This document specifies a method for the determination of cetane number of diesel fuels by air flow regulation in a standard test engine. This document is applicable to various types of diesel fuels, including vehicle diesel, bio-diesel, synthetic diesel, and similar unconventional products. The cetane number measurement range is from 0 CN to 100 CN, whereas a typical cetane number range of 25 CN to 70 CN. However, the precision for synthetic and unconventional diesel has not been established.