Cetane Number (D-613)
ASTM D975 minimum is 40. Cetane Number is a measure of the ignition quality
of the fuel and influences combustion roughness. The Cetane number
requirements depend on engine design, size, nature of speed and load
variations, and on starting and atmospheric conditions. Increase in Cetane
number over values actually required does not materially improve engine
performance. Accordingly, the Cetane number specified should be as low as
possible to insure maximum fuel availability.
Cetane Index (D-976, D4737)
ASTM D975 minimum is 40. Cetane Index is a measure of the ignition quality
of a diesel fuel. It is often mistaken as a measure of fuel quality. Cetane
Index is a measure of a fuel's ignition delay. This is the time period
between the start of injection and start of combustion of the fuel. Cetane
Index cannot account for Cetane improver additives and therefore does not
measure total Cetane Number for additized fuels. Cetane Index is an
estimation of the Cetane Number of unadditized fuel. Cetane Index is also
specified as a limitation on the amount of high aromatic components in
Grades No. 1-D S15, No. 1-D S500, No. 2-D S15 and No. 2-D S500.
Diesel fuels with a Cetane Index lower than the minimum engine requirements
can cause rough engine operation. They are more difficult to start,
especially in cold weather or at high altitudes. They accelerate lube oil
sludge formation. Many low Cetane fuels increase engine deposits resulting
in more smoke, increased exhaust emissions and greater engine wear.
Water by Karl Fischer method (D-6304)
Suggested maximum is 500 ppm. Some OEM’s with common rail and other high
pressure injection fuel systems require 200 ppm maximum limits. Karl
Fischer is a method of determining water content in fuels. Unlike the water
and sediment test, Karl Fischer detects free water, dissolved water and
emulsified water in the fuel. Some high pressure injectors are sensitive to
water levels as low as 200 parts per million. Water also provides a
breeding ground for bacteria and fungus.
Water & Sediment (D1796)
ASTM maximum 0.05%. Some OEM’s require water to be measured by Karl Fischer
method and use a much stricter limit. Water and sediment is a measure of
the amount of free water and particulate in the fuel that can be removed
from the fuel by centrifuging. Water and sediment affect the life of fuel
filters and can cause damage to injectors and fuel pumps and cause rust in
metal fuel tanks.
ISO Cleanliness (ISO 4406)
While ASTM suggests particle counts, no limits have been set. We suggest a
maximum of 20/19/15 for most high pressure injection engines. Some OEM’s
require much stricter cleanliness levels as low as 18/16/13. Particle
counts give us the ISO Cleanliness Code. Simply put, it is a measure of how
clean the fuel is. Particle counters count the number of particles per
milliliter and the resulting ISO Cleanliness Code is based on these counts.
API Gravity (D-287)
ASTM D975 does not set a requirement for API. 30 to 38 is typical for #2
diesel. 40 and above is typical for #1. Blending with No. 1 is common
during winter months and will increase the API gravity. Biodiesel and
blends are typically under 30. API Gravity is related to heat content which
affects power and economy. Gravity is an indication of the energy content
of fuel and is also a measure of a fuel’s density (or weight per gallon). A
fuel with a high density (low API gravity) contains more BTU's per gallon
than a fuel with a low density (higher API gravity). API is also a measure
of a fuel's density (or weight per gallon). The higher the API gravity, the
less a gallon of fuel weighs and the less energy it contains. As a general
rule, there is a three to five percent decrease in the thermal energy
content of fuel for every 10 degree increase in API gravity which is
roughly the same percentage decrease in engine power.
ASTM maximums and minimums vary by fuel grade and intended use. The 90%
evaporated limits for No. 2 diesel has a minimum of 540° F and a maximum of
640° F. The 90% maximum for No. 1 diesel is 550° F. Limits at various
evaporated levels for fuel used for heating oil, kerosene, jet fuels and
fuels used for other purposes vary. Limits for No. 2 diesel during cold
weather may also be waived as mixing with #1 diesel to provide sufficient
cold flow properties is common practice. Distillation provides a measure of
the temperature range over which fuel volatilizes or turns to vapor.
