Patent Application
20110047962
In pulse detonation combustors, a mixture of fuel and oxidizer, such as air, is ignited and is transitioned from deflagration to detonation, so as to produce detonation waves, which can be used to provide thrust, among other functions. This deflagration to detonation transition (DDT) typically occurs in a tube or pipe structure, having an open end through which the exhaust exits.
The deflagration to detonation process begins when a fuel-oxidizer mixture in a tube is ignited via a spark or other source. The subsonic flame generated from the spark accelerates as it travels along the length of the tube due to various flow mechanics. As the flame reaches sonic velocity, shocks are formed which reflect and focus creating “hot spots” and localized explosions, eventually transitioning the flame to a supersonic detonation wave.
As indicated previously, the above-described process takes place along the length of a tube, and is often referred to as the run-up to detonation, i.e. the distance/time from spark to detonation.
However, a problem with existing smooth walled tube structures is the relatively long run-up length necessary to achieve detonation of the fuel-air mixture. In fact, in many applications the run-up length, up to detonation, can be such that the ratio L/D (i.e. tube length over tube diameter) is greater than 100. This run-up length is problematic when trying to incorporate the pulse detonation combustor in applications where space and weight are important factors, such as aircraft engines. Efforts have been made to reduce the run-up length to detonation by using obstacles within the flow, in an effort to enhance mixing of the fuel-oxidizer mixture, and typical run-up lengths with obstacles is around L/D of 30. However, there still exists a need to reduce the run-up length and accelerate the development of the flame kernel around the spark or ignition source.
For these and other reasons, there is a need for the present invention.
According to one aspect of the invention, a pulse detonation combustor chamber is provided having an ignition chamber and a detonation chamber. The cross-sectional area of the ignition chamber is greater than the cross-sectional area of the detonation chamber. A flame is generated in the ignition chamber upon ignition of a flammable mixture. The flame propagates into the detonation chamber and detonates within the detonation chamber.
The nature and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments of the invention which are schematically set forth in the figures. Like reference numerals represent corresponding parts.
As used herein, a “pulse detonation combustor” PDC is understood to mean any device or system that produces both a pressure rise and velocity increase from a series of repeated detonations or quasi-detonations within the device. A “quasi-detonation” is a supersonic turbulent combustion process that produces a pressure rise and velocity increase higher than the pressure rise and velocity increase produced by a deflagration wave. Embodiments of PDCs include a means of igniting a fuel/oxidizer mixture, for example a fuel/air mixture, and a detonation chamber, in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation and quasi-detonation. Each detonation or quasi-detonation is initiated either by external ignition, such as spark discharge or laser pulse, or by gas dynamic processes, such as shock focusing, auto ignition or by another detonation (i.e. cross-fire). Pulse detonation may be accomplished in a number of types of detonation chambers including detonation tubes, shock tubes, resonating detonation cavities, for example. In addition, a PDC can include one or more detonation chambers.
Pulse detonation combustors are used for example in aircraft engines, missiles, and rockets. As used herein, “engine” means any device used to generate thrust and/or power. As used herein, “detonation” includes both detonations and quasi-detonations.
Embodiments of the present invention will be explained in further detail by making reference to the accompanying drawings, which do not limit the scope of the invention in any way.
In the embodiments shown, the detonation chamber 12 includes an obstacle field or center body 20 to promote turbulence within the detonation chamber 12. The center body 20 is often referred to as deflagration to detonation transition (DDT) geometry. DDT geometry enhances the deflagration to detonation transition process by increasing turbulence in the detonation chamber 12. There are a variety of DDT geometries. The overall length and diameter of the center body 20 is determined based on operational parameters and characteristics to optimize performance. It is to be noted that the invention is not limited to the use of the center body 20 or DDT geometry.
In each of the exemplary embodiments shown in
The enlarged ignition chamber 10 slows the oxidizer flow to promote fuel-oxidizer mixing, flame kernel growth and serves to prevent liquid fuel from wetting the walls of the ignition chamber 10. More particularly, by injecting fuel and oxidizer in the enlarged ignition chamber 10, the mixture velocity is slow at the point of ignition. This allows the flame kernel plenty of time to grow, even in relatively high bulk velocities. The mixture velocity then increases as the mixture transitions to the smaller detonation chamber 12. This transition increases turbulent mixing and promotes DDT. Cross-sectional area variations in the ignition chamber 10 and the detonation chamber 12 allow for control of the bulk flow velocity. This enhances liquid fuel injection, fuel-air mixing, initial flame kernel growth, DDT turbulence, and minimizes loads on the upstream components in the assembly.
The enlarged ignition chamber 10 allows for larger fuel spray without wetting the walls of the chamber. In addition, the enlarged ignition chamber 10 increases the residence time of the fuel-air mixture in the ignition chamber 10, which results in greater evaporation of the fuel and enables stable flame kernel growth. The enlarged ignition chamber 10 also reduces pressure drop and aerodynamic flow losses.
By transitioning from a large ignition chamber 10 to a smaller detonation chamber 14, the run-up distance and time are reduced and the overall pulse detonation combustor chamber length is reduced. This allows for the possibility of more practical applications of pulse detonation combustors, such as use in hybrid turbine engines. Other arrangements require a combustor length to diameter ratio (L/D) up to as much as 30 to transition to detonation, while the embodiments disclosed herein require L/D ratios of 20 or less, for example.
Reduced run-up length results in reduced run-up time. Reduced run-up time enables the combustor to operate at higher frequencies. Higher frequency will generate more pressure rise and increase the usable output of the PDE device.
Turning now to
The ignition source 18 in this embodiment is arranged downstream from the fuel and oxidizer inlets. As previously discussed, although a single ignition source is shown, the combustor can include multiple ignition sources including ignition sources in the detonation chamber 12. Referring to
Referring to
Referring to
The pulse detonation combustor chamber according to the exemplary embodiments disclosed herein is configured to reduce the run-up length, and consequently, run-up time. This is achieved by including an enlarged ignition chamber with respect to the detonation chamber. This arrangement allows for the reduced length of the pulse detonation combustor chamber, and consequently, reduced length of the pulse detonation combustor. More specifically, the enlarged ignition chamber provides for slow mixture velocity at the time of ignition, which promotes stable flame kernel growth. The mixture velocity then increases as the mixture transitions to the smaller detonation chamber. This transition increases turbulent mixing and promotes DDT. Cross-sectional area variations in the ignition chamber and the detonation chamber allow for control of the bulk flow velocity. This enhances liquid fuel injection, fuel-air mixing, initial flame kernel growth, DDT turbulence, which results in reduced run-up time.
The reduced length of the combustor chamber provides for more practical applications of combustors including these combustor chambers in turbine engines, for example. In addition, the reduced run-up length enables operation at higher frequencies to increase the pressure rise resulting in more output to the device and provides a higher efficiency gain when replacing a constant pressure combustor with a PDC.
It is noted that the above embodiments have been shown with respect to a single pulse detonation combustor chamber. However, the concept of the present invention is not limited to single pulse detonation combustor chamber embodiments.
It is noted that although embodiments of the present invention have been discussed above specifically with respect to aircraft and power generation turbine engine applications, the present invention is not limited to this and can be in any similar detonation/deflagration device in which the benefits of the present invention are desirable.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
