Why Lean Engines Do NOT Run Hot - Myth Busted

[@chrisfix]

Great explanation Jason! That makes sense! I did an egr cleaning video where I said injecting exhaust gases cools the cylinder temps and people were not understanding. I will reference them to this video now!

[@Diddy_Doodat]

I'd like to see it Chris

[@markusmords9662]

Just want some advice sir,, my forester 16 at 60k km is starting to show idle problem.. only at warm start, rpm drops low (almost stall) and bounces back up.. at cold start its idling normally high as cold engine then gradually drops.. the problem usually only occurs at warm, like after a long trip and engine rest for an hour,. Any advice sir,, where to look first before I bring it to mechanic.. thanks. More power

[@kylelentz3801]

Thats only if your vehicle has an EGR cooler. My 2011 jeep grand cherokee does NOT have an EGR cooler.

[@azargelin]

Markus Mordeno i think it might be a crank shaft position sensor

[@IainWandersButIsNotLost]

I am definitely using this explanation next time this debate comes up. You make me sound smart!

[@hpux735]

In aviation engines, where you have to manage mixture manually, we talk about it in LoP and RoP (lean of peak, and rich of peak). I love running LoP in cruise because it saves so much fuel. On our large-bore, low-compression, 1950's engines, you can't really run them anywhere near peak when making full power, so you're either cooling the engine with fuel or air. Air is free :)

[@captainjosue]

Hmmm. Air is free. I like that. Well, lets run a little lean moving forward. It's free and cools the engine LOL

[@ch98hb]

German automotive engineer here: The Peak NOx (and also max temperature) is around λ=1,1 which is lean. You gotta use λ, which is airflow/(fuelflow*14,7). Stochiometric is thus at λ=1 which makes a lot more sense if you try to visualize it and make conclusions. But all in all you explained it well. Combustion temperature is primarily a function of the compression ratio, and peaks at the LEAN λ=1,1. The Temperature of the engine block depends on your efficiency and cooling system as well. Youre right that at peak power the mixture gets thiccer to keep the engine cool.

[@BP-fx3qc]

All i was able to read was : german, lean, airflow, temperature, visualize and combustion. English please!

[@KF1]

@@BP-fx3qc dude, just read it. The top of the nox curve is slightly to the right of where it is on the diagram. I don't speak German or Math, but still it's worth a try

[@TheMTrider16]

Yep, in this case he is talking about running at 1.5-1.6. (Provided I’m calculating Lamda right) NSCR catalysts need about ~0.7 for proper operation on gasoline engines?

[@greebj]

@@TheMTrider16 Lambda of 1.0 is AFR 14.7. Lambda of 1.1 is AFR of ~16.2. Its the same as AFR with a fudge factor applied so values center around 1.0, instead of 14.7

[@mrmysterious6006]

Germans tune their cars better than most but are still too rich with too much power left on the table

[@danieljensen2626]

Lol at all the comments who completely missed the point. If you're already running rich then running leaner will increase the temperature to a certain point, but then it will start to go back down again once you pass stoichiometric. Your experience of being on the rich side of stoichiometric does not invalidate what Jason is saying about what happens on the other side.

[@DxCBuG]

Thank you - someone who listened and got it, almost lost faith here for a minute :D

[@DukenukemX]

So this lean running hot urban legend comes from people who run boosted engines that need to run rich to cool them down at wide open throttle?

[@danieltabrizian]

This myth origins from 2 stroke dirt bikes where having a lean mixture will really quicky blow a hole in your piston. But 2 strokes have a relativly rich mixture to begin with and a lean mixture happens above stochiometric levels

[@Enthropical_Thunder]

Maybe the myth also comes from the fact that NOx emissions are the highest at a Lambda of around 1.1 (lean mixture) and a lot of people think that high NOx emissions originate from high combustion temperatures.

[@danieljensen2626]

@@DukenukemX As Jason explained, at full throttle most/all engines will run rich, so being slightly leaner will put you closer to stoichiometric. At lower throttle levels though many engines today will run lean because it is more fuel efficient, it just makes less power. As long as you aren't too close to the stoichiometric air to fuel ratio you can have safe temperatures either rich or lean.

[@mr.boostang2064]

My bank account is always running on the lean side and never rich enough 😭

[@chris_the_skip1822]

You must be really cool then

[@Lonnie91a]

I think the running lean/hot originally came from the 2 stroke dirt bikes where the gas and oil mixture lubricated the engine. Running a super lean mix (more power) would cause the engine to seize up from lack of lubrication. In this case lean=hot from lack of lube=engine meltdown.

[@Muppiejuice]

I completely agree with your statement that leaning an engine out actually cools it. In aviation, pilots and engineers call it running an engine "Lean Of Peak" (LOP). Mixture is adjusted manually and the monitoring of both EGT and CHT is vital in the safe running of highly stressed engines to avoid PEAK EGT. This prevents hot spots and eventual detonation under load. The aim is the same as for cars - to get the most MPG without detonating your engine. Typically, LOP flying saves gas but the aircraft slows down.

[@adam145]

In conclusion - if you're ideal then you're not cool

[@987ntn]

Hahaha you could not have said it better!

[@Joe11Blue]

The women say the ideal man is a douche.

[@recommit]

A more accurate description for lean engines running hot is, once you put a lean engine under high work load, the combustion temperatures will increase. Engine knock is usually the audible result of this condition, but starving a working engine of adequate fuel will definitely increase combustion temps.

[@Appletank8]

I don't see how you can burn hot when you have barely any fuel in the engine. Its like saying putting less wood on the campfire would make it burn too hot. If you're trying to climb a hill in super lean mode you'll probably just slow down.

[@hoyay850]

@@Appletank8 because the fuel being injected is around 70-90* being injected into a hot chamber so it could cool it down some? Also, sometimes fuel helps with lubrication too?

[@Appletank8]

@Nbomber Isn't a blowtorch is feeding more fuel into the flame?

[@Appletank8]

@Nbomber yeah, because you need both oxygen and fuel to sustain a fire. but more oxygen when you don’t have any fuel to burn isn’t going to cause more combustion. I can believe the flame generated from a bit of fuel in a very oxygen heavy environment would be pretty dang hot, but it’d also burn out really quickly. Starving the blowtorch of fuel isn’t going to make it suddenly very good at burning things.

[@Appletank8]

@Nbomber Shouldn't there still be a point where you go so lean that temperatures barely go anywhere? An engine with no fuel produces no heat, there's gotta be a line connecting hot engine and dead engine. A single molecule of gas injected into 3L of air shouldn't be burning like the surface of the sun. Sure, the engine also produces so little torque it can barely move, but still.

[@TortureTestMagazine]

Thank you for this video! It looks like people in the comments that disagree are mostly not watching the whole video or are not opening their mind to the fact that there is a big difference between the technical term "lean" and the garage tuner's term "lean."

[@kevinghifari2330]

you mean like garage tuner's lean doesn't refer to the knoking problem?

[@joby602]

@@kevinghifari2330 I think he means the technical term lean indicates running above the stoichiometric ratio, where temperatures will be cooler than at the ratio. What a tuner means by lean is below stoichiometric, but above a ratio of 11-12, where the temperatures will still be rising the leaner you get until you get to above 14.7 (which in practice most current cars will not reach in WOT situations).

[@mark7067]

Agreed. People use "lean" as a relative measure, not by using the stoichiometric measure of ratio. In a way, they are being correct, but they aren't using a technical term.

[@patrickwatkins7572]

here is my video video on perpetual motion engines

[@MrGuano11]

Lean means higher combustion temps; that's why lean mixtures are responsible for creating NOx. Fuel droplets evaporate as they enter the combustion chamber, lowering charge temperature. This is one of the advantages of E85 fuel, as the lower energy density requires increased volume, which in turn lowers charge temps further. The engine running "cool" or "hot" has nothing to do with the mixture. That's a function of the cooling system. Governments, manufacturers, and chemists will all disagree with him. Fail a tail-pipe "sniffer" smog test for high NOx, the answer is always the same. Lean mixture. Either address the lean condition, or fix the EGR system designed to lower cylinder temps and drop the smog.

