Combustion Chamber Investigations by Means of Microwave Resonances

This paper describes a new concept in combustion chamber diagnostic systems. The sensor used by this concept is unique because it can be conveniently used to probe activity occurring within the combustion chamber of internal combustion engines, during high speed operation and at maximum loading. Sensing takes place through a spark plug port without interfering with normal ignition process and without modification to the engine. The sensing means is one that utilizes microwave absorptions of radiated energy, which occur as the piston moves up and down within the cylindrical combustion chamber. These absorptions provide information concerning among other parameters, (a) top dead center (via a BDC reference mark), (b) rate of chemical ionization, (c) direction and rate of instantaneous piston motion (d) ignition, and (e) engine operating efficiency. The system has undergone tests using utility single cylinder engines, six cylinder and V-8 automobile engines. Microwave resonances in the X-band and also the C-band have been used to examine the cylinder bore. Illustrations are provided describing typical microwave field configurations employed by the concept and also the time character of the resonances that occur throughout the combustion cycle. References are supplied which deal with the subject of ionization in flames and also the interaction of ions with microwave fields.