Editing Cetane number (section)

== Measuring cetane number ==
Cetane numbers are rather difficult to measure accurately, as it requires a special diesel engine called a Cooperative Fuel Research (CFR) engine. Under standard test conditions, the operator of the CFR engine uses a manual-wheel to increase the compression ratio (and therefore the peak pressure within the cylinder) of the engine until the time between fuel injection and ignition is 2.407 ms.  The resulting cetane number is then calculated by determining which mixture of [[cetane]] ([[hexadecane]]) and [[isocetane]] (2,2,4,4,6,8,8-heptamethylnonane) will result in the same ignition delay.

===Ignition Quality Tester (IQT)===
Another reliable method of measuring the derived cetane number (DCN) of diesel fuel is the Ignition Quality Tester (IQT). This instrument applies a simpler, more robust approach to CN measurement than the CFR. Fuel is injected into a constant volume combustion chamber at approximately 575&nbsp;°C and {{convert|310|psi|bar|abbr=on}}. The time between the start of injection and the recovery of the combustion chamber pressure to {{convert|310|psi|bar|abbr=on}} is defined as the ignition delay. This measured ignition delay is then used to calculate the DCN of the fuel. The fuel's DCN is then calculated using an empirical inverse relationship to ignition delay. Because of the reproducibility, material cost, and speed of the IQT, this has been the definitive source for DCN measurements of fuels since the late 2000s.<ref>Heyne, Kirby, Boehman, ''Energy & Fuels'', 2009. {{doi|10.1021/ef900715m}}</ref>
<ref>{{cite journal | last1 = Dooley | first1 = Stephen | last2 = Hee Won | first2 = Sang | last3 = Heyne | first3 = Joshua | last4 = Farouk | first4 = Tanvir I. | last5 = Ju | first5 = Yiguang | last6 = Dryer | first6 = Frederick L. | last7 = Kumar | first7 = Kamal | last8 = Hui | first8 = Xin | last9 = Sung | first9 = Chih-Jen | last10 = Wang | first10 = Haowei | last11 = Oehlschlaeger | first11 = Matthew A. | last12 = Iyer | first12 = Venkatesh | last13 = Iyer | first13 = Suresh | last14 = Litzinger | first14 = Thomas A. | last15 = Santoro | first15 = Robert J. | last16 = Malewicki | first16 = Tomasz | last17 = Brezinsky | first17 = Kenneth | year = 2012 | title = The experimental evaluation of a methodology for surrogate fuel formulation to emulate gas phase combustion kinetic phenomena | journal = Combustion and Flame | volume = 159| issue = 4 | pages = 1444–1466| doi = 10.1016/j.combustflame.2011.11.002 }}</ref>
<ref>{{cite journal | last1 = Dooley | first1 = Stephen | last2 = Hee Won | first2 = Sang | last3 = Chaos | first3 = Marcos | last4 = Heyne | first4 = Joshua | last5 = Ju | first5 = Yiguang | last6 = Dryer | first6 = Frederick L. | last7 = Kumar | first7 = Kamal | last8 = Sung | first8 = Chih-Jen | last9 = Wang | first9 = Haowei | last10 = Oehlschlaeger | first10 = Matthew A. | last11 = Santoro | first11 = Robert J. | last12 = Litzinger | first12 = Thomas A. | year = 2010 | title = A jet fuel surrogate formulated by real fuel properties | journal = Combustion and Flame | volume = 157| issue = 12 | pages = 2333–2339| doi = 10.1016/j.combustflame.2010.07.001 }}</ref>

===Fuel ignition tester===
Another reliable method of measuring the derived cetane number of diesel fuel is the Fuel Ignition Tester (FIT). This instrument applies a simpler, more robust approach to CN measurement than the CFR. Fuel is injected into a constant volume combustion chamber in which the ambient temperature is approximately 575&nbsp;°C. The fuel combusts, and the high rate of pressure change within the chamber defines the start of combustion. The ignition delay of the fuel can then be calculated as the time elapsed between the start of fuel injection and the start of combustion. The fuel's derived cetane number can then be calculated using an empirical inverse relationship to ignition delay.

===Cetane index===
{{Main|Cetane index}}
Another statistic used by fuel-users to control quality is the cetane index (CI), which is a calculated number based on the [[density]] and a distillation range of the fuel. There are various versions of this, depending on whether metric or Imperial units are used, and the number of distillation points that are used. These days most [[petroleum industry|oil companies]] use the '4-point method', ASTM D4737, based on density and 10% 50% and 90% recovery temperatures. The '2-point method' is defined in [[ASTM]] D976 and uses just density and the 50% recovery temperature. This 2-point method tends to overestimate the cetane index and is not recommended. Cetane index calculations cannot account for cetane improver additives and therefore do not measure the total cetane number for additized diesel fuels. Diesel engine operation is primarily related to the actual cetane number, and the cetane index is merely an estimation of the base (unadditized){{clarify|date=October 2023}} cetane number.

===Industry standards===
The industry standards for measuring cetane number are ASTM D613 (ISO 5165) for the CFR engine, D6890 for the IQT, and D7170 for the FIT.