Diesel - does it go off?

Follow on about the petrol, have you notice in films about finding a deserted airplane or vehicle with fuel still in it and it fires up, talk about a load of cattle dung, as if petrol lasts 30 yrs, producers must think we're all dimwits

A bit off topic.

I have a jerry can of petrol that is about 7 years old.

I use it occasionally in the lawn mower. (don't mow the lawns much)

Seems to work OK, so I guess it depends on storage conditions.

Hi Mal

I reckon one of my best investments ever was buying a 44 of petrol and keeping it for around 10 years before use (actually the container base rusted).

I agree that some of the volatile components are lost over time and this relates to how good the container is as you say , but over the ten years the cost of the fuel rose enormously and seriously out performed some super funds I had.

Tim

I have no experience with diesels from a mechanical standpoint; only filling them up. I have always read, and been told, that water in the fuel is a strict no/no for them and even small amounts can cause issues, and is the reason for the water sensor on the fuel filter.

It’s been 35 years since I have done any physics, and my memory is a bit sketchy, but I was taught that compression of a gas or fluid raises its temperature (the old bike pump experiment). In a diesel, the stronger compression of the diesel raises the temperature of the fuel so that the volatile fractions within the fuel reach the ignition point and “spontaneously” ignite. Therefore, an ignition source is not needed (apart from the glow plug until such time as engine block heats up)

The logic in my answer, (and please tell me where I’m wrong in either practice or theory) is that if enough “light” or volatile fractions of the diesel have evaporated, the compression of the motor will not ignite the fuel and the motor will be compressing oil which is not being burnt and added to on each pulse of the injectors. As the fuel is not igniting and expanding, this is not being discharged through the exhaust either

As I said, my logic could be totally wrong and diesels may not be as susceptible to hydraulic issues as I have thought

Nargun
It may not be ignited but it is certainly being pushed out the exhaust on every second revolution and the quantities as so small there is no chance of Hydraulicing

Cheers

The injectors would not deliver enough fuel to cause an engine to hydraulic. Also diesel engines can run on sump oil when warm so even if the diesel has lost its volatility it should still burn.
Any water in the system will be burnt away in combustion but may cause problems with the injectors and pump not delivering correct amounts of fuel.

Cheers Matt

Yes, water in the fuel is bad news but as far as I know, it's not because of the compression. The problem is more likely to do with lubrication and cooling of the high-pressure fuel pump and injectors (oily diesel is far better for this than water) and the potential for rust in these components.

The injectors only deliver a very small amount of fuel each pulse and this is dispersed so finely as a 'mist' (ideally it is virtually in vapour form) so unburnt fuel shouldn't accumulate in the combustion chamber because it will be forced out during each exhaust cycle, along with everything else. Incomplete/inefficient combustion won't cause fuel to accumulate in the combustion chamber - in fact, incomplete combustion is the reason for the black smoke from poorly maintained diesels. The only way I know to get enough liquid into the combustion chamber quickly enough to cause damage (ie. so it isn't forced out on each exhaust cycle) is in through the air intake.

As far as I understand, the problem with storing diesel for long periods of time relate mainly to the likelihood of condensation in the storage tank (therefore adding water to the fuel) and the potential for algae growth.

Thank you to all for the information, which clearly gave the reasons, experiences and logic to correct behind my insufficient and misguided (deluded?) response.

Another example of the positive role that EO can provide

Of interest is this.

Diesel's biggest problem is alge growth.
This happens when you have water in with the fuel.
The alge grows on the barrier between the water and the fuel.
The alge feeds on the sulphur.

Now we have low sulphur fuel compared to a few years ago, so the longevity of the fuel, if kept in an airtight, free from water environment is pretty good.

Nulon state that their diesel fuel additive has benefits for prolonged storage of fuel.

Diesel will store for well over 1 year if kept out of excessive heat, and is clean to start with.
Add a dose of nulon, or other additives that prolong storage life, and your good to go.
Petrol on the other hand does not have the same abilty to store due to its additives, and volitile nature.
So, diesel is ideal for those generators that only get used every now and then, and for waterpumps etc for the very same reason.

With our farm machinery, and bulk fuel, we had the same questions, and after some investigation, and research, have kept diesel for many years without problems.

with bulk storage, fit a moisture trap, and a basic filter on the end of that, ensure the tank is free from moisture, and contaminates to begin with, and your good to go.

Just my findings after storing fuel between times of use on the farm.

Trains

Wow!! Thanks for all the advice. I'll filter it in slowly. I have a 75 series troopy.