) is where a subsonic deflagration, created using low energy initiation, transitions to a supersonic detonation. The process can be broken down into four phases: (i) mixture ignition, (ii) combustion wave acceleration, (iii) formation of explosion centres, and (iv) development of the detonation front. The distance and time necessary for transition to detonation is called the run-up distance and time, respectively. Stages (i) to (iii) take up the majority of the total run-up DDT distance and time. The majority of the time for DDT is consumed largely by the laminar to turbulent flame transition. The distance for DDT is more sensitive to the acceleration of the turbulent flame. Obstacles along the flow path such as Shchelkin spirals are known to decrease DDT by shortening the distance and time for stages (ii) and (iii). It is thus desirable to provide a pulse detonation combustor which achieves high operating frequencies for better efficiency and performance. Particularly, it is desirable to provide a pulse detonation combustor which has a reduced total run-up DDT distance and time, thereby enabling high operating frequencies and corresponding improved combustor performance and higher power density.
Another challenge to efficient and effective operation of pulse detonation combustors is controlling combustion product backflow and backpressure caused by detonation shockwaves. One known approach to preventing backflow is to use a mechanical valving system. In pulse detonation combustors with such valving systems, a mechanical valve opens to fill a detonation chamber with a combustible mixture and closes thereafter during the detonation initiation and propagation stages as well as the blowdown stages. Exemplary valving mechanisms are described in U.S. Pat. No. 7,621,118 and U.S. Pat. No. 6,505,462. These valving mechanism impose mechanical complexity and tend to be prone to mechanical and thermal fatigue issues that lead to limited service life and additional service maintenance requirements. The operational frequency of the apparatus can also be limited by a mechanical valving system.
According to one aspect of the invention there is provided a pressure gain combustor comprising a detonation chamber, a pre-combustion chamber, an oxidant swirl generator, an expansion-deflection (E-D) nozzle, and an ignition source. The detonation chamber has an upstream intake end and a downstream discharge end, and is configured to allow a supersonic combustion event to propagate therethrough. The pre-combustion chamber has a downstream end in fluid communication with the detonation chamber intake end, an upstream end in communication with a fuel delivery pathway, and a circumferential perimeter between the upstream and downstream ends with an annular opening in communication with an annular oxidant delivery pathway. The oxidant swirl generator is located in the oxidant delivery pathway and comprises vanes configured to cause oxidant flowing past the vanes to flow tangentially and turbulently into the pre-combustion chamber thereby creating a high swirl velocity zone around the annular opening and a low swirl velocity zone in a central portion of the pre-combustion chamber. The E-D nozzle is positioned in between the pre-combustion chamber and detonation chamber and provides a diffusive fluid pathway therebetween. The ignition source is in communication with the low swirl velocity zone of the pre-combustion chamber, and can be selected from a group consisting of an electrical spark discharge source, a plasma pulse source, and a laser pulse source. This configuration is expected to provide a combustor with a relatively low total run-up DDT distance and time, thereby enabling high operating frequencies and corresponding high combustor performance.
The E-D nozzle can comprise a generally cylindrical body with an internal bore having a downstream end in fluid communication with the detonation chamber, and at least one circumferentially disposed port in the body that is in fluid communication with the bore; an annular rim extending outwards from the body and which contacts an outer rim of the detonation chamber's intake end; a generally cylindrical cowling that extends from the annular rim past an upstream end of the cylindrical body such that an annular space is defined between the cowl and the cylindrical body; and an end plate at the upstream end of the bore and having at least one diffuser channel extending through the plate and providing fluid communication between the bore and the pre-combustion chamber. The diffuser channel and port provide the diffusive pathway between the pre-combustion chamber and the detonation chamber. The cowling can have a mantle with a partial toroidal form and which extends into the pre-combustion chamber and into sufficient proximity with the annular opening thereof to create a Coanda effect which deflects tangentially flowing oxidant radially inwards towards the center of the pre-combustion chamber. The end plate can comprise a plurality of diffuser channels, each of which extend at an angle outwardly from the bore such that each channel is directed toward an inside surface of the cowling and not the pre-combustion chamber.
