Gasoline Diesel

[Fritz The Cat]

Did any manufacturer ever produce a gasoline powered diesel engine?

[Sluttypatton]

If it was gasoline powered, how would it be a diesel?

[GMMerlin]

The military has used a "multi-fuel" engine..but I dont know the specifics

[pod]

the multi fuel runs on any flamible liquid deiesel is recomended though

[pod]

mitsubishi has a "direct injection" gas engine

[2strokebloke]

When the Diesel engine was invented, many fuels were tried (a Diesel engine does not have to burn "Diesel" oil, which didn't even exist when the engine was invented) including Ammonia, Alcohol, and a mixture of Gasoline and Kerosene. Some years later the switch was made to a heavier oil (now known as diesel)

[454Casull]

Right. A diesel engine is any engine whose fuel is compression ignited. Remember, Diesel is somebody's last name.

[Sluttypatton]

I am aware of how diesel engines differ from gasoline engines, but I thought that the engine was named after the fuel it used, rather than the man who invented it. I thought it was called a diesel because it used diesel fuel. My bad.

[Neutrino]

well to get back to the original post....it would be hard since gasoline is supposed to resist detonation under presure...hence the octane number



but i guess if you would make an engine with high enough compresion and run it hot enough then and make sure it explodes when you need it too (and not early) I don't see why not


also i just remembered that some older gasoline cars in bad tune or after been run hard....would continue to run after you turned off the ignition i belive its called dieseling or somethink like that

[Sluttypatton]

Yep, dieseling or run-on. I would think that the problem with a compression ignited motor would be getting a controlled combustion, rather than detonation. I would think that you would need a fairly well designed head to ensure uniform combustion. With a spark plug, it ignites the fuel from the center out, but using compression ignition with gasoline, who knows where the fuel would ignite. Seems feasable, but I would think that you would need to design the head to ensure combustion from the center, out.

[Neutrino]

Originally Posted by Sluttypatton

Yep, dieseling or run-on. I would think that the problem with a compression ignited motor would be getting a controlled combustion, rather than detonation. I would think that you would need a fairly well designed head to ensure uniform combustion. With a spark plug, it ignites the fuel from the center out, but using compression ignition with gasoline, who knows where the fuel would ignite. Seems feasable, but I would think that you would need to design the head to ensure combustion from the center, out.

while we are talking about dieseling can anyone explain this to me? I was readind in last's month Road and Track(i think or one of my other magazines anyway) and they had an article about a HKS modded Evo8 and they mentioned this dieseling problem at shutdown.


Now my question is...how can you have a car diesel when it has electronic injectors...you cut the ignition you cut the fuel and without fuel the car cannot keep dieseling....

am i missing something....the only explanation i can think of is some electrical problem that will keep the injectors running even with the ignition off

[Moppie]

Most likely they had it running so rich that there was so much fuel left in the inlet and combustion chamber after being switched off from idle that it would run on for a second or two.

I used to have on old Triumph that would run on for nearly a minute, or as long as there was still fuel in the Carberter floats. I could actualy switch the ignition off and it would run at idle on 4-5 cylinders and just manage to drive up the drive way.
As you can imagine it was running very high compression, and sadly cracked a piston ring land as a result.

well to get back to the original post....it would be hard since gasoline is supposed to resist detonation under presure...hence the octane number

Desiel actualy has a higher octane rating than petrol, and the comppresion ratio needed to ignite it is much much higer, a minimum of about 14:1 I think is required, but most engines run around 20:1 and when Turbo'd can handle as much as 40lbs of boost, or more.

The problem with useing just compresion to ignite petrol is that it burns very quickly, and in a very uncontrolled way under high pressure. By useing a spark plug, or other form of ignition petrol can be burnt in a much more controlled environment at lower compression.
Diesel oil however requires a lot of heat to ignite, and will still maintian a slow and controlled burn even under very high pressure, hence why it can be safely ignited under high comppresion.

[SaabJohan]

SI = Spark Ignition
CI = Compression Ignition

Fuel requirements are diffrent in SI and CI engines. For SI engines we talk about octane and for CI we talk about cetane.

Octane is a rating how good the fuel can resist detonation (100 = resistance equal to iso-octane).
Cetane is a rating on how fast the fuel will self ignite.

Modern fast running diesels need a fuel with a high cetane rating, so the combustion will occur fast enough.

In general high octane means low cetane and the other way around, therefore one should not try to run a SI engine on diesel because it will knock and a CI engine will have problems running on diesel.

Post-ignition, like when an SI engine is running after it has been shut down is because of the temperature and pressure in the combustion chamber is high enough for the fuel to vaporise and self ignite. This problem is often caused by hot spots in the combustion chamber.

In an CI engine there is no flame front travelling from the ignition point to the cylinderwalls. In a CI engine the fuel is vaporised and ignited as fast as they come into contact with oxygen (reaction time depending on cetane), that's also the reason why they are using air excess.

The reaction time is one of the problems with Ci engines, this makes it impossible to use high revs, and therefore the power compared to engine size or weight gets low. Another problem is the high NOx caused by the air excess, or soot emissions when running closed to the SAFR.

The big advantage with CI is the high compression ratios that can be used, higher compression ratio means higher thermodynamic efficiency. For cars this means a efficiency of above 40% instead of above 30% but for large ship engines it can mean a efficiency of up to 60% or so.

