Effect of ambient pressure on penetration of a diesel spray I.V. Roisman * , Lucio Araneo 1 , C. Tropea Darmstadt University of Technology, Chair of Fluid Mechanics and Aerodynamics, Petersenstr. 30, 64287 Darmstadt, Germany Received 17 July 2006; received in revised form 22 January 2007 Abstract In the present experimental and theoretical work the propagation of a high-speed fuel spray at distances much longer than the breakup length is studied. The motion of the spray is modeled in two regions: the main region of the steady flow and the front region of the spray. The analysis yields the equation of propagation of the tip of the spray. These theoretical results have been validated against experimental data obtained from a common-rail diesel injection nozzle and from other data available in the literature. The importance of the shock wave propagation at the initial stage of the spray injection is demonstrated. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Spray; Spray penetration; Fuel injection; Ambient pressure 1. Introduction Experimental investigation and modeling of fuel spray are extremely challenging problems. The spray, espe- cially in the neighborhood of the nozzle, is very dense, making the use of conventional optical measurement techniques (such as the phase Doppler technique or PIV) very difficult. This is the reason why spray penetra- tion and cone-angle, which can both be obtained using photographic techniques, are among the most fre- quently reported parameters in fuel-spray research. Such a technique has been used in one of the first experimental studies (Miller and Beardsley, 1926) on the effect of the ambient pressure (or in fact the density of the ambient gas) on the penetration length of an engine spray. There are several models, semi-empirical or numerical, of spray penetration. In these studies (Wan and Peters, 1999; Sazhin et al., 2001; Naber and Siebers, 1996) the penetration of a spray was calculated by solving the cross-sectionally averaged equations of the flow, describing the mass and the momentum balance in the spray. The conditions at the front edge of the spray have not yet been considered for dense sprays. Experimental observations of spray penetration under high-ambient pressure conditions show that near the spray tip vortex-ring-like structures are frequently developed. Such structures have been observed in most of 0301-9322/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmultiphaseflow.2007.01.004 * Corresponding author. Tel.: +49 6151 163 554. E-mail address: roisman@sla.tu-darmstadt.de (I.V. Roisman). 1 Present address: Politecnico di Milano, Dipartimento di Energetica, via La Masa 34, Milano, Italy. International Journal of Multiphase Flow 33 (2007) 904–920 www.elsevier.com/locate/ijmulflow