According to another aspect of the invention, there is provided a method for operating a pressure gain combustor comprising: tangentially and turbulently flowing an oxidant into a pre-combustion chamber to form a high swirl velocity zone at an outer portion of the pre-combustion chamber and a low swirl velocity zone at an inner portion of the pre-combustion chamber; injecting fuel into the high swirl velocity zone of the pre-combustion chamber; flowing a mixture of the fuel and oxidant into a detonation chamber in fluid communication with the pre-combustion chamber; igniting the fuel and oxidant in a low velocity swirl zone of the pre-combustion chamber to form a flame kernel after a selected dwell period; and directing a flame front formed from the flame kernel though an E-D nozzle into the detonation chamber such that oxidant and fuel in the detonation chamber is detonated, causing a supersonic combustion event wherein the flame front becomes coupled to a shock wave and propagates through the detonation chamber at sonic velocities. Operating the combustor in such a manner is expected to provide for a relatively low total run-up DDT distance and time, thereby enabling high operating frequencies and corresponding high combustor performance.
According to yet another aspect of the invention, there is provided a pressure gain combustor comprising: a detonation chamber having an upstream intake end and a downstream discharge end, wherein the detonation chamber is configured to allow a supersonic combustion event to propagate therethrough; a pre-combustion chamber in fluid communication with the detonation chamber intake end and in fluid communication with a fuel delivery pathway and an oxidant delivery pathway; an ignition source in communication with the pre-combustion chamber and positioned to ignite a fuel/oxidizer mixture therein; an E-D nozzle in between the pre-combustion chamber and detonation chamber and comprising a diffusive fluid pathway configured to be less restrictive to fluid flow in a downstream direction than in an upstream direction. This configuration is expected to effectively control combustion product backflow and backpressure caused by detonation shockwaves inside the combustor.
The E-D nozzle can be configured in the manner described above. With this E-D nozzle, upstream fluid flow is more restrictive than the downstream fluid flow due to the cowling directing at least a portion of upstream fluid flow from the channels into the annular space thereby interfering with upstream fluid flow that flows into the annular space via the port.
According to another aspect of the invention, there is provided a pressure gain combustor comprising: a detonation chamber having an upstream intake end and a downstream discharge end, wherein the detonation chamber is configured to allow a supersonic combustion event to propagate therethrough; a pre-combustion chamber in fluid communication with the detonation chamber intake end and in fluid communication with a fuel delivery pathway and an oxidant delivery pathway; an ignition source in communication with the pre-combustion chamber and positioned to ignite a fuel/oxidizer mixture therein; an E-D nozzle in between the pre-combustion chamber and detonation chamber and comprising a diffusive fluid pathway therebetween; and an expansion chamber in fluid communication with an oxidant inlet and the pre-combustion chamber, and comprising a volume selected to reduce a backpressure caused by detonation in the detonation chamber to a desired static pressure inside the expansion chamber. The desired static pressure can be a pressure that is less than an oxidant pressure at the oxidant inlet. This configuration is expected to effectively control combustion product backflow and backpressure caused by detonation shockwaves.
The expansion chamber can comprise a preheat chamber in thermal communication with the detonation chamber and be in fluid communication with the pre-combustion chamber, and a plenum chamber that is in fluid communication with the preheat chamber and with the oxidant inlet. A deflector shell can have a frusto-conical shape and be positioned inside the plenum chamber to form a sinuous oxidant flow pathway therein.
According to yet another aspect of the invention there is provided a pressure gain combustor comprising: a detonation chamber having an upstream intake end and a downstream discharge end, wherein the detonation chamber is configured to allow a supersonic combustion event to propagate therethrough; a fuel-oxidant mixing chamber in fluid communication with the detonation chamber intake end and in fluid communication with a fuel delivery pathway and an oxidant delivery pathway; an ignition source in communication with the detonation chamber and positioned to ignite a fuel/oxidizer mixture therein; a diffuser in between the mixing chamber and detonation chamber and comprising a diffusive fluid pathway for diffusing a downstream flow fluid from the mixing chamber to the detonation chamber; and an aerodynamic valve subassembly in the oxidant delivery pathway comprising at least one annular ring segment having a bore tapering radially inwards to form a frusto-conical nozzle facing a downstream direction, thereby defining an oxidant delivery pathway configured that is less restrictive in the downstream direction than in an upstream direction. The pressure gain combustor can further comprise at least one oxidant duct fluidly coupled to the expansion chamber and mixing chamber, in which case the aerodynamic valve subassembly is located in the duct. This configuration is expected to effectively control combustion product backflow and backpressure caused by detonation shockwaves in the combustor.
