EMA Recommended Guidelines


This Recommended Guideline of the Engine Manufacturers Association is intended to define a diesel fuel that is superior in quality than the commercial fuel specification ASTM D 975.

The diesel fuel is considered to be "superior in quality" insofar as it may assist in improving the performance and durability of engines currently in use and those to be produced prior to 2004. It is not intended to enable diesel engines to meet 1998 Federal emission standards or, in general, to improve engine exhaust emissions.

The most significant aspects of this Recommended Guideline are its requirements for a minimum fuel lubricity, increased cetane number and improved cold weather performance. These properties, described in detail below, should help address many current customer satisfaction and engine performance issues.


For the benefit of our customers and other interested parties, the following section summarizes the critical properties of diesel fuel and, where appropriate, the reason for EMA’s selection of a particular quality level of that property.

Flash Point

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.

Water and Sediment

Diesel fuel should be clear in appearance and free of water and sediment. The presence of these materials generally indicates poor fuel handling practices. Water and sediment can and will cause shortened filter life or plugged fuel filters which can in turn lead to fuel starvation in the engine. In addition, water can have negative impact on fuel corrosion and on microbial growth. It is for that reason we recommend separate analysis and maximum levels.


This property provides a measure of the temperature range over which a fuel volatilize or turns to a vapor. Volatility is one of the primary factors which distinguish #1 from #2 diesel fuel. No. 1 diesel typically has greater volatility than No. 2. The highest temperature recorded during distillation is called the end point. Ideally, one would specify an end point in the definition of fuel properties. However, because a fuel’s end point is difficult to measure with good repeatability, the fuel’s 90% or 95% distillation point is commonly used. EMA prefers the 95% distillation point since its reproducibility is acceptable and it is closer to the fuel’s end point than the 90% point currently measured in D 975.

In applications which operate at low loads and frequent idle periods, like bus engines, lower end point is desirable to reduce smoke and combustion deposits. Hence EMA recommends distillation temperature specifications lower than the current D 975 specification to cover those applications.

Kinematic Viscosity

Viscosity affects 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 and emissions.

Ash Content

Ash is a measure of the amount of metals contained in the fuel. High concentrations 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 filter plugging.


To assist diesel engine manufacturers in meeting mandated limits for particulate matter in diesel engine exhaust, sulfur content is limited by law to 0.05% for diesel fuel used in on-road applications.

Copper Corrosion

The copper strip corrosion test indicates potential compatibility problems with fuel system components made of copper, brass or bronze. The limit requires that the fuel not darken these parts under the test conditions.

Cetane Number/Cetane Index

Cetane number is a relative measure of the interval between the beginning of injection and autoignition of the fuel. The higher the number, the shorter the delay interval. Fuels with low Cetane Numbers will cause hard starting, rough operation, noise and exhaust smoke. Current commercial fuel cetane requirements may not adequately address these customer satisfaction issues. Generally, diesel engines will operate better on fuels with cetane numbers above 50 compared to fuels with cetane numbers of the national average of approximately 45.

Cetane number may be increased through the refining process or the blending of combustion ignition improving additives by fuel suppliers.

Cetane index is an approximation of fuel ignition quality through measurement of distillation range and specific gravity. It is not affected by the use of combustion improver additives; therefore it produces an indication of the base cetane number of the fuel.

Ramsbottom Carbon Residue

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.

API Gravity

This is a measure of fuel’s specific gravity or density. While specific gravity has no units, density is defined as mass per unit volume and both are temperature dependent. API gravity is defined as follows.

API gravity of diesel fuel has a profound effect on engine power. As a general rule, there is a 3-5% decrease in the thermal energy content of fuel for every 10 degree increase in API gravity. This decrease in energy content will result in roughly the same percentage decrease in engine power. Use of fuels with higher API gravity will also result in higher fuel consumption (lower mpg). EMA’s recommendation to include a maximum API gravity is based on our understanding of customer needs to maintain engine power, while minimizing fuel consumption


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 somewhat on the lubricating properties of the fuel. Shortened life of engine components such as fuel injection pumps and unit injectors usually can be ascribed to a lack of fuel lubricity and hence is a concern to engine manufacturers. This property is not addressed adequately by ASTM D 975.

ASTM has issued two tests to measure lubricity: the High Frequency Reciprocating Rig (HFRR) and the Scuffing Load Wear (SBOCLE) test. Current acceptability guidelines for both tests are provided in our chart. Aftermarket additives for improving diesel fuel lubricity should not be necessary and are not covered by this recommended guideline since they may react chemically with other additives causing them to lose their effectiveness, drop out of solution or even plug filters.

