Light-Emitting Diode-Based Pulsed Illumination Source for Continuous, Cycle-Resolved Spray Measurements

This paper presents a modular, high-powered light emitting diode (LED)-based illumination source to be used for spray measurements of the liquid phase via Mie scattering. The recent availability of consumer-grade LED arrays with average rated radiant powers of more than 100 W have enabled lower-cost designs than were possible with the previous laser illuminants. Flash tubes suffer from a non-constant rate of emission intensity and a fixed discharge time, which can be a restricting factor, especially with multiple injections. The narrow spectral distribution of LEDs, with a full width at half maximum of 17nm, aids in distinguishing the measurement signal from unwanted background noise. Using frame-synchronous LED pulse generation at repetition rates of 100 kHz, it is possible to record both arbitrarily spaced multiple injections as well as consecutive working cycles, for example in internal combustion engines. Pulse durations are currently variable in the range 1-78 µs. Luminous flux is boosted by driving the light source at a significantly higher current and voltage as compared to the continuously rated specifications, which results in a high temporal resolution, as exposure times as low as one µs provide ample recorded intensities. Benchmarks based on a commercial xenon flash tube and laser diode demonstrate the design’s versatility along with first applications in an optically accessibly research engine.