Method and apparatus for indicating an operating characteristic of an

Abstract

A method and apparatus are provided for indicating an operating characteristic of a periodically combusting internal combustion engine, such as a diesel engine, having exhaust gas issuing from one or more combustion chambers in a periodic manner through a duct. The particulate in the exhaust gas stream are electrically charged and of the same polarity, and are grouped in packets associated with the periodic combustion in the respective chambers. An electrically conductive, passive electrode, preferably annular in shape, is disposed such that most or all of the exhaust gas flows therethrough so as to electrostatically sense, principally by induced image charge, the passage of the respective packets of charged particles. The electrode is electrically isolated from the duct. Circuitry with the probe converts the sensed induced image charge to a signal containing a series of pulsating components corresponding in time with the respective particle packets and corresponding quantitatively with the charge-quantity of the respective particle packets. An indicating device responds to the pulsating signal and provides an indication of an operating characteristic of the engine. The electrode is preferably of short axial extent relative to the packet interval to enhance resolution. Structure and circuitry may be provided to minimize soot deposition and/or leakage currents across an insulator between the electrode and duct. In one instance, the indicating device may respond to the root mean square of the pulsating signal to provide a quantitative indication of the level of particulate in the exhaust gas stream. In another instance, the successive pulsations of the signal waveform may be displayed to afford evaluation of the performance of the respective combustion chambers and/or injectors.