I read somewhere on tinternet that VW were dropping their PD diesels for a common rail diesels. Something to do with emissions. I thought the PD system was a better than the common rail one. If that makes sense. Does anyone know if it is true?

pd is common rail. kind of!

Yeah, PD is common rail. I believe the future of the 1.9 PD is in jeopardy. The 2.0 may go on for some time, especially with the new pd170 coming out. Even if the injectors are some kind of "new" pd.

PD is being dropped but because of cost. CR is now catching up performance / pressure wise, so Unit injectors are possibly an uncompetitively expensive way of getting the job done. Personally, I really like the way the PD engines drive and having come from a very crappy Ford CR setup to the PD lump, I will need some convincing to go back.

Chris

PD isn't common rail is it? PD uses a pump per injector whereas common rail uses a single pump to feed a rail which feeds all the injectors? :confused:

Common rail is quieter and more refined in my experience, but tuning-wise may not be as tweakable

Chris

PD isn't common rail is it? PD uses a pump per injector whereas common rail uses a single pump to feed a rail which feeds all the injectors? :confused:

Common rail is quieter and more refined in my experience' date=' but tuning-wise may not be as tweakable

Chris[/quote']

pd engines only have one fuel pump which is driven by the camshaft.

pd engines only have one fuel pump which is driven by the camshaft.

http://groups.google.co.uk/group/rec.autos.makers.vw.watercooled/browse_thread/thread/52c93785c8ecbbe/524627a46afd1f7f?lnk=st&q=pumpe+duese+how+it+works&rnum=1#524627a46afd1f7f

Chris

one of my old lupos had a pd engine and i managed to squeeze over 140bhp from it. to do this i had to become very aquainted with the fuel system in order to under stand how to wring more gg's from it.

right, the injectors are operated by lobes on the camshaft which push a rocker ontop of the injector which pressurizes the fuel. this results in an extreemly high injection pressure....

they look like this

the question everybody is now asking is... "well how does the fuel get to the injectors then". this is done by a pump which is driven by a spigot on the end of the camshaft. the fuel goes through an internal channel and is fed to each injector from the same channel..(hence common rail)

the pump looks like this.

Thanks for explaining that, Tom - much clearer now

Chris

oh yes, and in addition to this there is the normal lift pump in the fuel tank as well

Is it that common rail cannot pressure the fuel as high as the PD, thats waht makes the PD a better performer.

From my limited knowledge of diesel engine technology - I would say that is correct. Higher injection pressures = better fuel atomisation = more power per volume of fuel injected

However, I stand to be corrected if necessary

the common rail systems are getting mush better nowadays. renault and volvo have developed these quite extensively in recent years.. but the vw/bosch pd system is better for a few reasons... firstly because of the higher pressures it takes less time to inject the same amount of fuel than a pump injected engine would. and also the bosch ed15 ecu which is used on the pd jobby can alter the timing of the injection cycles too in a similar way to how a sequential petrol injection system works.. so for example at higher revs it injects the fuel earlier. but we're only talking milliseconds tho. but the main reason for the huge sucess of modern turbodiesels is the use of the variable geometry vnt turbochargers..

the only downsside to any direct injection diesel wether it is pd, common rail or whatever is that the pistons have to be shaped in a certain way on thier crowns which weakens them slightly

I think VW will go common rail eventually, the PD is suffering a bit when it comes to Euro regulations, only a matter of time I think.

Strictly speaking the PD isnt a common rail. The injector is considered a pump in the diesel system so as it has a pump per cylinder and isnt solely electrically operated its not a common rail per se.

Didn't they say all this before the 2.0 came out too?

Yes, but even the 2.0 will end up with particulate filters so I dont think they will last.