Warning to SVO users

[littlelegs]

This carbon can be caused by any number of things even slow driving, you can't point the finger just at SVO without proof, especially as your engine obviously has oil burning mechanical problems which would more than likely be the first cause. An engine is a heat machine and a frequent good run burns off any normal fuel related carbon but the engine can't deal with the carbon from continual engine oil burning or always pottering about. There is obviously also a sensible limit to the amount of SVO/diesel mix ratio that can be reliably used, related to how hard it's driven.

[Snagger]

This carbon can be caused by any number of things even slow driving, you can't point the finger just at SVO without proof, especially as your engine obviously has oil burning mechanical problems which would more than likely be the first cause. An engine is a heat machine and a frequent good run burns off any normal fuel related carbon but the engine can't deal with the carbon from continual engine oil burning or always pottering about. There is obviously also a sensible limit to the amount of SVO/diesel mix ratio that can be reliably used, related to how hard it's driven.

The rings in cylinders 1 and 4 are perfect, but they had the worst carbon deposits. This problem is not due to the engine itself. The injectors and injection pump were rebuilt by a reputable company at the same time as I did the rest of the engine, so spray pattern and timing were also not at fault. While driving style, especially excessively gentle driving, will cause problems, I can't see it happening over 2,500 miles.

Jim, I also had adverse effects on my unmodified 300Tdi when I tried a 50% mix a few summers ago - the rpm was hunting in the mid range by about 500rpm, and though I quickly diluted the mix as much as possible, put several bottles of treatments of Millers diesel additive through, it has never been the same since - the hunting is very small, but still present, and I get a lot of judder in 4th when accelerating from low revs which didn't used to be the case.

[PinkSeriesIII]

Was this Soya based SVO ?

How well was the system purged before shut down and how do you know?

[littlelegs]

I've had another look at your piston picture and although it's not very clear it doesn't look too unusual and the top ring appears free, the carbon ring helps to seal it and I've seen worse on a straight petrol engine! Rings can carbon up on any fuel if it was going that way but it's usually due to burnt engine oil caused by wear or broken/sticking rings. If you've put new pistons and rings into a worn, glazed cylinder, they are not going to bed in properly and will burn oil. I don't know the engine history but the fact that after 2500 miles you've got high oil consumption and broken rings means to me that something wasn't completely right at the rebuild.

[Snagger]

Closer inspection of the two broken oil rings suggests that the broke as the pistons were removed - Frida Turner had a similar suspicion, and she commented on the lack of actual scoring (as opposed to the polishing lines) in the bores as proof of this. This is evidenced by the side on which the circumferencial cracks are - the rings may have caught on on the coke ridge as they were extracted.

The block was rebored and honed for the new AE pistons and rings, and the ring gaps were all set correctly. The injectors and pump were all freshly rebuilt. This heavy coking was not due to engine faults.

It's possible that I haven't been purging the system for long enough at the end of each drive to clear the SVO completely before the next diesel start up - I have been using a 3 mile change over point. However, the point is that this coking is definitely due to SVO, and Frida again told me this morning how they can instantly tell which engines have been using it as soon as they open them up. There are also several other blogs and forums discussing the issue, with this http://forums.tdiclub.com/showthread.php?t=186108 being a very good example with plenty of good photos of his coking and damage. Many respondents on that thread report the exact main symptom I have encountered - heavy oil loss through the breather into the induction tract. Some are trying to blame EGR systems, but that's not the cause - my 200 and 300 engine both lack EGR.

Whether insufficient engine, and thus heat exchanger, temperature are to blame, or whether it's because I left the diesel selection too late in the drive are potential debates, but it's pretty clear that SVO is a lot more troublesome than generally percieved. I will be returning my fuel system to plain diesel and removing the heat exchanger unless I can find an additive that will keep the carbon at bay at an economical price.

[Snagger]

Here's another good article, which also brigs up PinkSeriesIII's point : http://www.biofuelsforum.com/svo_use...need_know.html

[Muttley]

Surely the reason it's coking is that your cylinder temperatures are too cool so you are getting incomplete combustion. Particularly seeing this issue is worse in cylinders 1 & 4 (the cooler outer cylinders).

Have a look at putting LPG onto that.. that'll cure the coking problem and give you a lot cleaner burn on SVO (& diesel for that matter) plus you'll get more power








Wait for it.....

[Snagger]

Surely the reason it's coking is that your cylinder temperatures are too cool so you are getting incomplete combustion. Particularly seeing this issue is worse in cylinders 1 & 4 (the cooler outer cylinders).

