Investigations of Diesel Injector Deposits Characterization and Testing

Over the last decade, there has been an impetus in the automobile industry to develop new diesel injector systems, driven by a desire to reduce fuel consumption and proscribed by the requirement to fulfil legislation emissions. The modern common-rail diesel injector system has been developed by the industry to fulfil these aspirations, designed with ever-higher tolerances and pressures, which have led to concomitant increases in fuel temperatures after compression with reports of fuel temperatures of ~150°C at 1500-2500 bar. This engineering solution in combination with the introduction of Ultra Low Sulphur diesel fuel (ULSD) has been found to be highly sensitive to deposit formation both external injector deposits (EDID) and internal (IDID). The deposits have caused concerns for customers with poor spray patterns misfiring injector malfunction and failure, producing increased fuel consumption and emissions. The importance to the industry of understanding the nature of diesel injector deposits has led to significant research in this area with a number of industry tests being developed. However, the introduction of new generation fuels e.g. hydrogenated vegetable oil (HVO) and the reports of injector problems such as “abrasive particles” in Europe continue to stimulate investigation. The interest in characterizing diesel injector deposits has also seen a number of recent contributions being published. Many of these reports describe analyses that either consider only the surface of deposits or use methods which destroy any provenance. In this paper, we will describe the latest data from the deployment of modern analytical techniques to characterize these deposits. As a further contribution to the understanding of diesel injector deposits, this paper will describe the use of Principal Component Analysis (PCA) in conjunction with Time of Flight Secondary Ion Mass spectrometry (ToF-SIMS) to determine trends in IDID chemistries worldwide. The application of the ToF-SIMS technique to EIDS will be described. The latest industry standard engine tests will be discussed with regard to the chemistries involved and the latest advances in the application of a new generation of deposit control additives (DCA) will be described.