In-water injection of high-pressure pulsed gas jet: A simple analytical tool for direct injection of gaseous fuels in automotive engine Taib Iskandar Mohamad Department of Mechanical and Materials Engineering & Center for Automotive Research, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia article info Article history: Received 28 April 2015 Received in revised form 7 June 2015 Accepted 25 July 2015 Available online 6 August 2015 Keywords: Compressed natural gas Flow visualization Gas jet dynamics Direct injection Sonic flow abstract Visualizing high pressure pulsed gas jet can be challenging due to its weak scattering of light which requires reliable flow tracer. Complex and costly laser source and high speed camera settings using shad- owgraph, Schlieren and Laser Induced Fluorescent (LIF) techniques with seeding of flow tracers such as acetone have been used. In the spirit of simplification, this paper presents a technique to visualize high pressure pulsed gas jet in liquid ambient. It can be used as predictive tool to investigate the structure, dynamic and interaction of gas jet with the environment [1]. A gas injector with square-shaped nozzle was used. High pressure nitrogen gas at 5 and 6 MPa with 12 ms injection pulse exits the injector through a 1 mm 2 square nozzle into quiescent water. The injector tip is immersed below water surface in an optically-accessed container and placed inside an extremely low illuminated square chamber. Two small windows on opposite walls of the chamber allow image capturing with injection-flash light synchroniza- tion. Images of the gas jets formed from nozzle at various time after the start of the injection (SOI) were captured by a digital camera. During exposure, the flash light was triggered for 1 ms at some times after SOI, thus images captured correspond to the flash timing. Results showed that the shape of the gas jet was in agreement with the vortex ball model but with dif- ference in the magnitude of penetration with respect to previous works. Some similarities in the gas injection behavior are found in the liquid and gas ambient. The tip penetration and gas width in water environment are about half of the magnitude in the gas environment. A dimensionless gas dynamic anal- ysis shows a good agreement in the trend of jet development between the gas environment using Planar Laser Induced Fluorescent (PLIF) imaging and in-water imaging techniques. Results indicate that both gas jet length and width are very sensitive to injection pressure. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Application of high pressure gas injection can be found in many industries. In order to optimize the results of applying gas jet, a good understanding of gas jet behavior is highly necessary. One of these applications is in automotive engines. In the recent years, direct fuel injection has gain considerable interest in automotive technology and has even entered production stages, but mainly in direct injection of liquid fuels such as diesel and gasoline. Direct injection of natural gas in spark and compression ignition engines were also developed and studied extensively. Natural gas (NG) has been extensively used in internal combus- tion engines powering more than 15 million vehicles worldwide [5]. The interest of using natural gas is mainly driven by low fuel cost as well as higher potential of increased thermal efficiency and significantly low exhaust emissions [6,7]. However many NG powered vehicles suffer from reduction of peak power. This is pre- vailing when converting mixer-type, port or manifold injection gasoline to natural gas. The main reason for it is because the den- sity and flame speed of methane are lower than those of gasoline causing reduced volumetric efficiency and limited upper speed [8]. One way to reduce these problems is using direct fuel injection (DFI). With DFI, volumetric efficiency is increased by injecting fuel after the intake valve closes. High pressure gas jet can enhance intensity of turbulence, thus leads to improving air–fuel mixing. Many optical diagnostic techniques for visualizing fluid flows such as Planar Laser-Induced Fluorescent (PLIF), Schlieren, shad- owgraph and Particle Image Velocimetry (PIV) have been used, producing accurate performance predictions [3,4]. Phase Doppler anemometry (PDA) were used to measure near-nozzle microscopic http://dx.doi.org/10.1016/j.fuel.2015.07.083 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved. E-mail address: taib@ukm.edu.my Fuel 160 (2015) 386–392 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel