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The steady flow-field inside a monolith catalytic converter was examined by means of water-flow visualization. These tests, conducted with transparent, full-scale converter models with several different header geometries, showed that flow invariably separated from the inlet-header diffuser walls. A constant-diameter jet proceeded to the front monolith face, where it impacted and expanded to cover the substrate frontal area. For some visualization tests, the jet was constrained within a transparent tube which was translated toward the front monolith face, simulating shorter and shorter headers. The monolith internal flow field and pressure loss were found to be unaffected until the tube was within a few centimeters of the substrate. A converter with very short inlet and outlet headers is termed a truncated converter.

Internal flow details of a prototype dual-bed monolith converter were determined in water-flow visualization tests run on a full-scale transparent acrylic model. Using steadily flowing water seeded with a small quantity of tracer particles, fluid motion within transparent sections of the flow model was deduced from particle pathlines illuminated with a thin plane of laser light. Flow in the inlet transition separated from the diffuser walls and impinged as a constant-diameter jet on the leading face of the first monolith. Velocity profiles from streak photographs showed that the level of flow maldistribution in the first monolith was a function of Reynolds number. Secondary air injected between the monoliths was uniformly distributed along the major axis of the converter under all flow conditions. At dilution ratios of 16% or more the jet penetration was adequate to provide a uniform, well-mixed diluent distribution.

An investigation has been made to determine the effects of the degree of fuel atomization on exhaust emissions, fuel consumption, lean limit, MBT spark timing, and cyclic variations in peak cylinder pressure. A single-cylinder engine was used to isolate the effects of atomization on combustion from the additional effects of maldistribution that would be present in a multicylinder engine. Three degrees of gasoline atomization were investigated, along with the case of a well-mixed charge of gaseous propane. The degrees of atomization investigated varied from “Good” (10-20 μm droplets) to “Bad” (400-700 μm droplets) to “Wall-Wetted” (400-700 μm droplets deposited on the intake-port walls). Results from this investigation show that the degree of atomization can have considerable effect on exhaust emissions, but little effect on fuel consumption.