Worth noting the design of the internal combustion engine hasn't changed much in 50 years.
The thing that has changed is the control systems.
What used to be a primitive mechanical way of mixing fuel and air (the carburettor), is now an electronic fuel injection system, with the fuel air ratio very carefully matched to reduce pollution (fun fact: modern cars release so little carbon monoxide, you won't kill yourself by starting one in a garage (but don't try it just incase your car is faulty)). Catalytic converters use any tiny fuel air imbalance to reduce carbon monoxide and soot, and on the other side nitrous oxides, by slightly increasing and decreasing fuel air ratios.
> 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 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.
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.
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.
Worth noting the design of the internal combustion engine hasn't changed much in 50 years.
The thing that has changed is the control systems.
What used to be a primitive mechanical way of mixing fuel and air (the carburettor), is now an electronic fuel injection system, with the fuel air ratio very carefully matched to reduce pollution (fun fact: modern cars release so little carbon monoxide, you won't kill yourself by starting one in a garage (but don't try it just incase your car is faulty)). Catalytic converters use any tiny fuel air imbalance to reduce carbon monoxide and soot, and on the other side nitrous oxides, by slightly increasing and decreasing fuel air ratios.
> 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.
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.
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
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.
"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.
You are quite right, the oil also serves to transport the heat away.
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.
[2021] Originally 2333 points and 392 comments:
https://news.ycombinator.com/item?id=26991300
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.
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?