The Derived Cetane Number (DCN) is obtained using Fuel Ignition Tester (FIT) manufactured by Waukesha Engine Dresser, Inc. This FIT unit utilizes a unique method of determining DCN by using a constant volume combustion chamber with direct fuel injection into heated, compressed air.

The combustion chamber is pressurized to 22 bar and heated to a temperature of around 577 °C prior to liquid fuel injection. Each fuel injection produces a single-shot, compression ignition combustion cycle. The fuel self-ignites and the time from injection to the start of combustion defines the ignition delay time. This ignition delay time is recorded and then correlated to calculate DCN value.