[@LilBoyHexley]

So essentially we're just dealing with two definitions of what "lean" means. In the big picture (the graph on the left), running lean is running leaner than stoichiometric. With stoich being where the most heat occurs. Whereas in the performance car/tuner scene running lean means running *closer* to stoichiometric, with the baseline being a rich air/fuel ratio. So really what they're saying when they are "running lean", is that they're running lean*er* (but still rich), and not actually lean relative to stoichiometric.

[@webby2275]

Yes this is a silly video with regards to context. When people talk about an engine running rich or lean, they mean relative to it's optimal ratio, likely around the automotive standard of approximately 16:1.

[@terjehansen0101]

@@webby2275 Most people do not think of it that way. Which was the point of this video. And 16:1 is absolutely NOT an "automotive standard".

[@magtechmotorsport]

Hey Jason, This Video make my friend think he can run his car engine at 30:1 afr and still can keep the engine cool and wont harm the engine. He trusted you 100%

[@ryanbernard6550]

Great video as usual! But i feel like you missed an important part of whats going on.. First differentiating what temperatures your talking about. Exhaust gas temps or cylinder wall/piston temps? Cause theres a pretty big delta between the two and they dont follow each other as you go through the afr range due to my second point. The Leidenfrost effect. Basically have you sprinkled water on a hot pan? The water droplets dont immediately stick the the pan and boil off. They dance around for a bit on a very thin layer of insulating steam almost like an air hokey puck. The effect can also be seen with videos of people pour liquid nitrogen on their bare hands without freezing. Well this effect happens in your engines combustion chambers/cylinders with gasoline. The gasoline rapidly vaporized when it comes into contact with the hot cylinder walls creating a protective insulating barrier. This paired with gasoline's tendency to not burn close to surfaces (you mentioned it in one of the hydrogen combustion videos) gives your cylinder walls and extra insulating layer of hot gasses that prevents excessive wall temperatures.. When an engine is leaned out this effect is reduced causing cylinder wall temps to increase to potentially unsafe levels even (increasing chances of knock due to hot spots) tho exhaust gas temp would be roughly the same

[@dezertraider]

Ryan,Drag racers understand your thought and will burn tops of pistons off if ran lean,.So I still am confused at explanation...Happy New years 73s

[@ryanbernard6550]

I do however wonder if this theory might not apply to efficient consumer engine with egr systems vs their racing counter parts..

[@yarbles_]

Um.. You seemed to say running lean won't make your engine hotter but not running rich enough will. Am I confused or are you??

[@yarbles_]

Looking forward to a response video from The Workshop :)

[@dezertraider]

@@ryanbernard6550 IDK,Im Confused..Run my snow blower lean she gets hot?

[@ElAnciano92071]

I am viewing this video from the point of view of a general aviation pilot (in flight sims only!!!). For MOST piston aircraft the mixture is left up to the pilot. Full rich for takeoffs and landings, and since most of them are air cooled, the mixture is set to control Exhaust Gas Temp and Cylinder Head Temp. For climbing, somewhat rich, and for eco-cruise, somewhat lean of peak temp. Pull the mixture control out until just past peak EGT. The engine cruising is making less heat due to the throttle setting being reduced after climbing, so lean of peak doesn't cause overheating of the cylinder head. I think some planes have automated this, and I feel all should! The pilot already has enough to do! This needs to be adjusted constantly as the plane climbs higher. ( The higher you climb, but more you need to pull the control out.) I had my Prius Prime up to 14,??? feet at Pike's Peak, and never had to adjust anything. 15K' is the ceiling for most naturally aspirated piston aircraft, so my Prius outclimed most of them with no adjustments on my part. (Or in any car!). Of course no cars currently sold that I know of are still air cooled as most GA aircraft are. The Cessna 152 starts struggling at 5K' (in my sim, I have never flown any plane IRL). My 182 Turbo craps out at around 22K, but is way happy over 15K. Very necessary flying in Papua and Papau New Guinea, or Chile.

[@aussiebloke609]

When I was a kid (many moons ago now), I was taught that "lean" had nothing to do with stoich...it simply meant leaner than the engine wanted. So if the usual a/f ratio was around 12 or 13:1...that was "normal" for that engine. Any more air was considered lean (i.e., more lean than the engine wanted.) Any more fuel was considered rich. But it was all considered from the point of what the engine actually wanted - not the 14.7:1 stoich ratio that didn't really apply to engines in the real world.

[@ZioStalin]

Same here!

[@DaveOh643]

Part and parcel of this video has to be a discussion about laminar flame speed. That decribes why a lean engine, although having lower *peak* combustion temperature, can have higher *mean* temps.

[@PackPractical]

Been doing this for years in aviation to keep the engine healthy, cool, and get better ( less) fuel flow. On Cessna 172s you can see upwards of 4gph savings while running lean of peak, and that is pretty significant.

[@elderatthegates6628]

Can I play with the fuel system and lean out my engine, or will the PCM just overide it? I'm trying this on my old Ford truck. I've seen this lean thing in aviation for years. I know way too lean and pistons will get hot and knock occurs. I'll post a vid if I can lower the mpg on my 95 truck.

[@car_ventures]

@@elderatthegates6628 did you ever get around to trying this? If not the way to go is using an exhaust temp gauge. You lean out till you see peak exhaust temp, and anything leaner is where temps fall, and gets it into lean of peak (temp) state. The engine is mostly running on air. Loses about 10% power but uses about 50% less fuel.

[@TomSmith-cv8hk]

You're talking combustion temperature near TDC. Lean burn without added ignition advance fires off too late, heats the cylinder walls and exhaust valves, shows up as water temp (in marginal cooling systems), torched valves and glowing exhaust manifolds.

[@bruceparr1678]

An old friend of mine who engineered on super constellations described adjusting the mixture on the (I think) R3350 turbo compound engines. It was something, like lean out the mixture until the manifold temps started to drop then richen it up a bit to get the lowest fuel burn.

[@owenflynn9806]

When I saw a lean engine, I thought about an engine running on lean. The drink. Whoops

[@ottocevrimi]

Actually, people say that running lean causes increasing the EGT. Because, lean combustion is slower than the rich combustion. That's why combustion speed is decreasing and combustion shifts towards to BDC. Exhaust valves are opening before BDC. Then you are exhausting the gas that just completely burned or already burning.

[@Fizzer99]

Yes this is also why your headers turn red hot if you lean out your a/f mix.

[@Cragified]

@@B10401 You can only advance timing so much until you run into detonation issues because you are igniting the charge while it is still getting squeezed for a while. You also loose mechanical advantage. The leverage the rod has on the crank is the lowest at TDC. TDI's exploit increasing mechanical advantage by putting in the fuel in pulses so that the fuel burning happens after TDC as well as mechanical advantage is increasing. Also engines don't run at an ideal. O2 sensor feedback is switching based. Your engine is actually running a bit lean and then a bit fat compared to the ideal over and over again as the O2/Fuel air sensor switches back and forth. You'd need a sensor on each exhaust port and individual exhausts as well as TDI to even try to run at a constant ideal mixture for the engine design. But in summation the problem is EE here is saying ideal is stoichiometric ideal. When in reality ideal is the ideal ratio for the engine design. When someone says leaned out and got too hot they aren't saying it went over 14.7 A/F they are saying it leaned out compared to the ideal design ratio which can be anywhere from 11-14 for the engine.

[@apexseal2811]

​@@B10401 Yes, I am thinking mostly the same. If an engine is running Lean, meaning there is a greater part of air mass for each amount of fuel mass, beyond the stoichiometric ratio, the mixture should (from what I can suppose) burn faster, as it would be "easier" for each fuel molecule to bond with an O2 molecule because these are in excess. Still I do think poor mixing is the main reason why an engine may run hotter, considering not every fuel molecule can bond with its corresponding O2 molecule properly, resulting in greater fuel consumption and a reduced effective power (power produced for a specific volume of fuel burnt).

[@chaser27]

Combustion velocity will decrease on both sides of stoich as well

[@ottocevrimi]

@chaser27 Combustion velocity is maximum at slightly rich mixture. It's the same nearly all kinds of fuel.

[@MuffinRacing]

Seems like a very nitpicky conclusion. Running lean increases cylinder and exhaust temperatures, which the graph on the right shows, even though the "technical" answer is that the flame itself burns cooler both lean and rich. Running lean runs to knocking which causes pitting and can damage the catalytic converter from hot exhaust gasses, so saying "running lean causes higher temperatures" is a valid thing to say.

