Thread: Common rail diesel injection

Hi gtemco,

Someone was only asking a couple of days ago about using biodiesel in a Ford Transit van...

As for common rail, there is something in the warning about the use of bio in a common rail engine, but not what the manufacturers would have you believe. In a common rail, fuel can be exposed to higher temperatures and more recirculation than otherwise. The fuel that is in the rail gets up to 100°C and most of this does not get injected, but recirculated back to the tank, where it has the chance to be exposed to air again. This increases the chance that it might oxidise.
Now, biodiesel that meets spec will have a very high oxidation stability, meaning that it takes a long time before it can go bad. In a common rail system, the speed that oxidation can happen is increased, or the time at which it can resist is decreased. This is not a concern if your biodiesel meets spec, but if not, then it could be an issue.
This does not seem to prevent manufacturers telling you that biodiesel is not suitable because of common rail. Fortunately, you are better informed than just to blank it out.

There has been some discussion in the forums here on this recently. Have a search, or look at this thread where this is also discussed.

Thank you Robert. The possibility of accelerated oxidation of biodiesel in common rail systems hasn't been explained to me before and I therefore find your posting extremely informative. Other reasons that have been put to me to not use bio in common rail engines, mainly relate to the onboard computer systems that these engines use, i.e. bio may upset the various sensors that these systems use and cause the computer to shut the engine down to 'limp mode'. As a home brewer of BD I don't have the means to ensure that every batch I make meets the ISO or EN spec. I titrate accurately and my finished product looks good, feels good and runs well in my present vehicle......but do I have the nerve to use it in a brand new £20,000 CDi or DCi common rail vehicle? Not yet. I guess I am waiting for some other home brewer, far braver than me, to take the risk and report the results. Of course I could try commercially produced BD that is guaranteed to meet spec, but in the UK commercially produced BD is no cheaper than petro diesel, because our government still want their tax cut, unlike some other European countries where BD is duty free. Regards - Ian

Hi Ian,

Tax is the same issue here in Australia, but most of us are not using biodiesel purely for the economic benefits.
Not sure re the sensors, I think that may be a red herring, as the sensors do not sense any chemical properties of the fuel, they will sense flow speed, temp, etc, so I'd guess this sounds like the sort of thing that "expert" service people come up with to justify a position that they think they should have on biodiesel without ever having done any real tests on it themselves. I do know that the old Freelander L-Series model used a sensor on the first injector that was contained rubber component that swelled with biodiesel (i.e. not Viton) and this caused that sensor to malfunction. I'd doubt that modern engines would employ such materials any more.

If you wanted some confidence about the oxidation stability of your home brew, you could possibly build your own rancimat tester. A rancimat is a very expensive machine that test labs complain about having to buy for biodiesel testing. It accelerates the oxidation of the fuel by heating it and bubbling air through it. During this process, acids are formed which will drip into distilled water. Testing electrical conductivity in the water will tell you when a certain degree of acidity has been reached. I've often thought that a person with enough of an interest in this could probably build their own home made rancimat with aquarium heaters, air pumps, some simple chemical brewing apparatus and a multimeter. If anyone ever does (or ever has), I'd be keen to know about it.

With regard to all this may I add that my 2004 Peugeot 307 HDi has not yet complained about my homemade biodiesel, 39,000 km and counting. I have not had any tests done apart from my obsesiveness. Run on it since new, almost, the initial tank was mineral diesel.

Please do not mention the sensor thing as my car has not yet figured that one out. In my mind if the sensors play up then they have been made of inferior materials anyway, what consolation that is, is debatable though.
Matt

Hi Matt - Very interesting; your input has boosted my confidence in using 100% bio in my new common rail diesel when I get round to buying it. Anybody else out there who has been using 100% Bio in a common rail diesel or VW PD diesel, then I'd love to hear from you. Thanks - Ian

hi Ian- I have exactly the same dilemma. I drive a 98 toyota hilux on 100% biodiesel without any problem and am considering changing it for a newer model that has a common rail injection system.
I would like to know if there is problem using b100 with a common rail , will it be felt immeidiatly from the first tank.

Guys, I have read about the possibility of polymerisation and oxidisation in the high pressure and consequent high temperature environment in the injection rail and engine area.

Firstly I do not believe that temperatures will exceed a normal engine compartment by a great deal and polymerisation is a fuel quality factor so with good fuel I do not think this is an issue. After 41,000km I have not detected any injection issues, its running the same as it was when new. As for the oxidisation factors with out the presence of oxygen in the common rail system it simply will not oxidise or breakdown. How it behaves in such a high pressure environment is the major issue I cannot quantify. If Peugeot are saying 30% bio is fine then it must not be too much of an issue as I sincerely doubt mineral diesel will be any form of solvent or cleaner.

I ran on it since new and do not as yet regret one moment (well maybe one when I was filling by hand and did not register when the tank was full.)

Matt

My R5 TDI VW engine (PD) has now 70,000km on an average of about B20. When I have had the opportunity, it has been up to B100. No issues apart from the expected "power slightly down, fuel use slightly up" described in the VW manual.

Neil

Originally Posted by moonan

up" described in the VW manual.

I heard some WV manuals say biodiesel is the prefered fuel for the car. Wha does yours say? How much does it say is OK?