Have a look at putting LPG onto that.. that'll cure the coking problem and give you a lot cleaner burn on SVO (& diesel for that matter) plus you'll get more power

That's a good point about the temperatures.

I'd love to fit a propane catalyst injection system, but at over £2k, they're a bit pricey!

Iv'e been looking through this Aussie forum, www.biofuelsforum.com/svo_users , and many of them seem to have run their various engines with varying levels of success, from completely successful to complete destruction of the engine. What seems to be an issue is the purge time, especially since my return line is looped into the lift pump to dend warm fuel to the filter to prevent waxing and also to prevent tank cross-contamination. It may be that my sustem is only really any good for long trips, with purging being required for the last 10 mils or more.

[littlelegs]

Here's another good article, which also brigs up PinkSeriesIII's point : http://www.biofuelsforum.com/svo_use...need_know.html

Your first link case seems to be a problem with the turbo causing the initial carbon problem and this could just as easily have happened with diesel. It had also covered considerably more miles than you did.

The second link seems to be more of a rant and a scaremongering exercise and attempts to reverse the characteristics of direct and indirect engines suggesting that the direct run colder and will condense fuel more easily. If this really were the case then the indirect would be the easier to start and it's not because it has the larger combustion surface and loses more heat, hence harder to cold start! He makes absurd comparisons. The direct doesn't need the starting and running devices and is a much more efficient burning engine, unburnt excess fuel would mean it was not set up properly and appear as black smoke which should not be ignored. I don't think this person knows what he's talking about.

I'm not saying you can't have a problem with SVO if you use it wrongly or excessively and choke the engine with it but it just seems that normal mechanical or adjustment problems are being blamed on SVO without any proper evidence to support it. The effects we've seen can just as likely be caused by diesel with too much fuel or not enough air or from a worn oil burner. The only true bit is where once the carbon starts to build up and affects the rings it rapidly gets worse.

You say the rings were broken on removal but the top rings were ok. If the carbon ring was to blame and that bad, shouldn't it have been removed first? I'm sorry if this seems like a grilling but nothing seems to make sense to me and I've been working with diesels for a long time, many of them similarily coked up, usually stationary or marine type that are overloaded. Perhaps you just need to change down a gear more often?

[RUXY]

An improved vortex would prevent the carbon sticking -fit a Hiclone - end of problem

[justMike]

It may be that my sustem is only really any good for long trips, with purging being required for the last 10 mils or more.

My change of employer has seen my commute to work go up from 250 to 1000+ miles a month.. eith warm up and purge times like you're suggesting, even with the mileage I'm doing now, it'd never be a worthwhile conversion for me... I'd be able to use oil injection for maybe 2 miles a day..(??) before starting to purge the system...

Honestly not trying to shoot down your system Nick, but along with the chemistry issues, I can't get my head around how 2 totally different fuels with completely different burn charactoristics and BTU content can be injected through the same pump and fuel metering without having to make changes to the metering when you change fuel types.

[Snagger]

An improved vortex would prevent the carbon sticking -fit a Hiclone - end of problem

I hope that's a joke! How would a vortex in the snorkel make the slightest difference to fuel spray patterns. Let's leave vortex generators and other snake oil ideas out of this and stick to things that may actually work.

[Snagger]

Your first link case seems to be a problem with the turbo causing the initial carbon problem and this could just as easily have happened with diesel. It had also covered considerably more miles than you did.

The second link seems to be more of a rant and a scaremongering exercise and attempts to reverse the characteristics of direct and indirect engines suggesting that the direct run colder and will condense fuel more easily. If this really were the case then the indirect would be the easier to start and it's not because it has the larger combustion surface and loses more heat, hence harder to cold start! He makes absurd comparisons. The direct doesn't need the starting and running devices and is a much more efficient burning engine, unburnt excess fuel would mean it was not set up properly and appear as black smoke which should not be ignored. I don't think this person knows what he's talking about.

I'm not saying you can't have a problem with SVO if you use it wrongly or excessively and choke the engine with it but it just seems that normal mechanical or adjustment problems are being blamed on SVO without any proper evidence to support it. The effects we've seen can just as likely be caused by diesel with too much fuel or not enough air or from a worn oil burner. The only true bit is where once the carbon starts to build up and affects the rings it rapidly gets worse.

You say the rings were broken on removal but the top rings were ok. If the carbon ring was to blame and that bad, shouldn't it have been removed first? I'm sorry if this seems like a grilling but nothing seems to make sense to me and I've been working with diesels for a long time, many of them similarily coked up, usually stationary or marine type that are overloaded. Perhaps you just need to change down a gear more often?

