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Eliminating engine knock increases operating efficiency.



A new method for detecting engine knock holds promise for more efficient automobiles, according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 researchers at Ohio State University Ohio State University, main campus at Columbus; land-grant and state supported; coeducational; chartered 1870, opened 1873 as Ohio Agricultural and Mechanical College, renamed 1878. There are also campuses at Lima, Mansfield, Marion, and Newark. , Columbus. As part of an on-board On board usually means to be traveling on some vehicle. For example, Baby On Board. Compare with overboard.

Metaphorically, the term on-board is often used to refer to some piece of technology that is integrated in a moving vehicle, for example:
 knock-control system, the method could help engines consume gasoline more efficiently and last longer.

Knock begins in the combustion chamber Combustion chamber

The space at the head end of an internal combustion engine cylinder where most of the combustion takes place. See Combustion
, where spark plugs spark plug: see ignition.
spark plug

Device that fits into the cylinder head of an internal-combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, creating a spark
 ignite gasoline to power the engine. When the spark plugs fire too early, the fuel octane rating Noun 1. octane rating - a measure of the antiknock properties of gasoline
octane number

quantity, measure, amount - how much there is or how many there are of something that you can quantify
 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 Acoustic resonance is the tendency of an acoustic system to absorb more energy when the frequency of its oscillations matches the system's natural frequency of vibration (its resonance frequency) than it does at other frequencies. ) 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 Noun 1. gas mileage - the ratio of the number of miles traveled to the number of gallons of gasoline burned
fuel consumption rate, gasoline mileage, mileage

ratio - the relative magnitudes of two quantities (usually expressed as a quotient)
, 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.

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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
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