Catalytic Stripper for Solid
Particle Number, Size, and Mass Emission
Inclusive Dates: 01//01/02 - Current
Background - The Environmental Protection Agency (EPA) defines engine exhaust particulate matter as the material collected on a filter from a stream of exhaust that is cooled and diluted by air to a temperature of less than 52 °C. Particulate matter (PM) emitted from combustion sources, particularly diesel engines, is typically composed of volatile and solid material. The solid material (soot) consists mainly of carbon and a small amount of inorganic ash. The volatile material consists of unburned and partially burned fuel and lubricating oil and sulfur compounds. Dry soot particles are formed in the combustion chamber of an engine, while most of the volatile material enters the particle phase from the gas phase as the exhaust cools. Hence, particulate matter is a combined measure of solid and volatile particles. It is important to be able to distinguish between the two components because the means used to control them are different.
Currently, no available method is capable of facilitating the measurement of solid particle mass, number, and size emission in real time. Most available methods rely on chemical workup, and they are slow, taking several hours to several days from the time of initial measurement. In addition, the results are not applicable to establishing particle number and size, but only particle mass. Thus, finding a method that facilitates the measurement of solid particles in real time would be of great value to engine developers and emission researchers. It would help identify in a quick manner the nature of PM emissions. It also would help in identifying solid particle number and size that may be the subject of future PM regulation, particularly in Europe.
Approach - The objective of this project was to design and build a catalytic stripper system (CSS) to remove volatile material from a dilute sample of diesel exhaust to facilitate the measurement of solid exhaust particles in real time by various methods. The CSS consists of a heated diesel oxidation catalyst, temperature probes at inlet and outlet, and a micro-dilution tunnel (at its outlet) to achieve the desired temperature prior to solid particle analysis. The CSS utilizes a conventional diesel oxidation catalyst. The catalyst and geometry of the substrate were characterized and sized to prevent solid particle losses, in the size range typical of diesel exhaust, and yet achieve near 100-percent removal of volatile materials. Particle and gas dynamic theories were used to guide the design criteria. Experimental verification will be achieved using laboratory aerosol such as sodium chloride, ammonium sulfate, and oil droplets. The performance of the final design of the CSS will be tested and evaluated in a diesel engine test cell. The performance will also be compared to existing analytical methods.
Accomplishments - The CSS was designed and built. Preliminary characterization with sodium chloride particles were carried out at different flow rates. The results were satisfactory. More work is needed to investigate fully its performance with sodium chloride, lubrication oil, and diesel exhaust particles.