Did you guys know about this already? I've been reading a lot about Eclipses, Lancer, Evolution, etc. but I've never heard of GDI engine until today. I've been reading about it on this site this site and it's really interesting. I always thought honda is the only one making (or at least making a big deal about it) environmentally friendly/fuel economy vehicles. I guess I'm wrong.

 

http://www.lancerforums.com/forums/s...&highlight=GDI

Old news but a rather interesting technology to say the least...run a search on the forum and you'll find more info and debate on it.

 

Ah I see. So we can't use GDI yet cause of sulphur content in US fuel.

Thanks!

 

I wrote in a couple of other threads about the chemistry of combustion but noone seemed to respond. Where did the idea that sulphur content prevents using GDI engine come from?? Where did the idea that lower octane means that the GDI won't run right? The better mixing and vaporization of the AF mixture should provide better combustion regardless. i could be wrong on this but I would like to know how it is that the benefits are eliminated by sulphur content or lower octane. Doesn't make sense chemically.
Also, higher octane fuels were, I thought, more volatile than lower octane fuels. If that is the case, then certainly deisel fuel would NEVER work (but it does)

Anybody know something?

 

Octane is a measurement of the resistence to detonation - in other words, oxidizing (burning) due to heat and/or pressure. Higher octane fuels are less likely to burn as a result of ambient heat or compression-induced pressure. Thus a 100 octane fuel can withstand 11:1 or 12:1 compression, while 87 octane will detonate under similar compression. Detonation is what causes knocking.

As for the sulfur theory, my only thoughts are that it would slow down the mixing of air and fuel to a degree that would hinder complete combustion (the same problem that non direct injection engines suffer). However, as stated elsewhere, this affects all IC engines, not just direct injection. The tolerance level is probably lower in a GDI engine, though.

Anyway, it would not surprise me at all to see this sort of technology on a high tech car like the Evo. The slight increase in fuel efficiency and reduction in emissions is more beneficial when dealing with high output engines, as opposed to an economy car engine which places cleanliness and efficiency above power output.

 

I believe what the original sulphur post was saying was that the sulphur didn't allow the fuel to properly atomize when sprayed. The mist wouldn't be so much misty as made of droplets. Anyone else read it that way?

I'm not going to pretend to know squat about chemistry.

 

That would be my take on it as well. Excess sulfur in the fuel would negatively affect atomization in non-direct injection engines too, which makes me wonder why US fuel would be a problem for GDI to handle.

Another possibility is that the excess sulfur might build up on the injectors - similar to carbon deposits on spark plugs - and screw things up with the injection.

 

ALRIGHT!!! Thanks guys!
I think I understand this a bit better.
The higher octane levels preventing premature ignition (detonation) and thus preventing knocking makes sense.

ONLY For those who want it...

Octane is an 8-carbon chain:

C-C-C-C-C-C-C-C

Because each carbon atom forms four bonds (in "hydrocarbons" these bonds are with hydrogen) you end up with:

H H H H H H H H
l l l l l l l l
H-- C-C- C-C-C- C-C-C--H ...written: C8H18
l l l l l l l l
H H H H H H H H

When it "burns" (combines with oxygen) it breaks up into gases...
Mostly CO2 (carbon dioxide, like we breathe out) and H2O (water)
This is "clean" combustion...just CO2 and water. No pollution (except that CO2 builds up in our atmosphere and gives us the "greenhouse effect" (It absorbs heat radiating from the surface of the planet...sunlight... and traps it so not as much radiates back into space. CO2 is the primary greenhouse gas contributing to global warming).

In engines, the temperatures and pressures are so high that you get all kinds of other byproducts such as:

Ozone (O3)...good to block UV radiation at the outer limits of our atmosphere...but toxic to living things...reacts to anything it contacts...NOT good to breathe ozone.

and also the impurities in the fuel (anything other than hydrogen and carbon) form pollutants such as:

sulphur (S)...combines to form SO3...which then combines with H2O to form H2SO4 (sulphuric acid) which then dissolves into droplets of water in clouds and gives us acid rain.

A WHOLE LOT of other crap gets made too, and some of the fuel does not burn completely, thus being released as unburned hydrocarbons:

methane, CH4 (one carbon)
ethane C2H6 (two carbons)
propane--3
butane--4
pentane
hexane
heptane
OCTANE --8
nonane--9
decane--10

etc, etc, etc.

The fewer carbons in the chain, the more volatile (gaseous and explosive) the fuel is. As you go from methane and butane and propane (gases at room temperature) to octane...it gets "thicker"...thus liquid...and burns slower (it vaporizes in the cylinder due to temp before the spark plug ignites it). The detonation comes from the tendency for the gases to explode without a spark...just because the temperature and pressure in the cylinder are too high as the piston is making its compression stroke...before it is at the top of its compression stroke...causing a sudden, abrupt explosion instead of a "slow" pushing-expanding explosion like we want.

Candle wax has chains of 20+ carbons, cooking oil a bit less...
and you can see they don't burn all too fast. Spark plug wouldn't likely do much for a candle.

So I guess if there is high octane rating, we get good clean, strong sustained force against the piston through its whole downstroke...as intended...but too low of octane content and we either have too quick a bang, or we're pumping out unburned fuel...both of which reduce the explosive energy converted to mechanical force.

WHAT THE HELL!!!! YOU BASTIGES GET ME UP IN THE MIDDLE OF THE NIGHT JONESING FOR AN EVO AND I BECOME SOME OBSESSED WACKO GOING OFF LIKE A CHEMISTRY TEXT!!!!

SHZEEEEESH!!!! That is a bit scary....really... ... ...
... ...frightening

OK so who knows what we can treat our fuel with (I KNOW octane booster...but...) seriously...I don't know what kind of fuel additives there are, what's good/not...etc etc. What we can do, if we can sort out this whole fuel thing...is figure out what to add (like methanol? ethanol? nitromethane? moonrocks?) then buy the stuff wholesale in 55-gallon drums and mix measured amounts into the gasoline (into our tanks or into another 55-gallon drum we fill with fuel then fill our tanks from).

Obsessive compulsive disorder thoroughly demonstrated.

Going to bed.

 

Great post even if you are a psycho.

Very interesting. Thanks for the lesson.

 

Thanks. I think I'll try to keep 'em a bit shorter from now on

I have a feeling that there is a pretty low probability of getting the GDI engine on the Evo 8. The decreased atomization because of sulphur may be the reason for a problem with the GDI engine and our (US) fuel. That's a plausible thing to have sulphur content cause...or the mucking up of the injectors (another plausible problem). I just don't know anything about it. I may hit the net one of these nights and see what I can find out about GDI's and fuels.

Anybody knowing something related, please share. Thx.

PS--that "overuse of headbang" reply had me laughing out loud (some other thread)

 

OK...a bit to chew on....still working on it, but a really good overview of fuels, additives, "octane" ratings, etc:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/section-4.html