Quantification of diesel injector dribble using 3D reconstruction from x-ray and DBI imaging

Abstract

Post-injection dribble is known to lead to incomplete atomisation and combustion due to the release of slow moving, and often surface-bound, liquid fuel after the end of the injection event. This can have a negative effect on engine emissions, performance, and injector durability. To better quantify this phenomenon we present a new image processing approach to quantify the volume and surface area of ligaments produced during the end of injection, for an ECN 'Spray B' 3-hole injector. Circular approximation for cross-sections was used to estimate three-dimensional parameters of droplets and ligaments. The image processing consisted in three stages: edge detection, morphological reconstruction, and 3D reconstruction. For the last stage of 3D reconstruction, smooth surfaces were obtained by computation of the alpha shape which represents a bounding volume enveloping a set of 3D points. The object model was verified by calculation of surface area and volume from 2D images of figures with well-known shapes. We show that the object model fits non-spherical droplets and pseudo-cylindrical ligaments reasonably well. We applied our processing approach to datasets generated by different research groups to decouple the effect of gas temperature and pressure on the fuel dribble process. High-speed X-ray phase-contrast images obtained at room temperature conditions (297 K) at the 7-ID beamline of the Advanced Photon Source at Argonne National Laboratory, together with diffused back-illumination (DBI) images captured at a wide range of temperature conditions (293-900 K) by CMT Motores Térmicos, were analysed and compared quantitatively. KeywordsDiesel injector; dribble; ligament; droplet shape; atomisation. IntroductionThe end-of-injection (EOI) fuel dribble causes a formation of unburned hydrocarbons and decreases the performance of internal combustion engines in a variety of ways. For example, deposits lead to an increase in air pollutant emissions [1, 2], a decrease in quality of injection [2,3,4] and further coking of the nozzle [5]. Understanding of the fuel dribbling process is particularly important for the development of a strategy for optimal use of fuels. However, observing the transient end-of-injection processes is particularly challenging due to the extreme operating conditions and the microscopic scales involved. Consequently, there is a lack of quantitative information on the fuel dribble events and the parameters that affect them. Recently published studies [6][7][8][9][10] demonstrate different aspects of the EOI fuel dribble based on a qualitative and quantitative analysis of experimental images of the injection process. The following important factors affecting the mechanism of the fuel dribble were studied: peak injection velocity [7], needle closing speed [7], in-cylinder pressure [6,7], injection pressure [6], fuel mass expulsion [9], bubble ingestion at the EOI [10], liquid length recession at the EOI [8] and different flow characteristics at the EOI [11]. The present study is dedicated to a qua...

Experimental investigation of the Kelvin–Helmholtz instabilities of cylindrical gas columns in viscous fluids

“…The two cameras were both set at 2000 frames per second and 1280 x 800 pixel resolution to capture the detailed air column break-up processes. The generated pairs of images were then digitally cropped and enhanced before being used to reconstruct the three-dimensional structures of the air column using an algorithm developed by Sechenyh et al (2017), as shown in Fig. 3.…”