Velocity measurements were made in the catalyst system of a firing engine using a one-component laser Doppler velocimetry system. The 1.4 l engine was operated at 2000 r/min and 88 per cent full-load condition. Velocity pulsations were observed in one of the runners supplying the catalyst and downstream of the catalyst. The velocity pulsations measured downstream of the catalyst enabled the mean velocity profile to be found. Observations were compared with simulations obtained from a coupling of the Star-CD computational fluid dynamics code, which modelled the catalyst as a three-dimensional component, with the Ricardo WAVE one-dimensional engine-cycle simulation code. The velocities in the runners were predicted to fluctuate between –65 m/s and 240 m/s. The observed velocity showed a similar pulse shape but a smaller magnitude of reversed flow. The velocities downstream of the catalyst were predicted to fluctuate between –5 and 22 m/s. The observed velocities showed smaller amplitude pulsations and significantly lower magnitudes of reversed flow, consistent with the input runner observations. The coupled simulation was shown to give good qualitative agreement with measurements, with quantitative predictions being most accurate near the catalyst centre but less accurate at locations closer to the outer wall.
Degradation of catalyst performance with time is described as ageing. There are two significant ageing mechanisms: poisoning and sintering. Experimental data on ageing have been obtained on an engine test bed using a specially designed catalyst core holder; the catalyst samples were subjected to different accelerated ageing regimes and durations. The ageing regimes were as follows: low temperature dosed (mainly poisoning); high temperature not dosed (mainly sintering); high temperature dosed (both sintering and poisoning). The experiments provided a series of samples from which the spatial and time dependences of the poisoning have been found. Portions of the samples were subjected to X-ray fluorescence analysis after ageing. A combined model of poisoning and sintering was developed and incorporated into a computational fluid dynamics model. This combined model can predict the level of deactivation as a function of length along the catalyst and as a function of time. Agreement between measured poison accumulation and predictions was achieved by tuning the sintering parameter.
Accumulation of phosphorus in an automotive catalyst is detrimental to catalyst performance, leading to partial or total deactivation. The deactivation model described in this paper utilises CFD to derive a one-dimensional mathematical solution to obtain phosphorus accumulation profiles down the length of a catalyst. The early work of Oh and Cavendish [1] is the basis for this study. A model output, θ, represents the fraction of
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