Evaporation of Alternative Fuel Mixtures in Engine Sprays

The addition of renewable fuels such as ethanol or methanol to conventional fuels can contribute significantly to the net reduction of CO2. However, the addition of alternative fuels can significantly influence combustion properties and pollutant formation. A decisive factor here is the complex evaporation behaviour of multi-component fuel mixtures. Depending on the original composition, one component may evaporate preferentially, leading to a temporal change in the fuel composition in the spray.

To characterise this preferential evaporation in the fuel spray, an optical measurement method was developed that enables two-dimensional imaging measurement of concentrations and droplet sizes in sprays. For simultaneous measurement of both parameters, laser-induced fluorescence (LIF) on a dye, whose emission signal is detected in two wavelength ranges, is coupled with elastic light scattering. For the development of the method, successive measurements were carried out on levitated and falling individual droplets and the results were gradually validated up to the point of application in the spray. The project yielded valuable insights into the evaporation of multi-component mixtures, and a new measurement method was developed and validated that can be applied to a wide variety of sprays.