There has been a lot of debate on the infopop site about the benefits of adjusting the injector timing to suit biodiesel. However, there doesn't seem to be any agreement on whether it should be advanced or retarded.

Biodiesel has a higher cetane number than petro which means it ignites more readily. This would seem to indicate that a few degrees of retardation is required to ensure that peak cylinder pressure isn't reached before top dead centre. Also, it's reported that NOx emissions are reduced by retarding the timing.

On the other hand, it's also stated that biodiesel has a longer burn time than petro, so requires advanced timing to keep the burning mixture in the cylinder for longer.

Does anyone on this Forum have any experience with adjusting injection timing to suit biodiesel? Any diesel technicians out there have any Dyno test data or impirical/anecdotal evidence one way or the other?

In my experience I have always had to retard the injector timing.

And I guess if you getting oils from different sources, the cetane ratings are going to be all different. How do you plan for that? Maybe you mix all of the oils together. At the moment I'm getting 20 litre lots from 5 different sources each week. I dont titrate every batch but every 20 litres of oil that goes in will differ. Maybe I need to get crackin on my larger processor.

Joe

I found that the engine produces more torque at lower revs than on dinodiesel. In practice, this meant that I usually selected a higher gear than I would have normally have chosen if running on dinodiesel. If I could guarantee permanent access to BD, therfore warranting changing engine timing, I would be looking to ADVANCING my injector pump timing to move the torque band into a higher rev range.

Gunner, I notice the higher torque off of idle myself. However, the accelerator pedal is not full throttle. At part throttle the faster burning of the biodiesel gives a better burn. It is when I am full throttle up a hill that I notice a significant decrease.

After writing the above I felt I should add a bit more. The above comment pertains to an ignition that is already too far advanced.

I don't know what the torque curve is on Gunner's vehicle. However, most engines, including diesels, have a torque curve of some descripton. The torque curve is based upon the speed of the engine and the resulting twisting force at the crankshaft.

When an engine is at peak torque, that is when it is volumetrically the most efficient. That is, the engine is getting the best cylinder filling. At low rpms the valve timing may have a detrimental effect because of valve overlap between the exhaust phase and the time after bottom dead centre that the intake valve closes. The wave dynamics in both the intake and exhaust system also play a large part in the volumentric efficiency at any given rpm.

When the volumentric efficency is the highest is usually when the ignition timing is set. I say usually as if you slightly advance the timing you can pick up a bit on each side of the peak with only a slight decrease in the peak torque.

So how does this relate to biodiesel? If the timing is too far advanced at peak torque, then you will pick up power (full throttle and part throttle) on each side of the torque peak. However, at peak volumetric efficiency you will be trying to compress a mixture that is rapidly trying to expand, the result is a loss of work or power.

If on the other hand the timing is too far retarded, then the loss of power either side of peak torque will be felt even more. The torque peak will also be down and tend to be more pronounced, that is you will tend to feel it when the engine has some power.

Biodiesel burns a bit quicker than petrol diesel, thus at peak torque the timing should be retarded a bit.

You can play some games with this timing gambit. You can leave the timing advanced, but you could reduce the amount of fuel that you pump into the cylinder (leaner mixture) to reduce the rise time. This slows down the flame front and thus the cylinder does not come up to peak pressure as fast. Of course, the engine will not have as much power, but you will increase you fuel mileage.

I set my timing for a mixture of biodiesel and petrol diesel. Thus, most of the time I am in the ball park. If I end up running straight biodiesel or petrol diesel, again the timing is at least close.

Forget about setting ignition timing by a factory manual. I recommend setting the timing by the seat of your pants method. See what feels the best.

Very interesting info.

For those of us with fancy-pants computer controlled fuel injection, this sounds like a great opportunity to "chip" the vehicle for biodiesel.

When I used to play with LPG systems many years back, one could advance the timing, sometimes significantly, but to get the real benefit, the timing advance was not just a straight x° at all RPM, it was a curve that depended on many factors.