The pressure gain combustor can further comprise an expansion chamber in fluid communication with an oxidant inlet and the mixing chamber; this expansion chamber comprises a volume selected to reduce a backpressure caused by detonation in the detonation chamber to a desired static pressure inside the expansion chamber. The expansion chamber can be in thermal communication with the detonation chamber thereby serving as a pre-heat chamber to heat oxidant flowing therethrough.
Directional terms such as “front”, “back”, “rear” are used in the following description for the purpose of providing relative reference only, and are not intended to suggest any limitations on how any apparatus is to be positioned during use, or to be mounted in an assembly or relative to an environment. For example, embodiments of a pulse detonation combustor are described herein to have a “back end” where a combustible mixture is ignited, and a “front end” where combustion products are discharged. Similarly, the terms “forward flow” is defined as fuel-oxidant and combustion product flow travelling from the intake port to the discharge nozzle of the combustor, “reverse flow” as flow travelling in the opposite direction, and “upstream” and “downstream” are directional terms that are relative to the flow direction through the combustor.
Described herein is an embodiment of a combustion apparatus (“combustor”) that is configured for pressure-gain pulse detonation to efficiently combust a fuel and oxidant (e.g. air) mixture to convert chemical energy in the fuel into useable heat energy for use in thermal applications, or kinetic energy in the form of thrust, or to produce mechanical power in conjunction with an expansion device such as a rotary positive displacement turbine. The combustor features a preheat chamber which utilizes fugitive heat from the combustion to heat incoming oxidant as it flows past the length of a detonation tube. Fugitive heat refers to heat that would otherwise be lost to conduction or convection, but which is utilized in this case to pre-heat incoming air or other oxidant. After pre-heating, the oxidant is flowed through a swirl generator (swirler) configured to generate turbulent tangential oxidant flow into a pre-combustion chamber (quarl). The quarl and swirler create a high velocity swirl zone which enhances the mixing of fuel and oxidant, thereby enhancing local combustion intensity. An ignition source is disposed in the quarl in a region having relatively low swirl velocities to allow a small flame kernel to grow.
The quarl provides a means of initially creating a highly turbulent flame which is allowed to expand into a detonation chamber via abrupt expansion or passage through a restriction like an expansion-deflection (E-D) nozzle. This pre-combustion chamber creates a turbulent flame quickly, which can substantially reduce the time required for DDT compared to combustors using spark plug ignition, thereby enabling higher frequency operation and corresponding improved combustor performance. Furthermore, the combustor is provided with stationary backpressure and backflow suppression means to impede or prevent combustion product backflow and backpressure through the combustor; in particular, the E-D nozzle can be configured to impede backflow and backpressure, and the pre-heat chamber alone or in combination with an oxidant plenum chamber can be designed to serve as an expansion chamber which reduces backpressure to below an oxidant supply pressure.
Referring now to
The end cap 3 is shown in more detail in
The endcap 3 is bolted to the back end of the combustor 1 at a flange 32, which itself defines a rear opening 12 into the combustor 1. A sealing element 33 made from a high temperature resistant material forms a fluid-tight seal between the endcap 3 and flange 32. The ends of the combustor 1 have an ellipsoidal shape and integral as to form with a fluid tight seal with mounting flanges 32 and 30.
Referring particularly to
As can be seen most clearly in
The plenum and pre-heat chambers 7, 8, the quarl 13 and detonation chamber 10 are fluidly connected by the following ports and openings: the intake port 31 opens into the front of the plenum chamber 7; the preheat chamber shell openings 29 located near the front end of the annular shell 27 provide fluid communication between the plenum chamber 7 and pre-heat chamber 8; an annular opening 12 formed between the annular shells 27 and 28 at the back end of the detonation chamber 10 provides fluid communication between the pre-heat chamber 8 and the quarl 13; and the E-D nozzle 14 located between the quarl 13 and the back end of the detonation chamber 10 provides fluid communication between these two chambers 10 and 13. The rear end of the detonation shell 28 is curved inwards to define a nose cowling 9 having a semi-torodial form and defining an opening into the E-D nozzle 14.
