What if diesel got mixed into 93 octane

[98LS-WON]

The gas station on base screwed up and mixed some diesel in w/ their premium. A lot of people have been having their cars run like #@$%! and get real hard to start. I have't had any problems...yet. I drained my tank, ran a bottle of Techron through it, changed the fuel filter and seafoamed it to get any residual #@$%! out of the engine. Anything else you can think of that needs to be checked.

Anyone know if diesel fuel will completely combust in a gas engine or if it will leave a bunch of carbon on the pistons/heads. I might seafoam it again to be safe.

What problems could come from this 10000 miles down the road that won't show up now?

 

[Pablo]

If you get it out of the fuel system there should be no future problems. But yeah diesel will effectively lower the octane level - at LOT. No start, run like khrap. But don't run it as the pre-detonation can cause real damage.

 

[SargeGTO]

Sounds like you did all you can do. I would not make any WOT runs for a tankful or two. Pre Ignition maybe a small factor...nevertheless a deadly one....

 

[Drew99GT]

What if gasoline got mixed in with diesel? That would probably blow the cylinder head off a Cummins!

 

[Max_Wander]

I once got up to 40% diesel in a tank. 2.5L V6 with 10:1 compression. All that really happened was the exhaust stunk, and it blew black smoke at wide open throttle, other than that, it ran and started fine. I ran it out without incident, I just hope my cats not coated in particulate. YMMV!

 

[Jon]

I don't understand why you say that diesel *lowers* the octane. Octane = resistance to knock = resistance to preignition. In a gas engine, diesel isn't going to get anywhere near the kind of pressures necessary to pre-ignite, consequently it can only ignite as a result of the ignition process begun by the spark plug and the gasoline. Therefore, diesel must have a /higher/ octane rating.

Yes? No?
Where did I go wrong?

 

[rpn453]

I was also under the impression that diesel requires more temperature/pressure to ignite.

Based on that, I'd think that some of the emissions control components are at risk of damage due to the incomplete combustion.

 

[Pablo]

I think you went wrong on assuming (perhaps) the only cause of preignition or pinging is pressure.

You are correct - octane rating in gasoline is the resistance to ping/knock. Adding oil or diesel fuel to gasoline causes the gasoline have strange/incomplete combustion which in and of itself is a problem, it creates enough hot spots to preignite or cause premature ignition as the air/fuel enters the combustion chamber. Lastly - you may not think 12:1 is enough pressure to cause ignition, but it happens.

 

[Jon]

Sorry, "out of band" I recalled something a very smart person once told me about this issue - it's that the diesel (or oil) essentially creates a *lean* condition because less (percentile-wise) of the volume is *burnable* fuel and what remains (the diesel/oil) doesn't burn the same.

Now, in my old NightHawk 550 engine a little diesel didn't seem to make much difference except it wouldn't rev up ver well, but it ran otherwise just fine.

Pablo - sorry to hear about your neck.

 

[Pablo]

That's the same principle as too much oil in 2-stroke mix.

Another viewpoint is a turbocharged gas engine that is blowing oil into the (compressed) air side - engine will ping and eventually blow.

 

[mrsilv04]

I ran some pure diesel through a Kawasaki 2 cylinder liquid cooled John Deere garden tractor. Ran just fine until the engine started sucking in the diesel. Smoked like a mosquito fogger, lost about half of its power, and the engine kept "running on" every time I tried to shut it down.

Siphoned everything out of the tank, changed the fuel filter, and the engine was fine.

Come to find out, Dad had just finished demo'ing a new John Deere front mount mower (F935) that was diesel, and had a few gallons of diesel for the demo unit in a RED 5 gallon can.

 

[Quattro Pete]

Quote:

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What if gasoline got mixed in with diesel?

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Depends on quantities. In very cold climates people actually mix in a little bit of gasoline with their diesels. Apparently it helps to get the engine going and prevents fuel system from freezing on very cold days.

 

[PT1]

You are fine because you drained the tank and used techron. I doubt you will notice anything. If you want to be sure run some 91 octane & another dose of techron. Then change your oil.

 

[ekpolk]

Quote:

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I don't understand why you say that diesel *lowers* the octane. Octane = resistance to knock = resistance to preignition. In a gas engine, diesel isn't going to get anywhere near the kind of pressures necessary to pre-ignite, consequently it can only ignite as a result of the ignition process begun by the spark plug and the gasoline. Therefore, diesel must have a /higher/ octane rating.

