Effect of Impingement Distance on Penetration and Volume of Post-impingement Diesel Spray
K. Ko*, T. Momiyama*, K. Amagai** and M. Arai**
Diesel spray impinged normally on a flat wall was investigated. Spray tip penetration and spray volume of before and after impingement were measured on high speed photographs of the sprays which were injected by a single shot injection system into a high pressure chamber of cold state. An imaginary origin of the radial spray flow was set on an impingement center on the wall. The effects of the period and rate of injection on the spray tip penetration, spray volume and entrainment air were discussed on the sprays of before and after impingement. The spray volume of the post-impingement spray was greatly affected by the distance between the injection nozzle and the wall. When the impingement distance was shorter than the break-up length of the original spray, the entrainment air as well as the volume of post-impingement spray was larger than those of the original spray at the same inspection time. Also, when the injection rates at early stages were same with each other, the entrainment air after those stages was dependent on injection rate history.
Key Words: Diesel spray, Wall impingement, Penetration, Break-up length, Spray volume, Entrainment air
According as DI diesel engine has become small size, it has been important for many engine researchers to understand the wall impingement phenomena of fuel spray because of the short distance between the injection nozzle and the piston cavity. It has been well known that impinging spray has fine atomization and a good spatial distribution of the fuel droplets. However the spatial distribution of fuel and air entrainment into the impingement spray are still remained as unclear problems which affected great influence on combustion characteristics. By the spray impingement, Sakane et al. had clarified that the quantity of ambient gas entrained into spray was enlarged and the mixing between fuel and ambient gas was promoted. It was predicted by Kawamura et al. that the thickness of fuel adhered on the wall decreased with an increase of injection pressure, and droplet size decreased with a decrease of the nozzle diameter.
Senda et al. had proposed a new model for the spray/wall interaction process. It was found that the important factors of mixture formation near the combustion chamber wall were an impinging angle to the wall and a spray impinging position. By means of the wall inclined angle being varied from 10 deg. to 90 deg., Ebara et al. investigated the structure and movement of a diesel spray.
They verified that when the spray was impinging on a shallowly inclined wall, the high density zone of impinging spray was very near to the wall, while in case of impinging vertically on the wall, the high density zone was separated from the wall surface.
By using electronically controllable fuel injection system which allowed same injection period and same injection quantity but injection rate shaping was not same, Wakisaka et at.[7, 8] found that the slope of injection rate rise had great influences on combustion period and high temperature region in a flame as well as the spatial fuel distribution. With injection rate control using a newly designed camprofile, Miura et al. showed the possibility of improvement in the trade off relationship between NOx emission and fuel consumption.
However for the purpose of combustion design, it has been still insufficient to investigate spray characteristics after impingement. Especially, no attempt has been made to study effect of injection period and impingement distance on impinging spray. In this study, we examined the influence of the injection period and injection rate on vertical impinging spray on the wall. The spray volumes at various wall locations were analyzed, and entrainment air, which was changed after impingement was investigated experimentally.
2. EXPERIMENTAL SETUP AND PARAMETERS
The experimental apparatus is shown in Fig.1. In order to make a single injection, a single shot pulse generator, a solenoid valve and a dummy nozzle were used. A single-hole type diesel injection nozzle was used. The diameter D and length L of the nozzle hole were 0.24 mm and 0.6 mm (L/D = 2.5).
* Graduate student of Gunma-Univ.
Dept. of Mechanical System Engineering, School of
Engineering, Gunma University, Tenjincho 1-5-1, Kiryu,
Gunma, 376-8515. JAPAN
Fax: +81-277-30-1521 E-mail: email@example.com,
** Dept. of Mechanical System Engineering of Gunma-Univ.