The annular shells 2, 27, 28 and the frusto-conical nozzle 26 in the combustor 1 define a continuous sinuous flow path (oxidant delivery pathway) for the oxidant to travel from the intake port 31 to the quarl 13; more particularly, the oxidant flows through the intake port 31, through the plenum chamber 7, through the pre-heat chamber 8 via the pre-heat shell openings 29, past a swirler 11 in the pre-heat chamber 8, and into the quarl 13 via the annular opening 12. The combustion pathway starts at the quarl 13, where ignition of the fuel-oxidant is initiated, and flows into the detonation chamber 10 wherein detonation occurs and then out of the front of combustor 1 wherein combustion products are discharged through the nozzle 15. The detonation chamber 10 is in thermal communication with the pre-heat chamber 8 and is configured to transfer heat from combustion through the detonation chamber shell 28 into the pre-heat chamber 8 to heat the oxidant flowing through the pre-heat chamber 8.
The plenum chamber 7 is formed by the enclosed volume between the outer shell 2 and the preheat chamber shell 27. Acting as a receiver, the plenum chamber 7 facilitates incoming oxidant fluid (e.g. air) delivered at positive pressure from a blower or compressor (not shown). In conjunction with the frusto-conical deflector shell 26, the plenum chamber 7 is also designed to absorb pressure waves from the pulsed detonations travelling in the reverse direction. The frusto-conical deflector shell 26 has its truncated portion of the cone having the smaller diameter (“front end”) connected to the front end of the pre-heat chamber shell 27 such that a fluid-tight seal is established at this interconnection. The opposite rear end of the deflector shell 26 is spaced between the inside wall of the annular outer shell 2 and pre-heat chamber shell 27 and terminates just before the back end of the outer shell 2 leaving a sufficient gap for unrestricted fluid flow. The rear end of the frusto-conical shell 26 is secured in place by a perforated baffle ring 22 mounted to the inside surface of the outer shell 2; the perforations in the baffle ring 22 enable fluid flow through the baffle ring 22. As can be seen in
The purpose of backpressure suppression means such as the plenum chamber 7, the frusto-conical shell 26, and the sinuous flow pathway is to significantly reduce the intensity of shock waves traveling in the upstream direction. The pressure rise from detonation may not be reduced by the backpressure suppression means but they are expected to impede upstream flow to some degree. Pressure waves from detonation traveling in the upstream direction will further compress the fluid already present in upstream chambers, which is desirable. The upstream pressure waves from detonation will momentarily impede forward flow into the combustion chamber similar to the action of a mechanical valve.
The preheat chamber 8 is formed by the annular space created between the preheat chamber shell 27 and the detonation chamber shell 28; the front end of the preheat chamber 8 is capped and fluidly sealed by a flanged portion of the nozzle 15.
The plenum chamber 7 and the pre-heat chamber 8 together can be considered to be an expansion chamber that has a sufficient volume to reduce backpressure from the detonation chamber 10. More particularly, the combined volume of the plenum chamber 7 and the preheat chamber 8 is configured to be larger than the detonation chamber 10 such that the static pressure in the plenum chamber 7 is reduced by a selected degree from the detonation pressure in the detonation chamber 10. The expansion of the (backpressure) gas may be approximated as an adiabatic process since the expansion occurs over a very short period of time. The pressure and volume relationship for an adiabatic process is given by,
P·Vγ=constant
Therefore, the volume of the expansion chamber Ve may be derived by the equation,
Pd·Vdγ=Pe·Veγ
where P and V are the pressure and volume of the chambers, respectively, and the subscripts “d” represents the detonation chamber and “e” the expansion chamber. The factor “γ” is called the adiabatic index which is a property of the gas. The detonation chamber volume and pressure values Vd, Pd are usually dictated by combustor operation specifications, and the expansion chamber pressure Pe can be dictated by certain design constraints of the expansion chamber, such as the stress limit of the expansion chamber walls. If the expansion chamber features a pressure relief valve (not shown), the expansion chamber pressure Pe can be selected to be the pressure setting of the pressure relief valve.
Alternatively, one of the plenum chamber 7 and pre-heat chamber can be configured with a volume that enables that chamber alone to serve as an expansion chamber.
