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 a pulse generator, 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 at least one follow-on pulse 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 for plasma generation, the circuit comprising:
 an igniter having at least a pair of electrodes and configured to have applied thereto 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   a switching element in a discharge path of a pulse generator, wherein the switching element is configured to be switched and is of a type that can be switched while current therethrough is not zero.   
     
     
         13 . The circuit of  claim 12 , further comprising a plasma-sustaining capacitor configured to, following breakdown, apply to the electrodes at least one follow-on pulse by discharging via the discharge path. 
     
     
         14 . The circuit of  claim 13 , wherein one or more of the at least one follow-on pulse are voltage pulses generated by the capacitor pulling its discharge current through an inductance. 
     
     
         15 . The circuit of  claim 14 , wherein the inductance is in series with the capacitor and one of the electrodes. 
     
     
         16 . The circuit of  claim 13 , wherein the discharge path modulates a discharge current of the capacitor. 
     
     
         17 . The circuit of  claim 12 , wherein switching the switching element includes turning off the switching element while the current through the switching element is not zero. 
     
     
         18 . The circuit of  claim 12 , further including a capacitor connected in series between one electrode of the pair of electrodes and the switching element and the current through the discharge path is produced at least in part by discharging the capacitor. 
     
     
         19 . The circuit of  claim 12 , wherein the igniter is a traveling spark igniter. 
     
     
         20 . The method of  claim 7 , wherein the switching element is of a type that can be switched while the current therethrough is not constant. 
     
     
         21 . The circuit of  claim 12 , wherein the switching element is of a type that can be switched while the current therethrough is not constant. 
     
     
         22 . The method of  claim 7 , wherein the switching of the switching element occurs after the formation of the plasma kernel. 
     
     
         23 . The circuit of  claim 12 , wherein the switching element is configured to be switched after the formation of the plasma kernel.