City Research Online

Abstract

Recent advancements in the diesel fuel injection equipment (FIE) have resulted in increased reports of internal injector deposits (IIDs) and fuel filter fouling. The nature and deposition location of particulates has led to the belief that the deposits are formed due to pyrolytic reactions resulting from the recirculating cavitating flow that occurs inside the diesel vehicles.
In this study, diesel fuels of varying compositions have been subjected to high-pressure cavitation experiments and the resulting change in their optical and chemical characteristics have been identified. To this end, a purpose built high pressure hydrodynamic cavitation test-rig was employed to recirculate the diesel fuels under sustained cavitation conditions. An optical setup was utilised to measure the in situ change in optical extinction coefficient of the fuels at 405 nm. Samples of the cavitated diesel fuels were drawn and subjected to spectroscopic measurements and two dimensional gas chromatography analysis. Results from the optical characterisation of diesel fuels revealed a consistent change in the fuels' optical properties as they were subjected to cavitation. All tests have indicated a build-up of particulate suspension in the recirculating fuel charges with cavitation duration. Analysis of diesel fuel spectra indicated a breakdown of primary aromatic compounds in the fuels, with indications for the formation of polycyclic aromatic hydrocarbons. Gas chromatography results have revealed a consistent chemical behaviour of naphthenic monocyclic aromatic hydrocarbons in all fuels.
Chemical kinetic modelling of the pyrolysis of diesel fuel vapour cavities emulating the high temperature and pressure conditions generated upon a cavitation bubble collapse have revealed the different reaction pathways for the formation of particulates. Increased potency of naphthenic mono aromatics towards soot formations has been identified. Although low, other chemical components of the diesel fuels have also been shown to have soot formation tendencies. The obtained results for the investigation have provided an indication of the chemical effects of hydrodynamic cavitation on diesel fuels that may lead to the formation of soot material similar to the IIDs observed in diesel engines.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology > Engineering

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