The combustor 1 is divided into three subassemblies as shown in
Referring to
Referring to
The Shchelkin spirals 82 are provided along the inside surface of the detonation chamber shell 28, and can be in a helical orientation and in one form be an insert, such as a helical member inserted and fixedly attached to the detonation chamber shell 28. The distance between the rotations of the helical portion of the Shchelkin spirals can increase in frequency, or otherwise the pitch between spirals can be reduced (or in some forms increase depending on the expansion of the gas) pursuant to the operational design of the combustor.
The swirler 11 is a pre-mixing swirl generator and is located in the back end of the preheat chamber 8 which leads to the opening 12 and into the quarl 13. Referring to
where;
A suitable number of swirls is between 0.3 to 0.6. The swirler 11 in one embodiment features a 30° deviation angle which results in a swirl number of 0.51. The swirler 11 imparts a tangential flow field of oxidant in the quarl 13. The swirler 11 is designed to produce a low pressure drop and impart sufficient turbulence to the flow to facilitate rapid fuel mixing in the quarl 13.
Turbulence has the effect of greatly enhancing fuel and oxidant mixing thereby enhancing local combustion intensity. Referring to
The quarl 13 volume is defined by the inside surface of endcap 3 which defines the upstream end of the quarl, an end plate of E-D nozzle 14 which defines the downstream end of the quarl 13, and by the inside surface of preheat chamber shell 27 which defines the circumferential perimeter of the quarl 13. The intersection of the nose cowling 9 and the inside surface of the preheat chamber shell 27 defines the annular opening 12 which communicates with the annular discharge end of the preheat chamber 8. As noted above, the combination of the annular opening, the nose cowling mantle, and the swirler 11 cause oxidant flowing into the quarl to flow in a tangential turbulent manner, thereby creating an outer zone in the pre-combustion chamber that has a relatively higher fluid velocity (high swirl velocity zone) than in a central zone of the pre-combustion chamber (low swirl velocity zone). Notably, the discharge openings 41 of the fuel delivery pathway are located in the high swirl velocity zone to allow fuel to mix efficiently with the oxidant in that high swirl velocity zone, and the ignition source is located in the low swirl velocity zone to allow efficient and effective ignition of fuel-oxidant mixture in that zone.
Fuel is cyclically injected into the quarl 13 and as the oxidant flow is under high turbulence entering the quarl 13, the fuel rapidly mixes with the oxidant before entering the detonation chamber 10. The turbulent flow in the quarl 13 is channeled through ports 20 and channels 21 shaped into the E-D nozzle 14 to fill the detonation chamber 10 with the combustible mixture (see
The E-D nozzle 14 serves as a diffuser to stratify the fuel/air mixture as it flows in to the detonation chamber 10. Furthermore, the E-D nozzle 14 alone and in conjunction with nose cowling 9 in this embodiment serves as a backflow suppression means which will impede backflow as well as suppress shockwaves. To achieve these purposes, the E-D nozzle 14 has a generally cylindrical body with a bore extending therethrough, and an annular rim extending outwards from the body and which contacts an outer rim of the detonation chamber shell 28, and an end plate at the upstream end of the cylindrical body. The E-D nozzle 14 is provided with multiple openings, namely circumferential ports 20 in the cylindrical body and channels 21 in the end plate; these opening permit fluid flow towards the detonation chamber 10 with relatively little resistance, but which alone and in conjunction with the nose cowling 9 shown in
The channels 21 are aligned at an angle with the axial direction of the bore and are oriented towards the nose cowling 9 to cause reverse or backflow of non-combusted fuel and oxidant and combustion products (collectively “exhaust”) from the detonation chamber 10 to interfere with exhaust backflow exiting from the openings 20 into the annular space, thus counteracting a significant portion of the back flow of exhaust from entering the quarl 13 and further restricting backflow to the preheat chamber 8. In other words, these features cause some of the exhaust back flow to change direction 180 degrees and move in the opposite direction of the rest of the exhaust back flow; this feature uses the dynamic pressure of gases to work against the back pressure and hold the exhaust back flow from moving further into the pre-heat chamber 8.
As recited above, the combustor 1, the E-D nozzle 14, the expansion chamber 7,8 and the frusto-conical deflector shell 26 each function as a stationary backflow and backpressure suppression components in the combustor 1 and act together to suppress or absorb backflow caused by backpressure from the combustion reaction. Notably, the combustor 1 does not feature mechanical inlet valving to prevent backflow. As inlet valves have shown a tendency to fail quickly in conventional pulse detonation combustors, it is expected that the stationary backflow suppression components 7, 8, 14, and 26 will be more robust and thus be more effective than inlet valves and other movable backflow suppression means.
