Re: My most expensive fuelling - ever
Quote:
Originally Posted by
Butcher
Diesel in a petrol is less of an issue as a run of petrol will clean any diesel out in short order.
It'll play merry hell with the cat and any other filters it contacts though. Gunk them up nicely. Car will still run but emissions tests won't go well.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
Butcher
It's not just it being thinner - petrol is a rather effective degreaser, so it will strip the lubrication off the pump, injectors, anything else really. Definitely not good news.
So what do they use in a petrol car then? Having gone to the bother of sourcing petrol resistant parts for use in petrol engines I wouldn't be surprised if they reused the same components where possible for diesel engines.
Re: My most expensive fuelling - ever
I just moved to petrol from diesel, I am dreading the day I do this also....
Re: My most expensive fuelling - ever
The pressures are much lower in a petrol injector system, so I suspect the tolerances may be less demanding.
A diesel is injecting against the cylinder pressure at or near tdc, a petrol injector is injecting at near atmospheric pressure well before the compression stroke completes. The compression ratio of a diesel is also higher than a petrol engine.
The lubrication requirements of high pressure pumps is more demanding than of lower pressure pumps.
Re: My most expensive fuelling - ever
I did this a few years ago, I'd driven a diesel for a while but it was in the garage and I'd borrowed a petrol for a couple of weeks, got used to putting petrol in. Got the diesel back, practically empty and autopilotted about £10-£15 worth of petrol before I realised what I'd done
I just brimmed it with diesel and kept it topped up for a few days. Engine was fine. German, of course.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
peterb
The pressures are much lower in a petrol injector system, so I suspect the tolerances may be less demanding.
A diesel is injecting against the cylinder pressure at or near tdc, a petrol injector is injecting at near atmospheric pressure well before the compression stroke completes. The compression ratio of a diesel is also higher than a petrol engine.
The lubrication requirements of high pressure pumps is more demanding than of lower pressure pumps.
but because diesel is more viscous it can clog petrol injectors and you get loss of peak power and laggy response - we got that when a garage put diesel contaminated petrol in our car a while back. It never was the same again, even after all the cleaning solvents they threw into it. Petrol in a diesel is more dangerous due to the compression causing auto-ignition explosions contrary to the timing strokes and cylinder positions - so actual mechanical damage to multiple components is possible if you keep it running.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
ik9000
but because diesel is more viscous it can clog petrol injectors and you get loss of peak power and laggy response - we got that when a garage put diesel contaminated petrol in our car a while back. It never was the same again, even after all the cleaning solvents they threw into it. Petrol in a diesel is more dangerous due to the compression causing auto-ignition explosions contrary to the timing strokes and cylinder positions - so actual mechanical damage to multiple components is possible if you keep it running.
Absolutely, and there is risk of catalyst poisoning. From what the guy who came out to me said, a Diesel engine will just die when the petrol gets to the engine (having created havoc to the fuel components on the way)
Diesel in a petrol engine may run, but it won’t be doing a modern petrol engine any favours at all. You might get away with it in a carburettor B series engine or an old Ford Kent engine, but that’s about it.
As an aside, some old farm engines used to run on something called tractor vaporising oil - something akin to paraffin. They used to start on petrol, then once started and warmed up, they would be switched to TVO. But that was in the days when a cat was something to control the rat and mouse population (and keep the farm dogs in order :) )
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
peterb
The pressures are much lower in a petrol injector system, so I suspect the tolerances may be less demanding.
A diesel is injecting against the cylinder pressure at or near tdc, a petrol injector is injecting at near atmospheric pressure well before the compression stroke completes. The compression ratio of a diesel is also higher than a petrol engine.
The lubrication requirements of high pressure pumps is more demanding than of lower pressure pumps.
The cylinder pressure is irrelevant in remotely modern engines. A Direct Injection petrol engine will have its fuel pressured to around 500 atmospheres! A common rail diesel is closer to 2500 atmospheres.
Unbelievable pressure for the fuel before it even goes bang!
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
badass
The cylinder pressure is irrelevant in remotely modern engines. A Direct Injection petrol engine will have its fuel pressured to around 500 atmospheres! A common rail diesel is closer to 2500 atmospheres.
Unbelievable pressure for the fuel before it even goes bang!
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.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
peterb
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.
and that's the point, try and compress petrol to common rail pressures and it will auto-ignite before it gets half-way.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
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.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
ik9000
and that's the point, try and compress petrol to common rail pressures and it will auto-ignite before it gets half-way.
Quote:
Originally Posted by
DanceswithUnix
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.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
peterb
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.
Oh petrol will burn very happily in those conditions, which is why petrol engines work at lower compression ratios than diesel engines so that they don't "diesel" and the spark plug can control the combustion.
There is a video on youtube of someone driving an old diesel car filled with petrol. Apparently it drove quite well. That wouldn't have had the modern common rail diesel pump though, those do seem to be the weak link if not the injectors which won't be designed for a fuel that runny.
Re: My most expensive fuelling - ever
Liquids don't compress as much as gases, so would there even be enough heat for autoignition with an oxidiser when you're compressing liquid fuel?
Quote:
Originally Posted by
peterb
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 beemer M47 diesel (from 20 years ago or so) has an injection pressure of 250-1350 bar[1], so it wouldn't surprise me for a modern diesel to hit double that peak pressure.
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.
[1]: Rover 75 & MG ZT owners workshop manual, haynes (2010) (not sure why they quoted a range)
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
DanceswithUnix
Oh petrol will burn very happily in those conditions, which is why petrol engines work at lower compression ratios than diesel engines so that they don't "diesel" and the spark plug can control the combustion.
IIRC that was an old trick with an air rifle - a drop of light oil behind the pellet.
But yes, you are right about compression ratios - I didn't explain myself very well.
Re: My most expensive fuelling - ever
Quote:
Originally Posted by
peterb
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.
Common rail diesels are up to around 2000 bar these days. My car's petrol direct injectors run at up to 210 bar (compare to ~4 bar for the port injectors).