Thread: Common rail explained

Originally Posted by spudboy

This may perhaps not be the right thread, but here goes with a question:

Modern diesel engines have gone to common rail and electronics to be more efficient and cleaner.

But:
- My 20yo TDi300 gets 9 or 10L /100
- My 10yo TD5 gets 10 or 11L/100
- My new PUMA gets 11 or 12L/100

How come we've got all this newer tech stuff but the fuel efficiency is going in the other direction? What am I missing here? Power probably....


Cheers
David

im guessing if you drove the Td5 and the Puma to the same performance level as the Tdi you would then be achieving the fuel efficiency.

I recently drove my Td5 1700km at 80kmh because of a stuffed gearbox and I got 8.5 L/100 , when I got the new gearbox and was able to hit 110 again it felt supersonic, oh well, back to 10.5 L/100k

Originally Posted by Judo

Q. It is suggested that CRD can't handle dirty fuel as well as a mechanical pump diesel, but can anyone put this into context? Is it at the injector that the containment is likely to cause problems? Or elsewhere in the system? What size particles are we talking about that will block these choke points? How different is the size limit on particles in a mechanical pump?

Originally Posted by PAT303

I've had two and never had an issue,it's abit like the old folks who think modern electrics will fail as soon as you reach the centre of the simpson. Pat

Originally Posted by garrycol

Yes it was those people who complained when cars changed from magnetos, manual mixture and timing controls and went to distributors with vacuum and mechanical timing control.

garry

So I take it that Pat and Garry, both think crook fuel will not cause any problem

Originally Posted by Bush65

So I take it that Pat and Garry, both think crook fuel will not cause any problem

How did you arrive at that conclusion - we were talking about silly old farts (are you one ) who are resistant to change and always think the good ole days are better and everything old is more reliable.

I certainly didn't even mention or comment on anything related to crook fuel etc.

on a serious note, how common is crook fuel in Oz?

Fuel in Oz is not crook - it is how it is stored that causes the issues - the dangers from filling from drums and jerries is obvious but lack of maintenance of tanks at servos is also a concern.

Originally Posted by Judo

Q. It is suggested that CRD can't handle dirty fuel as well as a mechanical pump diesel, but can anyone put this into context? Is it at the injector that the containment is likely to cause problems? Or elsewhere in the system? What size particles are we talking about that will block these choke points? How different is the size limit on particles in a mechanical pump?

Firstly a thanks to JustinC for starting this interesting thread! We all hear/read the odd comment about why CRD is better, but I certainly didn't know any specifics in this regard. So a thread like this one gets me (and others) looking around and trying to get a better handle on the topic.

It seems that CRD's dependence upon clean fuel arises from both the small fuel passageways within the injectors, and from greater sensitivity to performance deterioration resulting from wear within the injectors. Poorly filtered fuel can foul the injector itself (plug it completely or lock it fully or partly open), and dirty fuel can accelerate wear to the injector's ball seat, resulting in inadequate sealing. Single-plunger mechanical pumps as those used on the LR TDIs use larger fuelways within the injector as well as much lower pressures, and are hence more tolerant of 'dirty' fuel.

Originally Posted by garrycol

How did you arrive at that conclusion - we were talking about silly old farts (are you one ) who are resistant to change and always think the good ole days are better and everything old is more reliable.

I certainly didn't even mention or comment on anything related to crook fuel etc.

I love the way these discussions always wind up with this sort of assumption.

Some facts are if you store diesel in a container, be it under ground, above ground or in a vehicle, the diesel will get water in it.
Condensation out of the atmosphere though diesel tank breathers places water in the bottom of diesel tanks and that water can lead to diesel bacteria in the diesel.
Our diesel today is in low sulphur and to remove that sulphur also removes any lubrication effects of diesel fuel.
Modern injection and now older systems work with little lubrication .