[@JarredRandom]

When I was a kid someone told me lean meant not enough O2 and rich vise versa. Messed me up for years.

[@johnnieburkhalter5265]

Perfect time to talk about this when its cold outside!

[@ThePentosin]

... there is no kind of atmosphere

[@maxspinks2181]

I want gluten free engines please

[@ytechnology]

They already exist. Free range too. Waiting for organic.

[@BurittoSandwich]

Some quality grass fed inline 6s.

[@ytechnology]

@@Pooneil1984 Haha. I read and watch too much science fiction. I was thinking of "living" engines made of bone, tissue, muscle, and blood vessels.

[@ariesmight4141]

My automobile engine requires unleaded glutin free gasoline. Preferably in 100 octane.

[@fieldsofomagh]

Need low salt, sugar free and less saturated fat in my gasoline V12 engine.

[@mundoracer]

Great video. People who tune their own engines for power/performance will typically never run leaner than 14.7:1 for partial throttle situations. 14.7 is looked at as the max lean you'd ever want to go, if you even go that high. So, relative to say 10.5:1, all the way to the now established maximum of 14.7:1.... The leaner you go, the hotter u get.

[@jf4872]

Easier way to explain it....Load = Throttle position When on the progression circuit get above the 14-15 zone (Hottest EGTs) when below it (Load/WOT) 12-13. Having excessive timing combined with a lean mix when under moderate-heavy load (WOT) is what causes detonation. Running an AFR of 16:0 - 17:0 at light/part throttle cruise is cooler running than at 12:0 - 13:0.

[@wolu9456]

explain why a car can run at4000rpms at 75MPH can changing that to be 3500rpm's at75mph by freeing a little breathing restriction. explain this. anyone.

[@6226superhurricane]

@@wolu9456 impossible without changing the final drive ratio or less transmission slip.

[@6226superhurricane]

or tyre diameter/pressure

[@Vlaadik]

Very good video, but I have some remarks. I understand, that you explain material not for engineers, but here you told some misconceptions. 1. Phase change has not very big influence on temperature. Theres no phase change in gaseous fuel powered cars, but temperature still decreases with the drop of AFR. Much bigger influence has partial burn of the fuel. For example oxidizing carbon to its monoxide gives only 1/3 of energy that could be released when carbon oxidized to CO2. Same thing is about partialy unburnt hydrocarbons. 2. Of course even after a rich A/F mixture is burned there is still some oxygen in the exhaust. But that's not the main reason why richer mixture gives more power then stoichiometric. The main reasons are flame velosity and ability to use more advanced ignition. 3. Final and main misconception is about the main topic of this video. Lean mixture produces less temperature that is a fact, nevertheless lean mixture can be hotter then rich and even stoichiometric. Lean mixture flame velocity is much lower. Combustion may still be in process during the exhaust stroke or even during valves overlap (this usualy causes explosions in the intake manifold). When you are running to lean, especially if you are not changing ignition, you are also loosing power. To compensate it, you start to push the throttle, engine gets higher lean mix flow. As flame speed is low more heat energy is transfered to the pistons, head, valves and cylinder walls causing engine overheat instead of produsing usefull power. And ofcourse combustion temperature itself will be lower. So in constant power scenario with wrong ignition, lean mixture can become hotter, then stoichiometric. If you just make fuel flow lower with constant airflow, temperature will definitely go down. It's just like diesel engine.

[@loverboy8476]

Phase change is nice and easy concept to understand, too bad that’s not the case. Gasoline experiences its fastest laminar burning velocity at roughly Lambda 0.85, correct? Any richer or leaner and the velocity decreases. I’m not sure but I guess you mean that faster the flame front, the better for power but how? Common sense would say that you have to use less timing, which typically is generalized to be bad for torque. I don’t understand how partially oxidized fuel decrease temperature, because you have to partially oxidize more HC to get the same energy than fully oxidizing less HC-molecules? Or is there some sort sweet spot? Could you please elaborate? It would be much appreciated!

[@stefansmiljkovik9841]

Hey i have a fun topic. Engine power is greater with colder air. What are the rates for atmospheric and forced induction horsepower bumps summer vs winter. It would make a fun video!

[@yinzer_412_]

Power is not, in all cases, greater with colder air. Humidity will combat the colder density. That is why density/ altitude is used to calculate actual horse power. I.E. you will make less horsepower in Colorado at 30° than in Maryland at 60°. Because of altitude and air density.

[@MrHeHim]

@@yinzer_412_ Think he was saying something more like Maryland at 60° vs Maryland at 30° and the effects on both N/A and forced induction. Furthermore, i would also like to see N/A vs turbo vs supercharger. Then throw in humidity to talk about molecular weight while we're at it.

[@yinzer_412_]

In all cases N/A will have bigger gains over power adders when the D/A is lower. This would make a good video for everyone to see the difference.

[@architecteye6089]

65° at about 23% humidity is pretty much the perfect condition for a dyno test. Yes, air is more dense when colder but that requires more fuel. Fuel that has to be more reactive to ignite the colder air. This typically requires a lower octane. Thats why E85 guys always have somewhere between E40 and E60 in the winter time otherwise the car may misfire. In a nut shell the extra fuel needed for ignition will actually take up more volume in the combustion chamber. It has to be more reactive (lower octane) and there has to be more of it. Not good for HP because its like the car is running rich just to operate.

[@REDVETTExxx]

I have a 2011 CTS-V and live in hot ass GA. I know it feels like alot of power loss when its 90 and above vs 50 during winter.

[@Lucas_andos]

I’m only a kid interested in cars and whatever that has an engine. Sometimes your videos make mot much sense to me but I still watch it and look at your fantastic drawings. Good work Jason :)

[@mikiofunamorijr.1374]

Based on my experience, running lean makes engine hot faster.

[@aruseb]

Lean w.r.t. stoichiometry, or lean w.r.t. to your normally enriched operating point? The confusion happens when you use 'rich' and 'lean' relatively. 5:26

[@zumabbar]

@@aruseb yeah, not to mention the dude said it anecdotally

[@cwt5654]

Lean mixtures are likely to have a slower flame front therefore, without advancing the ignition timing, causes more of the combustion to take place after the peak compression density of the working fluid reducing the heat absorption (which then dissipates into the metallic components of the engine. Think of the difference between a cloudy (dense) and a sunny day. So yes, lean mixtures do not necessarily run hotter but combustion has to completed within the optimal compression zone.

[@exparrot9074]

This is one of the big advantages of port and especially direct injection. With older CPFI and Carbureted setups you could have uneven A/F ratios in each cylinder causing poor combustion. The other item to consider is that in many cases LOP operation does not provide adequate cooling to the cylinder head and can cause damage.

[@somefuckstolemynick]

Can you explain why a bit of why LOP operation doesn't provide adequate cooling to the cylinder head? Air isn't dense enough to transfer a significant amount of heat from it?

[@exparrot9074]

@@somefuckstolemynick should have specified that it is most applicable to air cooled aircraft engines. Vaporization of fuel is a big heat sink and pulls thermal energy out of the head.

[@somefuckstolemynick]

@@exparrot9074 Great, my thinking wasn't all that off at least, always forget about that heat of vaporization. Thank you!

[@eichenbrain6170]

It may not make the engine hot, but it makes the exhaust manifold glow red.

[@diamendking]

It will toast the engine oil prematurely. And burn the engine if it's not closely dial in .

[@An.Individual]

Basis of his argument is that any mixture < 14.7 : 1 is rich People say your engine is hot because it is too lean, which does not mean > 14.7 : 1 e.g. 14:1 is too lean

[@R3lay0]

It's just how language works.

[@stevenjohnson1692]

Exactly, I see a lot of people on here not understanding that. Lol next video there's going to be people wanting EE to pay for their blown engines...

[@ARentz07]

Exactly. "Lean" is not the same as "too lean for what you are trying to do with it".

[@greebj]

TL;DR of video: "lean relative to ideal stoichiometric combustion" is different to "lean relative to ideal AFR for maximum power which can still be technically rich of 14.7:1"

[@jf4872]

14 - 15 is the deathzone. It has the hottest EGT's. Combine that when under load.....BOOM!