Accelerated Stability

Diesel fuel should be stable under normal storage and use conditions. Unstable fuel will darken and form black particulate materials which will cloud fuels and create gum residues in the fuel system. Although the accelerated stability test is intended to predict primarily storage stability, it can provide indication of overall fuel stability.


All diesel fuels which do not contain detergents have a tendency to form carbon deposits on fuel injectors. It has generally been found that low sulfur fuels and thermally unstable fuels have a greater tendency to form these deposits. Detergent additives will prevent carbon deposits, which interfere with fueling and fuel spray patterns, from forming.

Dirty injectors will invariability give rise to higher smoke levels in all equipment and in some equipment can limit power by restricting fuel flow. Diesel fuel detergency can be measured using the L10 Injector Depositing test. Passing limits for the test are provided in the attached table. These limits are expressed in terms of a CRC rating for injector cleanliness and a flow loss criterion.

Low Temperature Operability

Several tests are commonly used to characterize the low temperature operability of diesel fuel. These are Cloud Point, Cold Filter Plugging Point (CFPP), and Low Temperature Flow Test (LTFT). Among these, the LTFT is preferred by EMA as providing the best overall correlation with field performance. However, for non-additized fuel, cloud point and LTFT correlate very well. Since Cloud Point is more practical as a refinery quality control test, it is listed as our primary recommendation. Low temperature operability of bulk diesel fuel can be negotiated by the customer and fuel supplier. However, in the retail fuel market, low temperature operability is the responsibility of the fuel supplier. It is adjusted on a monthly basis during the winter, or sometimes sooner depending on expected ambient temperatures at the point of sale.

Low temperature flow requirements usually vary depending upon fuel filter media and the presence of fuel heaters. However, to avoid operational problems the selection of a fuel’s low temperature properties should be made based on the lowest ambient conditions expected during operation.

Unless specifically recommended by the engine manufacturer or discussed with the fuel supplier in advance, modification of the waxing properties of fuels using aftermarket fuel additives is not recommended as an option for meeting the low temperature operability requirement, because of possible incompatibility with other additives already contained in the fuel.

EMA Recommended Guidelines on Diesel Fuel






#1 DF(1)



#2 DF(1)

Flash Point, °C min. D 93



Water, ppm max D1744



Sediment, ppm max D2276 or D5452



Distillation % Vol. Recovery, °C D 86    
90%, max.  



95%, max.  



Kinematic Viscosity, 40 °C D 445

1.3 - 2.4

1.9 - 4.1

Ash, % max. D 482



Sulfur, % max. D 2622



Copper Corrosion, max. D 130



Cetane Number, min. D 613



Cetane Index, min. D 4737



Rams Carbon, 10% residue max. D 524



API Gravity, max. D 287



Lubricity, g. min.




Accelerated Stability, mg/L max. D 2274



Detergency - L10 Injector

CRC Rating



Depositing Test

% Flow Loss



Low Temperature Flow, °C D2500 or D4539



Microbial Growth  



1) #1 DF and #2 DF are intended for use in the same applications described in the definitions of Grade No. 1-D and Grade No. 2-D respectively in ASTM D 975.

2) EMA recommends that lubricity levels be determined by ASTM D6078 ,Scuffing Load Wear Test (SBOCLE). Alternatively, lubricity may be measured using the High Frequency Reciprocating Rig (HFRR), ASTM D6079. Using this test, a wear scar of 0.45 mm at 60°C is equivalent to a SBOCLE result of 3100 g.

3) Diesel fuels must pass the Cloud Point (D2500) 0r Low Temperature Flow Test (D4539) at the use temperature. Low temperature flow capability is the responsibility of the fuel supplier for retail fuels. It is adjusted monthly during the winter, depending on local climate. Unless specifically recommended by the engine manufacturer or discussed with the fuel supplier in advance, modification of the waxing properties of fuels using aftermarket fuel additives is not recommended as an option for meeting the low temperature operability requirement.

While EMA has not included any recommendation with respect to Microbial Growth, it should be noted that microbial growth can cause operational problems, corrosion and sediment build-up in diesel engine fuel systems. The growth of microbes in fuel storage tanks and vehicle/equipment fuel tanks is believed to be related to pipeline and storage techniques and times and cannot be sufficiently addressed in a fuel specification.

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