What are the Chemical Properties of Diesel Fuel?

The chemical properties of diesel fuel are totally different from petrol. In this article, I Will discuss the important chemical properties of diesel fuel.

Chemical Properties of Diesel Fuel

Chemical Properties of Diesel Fuel

Diesel fuel, also known as hydrocarbon fuel, is used in diesel engines for vehicles and industrial applications. The diesel fuel is totally different from the petrol fuel. In a diesel engine, there is no need for the spark plug to ignite the fuel, because of the chemical properties of diesel fuel. It is derived from crude oil through a refining process known as distillation.
The properties required in diesel fuel are different from those required in petrol. The desirable properties are-
  1. Chemical composition.
  2. Viscosity.
  3. Sulfur content.
  4. Volatility.
  5. Ignition quality. 
  6. Free from water and sediments.
  7. Cetane number.
  8. Additives. 

1. Chemical Composition

Diesel fuel is a mixture of hydrocarbons, which are compounds composed of hydrogen and carbon atoms. The exact composition can vary depending on the source of crude oil and the refining process used. After refining the crude oil the diesel fuel extracts. The chemical compositions of diesel fuel are-
  • Alkanes.
  • Cycloalkanes.
  • Aromatics.
  • Isoparaffins.
  • Olefins.
  • Saturated hydrocarbons.

2. Viscosity

Viscosity indicates the internal resistance between the fuel molecules. Fuel is injected into the combustion chamber. Highly viscous diesel fuel is not finely atomized and requires more injection pressure, whereas less viscous diesel fuel is not finely atomized, but causes more wear in the injection unit and leaks through the clearance. This means that the injection pressure and the degree of atomization of the injected fuel depend on diesel viscosity. The injection units are designed considering the viscosity of diesel.

3. Sulfur Content

The presence of sulfur in diesel fuel reduces the self-ignition temperature of diesel. Due to the Sulfur content, the injected fuel starts burning at a low temperature in the combustion chamber. The quantity of Sulfur should not exceed 0.5%, which is the desirable quantity of sulfur in diesel fuel. Excess Sulfur increases wear due to acidic corrosion and the formation and deposition of carbonaceous materials over the piston rings. Burned Sulfur forms SO2 which reacts with lubricating oil and forms gum, varnish, and hard substance. 

4. Volatility

Diesel fuel must be volatile at the cylinder temperature. The heavy ends of diesel which evaporate at a high temperature are partially burned and leave carbon deposits. Such carbon deposits in the cylinder cause cylinder wear and problems with the spraying of fuel from the injector if carbon is deposited over the injector orifice.

5. Ignition Quality

The diesel fuel must have a good ignition quality. The ignition quality of diesel is ascertained from its ignition lag. Ignition lag is the time interval, between the entrance of the fuel particle in the combustion chamber and its subsequent ignition It has been found that a fuel particle takes a certain time to ignite. The time interval is known as the ignition lag. the less time the ignition lags, the better the ignition quality of diesel fuel.

The ignition quality of diesel is indicated by its cetane number. This cetane number is determined by comparing the mixture of reference fuels to the sample diesel fuel in a variable compression ratio engine. When the sample diesel fuel and the mixture of the reference fuels give the same combustion quality, the diesel fuel is assigned a cetane number equal to the percentage of cetane in the reference fuel mixture. For example, if the combustion quality of the sample diesel fuel is the same as the mixture of 85% cetane and 15% methyl naphthalene, then the sample diesel fuel is assigned a cetane number of 85. 

6. Free from Water and Sediments

The injection unit is fitted very precisely to minimize diesel leakage under high pressure. Any sediments such as dust damage the injection unit(fuel pump assembly and injector assembly). Due to the viscosity of diesel, these sediments do not settle down in the tank.  

7. Cetane number

The cetane number is a measure of the ignition quality of diesel fuel. Higher cetane numbers indicate better ignition characteristics. Diesel fuel with a high cetane number ignites more easily, leading to smoother combustion and less noise in diesel engines. The cetane number of diesel fuel is determined through standardized testing methods, such as the ASTM D613 or ISO 5165 procedures. It is reported as a numerical value, with higher values indicating better ignition quality.

8. Additives

Additives are required in diesel fuel to make the diesel fuel flammable and easy to burn. Diesel fuel may contain additives to enhance various properties, such as stability, lubricity, and corrosion resistance. Additives can also help mitigate issues related to cold weather operations, water separation, and emissions.

Ending up with

The chemical properties of diesel fuel help the diesel fuel burn and help to reduce the antiknock property. I hope you like this article. Subscribe to our website for more content. 
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