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THE OTTO FOUR-STROKE—SELF TAUGHT

THE UBIQUITOUS Otto four-stroke internal combustion engine didn’t originate with Otto. For instance, Frenchman Alphonse Eugène Beau de Rochas patented the four-stroke concept in 1861, fifteen years before German Nicolaus Otto showed just how practical it could be.

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Nicolaus August Otto, 1832 – 1891, German inventor who perfected the concept of the internal-combustion engine.

Ten years after Otto’s 1876 accomplishment, a German patent office discovered Beau de Rochas’ earlier work and Otto’s company, Deutz, lost its monopoly. Within three years, more than 50 companies were manufacturing engines employing the Otto cycle.

Somehow the term “Beau de Rochas cycle” didn’t catch on.

In any case, today’s automotive engines (with the exception of diesels, battery electrics and just-emerging fuel cells) trace their heritage to the 1876 Otto Silent Engine. Which, I should note, was anything but silent. Its clatters and whirs overwhelmed the almost insignificant pops of internal combustion. But these pops would eventually put the world on wheels.

I’ve built a GMax computer model along the lines of an early Otto engine. In the next several days, I’ll use the model to illustrate Otto’s four strokes, the wonderful intricacies of his engine’s exposed crankshaft, valve gear and slide-valve flame ignition, and several of the GMax and Microsoft Computer Flight Simulator tricks discovered in its modeling. (For GMax background, see http://wp.me/p2ETap-2bV.)

All in good time-gobbling fun.

An Otto engine’s four-stroke operation is amazing when you consider how unobtrusive it has become in today’s cars.

An Otto Silent Engine. Model built with GMax and exported to Microsoft Flight Simulator.

An Otto Silent Engine. Model built with GMax and exported to Microsoft Flight Simulator.

Otto’s original engines were all stationary ones, operating pumps, driving belts to run machine tools and other non-mobile applications. The engine typically had a single cylinder set horizontally.

The four strokes of an Otto engine’s piston reciprocation are remembered by some as “suck, squeeze, pop, pooey.” More formally:

• Intake stroke. As the piston moves away from Top Dead Center, it generates a void in the cylinder to be filled. It sucks in air and fuel.

• Compression stroke. On its return from Bottom Dead Center, the piston squeezes the combustible mixture, thus increasing its density.

• Power stroke. At or near this next Top Dead Center, the piston and its air/fuel mixture encounter a means of ignition. The ensuing combustion drives the piston forcefully back down to Bottom Dead Center.

• Exhaust stroke. Returning to Top Dead Center on its fourth stroke, the piston pushes the spent products of combustion out of the cylinder.

Suck, squeeze, pop, pooey.

The intake stroke requires a means of admitting the air and fuel; the exhaust stroke, a way to purge the cylinder. A modern engine has intake and exhaust valves of the poppet variety.

The Otto engine’s exhaust valve looks quite modern. But its intake hardware is completely different, with a slide valve performing both intake and ignition functions; more on this anon.

The Otto’s crankshaft is exposed, with an oiler integrated onto its connecting rod. One end of the crankshaft is linked to a sizable flywheel, the inertial rotation of which carries the piston through its non-power strokes.

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An Otto Silent Engine, rear three-quarter view. GMax model exported to Microsoft Flight Simulator.

The other end contains a bevel gear that’s the origin of valve actuation, a description of which comes in the next item. ds

© Dennis Simanaitis, SimanaitisSays.com, 2014

2 comments on “THE OTTO FOUR-STROKE—SELF TAUGHT

  1. Mark W
    July 12, 2014

    Love this sort of stuff – makes me sound so smart when I casually drop a few technical phrases 🙂

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This entry was posted on July 12, 2014 by in Classic Bits, Sci-Tech and tagged , , , .
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