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Influence of carrier air preheating on autoignition of inline-injected hydrogen-nitrogen mixtures in vitiated air of high temperature

[+] Author and Article Information
Christoph Schmalhofer

German Aerospace Center (DLR), Institute of Combustion Technology, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
christoph.schmalhofer@dlr.de

Peter Griebel

German Aerospace Center (DLR), Institute of Combustion Technology, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
peter.griebel@dlr.de

Manfred Aigner

German Aerospace Center (DLR), Institute of Combustion Technology, faffenwaldring 38-40, 70569 Stuttgart, Germany
manfred.aigner@dlr.de

1Corresponding author.

ASME doi:10.1115/1.4037918 History: Received July 03, 2017; Revised July 24, 2017

Abstract

The use of highly reactive hydrogen rich fuels in lean premixed combustion systems strongly affects the operability of stationary gas turbines leading to higher autoignition and flashback risks. The present study investigates the autoignition of hydrogen-nitrogen fuel mixtures in an inline coflow injector configuration at relevant reheat combustor operating conditions. The influence of mixing section temperature and carrier air preheating on autoignition limits is studied. The effects of hydrogen volume fraction on kernel formation and development are investigated by analysing autoignition kernels and the kernel distribution. Experiments were carried out in a generic, optically accessible reheat combustor. Hydrogen-nitrogen fuel mixtures of increasing hydrogen content were embedded in a carrier air coflow, which was preheated up to 700K, and injected inline into hot flue gas. Autoignition events were recorded by high-speed imaging at 30kHz. The velocity field was measured by Particle-Image-Velocimetry (PIV). The dependence of autoignition and flame stabilisation limits on vitiated air temperatures and carrier preheating temperatures is shown, alongside the spatial distribution of different types of autoignition kernels, developing at different stages of the autoignition process. Higher hydrogen content significantly promotes the formation and development of autoignition kernels: The amount of kernels increases with higher hydrogen volume fractions showing the promoting effect of equivalence ratio on local ignition events. The kernels develop downstream a certain distance from the injector, indicating ignition delay significantly influences kernel development. The development of autoignition kernels could be linked to the shear layer development derived from global experimental conditions.

Copyright (c) 2017 by ASME
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