--- When will gas self ignite?? --- Temp?

[dremd]

DATA! YES!


I know this is against the spirit of the discussion, but why not just go Diesel? You can run lots more compression then!

[basslover911]

So why cant diesels run gasoline instead?!

I mean they can start in colder climates much better because of the lower flash point of gasoline, and they can burn and work much cooler and waste less energy in the form of heat... ??

Sure, they can just drop the compression a bit I suppose, but wouldnt gas be better for lets say colder climates and just not running so hot...?

[CobraBall]

Auto-ignition of gasoline occurs at 280C/536F. <http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html>

The starter motor and batteries for an engine with a 100:1 compression ratio would be HUGE.

A top fuel dragster/funny car engine estimated H.P. is somewhere above 8000. The stresses on pistons, connecting rods, crankshaft, bearings, cylinder walls limit the life of the engine at wide open throttle to no more than 5-6 seconds.

IMHO a gasoline engine with 100:1 compression ratio would last somewhere between a few minutes and one hour if you could get it started.

[basslover911]

An let me get this straight, would the engine need to run hotter or cooler at 100:1 compression to ignite whatever fuel it is you are using?

[some_other_dave]

Also note that self-ignition would happen when the temperature in the chamber got high enough, which isn't necessarily when you want it to happen. Spark-ignition happens before TDC, which (absent any combustion) would be the point of highest pressure. You do that so the mixture has time to burn while the piston is still in a position in its stroke to turn that into motive power.

Frankly, I'm not sure exactly how older diesels deal with that. I know that a lot of the more modern ones inject directly into the combustion chamber, and that is how they regulate when ignition starts.

Gasoline injected into a diesel motor might burn too quickly???

-soD

[bgd73]

for a fuel that disspiates easily in air? Compression ratios are kept low, demanding a timed spark, to get the most out of it. IE a 9:1 dump truck with a gas engine has more towing ability than a 11:1 gas engine in the same truck. the fuel is way to fast to let it smack around like an inline four does with it...or inline 6.You would get the compression, and then need 35000 rpms to make up for the shear speed of loss, like a bad engine that doesn't want to run efficently...

[PhysicsWasMyGame]

Originally Posted by basslover911

Hey guys, what is the equation that link at what pressure and temperature gasoline self ignites?

Like, lets say in diesel engines at 25:1 compression; what temperature must the air/fuel be to self ignite?

Also, why couldn't you just do 100:1 compression and be able to self ignite gas at much lower temperatures??



Thanks!

The ideal gas Law PV = nRT. Where does this come from? Robert Boyle found PV = a constant. That is, the product of the pressure of a gas times the volume of a gas is a constant for a given sample of gas. In Boyle's experiments the Temperature (T) did not change, nor did the number of moles (n) of gas present.

[RustyLugNut]

is what you need to look for.

Gasoline is a variable mixture so the 280 degC auto-ignition temperature (AIT) is variable. The AIT must be tested for each gasoline mixture and plotted.

In general, the higher the pressure, the lower the AIT.

The higher the mixture turbulence the lower the AIT.

This is why a homogeneous gasoline mixture is compression limited. It is also the principle used in Homogeneous Charge Compression Ignition (HCCI) engines. HCCI engines will vary fuel lamda from stoichiometric to lean to vary the AIT. Mixture temperature is also a variable. So is mixture turbulence.

Again, duel to the complexity of gasoline mixtures, there is no simple equation. Testing and plotting is the usual procedure. Powerful computing is making combustion modelling a viable tool, however.

[Shaneajanderson]

Zombie Thread.

this thread is 11 years old. I see though that no one really stated the obvious. Gasoline is used in lower compression engines because it ignites at a lower temperature than diesel. Anyone who's had a high-rpm detonation bust a crankshaft in two knows this first hand.

[RustyLugNut]

Originally Posted by Shaneajanderson

Zombie Thread.

this thread is 11 years old. I see though that no one really stated the obvious. Gasoline is used in lower compression engines because it ignites at a lower temperature than diesel. Anyone who's had a high-rpm detonation bust a crankshaft in two knows this first hand.

In the 11 years since the first posting a LOT has been learned . Your "obvious" information is hardly the answer to the original question. Work by forum members such as Ivey and pgfpro show manipulation of variables can change combustion in a spark ignited gasoline engine. I relish the re-visitation of the subject.

I've run gasoline in a spark ignited engine with 20:1 compression ratio by messing with the "obvious". pgfpro has gone even higher with dynamic ratios exceeding 30:1. How? By running much leaner combustion mixtures than even Honda's Lean-burn engines. Go look up his work on various threads. It's deep reading if you know a thing or two about combustion thermodynamics and thermo-chemistry. Its simply outright fun if you don't.