My most expensive fuelling - ever

[DanceswithUnix]

Faster you can get the fuel in, the less the piston moves during the burny bit - and the less the piston moves during the burny bit, the less wasted energy goes down the exhaust.

Fuel going in fast makes the car sound even more like a tractor. The whole point of common rail is to break the burn up into lots of smaller injections to spread out the noise into something more like the flame front of a petrol explosion and make the engine acceptable in a consumer vehicle.

[Ttaskmaster]

I cannot wait for electric vehicles to become the norm and read all the threads about people putting in AC batteries instead of DC, or a Twenty-Seven Hundred (2700) cell instead of a Twenty Seven-Hundred (20700) one and borking their cars!!
You just know it will happen...

Outside y area of expertise, but my understanding is that common rail diesel injection pressures are 250Bar, while a Common rail petrol system is around 100Bar to achieve optimum atomisation and fuel/air mixing.

You're missing a zero off the back end of that figure
Source: 30-second Google.

I'm told there are some models up to 5,000bar (Citroen I think), but mostly that's just for maritime engines.

[badass]

Two responses. Both wrong but very different.

Outside y area of expertise, but my understanding is that common rail diesel injection pressures are 250Bar, while a Common rail petrol system is around 100Bar to achieve optimum atomisation and fuel/air mixing.

A polite "that doesn't sound right but not my area of expertise type response" Perfectly reasonable.

and that's the point, try and compress petrol to common rail pressures and it will auto-ignite before it gets half-way.

The usual internet type response. Complete rubbish based on a knowing nothing about the subject at hand, but nonetheless stating opinion as fact.

In both cases, 30 seconds on Google would reveal my figures are correct. In the first case, that's just politely adding to the discussion. In the second - well you can see how fake news spreads so rapidly. See also: automotive forum advice on needing jet engine grade oil and needing to change it every 3000 miles or you'll destroy your engine.

[badass]

Hmm my above post looks grumpy. Probably because I am. Mainly because of my diesel [s]piece of[/s] car.

[TeePee]

Two responses. Both wrong but very different.



A polite "that doesn't sound right but not my area of expertise type response" Perfectly reasonable.



The usual internet type response. Complete rubbish based on a knowing nothing about the subject at hand, but nonetheless stating opinion as fact.

In both cases, 30 seconds on Google would reveal my figures are correct. In the first case, that's just politely adding to the discussion. In the second - well you can see how fake news spreads so rapidly. See also: automotive forum advice on needing jet engine grade oil and needing to change it every 3000 miles or you'll destroy your engine.

It's the idea of jet fuel being a high grade that amuses me. Jets will run on anything. You can run them on gasoline for a set period of time, and that's only a limitation on the fuel pumps that rely on the oily fuel for lubrication. Change the pump and the engine is good for more hours of gasoline abuse.

Jet Engine Oil is a high grade synthetic. But it's a very low weight oil, so not good for a car engine.

[Butcher]

Isn't jet fuel similar to diesel but less carefully refined (and thus cheaper) because jet engines don't really care?

[badass]

Jet Engine Oil is a high grade synthetic. But it's a very low weight oil, so not good for a car engine.

Indeed. Capable of withstanding very high temperatures for a decent amount of time without breaking down too quickly. Not easy for organic compounds.

[ik9000]

Two responses. Both wrong but very different.



A polite "that doesn't sound right but not my area of expertise type response" Perfectly reasonable.



The usual internet type response. Complete rubbish based on a knowing nothing about the subject at hand, but nonetheless stating opinion as fact.

In both cases, 30 seconds on Google would reveal my figures are correct. In the first case, that's just politely adding to the discussion. In the second - well you can see how fake news spreads so rapidly. See also: automotive forum advice on needing jet engine grade oil and needing to change it every 3000 miles or you'll destroy your engine.

you know I shall listen to my own advice and not inflame the situation. Better response further down

[ik9000]

Hmm my above post looks grumpy. Probably because I am. Mainly because of my diesel [s]piece of[/s] car.

yes it does look grumpy. because it is. Try the edit button.

[CAT-THE-FIFTH]

It's the idea of jet fuel being a high grade that amuses me. Jets will run on anything. You can run them on gasoline for a set period of time, and that's only a limitation on the fuel pumps that rely on the oily fuel for lubrication. Change the pump and the engine is good for more hours of gasoline abuse.

Jet Engine Oil is a high grade synthetic. But it's a very low weight oil, so not good for a car engine.

Interestingly enough the first jet engines like the BMW 003 actually ran on petrol or diesel,unlike modern ones which seem to be more orientated towards keroscene.

Having said that I thought there were military engines in MBTs which could run different kinds of fuels fine??

[ik9000]

and that's the point, try and compress petrol to common rail pressures and it will auto-ignite before it gets half-way.

Where does it get the oxygen from to ignite? It can only burn when injected into the cylinder.

Quite so - neither petrol nor diesel ignite under pressure. Diesel burns when it is injected into the cylinder because the air in there has been compressed and is hot. Petrol won't readily ignite under those conditions, which is why it needs a spark plug to get it burning.

Two responses. Both wrong but very different.



A polite "that doesn't sound right but not my area of expertise type response" Perfectly reasonable.



The usual internet type response. Complete rubbish based on a knowing nothing about the subject at hand, but nonetheless stating opinion as fact.

