Biodiesel and economy/performance

[Dexta Biofuels Forum Newbie Find all posts View Profile Close Dexta]

Hi, I have been viewing these forums for a while now as all our vehicles are diesel powered (Mazda BT-50, Mazda 3 Diesel, Fordson Dexta tractor, Backup Genset). I have been running B20 (from SAFF) in the tractor and generator (Honda 13HP Diesel) without problems for several years, and just recently tried it in the BT-50. I noticed a decline in the economy, about an 8% increase in fuel usage. I would have thought with the increased cetane rating I should get better economy/power (even the SAFF website says "Premium Diesel improves performance, torque, fuel economy & power". I then tried normal diesel in the genset and noticed that it could maintain a higher output than it could on B20.
Is there anything I need to do to the engines to get the best out of them on biodiesel? Is SAFF not telling the truth, or is it the case that most people get less economy/power on B20?
I'd prefer to use the B20 in the cars/generator but as it is the same price as dino but less efficient I'm inclined to hold off for now. However my long term goal is to grow my own oil seed and make my own fuel, but till then...

[yorta2 Senior Member Find all posts View Profile Close yorta2]

Re: Biodiesel and economy/performance

I use B100 in my Surf, but make it myself. There is a slight loss of economy as in a reduction in litres per 100 kilometres, and also a slight reduction in total power. But at the cost of production, it isn't a worry.

[Robert Administrator Find all posts View Profile Close Robert]

Re: Biodiesel and economy/performance

Generally, the figure quoted is about a 5% net loss in fuel economy. The calorific value of biodiesel is more like 10-15% less than diesel (from the top of my head, so the figure may well be different - someone please correct me if you have the right figure to hand), but because biodiesel burns more effectively, is oxygenated etc, when it actually works the engine, this recovers to about 5%.

However, it really depends on many factors, such as the condition of the engine, the design, the way it is driven, the load it pulls, the gear ratios etc, etc, etc. It will also depend on the feedstock that the biodiesel was made from. Purely vegetable biodiesel usually packs less of a punch than biodiesel made from animal fats (tallow). Then there is also the consideration of whether the biodiesel is washed or unwashed (can be methanol left in it).

If you are buying the stuff from SAFF, the feedstocks will vary, but I'd guess not by too much and it would certainly be washed and hopefully meets all the relevant specs, particularly on things like cetane.

There is also the question of injector timing, which may be optimised better for biodiesel as it's burn rate is a little different to dino diesel.

I've found that in the lower revs and under load, I can get equal or mildly better economy from biodiesel in some cars, but overall, I often get worse economy. I have never tried tuning my timing to match, but I would like to one day, I'm sure I'd get better economy from that.

I'm sure that the SAFF quote of "Premium Diesel improves performance, torque, fuel economy & power" would be referring to a large truck, carrying a heavy load and being able to stay in a higher gear at low revs up hills better to take advantage of the increased torque that the biodiesel combustion would give them in these conditions.

[Dexta Biofuels Forum Newbie Find all posts View Profile Close Dexta]

Re: Biodiesel and economy/performance

Thanks for that Robert, that answers my question perfectly! That would explain why my tractor goes well (max revs about 1500 RPM) whilst the cars (usually between 1800 to 3000) and the genset (3000) do not do as well.
i'll now concentrate on making my own as I'm happy to loose a bit of economy and power for a greatly reduced overall cost.