posh diesle vs common as much diesle

[jacksun1987]

Well i put no end of that redex stuff. So thats prob why i dont relaise the differnce. It says with a full tank but i just bang it in lol.
If you g in to wilkingsons. They have it at a lower pice. Its about 3 to 4 pound. compared to 6 pound.

[Xaccers]

If you buy 10x20L boxes of the KTC stuff you get a tiny discount.
Just walk in and buy what you want (as a member). I've even filled Casey up in the carpark.
Certain things like bulk packs of ibuprofen/paracetamol can only be sold to trade members, but veg is available to all.


Jim, the longer the fuel has to burn, the more of it can burn, so if you ignite it sooner it will have more time to burn, even milliseconds will produce many many more oxidation reactions.
Look at how little it needs to be adjusted to advance or retard combustion enough to have quite an impact.

[CitroJim]

Jim, the longer the fuel has to burn, the more of it can burn, so if you ignite it sooner it will have more time to burn, even milliseconds will produce many many more oxidation reactions.
Look at how little it needs to be adjusted to advance or retard combustion enough to have quite an impact.

Oh indeed yes but it's only the very, very latest diesels that can adjust their timing on the fly like this to really take advantage. Certainly Richard's C15D didn't have this. I know Lucas pumps good but they're not that good

In fact, thinking about it, I may have the answer. Sorry I really must get the brain sorted out. It's slower than a Xantia SD at the moment...

Right. Listen. Cetane is essentially a measure of the small delay, known as ignition delay, that occurs between start of injection and the commencement of the burn. It does not start burning the moment it's injected but waits a finite time. Ignition delay.

The higher the cetane rating is the shorter this delay becomes. As I said earlier the cetane rating determines how susceptible a fuel is to spontaneous combustion under heat and pressure. The higher the more readily it does so.

So, it follows that if an engine is run on fuel with a higher cetane value the ignition delay will be shorter and effectively this will advance the timing by a small amount and the charge may burn for longer, start doing so earlier and thus release more energy. But..

Cetane values are a bit logarithmic and nowhere near as dramatic as petrol octane values and unless the injection duration is also upped there may be no nett change as the same volume of fuel is being burned, just a bit sooner. Also oxygen may run out before the natural end of the burn...

So, on that basis, if your Magical Millers gives a significant cetane boost Richard then this will account for the improvements. It's not huge but consistent with the above. Radially upping the cetane value will not make a significant difference and nothing like the change seen say, when 100 octane petrol is used with suitable ignition mods in a well sorted petrol motor, High cetane values will make for easier starting and cold running in all cases but not a lot else. It's not a magical way to get performance as high octane petrol is.

Are we all happy now

[CitroJim]

And you can't go too high with the cetane rating or the fuel becomes dangerously unstable and will go off pop at the drop of a hat. In an engine it would cause destructive denotation (pre-ignition or pinking).

Ether is a substance with a very high cetane rating and look how dangerous that is... It's the main constituent of 'EasyStart' and why it's both effective at starting and at the same time destroying a reluctant engine...

[Northern_Mike]

Sorry I really must get the brain sorted out. It's slower than a Xantia SD at the moment...

I don't care how bad you are feeling, that statement is simply not true

[CitroJim]

Sorry I really must get the brain sorted out. It's slower than a Xantia SD at the moment...

I don't care how bad you are feeling, that statement is simply not true

Sorry Mike, I was wrong. It feels more like a non-turbo Diesel Xantia....

[Xaccers]

Diesels run lean, so for a given squirt of fuel there will be more than enough oxygen to burn all the fuel if it has enough time to burn that is.
So if you start that burn sooner you're giving it more time to burn more fuel.
You're adjusting the timing not by the engine/pump but with the fuel so the fuel doesn't get injected sooner but acts like it has been.


One thing I've found looking into this is that biodiesel from animal fats has a higher cetane number than E590! So that plastic surgeon in LA who was using the waste from liposuction operations to fuel his SUV was on to something (alright, something illegal, but I bet he neve had starting problems)

[CitroJim]

Diesels run lean, so for a given squirt of fuel there will be more than enough oxygen to burn all the fuel if it has enough time to burn that is.

Ahh not necessarily so! It all depends if the available oxygen can effectively mix with the remaining molecules of fuel in a precise 14.7:1 (stoichiometric) ratio to burn. Even though diesels operate in an excess oxygen regime combustion only occurs when the ratio of fuel to air is stoichiometric. If it can't even if there’s apparently loads of oxygen about then there's no combustion. This happens near the end of the burn where turbulence and swirl are low (both very necessary to mix the oxygen and fuel molecules effectively) and the oxygen molecules might be at the opposite sides of the combustion chamber to where the remaining fuel molecules are gathered. If there's not enough turbulence to mix them they're not going to burn even if there is enough heat left to initiate potential combustion.

