Gas in Diesel - help!!

[jwcolby54]

Originally Posted by mrm

Apologies for being blunt, but the above is pure misinformation..

There is no such thing as knock in Diesel engines. Knock is premature (before spark is fired) combustion in spark ignition engines, where fuel-air mixture is already present in cylinders. Diesels compress air and then inject fuel at a precisely calculated moment (expressed in degrees before TDC). In fact an important property of Diesel fuel is its cetane number which indicates the combustion speed of a given batch of fuel. The higher the number the faster the fuel will 'explode' when injected and the better for compression ignition (Diesel) engines.

For reference: https://en.wikipedia.org/wiki/Cetane_number

It is unlikely to cause damage to the block with diesel-gas mixture, in fact European car manufacturers for a long time officially published advice to drivers to 'winterize' their summer blend of Diesel fuel with up to 30% of gasoline, should they be caught by freezing temperatures with a tank of summer Diesel blend..

What is likely is damage to injection pump and injectors, because of poor lubrication properties of gas-Diesel mixture. The OP may be in for a new/rebuild injection pump and/or injectors.

I drive a diesel tractor and they have knock sensors which if sensed drop the power to 85%.

In the 80s I worked on a knock sensor project for big diesels for locomotives. This system would alter injection timing up to the point of knock then back it off just a hair. This increased efficiency of the engine. Knocking is caused by injecting the fuel too soon.

[FionaJC]

Originally Posted by hamburking

Aside from colour and smell, is there a quick test that anyone could do to tell the difference between diesel and gasoline?

We regularly buy petrol (gas) and diesel in 20 litre jerricans. We fill up a car and two cans so we get fuel at £1.20 less 8p ($1.41 a litre) We have 12 of them. To make sure I get it right, as we have two diesel cars and three petrol I test it.
1. I smell it
2. I swoosh it around lightly, Gas flops around more than diesel which is like treacle.
3. I put a screwdriver in and put a drop on the top of the can. Diesel flows with gravity, gas does a starburst
4. I look at the colour Gas is clearer, diesel has a colour / glow
5. If I still cant tell I rub a drop between two fingers Gas doesn't lubricate my fingers.

6. I try to tie on labels to the cans with a date but I still go through the above before I use it. Usually the smell, liquidity and drip test are enough.

[wyb2]

Originally Posted by jwcolby54

I drive a diesel tractor and they have knock sensors which if sensed drop the power to 85%.

In the 80s I worked on a knock sensor project for big diesels for locomotives. This system would alter injection timing up to the point of knock then back it off just a hair. This increased efficiency of the engine. Knocking is caused by injecting the fuel too soon.

I was also confused with everyone talking about knock in a diesel. I think the key here is the system was altering injection timing, so knock is only possible if the injection starts before TDC. If an engine with non-adjustable injection timing begins it's injection at or after TDC, knock is impossible regardless of fuel. Not sure how to establish the injection timing on a given engine.

Without knock, possible internal damage should be limited to too-hot combustion and carbon fouling from poor combustion.

Edit: I guess I glossed over your last sentence, so basically yeah, pointless post.

[Cadence]

Originally Posted by jwcolby54

I drive a diesel tractor and they have knock sensors which if sensed drop the power to 85%.

In the 80s I worked on a knock sensor project for big diesels for locomotives. This system would alter injection timing up to the point of knock then back it off just a hair. This increased efficiency of the engine. Knocking is caused by injecting the fuel too soon.

They change injector timing for load and efficiency. I had one with two settings my brother had one with three. Both vehicles. I have heard of truckers mixing some gas in when in extremely cold climates to lower the flash point. I'm not sure it is a good idea under normal circumstances or an engine that isn't a huge chunk of iron made for extreme loads and conditions. I had a neighbor ask me if I would look at her Volvo. She had let her young daughter use it for the first time. The kid was going to say thanks by putting gas in. A rod was sticking out of the block. Hated saying your engine is dead. I doubt the 15 yr. old kid put much in.

[Stu Jackson]

Originally Posted by a64pilot

I have a bad feeling that since you were handed the nozzle and you put the fuel into the boat it's on you even though you asked repeatedly. This is all hear say, I assume you have nothing in writing..................................
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Seems now that the boat owner always pumps the fuel, never seen Marina staff do it anymore, there must be a reason for that.

Yes, I have recently seen that, too. I always did my own fueling when I used to live in California, and never thought about it on my way up the coast last summer. It was just something I did, because unlike "back East" we didn't have "boat boys" at the pumps.

When I first fueled up here in BC, the attendant actually said: "I am not allowed to put the fuel in your boat, you must do it yourself."

So, before I opened the nozzle, I followed the hose back to the pump and made sure it was diesel.

Sorry to hear about your troubles, but diesel and gasoline SMELL completely different, don't they? Not sure how this relates to your "newbie-ness," but being in a hurry never helps anything.

Good luck with your issue.

[Fence Man]

That's worse than ordering un-sweet tea, and having your first drink of Coke in 10 years delivered to the table. Good luck with with your repairs.

[Mauro47]

Gas in diesel 50:50?
The major problem I can see, besides the explosion danger is that the two fuels burn at a different rate. The diesel detonates much faster than the gasoline burns. In turns if a mixture of the two fuels is injected in a diesel engine pretty close to the tdc, the diesel oil will combust but the gasoline will cause a longer combustion time, continuing in the exaust valves and in the exaust manifold, increasing the exaust temperature and damaging the valves and seats. So, with any luck, besides for a good inspection, a valve job is all is required.

