Spark plug and associated propellant ignition system

Abstract

A spark plug having an insulating body defining a longitudinal axis and including a base portion and an obstruction portion, a first electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the first electrode extending through the base portion of the insulating body, and a second electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the second electrode extending through the base portion and the obstruction portion of the insulating body, wherein the obstruction portion axially extends beyond the distal portion of the first electrode.

What is claimed is: 
     
         1 . A spark plug comprising:
 an insulating body defining a longitudinal axis and comprising a base portion and an obstruction portion;   a first electrode comprising a proximal portion, a distal portion and a sheathed portion between said proximal portion and said distal portion, said sheathed portion of said first electrode extending through said base portion of said insulating body; and   a second electrode comprising a proximal portion, a distal portion and a sheathed portion between said proximal portion and said distal portion, said sheathed portion of said second electrode extending through said base portion and said obstruction portion of said insulating body, said first electrode and said second electrode being spaced apart to define a gap therebetween,   wherein said obstruction portion axially extends beyond said distal portion of said first electrode and is positioned in flow alignment with said gap with respect to a flow path of a propellant to sustain a flame proximate said gap.   
     
     
         2 . The spark plug of  claim 1  wherein said insulating body is monolithic. 
     
     
         3 . The spark plug of  claim 1  wherein said insulating body comprises an electrical insulator material. 
     
     
         4 . The spark plug of  claim 3  wherein said electrical insulator material comprises a ceramic material. 
     
     
         5 . The spark plug of  claim 1  further comprising a threaded collar connected to said base portion of said insulating body. 
     
     
         6 . The spark plug of  claim 1  wherein said obstruction portion has a first length along said longitudinal axis, wherein said gap is defined between said distal portion of said first electrode and said distal portion of said second electrode, said gap having a second length along said longitudinal axis, and wherein said second length is greater than said first length. 
     
     
         7 . The spark plug of  claim 6  wherein said first length is at least 20 percent of said second length. 
     
     
         8 . The spark plug of  claim 1  wherein said second electrode comprises a bend such that a distal-most tip of said second electrode is substantially axially aligned with a distal-most tip of said first electrode. 
     
     
         9 . The spark plug of  claim 1  wherein said obstruction portion comprises a circular cross-sectional shape. 
     
     
         10 . The spark plug of  claim 1  wherein said obstruction portion comprises an obround or elliptical cross-sectional shape. 
     
     
         11 . A propellant ignition system comprising:
 a combustion chamber defining a longitudinal axis;   a propellant flowing through said combustion chamber in a flow path; and   a spark plug extending into said combustion chamber, said spark plug comprising:
 an insulating body comprising a base portion and an obstruction portion; 
 a first electrode extending through said base portion of said insulating body, wherein said first electrode comprises a distal-most tip; and 
 a second electrode extending through said base portion and said obstruction portion of said insulating body, said second electrode being spaced apart from said first electrode to define a gap therebetween, 
 wherein said obstruction portion axially extends beyond said distal-most tip and is in flow alignment with said gap with respect to said flow path of said propellant. 
   
     
     
         12 . The propellant ignition system of  claim 11  wherein said combustion chamber is cylindrical. 
     
     
         13 . The propellant ignition system of  claim 11  wherein said propellant comprises a fuel component and an oxidizer component. 
     
     
         14 . The propellant ignition system of  claim 11  wherein said propellant has a flame speed, and wherein a superficial velocity of said propellant is greater than said flame speed. 
     
     
         15 . The propellant ignition system of  claim 11  wherein said insulating body is monolithic. 
     
     
         16 . The propellant ignition system of  claim 11  wherein said obstruction portion comprises a circular cross-sectional shape. 
     
     
         17 . A vehicle comprising said propellant ignition system of  claim 11 . 
     
     
         18 . The vehicle of  claim 17  being a rocket. 
     
     
         19 . A method for igniting a flowing propellant comprising the steps of:
 flowing said propellant in a flow path through a gap formed between a first electrode and a second electrode, wherein said first electrode passes through a base portion of an insulating body, wherein said first electrode comprises a distal-most tip, wherein said second electrode passes through an obstruction portion of said insulating body and said base portion of said insulating body, wherein said obstruction portion axially extends beyond said distal-most tip, wherein said obstruction portion is positioned in flow alignment with said gap with respect to said flow path of said propellant to obstruct said flow path of said propellant;   applying a voltage across said first electrode and said second electrode to generate a spark in said gap to ignite the flowing propellant; and   sustaining a flame in said obstructed flow path after said spark ceases to exist.   
     
     
         20 . The method of  claim 19  wherein said propellant has a flame speed, and wherein a superficial velocity of said propellant is greater than said flame speed.