How to save petrol in a Petrol Engine

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  • Thread starter Thread starter Ashraf Siddiqui
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Discussion Overview

The discussion revolves around the feasibility of using vaporized petrol in a petrol engine, similar to how gas engines operate. Participants explore the implications of injecting petrol vapors instead of liquid petrol, examining potential fuel savings and the mechanics involved in vaporization and combustion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose the idea of injecting petrol vapors into the engine using a vacuum pump to save fuel, questioning the practicality of running a car on vapors.
  • Others argue that petrol is already vaporized before combustion, either through injection into the intake or directly into the cylinders, and that this process occurs rapidly due to the fuel's volatility.
  • A participant raises concerns about the energy costs associated with using a vacuum pump and compressor, suggesting that it may not be an efficient method for fuel savings.
  • There is a discussion about the mechanics of fuel vaporization, with some participants noting that the injection occurs while the intake valve is open, and questioning whether the fuel vaporizes completely before the valve closes.
  • One participant mentions historical patents related to vapor carburetors, referencing the Pogue carburetor and its association with claims of high fuel efficiency.
  • Several participants discuss the importance of controlling the burning rate of fuel to avoid explosive combustion, emphasizing the need for a homogeneous mixture in the cylinder before ignition.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness and practicality of using vaporized petrol in engines. There is no consensus on whether this approach would lead to fuel savings or if it is feasible given the current understanding of engine mechanics.

Contextual Notes

Participants highlight various assumptions about the vaporization process, the role of fuel injection, and the efficiency of different engine designs. The discussion includes unresolved questions about the mechanics of vaporization and combustion timing.

Ashraf Siddiqui
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Like Gas Engine can we use Petrol Engine working as Gas Engine?
I mean instead injecting petrol directly into engine can we inject vapours of petrol
into engine using vacuum pump? Can we save petrol in this way without using stroke oil?
 
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The fuel is vaporized before it is burned - that's why it's sprayed into the intake (or, on newer designs, into the cylinders) as a very fine mist.
 
Ashraf Siddiqui said:
Like Gas Engine can we use Petrol Engine working as Gas Engine?
I mean instead injecting petrol directly into engine can we inject vapours of petrol
into engine using vacuum pump? Can we save petrol in this way without using stroke oil?
Your post is pretty incoherent, but are you saying you want to literally run a car on fumes? Have you calculated how fast you can get petrol to evaporate? How much power the vacuum pump and compressor takes? How much heat you have to absorb from the environment? My suspicion is this is a net loser because of the compressor/pump energy and loss of the liquid to gas expansion in the cylinder, but I'm not sure.

Also, by "stroke oil", do you mean motor oil? I'm not sure what that has to do with anything.
 
Russ - the fuel is vaporized prior to entering the cylinder in a lot of designs though, and even in direct injection engines, the injection occurs with the intake valve still open (except when running in stratified charge lean burn mode). The liquid to gas expansion doesn't help with cylinder pressure at all, though it is beneficial to help cool the intake charge.
 
cjl said:
Russ - the fuel is vaporized prior to entering the cylinder in a lot of designs though,
How is that accomplished? By means of a vacuum pump?
the injection occurs with the intake valve still open (except when running in stratified charge lean burn mode). The liquid to gas expansion doesn't help with cylinder pressure at all, though it is beneficial to help cool the intake charge.
Does the fuel that is injected as a liquid vaporize prior to the intake valve closing?
 
russ_watters said:
How is that accomplished? By means of a vacuum pump?
Nope, just by spraying the (fairly volatile) fuel in a very fine mist in the intake or cylinder, where it will vaporize nearly instantly due to the very large surface area and hot environment.
russ_watters said:
Does the fuel that is injected as a liquid vaporize prior to the intake valve closing?
I would tend to assume so, but I don't actually know for sure.
 
cjl said:
Nope, just by spraying the (fairly volatile) fuel in a very fine mist in the intake or cylinder, where it will vaporize nearly instantly due to the very large surface area and hot environment.
Ok, so I don't think that's what the OP was after.
I would tend to assume so, but I don't actually know for sure.
It seems I got the mechanism wrong. I was thinking a similar principle to water injection, but looking it up, I see that is also done before closing the inlet valve. The vaporization of the water (or gas) cools the inlet air, allowing more air into the engine. Two sides of the same coin (pressure ratio), but the improvement is in dropping the low end, not increasing the high end.
 
It won't really reduce the low end pressure - what it will do is increase air density due to cooling, which let's more oxygen in and therefore allows greater power production (plus it helps if the engine is thermally constrained).
 
There are several patents to Charles Pogue that were filed in the late 1920's through early 1930's for vapor carburetors. The Pogue carburetor is the basis for the mythical 100 MPG full size car. There have been consistent rumors from then through even today of this car being driven around until it was suppressed by your choice of the evil (car companies) (oil companies) (other villains). These rumors all ignore the fact that all patents are public information. You can read the patents by going to patents.google.com, and using search terms pogue carburetor.
 
  • #10
cjl said:
The fuel is vaporized before it is burned - that's why it's sprayed into the intake (or, on newer designs, into the cylinders) as a very fine mist.
I seem to remember that the burning rate needs to be controlled and not explosive (high octane fuel is used for this reason) so is it really necessary to vaporise all the fuel at the same time? Fuel injection is more effective than a conventional carburettor so there will presumably be some optimum combustion time.
The proportion of the total stroke that's taken up by combustion is quite small, I believe.
 
  • #11
Yes, you want the burning to occur along a single propagating flame front rather than occurring spontaneously throughout the cylinder, and you want it to not occur until the spark fires. That's a separate matter though - the fuel is all vaporized and the mixture in the cylinder is homogeneous before this ever happens. Fuel injection is more effective than a carburetor, but the reason isn't because of any difference in rate of vaporization or liquid fraction in the cylinder - it's more just about precisely controlling how much fuel makes it to each cylinder at any given time, and being able to control this across a wide range of operating conditions, RPM, and throttle settings. As for the combustion time, yes, it's generally assumed to be quite short, unlike a diesel engine where it takes a significant fraction of the power stroke.
 
  • #12
Ashraf Siddiqui said:
Like Gas Engine can we use Petrol Engine working as Gas Engine?
I just read this again. Even in a gas engine, there needs to be mixing of the gas and air.
 
Last edited:

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