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It is widely known that different factors, such as cold properties of a fuel as well as a vehicle design, affect the cold operability limit of vehicles. In this study, the aim was to get a better understanding of the properties of modern Light Duty Diesel (LDD) vehicles (2014-2020) that define their cold operability temperature limit. Moreover, the aim was to find out what a responsible fuel producer can do, in addition to providing a proper fuel that meets the specification, to ensure that a vehicle stays operable at cold temperatures. Similar study was done 10 years ago by Neste with the LDD vehicles of that time [1]. Therefore there was a need to update the info to concern the modern LDD vehicles. In this study the operability limit difference between the worst and the best operating LDD vehicle was >10°C (nbr of LDD vehicles = 5) with the same fuel. The limits were determined in a cold chamber using a chassis dynamometer.

Gasoline blending is known to be complicated, because individual gasoline fractions with different octane numbers, Research Octane Number (RON) or Motor Octane Number (MON) do not always blend linearly. Instead, they may blend non-linearly, in a synergistic or antagonistic manner. Even though RON and MON are regulated properties, linear and non-linear octane blending is not a broadly understood topic. The target in the developing process of a modern SI engine is to have 100% combustion efficiency which would lead to the reduction of hydrocarbon and carbon monoxide emissions. Therefore, the properties of gasoline, especially RON and MON, need to be optimized to ensure proper ignition in the engine and prevent harmful autoignition reactions. There are hundreds of hydrocarbons in gasoline which have different octane numbers (ON). The explanations for these variations are the structural differences in hydrocarbon molecules that influence on their reactivity.

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.

Cold operability is estimated by fuel's cold filter plugging point (CFPP). However, correlation of CFPP with diesel vehicle performance originates from a period when simple in-line or distributor fuel injection systems were applied and fuels did not contain biocomponents. Today, common rail fuel injection systems are used and there seem to be remarkable differences in their design between vehicle models. Seven cars were tested in a climate chamber. The best cars operated down to 8°C below fuel's CFPP but the worst get into problems 5°C above CFPP with the same fuel. It is challenging to define what CFPP is needed in order to guarantee trouble-free winter performance because there are big differences between car models. It is fundamental to get the fuel temperature of a vehicle's fuel filter above the fuel's cloud point during driving, and this depends on fuel system design factors, such as location and size of fuel filter and fuel heater if it is used.

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.