10 th Pacific Symposium on Flow Visualization and Image Processing Naples, Italy, 15-18 June, 2015 Paper ID:095 1 Schlieren/Mie-Scattering Images of a High-Volatility Fluid Impacting on a Heated Surface: Liquid/Vapor Phase Detection Luigi Allocca * , Maurizio Lazzaro, Giovanni Meccariello, Alessandro Montanaro Istituto Motori – Consiglio Nazionale delle Ricerche, Via Marconi 8 – 80125 Napoli – Italy *corresponding author: l.allocca@im.cnr.it Abstract The paper reports the vapor and liquid phase evolutions of sprays impacting on an aluminum flat wall, controlled in temperatures in the range from 300 to 573 K. The fluid is iso-octane, injected at pressures up to 25.0 MPa by a Common Rail apparatus. The spray-wall interaction was characterized by means of high-speed imaging. Schlieren and Mie-scattering images of the sprays were acquired nearly simultaneously along the same line-of-sight. The technique is suitable to highlight fluid with inner density gradients, allowing to detect both the liquid and vapor phase of the evolving spray. The optical system, coupled with a high-speed C-Mos camera, permitted to acquire the evolution of the spray on the wall at a frequency of 25,000 frames/s with images of 640x464 pixels. A customized image-processing procedure was developed was used to batch processing and outlining the contours of the liquid and vapor phase. Keywords: DISI engines, spray-wall interaction, Schlieren, Mie-Scattering, Image processing 1 Introduction The direct injection in spark ignition (DISI) engines offers undoubtedly substantial advantages with respect to the traditional port fuel injection (PFI) configuration [1]. Respect to the last one, they can operate at higher compression ratios, higher thermal efficiencies and power outputs, adopting different injection strategies and operation modes, and allowing an accurate metering of the air fuel ratio. They can work under lean fuel conditions in stratified charge mode, approaching to efficiencies and emission indexes typical of compression ignition engines. However, the achievement of a proper air-fuel mixture inside the combustion chamber, varying the engine load and the strategy of fuel injection, remains a critical point [2]. The evolution of the fuel spray inside the cylinder is governed by the injector nozzle design, the fuel pressure, the injection timing and by its interaction with the cylinder/piston walls [3-5]. Spray droplets hitting on the surface may rebound, stick to form a film on the wall, or undergo heating and evaporation. In particular, wall wetting should be avoided, because of its strong impact on the mixture formation and emission of particulate and unburned hydrocarbons. As a result, the widespread of DISI engines has given new impetus to the study of fuel spray behavior [6-9]. The new generation of GDI injectors adopts a non- axisymmetric multi-hole architecture, and at present, their behavior does not have yet exhaustively investigated [10-12]. To overcome the complexities inherent to the study of the spray-wall, the jet-jet or jet- flow field interactions, and their impact on the combustion in the engine, simplified experimental configurations considering single-hole injectors and heated flat walls can be profitably investigated [13,14]. In this work, the behavior of an isooctane spray impinging on a flat metal surface, varying the fuel injection pressure and wall temperature, was investigated in an optically accessible quiescent vessel. A single-hole axially-disposed injector was used, 0.200 mm in diameter and L/d=1.0, while the injection pressure and the wall temperature ranged between 5.0 - 20.0 MPa and room to 573 K, respectively. The phenomenon was analyzed by means of high-speed imaging. Schlieren and Mie-scattering images of the spray were acquired alternatively and in a quasi-simultaneous way along the same line-of-sight, using a C-Mos high-speed camera. The tests were performed at atmospheric backpressure and room gas temperature. The images were processed through a customized algorithm to better outline the contours of the liquid phase and the vapor/atomized zone. Spatial and temporal evolutions were measured for both the phases in terms of width penetration and thickness growth.