Operation
The operation of the combustor 1 will now be discussed in respect of a single detonation cycle. The combustor 1 can generate tens or several hundred detonation cycles per second, to produce essentially a continuous power output. First, an oxidant such as air is supplied through the intake port 31, through the outer plenum chamber 7 and into the pre-heat chamber 8 where it is pre-heated by heat from previous detonations in the detonation chamber 10; the heated air then flows through annular opening 12 and into the quarl 13. During the filling stage, the preheated oxidant passes through the swirler 11 which imparts a turbulent tangential flow field as it enters the quarl 13. Fuel is then injected into the quarl 13 by the fuel injector through multiple orifices 41 in the end cap 3 directed at the high swirl velocity zone of the pre-combustion chamber. The fuel under pressure is forced through the small holes and enters the quarl 13 as an atomized spray. The atomized fuel then encounters the turbulent oxidant flow field in the quarl 13, resulting in good mixing of the fuel and oxidant. The temperature inside the quarl 13 tends to be sufficient to vaporize the fuel before a combustion event occurs, which gives the combustor multi-fuel capability.
The fuel-oxidant charge then flows through openings 20, 21 through the E-D nozzle 14 and into the detonation chamber 10. Fuel injection is continued for a selected duration specified by a control unit (not shown).
A dwell period is provided between the time that the fuel injector 24 is closed and the ignition source 25 is ignited and the combustion process is started. After the detonation chamber 10 is completely filled with the combustible fuel/oxidant mixture, the detonation sequence is initiated by the ignition source 25 which may be from an electrical spark discharge, plasma pulse or laser pulse. The process begins with ignition of the combustible fuel-oxidant mixture in the quarl 13, wherein the tangential flow field present in the quarl 13 will have its highest flow velocity along the outer regions of the chamber (where the atomized fuel is introduced) and the lowest swirl velocity at its centre. As the ignition source 25 is located in the central region of the quarl 13 where swirl velocity is relatively low, a relatively small flame kernel can be created and allowed to grow.
The ignition in the quarl 13 results in an expanding deflagration and a subsequent overpressure in the quarl 13 causes the flame front to expand and pass through the E-D nozzle 14 into the detonation chamber 10 where it ignites the remaining combustible mixture in the detonation chamber 10. The turbulent expansion of the flame front and the coalescing pressure wave as it exits the E-D nozzle 14 into the detonation chamber 10 causes quasi-detonations which initiates the detonation of the combustible mixture in the detonation chamber 10. The difference of the density of hot burned and cold unburned gas leads to an expansion flow in front of the flame. This expansion flow becomes highly turbulent as it interacts with obstacles. Turbulence generators such as the Shchelkin spirals 82 downstream of the E-D nozzle 14 cause further turbulence which consequently speed up and accelerate the flame front until it reaches the Chapman-Jouguet condition, known as the ideal detonation speed, wherein the flame front becomes attached to the shock waves as it sweeps through the remaining combustible mixture in the detonation chamber 10 and towards the discharge nozzle 15.
Large eddies tend to increase the effective flame surface, which results in an acceleration of the flame. Small scale eddies increase the heat and mass transfer in the preheating zone of the flame, which results in a thickening of the reaction zone and increasing the reaction rate.
A pre-combustion chamber such as the quarl 13 is used in this combustor 1 as a means of initially creating a highly turbulent flame which is allowed to expand into the detonation chamber via abrupt expansion or passage through a restriction like the E-D nozzle. This pre-combustion chamber creates a turbulent flame quickly, which can substantially reduce the time required for DDT compared to combustors using spark plug ignition.
Referring now to
Unlike the first embodiment, this second embodiment pressure gain combustor 101 does not feature a pre-combustion chamber 13 where fuel and oxidant are mixed and ignited, nor an E-D nozzle 14. Instead, the second embodiment features a fuel/oxidant mixing chamber 113 where the oxidant and fuel are turbulently mixed, a diffuser 114 for calming and stratifying the fuel-oxidant mixture flowing from the mixing chamber 113 into the detonation chamber 110, and an ignition source 125 that is located downstream of the diffuser 114. In other words, ignition of the fuel-oxidant mixture occurs in the detonation chamber 110, rather than in the pre-combustion chamber 10 as taught by the first embodiment. A diverging nozzle 115 interconnects the smaller diameter mixing chamber 113 with the larger diameter detonation chamber 110; the diffuser 114 is located immediately downstream of this diverging nozzle 115.
