Retarded timing
Diesel JD, thanks for the reply. There is a lot of good info there.
There appears to be contradictory information out there. Some of which appears to contradict logic.
Unfortunately, I do not have a fuel meter on the tank pump, so I have no accurate way to measure the fuel being used other than by the tank full. Maybe your post will convince the wife I need to buy a fuel meter.
That said, estimating the mileage by kilometers to the tank full, I guesstimate about 13-14 miles/ US gal. which is pretty close to what you are getting and that was with the 1992 F-250 7.3l E4OD with 4.10 gears. The 1986 F-250 4x4 ZF 5 spd with 4.10 gears has not been optimized yet. I am still retarding the timing on that one. When I got it, it was waaaay too advanced. It rattled like it was going to come apart! The guy I bought it from said it was down on power. No...really?
Also, I do not have a luminosity probe, or pulse meter. It would be very useful to get actual timing readings. My son-in-law works at a Ford dealership here in Calgary, maybe I can work something out with him.
I misread the Haynes Diesel Techbook
Looking at the Haynes Techbook again, I see that following:
Fuel Cetane Value Calibration
4-468J ROO 4-68X ROO
38-42 3.5* ATDC 4.5* ATDC
43-46 2.5* ATDC 3.5* ATDC
47 or greater 1.5* ATDC 2.5* ATDC
That indicates that timing needs to be ADVANCED for higher cetane fuel, which is counter intuitive.
Is that a typo? Can someone verify that with the Ford Service Manual?
Higher cetane value fuels burn faster, which require less advance.
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This chart, which I borrowed from Lubrizol, says "Shorter Ignition Delay = Lower Rate of Pressure Rise". However, they provide no explanation of why that is. For a fast burning fuel it would make sense that pressure rise would be quicker/higher rather than lower.
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This is a typical chart of cylinder pressure vs crank angle. Ideally, for maximum efficiency we want the greatest area under the curve after TDC. Its actually a little more complicated than that. ie. the same area under the curve will produce more work if it is moved to the right of the chart. (retarded timing).
From Journeytoforever.org, "Diesel engines vary widely in their cetane requirements, and there is no commonly recognized way to measure this value. In general, the lower an engine's operating speed, the lower the CN of the fuel it can use. Large marine engines can tolerate fuels with CNs as low as 20, while some manufacturers of high-speed passenger car diesel engines specify 55 CN fuel."
This would indicate that slow turning engines can use slow burning fuels, and fast turning engines use fast burning fuel. This would make sense.
Perhaps it comes down to "what do you want?". If you are looking for peak HorsePower, advancing the timing to take advantage of the fast burning properties of bio-diesel at high RPM makes sense. If you are looking for peak torque or peak fuel efficiency, which occur simultaneously, then optimizing the timing for maximum area under the curve to the right is the way to go.
Peak HP burns all the oxygen/air in the cylinder. Peak fuel efficiency burns all the fuel in the cylinder. Peak torque occurs when peak fuel efficiency matches with the design of the engine: compresssion ratio, bore/stroke ratio, rod ratio, camshaft design etc.
Has anyone done any dyno runs to find optimal timing for bio-diesel?
My results are only related to how my timing was set on my vehicles, and is aimed at finding peak fuel efficiency. Perhaps my conclusions are premature?
Thanks again for making me think.