Back pressure effect on three-way catalyst light-off

The effect of back pressure on the light-off of a modern spark ignition engine three-way catalyst has been assessed by measuring the hydrocarbon conversion efficiency in a hot flow bench and in the cold-idle period in an engine. In the flow bench experiment, a small amount of propane/air mixture is used as a surrogate for the hydrocarbon mixture. The conversion efficiency is found to be only a function of temperature. The efficiency is independent of pressure, space velocity, and the equivalence ratio of the hydrocarbon mixture for λ ≥ 1. In the engine test, while the engine-out exhaust gas temperature is higher at a higher back pressure, there is little difference between the gas temperatures at the catalyst entrance for different back pressures at retarded spark timing. This observation is attributed to the larger amount of exhaust hydrocarbon conversion oxidation between the engine exit and the catalyst entrance with the lower back pressure. The heat release from this oxidation compensates for the lower engine-out exhaust temperature at the lower back pressure. The catalyst temperature increases modestly and light-off time shortens correspondingly at the higher back pressure. This observation is attributed solely to the increase in mass flow rate (and thus exhaust sensible enthalpy flow rate) of the engine needed to overcome the additional pumping loss due to the throttling of the exhaust. These results have been confirmed with a simple one-dimensional catalyst model.

An Experimental Study of Reducing Back Pressure of Fine Air Diffuser Used in Wastewater Plants

Aeration is the process at which air is added to water, an essential stage in wastewater treatment plants, since most of organic compounds are being treated through such an aeration process. This process also helps aerobic bacteria to survive from oxygenation to proliferate and digest organic materials. However, aeration consumes around 60% of the total cost of remediation. Therefore, any improvement in aeration efficiency (AE) will save a considerable amount of energy consumption. One way of reducing the power required is to decrease the back pressure of the air diffuser itself. In this study, a new material for manufacturing of fine air diffuser is presented. Polypropylene (PP) membrane, which is the new material chosen, shows lower back pressure values in comparison with Silver Series 2 (SS2) membrane at relatively low flow rates. The main reason behind choosing Polypropylene (PP) is that it has lower material resistance than SS2 with maintaining the capability of operation at the same pressure ranges in the aeration process. Despite the fact that SS2 has better oxygen transfer efficiency (OTE), PP membranes have significantly lower back pressure at relatively low flow rates which resulted in higher AE. In addition, contact angle measurements were done for PP and compared with previous measurements for the contact angle of SS2.

Experimental Analysis of Swirl in Short Annular Diffusers With Negative Wall Angles

Short annular diffuser systems consisting of a conical expansion section with negative wall angles and a solid (full outer diameter) diffusing section were tested experimentally at several inlet swirl angles of 0–40°. Tests analyzed were completed over a range of inlet Reynolds number of Ret = 0.9–2.2 × 105 and considered fully turbulent. Performance — back pressure coefficient, outlet velocity uniformity, and total pressure loss — were appreciably depreciated for inlet swirl number larger than 0.7 and the average 10° curved vane swirler out-performed its straight vaned equivalent. Three centre bodies with length half that of the diffuser and different curvatures were manufactured. Similar performance was achieved but each centre body provided marginal improvements to a particular objective. Most notably, the centre body that gave an initial flow expansion angle of 14° resulted in 1–4% lower back pressure than the other two whose expansion angles were 12° and 16°.