Mechanism for Internal Injector Deposits Formation in Heavy-duty Engines using Drop-in Fuels

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.