> Presence of oil is critical here as it creates conditions for hydrodynamic lubrication.
You can hear this effect in some vehicles at initial startup time for a few seconds. I know of certain Ford engines where it actually causes issues over time. The model years with auto start/stop have the worst of the cam rattle disease.
Note that that sentence is talking about the crankshaft bearings and their hydrodynamic lubrication, which is, well, elsewhere and separate from any cam rattle issues (including the cam phaser oil starvation that you might be referring to).
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 regular car on a race track, cornering forces slosh oil away from the oil pickup in the sump) issues, you'll damage your engine nearly immediately.
The thing that's missing here that really drastically changes the story is all the emissions control hardware that would exist on such an engine.
This is a circa 1990s engine in the US market i think? Dual Overhead Cam didn't really become popular in the US market until then i think. 70s-80s for single overhead cam to become established.
The diagrams are beautiful and informative as always from this author.
Wonderful but it irritates me that so many descriptions of internal combustion engines refer to "explosions" of the fuel. You don't want that. It causes knocking and pinging and engine damage. You want a controlled burn that generates heat smoothly.
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.
If you like this kind of stuff go and look up videos on the Rolls Royce Crecy engine from WWII. Absolutely insane engineering that died due the dawn of jet propulsion.
You meant - awful knocking combustion in the first, main animation?
I never catches any real bug is those great posts, but this one, especially as first animation on the page - weird.
You might be misreading the animation. It's a direct injection engine, the thing that happens during the compression stroke is fuel injection. Ignition happens a few degrees before TDC, which is realistic.
> Presence of oil is critical here as it creates conditions for hydrodynamic lubrication.
You can hear this effect in some vehicles at initial startup time for a few seconds. I know of certain Ford engines where it actually causes issues over time. The model years with auto start/stop have the worst of the cam rattle disease.
Note that that sentence is talking about the crankshaft bearings and their hydrodynamic lubrication, which is, well, elsewhere and separate from any cam rattle issues (including the cam phaser oil starvation that you might be referring to).
Lifters also often drain while sitting and valve lash is greater at start until they get slapped a few times
"in real running engines the rotating crankshaft should float completely on a very thin surface of oil" - I found this to be a great insight.
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 regular car on a race track, cornering forces slosh oil away from the oil pickup in the sump) issues, you'll damage your engine nearly immediately.
That's the point of all uses of oil, other than rust prevention.
Some engines are also substantially cooled by oil, but those are either older designs (think “air-cooled” Porche) or industrial prime-movers.
The thing that's missing here that really drastically changes the story is all the emissions control hardware that would exist on such an engine.
This is a circa 1990s engine in the US market i think? Dual Overhead Cam didn't really become popular in the US market until then i think. 70s-80s for single overhead cam to become established.
The diagrams are beautiful and informative as always from this author.
Pro tip: Show a message if WebGL is disabled instead of a blank space.
Wonderful but it irritates me that so many descriptions of internal combustion engines refer to "explosions" of the fuel. You don't want that. It causes knocking and pinging and engine damage. You want a controlled burn that generates heat smoothly.
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.
You don’t want detonation, but you do want deflagration.
Very interesting technology. Would be exciting to see a hardware startup build a product around this.
If you like this kind of stuff go and look up videos on the Rolls Royce Crecy engine from WWII. Absolutely insane engineering that died due the dawn of jet propulsion.
[2021] Originally 2333 points and 392 comments:
https://news.ycombinator.com/item?id=26991300
Excellent animations.
You meant - awful knocking combustion in the first, main animation? I never catches any real bug is those great posts, but this one, especially as first animation on the page - weird.
You might be misreading the animation. It's a direct injection engine, the thing that happens during the compression stroke is fuel injection. Ignition happens a few degrees before TDC, which is realistic.
One of the rare situations where someone wants a bit of retard?