CHARACTERIZATION AND SIGNAL RECONSTRUCTION OF AN NDIR AUTOMOTIVE EMISSIONS ANALYZER USED FOR DYNAMIC MEASUREMENT

Normally the slow-response conventional gaseous-emission analysers bas ed on non-dispersive infra-red measuring techniques are not widely use d for measurement of transient engine-exhaust emissions, because the d ynamics of these analysers distort emission signals during sampling pr ocesses. A phenomenological modelling approach is proposed which simul ates the behaviour of gas transport through an emission analyser by a series of alternately arranged pipes and surge chambers, such that the distortion of the emission signal can be physically explained and mod elled. The characterisation of an emission analyser by means of two ph ysical models-viz diffusion and perfect gas-mixing models-is adopted a s the basis for analysis, so that physical interpretation can be made to account for the resulting distortion and variation of measured emis sion signals. The actual emission signal before being distorted by the slow-response emission analyser can be reconstructed by solving these models numerically. A computer program has been developed which provi des a continuous signal reconstruction from a series of distorted emis sion pulses measured during transient engine operation.