Identification of cross-sensitivity of smart nox sensors to ammonia in urea-selective catalyst reduction systems via fast fourier transform

Abstract

The smart NOx sensor (SNS) is prevailingly used in exhaust after-treatment systems such as urea-selective catalytic reduction (SCR) to monitor the concentration of NO, emission. Owing to the cross-sensitivity of SNS to ammonia concentration, however, the sensor signal suffers significant interference and leads to false reading if excessive ammonia is present. In this paper, an effective method that avoids the cross-sensitivity of SNS to ammonia is proposed on the basis of a periodic modulation of the urea dosage rate and Fast Fourier Transform (FFT) of the SNS signal. This method enables us to measure the true NOx concentration correctly even if the NO x is overkilled by excessive ammonia.