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guerroconpollo t1_iwdok29 wrote

How a four stroke engine works.

A thing of beauty.

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zomboromcom t1_iwdpa7q wrote

Don't put your dick in that I'm not the boss of you.

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evilleppy87 t1_iwdrhoe wrote

Is it just me, or is the exhaust timing wrong?

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evilleppy87 t1_iwdssjt wrote

Replying to drsbd (#530,084)

Shouldn't it be open til the piston reaches TDC? If so that means with those cams it should open later in the exhaust stroke. It seems like they start opening just before the piston reaches BDC, and close half way up the exhaust stroke.

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J_Megadeth_J t1_iwe1zr7 wrote

This is definitely inaccurate with the fuel injection and exhaust.

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Snufflepuffster t1_iwe3wrq wrote

Replying to evilleppy87 (#530,102)

often valves close or open early to take advantage of acoustics (shock waves) to ram air into the cylinder or throw it out. So timing is very nuanced and can be adjusted drastically from engine to engine. In general the exhaust valve isn’t going to match the stroke, it might be early or late, extended or short due to design.

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MeGrendel t1_iwe6r1v wrote

Suck, squeeze, bang, blow.

Repeat

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evilleppy87 t1_iwe8c32 wrote

Replying to Snufflepuffster (#530,590)

I'm aware that there's going to be some variability, it just seemed to me that closing 90° before TDC was a little extreme, especially considering in most cases the exhaust valve closes a little after TDC

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mrgenier t1_iweaemi wrote

Introduced today the combustion engine would never make it, advanced yet so primitive

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keuzkeuz t1_iwebfyx wrote

The ole 1-2-3 firing order. I'm more fond of the 2-3-1 myself.

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DekaFate t1_iwepi1c wrote

So what happens when you “ throw a rod “

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Waldron1943 t1_iwerj2m wrote

Replying to evilleppy87 (#530,102)

They do open before BDC. Imagine a graph with two curves plotted. One curve is the "benefit" you get from leaving the valve closed and using every last bit of pressure. The other curve is the "benefit" you get from opening the valve early and starting exhaust flow. Those two graphs cross before BDC; there's more "benefit" to opening the valve than there is to keeping it closed.

Also, it's actually open past TDC. Right at TDC you've invested energy in establishing flow; if you slam the exhaust valve right then that flow just "piles up" against the valve, which doesn't help you. As a matter of fact, the intake valve opens (and stays open a surprisingly long time) before the exhaust valve closes...that's called "valve overlap". Less overlap = low RPM power, longer overlap = high RPM power. Overlap uses that flow through the exhaust valve to pull more fuel & air mixture into the cylinder.

Valve Overlap

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mkillham t1_iwewndf wrote

I still have no damn idea

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polyic t1_iwey3jn wrote

Replying to g2g079 (#529,958)

Oh my gosh! I’m so happy to see this site is still around. I remember using this to learn about engines when I was little. Thank you for sharing!

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alx924 t1_iwf5dl6 wrote

Looks like a Geo

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Flagil_Reinhumps t1_iwf5n72 wrote

This is so amazingly complicated I feel like electric motors will make us dummer.

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Dynasuarez-Wrecks t1_iwf6pnz wrote

Replying to DekaFate (#531,860)

"Throwing a rod" means that a connecting rod breaks. In this example, the connecting rods are the three green pieces near the bottom connecting the crankshaft (the yellow part) to the pistons (the three orange parts). Everything is moving very slowly here, but in an actual engine, connecting rods can be moving with enough energy to eject them completely through the crankcase (the engine's body), hence the term "throwing."

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Rhodog1234 t1_iwfa3eo wrote

Replying to alx924 (#532,829)

I had a 92 Geo Storm ( so I actually had 4 cylinders 😜).

I Absolutely LOVED that car. Got it right after a desert deployment, and after the rebates and military factory incentives , I got it for @ $6,000 . It would do 120 mph [source: was pulled over by Kansas state patrol officer who had a stopwatch showing exactly 30 seconds, and he told me that was my last mile. Was standing at parade rest the entire time and the good ol boy let me go with a warning! Whew] It would get as many as 48 mpg ! ( When driving considerably under 120) And the stereo with installed 12 band graphic equalizer w booster and detachable woofer box in the back ROCKED ! Ended up selling it for $4,800 4½ years later when I went to Korea.

Sorry... Little trip down memory lane... But yeah, the other Geo model had a 3 cylinder motor 🙂

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Rhodog1234 t1_iwfajx8 wrote

Replying to CBus660R (#532,396)

This can easily be accomplished by driving a 1978 Trans am 6.6 with a 400 big block at about 68 mph and quickly downshifting ( without sufficiently pre braking )... Still brings a tear to the eye

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Wallace_W_Whitfield t1_iwfbadf wrote

I’m a little confused. I know nothing of engines, but those lights look like they are not synced up

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mellbs t1_iwfbp3b wrote

Much easier to demonstrate with a single cylinder, and the diagram needs an element depicting airflow in its different stages

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Mr_Ted_Stickle t1_iwfbswn wrote

Slap this bad boy in a civic and you’re good to go. Add a piston and a cam if you’re feeling frisky.