Yes? No?
Where did I go wrong?

---

Jon:

One key thing I suspect you're overlooking: pre-ignition and detonation are two different phenomena. The latter (detonation) is an irregular, but basically correctly timed, burning of the compressed fuel-air mixture in the cylinder. Rather than burning smoothly and progressively (albeit in microseconds), the fuel explodes instead, sending out a shock wave that can be heard as "ping" and if strong and persistent enough, can cause engine damage.

By contrast, pre-ignition is a different and much more dangerous animal. It involves the mixture lighting off way before it's supposed to, early in the compression stroke. This leaves the engine attempting to compress a mass of gas that's already wildly expanding and very, very hot. Thankfully, I've never experienced this. I understand that the process is actually very quiet and hard to detect -- until either a con rod snaps or the process just blows the head clean off your engine (OK, maybe that's overstating it a tad...). In short, if you have true, sustained pre-ignition, that is a condition that is not consistent with continued engine life, and you're going to find out about it quickly and decisively.

Diesel in your gas will lower octane, and probably just cause bad detonation (and maybe in some cases some true pre-ignition). Bad either way, but as the reports here indicate, easily survivable in many instances.

 

[onion]

Now that the tank is flushed, I'd just drive it easy until that tank is gone... then I'd fill it up with 93 octane and forget that it ever happened.

I'm gonna agree with Pablo, here. I've dealt with diesel-in-gas and gas-in diesel a few times. When a little diesel gets mixed into gas, it'll make the engine just generally run bad... it'll have low power, run rough, smoke like a tractor, etc- but the most noticeable thing is that it'll ping badly- and that's why I'd reccomend that you drive the car easy until this tank is emptied out. Severe pinging can blow a head gasket real quick.

When gas gets mixed into diesel... it just depends on the amount. I've seen farmers put a quart of gasoline into their 50 gallon tank of diesel- it makes the engine start easy in cold weather with no other apparent effects. Probably helps compensate for that two gallons of used motor oil that they also dumped in. Now, when LOTS of gasoline gets pumped into the tank... things get ugly. I worked on a school bus years ago with a Cummins B5.9- just like in the early 90's dodge pickups. The injection pump and nozzles were trashed... and the tops of the pistons were melted. I wish I could've heard it run.

 

[Shannow]

The diesel/petrol confusion is primarily because otto cycle engines typically run with air and fuel pre-mixed before the compression stroke, while diesel engines have the compression stroke take place with air only and then introduce fuel near TDC.

When an otto cycle starts the compression stroke, the fuel/air is progressively (and quickly) compressed, raising it's temperature.

A fuel with a low octane can ignite on it's own, just due to the temperature created during compression. Higher octane fuel will survive this, allowing combustion to start when the sparkplug dictates.

Hot-spots, due to carbon, or glowing artifacts like carbon or a too hot spark plug electrode can start pre-ignition, or the commencement of burning before the scheduled spark (run on is a bit of this also). Octane may or may not help this.

"detonation", or end gas auto ignition occurs when the flame starts to increase the pressure in the chamber, to the point that at a remote part of the chamber, the gas autoignites and you end up with an opposing flame front heading back at the original front. This is typically signified by pinging or knocking.

Better engine design (shorter flame path, heron heads etc), better cooling, more revs (ever heard engines knocking away from traffic lights) lower chamber deposits, or higher octane help alleviate this.

If you want, chick a litre of gear oil in a half tank of fuel, and you can see this for yourself.

Diesels have another set of problems.

The fuel is injected into a high pressure, high temperature environment.

The fuel has firstly to start mixing with the air, to get into the combustible range. When a combustible mixture is reached, it has to ignite by itself.

If the fuel has too low a cetane value (opposite of Octane) a whole load of it evaporates before it finally fires, leading to nasty knock. Can be fixed by improved chamber turbulence, purposeful hot spots, better cetane (lower octane) fuel, improved atomisation (some modern diesels have a dozen separate injection events in a single cycle to control the evaporation and combustion of fuel.

So diesel ignites easier, and petrol harder...In their own operating environments.

As to the original topic, there should be little damage, as long as you don't run with rampant detonation. Preferably drain the tank, otherwise top up with premium as soon as you can.