Of course, most straight LPG mods would just advance the timing 10° and be done with it. In a dual fuel setup, most installers would simply "trade-off" and put it at 5°. Not the best for petrol, or for LPG, but somewhere inbetween. I was not happy with this idea, so I managed to source a little box that would modify the timing curve depending on your RPM and other factors that you could program. It was switchable, so you could wire it up to your LPG switch and have it kick in only when needed. This way you could get the best of both worlds. Obviously, this sort of device is much easier when your timing is electrical, not mechanical, as it is for diesel.

Nevertheless, in theory, it would be possible to program a modern ECU to have 3 different profiles: 1. Dino, 2. Biodiesel, 3. SVO. How cool would that be?

I doubt that any manufacturers or 3rd parties would be doing this sort of thing for a while, but wouldn't it be nice? I'd certainly buy it.

__________________
Robert Fyvie
Site Admin
Sydney Biodiesel Users' Group and Australian Biofuel Users


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2007 Mazda 6 Diesel ..................................2000 Peugeot 306..........................2001 Landrover (retired)
2L Turbo charged (Common Rail) ...................XTdt 1.9L Turbo ............................Freelander TD4 (Common Rail)
on B100.................................................. ...on B100.......................................on B100

Hi Terry, seat of the pants method eh? That suits me, is it easy to do? I have a Haynes manual for the Pug 405 which talks about special tools and dial gauges and is 'a job best left to a diesel technician'. The car has a Bosch injection pump which sits in an easy to get to location, mounted on the front of the block.

I'm used to tinkering with carburetors and distributors, diesel lumps are new to me. Years ago I had a mini and I could set the ignition by trial & error rotation of the dissy, results were just as good as any strobe light.

On most diesels the injector pump can be shifted to change the timing. Just loosen the mounting bolts, shift the injector with a crowbar, and then re-tighten the bolts.

On some diesels it is necessary to disconnet the injector fittings. This is because the pump might shift a bit, but will quickly spring back.

On my Toyota 2.4L I can shift the timing by loosening the two front mounting bolts and the two rear mounting bolts that attach to a steel plate. If I pull the pump away from the engine the pump gets advanced. Inward is retard.

On my brother's Mercedes the opposite is the case. He has to pull the pump away from the engine to retard the timing.

Whereas I can change the timing without removing the fittings, he has to take them off.

Before you change the timing, mark the existing timing spot. That way you can always go back to the factory setting. Having said that, a timing mark on a flange is only a starting point. Even in manufacturing there are various clearances that vary between vehicles. Further, after the timing belt has been used for some time it stretches. This will then to retard not only the camshaft, but also the injector timing.

Try shifting the timing a fair bit the first time. Then if it proves to be too much, you split the difference from where it was originally. If that is still too much, then split it again. You want to find out what is too much of a shift. If you start with small increments it may take you a while to get to the too much stage, and then you still have to go back again. Just move it a fair amount and then start splitting the difference.

Well, I have to admit defeat. I tried for two hours yesterday to loosen the injector pump. It's secured by three nuts; the first is real easy to get to, the second is a struggle and the third is bloody impossible. Buried deep below fuel lines, A/C compressor, radiator, oil filter and an engine mount bracket. I tried just releasing the first two and levering with a length of angle iron, but I only succeeded in bending the angle iron.

It's so frustrating as the pump sits in a prime location on the front of the transverse mounted block. Bloomin' froggy design, every nut or bolt is obscured by something else. I hope the pump never fails, it appears like it would be quicker to lift the engine out rather than strip everything off the front of the car.

Hi all i stumbled accross this old thread and thought that i should post my ideas.

At the mo i'm rebuilding ELSA so i'll be setting the start of delivery by spill timing method. After its going then i plan to run her on my homebrew and take it straight to the diesel shop and get them to fuel her up and adjust the timing for my fuel. I also plan on getting the ROIDIO done at the same time. It will be interesting to see how much they adjust these two extremes of engine types up for top performance.
Any thoughts, comments or suggestions?

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Cheers
Nick.

Roidio 2001 Holden Rodeo 4x4 2.8L TD. 2.5" Straight through exhaust sytem, heat exchanger shower system. 2" Body Lift,
And lots of fruit, B100 for 25,000 no problems.

Elsa 1983 Mercedes-Benz W123 300D. The Fastest Merc in Oz, Loving B100 Burgers