Comparative Study of Biodiesel and Diesel Jets in Gaseous Crossflow

Abstract

This study compares the fundamental spray characteristics, such as penetration depth, droplet diameter, velocity, and volume flux of, biodiesel and diesel as well as their blends. Liquid jet is injected into an air crossflow with a speed of 58 m∕s. A series of experimental tests covering Weber numbers from 29-82, and momentum flux ratios from 10-133, are conducted using the shadowgraph method and phase Doppler particle analyzer. The shadowgraph images are processed to find the penetration depth and to investigate different regimes of breakup. The phase Doppler particle analyzer is used to capture droplet size distribution, velocity, and volume flux. The results differ remarkably in terms of breakup regimes and trajectory for biodiesel blends, which may be due to the high viscosity of biodiesel in comparison to diesel. For example, at a Weber number of 80, some bag breakups are observed on the biodiesel jet against the expectation that, at this Weber number, most of the liquids experience atomization mode.

How do liquid fuel physical properties affect liquid jet development in atomisers?

“…Although a definitive correlation with the liquid viscosity was not possible in their study, various effects were proposed as possible influences, including the liquid properties, atomization, and the column break mode. The influence of the breakup mode is in agreement with that in the work of Farvardin et al 15 As such, predictions of the spray characteristics when one type of fuel is directly substituted with another may not be always reliable. Consequently, the direct substitution of fuels with similar physical properties may not produce the expected spray development.…”

“…Experimentally, it has been observed that more viscous liquid jets are deflected laterally by the cross flow, more than the less viscous jets. 14,15,40 An interpretation of this observation can be based on the more developed liquid velocity radial profile in the more viscous liquid jet.…”

“…For example, in two recent studies of liquid fuel injection in a crossflow of air, when scaling the penetration of the liquid jet in the gaseous cross flow, the exponent of the viscosity in the derived correlations has been quoted as −0.108 14 and −0.222. 15 While the former study considered a range of viscosities about 50% lower than the latter, the exponent changes by a factor of 2 which is considerable. The change in the exponent was attributed to changes in the morphology of the liquid jet between the two studies affecting the drag of the liquid jet.…”

“…The change in the exponent was attributed to changes in the morphology of the liquid jet between the two studies affecting the drag of the liquid jet. 15 However, changes in the liquid jet morphology were not measured. In addition, the range of liquid viscosities that was considered in the above two investigation was considerably wide, with changes over 100% in the fuel viscosities from which the liquid jet trajectories were determined.…”