Notes from the lab


REDUCING `PISTON SLAP' IN ENGINES

Few technologies have received more engineering attention than the internal combustion engine. Yet engine designers continue to be troubled by a phenomenon known as "piston slap." As a piston moves up and down inside its cylinder, it also shifts from side to side, bumping first one side and then the other-a behavior that wastes fuel, wears out engines and makes an annoying bang.

A computer model developed by MIT researchers can disentangle the factors that lead to piston slap, helping engineers make design decisions that will reduce its intensity. Given a description of the operating conditions and design of an engine, the model can describe the pathway the piston follows inside the cylinder, the force with which it hits the wall and even how its shape changes due to the impact. The researchers have validated the model using an operating experimental engine.

The team was led by Dr. Victor Wong, a principal research scientist in the Energy Laboratory and lecturer in the Department of Mechanical Engineering. The work was funded by Nissan Motor Company. (Source: Nancy Stauffer, e-lab newsletter)

IMPROVING A TOOL FOR DATA TRANSMISSION

Today, complex information such as an image or a video signal can be put into digital form, transmitted over communications channels and reconstructed in close to its original form. The conventional technique for selecting the smallest amount of information needed to reconstruct the original signal involves describing the signal in terms of cosine waves that theoretically continue forever.

Enter a new technique based on a mathematical concept known as wavelets. Wavelets have a finite length, and for many applications they work better than cosines. While others develop new applications for wavelets, MIT mathematicians are improving the analytical tool itself. For example, they are using combinations of several different wavelets to represent the signal. Results of compressing and reconstructing the signal using the new ideas have been promising.

The ideas are described by Professor Gilbert Strang of the Department of Mathematics in his new text for the MIT course "Wavelets and Filter Banks." (Source: Nancy Stauffer, e-lab newsletter)

A version of this article appeared in MIT Tech Talk on September 18, 1996.


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