Patent ID: 8140248

Claim:
A control system for providing an optimal estimate of NOx emission in an exhaust during a selective catalytic reduction process, the control system comprising: a continuous emission monitoring sensor configured to generate a responsive signal representing a first estimate of NOx emission; the responsive signal having a first time lag between a time of measurement of NOx emission and the time when the corresponding responsive signal is made available by the continuous emission monitoring sensor, and the continuous emission monitoring sensor having a first time constant; a virtual sensor configured to generate a relatively faster responsive signal representing a second estimate of NOx emission; and a processor comprising: a time delay compensation circuit configured to introduce a second time lag in the relatively faster responsive signal, the second time lag matching the first time lag; a low pass filter circuit coupled to the time delay compensating circuit, the low pass filter circuit having a second time constant matching the first time constant to generate a time delayed signal representing a third estimate of NOx emission; the processor further configured to subtract the time delayed signal from the summation of the responsive signal and the relatively faster responsive signal to generate the optimal estimate of the NOx emission, wherein the optimal estimate is fed as a feedforward signal into an injection system in the selective catalytic reduction process.