Experimental Validation of the Addition Principle for Pulsating Flow in Close-Coupled Catalyst Manifolds

Abstract

Designing an exhaust manifold with close-coupled catalyst (CCC) relies heavily on time-consuming transient computional fluid dynamics. The current paper provides experimental validation of the addition principle for pulsating flow in CCC manifolds. The addition principle states that the time-averaged catalyst velocity distribution in pulsating flow equals a linear combination of velocity distributions obtained for steady flow through each of the exhaust runners. A charged motored engine flow rig provides cold pulsating flow in the exhaust manifold featuring blow down and displacement phases, typical of fired engine conditions. Oscillating hot-wire anemometry is used to measure the bidirectional velocity, with a maximum measurable negative velocity of −1m∕s. In part load and zero load conditions, instantaneous reverse flow occurs following the blow-down phase. The two-stage nature of the exhaust stroke combined with strong Helmholtz resonances results in strong fluctuations of the time-resolved mean catalyst velocity. The validity of the addition principle is quantified based on the shape and magnitude similarity between steady and pulsating flow distributions. Appropriate nondimensional groups are used to characterize the flow and quantify the similarity. Statistical significances are provided for the addition principle’s validity. The addition principle is valid when the nondimensional scavenging number S exceeds a critical value Scrit, corresponding to cases of low engine speed and/or high flow rate. This study suggests that the CCC manifold efficiency with respect to catalyst flow uniformity could be quantified using a single scalar parameter, i.e., Scrit. The results from the current study are discussed with respect to previously reported results. The combined results are in good agreement and provide a thorough statistically founded experimental validation of the addition principle, based on a broad applicability range.

Stereoscopic PIV measurements of swirling flow entering a catalyst substrate

“…Since the flow in the catalyst is laminar (typically 200 < Re < 2000), the pressure loss in the channel is approximately linearly proportional to the axial velocity, whereas the additional pressure loss is proportional to the square of the tangential approach velocity. This effect is not negligible and has been shown to strongly affect the flow distribution [2][3][4] and as such, the mass or heat exchange efficiency.…”

Oblique inlet pressure loss for swirling flow entering a catalyst substrate

“…For the case of automotive catalysts, a number of experimental studies [2,3,4] investigate the influence of stationary and pulsating flow conditions and diffuser geometry on the catalyst flow uniformity. However, industrial design of inlet ducts and headers relies mainly on computational fluid dynamics (CFD).…”

“…all transverse dynamic pressure is lost. The dotted line represents the second model (K(2) α , Eq. (1), which assumes that no losses occur up to a critical flow angle, depending on the overall channel pressure loss.…”

Experimental study of flow dynamics in close-coupled catalyst manifolds

“…The main contribution of Persoons et al [1] is the experimental validation of the addition principle. Persoons et al [2] extends these findings using the CME flow rig. This principle states that the time-averaged velocity distribution in pulsating flow can be predicted by a linear combination of velocity distributions that results from stationary flow through each of the exhaust runners.…”

“…Eqs. (1) and (2) show that the peak mass flow rate increases during blowdown and decreases during displacement. For the CME flow rig, in the absence of combustion, the intake system pressure should result in peak flow rates comparable to fired engine conditions.…”