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 . 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. following breakdown, applying to said electrodes at least one follow-on pulse by discharging a plasma-sustaining capacitor via a current-controlling discharge path.   
     
     
         2 . The method of  claim 1 , wherein the discharge path comprises a switching element of a type that can be switched while current therethrough is not zero. 
     
     
         3 . The method of  claim 2 , wherein the switching of the switching element includes turning off the switching element while the current therethrough is not zero. 
     
     
         4 . The method of  claim 2 , wherein one or more of the follow-on pulses are voltage pulses generated by the capacitor pulling its discharge current through an inductance. 
     
     
         5 . The method of  claim 4 , wherein the inductance is in series with the capacitor and one of the electrodes. 
     
     
         6 . The method of  claim 1 , wherein the discharge path modulates a discharge current of the capacitor.