Victor Lafaurie defended his PhD "Pulsed plasma approach for mild or strong ignition of a detonation wave using gradient of atomic species"
On March, 2025, Victor Lafaurie defended his PhD "Pulsed plasma approach for mild or strong ignition of a detonation wave using gradient of atomic species".
Abstract :
This thesis presents a study conducted on the ignition of a detonation wave with non-equilibrium plasma. This form of plasma-assisted combustion has been of recent increased interest with the developments of new forms of detonation-based propulsion and their implementation into real flight structures. A key component of these propulsive devices is the requirement for reliable, efficient, “at will” ignition of a detonation wave. Typically, a detonation wave is formed either by depositing a large amount of energy (of the order of Joules) in a combustible mixture to directly form a detonation, or by igniting a flame with a weak energy source which accelerates before transitioning to a detonation (known as deflagration to detonation transition, or DDT). This work suggests the use of nanosecond plasma to produce a gradient of active species as a means of promoting the DDT process. For this purpose, the thesis is split into two parts.
The initial focus is on the development of a new set of electrodes to achieve a gradient of atomic species. Nanosecond pulsed plasma (30 ns FWHM) in the range of -6 to -22.5 kV are used in this study. After an extensive set of possible geometries is tested, a plane-to-plane configuration with a varying gap size (28 to 50 mm over an 80 mm span) is developed and characterised using a variety of diagnostics. The formation of a gradient of atomic oxygen along the span in air at multiple pressures in the range of 100 to 150 mbar is shown by two-photon absorption laser-induced fluorescence (TALIF). The longitudinal reduced electric field is measured through multiple techniques such as optical emission spectroscopy, capacitive probe detector and electric-field induced second-harmonic generation (E-FISH). These give information on both the range of absolute values of field in the plasma (100 to 200 Td) and the early development of the discharge.
The discharge is then tested in multiple combustible mixtures (2 H2 + O2, C2H2 + 2.5 O2, C2H4 + 4 O2) or a wide range of pressure (100 to 200 mbar) and deposited energy (50 to 600 mJ). The DDT length is recorded. Schlieren imaging is performed and shows the formation of both mild and strong ignition of a detonation wave. This study therefore participates in a deeper understanding of the mechanisms through which plasma can enhance detonability.