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The sulphur level of diesel fuels began to be limited in Europe at the end the 20th century. Quite soon after that it was noticed that the processes for removing sulphur also removed other polar compounds and the natural lubricity of the diesel fuel was lost. Lubricity additives were introduced to restore lubricity properties. Also, a rapid laboratory method was developed to measure lubricity i.e. High Frequency Reciprocating Rig (HFRR). The method (HFRR) ISO 12156-1 was introduced in 1997 and included in EN 590. In recent years purely paraffinic diesel fuels, such as GTL (Gas To Liquid) and renewable HVO (Hydrotreated Vegetable Oil), have been introduced to the market. Unlike traditional biodiesel (FAME, Fatty Acid Methyl Ester), paraffinic diesel fuels require the use of lubricity additives to reach a sufficiently high level of lubricity.

Diesel fuel requires sufficient lubricity to prevent excessive wear in fuel injection equipment. The processes for removing sulfur from diesel fuel also eliminate compounds that are responsible for its lubricating properties. This phenomenon is counterbalanced by employing lubricity additives to restore fuel lubricity to an acceptable level. The aim of this study was to compare the two different laboratory methods for testing lubricity. The two methods were the EN 590 standard method high frequency reciprocating rig (HFRR) and a less utilized method scuffing load ball-on-cylinder lubricity evaluator (SLBOCLE). Two different commercial lubricity additives were used. In addition, rapeseed methyl ester (RME) was used for lubricity purposes in the same way as the additives. To study the possible effect of the base fuel, the tests were performed with fossil diesel fuel, paraffinic diesel (Hydrotreated vegetable oil, HVO), and a blend of these.

For decades, ENISO12205 test has been used to evaluate the long term storage stability of diesel fuels. Nowadays, new biocomponents especially FAME has increased the need to create faster and more appropriate test method to measure the long term storage stability. Developments in engine technology have also raised the need to create a new method to evaluate the thermal stability of diesel fuels. These new methods should have correlation to field experience. As an example it has been shown that Rancimat (EN15751) and PetroOXY EN16091 have a correlation when fuel contains more than 2% FAME. Rancimat is not applicable for FAME free fuels, so correlation based PetroOXY limit should be limited to fuels containing more than 2 vol% FAME. Study on oxidation stability test methods and their correlation to real life were continued and deepened (part 1: SAE 2013-01-2678). ENISO12205 and PetroOXY EN16091 test methods did not have a correlation according to the earlier studies.

Oxidation stability tests have been developed for estimation of the long term storage stability of diesel fuels. Currently, several oxidation stability test methods (eg. ENISO12205, Rancimat (EN15751), PetroOXY (EN16091)) are used for this purpose. It is common for these tests to have an elevated temperature and to add oxygen or air to accelerate the oxidation of the test fuel, and hence accelerate conduction of the test. It has been under discussion whether these tests actually represent real-life conditions. Also, it has been proposed that these oxidation stability tests could be used to estimate the thermal stability of the diesel fuels. In many cases the correlation to real-life is unclear. Stability of EN590 B0 (winter and summer grade) and B7, B30, EN590 with 30% HVO, 100% HVO, WWFC category 4 diesel, Swedish class 1 as well as the effect of cetane improver was evaluated with different oxidation stability methods.

The objective of this paper is to compile the findings of more than 40 scientific publications and provide information on the technical performance of HVO (Hydrotreated Vegetable Oil) in diesel engines. Fuel properties, emission performance and engine behavior of HVO is evaluated in comparison to fossil diesel. Based on the studies and large field trials it can be concluded that HVO can be used as a drop-in-fuel and that it has properties beneficial for the engine and the environment. HVO has high cetane number, low density, good lubricity when treated with lubricity additives, bulk modulus comparable to fossil diesel, material compatibility similar to fossil diesel and good cold properties regardless of the feedstock. HVO is capable of reducing regulated and unregulated emissions as well as greenhouse gasses. HVO has beneficial effects to aftertreatment systems. Oil dilution with HVO is not a concern and HVO does not cause incompatibility with lubrication oil.

This study presents emission results measured with renewable and synthetic diesel fuels. Three engines and five city buses were studied. The efficiency of diesel oxidation catalyst combined to particle oxidation catalyst (POC®) was measured with two engines. The studied diesel fuels were EN590, FAME, HVO and GTL. In most cases all regulated emissions decreased with HVO and GTL fuels compared to conventional EN590 diesel fuel. With FAME, the NOx emissions were higher compared to EN590, but other emissions were reduced. Alternative fuels had a positive effect on emissions, which are considered harmful to human health.

Hydrotreated vegetable oil (HVO) named NExBTL is a 2nd generation renewable diesel fuel made by a refinery-based process converting vegetable oils to paraffins. Also animal fats are suitable for feedstocks. Properties of this non-ester type biobased fuel are very similar to GTL. It contains no sulfur, oxygen, nitrogen or aromatics. Cetane number is very high (∼90). Cloud point can be adjusted by severity of the process from -5 to -30°C, heating value is similar to diesel fuel, storage stability is good, and water solubility is low. Emissions of two heavy duty engines and two city buses are presented with HVO and sulfur free EN 590 diesel fuel. The effect of HVO on regulated emissions compared to EN 590 fuel was: NOx -7 % … -14 % PM -28 % … -46 % CO -5 % … -78 % HC 0 % … -48 % Aldehydes, PAHs, mutagenicity and particulate size were also measured.