Velocity predictions from a coupled one-dimensional/three-dimensional computational fluid dynamics simulation compared with measurements in the catalyst system of a firing engine

Velocity measurements were made in the catalyst system of a firing engine using a one component LDV system. The 1.4 litre engine was operated at 2000 rpm and 88% 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 CFD code, which modelled the catalyst as a 3D component, with the Ricardo WAVE 1D 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 to the catalyst centre but less accurate at locations closer to the outer wall