Re:How a 4-Pound Engine Can Replace a 40-Pound Engine
by kbob on Sunday June 19, 2016 @11:48AM
(#11933348)
A four-stroke engine fires every other crankshaft revolution. Each cylinder creates its own pulses. The exhaust manifold tries, with varying success, to blend those into a single higher-frequency pulse train.
The Liquid rotary fires thrice per revolution, or six times faster. The go-kart engine is designed for 10,000 RPM. That puts its fundamental frequency at a less objectionable 500 Hz.
But the go-kart video did not sound like 500 Hz -- it sounded like about 100 Hz.
As for the "alarming amount of fuel out the tailpipe" line, maybe they're comparing a two-stroke engine. I don't really know how unburned fuel affects a two-stroke's sound.
Re:How a 4-Pound Engine Can Replace a 40-Pound Engine
by karmakaze on Thursday June 16, 2016 @01:20PM
(#11917501)
I questioned whether should edit part of that out. Somewhere it does mention over-expansion to near 1 atmosphere in its cycle. So the theory is quiet, the go kart audio not withstanding.
The "an alarming amount of fuel goes out the tailpipe" is reminiscent of the wording associated with various fuel-saver scam gadgets. In practice, this is measured in HC emissions, which are usually in the low tens of PPM range on a properly tuned engine.
Disregarding mechanical sources, engine noise is largely caused by the high-pressure gases flowing out the exhaust with pulsations on each power stroke. The distinctive beating of a low-cylinder-count engine e.g. a motorcycle is entirely this phenomenon. To attribute the noise of a properly functioning (i.e. not backfiring) engine to "unburned fuel" is completely wrong.