The purpose of this paper is to present some innovative techniques developed for an unconventional utilization of currently standard exhaust sensors, such as HEGO, UEGO, and NOx probes. In order to comply with always more stringent legislation about pollutant emissions, intake-exhaust systems are becoming even more complex and sophisticated, especially for CI engines, often including one or two UEGO sensors and a NOx sensor, and potentially equipped with both short-route and long-route EGR. Within this context, the effort to carry out novel methods for measuring the main exhaust gas dynamic properties exploiting sensors installed for different purposes, could be useful both for control applications, such as EGR rates estimation, or cost reduction, minimizing the on-board devices number.
In this work, a gray-box model for measuring the gas mass flow rate, based on standard NOx sensor operating parameters of its heating circuit, is analyzed. Its accuracy is then compared to the one of a similar model applied to the UEGO probe, presented in a previous paper, to on-board standard MAF and speed-density measurements, and to a simple pressure loss-flow characteristic model, whose robustness derives from the particular NOx probe location in the exhaust pipe. The comparison is performed for steady-state tests. The sensitivity to model input variables is also considered, that is gas temperature and pressure, leading to the introduction of a complementary physical model and besides describing an adaptive method for estimating exhaust gas static pressure, which is based on the pressure-current dependence of UEGO and NOx sensors.
