Question about post-stream v. in-stream fuel injection

[doctorclark]

After doing a bit of homework (mainly http://www.biodieselmagazine.com/articles/2290/understanding-the-post-injection-problem/ but also some other, similar articles), I have a question about fuel dilution as it relates to TDI engines and biodiesel.

TDIs use in-cylinder post-injection to regenerate the diesel particulate filter, which causes trace amounts of diesel fuel to mix with the engine oil. This, along with the chemical properties of biodiesel, is the reason no blend of biodiesel above B5 should be used.

Here's my question: could a new (e.g. 2011) TDI theoretically be retrofitted with an in-stream injection system (potentially coupled with a burner)? This would presumably have to be done in concert with changing the injection scheme/program.

If feasible, would this be prohibitively expensive? Seems to me like avoiding dilution of engine oil with diesel fuel (bio or not), could only increase the longevity of the engine.

 

[doctorclark]

...and I have read my way through the two relevant threads just to check if there's been an answer. FYI, they are:

http://forums.tdiclub.com/showthread.php?t=246090&highlight=stream+injection

http://forums.tdiclub.com/showthread.php?t=249514&highlight=stream+injection

 

[JSWTDI09]

Here's my question: could a new (e.g. 2011) TDI theoretically be retrofitted with an in-stream injection system (potentially coupled with a burner)? This would presumably have to be done in concert with changing the injection scheme/program.

If feasible, would this be prohibitively expensive? Seems to me like avoiding dilution of engine oil with diesel fuel (bio or not), could only increase the longevity of the engine.

Anything is possible (with enough money). A post combustion injector could be put into the exhaust system, but it would have to be a very different type of injector to withstand the conditions. This injector would then have to be tied into the fuel system somehow. Then a custom made tune would be required to remove the in-cylinder injection and change it to an exhaust injection system. This custom tune would probably be the most expensive part of the plan (but I'm no expert on these things)

Engine oil dilution is not a serious problem with conventional D2 fuel because it will evaporate at the normal operating temperature of the engine's oil. Many people here have done UOAs (Used Oil Analysis) at 10,000 miles and found no significant oil dilution. However this is not the case when running B100. Biodiesel has a much higher evaporation temperature. This is the reason behind VW's recommendation of no more than B5.

Your idea of a fifth injector in the exhaust system is probably the only safe way to run B100 in a modern CR diesel engine. Actually, it is not a new idea, some big trucks do this by design. The extra injector would probably have to be inserted after the turbocharger and before the DPF to work properly.

Have Fun!

Don

P.S. If you decide to try this - be sure to post the results here.

 

[VWBeamer]

IMHO, it would be cheaper to remove the DPF and just get an off road tune.

Not legal, but from a moral stand point, why are we suffering with these DPFs and my next door neighbor can burn his fireplace putting more particles in the air in a 24 hour period than my car would in a life time of use?

BTW, any modification to the emission system is technically illegal, so your 5th injector idea would be also.