Air contains a certain amount of oxygen depending on altitude. Suppose the
oxygen intake was increased by just one to two percent (at sea level)
without adding all the additional stuff that's in the air. Could the engine
and mpg benefit by this or is the engine designed primarily for sea level
and above (oxygen amount) range only? Has oxygenated gasoline made it
impossible to add more thru an intake? Your thoughts?
At higher altitudes, more air is required in engines to get the proper
amount of O2 needed for optimum combustion. The air intake (hence the O2
intake) is adjusted automatically by modern cars via the electronic systems
in them. In the old days, this was done by adjusted the carburetor for high
altitude locations.
So it is already possible to adjust the amount of air (and O2) intake to
some degree. Also, the principle behind turbochargers and superchargers is
to force even more air into the engine to gain power, but this uses an
additional amount of gas that is mixed with the extra air to achieve the
increased power.
From "How Things Work":
"It turns out that there is a particular ratio of air and gasoline that is
"perfect," and that ratio is 14.7:1 (different fuels have different perfect
ratios -- the ratio depends on the amount of hydrogen and carbon found in a
given amount of fuel). If there is less air than this perfect ratio, then
there will be fuel left over after combustion. This is called a "rich"
mixture. Rich mixtures are bad because the unburned fuel creates pollution.
If there is more air than this perfect ratio, then there is excess oxygen.
This is called a "lean" mixture. A lean mixture tends to produce more
nitrogen-oxide pollutants, and, in some cases, it can cause poor performance
and even engine damage."
If you are talking about a modern computer controlled engine, the answer is
no.
Has oxygenated gasoline made it[color=blue]
> impossible to add more thru an intake? Your thoughts?[/color]
MPG will not necessarily improve.
As Mark A posted, the optimal ratio of air to fuel is 14.7 parts air to 1
part fuel. As air enters the throttle body, the amount of air is measured
by a device like a mass air flow sensor so the engine knows how long to
leave the injectors open (which controls the amount of fuel entering the
engine). The oxygen sensor measures the amount of O2 in the exhaust and
feeds this information back to the computer so it can further adjust fuel
injector pulse duration. If there is more O2, then more fuel will be
injected and MPG will go down. On the plus side, performance will improve,
so things will pretty much be a wash.
--
In my limited experience, oxygenated gas leads to cleaner air, NOT more
effeciency.
I suppose you could inject more air, but if all you needed was 2%, you could
manage that with a straighter intake tract (track).
I own an '81 Jeep with the factory inline 6 that came with a carburator. I
changed out hte carburation with a multi port fuel injection system
(something yo guys have already), and I also put on a header system and
low-restriction exhaust system. My fuel mileage went from something around
12 mpg to 18 mpg (for the combined city/highway driving tha tI do). Surely
the MPFI was the greatest increase in effeciency, but the alterations to the
exhaust system have to account for a fair amount of the improvement.
Since today's cars already have MPFI and they also have a pretty good
exhaust system, I'm not sure that you can do much with your car in the
driveway. Surely there is a limit of performance/efficiency that can be
attained in current production cars and trucks.
On my '95 Tercel, I added a Pilot (pronounced CHEAP!) 'cold air intake'.
It was basically a Mandrel bent tube with a big honkin' air cleaner, like
the Ricers use. It did somewhat produce a noticable amount of OOMPH right
off the line.
But, it also added about 4 MPG, basically because of the amount of air
getting to the engine. I'd say it was worth the $50 over the course of
40,000 miles.
You want to add extra oxygen? Simple. Turbocharger, Supercharger.
Forced induction - pump the air into the engine, and then you can add
more fuel and stay at a nice stochiometric 14.7-1.
Suddenly, you just effectively lowered Denver Colorado or Mexico
City to sea level, and you dropped sea level areas into the Dead Sea.
You might need to run Premium fuel for the added octane, but there's
enough added benefit to make the difference.
There's two ratios involved here. One is the air/fuel ratio and then there
is the oxygen/ air ratio. Let's say oxygen makes up 14% of the air. I
suppose that no matter how "thin" the air is, like let's say 14,000 feet up,
oxygen still only comprises 14% of the 50% available air compared to sea
level. Isn't the reason why fuel efficiency drops at higher altitude because
the engine is working harder to draw in air? Or am I all washed up on this?
I know when I was up 14,000 feet it was strange to have to put more effort
in drawing a breath although the wind was blowing. Maybe the oxygen to air
mixture doesn't remain constant?? Or maybe it does but there's more
pollutants up that high which interferes with metabolizing the oxygen?
I'm getting a headache ;) just thinking about this.
The oxygen ratio stays fairly constant through winds and atmospheric
circulation, though being in the middle of a forest with all the trees
expirating oxygen will tend to skew it a bit higher - I'd guess a
quarter percent at the most.
But due to the altitude the overall volume is lower. Meaning that
you (or the car engine) have to work harder at moving through more of
that thinner air to get the same volume of oxygen to work with.
sqdancerLynn wrote:[color=blue]
> increasing the air without additional gas will make the engine run lean.
> The egr valve injects air into the ex for emissions[/color]
This isnt correct, the EGR injects exhaust gasses back into the intake
to reduce nox imissions by reducing in-cylinder temps on cruise. This
doesn lean or enrich the mixture as the exhaust gasses are inert.
"Coyoteboy" <coyoteboyuk@hotmail.com> wrote[color=blue]
> This isnt correct, the EGR injects exhaust gasses back into the intake
> to reduce nox imissions by reducing in-cylinder temps on cruise. This
> doesn lean or enrich the mixture as the exhaust gasses are inert.[/color]
IMO, even "inert" exhaust gases being back-channeled into the intake will
change the resulting gas mixture in the cylinder, since only fresh air
provides the ca. 21% oxygen content. However, the computer should compensate
for it.
Herb Ludwig wrote:[color=blue]
> "Coyoteboy" <coyoteboyuk@hotmail.com> wrote[color=green]
> > This isnt correct, the EGR injects exhaust gasses back into the intake
> > to reduce nox imissions by reducing in-cylinder temps on cruise. This
> > doesn lean or enrich the mixture as the exhaust gasses are inert.[/color]
>
> IMO, even "inert" exhaust gases being back-channeled into the intake will
> change the resulting gas mixture in the cylinder, since only fresh air
> provides the ca. 21% oxygen content. However, the computer should compensate
> for it.[/color]
I see where you are coming from and it would change the mixture if it
were a carb'd car, but in EFI cars the ECU is aware of the EGR and
knows to scale back the fuelling as there is now less oxygen in the
cylinder fill - hence the mixture doesnt change due to its compensation
as you say.
There are many myths about EGR and plenty of people remove them from
performance cars to improve performance, not realising they know
nothing of its theory of operation and that it doesnt affect
performance as its only active in cruise conditions.
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