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Internal Combustion Engine (2021)

ciechanow.ski

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Re: Internal Combustion Engine (2021)

#41

Post by Toutouxc »

raffael_de wrote: post #32
Toutouxc wrote: post #21

Earlier quoted context omitted.

Not exactly. You do want a deflagration and not a detonation, but "explosion" is more loosely defined and, depending on who you're talking to, a self-sustaining subsonic flame front and a sharp pressure spike are a perfectly valid explosion.

explosion/detonation causes engine knocking or pre-ignition which is both very bad. a properly working combustion engine is driven by controlled burning.

You’re replying to a post that says that “explosion” doesn’t imply “detonation”.

Re: Internal Combustion Engine (2021)

#43

Post by cagey »

LeifCarrotson wrote: post #28
arlattimore wrote: post #13

Earlier quoted context omitted.

The bearing surfaces in an engine (ex: crankshaft main bearings) have very tight tolerances, usually in the 15-25 thousandths of an inch. The engines oil pump fills those tiny gaps with pressurized oil which allow the metal surfaces to spin thousands of times per minute without damage. This is also why if you have any issue with oil pressure (ex: oil pump failure, cracked oil line) or oil starvation (ex: driving a re…

It's 0.0015, that's 1.5 to 2.5 thousandths, or 15-25 "tenths" as they're called. That's not a particularly tiny gap in the machinist world, it's large so that you can pump viscous oil in it and deal with a wide variety of temperature changes. 25 thousandths would be sloppy, a nominal clearance hole for a 1/4x20 bolt is about that much.

> 25 thousandths would be sloppy, a nominal clearance hole for a 1/4x20 bolt is about that much.

Isn't that 0.250 which would be 250 thousandths?

Re: Internal Combustion Engine (2021)

#44

Post by Toutouxc »

toxik wrote: post #38
LeifCarrotson wrote: post #26

Earlier quoted context omitted.

Auto start/stop isn't off for enough time for the oil to drain from the galleries and especially not out of the bearing journals. It's the first few seconds after an engine has been off for hours (or worse, for potentially years) that are the problem.

I thought it pretty well established that auto on/off is bad for the engine, as is intermittently turning off some cylinders as some do. Is that wrong?

I don’t think it’s pretty well established, there are cars that will happily stop and start the engine multiple times per minute, e.g. Toyota hybrids with their “HSD” drivetrain. It just requires some engineering.

Re: Internal Combustion Engine (2021)

#46

Post by duped »

This is a stupid question but I'm a stupid EE/SWE who knows very little about physical objects.

In the all these animations of the pistons I see linear motion translated into rotary motion using the crank shaft - but how do you design the pison/crank to always turn clockwise or counter clockwise (based on how you view it, obviously)? Is it possible for the crank shaft to lock up if it's perfectly oriented at 0 degrees?

Re: Internal Combustion Engine (2021)

#47

Post by Toutouxc »

xenadu02 wrote: post #29
calmbonsai wrote: post #24

Earlier quoted context omitted.

Some engines are also substantially cooled by oil, but those are either older designs (think “air-cooled” Porche) or industrial prime-movers.

Most piston aircraft engines are still air-cooled which really means air and oil cooled. The oil is a big part of getting heat out of various parts of the engine. That also makes them harder on oil as the piston/rings have larger tolerances so they don't expand and bind up during operation. That means greater blow-by at startup and when operating at lower temps which puts a lot more combustion byproducts into the oil…

Fun thing about the sodium filled valves — these are also used in cars. The engine in my previous econobox, a 3-cylinder 1.0 TSI (EA211) uses them in the 81 kW variant.

Re: Internal Combustion Engine (2021)

#48

Post by trhway »

Toutouxc wrote: post #44
toxik wrote: post #38

Earlier quoted context omitted.

I thought it pretty well established that auto on/off is bad for the engine, as is intermittently turning off some cylinders as some do. Is that wrong?

I don’t think it’s pretty well established, there are cars that will happily stop and start the engine multiple times per minute, e.g. Toyota hybrids with their “HSD” drivetrain. It just requires some engineering.

I don’t think Toyota engine does traction from low rpm. Electric motor does it, and moments later already well spinning engine gets the load.

Hearing regular start-stop on intersection gives me sorry feeling for the engine.

Re: Internal Combustion Engine (2021)

#50

Post by pjc50 »

duped wrote: post #46

This is a stupid question but I'm a stupid EE/SWE who knows very little about physical objects. In the all these animations of the pistons I see linear motion translated into rotary motion using the crank shaft - but how do you design the pison/crank to always turn clockwise or counter clockwise (based on how you view it, obviously)? Is it possible for the crank shaft to lock up if it's perfectly oriented at 0 degree…

This is why the starter motor spins the shaft in a known direction.
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