Cetane Number (D-613)
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
Cetane Index (D-976)
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)
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)
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)
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. While ASTM has not yet specified a required cleanliness
level, our research has found that for most high pressure injection engines
today, a rating of 20/19/15 should be considered the maximum allowable.
Some engine manufacturers specify 18/16/13 or better.
API Gravity (D-287)
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.
Distillation provides a measure of the temperature range over which fuel
volatilizes or turns to vapor. 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.
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)
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)
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 fuel lubricity.
Sulfur (D-5453, D-2622)
Most fuel today is required to have a sulfur content of 15 ppm or less.
Beginning in 2014, all fuels are required to be 15 ppm or less.
Copper Corrosion (D-130)
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)
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)
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)
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)
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 life.
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)
Thermal Stability (D6468)
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.