Development and validation of a virtual soot sensor: Part 1: steady-state engine operation

Abstract

The reduction of the emission limits has lead to an increased complexity of the ECU calibration process and to the need for expensive aftertreatment methods in order to fulfil the legislated limits. Integrating feedback of the Particulate Matter (PM) and NO x emissions into the engine management could make fulfilment of legislation easier and reduce the complexity of the necessary calibration process. Since production type PM sensors for raw emission feedback are not available, a virtual soot sensor (VSS) has been developed. The VSS is a mean value soot model which provides predictions for the PM in real-time (cycle resolved). Its inputs are ECU variables and characteristic values of the heat release rate which are obtained on-line from in-cylinder pressure measurement. The structure of the VSS has been derived from optical kL-measurement data, i.e. from representative, crank angle resolved evolutions of the in-cylinder PM (3-color pyrometry). The model is structured into three consecutive phases which represent the in-cylinder PM evolution and is calibrated with measurements of the exhaust PM concentration of a standard engine operating map only. The three phases correspond to an initial phase where formation of PM dominates, a phase when formation and oxidation are roughly in balance, and a phase during which oxidation dominates. For steady state experiments, the VSS shows an excellent correlation with the exhaust gas soot (respectively elementary carbon) concentration that has been measured with a photo-acoustic soot sensor (PASS). In addition a reasonable ratio between soot formation and soot oxidation is reproduced.