VCSEL aids high-efficiency engine design
Laser diode manufacturer Vertilas has joined forces with ProcessEng Engineering to investigate combustion dynamics in a gasoline engine with a wavelength-tunable VCSEL.
The German partnership measured methane concentrations in a Volvo engine by tunable diode laser absorption spectroscopy.
According to Vertilas VCSELs are the only devices suitable for these measurements: "In contrast to conventional lasers, they can be tuned very far and very fast, two important prerequisites for the technique to work."
By tuning the VCSEL s laser wavelength it is possible to distinguish between resonant molecular absorption, which reveals the methane concentration, and unwanted physical effects such as light scattering from soot particles.
The team used a line-of-sight technique to determine the methane concentration at 40 µs intervals. Although this approach only provides path-averaged results, which are used to determine the overall combustion efficiency, by probing different areas within the engine the methane concentration in a particular region can be mapped.
The researchers studied the combustion process with a Volvo truck engine that was adapted for optical access by inserting four small windows. Although the engine modifications affect the physical processes (for example, heat transfer is not as efficient as with standard engines), Vertilas claims that the technique reveals data that are impossible to obtain with a conventional engines.
According to Vertilas, the high-efficiency engine used in the experiments provides clean combustion and diesel-like fuel efficiencies that could reduce gasoline consumption by half and virtually eliminate nitrogen oxide and soot emission.