[@UncleDon226]

I think the thing he overlooked was having a lean mixture means there is more oxygen in the cylinder which produces a faster and hotter flame-front, thus, overheating. Engineers have spent over a century studying this and I tend to believe them

[@Alobster1]

Only a hotter flame front if there is fuel to use with that oxygen. If there is extra oxygen then needed for perfect combustion that won't make the flame front hotter. You would just have unused oxygen.

[@UncleDon226]

@@Alobster1 That's not how it works. Oxygen is an accelerant- the flame absolutely burns hotter and faster when a higher concentration of oxygen is present.

[@Alobster1]

@@UncleDon226 Sure maybe faster but the overall amount of heat from the fuel burning is going to be the same.

[@RohanSanjith]

Its not about oxygen, fuel acts as a cooling agent, so when ran lean, there is no extra fuel in the combustion chamber, also coolant circulates around and top of the engine, not inside the engine's combustion chamber to cool down, same for the oil, it's lubricates inside the piston rings area, so when ran rich, there is extra fuel available which takes the heat away from the engine 😀

[@Alobster1]

@@UncleDon226 You said it yourself. "faster and hotter flame front" more heat over less time doesn't mean more overall heat.

[@recoilrob324]

Knock and maximum power aside, mixture affects the burn speed where maximum power normally means the charge is burning the fastest and hottest. As you lean from max power mixture the burn speed slows down and this is what causes the cylinder head and exhaust temperatures to increase....the charge is still burning going out the exhaust. To combat this you need to increase the ignition timing to get the charge at that leaner mixture burned by the time the engine is about 20 ATDC and depending on the strength of mixture this can take a whole lot of timing. It's not unusual to run 45+ degrees of lead at lean cruise on a motor that makes best power in the low to mid 30's. If you lean without increasing the timing for sure it's going to run hotter even though the combustion temperature peak is much less. Another thing worth remembering is that burning the fuel by combining with the oxygen in the chamber only makes heat and very little gas expansion.....the pressure is created by the heat expanding the nitrogen which makes up 78% of the charge. This has been demonstrated by people thinking they'll increase power by adding pure O2 and corresponding fuel but it only increased power a little bit before they melted the pistons. You need the expansion medium to make power and lean burning engines have lots of it in the chamber and can make a surprisingly high amount of power on a tiny bit of fuel and this gives you great fuel economy....just have to be careful to stay away from detonation.

[@loverboy8476]

Great explanation!

[@lyfandeth]

Theory sounds great. Now please explain why in flight training we are taught AND SHOWN that we can try to conserve fuel in flight by leaning out the mixture--until the cylinder head temp gauge starts to show it is too hot. You're missing something here, the flight instructors and the gauges don't fib.

[@scottyh72]

Because you are leaning out from a rich condition to closer to ideal. So the temps go up.

[@kirkaugustin2232]

@@scottyh72 , totally wrong. When the combustion temperatures maximize, then the least amount of heat is conducted to the engine because the explosion is MUCH faster, more efficient, more powerful, and shorter duration. An ideal maximum explosion is far to fast to be able to heat up the engine much at all. It is a weak and slow combustion that conducts the maximum heat to the engine. And in fact, excess oxygen is extremely corrosive at under those conditions, and you will melt pistons and valves. The way to make the engine run coolest and last longest is by achieving the highest possible temperatures, which then are exploding so efficiently that there is no time for hardly any heat to be conducted to the engine.

[@TwistedKestrel]

@@scottyh72 90% of this is a semantics problem - Jason was using rich = richer than stoichiometric and lean = leaner than stoichiometric, but as he states, stoichiometry is not really a target for internal combustion engines. The alternate definition that causes trouble is rich = richer than best power and lean = leaner than best power

[@xai1603]

School them Lyfan. The video and title is just misleading. Needs to be more specific with the level of lean he is talking about and not just point blank lean.

[@BigUriel]

@@kirkaugustin2232 He's not totally wrong he's absolutely spot on, you still misunderstand what he said, the video and how this whole temperature variation with AFR works. Air planes run rich, because a rich engine is less likely to stall. When cruising a pilot can increase air/fuel ratio to improve efficiency, and when doing so is taking the engine from rich to stoichiometric which is where temperature peaks. Air plane engines (piston ones anyway) never run lean, they run slightly rich to very rich.

[@AJ-ri5ee]

On some simple prop airplanes they have a mixture lever to lean or rich the fuel to air mixture, because the higher you go the less air there is/ less fuel you need. Richening the mix is also used to help cool the engine-- I was once flying on a hot day, left the fuel full rich, barely maintained max allowable temp and saved the day. The end

[@h.mushmann2351]

"Hot = lean" comes from 2 stroke engine management used in race environments where the fuel is mixed with the engine oil. The fuel/oil charge passes through the crankcase and lubricates the cylinder. In 2 stroke racing, the carburetor needs to be jetted for the altitude which varies at each race track. More lean means less lubrication = more hot.

[@Team-fabulous]

Agreed... I raced TZ350s back in the day..... They didn't like it lean..... Full of your hand on the clutch..

[@sween187]

Not even in racing all 2 strokes, eg your chainsaw, strimmer etc. Less oil in the engine means more friction, more friction equals more heat, 👍

[@barje.waffles5461]

This is where I thought the idea came from too. As I have melted a piston before when I had a brain fart and did not mix my oil right. The thing stuck a ring and destroyed my whole top end.

[@RandoTark]

Yeah, I was just now thinking about this whole topic in the context of nitro RC engines. They are 2 stroke ... and definitely do get warmer when u lean them out due to lack of lubrication.

[@YAMR1M]

Even a two stroke with an auto lube system will run hot if you lean them off not just race bikes....

[@CompproB237]

The "Lean runs hot, rich runs cold" comes from 2-stroke engines with oil mixed in the fuel. Less fuel -> Less lubrication -> Hotter cylinder, and consequently engine, temperatures but also better performance. More fuel -> More lubrication -> Cooler cylinder, and engine, temperatures but worse performance. Finding the balance between these two when "jetting" the engine is what can win or lose a race... or cost you a new piston+sleeve and possibly cause a crash when the piston "sticks" (heat-welds) to the sleeve (cylinder wall). This also applies to Rotary engines too since they work in a similar fashion to two-strokes where oil is mixed in with the fuel and/or directly injected into the combustion chamber. Four stroke engines don't have this problem and operate exactly as you've explained in the video.

[@samslichter3566]

Instructions too complicated, melted the #7 piston

[@bbarber1066]

That just means you have too many pistons. Anything over 6 is too much.

[@jradish]

@@bbarber1066 said no one ever

[@staalcyclesecurities1423]

@@jradish except honda guys

[@jblob5764]

@@bbarber1066 last time i checked more pistons almost always makes more power at equal displacement

[@bbarber1066]

@@jblob5764 Youre right. More power, and more problems.

[@staalcyclesecurities1423]

I think the video started out good good but u started stumble at around 6 min. in. Matt @ the workshop does a great job elaborating on the topic.

[@snap-off5383]

The Fuji triple 750 2 stroke in the 1990s polaris watercraft all had a design flaw: the 3 carburetors for each cylinder were hooked up in serial from a single-output fuel pump. After one season on pump gas, an owner would park the craft for the winter, start it up the next summer, take off skiing and within 5 or so minutes break down having burned a hole in the piston on the last cylinder, due to ethanol gunk clogging the previous two carburetors and starving the 3rd for fuel. Less fuel means less cooling effect, which is what people are referring to when they say "lean runs hot". it simply means "if you lessen the fuel, you'll create a hotter cylinder" not "if you're technically lean compared to stoichiometric, you're hotter than rich compared to stoichiometric" That's a meaningless statement anyway, because who cares? Perfectly stated, would probably be, "you're running rich obviously, but if you reduce that richness in the direction of leaner, you'll move more toward ideal ratios, and increase cylinder temps, and can damage your equipment, even if you were still technically "rich". Edit: the fix for the fujis, is to buy them cheap with burned pistons, rebuild the engine, and replace the single output fuel pump with a 3 output, and plug all carb outputs.

