The fuel used for compression ignition engines is usually Diesel. The fuel mixture (air and Diesel) is formed in the combustion chamber in a very short time, while it takes the fuel injection. For this process to undergo normal conditions the spraying of fuel by the injector must be made as finely as possible. Taking into account that, at the time of injection of Diesel (end of compression), the air has a high pressure (25-35 dan/cm2), the pressure with which the Diesel is injected is much higher (110-1500 dan/cm2). As a fuel injection in the combustion chamber, it does not immediately ignite, but first occurs when fine Diesel droplets in the mixture are heated until they vaporise. Then follows auto-ignition, triggering a very high propagation speed. The time elapsed when the injection begins until the Diesel self-ignition is called a delay in self-ignition. It is desirable that the delay in self-ignition is as short as possible. It depends on several factors including the type of diesel, the type of combustion chamber, the injection advance, the compression ratio, and others. The ability of Diesel to have a certain delay in auto-ignition is expressed by the cetane figure or its cetane index. The cetane digit of the Diesel is the percentage of cetane in a standard mixture of two hydrocarbons: the cetane which has a cetane figure 100 and alpha-methylnaphthalene which has a cetane figure 0. The higher the cetane figure, the lower the delay in self-ignition is.

tractors, agricultural machinery, vibrations, Diesel

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