Diesel particulate filter pressure drop

Fio. 1. An example of a future integrated soot-NOx emission control system. DPF stands for diesel particulate filter. Sensory inputs of temperature (7), pressure (/ ), pressure drop (AP), soot and NOx concentration will be required along the exhaust pipe. 

Konstandopoulos, A. G., and lohnson, I. H. Wall-flow diesel particulate filters-their pressure drop and collection efficiency. SAE Technical Paper No. 890405, SAE Trans. 98 sec. 3 (I. Engines), pp. 625-647 (1989). 

Konstandopoulos, A. G., Skaperdas, E., and Masoudi, M. Inertial contributions to the pressure drop of diesel particulate filters. SAE Technical Paper No. 2001-01-0909 (SP-1582) (2001). 

Vlachos, N., Housiada, P., Zarvalis, D., and Konstandopoulos, A. G., Transient filtration and pressure drop behavior of diesel particulate filters, in Particle Loading and Kinetics of Filtration in Fibrous Filters (M. J. Lehmann, and G. Kasper Eds.), pp. 13-26. University of Karlsruhe, Karlsruhe (2002). 

A schematic of a monolith catalyst is shown in Fig. 19-18a. In cases where pressure drop is limiting, such as for CO oxidation in cogeneration power plant exhausts, monolith catalyst panels may be stacked to form a thin (3- to 4-in-thick) wall. The other dimensions of the wall can be on the order of 35 x 40 ft. CO conversion is over 90 percent with a pressure drop across the catalyst of 1.5 in of water. Alternatively, the monolith may be used as a catalyst and filter, as is the case for a diesel particulate filter. In this case, monolith channels are blocked and the exhaust gases from a diesel truck are forced through the walls (Fig. 19-18b). The filter is a critical component in a continuous regenerable trap. NO in the exhaust... 

Mansoudi M, Heibel A, Then P M (2000) Predicting pressure drop of wall-flow diesel particulate filters - Theory and experiment. SAE Technical Paper 2000-01-0184... 

Fig. 15.5. Typical pressure drop and concentration-time curves of a diesel particulate trap in a closed gas-loop experiment with constant heating rate for the characterization of catalyst or filter performance for the combustion of diesel soot. Sintered SiC ceramic filter, without catalyst coating or fuel additive (from Ref. [46]).

Some mathematical models have been developed to predict the behavior of the pressure drop over the diesel particulate trap with time during the loading/regenera-tion cycles [62, 67-69], to calculate the effect of filter-medium properties on filter performance of fibrous filters [70] or to describe the flow and filtration process [71] and the regeneration process [72-75]. An illustrative example for the performance of such a pressure drop model is provided in Fig. 15.7. 

The second technique is based on a filter to capture the soot particulates. Common filters are wall flow monoliths or ceramic foams. Cordierite wall flow monoliths are probably currently the most used particulate traps. They can capture diesel particulates with an efficiency of 99%. At normal diesel engine exhaust gas temperatures, the captured soot is not reactive enough to prevent build up on the filter, with an intolerable high pressure drop over the exhaust system as a result. The oxidation rate of the soot should, therefore, be increased which can be achieved by increasing the temperature of the filter, resulting in higher fuel consumption and thus making this solution unfavourable. The other possibility is catalytic oxidation of the collected soot. Several catalytic systems will be discussed. 

Nevertheless, secondary measures are mostly still needed to reduce exhaust emissions of cars to meet current emission standard in most countries. These so-called end-of-pipe solutions are based on the catalytic conversion of all HCs, CO and NO (three-way catalyst). The success of the monolithic catalytic converter (which has a lower pressure drop than a fixed bed) is up to now limited to gasoline powered engines. However, in recent years progress has been made in the development of catalytic filters for the cleaning of exhaust gas (e.g., particulate matter) from diesel engines. 

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