Ignitor for liquid fuel rocket engines

Abstract: An ignitor 22 that energizes a hydrogen fuel into a high temperature plasma which is then injected into a mixture of fuel and oxidizer within a combustion chamber comprises an injector body 44, a first electrode 40 and a second electrode 42. The second electrode 42 is spaced from the first electrode 40 to define a gap 46. Gaseous fuel is fed to the gap via passages 54 and energised by application of a high voltage from a source 48 across the gap 46.

Description: This invention relates to ignitors for liquid fueled rocket engines, and more specifically, to ignitors which increase the reliability of engine re-lights on multiple ignition launches. Liquid fueled rocket engines are commonly used as upper stage propulsion systems on multiple stage launch vehicles. During a typical launch, for example, the placing of a satellite in near Earth orbit, an upper stage rocket engine may fire briefly, then coast, then fire again. Multiple firings of an engine during a single launch requires a highly reliable ignition system that is capable of multiple engine re-lights. Ignition systems of the prior art typically include a supplemental oxidizer supply line to provide additional oxidizer to the region surrounding the engine's ignitor during ignition to ensure proper lighting for re-lighting of the fuel/oxidizer mixture in the rocket engine combustion chamber. While supplying additional oxidizer to the ignitor has proven to produce a desirable fuel/oxidizer ratio at ignition, the supplemental oxidizer supply line requires a shut-off valve to avoid over-heating. Combustion products back flow into the valve during the start-up pressurization of the engine, causing the valve to freeze closed. With the valve frozen closed for subsequent re-light attempts, the engine will not light reliably. Attempts to accommodate and/or eliminate back flow have proven to be ineffective at preventing freezing of the shut-off valve. US 3 521 453 and US 3 861 137 disclose electrolytic ignitors. What is needed is an ignition system for liquid fueled rocket engines that increases the reliability of engine re-light on launches requiring multiple firings of the engine, while reducing the cost and weight of ignition systems of the prior art. From a first aspect the invention provides an ignitor as claimed in claim 1. The invention also extends to a method as claimed in claim 8. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIG. 1 is a schematic view of a rocket engine of the prior art. FIG. 2 is a plan view of the faceplate of the rocket engine of the prior art taken along line 2-2 of FIG. 1. FIG. 3 is a cross-sectional view of one of the injector elements. FIG. 4 is a schematic view of an ignitor embodying the present invention. FIG. 5 is an end view of an alternate design using multiple second electrodes taken along line 5-5 of HG. 4. As shown schematically in FIG. 1, a typical liquid fueled rocket engine 10 includes a thrust chamber 12, a combustion chamber 14 upstream of the thrust chamber 12, a faceplate 16 which contains a plurality of fuel/oxidizer injector elements 18 and an ignitor port 20. An ignitor 22 is mounted to the ignitor port 20, and a fuel supply line 24 and an oxidizer supply line 26 supply fuel and oxidizer to the fuel/oxidizer injector elements 18. A supplemental oxidizer supply system 28 is typically included for supplying additional oxidizer to the ignitor 22 during ignition. As shown in FIG. 2, the faceplate 16 of the rocket engine 10 has a centrally located ignitor port 20 and the ignitor 22 is mounted to the ignitor port 20. Radially outward of the port 20 are several annular rows of injector elements 18. Each of the injector elements 18 has a first orifice 34 defining a first flow area, and a second annular orifice 36 defining a second flow area, as shown in FIG. 3. The second annular orifice 36 is concentric with, and radially outward of, the first orifice 34 relative to the first orifice 34. Preferably, the first orifice 34 of each injector element 18 provides oxidizer to the combustion chamber 14, and the second annular orifice 36 provides fuel to the combustion chamber 14. An ignitor 22 embodying the present invention is shown schematically in FIG. 4 and includes at least one first electrode 40, and at least one second electrode 42 radially outward from the first electrode 40. The first and second electrodes 40, 42 are fixedly secured to an ignitor body 44, and the second electrode 42 is in spaced relation to the first electrode 40, defining a gap 46 therebetween. The second electrode 42 may be a single electrode that completely encircles the first electrode 40, as shown in FIG. 4, but preferably a plurality of the second electrodes 42, located equidistant from the first electrode, encircle the first electrode 40, as shown in FIG. 5. Referring back to FIG. 4, a power apparatus 48, such as a generator or power supply controlled by a switch 50, selectively produces an electrical voltage between the first and second electrodes 40, 42 to energize gaseous fuel, as described in greater detail below. The power apparatus 48 is capable of supplying electrical voltage of at least 15,000 volts to the electrodes 40, 42. A first electrical circuit 52 feeds electrical voltage through the first and second electrodes 40, 42. A gaseous fuel, such as hydrogen, is supplied into the gap 46 through one or more passages 54 that extend through the ignitor body 44. Each passage 54 has a first end 56 connected to a gaseous fuel source 58, and a second end 60 located adjacent the gap 46. As used herein, the term "gaseous fuel" means vaporized hydrogen, or a vaporized hydrocarbon, and does not include known oxidizers of hydrogen or hydrocarbons, such as oxygen. Immediately prior to engine ignition, fuel and oxidizer are fed to all of the injector elements 18 by the fuel supply line 24 and the oxidizer supply line 26, respectively. Fuel spray from the second annular orifice 36 of the injector elements 18, .and oxidizer spray from the first orifices 34 of the injector elements 18, form a mixture that is directed toward the ignitor port 20, thereby providing a combustible fuel/oxidizer mixture. Fuel from the fuel supply 58 flows in gaseous form through the passages 54 and into the gap 46, thereby purging the ignitor body 44 and the gap 46 of oxidizer. At engine ignition, the switch 50 is triggered to flow a high voltage electrical current between the first and second electrodes 40, 42. The electrical voltage energizes the gaseous fuel in the gap 46, thereby converting the gaseous fuel into a high temperature plasma. The temperature of the plasma is significantly greater than the threshold temperature necessary to initiate combustion, but since all of the oxidizer has been purged from the passages 54 and gap 46, no oxidation of the plasma occurs within the ignitor body 44 or gap 46. Instead, pushed by the continuing flow of gaseous fuel from the fuel supply 58, the high temperature plasma is driven out of the gap 46 and into contact with the fuel/oxidizer mixture in the combustion chamber 14. Due to its highly energized state, the high temperature plasma instantly reacts with the oxidizer in the fuel/oxidizer mixture, thereby initiating combustion of the mixture. As those skilled in the art will readily appreciate, rocket engines incorporating the ignitor described above avoid both the cost and ignition problems associated with the supplemental oxidizer supply system 28 of the prior art, while eliminating the weight of the supplemental oxidizer supply system 28 from the rocket engine. Although this invention has been shown and described with respect to a detailed embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the scope of the claimed invention.

