MEASUREMENT OF CONCENTRATIONS OF TRANSIENT GASES USING A CONVENTIONALNDIR ANALYZER

Conventional multi-gas emission analysers based upon the non-dispersiv e infrared measuring technique are of limited use in transient engine testing as the dynamic response of these analysers causes distortion o f the emission signal measured during transient engine operation. This problem is magnified when filters are installed upstream of the analy sers for the removal of solid carbon present in diesel exhausts. The c apacitive/damping effect of these filters makes the measurement of the concentrations of transient gases unreliable. A combined experimental and phenomenological model is hence proposed which simulates the beha viour of gas transport through an emission analyser by a series of alt ernately arranged pipes and surge volumes such that the distortion of the emission signal can be physically explained and modelled. Characte rization of the emission analyser by means of two physical models, nam ely diffusion and perfect gas-mixing models, is adopted as the basis f or analysis, so that physical interpretation can be made to account fo r the resulting distortion and variation of the measured emission sign al. The actual emission signal before being distorted by the slow-resp onse emission analyser can be inferred by solving these models numeric ally. A computer program has been developed which provides a continuou s signal inference from a series of distorted emission pulses measured during transient engine operation.