Diesel would be proud of the global acceptance of, and dramatic improvements made to, the diesel engine over the past 100 years. Diesel engines were developed to take advantage of the high energy content and generally lower cost of diesel fuels. Diesel fuel has various properties that need to be maintained to operate effectively in today’s modern diesel engines. We’ll talk about these various properties and it’ll become clear as to why you need to ensure your diesel fuel is safe and reliable for your engine:
- 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
In this blog post, we’ll talk about the first seven on the list. Stay tuned for the next seven in a blog post coming next week.
1. Heat Value
The Heat Value of diesel fuel is a measured using a calorimeter to determine how much energy the fuel provides when burned. Basically, a specific amount of fuel is burned, and the amount of heat is carefully measured in British Thermal Units (BTUs).
- The heat value of Number 2 diesel fuel is 139,500 BTUs per gallon.
- The heat value of Number 1 diesel fuel is 125,500 BTUs per gallon, approximately 10% lower than that of Number 2.
- For comparison, the heat value of gasoline is 124,500 BTUs per gallon.
The higher the heat value of the fuel, the more power the engine can generate, therefore consuming less fuel to do the same amount of work.
2. Ignition Quality/Cetane Rating
Cetane rating is a measure of the ignition quality of a fuel. The ease at which diesel fuel ignites, and the manner in which it burns, influences engine starting and combustion roughness. Pure cetane is a colourless liquid hydrocarbon with excellent ignition qualities and is rated at 100. The higher the cetane rating, the shorter the lag time between the time the fuel enters the combustion chamber and the time it begins to burn. A good quality diesel fuel with a high cetane rating has a lag time of approximately 0.001 seconds.
Cetane rating requirements depend on the engine size, design, load and atmospheric conditions. For example, engines operating at higher altitudes or lower temperature demand a higher cetane fuel to start and operate correctly. Typical cetane ratings for No. 2 diesel would be 46 – 48. No. 1 diesel is usually about 51 – 53.
Note: The cetane rating is not provided at most filling stations. Diesel owners should buy fuel at a well-known, good source that is frequently utilized to ensure fresh fuel is being purchased.
Note: The recommended minimum cetane rating for modern diesel engines is 40. Increasing the cetane rating above 48 is not recommended as it will not increase engine performance and, in fact, may cause fuel knocking.
3. Viscosity
Viscosity is simply a measure of resistance to flow. Viscosity decreases as the temperature increases. Fuel viscosity is an important factor in the operation in modern High-Pressure Common-Rail (HPCR) fuel system equipped engines.
Low viscosity fuel produces a fine, atomized mist of fuel which improves its mix with incoming air to encourage a complete combustion for better power and lower emissions.
High viscosity fuel tends to result in a heavier mist of fuel which can result in hard starting and white smoke issues.
4. Sulfur Content
The sulfur content of diesel fuel has recently drawn a great deal of attention because of increased wear on the following components:
- Pistons
- Rings
- Valves
- Cylinders
This increased wear is promoted by the corrosive effects of hydrogen sulfide in the fuel combined with sulfur dioxide (or sulfur trioxide), formed during the combustion process. The wear is less serious under constant loads and during high–temperature operation.
Some after-market companies are offering fuel additives to make up for the lubrication lost by the reduced sulfur content (reduced lubricity) of the diesel fuel. If fuel quality is questionable, replace with fuel from a good source to ensure the fuel system components are not at fault.
5. Water and Sediment Content
Water and sediment content in fuel can also cause rusting and damage to fuel system components. Diesel fuel with a high water content can cause iron oxide particles to form inside the fuel tank. This causes internal rusting of fuel lines, pumps and injection components when the engine is not in use.
We’ve seen this problem with engines stored in the fall that were running great all season. When taken out again in the spring we have found the engine needs fuel system components replaced due to rust/contamination issues.
6. Carbon Residue
The black, sooty material remaining after diesel fuel is burned is called carbon residue. The amount of carbon residue deposits permissibly depends on the engine manufacturer, and the running conditions of the engine.
7. Flash Point
The flash point of diesel fuel is defined as the minimum temperature to which the fuel must be heated before flammable vapour is produced which could ignite. The lower the flash point, the higher the risk of explosion.