With reference to
Fuel from a fuel supply port 135 is injected into the mixing chamber 113 by a fuel injector 124, and mixed with the oxidant in the mixing chamber 113 to produce a fuel-oxidant mixture. This fuel-oxidant mixture then flows through the diffuser 114 into the detonation chamber 110. The ignition source 125 initiates the deflagration of the fuel/oxidizer charge which immediately transforms to a detonation as a flame front travels forward to the front end of the combustor 101 where the exhaust is discharged through the nozzle 120.
After the charge is ignited, the deflagration is rapidly transformed to a detonation as the flame front runs up the length of the detonation chamber 110. The run-up distance (referred to as the deflagration-to-detonation-transition (DDT) zone in the detonation tube 119) occurs between the point where charge is ignited and prior to entering the exit nozzle 120. The Shchelkin spiral 132 promotes and accelerates the transition by increasing flame turbulence caused by the spiral coils along the path. Alternatively, other features such as grooves or obstacles placed along the detonation path could also be used in lieu of Shchelkin spiral 132. The length of the Shchelkin spiral 132 or obstacles placed in the DDT path should be at least 10 times the inside diameter of the detonation tube 119 and have a blockage ratio greater than 33% but less than 65% to be effective.
The ignition source 125 comprise a plurality of igniters radially mounted in the detonation chamber 110 slightly downstream of the diffuser 114. Cooling fins 134 are provided on ignition ports of the igniters to aid in dissipating heat from combustion. The igniters can be triggered simultaneously or fired sequentially in each cycle. The ignition ports are at least one half times but not more than one and one half the inside diameter of the detonation tube 119 measured from the centre of the front face of the diffuser 114 to the centre of the ignition sources 125. The igniters are configured to provide sufficient intensity to ignite the combustible mixture and may be from an electrical spark such as from an automotive spark plug or alternatively, although not shown, from a pulsed laser-induced ignition system or high energy plasma source.
The preheat chamber 121 in the second embodiment is operatively similar to the first embodiment wherein the thermal communication of the detonation tube 119 with the pre-heat chamber 121 allows heat to transfer from the detonation reaction to the oxidant flowing through the pre-heat chamber 121. The efficiency of the heat transfer is further increased by the presence of multiple baffles 118 that are evenly spaced within the preheat chamber 121; openings are provided in each baffle 118 to allow oxidizer to pass therethrough. Like the first embodiment, the pre-heat chamber 121 can also serve as an expansion chamber which has a volume selected to reduce the static pressure to a desired value, which can be less than the inlet pressure to prevent backflow out of the inlet.
After each detonation cycle, backpressure waves are attenuated firstly by encountering backpressure suppression means like the diffuser 114 which eliminate much of the shock waves; attenuating these shockwaves also has the effect of reducing backflow. Reverse flow is further resisted by the aerodynamic valve subassembly 139 in each oxidant supply duct 122. The aerodynamic valve subassembly 139 is a stationary backflow suppression component with no moving parts. As shown in
The aerodynamic valve subassembly 139 shown in
Any reverse flow that makes it past the aerodynamic valve assembly 138 will then flow into the pre-heat chamber 121; if the pre-heat chamber has been configured to serve as an expansion chamber, the reverse flow will expand and the pressure drop to the desired static pressure. Like the first embodiment, the expansion chamber volume can be selected to reduce the static pressure to a desired value, which can be less than the inlet pressure to prevent backflow out of the inlet.
Optionally (but not shown), the pre-heat/plenum chamber 121 can also include a frusto-conical deflector like that found in the first embodiment. Such a deflector creates a more sinuous oxidizer pathway and thus serve to increase suppressive effect of the chamber 121 to backflow and backpressure. The baffles 118 design will be modified to mate with the deflector.
While particular embodiments have been described in the foregoing, it is to be understood that other embodiments are possible and are intended to be included herein. It will be clear to any person skilled in the art that modifications of and adjustments to the foregoing embodiments, not shown, are possible.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2013/050856 | 11/7/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/071525 | 5/15/2014 | WO | A |
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