| Test instrument: | External laboratory |
| Determined values: | Cetane number |
| Analysis for: | Diesel fuels |
| Brief description: | A special engine is used to determine the cetane number. Ignition quality is determined at a defined, constant ignition delay. This is the time between the fuel being injected and it self-igniting. In the test engine, this delay is adjusted by changing the amount of intake air, which determines the compression and combustion pressure. Known cetane numbers are used for control fuels. These have been determined in advance by comparative measurements with other engines. |
| Statement: | The cetane number describes the ignition quality of diesel fuel: the higher the number, the better the quality. A low cetane number can result in ignition delay, which is the time taken for the fuel to ignite after being injected into the cylinder. This can result in a loud combustion noise, known as 'knocking', due to the sudden, explosive combustion. However, the desired result is controlled, directed combustion, not an explosion. In addition to reducing driving comfort and increasing noise pollution in the surrounding area, knocking also puts unnecessary strain on the engine and worsens exhaust emissions. |
| Underlying test standard: | DIN EN ISO 5165 |
