Breakup and atomization characteristics of mono-dispersed diesel droplets in a cross-flow air stream Sung Wook Park a , Sayop Kim b , Chang Sik Lee c, * a Mechanical Engineering and Technical Research Institute, Hanyang University, 17 Haengdang-dong, Sungdong-gu, Seoul 133-791, South Korea b Graduate School of Hanyang University, 17 Haengdang-dong, Sungdong-gu, Seoul 133-791, South Korea c Department of Mechanical Engineering, Hanyang University, 17 Haengdang-dong, Sungdong-gu, Seoul 133-791, South Korea Received 1 February 2006; received in revised form 23 February 2006 Abstract This paper describes the microscopic and macroscopic breakup characteristics, as well as the velocity and size distribu- tions, of mono-dispersed droplets in relation to the breakup regimes. For this experiment, a droplet generator equipped with a piezo stack produced mono-dispersed droplets. The droplet-breakup phenomenon due to the cross-flow was cap- tured in microscopic and macroscopic views by using the following: a spark lamp, a Nd:YAG laser, a long distance micro- scope and a CCD camera as a function of the Weber number. Along with the analysis of the images, the droplet size and velocity distributions were measured in the near nozzle region by a phase Doppler particle analyzer system at bag, stretch- ing and thinning, and catastrophic breakup regimes. The results of this study showed the size and velocity distributions of disintegrated droplets at the bag, stretching and thinning, and catastrophic breakup regimes. In the bag breakup regime, the droplets separated into small and large droplets during breakup. Alternatively, the droplets disintegrated at a shorter duration and formed a cloud, similar to a fuel spray injected through an injector, in the stretching and thinning and catastrophic breakup regimes. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Breakup mechanism; Mono-dispersed droplets; SMD (Sauter mean diameter); PDPA (phase Doppler particle analyzer) 1. Introduction In an internal combustion engine, the atomization of fuel spray is important because of its close relation to the engine efficiency and pollutant emissions. In particular, in the case of a diesel engine, the atomization of the fuel spray is very important because there is little atomization for diesel as compared to gasoline spray. In order to improve the atomization performance of a diesel spray, there have been many attempts for the better 0301-9322/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmultiphaseflow.2006.02.019 * Corresponding author. Tel.: +82 2 2220 0427; fax: +82 2 2281 5286. E-mail address: cslee@hanyang.ac.kr (C.S. Lee). International Journal of Multiphase Flow 32 (2006) 807–822 www.elsevier.com/locate/ijmulflow