1993-03-01

Particulate and Odor Control in Car Ventilation Systems 930014

Particulate control in car ventilation systems using electrically-charged synthetic filter media are becoming more popular. Adsorption units and low-temperature catalytic systems have been used to control odors and some chemical contaminants in top-of-the-line automobiles. This is a review analyzing these systems, the contaminants found in vehicle environments, and filtration theory. A detailed discussion of experimental work concentrates on overall and fractional filter efficiency and increase in pressure drop with dust loading of charged and uncharged filter media at high aerosol velocity. SAE fine and two natural polydisperse dusts with particles smaller than 5 and 10 μm were used for testing.
The health and comfort of car occupants depend on several factors, including air quality. Currently, several car manufacturers offer filtration systems for car interior air. In some cases, the system includes not only a particulate filter but also an adsorption unit to control odors, or even a low-temperature catalytic system to control some chemical contaminants. In contrast to the early stage of car interior air filtration technology in the 1980s when particulate filters were used only in the luxury models, current use of these filters has spread to the lower-end models.
It is justifiable to say that a majority of automobile manufacturers are now aware of the potential need for a filtration system to improve car interior air quality. Most filter manufacturers have upgraded existing particulate filter performance. Advanced filter media, including multilayer charged synthetics, has become standard for this application. On the other hand, odor and chemical contaminant control, are still in transition. It is a difficult application for classical adsorbers, such as activated carbon, because the flow velocity is high. Therefore, residence time is limited, and odor removal must proceed rapidly. Because the odor concentration is very low, in the parts per billion (ppb), the odor control system must be very efficient. Masking odors by means of special chemical agents is a method used by some companies, but it is not a method of odor removal.
In order to achieve high efficiency and low pressure drop of the filtration-adsorption system, filters should be relatively large. Because new car designers concentrate on low body profile, it is difficult to find the required space in a car HVAC system for high-efficiency filters required to control fine particles, e.g., diesel exhaust particles. Due to the low permeability of the filter media used to construct high-efficiency filters, filtration velocity is low; therefore, these filters are relatively large. In order to utilize these filters, an independent car ventilation system is an option being studied by car manufacturers. Another option is based on the idea of independent recirculating air flow. Due to relatively low flow rate and aerosol velocity through the filter media in this design, high-efficiency filter media can be used.
The purpose of this paper is to outline some of the most important problems associated with the development of a filtration-adsorption system for cars. Field conditions, requirements for clean air, the filtration process in filter media performance, odors and odor removal, and test methods for system evaluation are discussed.

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