Our Bio source is primarily from soybean esters and that was what was focused on here. What they did is went to the field and sampled petroleum based ULSD petroleum based stock and the Biofuel that would be blended in. They found the following...
Property ULSD Biodiesel
TX FL MD MN
Initial Water PPM 107 363 474 594 361
Sat. Water PPM 153 1829 1971 1574 1738
Partic. MG/L .5 5.5 23 6 7
What is clear to me is that the petroleum based ULSD is by far better raw fuel stock for both water content and particulate content. The Bio samples, because they are a single random samples in no way represent any worst case as to how bad these properties can get. In general in the bio-stock you can expect to have 5 to 15x the water concentration and 10 to 20 times the particulate level. The problem does not stop there because the bio-stock has much more affinity to absorb water in all the other phases of transportation and storage so these are best case raw stock numbers. The expected problems that are created by the bio-blend are outlined in the paragraph below where I note the conference paper.
What this all means to us in defense, is that we need as best we can in our travels, to plan our fuel stops and avoid B20 or other higher blend levels whenever we can. It is particularly important if you are storing your coach for a longer period of time in a humid area. My east coast side of the country travels this summer, fueling along I81, I was dismayed to see Flying J and Pilot were only selling B20. I pulled out of those stations and I am trying to buy just Chevron fuel which I have yet to see a Bio Blend level sticker on and I have verified several times that they are are not blending Chevron diesel with bio-stock, at least in my area.
Because of the water absorption issues and the particulate issue you can anticipate that the need for filter changes will happen sooner, but more importantly if you have to use B20, you will have more water available sitting in all of your fuel system due to the nature of the beast that can grow algae in the tank or damage parts. I think the over the road truckers whose rigs do not sit will have less of a problem with the water absorption issues then us RV folks but they will see more filter changes in general. A fuel that has an affinity and a capacity to absorb more water is a problem that our filtration and engine fuel system has not been designed to accommodate....so as with other things in life we need to manage it as best we can.
American Filtration & Separation Society Annual
Conference, May 19-22 (2008) Valley Forge, PA
The biodiesel molecules indeed have very high affinity to water though, as can be seen
from the water concentration analysis. The dissolved water concentration for diesel fuel
is typically in the range of 30 ppm to 180 ppm. Biodiesel does dissolve more water, over
300 ppm, and this is not a surprise considering the nature of those ester molecules, which
are more polar than petrodiesel fuel molecules consisting mainly of hydrogen and carbon
atoms. What’s more interesting is that, when biodiesel is mixed with free water to reach
phase equilibrium for water saturation in the fuel, 2.5-5 times more water is dissolved
depending on the source of the original biodiesel, as shown in Table 1. This is important
because we normally pay attention only to free or emulsified water filtration, but the huge
increase in water solubility in neat biodiesel compared to ULSD can also be a major
concern. The existence of such dissolved water can promote biodiesel hydrolysis to break
down the fuel molecules, which will raise the fuel’s surfactancy due to the formation of
carboxylic acids; it will also promote bacteria growth and fuel oxidation, and possibly
affect the fuel combustion and cause corrosion problems. The separation of significant
amount of dissolved water will redirect fuel filter design in practice. However, all these
problems could be mitigated by using biodiesel blend with relatively small blending ratio.
The challenge to avoiding major water ingression to biodiesel therefore lies in the
operational chain of fuel storage, shipping, handling and blending before the blended fuel
is used to power an engine.
Ed back again...I was also looking at issues beyond contamination, this is info on blending. This info comes from a Bio-Diesel Handling And Use Guide available in PDF form on the web. When it is labeled B20 are you pumping B20? That relies on many other factors and diligence and training of the fuel suppliers...This line gave me pause..."Biodiesel is heavier, so it may stay, unmixed, at the bottom of the tank."
It is not assured that the biodiesel component, which has a different specific gravity then petroleum based diesel was well mixed and the colder the temperature the harder it is to get the blend methods to work. Biodiesel is heavier and more viscous and it requires vigorous agitation to blend it. They note if added to the bottom of the tank it will sit in a layer, if added to the top of the tank it will sink to the bottom and make a layer. It requires vigorous agitation to create the final blend. Beyond the water, contamination, there is the blending problems that when you pull to the pump and it says B20, am I pumping B5 or B40 right now?...not sure I would say. Obviously most of us will have to pump B20 at some point, just do the best you can to manage how much of it you use, which is what I am doing, especially when the coach is going to sit. Hope this helps.
Later Ed