A detonation or a knock in an SI engine doesn't occur before but after the spark plug has ignited the air/fuel mix, this is because the pressure and temperature are increasing very much at this point and that we have a flame front (unburned endgases).

There is also a engine type which can be said to be a mix of an CI and SI engine, the HCCI engine (Homogeneous-Charge Compression-Ignition).
In a HCCI engine the fuel is mixed with the air in a normal SI engine but the fuel is ignited with compression pressure and temperature. This is supposed to ignite all the fuel at once, but it will also allow a high compression ratio. If we can get the combustion to happend at no piston movement it is possible to increase efficiency. Unlike an CI engine there is no fuel injected during combustion. This type of combustion should also make it possible to use higher revs. Ignition timing is done by regulate inlet temperature, compression ratio and recirculation of exhaust gases.

[Moppie]

Awsome post SaabJohan

[AnArKey]

Thought I'd bring this one back up, as I have been doing lots of investigation into this.

I'm looking to make a gasoline spark ignited engine into a compression ignited (diesel), throttleless engine. Fuel is still undetermined. Gasoline, perhaps, leaning toward propane.

Some interesting articles:

http://qube.mech.nitech.ac.jp/~lab/h&l-octane.html

http://qube.mech.nitech.ac.jp/~lab/formaldehyde.html

You can see any time you have compression ignition, where the whole charge just goes BOOM, and *very important* getting it near TDC, it's much more efficient than a spark ignition. The trick is, getting it to ignite at just the right spot, ie TDC.

This is NOT like knock, which actually starts AFTER ignition, and you have two forces smacking each other, spark induced combustion, and right after that autoignition forces that are "pushed over the edge" by the increase of pressure and temperature caused by the onset of normal combustion elsewhere in the chamber. They cause waves of pressure to bounce around and that is what makes the sound. This then elevates temperature, which in turn can heat up the chamber enough after x number of cycles, to turn into full blown preignition, which is now REAL bad for the motor, as it's happening during the up stroke. The same force if happening ATDC, would be a good thing, and more efficient.

The ability to run throttleless, another typical feature of common disel engines, is related to being able to reduce power production by running super lean total mixtures in the cylinders. No throttle choking the air down, it's atmospheric pressure (or more when a turbo is going) in the manifold all the time. It's like a throttled car at WOT. Except, you run the fuel:air ratio real lean. Sometimes as little as 20% of the stoich mixture, to get 20% power, instead of choking the engine down to x " of vacuum to keep it down. How can this be possible? Autoignition.

Autoignition, is the temp at which point the molecules of a fuel will spontanesouly react with any oxygen present. They all at once, go ZAP and combust with nearby oxygen.

The lean limits of fuels, the lowest concentration that will support a continual burn is rated by having a single ignition point, and seeing if the air:fuel mix will burn through. The spark itself creates a small point where the mix is heated over it's autoignition temperature, and burning occurs right there. It spreads outwards from that point, delivering heat energy as it advances.

The lean limit for propane, is about 2% by volume. Any lower than the lean limit and there won't be enough heat to keep propagating the reaction, to keep advancing a front of heat that is over the autoignition temperature of the rest of the mix. This is also why when you get near the lean limit using spark ignition, you start to lose power faster than the rate of fuel would dictate, and you start seeing HC emmisions come up real fast. When the flame front nears the corners of the chamber, it gets cooled enough by the combustion chamber surfaces, to go out. Poof. Go leaner and the only combustion you will have will occur in the tiny spot at the spark, and many spread a mm from there, but after that the air:fuel mix won't get hot enough to keep going. Total misfire, engine shuts off.

Now let's think about what happens, if the temperature during the compression stoke, it just about perfectly balanced with the octane of the fuel, and the temperature rise in the cylinder during compression, that the autoignition temperature is reached in the entire cylinder right before or at TDC. No need to start the reaction, it all goes at once. And because there is no need to create a moving wave of heat to keep everything going, and correct me if I'm wrong on this point, there isn't really much of a lean limit. Even with 20% of stoich mixture, the fuel atoms have enough energy to then start combustion, all at once, all over the chamber.

I'm pretty sure this is why diesels can have the same static octane rating of fuel, and operate from 60:1 down to 12:1 ratios of diesel oil:air, and still maintain a ignition point that is about right. There would be a slight shift due to extra charge cooling from more diesel at richer mxitures, but not too much. I think pressure from the turbo might change it a little, but obviously not too much, or else diesels wouldn't be fine at 40psi all day long like they are. Temperature however HAS to effect things, a hotter intake temp will equal sooner ignition. Luckily they are generally well intercooled as well, so that reduces that effect.

My hope is to be able to do basically the same thing, with propane and some kind of octane agent. If I just spray propane into 8.5:1 compression, it won't do a thing. Peak compression temperature is way under propanes autoignition point of 850-950F. I'm really wondering about the formaldehyde gas experiment they did, looks like it REALLY changed the autoignition of CNG, which is even higher octane than propane. Just wondering if the same thing would work on propane, and if by using more formaldehyde than they did, get it to autoignite on a 8.5:1 compression. The backup would be just like the first experiment, I'd have gaseous propane injection, and hepthane going through the injectors, using hepthane concentration to lower octane, and induce controlled autoignition.

DME may be the most promising, being a nice gas like propane, but with a low autoignition temp like diesel. Need to do a lot of math on this stuff.