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Old 26 October 2007, 11:20   #11
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And which jet fuel might that be?
Kero is lighter than diesel and it doesn't contain as much energy, consequently fueling needs to be modified to produce an equal power output to diesel. It also is more volatile and produces knocking unless the injection timing is adjusted and, even then, it can still be a bit noisy. It also doesn't start as well as diesel but that may be down to it's thickness. Adding a small quantity of oil makes it a bit more slippery but you'd need to add a considerable amount to get it up to the energy content of diesel. I'm not sure why you would choose vegetable oil over mineral oil as an additive. Just because you can make an engine run on it doesn't necessarily make it a good fuel.
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Old 26 October 2007, 11:25   #12
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JP8 - and before you start it is no different really to any of the others - they are just specs on paper.

as to using a veg based oil remember castor is still used in 2 strokes. Rape seed oil was found to have better lubricity than most mineral additives - and it's cheap!!!
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Old 26 October 2007, 11:33   #13
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Originally Posted by codprawn View Post
...as to using a veg based oil remember castor is still used in 2 strokes.
Well, I once ran out of two stroke oil when mowing me lawn but I had a tin of Castrol R40, the old castor based stuff. The mower took about 30 minutes to wear out beyond repair. Totally fecked.

The difference between us, Codders, is I never give advice based on something I haven't had experience of. Any posts I make which are not personal experience I make quite clear. I'm not claiming to always be right but I post as how I found it to be.
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Old 26 October 2007, 11:47   #14
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Who said I didn't have any experience - it's a subject i actually have a lot of experience of. I may have done my degree in Physics but chemistry was always my 1st love - 2nd is my love of infernal engines!!!

Just because you managed to wreck an old lawn mower does NOT mean that castor oil is not a good lube - in fact it is still regarded as the BEST but it does have a few problems. Some of my model 2 strokes will run quite happilly at 25,000rpm - the only read drawback of castor is that it does tend to gum up after a while - having said that the residue it leaves is great at preventing rust.
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Old 26 October 2007, 12:07   #15
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Just because you managed to wreck an old lawn mower does NOT mean that castor oil is not a good lube
Who said it was an old lawn mower? And, I didn't say castor based oil is not a good lubricant in the correct circumstance.
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- in fact it is still regarded as the BEST but it does have a few problems.
And, therein lies the problem with your generalised post.
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Some of my model 2 strokes will run quite happilly at 25,000rpm - the only read drawback of castor is that it does tend to gum up after a while
But you are mixing it with methanol not petrol and, unless you are on a special mix, the fuel will be at least 20% oil.
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- having said that the residue it leaves is great at preventing rust.
One might expect so but, no it's not. Unless your model engines are kept in a particularly dry environment, you'd be better putting some 3 in 1 oil into them because it contains a corrosion inhibitor, turn them over a few times to distribute the oil and then leave them with the ports covered by the piston but in a position where the venturi intake is still closed off.
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Old 26 October 2007, 12:16   #16
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My engines have never rusted but the bed of my old lathe did despite being buried in 3:1 - it's just too thin and seems to vanish after a while whilst the castor just varnishes........
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Old 26 October 2007, 13:47   #17
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My engines have never rusted but the bed of my old lathe did despite being buried in 3:1 - it's just too thin and seems to vanish
That's because it's open to the atmosphere and it evapourates. If you close it off inside the motor as I described, it will last a very long time.
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...whilst the castor just varnishes........
Yes, that's another problem with castor based lubricants.
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Old 26 October 2007, 14:01   #18
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You've posted that a couple of times, Codders but Kero +5% oil does not equal diesel.

You speak as though torque and power are not related. If you have high torque at a given rpm, you'll also have high power at that rpm. Diesels generally produce more power at lower rpm than equivalent petrol engines but they run out of breath as their revs rise so they don't ultimately manage the high power that a petrol motor does. The fact that they have lowish maximum RPM doesn't matter because the lower unit gearing can take care of that to ensure a satisfactory prop speed.
Power = Torque x engine speed.

The reason petrol engines make more power is partly because they can rev higher. A diesel engine's torque curve is pretty flat, whereas a petrol engine's is low at first, then rises gently, then falls off at higher revs. But even as it falls off, revs increase, and therefore power remains stable.

So yes, diesels make more torque at low revs and therefore more power, (than a petrol) But their torque drops off quickly at higher revs, and therefore their peak power is lower than that of petrol engines.

(At least that was the classic doctrine when I did mechanical engineering at university - modern technology is changing all the time, and diesels are quickly overcoming their old shortcomings).

As for the whole jet / diesel thing, perhaps I can add some info as I was responsible for international jet fuel cargo trading for the 4th largest oil major for 10 years.

Yes, the US Forces have successfully converted their motors to take JP8 (almost identical to Jet A1 used in commercial aviation). But this does not necessarily mean that you can do it with your Golf TDi. They also use a very high flash jet fuel, JP5 for aircraft carriers.

Codprawn, you need to be careful what you say regarding diesel unless you're very sure. It's a complex subject, and EN590 (Euro DERV) has about 20 specifications. It is a very high spec fuel. Modern diesels CANNOT run on any old rubbish - they are now using ultra high pressure injectors and lubricity must be good. The spec is 460 microns max, where a test plate is worn using the diesel as a lube. The scar must be no more than 460 microns deep. Also, the minimum cetane is 46/51. This is not guaranteed for jet fuel or heating oil. Viscosity has to fall within a certain range, as does density. Flash point must be above 55 or 60'C. Jet/kero is only 36'C, so watch out on hot days!

Adding veg oil as a lube may or may not work, but I wouldn't bank on it. In any case, the higher sulphur content in heating oil acts as an excellent lubrifier. (In fact it was the reduction in the sulphur in diesel in the late 90's that caused all the lube problems).

This is a big, complex subject, and cannot be dealt with lightly!
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Old 26 October 2007, 14:35   #19
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I understood that you couldn't run a 2 stroke on castor oil unless it was on it solely from new . probably the reason the lawn mower went bang.

years ago when it was used in 2 stroke race bikes I had mates who changed to and they all blew their motors in the first race . i stripped one and the oil deposits had kind of crystalised and ruined the bearings .

Surely burning it in a 4 stroke diesel will have the same effect after a while after sump oil fuel oil get burned together .

Now a 2 stroke diesel outboard could be interesting
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Old 26 October 2007, 17:53   #20
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The US forces did not convert their engines - they just use JP8 in them. In very hot countries they will sometimes add some extra lube but not always.

As far as biofuels are concerned remember that many countries including the EU are starting to add biodiesel wether you like it or not.

You mention HFFR tests - JP8 on it's own was pretty poor 700 micron - with 1% castor oil it achieved 185 micron - a hell of a difference - it was 285 with rapeseed oil - castor was the very best!!!

Yes it's an extremely complex subject but much research has gone into this - especially by the military,

And talking of the military it is quite common for small quantities of surplus jet fuel to go missing and end up powering all sorts of things..........
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