Predictive Maintenance Services, Inc.

How to read a Fuel Report

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.

Distillation (D-86)
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.

Micro-Organisms (D6469)
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 fuel lubricity.

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 life.

DuPont F21-31

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.

Rancimat (D-7467)

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.

BTU (D-240)

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 separation method.

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.

FAME (D-7963)

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)