Suck, squeeze, bang, blow.

December 22, 2015 7:06 PM

Slow motion video from inside the combustion chamber of a running flat head/L-head/Side valve engine with a rich mixture. Same engine running lean. Running at regular speed (misfires caused by carb tuning), (via /r/Justrolledintotheshop)

How was this filmed?

The normal head is replaced with an inch tall spacer to reduce the compression. On top of that is a piece of borosilicate glass that is high temperature and pressure resistant. It is clamped on using a rubberized high temp gasket. Above that is a lexan shield to protect the highspeed camera. The camera is mounted about 5 feet above that which is the minimum focal length of the camera.

Imgur gallery of the setup.

posted by Mitheral (19 comments total)

For me this raises more questions than it answers (I am not a car guy)
posted by RustyBrooks at 7:47 PM on December 22, 2015 [1 favorite]

Via related videos, Ken Schweim's Wood Flathead Four Cylinder Willys Jeep Engine will not only explain exactly how this engine works, but may also inspire you to go get some scrap pieces of wood and some tools and build your own wood automata.
posted by effbot at 7:55 PM on December 22, 2015 [6 favorites]

I was told that the process of detonation (knocking) was determined to be two flame fronts meeting at supersonic speed, by a filming an engine with a glass cylinder head. Google is not helping me with this story, I believe it was done by Ford in the 20's.
posted by 445supermag at 8:01 PM on December 22, 2015

The difference in flames you can see are the result of extra soot in the rich mixture. Because the combustion lacks oxygen (the very definition of a rich mixture) it ends up incomplete. The hydrogen is detached from the carbon and the carbon is then excited by the heat forming the yellow part of the flame. The blue flame you see on the lean mixture is complete combustion with no soot. You'd think with the lack of soot in complete combustion the ideal condition would be to run the engine lean. However, if the combustion temperature reaches above 2800F (which regularly happens in almost all engines) you start "burning" nitrogen and forming nitrogen oxides. So it becomes a delicate balance between NOx, unburnt hydrocarbons, and carbon monoxide.

Combustion is so interesting.
posted by Talez at 8:08 PM on December 22, 2015 [9 favorites]

OK, next question - why does the spark plug appear to fire every stroke (including the end of the exhaust stroke), instead of every 2nd stroke when it's needed? Is that just because the distributor cap can be made simpler that way, or perhaps I'm seeing things?
posted by Popular Ethics at 8:11 PM on December 22, 2015

It's waste spark ignition. Which just means it fires on every revolution. It's done that way because it's easier and cheaper.
posted by Mitheral at 8:18 PM on December 22, 2015 [3 favorites]

I was told that the process of detonation (knocking) was determined to be two flame fronts meeting at supersonic speed, by a filming an engine with a glass cylinder head. Google is not helping me with this story, I believe it was done by Ford in the 20's.

Yes. You also have the whole trying to compress a shockwave thing.
posted by Talez at 8:24 PM on December 22, 2015

Recently posted to Hackaday and related: Homemade Internal Combustion Engine, no machine shop required, just a few tools and a drill press.
posted by JoeXIII007 at 8:25 PM on December 22, 2015 [2 favorites]

The videos are neat. It took me a long time to wrap my head around how a four stroke engine works when I was a kid for some reason, and it would have been easier if I had been able to see videos like this, or that amazing wooden model.
posted by Dip Flash at 9:29 PM on December 22, 2015

When I was about 7 my dad woke me up from sleep (it was about 9:00 pm) over my mother's strenuous protests, told me to put some clothes over my pyjamas, and drove me out to the city dump.There was an eight-cylinder engine block sitting in the dirt, and Dad brought out his flashlight to point out the parts, and told me about the stages of a four-stroke combustion engine. As far as he was concerned, an engine block out in the open was a teaching tool not often available and well worth losing sleep over.

He died a bit over a year ago and he would have loved this.
posted by angiep at 10:09 PM on December 22, 2015 [18 favorites]

You had a cool dad.
posted by chisel at 11:22 PM on December 22, 2015 [6 favorites]

Got to play with a variety of Ricardo research engines with glass combustion visualization bits in university. Takes me back. At the time, we were aiming for compression-ignition lubricant-free uncooled ceramic engines running on methane. Never quite got more than two of the above to work at once.
posted by scruss at 1:42 AM on December 23, 2015 [3 favorites]

I actually ended up enjoying it more than what I expected based on the title. Fascinating!
posted by cryptolex at 5:38 AM on December 23, 2015

This is completely fascinating. Just yesterday when we were driving to town to do some Christmas shopping, my dad slightly sheepishly asked me to explain to him exactly how a turbocharger worked, and we ended up spending the entire trip and afternoon talking about how engines work in general. I will definitely be showing him this to illustrate a lot of what we ran through.
posted by Dysk at 7:32 AM on December 23, 2015

Did anybody else have a Visible V8 model kit as a kid? I loved that thing to death, but I don't think I ever actually got it working. There was something about how if you weren't very careful with the glue in the cylinders it would get bound up. It was a very complicated model for a child to put together. I remember that it had tiny little lights for spark plugs and everything.
posted by Rhomboid at 9:10 AM on December 23, 2015

About 3 years ago I bought my first ever car that came with a turbocharger. Of course I'd heard of turbos for years and knew they "made cars go faster", but I finally went looking for information on how they actually work. It's fascinating and clever and I love the sort of "free performance" angle. Turns out to be pretty cool in practice, too! Now I can imagine it whirring away under the hood as I drive along.
posted by Greg_Ace at 10:07 AM on December 23, 2015

(BTW, I know now that turbos don't make cars "go faster"; they increase power output, with the result being things like better acceleration. And I know the performance isn't exactly free, either. But I'll keep my car anyway!)
posted by Greg_Ace at 10:40 AM on December 23, 2015

Turbos increase performance because the limiting factor in any naturally aspirated engine is how fast air can flow in through the manifold into the cylinder at standard atmospheric pressure. No matter how hard your engine sucks in air the difference between the atmosphere and full vacuum is ~100kpa. One of the innovations that helped in this regard is going up to two or even three (N/A 20 valve 4 cylinders were a big thing in the 80s and 90s) intake valves per cylinder to suck in more air through the small valve ports. The more air you have the more fuel you can burn, the more power you can get out of a fixed displacement cylinder.

Turbos remove this limitation so that you force more air into the cylinder than can be supplied at standard atmospheric pressure. You dump 20% more air in the cylinder you can burn 20% more fuel at the expense of a higher compression ratio. Of course, the limiting point then becomes the strength of the block and the cylinder liners the result being catastrophic failure becomes a higher chance option because your cylinder is now handling more pressure, more air, more heat, bigger chance of predetonation, larger pressures on predetonation.

It all comes back to oxygen really. If you could force a pure oxygen atmosphere into the cylinder you could in theory burn an even larger amount of fuel fairly cleanly but there's no real way you can cheaply scavenge waste energy into removing nitrogen from the air coming in from the atmosphere. Turbos on the other hand can impose a small amount of back pressure on the exhaust system but give you a lot of compression and gobs more air in exchange.
posted by Talez at 5:31 PM on December 23, 2015

Stuffing more oxygen into the engine is how NOS works (with a minor boost from a denser intake charge).
posted by Mitheral at 5:56 PM on December 23, 2015 [1 favorite]