An engine that runs lean would mean that it would run hotter than one that runs rich? I know there are compression ratios but are there fuel mixture ratios that only work on an engine that is designed for it? What is the fuel mixture ratio of a '91 civic compared to that of a '70 charger? I was just thinking, do you necessarily get less power when running a fuel mixture ratio with more air and less fuel? Does a higher amount of air automatically mean higher fuel efficiency?
A lean running engine runs hotter, use less fuel?
- Thread starter fleabag
- Start date
zerocool84
Lifer
- Nov 11, 2004
- 36,041
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Leaner does mean you're using less gas...that's pretty obvious.
It also does tend to run a bit hotter, and that's where you'll make your best power...but it's a fine line.
On performance cars, if you're being conservative, you'll run it just slightly rich. But your best power will be as lean as it'll run without misfiring. Only problem with that, if you miss on the tune up of a race engine too far to the lean side, you're melting pistons. Miss on the rich side and you're just not as fast.
It also does tend to run a bit hotter, and that's where you'll make your best power...but it's a fine line.
On performance cars, if you're being conservative, you'll run it just slightly rich. But your best power will be as lean as it'll run without misfiring. Only problem with that, if you miss on the tune up of a race engine too far to the lean side, you're melting pistons. Miss on the rich side and you're just not as fast.
Google "detonation in piston engines", or go to Wikipedia and search for knocking, and air-fuel ratio. If you really want to delve, read up on stoichiometry.
In your question about the cars, the main thing that will matter is the type of fuel being used. Both engines run on gasoline and thus were designed to run at the same stoich ratio, but newer, fuel injected Civic engine will be able to control that much better, especially if a wideband O2 sensor is used. The ideal stoichiometric ratio for gasoline engines is ~14.7:1 or 14.7 times the mass of air to fuel. Running excessively lean mixtures for extended periods of time will certainly yield better gas mileage, as an engine with melted pistons or blown out sleeves will use no gasoline whatsoever.
In your question about the cars, the main thing that will matter is the type of fuel being used. Both engines run on gasoline and thus were designed to run at the same stoich ratio, but newer, fuel injected Civic engine will be able to control that much better, especially if a wideband O2 sensor is used. The ideal stoichiometric ratio for gasoline engines is ~14.7:1 or 14.7 times the mass of air to fuel. Running excessively lean mixtures for extended periods of time will certainly yield better gas mileage, as an engine with melted pistons or blown out sleeves will use no gasoline whatsoever.
DivideBYZero
Lifer
- May 18, 2001
- 24,117
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And you wash too much oil off the cylindar walls casuing premature wear. I've seen it first hand in many shops. Mainly on carb'd vehicles that needed the card rebuilt but depednign on how long you run on the rich side.
The easiest way to do a carb is lean it out till it sumbles then richen it. Drive it easy check the plus, drive it hard check the plugs. If not satisfied by a cheap A/F meter and see if you are around 14.x:1. All n/a engines of course.
Demon-Xanth
Lifer
- Feb 15, 2000
- 20,551
- 2
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The reason why direct injection gas engines took so long to get to the US was the fact that their "lean burn" mode caused them to put out way too much NOx emissions, since the cause of the NOx emissions is the high combustion temperatures. I have heard of headers glowing under light usage (ie: breaking in) because of engines running lean, usually the carb isn't setup with the right rods or jets.
Honda has been using lean burn technology since the 90'2. On my Insight I can usually see when the ECU puts the car into lean burn mode. When on a flat road below 70mph you let up on the accellerator, and the Instant mpg guage will jump from the 60mpg range, and spike to 80 - 120mpg, and hold for upto 30 secs, then drop back down for roughly 10 seconds while Nox is flushed from the Catalytic Converter. This will repeat as long as the engine is warm enough and there isn't excessive engine load. Cold weather, a head wind, or an incline will kill lean-burn. There is also a noticeable lack of power when in lean burn.
On a downhill slope it is hard to tell as the mpg meter will peg at 120 - 150mpg. My record downhill was 120 - 150mpg for 60 miles due to the downhill road. That was coming off of Lolo pass, MT, heading towards Lewiston, ID doing 60 - 65 mph.
