An optical diagnostic technique based on ultraviolet absorption and schlieren for components stratification in a binary-component fuel–air mixture

The evaporation characteristics of multi-component fuel have significant effects on the fuel–air mixing process and subsequent processes, such as ignition, combustion, and harmful pollutants emission formation. When a multi-component fuel is directly injected into the combustion chamber, spatial and temporal equivalence ratio stratification may happen due to the preferential evaporation of components with different volatilities. However, there is a lack of effective optical diagnostics of the spatial stratification in a multi-component fuel spray. In this study, new optical technique based on ultraviolet absorption and visible light schlieren (UAVS) is for the first time proposed to measure the stratification of vapor distributions stratification in a binary-component fuel spray. UAVS technique was applied to investigate the effects of mixing ratios in a binary-component fuel spray (p-xylene and n-hexane) and ambient temperature on the stratification of components with different volatilities. The results denote the UAVS technique as the effective method for the observation of stratification of a multi-component fuel spray. In this study, the stratification phenomenon was the most evident at the ratio of 1:1. At the same time, when the ambient temperature is much higher than the dew point temperature of mixture, the stratification rarely occurs, because of the rapid evaporation thus providing time not enough for preferential evaporation.