Monday, December 12, 2011

Thoughts of my Lungs and 2-Cycles

Two things are on my mind every time I bike up Observatory Drive, the lakes-hore road that brings you directly to the UW Madison campus, "Will this ever end? and "Why are mopeds so dirty?"

As I struggle for oxygen near the peak, I recognize that breathing would be a lot easier if I weren't also inhaling carbon-monoxide and unburned exhaust gasses from the screaming mopeds that are lurching by me.

Recall that there are two types of engines we use in the everyday, modern world, 2-strokes and 4-strokes. They are alternatively referred to as 2-cycle and 4-cycle. The difference between the two is how they work inside and also, that one is cleaner than the other.

Passenger vehicles such as this have a 4-cycle engine and are comparatively cleaner than 2-cycles. 

"The big transition to four stroke engines was because of emissions," says Professor Foster, Director of Engine Research Center at UW Madison. "It was more expensive to buy that engine but less polluting by the standpoint of the gasses coming out."

Professor Foster attributes the cleaner emissions of 4-stroke engines due to simple technological innovation. He also comments that 2-strokes can be just as clean as 4-strokes, but the tradeoff is cost.

So why is there still a mixture of 2-stroke and  4-stroke engines? Mopeds generally have 2-strokes, so do many boat motors. All four-wheeled passenger vehicles use 4-strokes as a result of regulatory pressures to clean their emissions. The continued mixture exists due to power outputs and namely, 2-cycles produce more of it. They have more "bang for their buck,"  so to say, but the tradeoff is a less-efficient combustion, meaning dirtier exhaust.

For a comparison between 2-strokes and 4-strokes, check out here and here.

2-stroke engines are still commonly used today for things such as mopeds and outboard boat motors and tug-boat engines. However, outboard motors, due to increased awareness of water pollution, have also made the transition to a 4-cycle platform.

Overall, Observatory Drive will remain temporarily clogged with the unburned, blue exhaust from passing mopeds, although 4-stroke designs have also been around for some time. On the plus side however, mopeds remain as an fuel efficient mode of transportation, averaging anywhere between 50-100 mpg.

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