Method and apparatus for operating traveling spark igniter at high pressure

Abstract

An ignition circuit and a method of operating an igniter (preferably a traveling spark igniter) in an internal combustion engine, including a high pressure engine. A high voltage is applied to electrodes of the igniter, sufficient to cause breakdown to occur between the electrodes, resulting in a high current electrical discharge in the igniter, over a surface of an isolator between the electrodes, and formation of a plasma kernel in a fuel-air mixture adjacent said surface. Following breakdown, a sequence of one or more lower voltage and lower current pulses is applied to said electrodes, with a low “simmer” current being sustained through the plasma between pulses, preventing total plasma recombination and allowing the plasma kernel to move toward a free end of the electrodes with each pulse.

What is claimed is: 
     
         1 - 6 . (canceled) 
     
     
         7 . A method of plasma generation, comprising:
 a. applying to an igniter having at least a pair of electrodes a voltage of amplitude sufficient to cause breakdown to occur between the electrodes, resulting in a high current electrical discharge in the igniter in an initiation region, and formation of a plasma kernel adjacent said initiation region; and   b. switching a switching element in a discharge path of the igniter, wherein the switching element is of a type that can be switched while current therethrough is not zero.   
     
     
         8 . The method of  claim 7 , further comprising, following breakdown, applying to said electrodes at least one follow-on pulse by discharging a plasma-sustaining capacitor via the discharge path. 
     
     
         9 . The method of  claim 8 , wherein one or more of the follow-on pulses are voltage pulses generated by the capacitor pulling its discharge current through an inductance. 
     
     
         10 . The method of  claim 9 , wherein the inductance is in series with the capacitor and one of the electrodes. 
     
     
         11 . The method of  claim 8 , wherein the discharge path modulates a discharge current of the capacitor. 
     
     
         12 . A circuit, comprising:
 a switch connected in a current discharge path, the current discharge path representing a path via which current through a plasma between a pair of electrodes is configured to flow, wherein the switch is of a type that can be switched while current through the switch is not zero, to modulate a current through the current discharge path by changing a magnitude of the current.   
     
     
         13 . The circuit of  claim 12 , wherein switching the switch includes turning off the switch while the current through the switch is not zero. 
     
     
         14 . The circuit of  claim 12 , further including a capacitor connected in series between one electrode of the pair of electrodes and the switch, and the current through the current discharge path is produced at least in part by discharging the capacitor. 
     
     
         15 . A method, comprising:
 passing a current through a discharge path comprising a plasma and a first switching element of a type that can be switched while current therethrough is not zero; and   modulating the current, using the first switching element, by changing a magnitude of the current.   
     
     
         16 . The method of  claim 15 , wherein the first switching element is of a type that can be turned off while current therethrough is not zero. 
     
     
         17 . The method of  claim 15 , further comprising creating the plasma in a medium by applying to the medium a breakdown voltage sufficient to cause breakdown of the medium, wherein passing the current through the discharge path is performed subsequent to creating the plasma. 
     
     
         18 . The method of  claim 15 , further comprising applying a current pulse to the plasma subsequent to creating the plasma, the current pulse traveling through the discharge path. 
     
     
         19 . A circuit, comprising:
 a current discharge path comprising a gap between two electrodes, wherein a current flows between the two electrodes; and   a switch, located in the current discharge path, configured to reduce a magnitude of the current between the two electrodes.   
     
     
         20 . The circuit of  claim 19 , wherein the two electrodes are part of an igniter for an ignition system. 
     
     
         21 . The circuit of  claim 20 , wherein the igniter is a traveling spark igniter. 
     
     
         22 - 43 . (canceled)