Preliminary study of smoke formed in the combustion of various jet fuels

A simplified, disk-stabilized combustor has been used to study participate sampling methodology and fuel effects on combustion zone particulate concentration. These samples were extracted via filtration with subsequent gravimetric analysis at six axial positions ranging from 3.8 to 29.2 cm from the fuel injector. Sampling techniques, including the effects of sample temperature, particle deposition, sample drying, and sampling rate, have been evaluated. Measurement guidelines are proposed. Five fuels—petroleum-based Jet A, low-aromatic Jet A, Jet A blended with 15% rubelene, petroleum based JP-4, and JP-5 refined from an oil shale derived syncrude—were investigated. Axial concentration profiles suggest a particulate emission dependence on fuel hydrogen (or aromatic) content as well as volatility. Measured primary zone particulate concentrations were two orders of magnitude greater than exhaust values. I. Introduction W ITHIN the last two years the necessity for future utilization of U.S. coal and oil shale reserves to supplement and eventually replace disappearing crude oil reserves has become increasingly apparent. Although oil shale syncrudes are quite similar to petroleum crudes in analysis,l they are generally somewhat more viscous, less volatile, and higher in aromatic content. Efficient utilization of these syncrudes will therefore require either that fuel processing and resultant expenses increase to meet present fuel specifications or that specifications be changed to minimize processing costs at the expense of engine emissions and performance in existing combustors. To create a reasonable balance between these alternatives, it will be necessary to better understand the effects of fuel properties on combustion processes. This paper presents the initial results from a study of the influence of fuel properties on smoke formation in gas turbine engines. Smoke formed in gas turbine combustors is composed of small, almost pure carbon particles.2 These particles have been reported to appear as agglomerates having diameters of about 0.5 /mi which are composed of solid particles an order of magnitude smaller.3 Problems arising from these smoke particles include engine damage due to increased radiative heat transfer to the combustor walls, deposition on and erosion of turbine blades, visible pollution in the engine exhaust plume, and health hazards resulting from particle inhalation. To date, these problems have been fairly well controlled in engines burning present specification petroleum based fuels; however, in recent tests with coal and oil shale derived fuels,1'4 smoke emissions (by SAE smoke no.) have been shown to be up to 70% higher than with similar petroleum fuels. This increase has generally been attributed to increased fuel aromatic content, but the mechanism by which aromatic content increases smoke emission is not well understood, and effects due to other fuel properties have not been fully investigated.