Cetane index is used as a substitute for the
cetane number of
diesel fuel
Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
. The cetane index is calculated based on the fuel's
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
and distillation range (
ASTM
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, a ...
D86). There are two methods used, ASTM D976 and D4737. The older D976, or "two-variable equation" is outdated and should no longer be used for cetane number estimation. It is, however, still required by the
United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
(EPA) as an alternative method for satisfying its
aromaticity
In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...
requirement for diesel fuel. D4737 is the newest method and is sometimes referred to as "the four-variable equation". D4737 is the same method as
ISO 4264. Cetane index in some
crude oil assays is often referred to as Cetane calcule, while the cetane number is referred to as Cetane measure.
Cetane improver additives
Cetane index calculations can not account for
cetane improver additives and therefore do not measure total cetane number for additized diesel fuels. Diesel engine operation is primarily related to the actual cetane number, and the cetane index is simply an estimation of the base (unadditized) cetane number. Cetane number should equal or exceed cetane index, depending on the amount of additive used. The most common additive is 2-ethylhexyl nitrate (2EHN).
See also
*
Cetane
*
Cetane Improver
*
Diesel
*
Octane rating
References
General
*
Internal Combustion Engine Fundamentals, John B. Heywood, McGraw Hill, 1988
*
Automotive Fuels Reference Book, Keith Owen, Trevor Coley SAE, 1995, {{ISBN, 1-56091-589-7
External links
Cetane number determination
Diesel fuel
Fuel technology
Petroleum production
Scales