Laser-initiated ignition

After an introduction illustrating the relevance and motivation of laser ignition of engines, the physical background is reviewed in a first technical section. This mainly comprises the mechanisms of plasma formation, which are the generation of first free electrons and their avalanche‐like multiplication, being illustrated by emission and Schlieren diagnostics. Thereafter, combustion fundamentals are discussed leading to an understanding of flammability and minimum ignition laser energies. An important section is represented by the description of the components of laser ignition. This covers the setup and function of a diode‐pumped passively Q‐switched solid‐state laser system, which preferentially is based on Nd:YAG. Other laser sources are mentioned for comparison. Furthermore, multiplexing schemes are discussed that are motivated by cost‐saving issues. It is explained why present‐day optical fibers are not capable of transporting nanosecond ignition pulses. As a last section, the concepts for an incoupling window and focusing optics are elucidated. Finally, after a summary, in an outlook the chances for commercial realization are analyzed. In this article the physical background of laser ignition of engines is reviewed. This mainly comprises the mechanisms of plasma formation, which are the generation of first free electrons and their avalanche‐like multiplication. Combustion fundamentals are discussed leading to an understanding of flammability and minimum ignition laser energies. An important section is represented by the description of the components of laser ignition, like the diode‐pumped passively Q‐switched solid‐state laser system, or multiplexing schemes, optical fibers, concepts for an incoupling window and focusing optics.