Suggested minimum for the Initial Boiling Point is 300° F. The initial
boiling point (IBP) should be high enough to prevent early ignition which
can damage the engine, reduce power output and fuel economy and vapor lock
the fuel system. If the IBP and low evaporated percentage numbers are high,
poor starting may result. Low IBP can indicate contamination with gasoline,
solvent or other light ends. High boiling rages from 5% to 50% evaporated
may increase warm up time. A lower 50% point is desirable to minimize smoke
and odor. Low 90% and end points tend to insure low carbon residuals and
minimum crankcase fuel dilution. 90% and end points that are too high may
indicate contamination with oils or other heavy distillates and can result
in incomplete combustion and fuel dilution in the crankcase.
Any micro-organisms detected should be considered a cause for concern and
corrective action taken. Micro-organisms (bacteria and fungus) breakdown or
degrade fuels and cause corrosion of metals - especially iron and steel.
They plug fuel filters and lines, cause fuel-gauge malfunctions and feed on
tank linings, hoses and coatings. They may also damage fuel pumps,
injectors and in-line instruments. 8 billion bacteria per gallon have no
effect on fuel clarity!
Low Temperature Operability. (Winter Fuel Testing)
It is unrealistic to attempt to set limits for cold flow properties but
care should be taken to insure proper operability when temperatures fall
below the cloud point of the fuel being used. Several tests are commonly
used to characterize the low temperature operability of diesel fuel. These
are Cloud Point (D-2500), Low Temperature Flow Test (LTFT - D-4539) and
Cold Filter Plugging Point (CFPP D-6371). For non-additized fuel, the Cloud
Point and the LTFT correlate very well. Since Cloud Point is more practical
as a quality control test, it is listed as the primary recommendation. CFPP
and LTFT are more real world indicators of low temperature performance,
especially for additized fuel.
Lubricity (HFRR - D-6079)
ASTM maximum 520 micron; however, 450 micron should provide sufficient
lubricity in all instances. Lubricity describes the ability of a fluid to
minimize friction between, and damage to, surfaces in relative motion under
loaded conditions. Diesel fuel injection equipment relies on the
lubricating properties of the fuel. Shortened life of engine components
such as fuel injection pumps and unit injectors can occur due to lack of
Sulfur (D-5453, D-2622)
Most fuel today is required by the EPA to have a sulfur content of 15 ppm
or less. Beginning in 2014, all fuels were required to be 15 ppm or less.
Copper Corrosion (D-130)
ASTM maximum 3. The copper strip corrosion test indicates potential
compatibility problems with fuel system components made of copper alloys
such as brass or bronze.
Flash Point (D-93, D-7094)
ASTM minimum for No.2 fuel is 125° F. No. 1 minimum is 100° F. Flash point
for No. 2 may be waived during cold weather when No. 1 fuel is blended with
No. 2 to provide sufficient cold flow properties. The flash point
temperature of diesel fuel is the minimum temperature at which the fuel
will ignite (flash) on application of an ignition source under specified
conditions. Flash point varies inversely with the fuel's volatility. Flash
point minimum temperatures are required for proper safety and handling of
diesel fuel. Due to its higher flash point temperature, diesel fuel is
inherently safer than many other fuels such as gasoline.
Kinematic Viscosity (D-445)
ASTM ranges for No.2 are 1.9 to 4.1 cSt at 40° C. No.1 ranges are 1.3 to
2.4 cSt at 40° C. Fuels used as heating oils, kerosene, other grades etc.
have different viscosity requirements. Viscosity affect injector
lubrication and fuel atomization. Fuels with low viscosity may not provide
sufficient lubrication for the precision fit of fuel injection pumps or
injector plungers resulting in leakage or increased wear. Fuels which do
not meet viscosity requirements can lead to performance complaints. Fuel
atomization is also affected by fuel viscosity. Diesel fuels with high
viscosity tend to form larger droplets on injection which can cause poor
combustion and increased exhaust smoke.
Ramsbottom Carbon Residue (D-524)
ASTM maximum is 0.3% mass for No. 2 and 0.15% for No. 1. The Ramsbottom
Carbon residue test is intended to provide some indication of the extent of
carbon residue that results from the combustion of a fuel. The limit is a
maximum percentage of deposits by weight.