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alx924 t1_iwfcnyu wrote

Replying to Rhodog1234 (#533,111)

The Storm was like half of a Camaro. I checked the curb weight of the two. The Geo was 67% the weight of the Camaro. So I checked the power. Depending on specs, the Geo was 57-67% as powerful as the Camaro. So I’m really not surprised you could get that thing moving so fast. The Camaro has a slightly better power to weight ratio, but only by 3lb/hp.

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ct_rugen t1_iwfdnrn wrote

Replying to evilleppy87 (#530,044)

You're telling me you see that but you haven't been 180 off on a cam or distributor timing. I know Ive missed a timing belt or chain a few tooths off a lot of times

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devnull1232 t1_iwfe7gi wrote

Are valves still mechanically controlled by an overhead cam or are they run by the ECU these days.

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alx924 t1_iwfgt32 wrote

Replying to Rhodog1234 (#533,268)

I had a 1992 Ford Probe with the 3.0 Liter V6 that my cousin gave me for free when my Jeep died. I drove that thing for 5 years with very few issues. It had the flip up headlights as well. I loved that car. I only sold it because I was moving out of state. My sister lived there another 4 years and she still saw it driving around. It was otter-pop blue, which was hard to miss. I remember beating mustangs off the line at stop lights from time to time. It was a fun car.

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Rhodog1234 t1_iwfhfvn wrote

Replying to alx924 (#533,450)

Nice .. totally forgot about those. Tbh I wasn't much of a Ford fan back in the day, but my cousin ( whose father had been a Ford plant employee so he got discounts ) had several different models over the years .

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bigbaltic t1_iwfhnov wrote

Replying to Skeetronic (#533,305)

Red is exhaust, blue is injection.

Blue opens to inject, piston draws in Piston compress Light (spark) ignites Piston expands from explosion Piston compresses exhaust Red Exhaust valve opens Piston expands because moment Piston compresses Repeat

The exhaust looks early but I am not familiar enough with the mechanics of engines to say definitely.

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TSMC_YT t1_iwfiu6i wrote

Well this explains everything

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Gordath t1_iwfj9mu wrote

It seems like the exhaust valve is closing a bit too soon?

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Riegel_Haribo t1_iwfl47l wrote

Replying to alx924 (#532,829)

2014+ Ford 1.0L ecoboost also is a three-cylinder engine with direct-acting bucket camshaft. It, however, is dual-overhead-cam, and quite unusual in having a oiled timing belt, oil-powered variable valve timing, belt-driven oil pump, and over 200% the power output of a Geo.

Here's a video with multiple angles of internal engine operation: https://www.youtube.com/watch?v=IFj5UIZx2cE

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weewillywinkee t1_iwflf7b wrote

Did work experience at a Shell research centre back in the 90s, they had managed to produce a crystal piston chamber for watching the combustion process after many attempts and failed prototypes. Not thought about that for years!

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gazette1895ky t1_iwflnf9 wrote

I was studying about this and discovered that gears do functions similar to levers, it is really amazing how one force acts on the other.

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wert1234576 t1_iwfmkhz wrote

Okay but where does the little wizard live?

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drjude518 t1_iwfo0e0 wrote

Very beautiful. Whether it works or not I want one. Are those emeralds at the top? Could do the whole thing again made out of precious metals; gold, argentium, platinum….

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hellcat_uk t1_iwfpbp7 wrote

Replying to Riegel_Haribo (#533,658)

Looks a lot like the Fiat TwinAir with the integrated exhaust manifold in the block and the oil powered variable valve timing though I can't see if the timing is individually controlled. Extra cylinder in the Ford obviously!

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thebeardknowstoomuch t1_iwfrap4 wrote

I don't know how an engine works and, after watching this, I still don't know

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shikuto t1_iwfsfkn wrote

Replying to Wallace_W_Whitfield (#533,161)

The lights (combustion of the fuel) happen at the top of every other movement of each piston. If you watch just the left-most piston, you’ll see the 4-stroke cycle (aka Otto/Diesel cycle, aka suck-squeeze-bang-blow.)

If you start watching the first piston right as the light flashes, the piston is at the top of the stroke length. This is the combustion portion of the cycle, or the “bang” part. This combustion creates rapidly expanding gas, pushing the piston down the cylinder.

Once it gets to the bottom of its travel, you’ll notice one of the valves at the top of the cylinder open up. Then the piston rises back up the length of the cylinder. This is pushing the exhaust gas out of the cylinder - the “blow” part.

