Search Results

Exhaust gas flow maldistribution can strongly affect the performance of catalytic converters. As part of an on-going programme concerned with optimising converter designs, flow maldistribution within catalyst monoliths resulting from the use of different shaped inlet cones was investigated. Computational fluid dynamics (CFD) techniques were used to predict gas velocities within the catalyst, and reaction of low levels of hydrogen sulfide in the gas was used to visualise the velocity profile on monoliths coated with a lead acetate indicator. This was done both in laboratory-scale experiments at room temperature with low flow-rates, and in a vehicle exhaust system under reduced temperature conditions. Flow patterns were produced for an underfloor catalyst system under real driving conditions with this unobtrusive chemical technique.

The emissions performance of catalytic converters under different conditions of flow distribution was investigated. Computational Fluid Dynamics methods were utilised to model the maldistribution effects of different inlet cones. The effects of maldistribution on ageing, light-off and conversion were investigated using steady state tests on an engine bench. Emission testing was also conducted on a vehicle throughout ECE and EUDC test cycles. Maldistribution was found to have a significant effect on the efficiency of the catalyst during the early stages of the ECE cycle for both fresh and aged catalysts. The effects were less significant over later stages of the ECE cycle and throughout the EUDC except NOx where maldistribution did have an effect on the conversion at higher flow rates during the later stages of the test.