Air/Fuel Ratio - How Does Being Rich/Lean Affect Your Engine?

In this video, we discuss air fuel ratio, why different fuels have different air/fuel ratios, what is meant by rich and lean, and what happens if you run your engine rich or lean. We also talk briefly about why you would target these conditions.

[stuartgilbert]

I think an interesting video would be explaining o2 sensors and what your exhaust can tell you about the health / efficiency of your engine.

[chiwong]

Diesel engines are not stoichiometric by design. stoichiometric simply means all the oxygen in the intake charge is consumed in a given combustion cycle. Diesel engines are lean burning in general and air/fuel ratio is varied to control the speed of the engine. Not all oxygen in each intake charge is consumed in a combustion cycle. This is the number one reason diesel engines tend to emit higher levels of NOx. The leftover oxygen in the cycle forms oxides of nitrogen which is AKA smog. This is mostly corrected by the SCR and urea (diesel exhaust fluid) injection. Diesel engines often also employ cooled EGR to reduce the oxygen level in the intake charge during part throttle conditions. Stoichiometric is only applicable to gasoline engines.

[jf]

Today's ethanol blends alter the standard 14:7 stoich. With a typical E10 fuel stoich is roughly 14:2-14:4 and with a carbed engine it generally requires going a bit richer on the jetting from stock jets. At a steady state 'cruise' one can run cooler at an AFR of 16-17 than you can with an AFR of 13-13:5 (same scenario) non turbo or boost application. But you will need vac advance or an EFI set up for the leaner burn at part throttle condition (no/light load).

[Fabio-jmjq]

We use E100 since 70’s in Brazil. Ethanol is a bit aggressive to fuel system but keep the engines clean of carbonization, and not dissolve oil film like gas. The cars before flex ( ethanol only ) work with 13:1+ CR and is more efficient.

[lucywucyyy]

being rich means you can afford better parts and maintanance for your engine

[mikef-gidg]

As a lifelong car nut.... this was very well done. I actually learned a few things.
I have trouble explaining a/f ratios to others, I think I will use this video as a reference to that. I will definitely subscribe and look for more.

[elonjun]

Thank you so much, as an aviation student, I could learn so much from your video related to the aircraft engine mixture system. Huge appreciate it!

[llewvirtue]

Eng knock can also be avoided by running a higher octane fuel, don't get confuse higher octane does not mean higher volatility.
Octane rating is an anti knock rating, developed in the second word war by the SAE to ensure that every batch of fuel for the spitfires was the same quality

[mikebaylis]

Great video.have you ever heard of a chevy 350 with hyperutictic pistons breaking the ring lands between compression rings? Only on one side, I mean all 4 on left side! No damage to cyl walls, valve, or top of pistons! Compression ratio was 10.9. Ran 93 octane.

[Kingswood]

Something interesting about diesel and gas is that the “combustion chamber” on the gas is in the cylinder head and on the diesel, its in the piston head. I dont know which is better for mpgs and/or power, i just thought that was neat.

[citypam]

would love to see a video on what is the best path to take when designing aero for a race car for the grass roots racer. what will yeild the best resaults for the least cost, modifications ect. cheers

[darryloflife]

In order to better understand air fuel ratios you need to show the optimum air intake temperature for efficient burn . For example optimum temperature for petrol is 60 degrees Celsius and LPG is around 90 to 110 degree's Celsius. Of course all of the fore mentioned temperatures rely upon an exhaust valve that is under proper temperature control.

[pinkdispatcher]

Cool stuff. This is relevant for small aircraft engines; these usually run very rich for takeoff to increase detonation margin, and lean off for cruise. In fact, most engines have manual mixture control, so it's useful to know what happens when you pull the red lever to lean the mixture for cruise. These engines have no ignition timing change (except a timing retardation for starting the engine); everything is simple and mechanical. Aviation gasoline still contains lead, but that will come to an end, and we will see how that works for high-performance engines, which still require an anti-knock index of 130 for takeoff power at full rich mixture.

You say Diesel engine *often* don't have a throttle body. Are there Diesel engine that do?

[tm]

I am interested in a video covering the suspension differences in a "street performance" car like say the Z06 and a GT car like say a Porsche GT CUP car. I'm interested to know where the break point is for something like too much total dampening, or what real world usable spring rates would look like. I have a hard time finding an example to compare the overall setup / experience.

[fanieschoeman]

Good information for those just starting to do some tinkering, or just curious. Thanks~!

[dangoe]

Most people go for that high miles per gallon of fuel. Where would I find this on the curve?Would that effect engine working life?

[CalaisRider]

Just what I needed. With Lambda I wasn't sure if low was high or low and visa versa. "Thanks for taking the time and posting, it was a "great education for me". I have a custom LS engine where the overkill cam and high compression causes me Knock grief and blow-by has been way high since new. Running so rich now its sort of embarrassing with the fumes and overlap especially with forged almost everything in it.

[omarnibiru]

Super helpful and informative man thanks a ton

[jimmygichohi]

Possible to show how to use diagnostic machine to adjust air/fuel ratio?

[jeremymurphy]

6:50 All the Hemi guys went nuts and then said "wait...four valves? Sorcery!"