After that, the exhaust valve closes, and the intake valve opens up. The piston is traveling back down the cylinder, due to the other pistons rotating the crankshaft. This pulls in air, and at the same time, modern internal combustion engines will spray the fuel of choice into the cylinder via fuel injectors. This is the “suck” part of the cycle.

Next up, at the bottom of the travel again, the intake valve closes. The piston travels back up the cylinder. Since it is now a sealed environment, the air-fuel mixture inside is compressed. This is the “squeeze” part. Then we’re back to the “bang” when the light goes off again.

In a diesel engine, the pressure and temperature alone cause the fuel to ignite, while gasoline engines utilize a spark plug for ignition. Ignition from pressure and temperature alone in a gasoline engine is referred to as detonation, and is a particularly bad thing to have happen.

It’s a little unorthodox to start the explanation of the power cycle at the ignition phase, but I think it’s useful to have the light as a good starting point when there’s a visual representation.

Hope this cleared something up for you!

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shikuto t1_iwfsmbv wrote

Replying to GustavSpanjor (#533,708)

>Now both exhaust and fuel intake is open on a downstroke.

No they’re not… Watch it again. Blue (intake) is open on a down stroke, red (exhaust) is open on the up stroke.

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SassyMoron t1_iwfwcxu wrote

It's an air pump, really. Locomotion is just a byproduct.

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spinjinn t1_iwfymu7 wrote

There are four pieces to the sequence. They are faking them with just three.

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Mayberley t1_iwfz58h wrote

Yeah. That is not showing me how it works.

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johnson_united t1_iwg5bhs wrote

Replying to mkillham (#532,282)

Intake - piston travels down to pull in air/fuel mix; compression - piston travels up to compress mix; power - mixture ignites, forcing piston down; exhaust - piston travels up to force out exhaust; process starts over.

Exhaust cycle for the valve timing seems a little bit off, but it’s close.

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zebrawithnostripes t1_iwg5co5 wrote

Replying to mkillham (#532,282)

Blue valve opens, gas gets injected, piston is pushed back up, gas compresses, spark, boom. Red valve opens and smoke exists. Note how the piston does 4 up/downs in a cycle. Only 1 of those steps is powered by gas dirextly. The 3 other steps are powered by the movement of another piston.

The real beauty in there is the cam shaft IMO. The green things moving the valve. They have to be perfectly configured andnthe gear ration needs to be precise otherwise the valve wouldn't open at the right time.

This is not my expertise though ... I could be wrong

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cbxsix t1_iwg5had wrote

Replying to evilleppy87 (#530,044)

It's off because of the huge amount of lash. The valves open too late and close too early because only the ~top half of the cam is actually hitting the valve stem. Otherwise it's a cool model!

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bbiggar500 t1_iwg5rt0 wrote

Way too much valve lash. Please adjust those.

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Nerdler17 t1_iwg6dqj wrote

This is why electric motors are so much more efficient.

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skylorddragon t1_iwg8xsg wrote

Can someone do this and explain 'gears' to me? 1st gear, second, third gear. Speed wise.

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cptstupendous t1_iwga5py wrote

At some point in the future, intimate knowledge about how these engines work will become as scarce as the knowledge of old programming languages like FORTRAN and COBOL.

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yodazer t1_iwgbyqz wrote

How a 4 stroke* engine works. Your weedwacker does not work like this.

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Wayed96 t1_iwgckmt wrote

Replying to zebrawithnostripes (#534,575)

>Blue valve opens, gas gets injected, piston is pushed back up, gas compresses, spark, boom

"Gas" is not injected. Air is sucked in because the piston moves down. Fuel could be injected either directly or just before the blue valve.

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Drunken-samurai t1_iwge1ej wrote

Replying to evilleppy87 (#530,818)

Bringing up variability, there is VVT (variable valve timing) which takes advantage of this in real time to use different valve timings at different RPM's to provide more efficiency or power.

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therandomopera t1_iwge90l wrote

How do the spinning cams opening the valves not wear out/get smaller from hitting the valves several thousand times a minute?

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Wuntoothrie t1_iwgeesg wrote

Replying to SassyMoron (#534,152)

Sort of. What this doesn't show is the synchronized explosions that force those pistons down. That little flash of light is the spark that ignites the gasses (air and gasoline, in many cases). The explosion is contained in the cylinder and pushes the piston and the arm down rotating the cam shaft.

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Aggrador t1_iwghsgt wrote

Replying to evilleppy87 (#530,044)

Doesn’t look wrong to me. Red exhaust valve opens as the piston rises and blue opens when the piston drops on each of the cylinders. I will say though, that this does look like an awfully unbalanced engine between cylinders 1 and 3 having so much time between the firing orders, as oppose to 1 to 2 or 2 to 3.

