Further Development of an Electronic Particulate Matter Sensor and Its Application to Diesel Engine Transients

This paper presents the latest developments in the design and performance of an electronic particulate matter (PM) sensor developed at The University of Texas at Austin (UT) and suitable, with further development, for applications in active engine control of PM emissions. The sensor detects the carbonaceous mass component of PM in the exhaust and has a time-resolution less than 20 (ms), allowing PM levels to be quantified for engine transients. Sample measurements made with the sensor in the exhaust of a single-cylinder light duty diesel engine are presented for both steady-state and transient operations: a steady-state correlation with gravimetric filter measurements is presented, and the sensor response to rapid increases in PM emission during engine transients is shown for several different tip-in (momentary increases in fuel delivery) conditions. The individual PM emission pulses from a tip-in event were found to have two contributions, the first from high velocity gases ejected from the engine cylinder during the exhaust blow-down to locations far downstream into the exhaust pipe, and a contribution from gases traveling at the mean exhaust gas flow velocity. The flow velocity sensitivity of the sensor was evident for the initial high velocity pulse. This velocity sensitivity, while complicating calibration, may have advantages for such applications as individual cylinder control, and may be suitable, with further development, for mass production and inclusion as original equipment as an integral part of an engine control system.