PREDICTIVE MAINTENANCE SERVICES, INC.

ASTM D975 minimum: 40 Outsourced

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.

ASTM D975 minimum: 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.

Suggested maximum: 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.

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.

Suggested maximum: 20/19/15

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.

Typical range: 30 to 38 for #2 diesel

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 limits vary by fuel grade

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 (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!

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 (ASTM D7689), Low Temperature Flow Test (LTFT – ASTM D4539) Outsourced and Cold Filter Plugging Point (CFPP ASTM D6371). 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.