Control Engineering

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Automotive process model for emissions control?
April 10, 2007

Last Sunday, the Chicago Tribune had a front page story with the headline "State gives old beaters a free ride; new emissions policy means dirtier air for Illinois."  The upshot of the article (once you get past all the official corruption issues, complaints about air quality, etc.) is that the auto emissions monitoring rules in Illinois are going to be changed to eliminate actual tailpipe sniffing in favor of checking the onboard computer that has been installed in every car since 1996. All the test procedure needs will be information from the computer to pass or flunk the car. (Pre-computer cars won't be tested at all. Yikes!)

I called Doug, my mechanic, and asked him what the car's computer is reporting. He said the testers are looking for stored trouble codes, which indicate when the engine has experienced problems that could affect emissions. They're the same kind of things that make your CHECK ENGINE light go on. "If there are no stored trouble codes, then you pass," he says. "It's like if you don't see blood squirting out of a person, you know he doesn't have a puncture wound."

In other words, the state assumes that a properly working engine is not putting out excessive amounts of pollution. There has to be an exception to indicate a problem. They are, effectively, using a process model of an operating engine to predict emissions. If you know what is going into the process, you'll know what is coming out.

This same kind of thing has been going on for a while now in some industrial applications. Customers in specific industries are allowed to monitor their emissions via a process model rather than actual measurement. I know of at least one company, Pavilion, who has products for this purpose, and the EPA has allowed their use in a few key industries. We are likely to see more of this, both in automotive circles and industrial applications. It increases the importance of effective instrumentation design and placement, along with more sophisticated process models. All are things that are of growing consequence to our industrial community, and we should be doing our best to advance these technologies.

Posted by Peter Welander on April 10, 2007 | Comments (0)