Pulse train ignition with passively Q-switched laser spark plugs

Abstract

Leaner burning and downsizing are two concepts pursued by engine developers to reduce fuel consumption and emissions. Both approaches lead to increasing challenges concerning ignition, as these concepts are typically associated with an increase in flow velocity and degree of turbulence as well as raised pressure at the moment of ignition. In this context, the use of miniaturized passively Q-switched laser spark plugs with pulse train ignition is considered as a promising alternative to conventional spark plugs.However, the application of these passively Q-switched laser spark plugs inevitably leads to the question of optimum pulse train parameters. For a better understanding, this study deals with improved flame formation by passively Qswitched laser pulse train ignition under engine-like conditions. The entire ignition process is investigated with a special focus on interactions of consecutive pulses. Therefore, three methods are combined: energy transfer measurements from laser pulse to plasma with high temporal and spatial resolution show the breakdown process depending on different pressures and fluid mixtures. The temperature decrease in the induced plasma is analyzed with measurement strategies for temporal high-resolved plasma spectroscopy especially adapted to passively Q-switched lasers. In combination with high-speed schlieren measurements, the changing local ignition conditions during pulse train ignition are demonstrated. The experiments show how consecutive pulses interact and contribute to the ignition in case of a gas flow. The used prototypes of laser spark plugs are provided by Robert Bosch GmbH.

Compact nanosecond laser system for the ignition of aeronautic combustion engines

“…While less intense, these laser pulses should be absorbed by the plasma generated by the first laser pulse heat; therefore, they will contribute to its stabilization. This strategy has already been explored for automotive combustion engines by different authors [7,41].…”

“…The plasma has to bring a minimum energy to sustain the initial combustion within the ignition kernel [7][8][9]. The minimum ignition energy depends upon the nature of the fuel (gas or liquid droplets).…”

Influence of focal point properties on energy transfer and plasma evolution during laser ignition process with a passively q-switched laser

“…9. The plasma disappears the teardrop-like shape and intensity distribution within the plasma becomes more homogenous (6). During the decrease of intensity, the plasma expands in all directions.…”

“…Laser induced ignition is a promising option to meet demands of a future ignition source. Miniaturized passively q-switched laser (PQL) spark plugs additionally have the potential to meet the requirements regarding costeffectiveness and robustness [6].…”

12th International Congress of Engine Combustion Processes: Current problems and modern techniques (ENCOM2015)

“…Holly et al 12 investigated the influence of different methane numbers in the fuel gas on self-ignition (knocking) and NO x formation. And a new laser ignition technique based on pulse train ignition with miniaturized passively Q-switched laser spark plugs is described by Lorenz et al, 13 which is considered as a promising alternative to conventional spark plugs.…”