The Application of New Approaches to the Analysis of Deposits from the Jet Fuel Thermal Oxidation Tester (JFTOT)

Abstract

Studies of diesel system deposits continue to be the subject of interest and publications worldwide. The introduction of high pressure common rail systems resulting in high fuel temperatures in the system with the concomitant use of fuels of varying solubilizing ability (e.g. ULSD and FAME blends) have seen deposits formed at the tip of the injector and on various internal injector components. Though deposit control additives (DCAs) have been successfully deployed to mitigate the deposit formation, work is still required to understand the nature and composition of these deposits. The study of both tip and internal diesel injector deposits (IDID) has seen the development of a number of bench techniques in an attempt to mimic field injector deposits in the laboratory. One of the most used of these is the Jet Fuel Thermal Oxidation Tester or JFTOT (ASTM D3241). The tester was originally designed to assess the oxidation of jet fuel, based on the principle that low stability fuels produce deposits that form on metal surfaces. Recently it has been modified so that under suitable conditions it may be used to determine the deposit forming potential of diesel fuels. The JFTOT technique has been used by a number of groups to try and understand diesel injector deposits. The ineradicable nature of the material on the JFTOT tube has seen the deposits analyzed by laser scanning microscopy, ellipsometry and recently infra-red microscopy. Other methods have been invasive involving either solvent washing or scraping off the deposit. In this paper other techniques for the analysis of deposits will be described yielding both chemical and metrological characteristics of the deposits. Fourier Transform Infrared Microscopy (FTIRM), and Time-of-Flight Secondary Ion Mass Spectrometry (ToFSIMS) will be used to describe the surface characteristics. Measurements from a Profile meter will be used to estimate deposit surface roughness and data from Scanning Electron Microscopy (SEM) will be employed to describe the morphology. The final techniques described will be Direct Analysis In Real Time Mass Spectrometry (DARTMS) using ambient mass spectrometry. and Fourier Transform Ion Cyclotron Resonance Mass spectrometry (FTICRMS) The advantage of the DART method is that mixtures and objects can be subjected to mass spectrometric analysis with the minimum of pre-treatment and sample preparation. Thus the technique is well suited for analyzing deposits on JFTOT tubes as it requires little sample preparation. A number of studies of materials deposited on JFTOT tubes will be described showing the suitability of these techniques for analyzing and providing the potential characterization of JFTOT deposits. The FTICRMS will be used to assign species in the JFTOT test fuels both pre and post test.

Investigations of Diesel Injector Deposits Characterization and Testing

“…There has also been extension of the use of the JFTOT technique by a number of groups [35 59-60] with Lacey et al correlating the deposit in the injector hardware with the deposit observed on the JFTOT tube. Bucholz [61] indicated its possible use as a preventative screen and Barker showed the wide variety of information which may be extracted from a tube deposit by modern analytical techniques [62].…”

“…The ToF-SIMS [47, 52, 54, 55, and 56] technique and Principle Component Analysis PCA methodology [62], have been described elsewhere in isolation and in combination to analyse fuel deposits. Hence a brief description follows.…”

Characterisation of carbonaceous deposits on diesel injector nozzles

“…Analysis methods such as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been used in the aforementioned studies to investigate deposit composition and structure to provide insights on deposit formation mechanisms. Barker et al combined a number of techniques (fourier-transform infrared spectroscopy, profilometry, scanning electron microscopy, time of flight secondary ion mass spectroscopy, and direct analaysis in real time mass spectroscopy) to obtain morphological, chemical and compositional data from nozzles [13]. However, there remains a significant gap in knowledge when it comes to understanding the initial mechanism which causes fuel deposits to form on the nozzle surface.…”