There about 50 specifications for diesel fuel. The most critical for standby diesel engines are as follows:
Bottom Sediment and Water (BS&W):
ASTM D-1796 This test measures the total amount of insoluble water and solids in the fuel by removing them via high-speed centrifugation. It is particularly useful in isolating foreign material in the fuel such as tank bottoms. ASTM maximum for #2 diesel fuel =0.05%.
Moisture Content:
ASTM D6306 A measure of both soluble and insoluble water present in the sample by an automated coulometric titration. Aspiration of water into the fuel tank during the warm/hot day – cool/cold evening cycle leads to a buildup of water in the fuel and accumulation at the bottom of the tank. Water and Sediment – When the fuel is saturated with moisture, water settles to the bottom along with smoke particles, road dust and bugs.
Microbial Contamination:
ASTM D-6469. Incubated Culture. Semiquantitative test for bacteria, molds, and fungi, all of which can grow in diesel fuel tanks and damage fuel injectors. Often detected, though not limited to, storage tanks where water contamination is present. It is important to sample the bottom of the fuel tank when checking for bacterial contamination. No ASTM specification, however, any presence indicates a need for fuel treatment. Microbes thrive at the interface between the water and diesel.
Distillation:
ASTM D-86 This test is a measure of the boiling range (volatility) of the fuel. Unlike water, which boils at a constant temperature, diesel fuel boils over a range of temperatures. These ranges vary for different petroleum products. Temperatures outside the norm can indicate contamination, weathering, or off-spec fuel. It is also used in the calculation of the Cetane Index. ASTM min. and max. for 90% recovered = 540-640 deg. F. A typical complete boiling range for #2 diesel fuel is 360-665 deg. F.
Fuel ages with time as the light hydrocarbon components evaporate and the heavier components oxidize. This increases the viscosity which may impede fuel flow in some engines. It can be an issue in standby generators where fuel consumption is low and refueling quite infrequent. A simulated distillation analysis by Gas Chromatography is used to confirm absence of aging and light element (gasoline) contamination.
Additional ASTM Testing Methods:
Calculated Cetane Index— ASTM D-4737 This test is used as an estimate of the Cetane Number, which is a measure of the ignition quality of the fuel and influences combustion roughness, similar to the octane rating of gasoline. ASTM minimum for #2 diesel fuel = 40.0.
Distillation:
ASTM D-86 This test is a measure of the boiling range (volatility) of the fuel. Unlike water, which boils at a constant temperature, diesel fuel boils over a range of temperatures. These ranges vary for different petroleum products.
Temperatures outside the norm can indicate contamination, weathering, or off-spec fuel. It is also used in the calculation of the Cetane Index. ASTM min. and max. for 90% recovered = 540-640 deg. F. A typical complete boiling range for #2 diesel fuel is 360-665 deg. F.
API/Specific Gravity:
ASTM D-287 A form of density, this test is used in the calculation of the Cetane Index. Typical value for #2 diesel= 33.0.
Bottom Sediment and Water (BS&W):
ASTM D-1796 This test measures the total amount of insoluble water and solids in the fuel by removing them via high-speed centrifugation. It is particularly useful in isolating foreign material in the fuel such as tank bottoms. ASTM maximum for #2 diesel fuel =0.05%.
Flash Point:
ASTM D-93 Normally specified to meet insurance and fire regulations with regards to a particular fuel, it is also very useful in checking for gasoline or other volatile contamination in diesel fuel.
ASTM minimum for #2 diesel fuel = 125 deg. F.
Ash:
ASTM D-482. A measure of the ash content after combustion. Ash results from the presence of abrasive solids or soluble metallic soaps. The former contributes to the injector, fuel pump, piston, and ring wear, in addition to engine deposits. The latter usually just contributes to engine deposits. ASTM maximum for #2 diesel fuel = 0.01%
Microbial Contamination:
ASTM D-6469. Incubated Culture. Semiquantitative tests for bacteria, molds, and fungi, all of which can grow in diesel fuel tanks and damaged fuel injectors. Often detected, though not limited to, storage tanks where water contamination is present. It is important to sample the bottom of the fuel tank when checking for bacterial contamination. No ASTM specification, however, any presence indicates a need for fuel treatment.
Cloud Point:
ASTM D-2500 A test used to predict the temperature at which wax crystals begin to precipitate from the fuel. It is an important test for fuels used in cold weather climates, where a maximum Cloud Point is often specified. ASTM guidelines vary with ambient temperatures of geographic locations.
Sulfur:
ASTM D-3120 A measure of the total sulfur present in the fuel. It is used to determine whether a
fuel meets low-sulfur and ultra-low-sulfur fuel requirements. ASTM maximum for #2 diesel fuel = 0.50.
Kinematic Viscosity:
ASTM D-445 A measure of the dynamic viscosity of the fuel. Viscosities below the acceptable minimum can lead to power loss due to injection pump and injector leakage. It can also help determine if a particular fuel has been contaminated with a product of different viscosity. ASTM min. and max. =1.9-4.1 CST.
Copper Strip Corrosion Rating:
ASTM D-130 A measure of the fuels’ corrosiveness toward copper. Corrosion and tarnish is usually an indication of certain types of sulfur compounds present, not an indication of the amount of total sulfur present in the fuel. ASTM Maximum tarnish rating for #2 diesel fuel =3. max. 3hr at 50 deg.