[@Azalen24]

So I want explain a few things that you didn't get right, because Engines do run hot when Lean and I will explain why. Source for all the Information below: I am a Mechanic from Germany and I also have Books and Charts from School from when I was still learning/training to be a Mechanic. I might sound nitpicky here, just dont want you creating more Myths, which you will have to bust in the Future :) 1:50 NOx Emissions peak at about Lambda 1.05 to 1.1 which is about 15.4/1 to 16.3/1 in Air Fuel Ratio in Engines that run a homogeneous Mixture. If you run a lot more lean that that(approaching Lambda 1.2), you will already see some misfires happening. Which means the Data isn't meaningful at that point because you don't have regular Combustion anymore (homogeneous Mixture). So the Reason that you get less NOx is because of bad Combustion. When you still have ''normal'' Combustion NOx will always rise when lean. You can see that because at the same Points that NOx start to drop, Carbon Emissions start to rise(because of misfires). 3:50 Its not about excess Fuel. All Fuel that to evaporates brings down the Temperature. 4:40 No its not. If it were the case, there would be no need for EGR at all. Would be redundant. The Reason why you use EGR is because you want to get rid of excess Oxygen(specifically Oxygen, not just Air), because if you have excess Oxygen it will ''take part'' in Combustion which is one of the two reasons why its hot when lean(the other reason being that there is less Fuel evaporating relative to the amount of Air, evaporating Fuel cools the Air). Its like starving a fire of oxygen or blowing on it. If you starve it Temperature drops, if you blow on it temperature rises which is the same thing if you have excess Oxygen in the Combustion Chamber. So if you reroute Exhaust Gases which ideally have no Oxygen left in them, its so that the Oxygen/Fuel Ratio is closer to a 14.7/1 like Air Fuel mixture, meaning no excess Oxygen(compared to the amount of Fuel) which just burns and also having no excess Oxygen which can bond to Nitrogen, which would be NOx. For NOx to be created you the need enough Heat and enough Pressure- So its very important to always remember that a very large part of the Temperature in the Combustion Chamber is just how much Fuel evaporated compared to the amount of Air. Evaporation cools --> 6:25 also 7:05. So the ''missing'' Fuel, which isnt evaporating because it isnt there when running Lean, is one Reason why Temperatures rise. The next thing is Diesel Engines. It's a perfect Example of how Lean causes a lot of NOx Emissions. Diesel Engines run above Lambda 1.3 to more than Lambda 10 in some cases. Extremely Lean. And then there are Gasoline/Petrol Engines that a heterogeneous Mixture in the Combustion Chamber. I didnt find the Translation to the Technical Term, sorry. But many german Manufacturers build these Engines around 2003 to 2008. An Example would be the 530i E60 BMW Engine and also many of the TSI Engines from VW from around that time. These Engines also produced a lot more NOx Emissions because of running a very Lean Mixture overall. But it was still possible to ignite the Mixture, because there was a rich Mixture just around the Spark Plug --> heterogeneous Mixture. What you are saying at the end about tuning the Engine makes sense and its true that Lambda 0.7 will be cooler than 0.9, but its still incorrect that a lean running Engine will also be cooler, as I explained above. Also I'm sure that I explained a lot of Stuff that you already knew, but I felt it was necessary for understanding the rest. Also please excuse my English, Grammar and Punctuation and please dont mistake me for a hater or something. I really like your Videos but this one bothered me so I made this Post. Also if I didn't explain clearly enough, say something and I will try again :)

[@BoostedFilms]

Did you watch the full video before you wrote your comment? No? Watch the full video, then comment.

[@EngineeringExplained]

Boosted Films bless you! 🙏🙏 Haha

[@fancyyahoo]

But I'll forget whatever garbage I have to comment after I finish the video!

[@tangles01]

@@fancyyahoo Watched it all saw no justification for unburned oxygen cooling cylinder temps.

[@Appletank8]

@@tangles01 Having much less fuel means there's less energy to heat up the cylinder in the first place.

[@michaelharrison1093]

Jason, Another great video and spot on correct with all your facts (if we ignore the EGR acronym mistake that you corrected in production). From reading the comments below it still seems that there are many people who struggle to understand the difference between "less rich" and lean.

[@t-train6534]

Every time I click on one of your videos I learn something new

[@EngineeringExplained]

Happy to hear it, thanks for watching!

[@wolu9456]

no citations= dont liston.

[@mmdirtyworkz]

too bad you have learned a load of bollocks that have nothing to do with the real world lol

[@karamalqussiri6533]

@@EngineeringExplained I have a question for you, why or why not to just use a compressed o2 tank connected to intake, (kind of a similar idea to nos) I know that more o2 without fuel is useless, but doesn't the o2 sensor sense that it is running too lean and therefore inject more fuel to preserve air fuel mixture? (Of course this may be not that safe or reliable, but is it a possible thing.) Thank tou

[@DynamixsEd]

Well I have to respectfully disagree with the significant points... running an engine lean ie fuel equivalence ratios less than 1 does cause an engine to run hot. The flame temperatures are reduced however a lean mixture burns more slowly increasing time available for heat transfer ie the polytropic index is lower for lean burn scenarios. That's why it's advantageous under full load scenarios to burn with an FEq ratio higher than 1 to speed up flame front propagation up to the knock limit.

[@ricardocalles140]

In a lean burn engine scenario, what is the advantage of running a 15:1 VS let's say a 17:1 ratio. I've even heard of some lean burn engines running a 20:1 ratio. It seems that adding any more air above and beyond 14.7:1 wouldn't provide any additional combustion benefits such as helping to ignite all available fuel. If anything, it would make the mixture less dense and make it more difficult to ignite since the fuel molecules are spaced further apart.

[@PantaBell]

Yes running lean makes the mixture more difficult to ignite. Main advantatge of running lean is fuel consumption.

[@lesliedsouza4077]

Jason: Your temp graphs are ok - BUT seems you missed a main point. At stoic, max heat is converted to mech output (Richer is engine preferred, under acceleration under load, from lower rpm) Leaner than stoic, at any load, would cause SLOWER combustion. Then: even tho cyl temp reduces, less heat is converted to mech work. Instead the heat is wasted - Thus heating the piston & exh valve, later in the cycle. The coolant absorbs some of this heat, but piston & exh valve failure result under prolonged lean mix. Yes, EGR reduces temp & NOX, but not the same as leaning down the mix which means, increased oxygen. This presentation of yours, did seem a bit confused? :)

[@louisluigi]

I think it comes from the aviation community, running rich (of peak) and running lean (of peak). In somewhat older planes you usually have manual mixture control, and in even older planes with engines that have carburators, you could not lean the engine to much due to uneven fuel distribution in different cilinders, which could cause overheating of certain cilinderheads. In fuel injected engines, there is no uneven fuel distribution into the cilinders, so running lean of peak in fuel injected engines saves gas, carbon build-up and reduces emissions

[@chitlitlah]

That all makes sense. However, my friend and I were desperately searching for a gas station because his gauge was on E. (This was an old carbureted Toyota Corolla by the way, no forced induction and probably made about 100 hp.) When we were finally across the street from a station and waiting for a street light to turn green, he noticed his temperature gauge starting to rise and mentioned it. I told him the carburetor bowl is probably low and he has a few seconds left before the car dies. Luckily we didn't have to wait long and made it to the pump, but now I'm conflicted between this logical explanation and my circumstancial evidence to the contrary.

[@mklaver31]

Maybe the engine was designed to run a bit rich to keep temperatures down and it got hot because it reached the “ideal” A/F ratio explained in the vid? Just a speculation of mine, I am not an expert by any means. Btw, I’m a bit late, it’s been 3 years 😅

[@morrisl7]

or it always heated slightly at a stop because it wasnt moving thus less air flow to cool.

[@chitlitlah]

@@morrisl7 I would think he would've noticed it before then, but he would've been paying extra attention to the gauges at that moment, so it's not out of the question.

[@FT099]

The technical term "lean" is different than what most people refer to as "lean". That's where the difference comes. Technical or "true lean" comes past 14.7, as you mentioned, and that's not what most people in the tuning community are talking about. They are talking about producing max power. Great video.

[@aajpeter]

"richer" and "leaner" are relative descriptions that work and are accurate terminology at any a:f ratio, even if rich is anything below stoichiometric 14.7:1 and lean is anything above. That is shortened to rich/lean by people with sufficient knowledge and context, which then confuses people without.

