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Analysis of Internal Common Rail Injector Deposits via Thermodesorption Photon Ionization Time of Flight Mass Spectrometry

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journal contribution
posted on 17.12.2015, 09:40 authored by Kornelia Lau, Rene Junk, Sophie Klingbeil, Ulrike Schümann, Thorsten Streibel
Increasing reports about malfunctions in common rail injector (CRI) systems lead to a more intensive research on diesel fuel injection systems, which are working under higher pressures and temperatures. Under these conditions, deposits were formed and deteriorated the injector performance. Therefore, it is necessary to investigate the formed deposits to avoid injector sticking. Previous studies have identified different substance classes, such as alkanes, carboxylic salts, and aromatic hydrocarbons in the deposits. In particular, aromatics and polycyclic aromatic hydrocarbons (PAHs) are suspected to produce insoluble solid precipitates. In this study, thermodesorption resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI–ToF–MS) as a novel analytical technique for direct measurements of aromatic-containing deposits on injector parts was performed. Experiments were carried out in a self-made test bench, where the CRI were installed. The influence of the temperature, injection pressure, injection amount of used fuel, and fuel composition on the tendency to form deposits on the metal surface of commercial CRI parts, especially its ring, was investigated. In most cases, the rings were directly analyzed by the aromatic-selective REMPI technique without any sample preparation. The temperature program of the used carbon analyzer (CA) helps to separate the desorbing material into volatile and non-volatile organic matter during the pyrolysis under a helium atmosphere within the oven of the CA. The results concentrate on the volatile organic matter desorbing step and indicate a strong influence of the temperature and fuel composition on the amount of analyzed aromatic compounds. They were not equal, with the results of thickness layer measurements in individual cases. Comprehensive analytical methods, such as single photon ionization (SPI), are needed for further information.