Complete combustion

[Guest gregp1962]

Years ago, there was a general belief that most engines fell way short of burning all of the liquid fuel. The reason given was that the droplets of fuel are too large to allow the entire droplet to completly burn. We heard claims that, if we could fully vaporize the liquid fuel, we could have 70 to 200 MPG cars. Obviously, these were exagerated claims.

But, I'm wondering just how much lost energy there typically is in most engines due to larger than optimal droplet size.

Is anyone aware of any recent studies on this subject?

[ecoli]

I doubt this is true. This is becasue when fuel burns, it is not the liquid that is burning. A spark causes the fumes to combust, generating heat that causes the rest of the liquid fuel to vaporize, then that fuel combustes. It is not actually the fuel droplet that is being burned.

[Guest gregp1962]

Yes, the fuel can burn only if it comes in contact with oxygen. But, it is also accepted that fuel injectors and carburetors create small droplets. They never fully vaporize the liquid. So, the only part of the fuel droplet that can combust is the outside part that actually comes in contact with oxygen. What I'm trying to find out is, "Is there much left of the center of the droplets in a typical engine? Would fully vaporizing part of the fuel without increasing intake and compression and compression stroke temperatures be a beneficial thing? Is anyone aware of any studies of this subject?

[5614]

well surface area always does play a vital role in all chemical reactions... i would have thought that car manufacturers were aware of this and have designed their cars accordingly although it'd be hard for me to prove that.

[Gilded]

It's a common (also illegal) way to see how much of the unburned fuel comes out of the exhaust pipe by lighting the exhaust gas. If it's a minimal amount, no flames appear but when you get 5 meter flames from the pipe you know you got something wrong with your intake. )

 

Of course, as 5614 said, gaseous fuel is almost always better than liquid. But hey, a tripropellant of liquid fluorine, liquid lithium and liquid hydrogen will get you far.

(The best rocket propellant ever tested if judging by specific impulse - http://en.wikipedia.org/wiki/Rocket_fuel)

[5614]

now we all know about spark gaps... but hey if a spark plug happened to slip down your exhaust it'd be a good experiment.

 

if i owned a car id do it!

 

come on, a spark caused by two wires over the end of the exhaust with a little gap between them producing a spark right at the exit of the exhaust - to kill the flame (if there is one) all ya have to do is ease off the fuel and your safe.

 

but one sec!!!!!!!!! wouldnt the flame kinda spread up the exhaust?

[Guest gregp1962]

ok, back to the topic at hand. Is anyone aware exactly how much unburned fuel is left on modern EFI cars? How much is droplet size still an issue?

[5614]

no clearly no one does know off by heart so we came to the conclusion that you must make an experiment to measure it.

 

lighting it up is an inaccurate way of measuring an approximate amount.

 

my last most was merely a human safety part of the experiment we decided would give us a rough estimate as an answer for the original question.

[YT2095]

Yes, the fuel can burn only if it comes in contact with oxygen. But, it is also accepted that fuel injectors and carburetors create small droplets. They never fully vaporize the liquid. So, the only part of the fuel droplet that can combust is the outside part that actually comes in contact with oxygen. What I'm trying to find out is, "Is there much left of the center of the droplets in a typical engine? Would fully vaporizing part of the fuel without increasing intake and compression and compression stroke temperatures be a beneficial thing? Is anyone aware of any studies of this subject?

most cars are "lean Burn" now, the O2 is in excess by a small amount and at the temps involved, anything more than a Vapor would be atomised anyway. the days of brown/black residue on spark plugs are all but gone now, infact you`re more likely to see the White residue typical of Lean Burn

[Guest gregp1962]

YT2095, You could be right. Our cars are much more effecient than they were years ago. EFI is a good thing.

 

However I hadn't heard that we had reached the point where almost all fuel is being combusted in most cars. I was under the impression that there was still a considerable amount of unburned fuel and that droplet size is still an issue.

 

Does anyone know where information is available on this subject?