Ignition Quality Tester (IQT) provides “referee” cetane measurements for EN 15940 renewable diesel fuel

The production of renewable diesel continues to expand as low-carbon fuel policies incentivise the use of fuels with low life cycle CO2 emissions.  Renewable diesel (also known as “green diesel”, HVO, and HDRD) typically has ultra-high cetane values, often exceeding 70 CN.  This enables the blending of renewable diesel with conventional diesel to offer both lower carbon and higher cetane.

In Europe, the quality specifications for renewable diesel are defined by the CEN standard for “paraffinic diesel from synthesis gas or hydrotreatment of bio-oils or fats”, EN 15940.  This standard (which also covers GTL) has a minimum cetane specification of 70 for high cetane, Class A fuel.  EN 15940 specifies that IQT test method EN 15195 is the method to be used in cases of dispute concerning cetane number (often called the “referee” method).  EN 15195 is the only Constant Volume Combustion Chamber (CVCC) method listed in the CEN paraffinic diesel standard.  

CEN working groups on ignition quality measurement and precision evaluation recently analysed IQT Derived Cetane Number (DCN) data, taken from a CFR Ignition Quality Tester from renewable diesel and GTL samples up to 77 DCN to compare the reproducibility achieved in fuel exchange programs with the published precision of EN 15195.  It was concluded that the reproducibility with these samples was consistent with the published values.  The scope of IQT test method ASTM D6890 is also suitable for renewable diesel, as it has a working range up to 75.1 DCN and the precision functions (r and R) are applicable up to 78.9 DCN (per ASTM D6300).  

When considering derived cetane test methods it is important to examine the upper cetane limit in the scope of each method, as this will determine whether or not the method has known precision at the high cetane values typical of renewable diesel.  Valid precision data is necessary to comply with standard practices such as conformance with specifications (ASTM D3244) and quality management (ASTM D6792).