4.4 DIESEL FUEL

1. Fuel Classification Diesel engine fuel ranges from a highly refined distillate fuel obtained from fractional distillation of crude oil, to a product of residual materials obtained from crude-oil distillation, cracking processes, and fractions removed during the production of crankcase oil. However, the fuels with which the diesel technician is most concerned are those known as middle distillates, that is, grades 1D, 2D, and occasionally 4D.
2. To meet the needs of the various engine designs and sizes, and to accommodate frequent speed and load changes, permissible limits of fuel properties have been suggested by the changes, limit American Society for Testing and Materials (ASTM) and by the United States Bureau of Mines. Choice of the correct fuel allows easier starting and abates wear of fuel-injection inj ion equipment, piston rings, valves, and cylinder sleeves.
3. The ASTM defines three grades, 1D, 2D, and 4D, which are equivalent to types C-B, TT, and RR of the United States Bureau of Mines. Most diesel engine manufacturers recommend the us of 2D grade except for ambient temperature below 0°C. It is adviseable to refer to the local oil companies to obtain the correct fuel.
4. Cetane Number (Ignition Quality) The cetane number of a diesel fuel expresses its igniting quality. The higher the cetane number, the shorter the ignition delay period.
   The cetane number may be defined as the percentage by volume of the normal cetane in a blend with alpha-methylnapthalene to match the ignition quality of the test fuel. The cetane number affects cold starting, combustion, warm-up, deposits under ideal-and light‑
   load operation, roughness, acceleration, and exhaust smoke density. However, the ignition requirement of a diesel engine changes with the design of the combustion r.
   chamber, engine speed, and operating condition as well as ambient temperature and altitude.
5. High-speed engines require a higher cetane number to prevent engine roughness and knock, but the shorter delay period may lead to a darker exhaust smoke under maximum torque. This is because the raw fuel which is sprayed into the combustion chamber at this point ignites because of the shorter delay period.
6. Sulfur The presence of excessive (more than 0.5 percent) sulfur content in the fuel will eventually damage the engine unless the intervals between oil changes are shortened. If the oil is not changed frequently enough, the cylinder liners, pistons and rings, exhaust valves, and the fuel-injection system components will rapidly deteriorate. Such deterioration is brought about by oxidation of the sulfur during combustion. As the sulfur combines with the moist intake air, it produces sulfuric acid. This acid collects in the engine's lubrication system, becomes suspended in the oil, and thus causes the damage. Diesel engines using direct injection are more affected than engines using a precombustion chamber, a turbulence chamber, or power cells. Direct-injection engine components are also more subject to acid attack when the coolant temperature is low.
7. Fuel Additives Additives are sometimes used to improve certain characteristics of diesel fuel. Inhibitors and preventatives may be used to improve ignition quality, to reduce oxidation and corrosion, and to keep the fuel-injection system clean. Sometimes additives are used to reduce smoke and odor.
8. Fuel Storage and Handling When it is not practical to use a large storage tank and Handling
   storage of fuel in drums is the only alternative, take all the precautions outlined in the section Storing and Handling Crank-case Oils . As far as possible, avoid storing the drums outside.
9. If fuel is being stored in drums, do not use them as a convenient method of transporting
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   the fuel to the tractor or motortruck. Instead, drive the equipment to the fuel location. This way the sediment in the drums will not be disturbed.
   When a hand dispensing pump is used to pump fuel out of the drum, make certain the standpipe is about 2 in. [50.8 mm] shorter than the drum and make certain the drum is tilted slightly at all times.