Ash Content (D-482)
ASTM maximum of 0.01% mass for No. 2 and No. 1 diesel. Ash is a measure of
the amount of metals contained in the fuel. High concentration of these
materials can cause injector tip plugging, combustion deposits and
injection system wear. Soluble metallic materials cause deposits while
abrasive solids will cause fuel injection equipment wear and shorten filter
Maximum pad rating of 7 according to the test method. This method is for
determining the relative stability of distillate fuels such as home heating
oils or diesel fuels under short-term, high temperature, aging conditions
involving air exposure. It may also be used to evaluate the effectiveness
of additives in inhibiting sediment formation and color degradation of
distillate fuels under conditions of the test. The test does not correlate
well with field storage or 3 month 43°C (110°F) dark storage.
Thermal Stability (D6468)
ASTM minimum of 80% reflectance at 180 minutes (required for premium
diesel) or 70% at 90 minutes. Can be used for investigation of operational
problems that might be related to fuel thermal stability. Testing samples
from the fuel tank or from bulk storage may give an indication as to the
cause of filter plugging.
RSSOT (Rapid Small Scale Oxidation Test D-7545)
Minimum value of 60 minutes. RSSOT has been shown to be suitable for
assessing the potential instability of S15, B100 and biodiesel blends of
S15 and for assessing the potential instability of S15 biodiesel blends.
The presence of Cetane improver (2-ethylhexyl nitrate) in diesel fuel can
degrade the test method performance. This test can be used for
investigation of operational problems that might be related to fuel thermal
stability. Testing samples from the fuel tank of from bulk storage may give
in indication as the cause of filter plugging.
Minimum of 20 minutes. This test is used to assess the instability of
biodiesel blends from B6-B20. May not provide accurate results for blends
of less than B2.
Suggested minimum of 140,000 BTU per gallon. This test method covers the
determination of the heat of combustion (commonly referred to as BTU) of
liquid hydrocarbon fuels ranging in volatility from that of light
distillates to that of residual fuels. Under normal conditions, this method
is directly applicable to such fuels a gasolines, kerosene, Nos. 1 and 2
diesel fuels and Nos. 0-GT – 2-GT gas turbine fuels.
Particulate Contamination by Laboratory Filtration (D-6217)
Suggested maximum 5 g/L. This is a method for assessing the mass quantity
of particulates in middle distillate fuels which is a significant factor to
determine the rapidity with which fuel system filters and other small
orifices in the fuel system can become plugged. It can be used in
specifications and purchase documents as a means of controlling particulate
contamination levels in fuels purchased. Maximum levels are often specified
in military fuel specifications.
Alcohol (Ethanol) by Water Separation (Laboratory Developed Method)
Maximum depends on Ethanol contend of the gasoline being tested. Used to
determine the approximate percent of alcohol (ethanol) in gasoline by water
Gasoline in Diesel Fuel by GC (Laboratory Developed Method)
No amount of gasoline contamination is acceptable in diesel fuel. This test
is used to determine the percent of gasoline contamination in diesel fuel
by Gas Chromatograph.
ASTM Color (D-1500)
No ASTM specification. Sometimes used as an indication of oxidation or
contamination of fuel (As fuel ages it tends to become darker). Usually
trended over time.
Haze Rating (D-4176)
Fuel must be clear and bright with no visible sediment or water visible.
Typically fuel must be no greater than 1. A sample of fuel is placed into a
clear jar and is examined for clarity. Fuel clarity is rated by placing a
bar chart behind the sample and comparing its visual appearance with the
standard haze rating photos.
Maximum value depends on the Biodiesel content of the fuel being tested.
This is a method for determining the level of Fatty Acid Methyl Esters by
Fourier Transform infrared Spectroscopy.
Oxidation Stability (D2274)
Suggested maximum is 20 mg/100 ml. This test method covers the measurement
of the inherent stability of middle distillate petroleum fuels under
specified oxidizing conditions at 95° C. This test method was developed for
fuels containing 500 and 5000 ppm of sulfur and may not provide an accurate
determination of the suitability for use for S15 diesel.
Cloud Point, Pour Point, Cold Filter Plugging point (See Low
Temperature Operability above)