Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

EVAPORATE fuel into FUMES rather than Fuel Injection?

Rather than injecting a mist of very fine fuel particulates, would it not be.tter to EVAPORATE the fuel into combustible fumes at the IDEAL fuel to air ratio
and blow the fumes into the cylinder?

Thank you.

The fuel injectors spray the fuel as a very fine mist. This, combined with the vacuum, turbulence, and heat pretty well evaporates the fuel on the trip through the intake valve into the cylinder.

Yes, the fuel vaporizes, it’s the vapor that burns, not liquid droplets. The fuel injection system/computer/sensors do keep it at the ideal fuel air ratio for the given set of conditions.

Fuel vapor IS a mist of fine liquid droplets. Evaporation is fumes, which are for lack of a better description molecules of hydrocarbon, that are no heavier than the surrouding air. Only surface molecules evaporate, and only when they contain enough heat energy to break their bond with the fluid molecules below. Cooled, with heat energy removed, the molecules again bond to their own and again become liquid.

You may have heard the term “relative humidity”. Air at a given temperature will only hold a given amount of fluid. If the temperature is lowered, the air will deposit its humidity. In the air it deposits it on particulates and it falls as rain. On a cold window it deposits as condensation. But the bottom line is that the air won’t hold the vapor if it cools.

The evaporated gas would not be sufficient in volume in the air to combust in an efficient manner in the chamber. It would disappear instantly, creating little heat in the process and little expansion. Little power.

Spraying the fuel in a very fine mist enables the system to maintain a vapor with sufficient fuel in it to provide the necessary power, to make the most of the power stroke. Turbulance is also designed into the flow into the chamber in order to keep the fuel droplets suspended.

As the others have pointed out in a diplomatic way, your technical knowledge regarding fuel injection (and some other engine-related topics) is…let’s just say…incomplete.
Are you sure that you have “rebuilt engines”, as you claimed in one of your earlier posts?


^ Haha. Yes. (Rebuilding engines does not require knowledge in combustion chemistry.)

FUMES combust better than tiny droplets which must outgas (evaporate) into fumes to combust.
Perhaps 100% fumes would burn too fast whereas tiny mist droplets must outgas into fumes. Presumably that takes longer for the outside surface of each mist droplet to outgas while the already existing fumes surrounding it combust and then the center of the mist droplet then outgasses and its newly-formed fumes combust.

So the stretched-out combustion would not be as much a shock but more of a PUSH measured in microseconds.

To repeat in summary form: evaporative fumes at ambient temperatures do not get the hydrocarbons into the air in sufficient volume to provide the power necessary to operate a car.

Droplets must evaporate into fumes to combust if they’re on the ground in a puddle, or in an unpressurized container. Under pressure and heat, the surface molecules of an HC droplet will combust. The heat energy will cause the hydrogen and carbon stoms on the surface molecules to break free, break apart, and bond to the oxygen. The heat energy from the spark starts the process, and the heat energy released by the seperating hydrogen and carbon atoms creates far more heat even…and continues the chain reation.

And as doubleclutch stated, the cylinder turbulance and heat essentially vaporize the fuel anyway.

Robert, I encourage you to set up experiments to prove your idea. Should you succeed, you’ll have invented a more efficient engine. I, for one, support you in this quest.

Mountainbike is quite correct as to the combustion physics of fuel injected gasoline.

However, Robert, do some Google research on propane conversion of gasoline engines, and you’ll find that the wheel has already been invented…I believe that in the case of propane conversions of carbureted engines, the propane enters the intake in vapor form, because propane requires pressure (at room temp) to keep it liquefied, and once it’s freed from the pressure tank it vaporizes itself…just like in your gas grill.

The first carburaters or what ever you could call them,worked sort of like this-wasnt very good or efficient.The big breakthrough in carburaters came when Karl Benz noticed his daughters perfume atomizer ,atomized or made a mist with a vacuum siphon(her name was Mercedes-ring any bells?) thus he got the idea for the carb as we know it, worked much better then the hot fumes-Kevin

Understood. The normal evaporation process would not be fast enough to providenough fumes.
It would need to be speeded up.
Lower pressure heated air would speed outgassing!
I could make this into a wonderfully complicated and difficult process vulnerable to problems!

"...I encourage you to set up experiments to prove your idea."
Ha! You just like explosions!

Congratulations !
You have just rediscovered the carburetor of the 1890s .

Yes , that design was used but was obviously suppressed by Big Oil because of it’s superior economy .

So that’s what happened to the 1890s carb! :wink:

Gasoline and propane have very similar properties, except that propane has a much higher “vapor pressure”…Gasoline will evaporate into fumes if left in an open container for any length of time…In an ICE, by the time the spark plug fires, there is NO liquid “vapor” in the combustion chamber. (except during cold starts). The gasoline will have completely evaporated into “fumes”, the same state that propane is in when the spark plug fires…Engine heat and the heat of compression ensure this…

Caddyman, not so. Gasoline and diesel engines are actually burning extremely tiny fuel droplets, not vapor. If you could see high speed video of the internal combustion process, at high magnification you’d see millions of tiny swirling balls of fire. The injection/compression/spark process happens so quickly that there’s not enough time for the droplets to completely vaporize before ignition.

Back in the day, intake manifolds were intentionally heated to COMPLETELY evaporate the fuel spray delivered by the crude carburetors…By the time the spark-plug fired, there were no liquid droplets left in the combustion chamber. A perfect 14 to 1 air/fuel ratio could be achieved even then…

Now, with the technology involved with today’s direct injection engines, just when is the fuel charge injected? How many degrees of crank rotation before ignition? The real magic here is that it somehow allows much higher compression than would otherwise be possible with 87 octane fuel…But we are drawing a VERY fine line between “vapor” and “fumes”…

I’m struggling with the difference between “tiny droplets” and “vapor.”

Vapor behaves like a gas perhaps?-Kevin

Vapor is a gas. For a better explanation.

A Flammable liquid does not burn. The vapor at its surface burns. Fuel droplets burn the same way a puddle does, from the surface.

Two reasons not to vaporize gasoline before it gets to the cylinder.

The ideal, stoichiometric, air-fuel mixture for gasoline is about 14.7 to1 by mass. (Not volume) Fill a container with 14.7 lbs of air, about 192.5 cubic feet. Add to that 1 lb of liquid gasoline, about .022 cubic feet. Distribute (atomize) the gasoline throughout the container and you have 192.522 cubic feet of “perfect” air fuel mixture. Gasoline expands about 162 times when it changes from liquid to vapor. .022 cubic feet of liquid gasoline becomes 3.5 cubic feet of vapor. If the gasoline is completely vaporized when mixed with the air you will have 196 cubit feet of air-fuel mixture. Assume the cylinder only holds 192.5 cubic feet. You have lost the ability to use 3.5 cubic feet (1.8%) of the mixture. Essentially you can get more air-fuel mixture into the cylinder if the gasoline is in liquid (atomized) form.

The second reason not to vaporize gasoline before it gets to the cylinder. It requires heat. You can preheat the fuel or preheat the air either way the mixture is less dense. It’s better to use the heat in the cylinder. Carburetors didn’t atomize fuel very well. Droplet sizes were large and inconsistent. You either preheated or ended up with unburned fuel out the tailpipe. Modern fuel injectors do a much better job.

^ Heathe gasoline and air. You have abundant waste heat available.