In our blog post last week, we discussed the first seven of fourteen characteristics of diesel that must be considered and maintained to ensure optimal performance from your diesel fuel engine.
Today we’ll discuss the second half of this list:
- Heat Value
- Ignition quality/cetane rating
- Viscosity
- Sulfur content
- Water and sediment content
- Carbon residue
- Flash point
- Pour point
- Cloud point
- Active sulfur copper strip corrosion content
- Ash
- Distillation
- Specific gravity
- Winter Fuel issues
Corrosion
The corrosion tendency of diesel fuel is a measure of its reaction with copper, brass or bronze parts of the fuel system components. Corrosion tendency is generally measured by immersing a strip of polished copper into the fuel for a period of three hours at 100°C (boiling temperature). Results are interpreted as either a slight tarnish, a moderate tarnish, a dark tarnish or corrosion.
Ash–Forming
Diesel fuel contains ash–forming materials in the form of abrasive solids or soluble metallic soaps. Abrasive solids cause wear of injection components, pistons, rings, and cylinder bores.
Ash from soluble metallic soaps contribute to engine deposits and wear. Analysts determine the amount of ash in fuel by burning a measured amount of fuel in an open crucible until all of the carbon deposits have been consumed. The weight of the remaining ash is expressed as a percentage of the weight of the original fuel sample.
Distillation/Volatility
Volatility is the ability of a liquid to change into a vapor. As volatility is decreased, carbon deposits and component wear may increase. Some engines produce more smoke as volatility is decreased.
Specific Gravity
The specific gravity of diesel fuel is defined as the ratio of the density of the fuel to the density of water measured with a hydrometer.
Specific gravity affects the spray pattern of the fuel as it is injected into the cylinder. To determine if diesel fuel quality should be considered a part of diagnosing an engine performance problem, a hydrometer reading can give strong indications of fuel quality and fuel temperature.
Winter Fuel issues – Cloud Point and Pour Point
The wax content is an important factor that can affect Diesel engine performance in cold conditions. The wax that may be present is referred to as “paraffin.” Because of the strong relationship between temperature and solubility of this wax, wax separation is a problem in handling and use of diesel fuel during cold weather operation.
Paraffin is a solid waxy crystalline mixture of straight–chain saturated hydrocarbons that occur naturally in all diesel fuels. Paraffin melts at approximately 40 to 60° C (104 to 140° F).
Wax content varies greatly, depending on the crude oil from which the fuel was originally produced and how the fuel was processed. As the fuel is cooled, a temperature is reached at which point the fuel becomes saturated with wax. Any further cooling causes the wax to “separate out of the fuel.”
These hydrocarbons become less soluble and begin to precipitate to form wax crystals. The temperature at which a sufficient number of these wax crystals become large enough to make the fuel appear hazy, or cloudy, is called the “cloud point.”
Cloud point indicates the “onset of filter plugging.” As the fuel is cooled further, the wax crystals continue to precipitate and grow. The lowest temperature at which the fuel is observed to flow is called the “pour point.” Additives can help by reducing the pour point temperature, but using. No. 1 diesel fuel is your better fuel option in cold weather.
Now that you’ve made yourself a diesel fuel expert, you’ll understand why it is so important to use good quality fuels to protect your investment and ensure consistent, reliable operation of your diesel engine over a long service life.
