Experimental investigation on wall film ratio of diesel, butanol/diesel, DME/diesel and gasoline/diesel blended fuels during the spray wall impingement process

- The wall film ratio is affected by mass proportion of evaporation and splashing.
- Impingement momentum is major impact factor when varying pressure or distance.
- Impingement flow mass is major impact factor when varying the impingement angle.
- Fuel properties (surface tension) are major impact factor when varying blending ratio.
- The relationships between wall film ratio and Weber number have been given.

Spray wall impingement in the early injection period has been proved be unavoidable in the diesel engine using early injection strategy. The formation of wall film directly affects fuel/air mixture formation, combustion, exhaust emissions and oil quality. In this study, experiments were carried out to investigate the wall film ratio of pure diesel, butanol/diesel, DME (Di Methyl Ether)/diesel and gasoline/diesel blended fuels. The variations of wall film ratio with different injection pressures, impingement distances, impingement angles and blending ratios were compared under both dry wall and wet wall conditions. For both dry wall and wet wall conditions, with increasing injection pressure and blending ratio, wall film ratio decreased, which is the opposite trend to impingement distance and impingement angle variations. Some dimensionless numbers also have been introduced in order to evaluate the effect of each impact factor on the variation of wall film ratio. Results showed that impingement momentum is the major impact factor on wall film ratio when varying the injection pressure or impingement distance. Impingement flow mass is the major impact factor when varying the impingement angle. For different blending ratios, the wall film ratio is mainly influenced by surface tension, followed by viscosity and saturated vapor pressure. In addition, the equations between the wall film ratio and Weber number of the impingement droplet were derived for each test fuel.