c o l u m n

Jim Winsor • Executive Editor
On Fuel

What Is ‘Premium’ Diesel?

Here’s what a premium fuel should include. You must decide if it’s worth the premium price.

When it comes to buying fuel, does your fleet have a diesel fuel spec at all? If you buy in bulk for your own tanks, do you take whatever the low bidder quotes you? If your drivers fuel on the road, do you give them specific instructions as to what to buy?
     What do you get in premium diesel? And is it worth the premium price? With cold weather not far away in many areas of the country, are you concerned about fuel waxing and filter plugging if you don’t use fuel heaters or fuel additives?
     This month’s column focuses on premium diesel and what you should be getting for the higher cost. Only you can decide if it’s cost-justified in your fleet. This information comes from The Maintenance Council of the American Trucking Assns. and the Engine Manufacturers Assn.
     The two organizations have jointly developed a new Recommended Practice (RP 340) that contains technical specs for a Premium No. 2 diesel. You’ll be able to get this four-page document from TMC at 2200 Mill Road, Alexandria, VA 22314-5388. Phone: (703) 838-1762. Fax: (703) 684-4328.
     The most significant aspects of this fuel spec are its requirements for:
     • Minimum fuel lubricity.
     • Increased cetane number (50 minimum).
     • Improved cold-weather performance and detergency with minimum cloud points based on local ambient temperature.
     • Thermal stability.
     • Minimum energy content (in Btu).
     • Specs relating to overall fuel cleanliness (water, sediment, bacteria and fungus).
     The amount of energy in a gallon of diesel relates to its weight per gallon. The higher the American Petroleum Institute gravity, the less a gallon weighs and the less energy it contains. The premium-diesel spec calls for a maximum of 39.
     The API gravity seriously impacts engine power. According to TMC and EMA, there’s a 3% to 5% decrease in a fuel’s energy content for every 10° increase in API gravity. Engine power decreases at the same rate, which also translates to reduced fuel economy. Check API gravity with your fuel supplier.
     Cloud point, low-temperature flow and cold filter plugging point each impact low-temperature starting and operation. The RP calls for fuel specs of at least 4° C,. lower than the anticipated low temperature for various areas of the country, by month.
     Cetane relates to diesel fuel much as octane relates to gasoline and engine knocking or pinging. Diesel with low cetane numbers will cause hard starting, rough operation and more noise and smoke.
     According to the RP, diesel engines will operate year-round with fuel cetane numbers above 50. The national average is said to be 45. Cetane numbers can be increased both through the refining process and by blending combustion-improving additives. The minimum cetane number for premium diesel is 50.
     Detergency level is another area separating regular No. 2 from premium No. 2 diesel. Detergent additives will prevent carbon deposits that interfere with injectors’ fuel spray patterns. Dirty injectors translate to increased exhaust smoke and can also reduce engine power by restricting fuel flow. RP 340 lists a test and spec for refiners to meet for their premium fuels.
     Water and/or sediment in fuel is often evidence of poor housekeeping and fuel handling. Either can plug filters or shorten filter life, leading to engine fuel starvation. Diesel should always appear clean when held up to the light. Water also promotes corrosion in the fuel system and microbial growth, especially in storage tanks. Water parts per million (PPM) should not exceed 200 based on an ASTM test procedure. For sediment, 10 is the max.
     Premium No. 2 diesel should meet these specs and others not covered here that are part of RP 340. If they do, fleets buying Premium diesel should not encounter operating problems typically related to lesser fuels.