What is Diesel ? Structure and Properties


Diesel, are used in diesel engines, derived from distillation of crude oil from 200 to 380 degrees C, a specific gravity of 0.89 kg / dm³, which is a fuel. Hc number of carbons in the structure varies between 8 and 16. hc outside the 1% sulfur, 0.02% on the amount of ash and is allowed very little nitrogen.minimum cetane number of Diesel should be 40.

Diesel Structure and Properties

Today, it is used in three different diesel. Nu.1-D,  Nu.3-D and  Nu.2-D.

Nu.1-D, obtained by the distillation of petroleum and is diesel fuel used in diesel engines working at different speeds.

Nu.2-D, obtained from petroleum distillation and cracking products. By evaporation Nu.1-D is less and less used in heavy duty industrial motor speed.

Nu.3-D, distillation, cracking and consisting of some waste. used in low or medium speed diesel engines.


The discovery of oil and diesel fuel from the refinery process has been used immediately after starting. efficiency of gasoline engines, and the price of gasoline has encouraged the development of cheaper and more efficient engine. They use diesel as fuel in diesel engines developed.

Some features three diesel in the following table are presented comparatively.

Feature 1-D 2-D 3-D
A minimum cetane number 40 40 40
Flashpoint 0F one hundred 125 130
S Viscosity (Saybolt)
100 0F’
30-34 33-45 45-125
Ash% mass 0.01 0.02 0.10
% Sulfur mass 0.50 1.0 2.0


Diesel engines for high-speed, medium speed and low speed are made. High-speed diesel in passenger vehicles, freight vehicles in the medium-speed diesel and low speed diesel are used in heavy machinery. This engine is the diesel fuel used in some important features.

Knock resistance

Of the ignition delay in diesel engines, fuel is sprayed onto the hot air is required to be low. Ignition delay too long, cylinder fuel combustion will increase the amount would have been more severe.This is harmful to the engine will result in unwanted high pressure and heat waves. Ignition delay, diesel cetane number is associated with. If high cetane number is reduced ignition delay, if the ignition delay increases the cetane number is low. Because of the formation it is to increase the maximum number of cetane number increase to 70 cetane lower limit is set at 40. diesel index is a number in the diesel fuel used to specify the cetane number. The following table shows the relationship between diesel and cetane index number.

Diesel Index Cetane number Diesel Index Cetane number
0 18 50 50
5 20 55 53
10 24 60 56
15 28 65 59
20 30 70 62
25 34 80 65
30 37 85 68
35 40 90 71
40 43 95 75
45 46 one hundred 78


Cold weather is good for the evaporation of the first movement. But evaporation worsen the self-ignition feature. The optimum value must be determined and diesel contain ingredients that should be used to ensure that value.


As against flow of fluid is called viscosity resistance. Viscosity is an important parameter in the motor. Very high viscosity, such as pumping the particles after spraying will complicate the work increases the ignition delay will cause that big. It also increases the amount of work. The low viscosity for providing good atomization together, sealing problems and pump causes Asint the element.


Diesel and itself, as is also desired that the properties will not cause corrosion of the combustion products. The amount of sulfur, the combustion is eventually generate acids having corrosive effect should be as low as possible. The brine contained in the fuel has corrosion effect.

Smut Amount

Diesel combustion contain much higher soot and ash from the fuel of the end products. To keep the amount is to be maintained at a minimum of 70 cetane number, cetane number below 40 on the deteriorating combustion ash and causes an increased amount of work. Here it was seen that the HC combustion ash and metallic salt of unwanted but found in diesel Given lights without leaving ash and soot to be effective in the job.

Activity against zinc

Diesel, is a tendency to create compounds with zinc. The compounds which form zinc has the effect of corrosion. Especially in steel tank containing zinc zinc activity to react with hiding zinc should be as low as possible.