This is why so much research effort is devoted to combustion chamber design and injector spray patterns. The old IDI engines like the XUD with their Ricardo Comet chambers were particularly good at ensuring full combustion because the pre-chamber with it's little port into the main combustion chamber generated such high levels of turbulence and could ensure very good combustion even with the relatively low injection pressure the distributor pumps of the time could produce. In fact the IDI engine was a bit of a fiddle to get efficient combustion at high speed but it paid the price in slightly lower thermal efficiency. It's why a good DI engine like the HDi is slightly more economical without being any more powerful. Good, clean and quiet DI engines could not exist until common rail injection at very high pressure could be made to work. DI engines of old were always fairly economical but were slow revving, bloody noisy, slow and smoky for the most part. Think of an old tranny van. Sorry, drifting off-topic here...

Xac, it's a deep subject and one I personally find very absorbing. I have a very thick book on the subject. It's a fascinating read...

You're welcome to borrow it. Excellent bedtime reading...

Running an SUV on liposuction eh? Good way of recycling it Just goes to show a diesel will run on anything with a reasonable content of weakly-bonded hydrogen and carbon! You might say the driver is living off the fat of the land...

[Citroening]

Talking of Diesel's running on anything, a mate of a mate runs his VW Golf on waste engine oil!

[Xaccers]

Diesels run lean, so for a given squirt of fuel there will be more than enough oxygen to burn all the fuel if it has enough time to burn that is.

Ahh not necessarily so! It all depends if the available oxygen can effectively mix with the remaining molecules of fuel in a precise 14.7:1 (stoichiometric) ratio to burn. Even though diesels operate in an excess oxygen regime combustion only occurs when the ratio of fuel to air is stoichiometric. If it can't even if there’s apparently loads of oxygen about then there's no combustion. This happens near the end of the burn where turbulence and swirl are low (both very necessary to mix the oxygen and fuel molecules effectively) and the oxygen molecules might be at the opposite sides of the combustion chamber to where the remaining fuel molecules are gathered. If there's not enough turbulence to mix them they're not going to burn even if there is enough heat left to initiate potential combustion.

This is why so much research effort is devoted to combustion chamber design and injector spray patterns. The old IDI engines like the XUD with their Ricardo Comet chambers were particularly good at ensuring full combustion because the pre-chamber with it's little port into the main combustion chamber generated such high levels of turbulence and could ensure very good combustion even with the relatively low injection pressure the distributor pumps of the time could produce. In fact the IDI engine was a bit of a fiddle to get efficient combustion at high speed but it paid the price in slightly lower thermal efficiency. It's why a good DI engine like the HDi is slightly more economical without being any more powerful. Good, clean and quiet DI engines could not exist until common rail injection at very high pressure could be made to work. DI engines of old were always fairly economical but were slow revving, bloody noisy, slow and smoky for the most part. Think of an old tranny van. Sorry, drifting off-topic here...

Xac, it's a deep subject and one I personally find very absorbing. I have a very thick book on the subject. It's a fascinating read...

You're welcome to borrow it. Excellent bedtime reading...

Running an SUV on liposuction eh? Good way of recycling it Just goes to show a diesel will run on anything with a reasonable content of weakly-bonded hydrogen and carbon! You might say the driver is living off the fat of the land...

I'd love to borrow the book Jim
Petrol engines are stoichiometric, if diesels were you'd get lots of soot as there isn't as much time for it to evaporate and mix as it ignites pretty much as it is sprayed into the hot compressed air, that's my understanding of it.

The chap who was using lipo waste converted to biodiesel only got found out because he started letting his girlfriend (one of his nurses) do some of the operations! Apparently in California human biological waste can only be disposed of through official channels.

One of Rudolph's early engines actually ran on coal dust.

Franklin, running on engine oil would be naughty unless he pays the required duty as it's diesel substitute

[HDI]

Rudolph originally intended his engine to run on coal dust, it was a political economic thing due to the abundance of coal. Obviously he ran into difficulty with abrasion !
Common rail diesels are very clever indeed now, they even have more than one injection event per combustion stroke !! There is pre, main and post injection all with varying timing to suit that individual combustion event on that cylinder at that revolution ! This may actually be able to take advantage of modern, posh diesel brews to produce more power and economy. Certainly the power now being extracted from common rail units is entirely due to this advanced technology, impossible to achieve by any other method.