Abstract
Keywords experimental, HWA, cycle-resolved, oscillating hot-wire, reverse flow
Abstract Increasingly stringent emissions legislation has led to the introduction of a close-coupled catalyst (CCC) in the exhaust gas aftertreatment of internal combustion engines. The CCC is placed close to the engine exhaust ports, providing fast heat-up to the operating temperature, and thus reducing cold-start emissions. Like in any other catalyst, the catalytic material is subject to degradation depending upon the amount of exhaust gas passing through it. Uniform catalyst ageing therefore requires a uniform time-averaged flow distribution. Designing the exhaust manifold for a CCC is a challenging task because of the highly transient, non-uniform flow issuing from the exhaust runners onto the CCC. In order to improve computational fluid dynamic (CFD) predictions of this complex flow, a better understanding of the flow phenomena is required. In particular, there is a need for accurate, detailed experimental data to validate CFD codes and turbulence models.
The present research into pulsating flow in CCC manifolds has provided accurate experimental velocity data of high spatial and temporal resolution. Velocity measurements have been performed on a charged motored engine (CME) in cold flow conditions, enabling the use of hot-wire anemometry (HWA). The CME flow rig generates a flow pattern that closely resembles conditions in the CCC manifold on a fired engine, featuring an exhaust stroke consisting of a blow-down and displacement phase.
Phase-locked HWA has been applied in combination with both ensemble-averaged and cycle-resolved data reduction. The cycle-resolved data reduction provides realistic values of turbulence intensity and singles out cycle-by-cycle variations. In order to circumvent the flow direction ambiguity in using HWA, the present research has used an oscillating hot-wire (OHW) in order to measure backflow. The OHW technique has been validated on the CME flow rig by comparing the flow rate calculated as the area-integrated velocity to a flow rate measurement in the intake system. The intake system flow rate measurement uses a laminar flow element (LFE) meter. The OHW approach has yielded promising results for measuring reverse flow in a charged motored engine flow rig.