Printer Friendly

Eliminating engine knock increases operating efficiency.

A new method for detecting engine knock holds promise for more efficient automobiles, according to researchers at Ohio State University, Columbus. As part of an on-board knock-control system, the method could help engines consume gasoline more efficiently and last longer.

Knock begins in the combustion chamber, where spark plugs ignite gasoline to power the engine. When the spark plugs fire too early, the fuel octane rating is too low, or carbon deposits inside the chamber grow hot enough to ignite the gasoline, the fuel doesn't burn gradually -- it detonates all at once. This explosion sends out violent shock waves that vibrate the entire engine. In addition, the phenomenon, also referred to as "pinging," causes combustion chamber temperatures to soar, with the risk of permanently damaging valves and pistons.

Millions of cars on the road today contain vibration sensors (usually located on the engine block) that are supposed to detect engine knock. However, the software that processes the signals from these sensors often confuses knock with normally occurring vibrations, especially at higher engine speeds. Many production knock-control systems are incapable of detecting engine knock until the levels are very high.

"Everything vibrates on an engine. You've got things rotating, things shaking, everything is moving," explains Giorgio Rizzoni, associate professor of mechanical engineering and director of Ohio State's Powertrain Control and Diagnostics Laboratory. "The difference between a normal and knocking condition is just not that obvious." This difficulty is made even greater by the fact that the vibration induced by knocking combustion occurs over the span of a few milliseconds.

Rizzoni and his colleagues wrote software that uses a different kind of mathematical technique -- time-frequency (TF) analysis -- to extract knock vibration from background noise more effectively. The researchers took advantage of the fact that the pitch of the sound (acoustic resonance) induced by knock changes with the combustion temperatures. As fuel combustion progresses, the temperature in the chamber rises and then falls.

Knock typically starts when combustion chamber temperature is near its peak. Thus, the pitch of the knocking sound becomes lower with time, and this gives rise to a characteristic vibration signature. The software tells the computer to look for vibrations with this characteristic drop in pitch and ignore all the others.

An automobile computer system that uses the TF method would detect low levels of knock quickly and accurately. It then could instruct the engine control system to make the appropriate adjustments (typically retarding the spark) and virtually eliminate knock altogether. Drivers would get better gas mileage, longer engine life, and lower maintenance costs.
COPYRIGHT 1997 Society for the Advancement of Education
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1997 Gale, Cengage Learning. All rights reserved.

 Reader Opinion

Title:

Comment:



 

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Ohio State Univ researchers have developed software that better differentiates between automobile engine knock and background noise
Publication:USA Today (Magazine)
Article Type:Brief Article
Date:Jun 1, 1997
Words:424
Previous Article:Fiery foils produce new sealing process.
Next Article:Teaching machines to recognize objects.
Topics:


Related Articles
Silicone making autos quieter than ever.
Reducing Emissions Boosts Performance.
Ready for a smooth FLIGHT; Aero engineers GE Caledonian deal with high-flyers, a description that fits their employees, too.
Resident transportation leaps ahead: transportation expert Halsey King anticipates enhanced safety, comfort, and engineering in this year's buses and...
BMW searches for efficiency.
MIT DEVELOPING HALF-SIZED GASOLINE ENGINE.
Ethanol boosts gas engines.
Alcohol can make cars more climate-friendly.

Terms of use | Copyright © 2014 Farlex, Inc. | Feedback | For webmasters