[wyb2]

Originally Posted by Mauro47

Gas in diesel 50:50?
The major problem I can see, besides the explosion danger is that the two fuels burn at a different rate. The diesel detonates much faster than the gasoline burns. In turns if a mixture of the two fuels is injected in a diesel engine pretty close to the tdc, the diesel oil will combust but the gasoline will cause a longer combustion time, continuing in the exaust valves and in the exaust manifold, increasing the exaust temperature and damaging the valves and seats. So, with any luck, besides for a good inspection, a valve job is all is required.

If this is true how come gas engines can do 6000-7000 rpm? If gas burned so slowly that it continued into the exhaust of a diesel at 2500 rpm, how could it work at all at 6000 rpm?

[dlymn]

diesel "explodes" under very high pressure. The finely atomised gas behaves like an explosive and detonates uniformly throughout the entire combustion chamber at the same moment. Detonation is caused because the vapour is heate uniformly as a result of compression. Petrol is ignited by a spark and starts burning from the spark plug. the burn continues from a few degrees before tdc to a few degress before bdc. In Diesel motor, petrol might continue burning after bdc and so might be exhausted while it's still burning.
We all love to see race cars flaming from their exhaust pipes. That's a result of too much fuel in the mixture and combustion continuing in the exhaust. The faster the engine goes the more unburnt vapour in the exhaust. Essentially. diesels explode and petrol burns.

[wyb2]

Right, flames out the exhaust because of a too rich mixture, leaving unburnt fuel to combust in the exhaust system. Not because the gas doesn't have enough time to burn. Besides, at diesel compression ratios, gas does detonate rather than burn.

[a64pilot]

Good Lord I am not sure where to begin.
First a running warm Diesel engine the fuel begins to burn the moment is leaves the injector, you cannot get detonation in a Diesel engine if it is warm, possibly on a cold motor, regardless of fuel type.
Second the definition of detonation is when a fuel air mixtures suddenly combusts, all at once. This is not what can happen in a Diesel because the fuel and air are not mixed, the fuel is sprayed in and the burn begins immediately, it is not sprayed in, mixed with the air and waiting on combustion heat to set it off, if it worked that way, you could not change timing on a Diesel, and you can in fact change timing.
A spark ignition engine can detonate as the fuel is mixed with the air, both are compressed and if the compression heat is high enough, the whole mix can simultaneously burn, explode if you will, high octane fuel helps prevent detonation, because high octane fuel is harder to ignite.
This is not pre-ignition, that is caused by too much spark lead or a glowing piece of carbon, wrong heat range spark plug overheated etc.

[a64pilot]

And yes, it was very common to mix 10% to 20% gasoline to Diesel fuel in cold weather to reduce the mixes wax point. In the cold wax will precipitate out of suspension in Diesel fuel and that of course clogs the fuel filter and the Diesel can't run without fuel, newer automotive engine like my trucks Duramax have heated filters to help prevent that.
What was preferred was to run #1 Diesel or winter fuel which was mostly Kerosene, but if you were a Southern trucker headed North you may have to mix your fuel. I don't know about ULSD, is there a winter fuel that is ULSD?
Biggest concern with light gasoline/Diesel fuel mix is the loss or lubrication as gasoline is a very "dry" fuel and that can greatly accelerate fuel pump and injector wear.

[a64pilot]

Oh, and ALL engines the fuel burn begins before TDC, the higher the RPM, the more advanced or sooner the burn begins, reason is the flame spread speed is not variable, and the higher the RPM, the less time the flame has to completely spread thru the whole combustion chamber.

[Ariose]

Hello & apologies for the delayed follow-up. We haven’t had internet access for a few weeks, which, as you can surmise, means good news on the Yanmar front, in that we have been able to continue our cruising agenda.

As some pointed out, the prognoses on our engine’s fate after feeding on a diet of 50% diesel – 50% gas varied quite widely on this forum from “it’ll be ok” through to “you’ll need a new engine”. We were reassured by some we consulted with that Yanmars, especially older ones, are the Timexes of the marine diesel world: they take a licking & keep on ticking.

Here’s what has happened.
The offending marina did arrange & pay for pump-out and a qualified mechanic. We then added a good dose of fresh diesel and pumped that out too. A certified Yanmar marine diesel mechanic bled all the fuel filters and lines several times, cranking the engine in between to pump the fuel through. He checked the common things like oil, coolant and didn’t see any signs of cross contamination. With some effort, we got the engine started. It ran rough at first (i.e. loud), but within a few minutes, it eased out and we headed out for a test ride with the mechanic. Because it sounded healthy for the ride, the mechanic assured us that this was a pretty good indication that we escaped the worst-case scenario possibilities (such as scoring, metal fragments, etc). The next day, we motored about 3 hours before noticing a distinctive diesel smell. We had a leak from a fuel line that hadn’t been properly tightened the day before. The engine also was overheating. Upon consultation with the mechanic, we wondered if the engine thermostat had been damaged by the excessively high temps when running on gas. We had a spare on board, changed it, and it has run without incident for approx 20 hours since, and all seems well.

We feel extremely fortunate to (hopefully!) have got off this potentially disastrous situation so easily. Thanks, everyone for your concern and great input. Needless to say, we now check our fuel (touch & smell test) before the nozzle gets anywhere close to our intake!

[JPA Cate]

Good on ya, mate, ya dodged the bullet!

Ann