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Particulate traps reduce particle emissions through the physical filtration of solid, predominantly carbonaceous particles and decreasing particle-bound hydrocarbon emissions. Catalyst coated and uncoated traps were examined for their ability to reduce particle-bound hydrocarbons. At low exhaust temperatures some volatile hydrocarbons are particle-bound in the trap and are physically retained. These components become gaseous and are purged from the trap with sharp exhaust temperature rises. Oxidation catalysts considerably improve the ability of traps to decrease particle-bound hydrocarbon emissions, particularly PAH at low exhaust temperatures. Precious metal coated traps generate sulfate particles so that especially at high exhaust temperatures the overall filter efficiency can be reduced.

This paper presents the results of experimental and theoretical investigations on measuring particulate emissions of diesel engines in a dilution tunnel. The results offer a contribution to understanding the influence of several parameters on the particle phase of exhaust gas when diluted and mixed with air. These parameters include the exhaust gas temperature, the dilution ratio of the exhaust gas in the air, the mixture temperature, the flow and mixture conditions, the amount of filter loading and the filter material. In order to determine which physical/chemical processes dominate particle formation in diluted exhaust gas, the results of calculations in terms of condensation and adsorption are compared with the experimental findings. An increase in measured particulate concentrations is generally favoured by short sampling times, fast mixing processes, high exhaust gas temperatures, low mixture temperatures and low dilution ratios.

An exhaust gas aftertreatment system employing thermal regeneration has been developed to lower the particulate emissions from the intercooled Volvo 760 turbo-diesei engine. This system consists, primarily, of a honeycomb trap, a modified exhaust manifold and controlled compressor and intercooler bypasses. With this aftertreatment system, the particulate emissions can be lowered below the 0.2 g/mi standard (FTP-75 cycle) without unacceptable deterioration of the other pollutant emissions and the vehicle driveability. After operating the vehicle for more than 220 miles over consecutive FTP test cycles, the backpressure was found to remain constant up to approximately 70 miles. A brief description of the vehicle test procedure, accomplished during low ambient temperatures, is also provided. Problem areas which still remain are temperature control and thermal resistance as they relate to trap durability.

Diesel soot collected in a catalytically coated ceramic honeycomb trap, burns self-supporting, if the heat loss is less than the heat release due to soot oxidation. Experimental verification has been accomplished using a 4.66″ × 6″, 100 CPI trap. Ignition time and regeneration time are measured. At low speeds, a minimum ignition time of 15 s would be sufficient for the trap regeneration. An extended channel with an observation window is provided to allow examination of the regeneration. The soot is ignited at the beginning of the channel and the flame propagation is then observed. The soot burns through the channel in a match-like manner. Manganese and iron fuel additives are observed to have an effect on the mechanism of flame propagation.

During the lifetime of an internal combustion engine, deposits are formed at various locations. In diesel engines, deposits in the combustion chamber and at the injection nozzles lead to an increase in the emissions, especially the particulate emissions, and the exhaust gas odor. Additionally, durability problems can also arise. Deposits in the combustion chamber of SI engines can increase the octane requirement, deposits at intake valves can reduce engine efficiency and driveability and increase emissions. A detailed theory on the mechanism of deposit formation, considering the physical effects, is presented. This theory contains a deposit transport mechanism, a mechanism of deposit attachment including an induction phase, a deposit growth phase and a deposit removal mechanism. This complex theory is based on fundamental investigations at different locations in and around internal combustion engines.