Performance Characteristics of a New On-Board Engine Exhaust Particulate Matter Sensor

A new electronic sensor has been developed to measure the time-resolved concentration of carbonaceous particulate matter (PM) emitted in engine exhaust. The sensor is approximately the size of a standard automotive spark-plug or lambda sensor and can be mounted directly in the engine exhaust. It consists of a pair of closely spaced electrically isolated electrodes that protrude into the exhaust flow. One electrode is given a voltage bias of 1000 V while the other is the signal electrode. The sensor is capable of providing cycle-resolved feedback on the carbonaceous PM concentration in the exhaust to the engine control unit (ECU), thereby enabling real-time control of engine operating parameters to lower PM emissions. This paper reports the results of an experimental study of various parameters that affect the performance of the electronic sensor. Parameters considered included sensor electrode length, diameter, electrode spacing, applied bias voltage, bulk flow velocity across the sensor electrodes, and the concentration of carbonaceous particulate matter in engine exhaust. The sensor was tested in the exhaust of a single cylinder diesel engine. The sensor signal varied linearly with the carbon mass concentration in the exhaust, the applied bias voltage and electrode length; it also showed some sensitivity to the bulk flow velocity, and an inverse power dependence on the spacing between the electrodes. Electrode diameter did not have a significant effect on the sensor signal. A correlation was developed to predict the sensor signal under any engine operating condition and values of these parameters. This correlation could be used to develop control strategies for the sensor for on-board operation in a production vehicle. The experiments also provided insight into the physical mechanism governing sensor behavior, regarding the charge transport between the two electrodes of the sensor.