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Aggrador t1_iwgil6q wrote

Replying to johnson_united (#534,973)

It is just a diagram after all, not a precision-built machine, so I don’t think we can expect much in terms of ultra-realism. There are other things wrong with it, too, like no valve overlap, and the firing order has a noticeable lag between cylinders 1 and 3, makes for a very unbalanced engine.

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amazn_azn t1_iwgj8wo wrote

This is moreso "what an engine looks like while running" than what actually makes the engine work. The thermodynamic cycles are how engines generate mechanical force from the thermal energy released in the combustion of gasoline molecules.

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Oaskary t1_iwgm3wt wrote

I'm so glad I don't have to invent an engine.

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myawesomeself t1_iwgmva8 wrote

Replying to Waldron1943 (#531,984)

I think this is what everyone expects, that the exhaust should be open near TDC so it might overlap with intake a little, however in the model it clearly closes completely somewhere around halfway up and there is a noticeable gap between the exhaust valve closing and intake opening which is the unusual timing people are talking about.

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witzed1 t1_iwgmy47 wrote

Replying to DekaFate (#531,860)

The part, the connecting rod, connecting the piston to the crankshaft breaks. Usually due to some catastrophic problem like overheating or oil starvation. Something has prevented normal piston travel.

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witzed1 t1_iwgnrd3 wrote

Strange valve timing gear configuration. Usually cam and crank turn in same direction. Maybe a model artifact but definitely not representative of modern engines.

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Strength-Speed t1_iwgp260 wrote

Just a question if anyone knows. The cycle is intake, compression, ignition, exhaust. That would seem to indicate the piston starts in the up position then draws in air-fuel as the first step. But what draws the initial piston down, before the engine starts, as no ignitions have happened yet?

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Stagamemnon t1_iwgpnas wrote

Yeah, but where’s the fleeb? Don’t you have to rub that cause the fleeb has all the fleeb juice?

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Brandon432 t1_iwgreof wrote

Replying to therandomopera (#535,180)

This animation/video is a bit simplified. In real life, a couple things are different. The part at the top of the valve (or linked via pushrods and rockers) that actually contacts the camshaft is called the tappet. Tappers can be “flat” (not literally, they still have a bit of crown) or roller style. In either case, the tappet is made of friction resistant alloy and does NOT break contact with the cam. It follows the entire lobe so there is no “striking” just rubbing. Roller tappers greatly reduce friction but increase mass. In either case, the cam and tappets are enclosed in the engine head and continually fed motor oil to reduce friction and dissipate heat.

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Aggrador t1_iwgso6i wrote

Replying to illBro (#535,992)

It would be easier, but it’s not super critical either. This gives you a general idea of how a 4-cycle engine works. All I was trying to say is you could pick it apart and find everything wrong with it, but at the end of the day, it is just a diagram. But yeah, i agree, it would be easier to make in a diagram vs real life.

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krinklekut t1_iwgwujo wrote

Ah. Makes perfect sense now....

1

69poop420 t1_iwgzyan wrote

I think about these kinds of things at night and forget to follow up to see what they look like. Thank you.

1

Elkazan t1_iwh07to wrote

Replying to shifty_coder (#535,832)

1-3-2 is the same as 3-2-1 which is also sequential, just in the other way. Would it change anything? Seems pretty equivalent to me.

Disclaimer: I don't know about engines.

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Wuntoothrie t1_iwh2oa7 wrote

Replying to SassyMoron (#536,694)

Pretty sure that's just the spark plugs, but it would be nearly simultaneous. So you could probably pretend that it somehow is the same thing and fool the not so bright kids into learning something.

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mellbs t1_iwh39zi wrote

Replying to Lille7 (#536,738)

Oh yea didnt realize this was an actual video and not an animation. I still dont think it adequately explains whats happening to today's average person.

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spiderborland t1_iwh5elh wrote

What I choose to not research and just assume "mmhmm, gaskets and low clearance, yep" is how the top of the orange has gas in it, and the bottom of the orange has oil in it, and in a perfect world, they don't mix.

1

spiderborland t1_iwh5y2v wrote

Replying to g2g079 (#529,958)

Looking at all of these I'm happy to know that computer precision and magnets are replacing our traditional engines. We've gotten really good at squeezing every bit of efficiency out of internal combustion, but it's wild to me that, as someone else said, "boom make car go." Controlled explosions feels very archaic for how much effort we put into driving.

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Aquamarooned t1_iwhheca wrote

Replying to spiderborland (#537,029)

Look up how an impact drill works.. in slow motion its literally teeth slamming into eachother to spin the motion and its not as smooth tolerance as it would seem when you play it normal speed

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Brucie67 t1_iwtwyo2 wrote

When you put it like that you make it look so simple.

1