Originally Posted by sailaway21
This just in.
One of my over the road truck driver buddies just told me that, in addition to there being less energy in the low sulpher, it seems to have a greater affinity for water. It is definitely gelling much quicker in cold weather. Sounds like filtering and water removal are going to be even more important.
Since June 2006 80% or more of highway deisel has been Ultra Low Sulfur Deisel (ULSD) which is 15 ppm sulfur compared to Low Sulfur Deisel (LSD, but not the kind Dr Leary wrote about) at 500 ppm sulfur.
ULSD is made by hydrotreating which makes it more susceptable to gelling. Untreated, it will gel at about 30F but this has nothing to do with water in the fuel. "Winterizing" ULSD involves either blending it with kerosene, which is very expensive for the refineries, or treating it with pour point depressants, cloud point depressants and cold flow improvers.
Hydrotreating also reduces the lubricity of the ULSD so that engine parts wear faster. Lubricity improvers are added to counteract this. Some of the natural antioxidants in the deisel are also removed by hydrotreating so there are antioxidant packages added to prevent gums and sludge.
These additives were used in regular deisel and LSD, it's just that more is used in ULSD. I work for a company that sells these additives and others to the refineries and distributors.
Hydrotreating causes the deisel to burn more quickly, reducing fuel efficiency slightly. Mileage reductions of about 5% are being seen. I'm not sure about ULSD having more affinity for water but I do know that the spec it has to meet for water content hasn't changed. I can find out for sure if someone has a specific interest.
The positive aspects, besides the main one of reducing the amount of sulfur going into the air, is that ULSD improves cold starting (since it burns faster), reduces white smoke during the warm up period and prolongs the period allowed between oil changes (since it burns cleaner).
Biodeisel is a more recent change in deisel. It's very much an emerging market with as much as 20% being blended into some deisel sources. This addresses some of the lubricity issues with ULSD but does not allow kerosene to be used to improve the cold flow properties. Specific biodeisel additive packages are used to ensure that the fuels continue to meet quality specifications.
Better living through chemistry.....for me especially.