In both cases, 30 seconds on Google would reveal my figures are correct. In the first case, that's just politely adding to the discussion. In the second - well you can see how fake news spreads so rapidly. See also: automotive forum advice on needing jet engine grade oil and needing to change it every 3000 miles or you'll destroy your engine.

compare and contrast the immediate helpful responses moving the discussion along vs the less helpful and by their own admission, grumpy post that presumably just seeks to provoke a response. You'll notice I'm sure the big pause in my posts while I chewed on their responses and did just what you accused me of not doing - looked it up. I started by wanting to simply caveat that my statement applied in the presence of oxygen - but actually it's more tricky than that as whatever the correct applicaiton of the old PV=nRT there is a big problem that diesel actually auto-ignites (at standard pressure) before petorl does. Which just pops my little head as it is heavier HC chained and less volatile but nope, there it is grinning at my like a fat cheese wedge and saying "you sure that guy at the garage told you truth there bruv?" and your old chemistry teacher - was he pulling your chain too? "

So I spent a while trying to chew on the science. And I have a weird car-crash in my head: PV=nRT so as you compress something (and do work in the process) it gets hot. At some point - assuming there's some air in there - you hit the point at which it goes bang without any spark required. But according to wiki's tables (yes those ones apparently I don't know how to look at) petrol should get there 2nd to diesel, so why is it a problem, and so bad that we should be told in our labs at Uni (oh those uneducated internet types...) that if we fed the petrol into the diesel test rig it would explode? Surely they had some basis for telling us this (more than just scare the dimwit undergrads needlessly).

Then I spent a wadge of time trying to find the papers on how auto-ingition might vary in non-standard pressure, and what that looks like inside a petrol engine vs diesel engine and their operating pressures. Sadly the decent papers on this are hidden behind the academic firewall and I am too long out to have access anymore. At that point I stopped while other life got in the way.

The slightly longer response is thus, and more detailed than perhaps I would have given it, hopefully suitably self-moderated for a public forum. Needless to say, I don't think much of a smug poster who reads his own posts, thinks he's been a bit unpleasant, publicly says so, then leaves it there just to stir up the pot. By all means contribute to the science debate and useful comments, even correct me if I get something wrong, but kindly refrain from any further unecessary snide remarks. Cheers.

[kalniel]

Turbines (eg jet engines, tanks, odd-ball cars/bikes, generators etc.) can indeed run on almost any old junk. But they're a bit pricey for mainstream cars.

[peterb]

IK9000: Thank you for your detailed reply.

I think (and I am second guessing another poster here) that the point being made about the pressures in the rail itself was emphasising that the fuel is still in the liquid phase and as such is pretty much incompressible - it may be pressurised, but it is not compressed in the gaseous sense.

Of course, in the cylinder the fuel is vapourised and is compressible and Boyle’s law then applies.

My own comment was pointing out that combustion cannot take place with an oxidising agent (gaseous atmospheric oxygen in this case but for some specialised ic engines a self oxidising fuel may be used) and while the fuel is in the fuel rail there is no oxygen. If my post came over as a bit smart Alec, I apologise.

One ‘problem’ with a forum (even one as good as HEXUS is that it isn’t always easy to determine the level of expertise of individual posters, which is why we tyre to encourage debate and discussion of ideas ( and abhor personal attacks)

[DanceswithUnix]

(more than just scare the dimwit undergrads needlessly).

Whilst I suspect there is always some entertainment in scaring the undergrads, I can only see the problem if air gets into the fuel line. Usually that is pretty rare, but I can imagine a machine in an undergrad lab would have a high chance of starting the day with an empty tank.

Couple of data points for the discussion though:

Diesel engines used to have much higher compression ratios than they do now for emission purposes and because of the turbo.So compression has changed, but not the fuel. AIUI the engine running depends on hot spots within the cylinder head rather than auto ignition. I gather some new engines are getting quite dependant on the glow plugs.

Pouring powdered magnesium into the air makes it burn. Being atomised is as important as compression.

[Ttaskmaster]

Turbines (eg jet engines, tanks, odd-ball cars/bikes, generators etc.) can indeed run on almost any old junk. But they're a bit pricey for mainstream cars.

Which is a crying shame, as turbines sound awesome starting up...
Tik-tik-tik-tik-tik-tik-tik-tiktiktiktiktiktiktikt-t-t-t-t-t-t-BWWWWWWWWWRRRRRRRRRRRHHHHHHHHHH!!!!!

it isn’t always easy to determine the level of expertise of individual posters

Yeah it is - If their profile says Admin, they're practically perfect in *every* way. If it don't, they're a peasant just like the rest of us

Chim-chimminey, chim-chimminey,
Chim-chim cherroo...
I posts stuff on Hexus, it's what I likes ta do
Chim-chimminey, chim-chimminey,
Chim-chim cherree...
It's just my opinion, so please don't ban me!

[peterb]

Yeah it is - If their profile says Admin, they're practically perfect in *every* way. If it don't, they're a peasant just like the rest of us

Chim-chimminey, chim-chimminey,
Chim-chim cherroo...
I posts stuff on Hexus, it's what I likes ta do
Chim-chimminey, chim-chimminey,
Chim-chim cherree...
It's just my opinion, so please don't ban me!

And the 2017 HEXUS award for the most shameless bit of grovelling goes to...