Velocity Predictions from a Coupled One-Dimensional/Three-Dimensional Computational Fluid Dynamics Simulation Compared with Measurements in the Catalyst System of a Firing Engine

Abstract

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.

Experimental study of flow dynamics in close-coupled catalyst manifolds

“…Regardless of differences in exhaust system geometries, the findings of the present research are in agreement with those of Adam et al [8], Liu et al [9], Park et al [10] and Benjamin et al [11]. §3.2 discusses and explains the Helmholtz resonances observed in the current study.…”

“…The results by the aforementioned authors [8,9,10,11] indicate strong flow reversal immediately following blowdown. The occurrence of reverse flow throughout the engine operating range may be surprising, considering the pressure drop generated by the CC catalyst.…”

“…Benjamin et al [11] present experimental data obtained using phase-locked LDA on a fired engine. The authors compare their velocity measurements to a numerical approach similar to Liu et al [9] and Adam et al [8].…”

“…However, the exit cone cannot be solely responsible for the occurrence of flow reversal. Liu et al [9], Park et al [10], Benjamin et al [11] and Kim et al [12] present experimental or numerical results showing reverse flow in a CC catalyst monolith in fired conditions, including an outlet section. Reverse flow consistently occurs after blowdown.…”

“…Benjamin et al [11] present LDA measurements downstream of a close-coupled catalyst, in a fired engine at 2000 rpm and high load. Similar to Liu et al [65], the experimental results are compared to a transient CFD simulation, coupled with a commercial one-dimensional gas dynamics code.…”