On a downhill slope it is hard to tell as the mpg meter will peg at 120 - 150mpg. My record downhill was 120 - 150mpg for 60 miles due to the downhill road. That was coming off of Lolo pass, MT, heading towards Lewiston, ID doing 60 - 65 mph.
So it sounds like to me that the reason why people don't use leaner mixtures is because they're worried about high temperatures, right? If temperature wasn't an issue, what would the stoichiometric ratio be then?
bruceb
Diamond Member
- Aug 20, 2004
- 8,874
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Too lean will hurt the pistons. And as mentioned, it can cause oil problems in
regards to lubing the walls of the cylinders. The only way lean works is at speed
under light load. It will not work well under hard acceleration such as from a stop
light or going up a hill. Gas engines are designed to run at 14:1 air / fuel raio as the
optimum. If you add any power adders to an engine, such as a Turbo / Supercharger
/ Nitrous or in a Diesel you can add Propane, you Always Add More Fuel when the power
adder is turned on (Nitrous has a Off Switch) .. Turbo and Supercharger are always on
and the fuel delivery is set accordingly. In a lot of cases, you need to add an extra fuel pump
or change the existing one to high volume. Nitrous adds a Fuel Solenoid at the Intake Manifold
to add the extra gas.
regards to lubing the walls of the cylinders. The only way lean works is at speed
under light load. It will not work well under hard acceleration such as from a stop
light or going up a hill. Gas engines are designed to run at 14:1 air / fuel raio as the
optimum. If you add any power adders to an engine, such as a Turbo / Supercharger
/ Nitrous or in a Diesel you can add Propane, you Always Add More Fuel when the power
adder is turned on (Nitrous has a Off Switch) .. Turbo and Supercharger are always on
and the fuel delivery is set accordingly. In a lot of cases, you need to add an extra fuel pump
or change the existing one to high volume. Nitrous adds a Fuel Solenoid at the Intake Manifold
to add the extra gas.
Except for the new direct injected turbo engines, they can run super lean compared to regular fuel injected ones.
My solstice gxp hovers at 14:1 till 4000rpm then dips to 12.7:1 until the rev limiter. At first i couldnt believe it but thats the commanded afr the ecm wants.
What do you guys think of injecting water into the cylinders after the 4th cycle and then exhausting that too before restarting the air fuel intake cycle again? Do you think pouring water into the cylinder would affect the oil? My thinking was that if you could add two more cycles to an engine (two power strokes) which would cool down the engine since you're injecting water, you wouldn't have to worry about running lean since the engine would run much colder.
I would like to know this as well. I always thought it was because oxygen burned at a higher temperature than gasoline, but with the low percentage of oxygen in the atmosphere, this does not seem too likely. However, I know that combustion variables are very different in an enclosed cylinder when compared to the open air, and there is no doubt that oxygen burns hot. It sort of pans out since lean mixtures produce lots of NOx emissions, but it still does not entirely explain how the temps got that hot in the first place. I know vaporized fuel has quite a cooling effect, but enough to keep the temp threshold below NOx formation?
The same reason that blowing on a fire when you're trying to start it makes the flame get bigger. More oxygen.
Edit: That's horribly over-simplified, but easy to understand.
Fuel in a normal ratio, 14.7, and especially if it's a bit rich, actually is a more controlled explosion and helps cool.
You can only get lean burn going for ~30 seconds?
I'm pretty sure I've gone at least 10 minutes.. It does eventually kick off, but like you say.. only for 10-15 seconds.
If you're really gentle with the throttle, you can keep lean burn up almost any incline, but you have to accept the decrease in speed.
Unfortunately, I'm too much of a spirited driver at heart and have eschewed that style of driving for a more normal style, and my MPG has suffered as a result, only averaging 52-55mpg.. lol
The Boston Dangler
Lifer
- Mar 10, 2005
- 14,647
- 2
- 0
according to that, your engine is kinda rich 'til 4000 rpm, the really rich to redline. lean mixture + forced induction = BOOM! (maybe)
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