High Altitude FE?

[superchow]

Being currently in Wyoming at a relatively high altitude (6000+ ft.) I noticed that my 07 Civic EX is accelerating very slowly. Well, makes sense, no? Less air, less power. But now I am viewing this from a different perspective (thanks to EM):

Less air should also mean less fuel injected, correct? Stoichiometric ratios should still apply? I understand that "the nut behind the wheel" is revving the engine more to get the car moving at a similar rate as at sea level, which will definitely ruin gas mileage.

But say I was stubborn and would drive the same as at sea level and just get used to the reduced power output? (Shifting early, accelerating slowly, engine braking, DWB, etc)

And taking it one step further, what if I restricted the air intake when back at sea level to artificially reduce the maount of air the engine can "inhale"?

[Daox]

Restricting the intake will definitly not help your FE. The engine will have to work harder to overcome this restriction. Its not the same as having less dense air.

Also, accelerating slowly is a good entry level driving technique. But, if you want to bring it up to the next level you'll need to change how you accelerate. The most efficient way of accelerating with a manual transmission is keeping rpms low but almost flooring the gas pedal. If you have a scangauge, engine loads of around 80% on average show the best results. This is usually around 1/2 to 3/4 throttle from my experience. I try to keep my rpms between 2000 and 3000, again an average that I have seen work. You can play around with the rpm range and load once you are comfortable with the new technique to see where you get the best mileage from your engine as they'll all be different. Using this technique gets you going fairly quick so you need to be careful not to go too crazy lest you find yourself using the brakes a lot (which negates any benefits you just gained). Try this out and see how it works for you.

[superchow]

I understand the low rpms/"wide-open-throttle" scenario, and it seemed to work fine in my old car (2002 Nissan Sentra) but I know the '06+ Civics have throttle-by-wire. (This creates some smoothness issues, but that's another topic. )

I think I read that the ECU opens the buttefly all the way in low load conditions and pushes some of the air sucked in back out (reducing the volume of air compressed to about the equivalent of a 1.5 liter vs 1.8 liter) and at the same time using some recirculated exhaust gases too.

I haven't consistently tried the fullt throttle/low rpm technique, but that may (I emphasize MAY) not work in this vehicle.

However - I have refueled here in high altitude Wyoming, and low and behold, ~36 mpg! OK, not great, but considering we didn't drive economically at all, I am quite happy about that.

The engine must (MUST) be above 2000 rpm to have any torque whatsoever, preferably above 2500-3000 rpm. Passing on the highways here is truly a minute long endeavor!

So maybe we should have CO2/nitrogen injection instead of nitrous oxide. Any ideas on what gas to let into the intake that would reduce the O2 in the engine that would stay stable?

[MetroMPG]

I like the idea of inert gas injection. You could do the same thing with EGR too. The trick is knowing at what proportion you're going to start adversely affecting combustion and making things worse!

You're right that higher altitudes should be better for fuel economy. Less aero drag too.

[Southcross]

Originally Posted by Daox

If you have a scangauge, engine loads of around 80% on average show the best results. This is usually around 1/2 to 3/4 throttle from my experience. I try to keep my rpms between 2000 and 3000, again an average that I have seen work. You can play around with the rpm range and load once you are comfortable with the new technique to see where you get the best mileage from your engine as they'll all be different. Using this technique gets you going fairly quick so you need to be careful not to go too crazy lest you find yourself using the brakes a lot (which negates any benefits you just gained). Try this out and see how it works for you.

I know this is an old OLD thread... I'm back searching/researching and since I too live at altitude, I thought this may be beneficial.

since I drive a pre-OBD car and I can not hook anything remotely like a ScanGauge up, can anyone confirm this acceleration technique?

[ConnClark]

In a gasoline powered car at high altitude, less air means less fuel burned but it also means less EGR. This all translates to less trapped mass in the cylinder and more heat of combustion going into the engine block and head. At a lower altitude the ECU would compensate by increasing EGR flow to increase the trapped mass in the cylinder. This extra mass will absorb heat that would otherwise heat the block and head and allows more work to be extracted by the piston.

So at higher altitudes your economy drops.

EDIT: Also inert gas injection will work better than EGR. Gases like helium and argon will raise the specific heat ratio of the combustion gasses during the power stroke. This results in more power being extracted by the piston. This is not cheap however.

[Christ]

RE: Argon -

What percentage of your total intake flow would have to be argon to see a gain? How much of a gain could you see? What could the adverse effects be?

[ConnClark]

Figuring out the percentage of flow where you would see a gain is kind of hard. To get the maximum gain you would simply replace your entire EGR flow with the inert gas.

The link below has some formulas (in the blue text) where you could come up with numbers if you were able to figure out what you changed the specific heat ratio to.

Improving IC Engine Efficiency

In general it won't help at full power.

[basjoos]

The FE boost you see when driving when the humidity is high is the equivalent of inert gas injection, since water molecules take the place of some of the oxygen that the engine could have been sucking in if the humidity was low.

[Christ]

So what if I just inject steam into the intake? (Steam, scavenging heat from exhaust.)