Claims: An ignitor (22) for liquid fueled engines comprising: at least one first electrode (40); at least one second electrode (42) radially outward from said first electrode (40), said second electrode (42) being in spaced relation to said first electrode so defining a gap (46) therebetween; means for selectively producing an electrical voltage between said first and second (40,42); and, means for supplying a gaseous fuel into said gap (46). characterised in that said means for selectively producing an electrical voltage is effective to convert said gaseous fuel into a high temperature plasma and in that gaseous fuel supply means is configured and arranged to purge said gap of oxidiser. The ignitor of claim 1 wherein said means for selectively producing an electrical voltage between said first and second electrodes comprises a first circuit (52) said first circuit (52) comprising a switchable power supply (48) that feeds electrical voltage through said first and second electrodes (40,42). The ignitor of claim 1 or 2 wherein said electrical voltage is at least 15,000 volts. The ignitor of any of claims 1 to 3 wherein said second electrode (42) encircles said first electrode (40). The ignitor of any of claims 1 to 3 wherein a plurality of said second electrodes (42) are located equidistant from said first electrode (40). The ignitor of any preceding claim further comprising a ignitor body (44), and wherein said first and second electrodes (40, 42) are fixedly secured to said ignitor body (44). The ignitor of claim 6 wherein said means for supplying a gaseous fuel into said gap comprise a passage (54) that extends through said ignitor body (44), said passage having a first end (56) and a second end (60), said first end (56) being connected to a gaseous fuel source (58) and said second end (60) being located adjacent said gap (46). A method of igniting fuel and oxidizer in a thrust chamber (12) of a liquid fueled rocket (10), said method comprising: providing an ignitor (22) including at least one first electrode (40), at least one second electrode (42) radially outward from said first electrode (40), said second electrode (42) being in spaced relation to said first electrode (40) so defining a gap (46) therebetween; introducing a mixture of said fuel and said oxidizer into said thrust chamber (12), characterised by : flowing said fuel in gaseous form into said gap (46), thereby purging said gap (46) of oxidizer; energizing said gaseous fuel in said gap (46), thereby converting said gaseous fuel into a high temperature plasma; and, flowing said high temperature plasma into contact with said mixture, thereby initiating combustion of said mixture. The method of claim 8 wherein the step of energizing said gaseous fuel in said gap includes providing an electrical voltage across said first and second electrodes (40,42).

Inventors: MARABLE ROBERT W, MARABLE, ROBERT W.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1999
Main classification: F02K9
IPC codes: F02K9