Predictive Maintenance Services, Inc.

How to read a Fuel Report

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 availability.

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 (D-86)
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 (D6469)
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)
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-92)
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.

DuPont F21-31
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)
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.