[@nh112]

Great video Jason. Please can you do a diesel specific version and the challenges with balancing out efficiency, NOx and soot? Is it better to accelerate a diesel in a lower gear rather than a higher gear from a soot perspective (vs fuel efficiency perspective)? Thanks!

[@darkraft100]

Yes!!! Please

[@H1tman47]

I can think of at least one mechanism through which, leaning the mixture will increase the *exhaust* temperature: My understanding is that leaning out the mixture slows down combustion. The slower the heat is released into the combustion chamber, the less time there is for this heat to be extracted as a mechanical work by the piston. An extreme version of this effect is turbo antilag by ignition retardation - if you don't extract the energy, the heat stays in the gas. Now the question of how big this effect is depends on how much is combustion slowed down by a lean mixture in the real world. I don't have any numeric data on this but I remember that leaning out the idle screw on my wr450 would cause the exhaust header to glow just when idling. It would be pretty cool to see if you could cover combustion speed and how it changes with the AF ratio. Cheers and thanks for all your awesome content!

[@DeltaSierra426]

Great vid, thanks Jason! It also needs to be said that that idea really came about during the era of carbureted engines as atomization didn't occur as well as EFI and DI and thus more fuel is needed to achieve peak power and keep cylinder temps down *compared to* leaner mixtures.

[@dpowderhound6598]

This comment is what I was looking for. Peak power at a really rich mixture didn't make any sense to me, but insufficient atomization (esp. for carbureted engines) explains it.

[@pojhe]

I'm glad to hear this. Because my motorbike run lean that I notice from the colour of spark plug. My spark plug is clean white that indicate lean mixture.

[@askpatrick]

Do I have to worry about this with my Toyota Celica?

[@alexandert696]

Its a toyota. Feed it fish once a month and you ll be fine

[@EngineeringExplained]

Only if you have 50 years experience. ;)

[@Mr19853]

No your 32 years old Celica is immune to that!

[@issanesheiwat1396]

Engineering Explained 51 years lol

[@Butterffinger5678]

Not if it's a 1994. Tehe.

[@ra.dawkins1441]

Thank you,i have been telling them for year that running lean is way better, thanks for stoicmetric explaining.

[@hughjass4838]

I've seen carbureted snowmobile engines melt the pistons from running lean. There was an air leak somewhere where it sucked in extra air and subsequently melted the pistons. I know of a couple engines that have had this happen. So how does that fit into what he's saying?

[@brettpayne8292]

Because lean it self does not melt pistons, detonation does. Detonation leads to higher temps, detonation leads to lifting ring lands which causes piston failure. I have ran plenty of nitrous engines lean and never hurt any any of them, but when I went rich, by my quarter turn valve failing on the nitrous valve causing an extremely rich mixture and detonation, I experienced piston failure. Detonation whether rich or lean causes piston failure.

[@smallengineguys]

We had these problems when they added ethanol. We thought it leaned out the engines but it turned out that it caused detonation and that is what burnt the pistons up. Switching to ethanol free stopped that.

[@loverboy8476]

@@brettpayne8292 What caused the detonation in this case?

[@owninggezer]

Thank you for the clear explanation. I really needed this as it was a shining light amongst a sea of confusing posts on forums.

[@kentvandervelden]

Very interesting, I love these videos. With planes I was taught to initially lean until engine just starts to run rough, then enrich the mixture slightly, and later use exhaust temperature to fine tune the mixture if so inclined, favoring a slightly rich mixture. These were all basic older Lycoming leaded gas engines.

[@KaDaJxClonE]

Same. Full rich on take off, climb, and landing. Leaning is for fuel conservation during cruise. Now computers handle it in both aircraft and automobiles. One of the Mooney I flew had a weird quirk that it made *more* power lean of peak than it did full rich. So more fuel =\= more power.

[@roycereynolds1514]

Interesting

[@marsgal42]

My plane has an engine monitor so I can do the same, lean by ear (power or economy) or lean for peak EGT, or however many degrees I want rich of peak. It's an old-school O-320 and lean of peak ain't gonna happen. :-)

[@davidbrayshaw3529]

@@KaDaJxClonE , I'm far from being an expert but I have worked as a "hanger rat" (A.M.E.) under a very competent L.A.M.E.. He described 14.7 to 1 mixtures being ideal at average sea level air pressure. As altitude is increased oxygen levels reduce and consequently air fuel ratios need to be varied to account for the change in available oxygen, not air. This gives the impression of "leaning out" as a fuel conservation measure when in fact the engine, in the context of oxygen supply, is not running lean at all but simply running efficiently. He was a great advocate of engine management systems. When I asked him if it is good Idea to run an engine a "little bit rich or a little bit lean" his answer was that "an engine should be run at the optimum mixture setting as specified by the manufacturer and only engine management hardware will give you that information!". No, he wasn't German. The quirk in the one that you were operating is interesting. I'm not a pilot and we don't have many Mooney's in Australia but they look like a pretty hot machine. Were they fun to fly?

[@emadnad33]

_ VesBraun what I have heard is that an engine running slightly lean will make more power to an extent, because the engine becomes hotter creating more power, hen it will run rich. Bearing in mind that the engine will cool down if it runs too lean, as shown in video.

[@akoponen]

To always get the maximum power out of the quantity of fuel used, the Augmented Compression Engine uses water injection (recycled from condensed exhaust) and EGR (more EGR and less water as power is decreased) to keep the combustion temperature low enough to avoid NOx. Since the throttle is determined by the EGR the stoichiometric mixture can be far from the combustion chamber intake, thus allowing time for full vaporization of the fuel.

[@gsenna472]

nonsens Jason.. back in the books!!! you obviously never wrenched on a 2-stroke!

[@davidphillips3953]

I am a DIY garage hack always trying to milk more MPG out of my vehicles and have found some stuff that works pretty well like increasing compression ratio, better atomization, tight quench hotter engine and IAT, cutting off cats to increase exhaust flow and so they don't melt down inside... but I also know these things can't always be done on production cars because of emissions regulations that they need to meet, what kind of gains in MPG do you think could be had on a typical ICE if they never had to meet any emissions regulations?

[@ricardocalles140]

Nonsense, in a properly designed system, maximum engine efficiency produces maximum MPG with the fewest emissions.

[@TM-lw8wn]

ok...so...not running lean, but "leaner" than you should.

[@DoRC]

Most tuners dont consider 14,7:1 the crossover from "rich" to "lean". Its just a frame of reference thing.

[@KDiGee]

... except in the real world it does run hot. Or at least in carbureted motorcycles, cause i actually did this during the tuning process. Also running lean helps in the midrange; than flooding an engine with gas. Again, just based on what ive experienced on a carbureted motorcycle. Surely there are numerous factors that affect the outcome, not at all discrediting the science behind the lean-rich concepts in this vid. 💖

[@UncleDon226]

This. On paper what he says makes sense. But, well, just google "Piston too lean" and behold! Melted pistons everywhere. In the real world, lean will bless the pistons and make them holy

[@Appletank8]

@@UncleDon226 A 2-stroke engine needs oil, running less may result in less oil. If you have no fuel in a spinning engine, its not going to magically heat up, assuming its cooling systems are still working properly.

[@UncleDon226]

@@Appletank8 Right, and diesel engine run incredibly lean- but I think this video is covering traditional four-stroke gas engines...

[@Motor_Cackle]

Flame velocity in a lean mixture is slower than in a stoichiometric or slightly rich mixture. Under the right conditions, that can result in the exhaust valve starting to open before combustion is completely finished. That causes an excessively hot exhaust valve (source of pre-ignition), and very high exhaust manifold/header temperatures (glowing cherry red hot).

