UC Riverside

The Environmental Protection Agency and European Commission are requiring in-situ on-board diagnostic systems to increase accuracy in monitoring nitrous oxides and particulate matter vehicle emissions. Particulate Matter (PM) sensors are a derivative of this regulation and have been implemented to assess diesel particulate filter failure, as well as solid particle number. The design of PM sensors is varied by company (e.g., Honeywell, Bosch, Emisense, and Delphi) in addition to the applied method. The method of investigation in this study is electrical charging and the capacity for corona discharge generation.

Boltzmann’s Law for charged particles is generally used to predict electrical charging (i.e., particle charging). However, the PM sensor design and method in this study generates a signal that is amplified higher than can be theoretically explained by this law. Signal amplification can only be attributed to ionization due to the presence of corona discharge, besides particle charging in an electric field. A fundamental study probing into the effects of corona discharge on PM sensor signal amplification is necessary to understand the underlying operational principles of the sensor. This study will provide qualitative insights into the electrical properties of PM and the conditions in which electrical properties are influenced by varying physical conditions. The investigation is performed by correlating sensor response to varying physical conditions of PM. The results show that the sensor response is linearly dependent on particle concentration and that signal strength is limited on the sample flow rate. Understanding the operational principles of this design could lead to the development of a relatively inexpensive PM sensor with unprecedented high signal sensitivity.