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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

TURBULENT INHOMOGENEOUS AUTOIGNITION OF POLYDISPERSED N-HEPTANE DROPLETS: AN EXPERIMENTAL STUDY

Ajay Gupta
Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

Christos N. Markides
Clean Energy Processes (CEP) Laboratory, Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

Abstract

We present experimental data on the autoignition of polydispersed droplets pure liquid n-heptane released axisymmetrically from a circular nozzle into a confined turbulent co-flow of high temperature air at atmospheric pressures. Our aim in this work is to examine the effect of flow inlet conditions on the emergence and behaviour of autoignition in the presence of flow inhomogeneities. Typically, autoignition is observed in the form of well-defined localised spots occurring randomly along the length of the tubular reactor. We record the autoignition location and delay times (based on the residence time from the fuel injector to the autoignition spots) as a function of the bulk temperature and velocity of the co-flowing air stream, and of the liquid fuel injection velocity. The near injection fuel droplet size distribution is also measured. It is established that the axial autoignition length shifts upstream (i.e. closer to the fuel injector) with increasing bulk air temperature; and moves downstream with increasing bulk air co-flow velocity at a constant liquid fuel injection velocity. The corresponding autoignition delay time decreases with increasing bulk air temperature and bulk air velocity, contrary to expectations from pre-vaporized n-heptane autoignition in an identical facility. Such experimental data can be used for developing and validating advanced models of non-premixed two-phase turbulent combustion and chemically reacting flows.

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