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RS ISO 5165: 2020
Petroleum products — Determination of the ignition quality of diesel fuels — Cetane engine method

Abstract

This document establishes the rating of diesel fuel oil in terms of an arbitrary scale of cetane numbers
(CNs) using a standard single cylinder, four-stroke cycle, variable compression ratio, indirect injected
diesel engine. The CN provides a measure of the ignition characteristics of diesel fuel oil in compression
ignition engines. The CN is determined at constant speed in a pre-combustion chamber-type
compression ignition test engine. However, the relationship of test engine performance to full scale,
variable speed and variable load engines is not completely understood.
This document is applicable for the entire scale range from 0 CN to 100 CN but typical testing is in the
range of 30 CN to 65 CN. An interlaboratory study executed by CEN in 2013 (10 samples in the range
52,4 CN to 73,8 CN)[3] confirmed that paraffinic diesel from synthesis or hydrotreatment, containing up
to a volume fraction of 7 % fatty acid methyl ester (FAME), can be tested by this test method and that
the precision is comparable to conventional fuels.
This test can be used for unconventional fuels such as synthetics or vegetable oils. However, the
precision for those fuels has not been established and the relationship to the performance of such
materials in full-scale engines is not completely understood.
Samples with fluid properties that interfere with the gravity flow of fuel to the fuel pump or delivery
through the injector nozzle are not suitable for rating by this method.
NOTE This document specifies operating conditions in SI units but engine measurements are specified in
inch-pound units or Fahrenheit because these are the historical units used in the manufacture of the equipment,
and thus some references in this document include these and other non-SI units in parenthesis.

General Information

Code	Classification	Theme	Pages	Publisher	Availability
RS ISO 5165: 2020	ADOPTED ISO STANDARDS	Chemical technology	29	Fifth Edition Jul 2026	Available