Neda Djordjevic

Knock Control in Shockless Explosion Combustion by Extension of Excitation Time

Shockless Explosion Combustion is a novel constant volume combustion concept with an expected efficiency increase compared to conventional gas turbines. However, Shockless Explosion Combustion is prone to knocking because it is based on autoignition. This study investigates the potential of prolonging the excitation time of the combustible mixture by dilution with exhaust gas and steam to suppress detonation formation and mitigate knocking. Analyses of the characteristic chemical time scales by zero-dimensional reactor simulations show that the excitation time can be prolonged by dilution such that it exceeds the ignition delay time perturbation caused by a difference in initial temperature. This may suppress the formation of a detonation because less energy is fed into the pressure wave running ahead of the reaction front. One-dimensional simulations are performed to investigate reaction front propagation from a hot spot with various amounts of dilution. They demonstrate that dilution with exhaust gas or steam suppresses the formation of a detonation compared to the undiluted case, where a detonation ensues from the hot spot.

Numerical Study on the Reduction of NOx Emissions From Pulse Detonation Combustion

A change in the combustion concept of gas turbines from conventional isobaric to constant volume combustion (CVC), such as in pulse detonation combustion (PDC), promises a significant increase in gas turbine efficiency. Current research focuses on the realization of reliable PDC operation and its challenging integration into a gas turbine. The topic of pollutant emissions from such systems has so far received very little attention. Few rare studies indicate that the extreme combustion conditions in PDC systems can lead to high emissions of nitrogen oxides (NOx). Therefore, it is essential already at this stage of development to begin working on primary measures for NOx emissions reduction, if commercialization is to be feasible. The present study evaluates the potential of different primary methods for reducing NOx emissions produced during pulsed detonation combustion of hydrogen. The considered primary methods involve utilization of lean combustion mixtures or its dilution by steam injection or exhaust gas recirculation. The influence of such measures on the detonability of the combustion mixture has been evaluated based on detonation cell sizes modelled with detailed chemistry. For the mixtures and operating conditions featuring promising detonability, NOx formation in the detonation wave has been simulated by solving the one-dimensional reacting Euler equations. The study enables an insight into the potential and limitations of considered measures for NOx emissions reduction and lays the groundwork for optimized operation of pulse detonation combustion systems.

SPH Simulation of a Twin-Fluid Atomizer Operating with a High Viscosity Liquid

G. Chaussonnet, S. Braun, L. Wieth, R. Koch, H.-J. Bauer A. Sänger, T. Jakobs, N. Djordjevic, T. Kolb Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany 1Institute of Thermal Turbomachines, KIT Campus South 2Institute of Technical Chemistry, KIT Campus North 3Engler-Bunte-Institute, KIT Campus South *geoffroy.chaussonnet@kit.edu Abstract A Smooth Particles Hydrodynamics (SPH) 2D simulation of a twin-fluid atomizer is presented and compared with experiments in the context of bio-fuel production. The configuration consists in an axial high viscosity liquid jet (μl ≈ 0.5 Pa.s) atomized by a coflowing high-speed air stream (ug ≈ 100 m/s) at atmospheric conditions, and the experiment shows two types of jet instability (flapping or pulsating) depending on operating conditions and the nozzle geometry. In order to capture the 3D effects of the axial geometry with a 2D simulation, the surface tension force and the viscosity operator are modified. The mean and RMS velocity profiles of the single phase simulations show a good agreement with the experiment. For multiphase simulations, despite a qualitative good agreement, the type of instabilities as well as its frequency are rarely well captured, highlighting the limitation of 2D geometry in the prediction of 3D configurations.