[@apexseal2811]

Thank you for the information, really helped clear things out. I knew and understood engines run rich A/F ratios (or inject more fuel into the combustion chamber) to reduce in-cylinder temperatures due to the Latent Heat of Vaporisation, where the liquid fuel absorbs heat when transforming into gaseous form, but got confused by thinking exactly the opposite would happen with a LEAN A/F ratio: "if running rich A/F ratios helps cool down the cylinder temperatures, most sure running lean will result in increased cylinder temperatures", although I couldn't find out a physical or chemical fundament to justify the second part of that statement. Of course many times in reality things don't work out as what the theory sustains due to various reasons; for example, reducing the ignition timing to avoid knock or as in this case, run a rich A/F ratio to have the engine produce its peak power, although the stoichiometric ratio suggest neither lean nor rich, but in reality not all the O2 in the cylinder is effectively burnt at a 14.7:1 A/F ratio for other reasons. Sure you can adjust valve timing or use a variable geometry turbocharger and else to pull more air into the cylinder, but in less "modern" engines with simpler technologies it is easier to vary the amount of fuel injected in order to have all the O2 in the combustion chamber burnt and get peak power from the engine.

[@johndoyle4723]

Thanks, I never believed running lean = running hot, you did explain it very well, but you are fighting the tide with entrenched views. I spent much time working on SNCR( the N is for non),for NOX reduction using NH3, perhaps you could do a video on catalytic reduction using Adblue, or similar additives. Thanks for the informative video.

[@omegarugal9283]

gasoline must be already vapor in order to burn, no matter how small are gasoline droplets, they don´t burn... guess who benefits from engines running rich?

[@archygrey9093]

The droplets are usually vaporised by the time the spark is set off, if not then you will end up with incomplete combustion and black exhaust smoke. smaller droplets are preferred as they vaporise quicker.

[@Joe11Blue]

The vaporization theory does not really effect much. The compression stroke vaporizes the fuel.

[@GuilhermeGomes2]

gas station

[@carterlee8344]

Pressure and Mass Fraction vs. Rotation. Otherwise known as the “sweet spot”. Ignition timing for power when lean means more advance in the ignition timing. Why? Because, leaner mixtures burn much slower. Therefore, the sweet spot just past TDC needs to have more ignition advance so, the pressure is present at the same time as it would have been. It’s the other side of the equation. If you do one thing(leaning the mixture)one must consider the other changes this creates and allow for it. In this case it’s more advance for the ignition event. David Vizard Performance has stuff on this. You guys will love it.

[@davidsanderson8464]

Hi Jason, love your work. I would just like to point out a slight correction/addendum regarding the NOx vs AFR graph you showed. Peak NOx formation is not usually at stoichometry (AFR = 14.7:1) but probably occurs closer to AFR = 16:1 (approx lambda 1.05-1.08). The temperature is part of the story but it is also about the excess oxygen left over after combustion to react with the nitrogen. This is one example of where EGR can be useful, as you run a partial charge (at lambda 1) but instead of excess oxygen you have inert exhaust gasses, which limits NOx formation.

[@MatafiedGaming]

I am glad you made this video. I had a mechanic tell me that running lean was going to make my engine explode.

[@MatafiedGaming]

JohnnyMo Which is why I’m glad he posted this, it reassured me I wasn’t being mislead. :)

[@Summerride]

I think you got all this wrong. First fuel acts as a coolant itself. Then a lean mixture will behave like a burst in flame instead of a controlled expansion then could cause knocking, and not by having another hot spot in the cylinder. The lean mixture will ignite too quickly and try to stop the piston to reach TDC that causes knocking. This is why cars have knock sensors that will retard the ignition in that case. So having too lean mixture will retain the heat longer into the cylinder, make the engine work harder and will make it running more hot. Too rich mixture then will cause it to continue burning after power stroke and dissipate heat into the exhaust valve and the pipe. So there is a sweet spot to get that is called "well tuned engine".

[@marktex9171]

Fantastic video! Working in the automotive service field, every manufacture is trying to get better fuel economy and maximise power output. However there is a major drawback that we are seeing on modern cars today. New cars are coming with very small engines that run ultra lean and take a very long while to warm up and as a result we are seeing oil dilution (gasoline not being burnt or vaporised fully and contaminating oil) We are even seeing when at idle, engine temp can drop quite a few degrees. When its -25 degrees C this is a HUGE problem. Something people in Florida have no clue about lol! Keep up the great work!

[@basithph8958]

How about the SkyactiveX engine?

[@Dinara1up]

@Benjamin Vadocz I might be wrong but I suppose diesel has more energy density per volume than gasoline.

[@athalfridhu]

53% Efficient. The same as termo electric power plant...

[@mituc]

The Skyactive-X will use lean burn 18-40:1 AFR for the low load/speed scenarios where fuel economy can be increased. It will not put any strain on the engine, but the lean burn will affect the cats which need to be different to last.

[@ditodeejay]

@Benjamin Vadocz I am pretty sure euro 6 diesel engines run rich(er) so that adblue/def injection(SCR) is properly reducing emissions.

[@Gustav_der_III]

@Benjamin Vadocz diesel have qualitative fuel injection. It "leanness" depends on the power your request from your engine. E.g. coal rollers running their diesel very rich. But for the environment this is probably not the best way☺

[@TechiesRSA]

The stokiometric ratio is the most efficient mixture of fuel and air needed to create and explosion without waste , but engines are tuned to run slightly bellow that to create a slower more controller burn that the engine components can withstand , this also prevents pre-ignition of the mixture as the engine temperature and pressure are enough to ignite a perfect mixture. So running Lean in engineering terms for an engine will definitely make it run hotter. The engine will make more power and respond better but it will fail at some point.

[@darrenmcfeaters6683]

Tell that to the melted plugs and catalytic converters I replaced from a lean fuel trim. That's why CPU will richer fuel trim to use excess fuel to cool converters when temps get high

[@upsidedowndog1256]

Being able to measure peak EGT is crucial to getting this right. Running a turbocharged aircraft engine at higher rpms than book, leaner settings than book takes extra tuning but can totally change an aircraft's performance envelope.

[@jimmyaber5920]

Older engines with no EGO sensor and no computerized ignition did run hot when lean. Lean burns slower and higher throttle takes away vacuum timing advance. Slower burn means flame, even though cooler, has more exposure to coolant given the greater capacity to pass heat into coolant through cylinder walls. The engine management systems of the last few decades would have check engine light on and would have controlled the situation and limited ill effects. Like many things, old ideas die hard.

[@gm683]

I have experimented with a carbureted engines and only observed the highest temperatures on stoichiometric AFRs (and a bit richer). Never observed an engine running hotter on lean AFR.

[@miralemnermina142]

Let me guess, you don't like new tech and newer cars either?

[@jimmyaber5920]

dosmastrify exhaust gas oxygen

[@jimmyaber5920]

My point is that this is no longer happening but it is not an unfounded urban legend. Years ago I worked in a GM dealer I’m the truck shop. C20 through C65 trucks running in the hills in my area would run hot even in cooler weather when they had the very common faulty fuel pumps with the return line that many big blocks and small blocks used. The driver would keep the pedal matted and drive a fuel starved vehicle up the hills and have gauges climb. The complaint of temp gauge going near the top would go away with a new pump and also return line restrictor and fuel pressure to carb staying at over 3 psi wide open loaded up hill.

[@jimmyaber5920]

Ante Radić no, I had a tech support and training role with a car manufacturer until a few months back. I was in that job for 30 years. My post was to address that this was not urban legend completely as older technology would overheat when lean with no other methods in play to limit the effects.

[@KM-by9gd]

As always great info . Thank you for explaining i have been having this same argument with few people that running lean does not mean hot combustion

[@captpaulhaugan]

I’m guessing most modern cars run lean most of the time. Multi port sequential electronic fuel injection lets you jump over the lower explosive level ( LEL ) upper explosive level ( UEL ) peak. This could not be done with a carburetor. Leaning out a carburetor will make an engine run hot. The fuel injected engines can produce approximately half rated power in economy lean mode and are touchy about throttle changes. When power is needed they jump to the rich side. Cruising at highway sped works well for the lean mode.

[@captpaulhaugan]

Light aircraft have a mixture adjustment. There are temperature gauges on the heads. Mixture is adjusted by head temperature. To lean a mixture will cause the heads to over heat.

[@elmuerte17]

You're wrong. Most modern cars run around stoichiometric or slightly rich almost all the time. Going leaner than stoich leads to the formation of far more nitrogen and sulphur oxides, which is far worse for the environment than a bit more CO and CO2 from running a bit rich. If your car runs lean at all, it'll only be during low load cruise.

[@chappy0061]

Can you please do a breakdown of why some people choose to use water injection in their engine? It seems like it would tie in nicely with this video.