Pour point

temperature at which they begin to lose their flowability of the liquid is called the yield point. Diesel pour point in working conditions to prevent frost and must be at a level not lose its ability to flow.Diesel fuel is given the name used in our country. Whereas diesel fuel is used as the lower speed diesel engines. The freezing point of diesel fuel while the freezing point of -10 ° C -65 ° C.

Flammability Hazard

Diesel, gasoline, although a relatively lower temperature in the combustion vaporization capability for that feature lower flammability hazard is lower. Diesel exacerbation of a hot surface for gasoline should spark the flame as a result of contact with the vapor layer is formed.

Participating Additives

Engines, cleaning mixture in order to allow cleaning of the fuel system components, the provider additives to distribute water in the fuel, cetane number increasing additives, cleaner fuel pump and the engine of the freezing in the winter inhibiting antifreeze and injectors additives are used.

Flammability and Cetane Number

Knock properties of the diesel engine, ie the ability to ignite the fuel depends on the cetane number.Flammability, mixed with air in the cylinder diesel is its ability to self-ignition. The high ignition capability of the motor used in the diesel engine is requested. It will be recalled gasoline was being asked to have lower ignition capability. At the end of the compression stroke of the diesel engine diesel fuel sprayed into the hot air that we know work with self-ignition. Diesel engine knock; Due to the accumulation of air into the fuel injected and the ignition delay is defined as a large amount caused by sudden combustion of the fuel high pressure wave and temperature. Diesel combustion capability varies depending on the cetane number. Increase the cetane number of the ignition delay (TG) decreases and the number of lower cetane increasing the ignition delay is caused by the diesel knock.

Cetane (C16H34) is a straight-chain paraffins and ignition capability is regarded as 100.Alfametilnaften’s (C10H7 CH3) ignition capability of “0” has been adopted. and the ratio of cetane in diesel alfametilnaf gives the cetane number of diesel. Cetane cetane number of 65% and 35% mixture alfametilnaf 65.

Diesel, the cetane number is not in the content produced is determined by experiments carried out in chemical laboratories. The cetane number of the fuel to be measured in a standard engine (CFR engine) of the measured ignition delay time TG, the result of comparison with the duration of mixtures of TG determined cetane alfametilnaf. cetane percentage of the mix which gives the same time the number of TG measured cetane fuels. It depends on the compression ratio with the cetane number of TG. Thus, while the compression ratio must be the same comparison. vuruntusuz change in the cetane number required for operation in different compression ratio are determined after a series of experiments conducted and measured fuel has a cetane number in the rate of compression is used. The figure below shows the changes in compression ratio and cetane number is given in a graph.

Cetane Molecular Structure

Cetane Molecular Structure

The cetane number in diesel engine combustion is deteriorated when the amount is over 70 and has been increasing. The cetane number is below 40 is prolonged duration of TG and diesel comes knocking occurs. the cetane number of diesel fuel used in diesel engines must be between 40 and 70 depending on operating conditions. A simpler way to measure the cetane number of diesel was to determine the index. D (diesel index) cetane number relationships are given in the table in knock resistance material. D aniline point for the calculation of specific gravity and API must be known.

Aniline point: Aniline, aromatic HC is a solvent which melt when heated but always melting, but paraffinic HC. These thinners are mixed in equal volume with diesel oil and heated. The mixture is allowed to cool thoroughly dissolved in each other. The cooled solution is decomposed and to form two separate layers (aniline HCl solution with aromatic and paraffinic HC layer) starts, the aniline point is called the fuel temperature at that moment. equations shown below, API and aniline point D is determined.

Di = Aniline Point × API / 100

rather than the specific gravity of the oil in the oil industry today is used degrees API gravity. The specific gravity of the oil with API gravity is an inverse correlation between the degree.

Gravity grows density is smaller and the quality of oil is rising. Gravity decreases, density increases and decreases the quality of the oil. API gravity degree with Ö There is a relationship as shown in the following equation.

API = [141.5 / (EA / 60 F)] – 131.5

Item specific gravity in the equation g / cm3 in the present specification.

Cetane number

Cetane number and compression ratio (ε) change

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