Two Tank Timing question.

For discussing the modifications needed for diesel vehicles to run with 2 tank veggie oil conversions.

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Two Tank Timing question.

Postby Welder » Sun Jun 01, 2008 8:47 pm

Hi everyone.

As many of you know, another thread was recently started regarding the fact that many people running their CI engines on SVO have noticed that their engines run quieter on VO than ULSD.

It was pointed out that quieter engine operation isn't necessarilly a good thing, since diesel knock can be a good indicator of proper injection timing. Further, it was mentioned that various different fuel blends may affect engine operation in different ways and there was some dissagreement regarding the causes and effects of solvent blends.

I opened this thread because although it has been said for years that advancing timing injection will allow more time for the slower burning veggie oil to more completely combust, I don't remember anyone ever bringing up the issue that running two different fuels in an engine with a single timing set point will necessarilly mean that the engine will be off-timed for one of the two fuels burned.

I don't want this thread to become refocussed about the combustion characteristics of blended fuels, as I think that "pure" WVO/SVO is likely the most economical alternative fuel commonly available and I'd like to see further optimisation of this fuel use. Brewing biodiesel and blending fuels are both great ways to save money and help the environment out some, but both involve spending money on petrofuels. I know that a two tank SVO conversion does indeed use some petrofuel to get up to switchover temp, but for someone who drives a lot, the petrofuel savings in a two tank system are likely significantly greater than most blend ratios I've ever read about.

Since singe tank SVO conversions require only one injection timing set point this thread is not regarding single tank systems.

The thread that spawned this thread can be read here:

Quieter engine on VO is not better

In that thread, I asked for peoples input on the two different fuels requiring two different injection settings, but there seems to be too much happening there now for anyone to bother responding now, so I opened this thread in the hopes that someone interested in peak optimisation of SVO fuelling would their insight and opinion on this topic.

So basically, I'm asking you folks whether it's better to time a two tank SVO converted CI engine to the start/stop fuel, or whether it's better to optimise for veggie?

The factors I see involved here are:

1. Which fuel is burned most of the time in that converted engine?

and,

2. If injected off-time, which fuel is more likely to do less long term dammage?


Thanks!
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Postby denson » Sun Jun 01, 2008 9:19 pm

I would say time it for WVO if that is the fuel your vehicle consumes more of. Also, it is my belief that start up diesel off time would do less long term damage than WVO during normal driving off time. That is my opinion, I'm sure you'll get many more(from more experienced folks than myself) :D
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Postby SunWizard » Sun Jun 01, 2008 9:26 pm

I agree advance it for VO for both reasons. More advance during D2 warm up helps it warm up quicker and many already do it for performance reasons. Its easy to do with an electronic IP and an adjustable tuner - so easy you could start on 1 timing setting, then change it when you switched to VO. That would be the best.
YVORMV - Your veg. oil results may vary.
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Postby Welder » Mon Jun 02, 2008 1:25 am

SunWizard wrote:I agree advance it for VO for both reasons. More advance during D2 warm up helps it warm up quicker and many already do it for performance reasons. Its easy to do with an electronic IP and an adjustable tuner - so easy you could start on 1 timing setting, then change it when you switched to VO. That would be the best.


Thanks to Denson and Sun for responding.

Okay, so now I'm glad to hear from Suns post that the original advice that Craig and Ed (Neoteric/Plantdrive) had given me wasn't such a compromise after all, but would actually give faster warm up times and was also a diesel performance mod.

I wish my old F-250 was a newer solenoid injected Powerstroke, or a Cummins with digital injection control! With a rig like those, being able to have two injection timing programs for the two different fuels would be a definate bonus!

Oh well, at least whenever I finally do get the old boat converted to veg, I can optimise it for veggie and know I'm not beating it to death on warm up.

If run on ULSD for extended periods, three degrees advancement of injection timing isn't enough to cause an engine to suffer from the flame front smacking against the rising piston tops, is it? The fuel charge won't actually start significant combustion until the pistons have begun the downstroke, right?

I'm not sure of what would be considered an extreme advancement of injection timing, so forgive me if I appear to ask questions already answered earlier... (I'm a weldor, not a diesel tech)
Last edited by Welder on Mon Jun 02, 2008 3:46 am, edited 1 time in total.
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Postby Radrick » Mon Jun 02, 2008 7:21 am

I am a member of another forum that helps me keep my truck working properly and has extensive info on performance modes for it. One of the comon performance mods is to advance the timing. This is done to gain perf. on diesel not vo. It does cause the engine to rattle more expecially on cold starts. It is quite complicated since my IP is computer controled. It involves both a mechanical change in the pump position and a computer change in the timing offset. I have been looking at doing this as part of my conversion but haven't resurched it thoughly yet, as I have been to busy just getting all the other issues straitened out so I can start my conversion. Unforinatly for me this also means I need to have a scan tool to do this mod.

You will ahve to excuse my bad spelling as my spell chekcer isn't working on my wokr computer. :o
1995 Chevy K1500 6.5 TD not on WVO yet but soon.
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Postby Welder » Mon Jun 02, 2008 3:34 pm

Thanks, Radrick.
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Best timing?

Postby HoldOnTight » Wed Jun 04, 2008 9:44 am

I am not an expert, but I use the following logic to support my belief.

1. Advancing the timing won't have as much impact on diesel performance if the diesel is being used primarily during engine warmup. I base this on the belief that a cold engine will have a slower flamefront than a hot engine, when running on diesel. The temp of the diesel does affect the efficiency of the burn rate.
2. Unless diesel is very inexpensive, I'll be running VO whenever possible, which is when the engine is hot -- hopefully more than 60% of the time for short trips and more than 99% of the time for long trips. Driving habits affect the timing choice.

3. A few degrees probably won't make that much difference when running on diesel. Timing of diesels in many cases is set conservatively by the manufacturer as cetane values vary significantly in the US. Hence, damage is not likely for the changes we are discussing.
Also related, my question is: Do the more modern computer controlled diesels monitor and adjust on-th-fly, the timing to achieve peak efficiency for the fuels being burned? I would think so if I consider the differences between summer and winter diesel. I believe gas engines compensate for octane variations and so why wouldn't diesels also compensate for cetane variations?

Comments?
Late 99 Ford F-250, Designed and installed at home, 30 kMi on VO. WVO temp at solenoid valve is 185-195+F, winter-summer.
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Postby denson » Wed Jun 04, 2008 10:56 am

I have also heard that modern computer controlled diesel engines advance or retard timing on the fly based on fuel temp sensors. Unfortunately, I have not been able to confirm this yet. Is there anyone out there who can?
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