ID 242

Tracer-free FAR and thermodynamic phase determination in sprays by Raman spectroscopy

 

Abstract:

Spray formation in high-pressure, high-temperature environments has been investigated by applying a wide range of optical measurement techniques. Measuring fuel-air-ratios (FAR) is possible within certain limitations, whereas the determination of the thermodynamic phase (gas or liquid) of the fuel becomes difficult when approaching critical conditions with respect to the fuel. In that case, techniques like Mie-scattering may become unreliable due to the extreme decrease in surface tension, failing to resolve liquid-like volumes with diffuse surfaces. Here we present one-dimensional Raman measurements carried out in an optically accessible high-pressure, high-temperature injection-chamber. With our calibrated Raman measurements, tracer-free determination of the FAR is possible for different fuels and at varying chamber and injection conditions. Furthermore, the shape of the OH-band of ethanol (one of the employed fuels) gives information about the thermodynamic state of the fuel, shedding light on the real liquid length of the spray at potentially supercritical conditions. This approach allows direct discrimination of liquid and gaseous fuel fractions and gives insight into the temperature of the liquid fraction. The setup of these measurements is described and a selection of the gained results will be shown, additionally the potential for further measurements will be discussed.