[@shapshooter7769]

Water injection is mostly used for cooling the A/F mixture - mostly for turbo setups. You also get more power due to denser air and the steam effect in-engine.

[@robnobbs28]

Egr is burnt inert gas thats why it lowers the combustion temperature, if you put oxygen rich egr into engine ( like a intake air leak) it would have more oxygen and burn hotter? i think you need to take into account the oxygen Content of the lean mixture! Thanks rob

[@robnobbs28]

@@jimmyaber5920 yes i agree more fuel less oxygen Content in the charge air.. So by making the mixture lean with inert gas (burnt exhaust gas Egr with no oxygen) causes it to burn cooler 👍

[@Shaun.Stephens]

Exactly. If it were as simple as leaning the mixture out then why would OEMs go to all of the trouble of designing and building EGR systems when they could do the 'same thing' in software?

[@Kavi4GP]

Shaun Stephens it's not the same thing as adjusting the software , the egr is active in most new cars , especially diesels to lower temperatures both in cylinder and in exhausts. It also helps reduce emissions

[@Shaun.Stephens]

@@Kavi4GP That's my point. If the same effect could be achieved by running a leaner mixture instead (as is alluded to in the video) then manufacturers wouldn't bother with EGR systems.

[@ellenorbjornsdottir1166]

lean+egr

[@C303ofSweden]

The first thing that came to mind is that you have to set engine tuning aside. Stock engine is built to run around 14:1 and it will survive. But if you have for example a 9:1 compression ratio and put like 1,5bar of boost on it, it will fail due to hot combustion. By running lean in tuning prospective is running above 13:1 which is not lean in normal cases. Edit you mentioned my point in the end.

[@rob9665]

This video is pedantic. The temperature increases up to around 15:1 and then plummets. It plummets because the engine will not run correctly, therefore the statement 'lean engines do not run hot' is wrong because it does run hot' in the region where the engine actually still runs. Anyone running a lean engine that still performs will see a temperature increase. You've countered the false statement that 'a lean engine runs hot' with another false statement that is ' it does not run hot' both are wrong as they don't account for eachother, but in the practical world with engines in the performing regions of afr ratios they will run hotter.

[@broark88]

I was modeling an engine trying to use boost/back pressure rather than throttle to moderate output and it kept showing that if it went lean, it actually ran cooler at the exhaust, even if it was compressing more air at a high CR. Hence, I found your video for a second opinion. Thanks!

[@zoltanr15]

I actually really like this guy

[@jamesplotkin4674]

Zoltan, yes and he'd make a great model at 19n, but he's married to a female.

[@oxman7]

Love the videos. Nitty gritty detail is the peak!

[@tonybailey89]

Very detailed and in depth explanation, but there are some folks who have real world experiences of say burning up CATS on lean running engines that say otherwise. I don't doubt your findings are accurate and once broken down they make sense... I just feel there are some potential elements beyond just the cylinder that needed more explanation. Excellent thought provoking and informative video as usual!

[@PuerRidcully]

"lean" probably means closer to that ideal stoichiometric ratio, which was explained in the video. If the engine and tune weren't designed for that, the temps will be too high

[@Bleachanna]

I'd Agree with you, if you've been around any air cooled engine that's running lean it SPEWS off heat like a nuclear reactor, I think his curve is backwards, it should run cooler across the board running rich than running lean, think about if there's not enough air for fuel to burn it's going to be cooler due to the added mass of the fuel(think about water injection) but if there's extra air then it's going to get as hot as possible, if the egr was out of the equation cars pulling hills would get severely worse mileage and melt pistons due to detonation. But with the egr putting non-combustible gas in the equation then you can have the same effect as running rich without all the fuel.

[@PuerRidcully]

@@Bleachanna unburn oxygen doesn't produce heat, so I don't see, how would that make sense. I can see how hot oxygen could react with some exhaust elements though. Maybe that plays a role.

[@tonybailey89]

@@Pooneil1984 I think your getting too far away from the point of the video and what folks are looking to clarify by being too complicated with yourself lol. The question is simply (no matter how you choose to articulate it) does a lean AF mixture cause engines to run hotter... Jason's scientific explanation makes sense in theory with stating that if less fuel is burned due to a lean AF ratio, less heat is generated... In practice however folks have experienced lean AF ratios burning up CATS and hotter exhaust Temps That's the additional clarification that's not tying everything together... In theory and in practice aren't coinciding.

[@airgliderz]

On a two cycle engine ruining lean heats up the motor greatly cause fuel oil mix also helps coo the engine I think this contributes to the misconception that a 4 cycle motor runs hot when lean.

[@HassanEido1]

Jason back with the good stuff. I should point out that when ppl refer to the mixture being lean, they mean relativity leaner than what it needs to be during high load full throttle. Eg. Part throttle usually runs 14.7 while wot runs 12.5 to 13.5 NA and 10.5 to

[@alexchong213]

Sorry normally like these videos but calling BS on this one. Running lean causes pistons and valves to melt

[@willyd4850]

Correct you are sir.....

[@monochrome_ilya]

On more melted piston from me to back you up ;)

[@richardschofield2201]

So does this mean that boosted engine run very rich at peak torque and running lean (or closer to ideal using new knowledge) is why things can go boom. So if they went way lean (i.e leaner than ideal) things could be fine for the engine (although down on power)? If so I'm confused how these cars ever meet emissions requirements. Do they just rely on the cat to remove the excess hydrocarbons at peak torque?

[@Fridgemusa]

Unless it's a pre-mix 2 stroke.

nope.same thing

[@Bleachanna]

@ hell no have you been around a lean running 2 stroke? When it starts running lean you can smell that it's running lean and you can't keep your hand within inches of it not to mention touching it would make your skin boil vs it running correctly.

[@hojnikb]

yep, air cooled 2 stroker cools a lot with the gas, so running lean will cause it to run very hot. experienced that myself

[@jaydunbar7538]

@@Bleachanna many times, if you actually check the air fuel ratios your still running rich. Running "to lean" and actually running above 14.7 are not necessarily the same thing, he details this in the video. The target for most 2 strokes is 12.0-12.6:1 AFR, so running at 14:1 is "to lean" and will cause excessive heat but it is still a rich AFR as it is below 14.7:1. If you actually go above 14.7:1 it's more likely to get lean miss fires and it just won't run.

[@DxCBuG]

@@jaydunbar7538 it as if they haven even watched them damn video. Jason trying to clear up this common misconception because terminology gets thrown around nilly willy and they don't get it. This confuses a lot of people unfamiliar with the whole concept. Just be accurate about what you say and do. This case shows why this is important.

[@superziemniak1]

Jason, I never expected such an insightful answer for my question in previous video, all makes sense now, thank You!

[@calholli]

This is just silly... If you want your engine to run at a certain fuel mixture.. and it is running less fuel than you want........... it's "TOO LEAN" ... whether or not it is technically "lean" or not, it is still leaner (or less rich) than you want it. There are two meanings of the word here.. One is a technical measurement, the other is a direction of tune.... So when you see an engine the is running "less rich" and running hot... and the way you fix it is to tune it to run more rich..... if it wasn't too lean, you need to make up a new term... because in my book, it was too lean and you fixed it by making it rich. (you're splitting hairs here and confusing the normies)

[@steventrott8714]

What needs to be explained is that there are two schools of thought. One is when we are trying to produce max power. A richer mixture will make the engine run cooler. The other is when we are at low RPM at highway speeds sipping gas and the engine will run cooler with a leaner mixture. The gear head wants a cooler engine with a richer mixture and a tree huger wants a cooler engine with a leaner mixture. They both get what they want and both are correct.

[@DrB1900]

And pity the poor gear headed tree huger. A very unhappy sort.

[@ozzy5368]

Agree. 14.7 is perfect in physics, but in engine tuning it is lean...because the goals are different. Optimal burning mixture is 14.7:1 but optimal engine mixture is more like 12.7:1.

[@garyhoward4064]

Flying piston aircraft with exhaust gaz temperature readers (EGT), it is quite clear that when you pull the red lever backwards to lean the mixture, as of a certain point the EGT goes down. However and to be complete with theory, we must not forget that a leaner mixture burns slower, hence exposing engine to « longer » hence more heat during the stroke.