Zhang, Z., del Re, L., and Fuerhapter, R., "Fast Hybrid Sensor for Soot of Production CI Engines," SAE Technical Paper 2017-24-0137, 2017.
During transients, engines tend to produce substantially higher peak emissions like soot - the main fraction of particular matter (PM) - which are the longer the more important as the steady state emissions are better controlled. While Diesel particulate filters are normally able to block them, preventing their occurrence would of course be more important. In order to achieve this goal, however, they must be measurable. While for most emissions commercial sensors of sufficient speed and performance are available, the same is not true for PMs, especially for production engines. Against this background, in the last years the possible use of a full stream 50Hz sensor based on Laser Induced Incandescence (LII) was investigated, and the results were very encouraging, showing that the sensor could recognize transient changes undetected by conventional measurement systems (like the AVL Opacimeter) but confirmed by the analysis of combustion. This was also related to the position of the sensor which can be mounted upstream or downstream of the turbine in a turbocharged CI engine. The measurement is instantaneous, without dilution or transport, and this raises also the question about accuracy, as the variability of the particulate flow near to the sensor will be directly visible in the sensor output. To reduce this effect, we propose a hybrid sensor approach in which the final reading is computed by a suitable combination of the output of the photodiodes and operation information of the engine, e.g. the pressure and temperature near to the sensor location. This paper presents the methodology as well as an experimental assessment. All measurements have been done on a production 2 lt Euro 5 CI engine.