Exploring the formation mechanisms of internal diesel injector deposits: A laboratory study

Abstract

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.