Why are There Multiple Grades of Fuel for Diesel Generator Sets?

Diesel is the main fuel for diesel generators, with safe use, low cost, low self ignition point, high viscosity, high density, high flash point, and stable performance. However, it is prone to volatilization and deterioration during transportation and storage. According to the different requirements for the use of various types of diesel generators, there are also different requirements for the performance of the fuel used. Therefore, there are multiple grades of diesel, which are closely related to the following indicators.

(1) Hexadecane number. The cetane number is an indicator for evaluating the spontaneous combustion of diesel fuel. The quality and performance of the combustion process in diesel engines are directly affected by the degree of spontaneous combustion. Diesel has a high cetane number and good self ignition ability. When injected into the cylinder during operation, it can quickly ignite, making the diesel engine work smoothly and easy to start at low temperatures. Conversely, diesel with a low cetane number has poor self ignition ability, making the diesel engine run rough and causing difficulty in starting. But it cannot be said that a higher cetane number is better. Due to its high cetane number, diesel fuel has poor stability. When injected into the combustion chamber, it ignites before it can fully mix with air, resulting in the cracking and separation of a large amount of free carbon at high temperatures. This carbon is then emitted with the exhaust gas, producing black smoke and increasing fuel consumption. Therefore, it is required to have an appropriate cetane number, and the cetane number of diesel used in general high-speed diesel engines is 40-60.

(2) Distillation range. Diesel injection into the cylinder is ignited and burned after intensification, and the evaporation of this diesel has a significant impact on the combustion process of the diesel engine. Distillation range represents the evaporation of diesel, with low distillation temperature (i.e. high content of light distillate fuel), good mixing of fuel and air, and easy starting of diesel engines. However, light distillate fuels are prone to premature evaporation, resulting in excessive simultaneous combustion of fuel and rough operation of diesel engines. On the contrary, heavy distillate fuels have high viscosity, poor atomization, slow vaporization, and are prone to incomplete combustion, resulting in severe carbon deposition. Therefore, it is required that the content of light and heavy fractions in diesel should not be too high, and the distillation range should be small.

(3) Kinematic viscosity. Viscosity indicates the fluidity of diesel oil, which is closely related to fuel atomization and normal operation of fuel supply system. If the viscosity is too high, the flow resistance of fuel in the pipeline and filter will increase, spray will deteriorate, and combustion will be poor. However, low viscosity deteriorates the lubrication conditions of precision components in the fuel system, accelerates component wear, and increases oil leakage. Viscosity is closely related to temperature, and the lower the temperature, the greater the viscosity. The viscosity of winter dog diesel will increase, and even flow in pipelines will be difficult. Therefore, when used at low temperatures, appropriate preheating should be carried out.

(4) Concentrate. The viscosity of diesel increases as the temperature decreases. When it reaches a certain temperature, the high molecular weight hydrocarbons contained in diesel crystallize, causing the diesel to lose its fluidity. This temperature is called the freezing point. The grades of standard light diesel oil are named based on their solidification point, and are divided into six types: 10, 0, -10, -20, -35, and -50. For example, the solidification point of -10 light diesel oil is -10 ° C. Diesel has a high pour point, which can easily cause blockages in the fuel circuit and filter when working in low-temperature environments, resulting in insufficient fuel supply or even interruption of fuel supply. Therefore, appropriate grades of diesel must be selected according to the ambient temperature conditions during use.

In addition to the main indicators mentioned above, the standard has made restrictions on the harmful components contained in diesel. For example, residual carbon, ash content, carbon content, mechanical impurities, moisture, acidity, water-soluble acids or bases, and actual colloids. The above components will have varying degrees of impact on the normal operation of diesel engine components.

Various diesel engines have different structural and performance requirements, and the applicable diesel grades are clearly specified in the instructions for use. High speed diesel engines generally use No. 0 light diesel in summer or when the ambient temperature is above 0 ° C; In winter or when the ambient temperature is below 0 ° C, choose -10 ° C light diesel.

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