Tdis do run cool, while 12J don't, so his logic seems to fit. There are other aspects of his arguement that also make sense about the advantages of iDi.

As I said, the compression rings are fine - it's only two of the oil rings that are damaged, and the lack of scoring on the bores strongly suggests that this was caused on piston removal as the rings caught on the coke lip - they're much more delicate than the compression rings. It's not impossible that I damaged them while cleaning the piston crowns, though unlikely.

The point is that the coking is not a product of an engine fault. Reading those Australian site threads points more and more towards it being an insufficient purging period at the end of the run, which will render my dual fuel system useless on the commute and only effective on long runs. It's still worth having, but it's a shame I can't benefit on my commute. If it's possible for me to fit a quick purge system of some sort, then this may help, but that will need electric pumps and solenoid controlled change-over valves, including for return lines - I'd have to completely redesign my fuel system.

[littlelegs]

Tdis do run cool, while 12J don't, so his logic seems to fit. There are other aspects of his arguement that also make sense about the advantages of iDi.

As I said, the compression rings are fine - it's only two of the oil rings that are damaged, and the lack of scoring on the bores strongly suggests that this was caused on piston removal as the rings caught on the coke lip - they're much more delicate than the compression rings. It's not impossible that I damaged them while cleaning the piston crowns, though unlikely.

The point is that the coking is not a product of an engine fault. Reading those Australian site threads points more and more towards it being an insufficient purging period at the end of the run, which will render my dual fuel system useless on the commute and only effective on long runs. It's still worth having, but it's a shame I can't benefit on my commute. If it's possible for me to fit a quick purge system of some sort, then this may help, but that will need electric pumps and solenoid controlled change-over valves, including for return lines - I'd have to completely redesign my fuel system.

You may well be right about insufficient purging and you can't do that properly if the return is not also controlled but that's an installation fault not an SVO problem as such. It may also be you are switching over to SVO before the engine is ready for it. Can you tell me what you mean by "TDis do run cool while 12j don't" do you mean the combustion temperature or coolant temperature and why you think this is?

[Muttley]

Keeping on with the issue of coking up.

1. Got to agree with a previous comment about putting a different fuel into an engine without having to alter the timing or fueling. Diesels are a fundamentally dynamic closed loop system so making such a major change like altering the fuel will have ALL sorts of unknown effects on the overall balance of the system. A 300TDi is optimised for using a fuel in a very tight set of specifications, a lot stricter tolerances than a petrol engined vehicle has. So no wonder some of them are throwing chuckies, the key question on the TDis that are lasting the course is to investigate tham and find out what was done differently in comparison to the ones that fail.
2. SVO has a far lower calorific value than Diesel (i.e. it doesn't contain as much chemical energy. hence it will burn cooler). Vis-a-vis the coking issue. Which is why I made my suggestion about propane injection.
3. In my opinion the issue of purging has NO effect on the coking issue. Purging is done to ensure that a) the injection pump and injectors are kept in perfect running order b) to insure that cold start performance is optimised. Coking is a timing/fuelling/burn temp issue.

I was looking at some of the articles mentioned here and they seem to be from predominantly WARM countries with a higher ambient temperature all year. I was looking at some of the kits availible and it seems to me that the heat exchangers are hopelessly small for the sort of weather we are subjected to in the UK and thats without taking into account the HUGE difference in average temperatures accross the UK. A system designed by a company located in the midlands is not going to perform anywhere as well in somewhere like the Highlands of Scotland. Conversely though a system optimised for use in low ambient temperatures (say Scandinavia) should work readily all over the UK.

BUT in order for the systems to work efficiently they must take account of the timing and fueling changes required when running between SVO and Diesel. System control is the key to it coupled with ensuring that the cylinder temperatures are kept higher than when running on SVO to account for the lower calorific value of SVO to ensure that engines don't coke up.

I am a huge fan of alternative fuels (as some of you will remember) but from what I'm reading there seems to be a fundamental failure in the understanding of how these systems operate which is resulting in long term issues. I'm not talking at a mechanical level... there is a lot of knowledge here of how they work and how to get them to work, where the knowledge is missing is at the systems level and the relationships of system components on each other - that takes a LOT of dedicated research (hence boot fulls of dosh) and a lot of clever people to optimise the technology.

It's the same with any type of new technology, it is going to be as unreliable as heck in the early years but as the knowledge base grows the technology will be modified to cope... it's just unfortunate that Snagger's motor is one of the casualties to this science

It could be something as daft as moving a flap accross 50% of the rad when running on SVO to up the cylinder temp or somthing as mundane as changing the thermostat that could be the key to the coking issue.