Theoretical and Experimental Discourse on Laser Ignition in Liquid Rocket Engines

Kurzfassung

Igniter technologies have seen an increased interest in the past decades due to the increasing re-ignition needs, such as for the upper stage Vinci engine. Weight reduction considerations and redundancy considerations have lead to an increased number of studies in alternative igniter technologies to the conventional pyrotechnical or spark plug igniters in use today. Such technologies include concepts such as resonance igniters, catalyst igniters and laser igniters. When compared to classical ignition methods, both in the automotive industry, i.e. spark ignition, and in the space industry, i.e. pyrotechnic/torch ignition, laser ignition system (LIS) offer multiple advantages. Literature classifies laser-gas interactions into four main categories which differ in the mechanisms leading to ignition: non-resonant breakdown ignition, resonant breakdown ignition, thermal ignition and photochemical ignition. Non-resonant laser ignition is the most common form of ignition and involves a well-focused pulsed laser beam thus creating a well localized plasma which can accumulate further energy leading to a local increase in temperature and finally ignition. Non-resonant laser ignition may occur via either a multiphoton ionization process or an electron cascade process. This paper addresses the main issues related with the various laser ignition methods via a literature review of research conducted in the field of laser ignition. The main findings of the experimental work done in the non-resonant laser ignition of a coaxial liquid oxygen and gaseous methane jet at the DLR Lampoldshausen M3.1 test bench is presented.