Sustainable fuels can help to decrease carbon dioxide emissions in road transportation compared to standard fossil fuels. The most common sustainable fuels used today in heavy-duty applications are biodiesel and hydrogenated vegetable oil (HVO). Biodiesel and HVO are known as drop-in fuels since they are fuels that can be blended with standard diesel. However, due to changes in the chemical properties when the fuels are mixed, solubility problems in terms of precipitates may be formed. These insolubilities can lead to deposits in the fuel system, e.g., blocked fuel filters and internal injector deposits, and thus driveability problems. This study is a part of a project where the goal is to study the processes that cause the formation of deposits inside the injectors in heavy-duty vehicles. The deposits inside the injectors are known as internal diesel injector deposits (IDID). To study the formation of IDID, a number of injectors from heavy duty vehicles were collected from two different European markets: one market that uses biodiesel fuel and another that uses HVO as a drop-in fuel. A technique not previously used to identify IDID, namely pyrolysis GC-MS, proved successful in this regard, and FTIR and SEM-EDX methods were also used to characterise the deposits. The results showed that the composition of the IDID s from different markets differed. Metal soaps, inorganic salts and nitrogen compounds were found in the deposits taken from the injectors in the biodiesel drop-in market. The source of these components is believed to be degradation and contamination of the biodiesel. In addition, fuel additives such as corrosion inhibitors and detergents were found in the injectors from the market using HVO as a drop-in fuel. This could imply that the poor solvency of HVO can give problems in some additive combinations.

  One way to reduce carbon dioxide emissions from the current heavy-duty vehicles fleet is to replace fossil fuel with renewable fuel. This can be done by blending so-called drop-in fuels into the standard diesel fuel. However, problems such as insoluble impurities may arise when the fuels are mixed. These precipitates, known as soft particles, can cause deposits in the fuel system, e.g., injectors and fuel filters, reducing the engine´s performance. The most used drop-in fuel today is biodiesel which, is blended with different concentrations. To better understand how soft particles are formed in the vehicle´s fuel system, the degradation of biodiesel blends in the engine has been investigated. This study explores biodiesel blends´ degradation process by comparing the incoming fuel with the return fuel from a modern diesel engine to investigate how the fuel is affected by this process. The engine was run using different blends of biodiesel fuel. To investigate the degradation of the biodiesel, engine tests at low, medium, and high torque at two engine speeds was performed. Fuel samples were collected before and after the engine for comparison. The tested fuels were examined with different analytical techniques. Rancimat, ion chromatography, inductively coupled plasma atomic emission spectroscopy and total acid number. A filtration test method was developed to collect the soft particles from the tested fuels. The results showed that fuel properties from the fuel return in biodiesel blends with high biodiesel content were more affected compared to lower biodiesel blends. For the lower biodiesel blends both the oxidation stability (Rancimat) and the filterability improved after passing the fuel system in the engine. While for the high biodiesel content, Rancimat and filterability were reduced. In biodiesels blends lower than 10%v/v, the change in oxidation stability was positive and around 30h and for B100 the change in oxidation stability was negative around 5 to 10 h. The filterability of blends with high biodiesel content showed that these fuels were more affected by different engine conditions, whereas B30 showed the highest variation in filtration time. Indicating that B30 is the most sensitive fuel. No big change was seen in the acid number for any biodiesel blends and a correlation was seen with biodiesel content. Further, the concentration of short chain fatty acid seems to correlate with the oxidation stability of the fuel. Increasing the level of short chain fatty acids, the oxidation stability of the fuel decreases.  

Heavy-duty transportation is one of the sectors that contributes to greenhouse gas emissions. One way to reduce CO2 emissions is to use drop-in fuels. However, when drop-in fuels are used, i.e., higher blends of alternative fuels are added to conventional fuels, solubility problems and precipitation in the fuel can occur. As a result, insolubles in the fuel can clog the fuel filters and interfere with the proper functioning of the injectors. This adversely affects engine performance and increases fuel consumption. These problems are expected to increase with the development of more advanced fuel systems to meet upcoming environmental regulations. This work investigates the composition of the deposits formed inside the injectors of the heavy-duty diesel engine and discusses their formation mechanism. Injectors with internal deposits were collected from field trucks throughout Europe. Similar content, location and structure were found for all the deposits in the studied injectors. The physical structure was analyzed using a Scanning Electron Microscope with an Energy Dispersive X-Ray (SEM-EDX). Pyrolysis coupled with Gas Chromatography Mass Spectrometry (Py GC-MS) and Fourier-transform Infrared Spectroscopy (FTIR) were also used to determine the composition of the injector deposits. The deposits consist of a mixture of organic and inorganic compounds, indicating that they originate from fuel and engine oil. To further analyze the origin of the formed deposits, samples were collected from various parts of the fuel system. The analysis suggests that the deposits were formed exclusively in the injectors, and by comparing and describing the composition and structure of the deposits from different parts of the injector, a mechanism is proposed.

