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A Counterattack on Contaminants
Excessive wear and malfunctions in automotive systems often can be traced to various contaminants or small particles that may be built-in, self-generated, or inhaled from the environment. In addition to causing premature abrasion wear of bearings, piston rings and other friction-sensitive components, contamination can lead to blockages, lockups, and failures involving valves, pumps, seals, and fuel injectors. The result is degradation of machine performance and shortened service life.
Contamination analysis, testing, modeling, and simulation methodologies have become a significant mission of the Engine and Vehicle Research Division of Southwest Research Institute (SwRI).
For components whose performance has been calculated according to a deterministic, ideal set of operating parameters, the presence of contaminants literally changes the equation to a stochastic (time varying, probability based) model involving random variables. However, contamination analysis, testing, modeling, and simulation methodologies can help manufacturers design components to an allowable contamination level. Other goals include the identification of key contamination-sensitive parameters and components, realistic service life estimates, and the achievement of targeted service life.
In many cases, SwRI scientists can elicit meaningful results in a relatively short period by accelerating wear and degradation rates through induced contamination using specific contaminants or standard test dusts. Engine ring wear analysis can be accomplished through real-time measurements using radioactive tracer technology during tests in which the engine is run and dust is injected into the intake air stream at specified intervals. Other component tests, such as lube oil sensitivity to dust contamination, also utilize radioactive tracer real-time wear measurement techniques.
It is also possible to analyze the contamination impact on other components. Transmission spool valves, for example, have been evaluated for their tendency to lock up under contaminated-fluid conditions, and filter elements have been analyzed for their performance under dust loading and dust agglomeration conditions.
Interestingly, agglomeration can account for the plugging of filters by particles smaller than the filter's pores. Rather than passing through the filter as might be expected, the particles may change flow direction many times before they pass completely through. This repetitive re-direction strengthens the motion behavior of the particles, making their dynamic size much larger than their physical size and also increasing the chances that small particles will collide with larger ones. Through the facilitation of some binding agents in the fluid and particle surface properties, many of these particles stick to each other after colliding. As this "sticking" process grows, the cluster of particles eventually plugs the filter's openings.
In some cases, agglomeration can be exploited beneficially. One approach to dust contaminant remediation exploits this tendency by using ultrasonic waves to promote agglomeration in a polydispersed suspension of fine particles in the inlet streams of automotive engines. The waves cause smaller particles to collide with large particles to promote growth, or agglomeration, to a size large enough to permit subsequent separation from the bulk fluid. Significantly, no pressure drop is associated with this process, as opposed to most other agglomeration and separation techniques.
In air cleaner experiments, ultrasonic agglomeration was used to enhance precleaner efficiency by redistributing the particle size distribution toward larger sizes, resulting in a 40 percent reduction in dust penetration.
In experiments involving the agglomeration of diesel exhaust particulate, the physical size of soot particles was increased four- to seven-fold in the presence of nonoptimized ultrasonic fields. This result is significant because it shows that soot particles can be altered to enhance downstream removal.
1. X. Tao and M.B. Treuhaft, "Contamination Sensitivity of Automotive Components," SAE Technical Paper Series No. 970552, February 1997.
2. M.B. Treuhaft, "Ultrasonic Agglomeration of Airborne Dusts and Diesel Exhaust Particulate to Enhance Inertial Separation," Report No. 03-9819, January 1, 1994-November 1, 1996.
3. E.C. Fitch, "Fluid Contamination Control," FES, Inc., Stillwater, Oklahoma, 1988.
4. J.K. Beddow, "Particulate Science and Technology," Chemical Publishing Co., Inc., New York, New York, 1980.
5. "Contamination Control and Filtration Fundamentals," Pall Industrial Hydraulics Co., 1994.
6. M.B. Treuhaft, "Engine Wear Experiments," SwRI Internal Research Final Report, 1989.
7. X. Tao, "Methodologies for Nonlinear Systems Subjected to Stochastic Parametric and External Excitations," Ph.D. Thesis, Oklahoma State University, December 1990.
Published in the Spring 1998 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.