 The formation of deposits in the fuel systems of heavy- duty engines, using drop-in fuels, has been reported in recent years. Drop-in fuels are of interest because they allow higher levels of alternative fuels to be blended with conventional fuels that are ompatible with today’s engines. The precipitation of insolubles in the drop-in fuel can lead to clogging of fuel filters and internal injector deposits, resulting in increased fuel consumption and engine drivability problems. The possible mechanisms for the formation of the deposits in the fuel system are not yet fully understood. Several explanations such as operating conditions, fuel quality and contamination have been reported. To investigate injector deposit formation, several screening laboratory test methods have been developed to avoid the use of more costly and complex engine testing. To further evaluate and understand the formation of internal injector deposits in heavy-duty engines, a thermal laboratory test method has been developed. The test method is called Thermal Deposits Test (TDT) and it is inspired by Jet Fuel Thermal Oxidation Test (JFTOT) method. This test unit can be used to study in applications where a fluid is in contact with a hot surface. The method uses common laboratory hardware and readily available off-the-shelf parts, making it inexpensive to build and very flexible to operate. Deposits are collected on a metal foil, which makes it easier to analyze. This paper describes the construction of the apparatus and its performance. Experimental tests with diesel fuel, doped with soap-type soft particles, which contain typical particles that can form deposits, are performed, and compared with JFTOT results. Analytical techniques, such as Scanning Electron Microscopy with Energy Dispersive X-Ray, Fouriertransform Infrared Spectroscopy, and Pyrolysis coupled with Gas Chromatography-Mass Spectroscopy and Ellipsometry were used. Conclusions about the performance of the doped fuel are drawn from the test. Future plans are to study the mechanisms behind the formation of internal diesel injector deposits. 

 To reduce carbon emissions in heavy-duty transportation, renewable fuels like biodiesel and hydrotreated vegetable oil are increasingly blended with fossil fuels as drop-in alternatives. However, these blends can lead to issues such as the formation of insoluble materials, or soft particles, within the fuel system. These precipitates, composed of inorganic salts and organic aggregates, cause filter clogging, nozzle fouling, and internal injector deposits, negatively impacting engine performance, increasing fuel consumption, and causing drivability issues. This study investigates internal injector deposits through an accelerated laboratory thermal test, replicating the deposits observed in injectors from heavy-duty vehicles. The goal is to understand the chemistry behind these deposits and explore the formation of inorganic salts, such as calcium crystals, and soft particle deposits. Temperature plays a critical role in deposit formation, influencing both morphology and composition. FTIR-ATR and SEM-EDX analyses reveal that metal carboxylates form between 100 ◦C and 170 ◦C, while calcium sulfate crystals form above 170 ◦C. The test successfully replicates the characteristics of real-world deposits, with findings suggesting that calcium sulfate deposits primarily form in the presence of engine oil contaminants. This points to engine oil leakage as a significant factor in the formation of internal diesel injector deposits (IDIDs). This research highlights the value of laboratory testing as a cost-effective alternative to engine tests for studying deposit formation in drop-in fuel systems. 

 In recent years, deposit formation in fuel systems for heavy-duty engines, using drop-in fuels, have become increasingly common. Drop-in fuels are particularly appealing because they are compatible with existing engines, allowing for higher proportions of alternative fuels to be blended with conventional fuels. However, the precipitation of insoluble substances from drop-in fuels can result in fuel filter clogging and the formation of internal injector deposits, leading to higher fuel consumption and issues with engine drivability. The precise reasons behind the formation of these deposits in the fuel system remain unclear, with factors such as operating conditions, fuel quality, and fuel contamination all suggested as potential contributors. In order to reproduce and study the formation of internal injector deposits, for heavy-duty engines under controlled conditions and to facilitate a more precise comparison to field trials, a novel injector test rig has been developed. This newly constructed, non-firing rig includes the main components of heavy-duty vehicle engines and uses an electric motor to simulate the revolutions per minute of an engine. A tailored run cycle has been developed to enable the continuous monitoring of injector performance during the deposit formation process, as well as to meticulously mimic the actual operations of a real engine. The deposits formed on injectors during the rig tests were analyzed using scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and pyrolysis connected to gas chromatography-mass spectroscopy (Py GC-MS). This work presents the outcome of the analysis of injector deposits using the test rig, and compares these findings with deposits gathered from field operations. The deposits obtained from the injector test rig were found to be similar in terms of deposit location, composition, and microstructure, with both sets of deposits containing metal carboxylates and derivatives of engine oil additives. These similarities demonstrate that the test rig effectively reproduces the formation of injector deposits observed in real-world conditions.