Spray Characteristics and Wall Impingement of Diesel-CNG Dual Fuel Jet Using Schlieren Imaging Technique

Abstract

.my).the natural gas inside the engine. In addition, this system does not favor the two-stroke engine due to the escape of some of the natural gas fuel into the exhaust [3]. The second method of using natural gas in diesel engines is the direct injection of natural gas near to the diesel fuel spray into the combustion chamber [4]. Thus a full stratification of the fuel-air mixture can be obtained with good flammability over the entire load range.Recently, successful operation has been demonstrated by applying this method using a prototype co-injector [5], resulting in diesel-gas two phase mixtures which were then injected into the chamber. The authors recommended that the jet penetration should be imaged and characterized to further understand the complex two-phase flow phenomena. It appears that direct injection of natural gas with diesel pilot ignition is one of the most promising ways of meeting the energy crises and emissions regulation, analogous to the benefits provided by a common rail high pressure direct injection engine.Actually, the development of high performance natural gas DIEs is unclear as the macroscopic characteristics of the diesel-CNG dual fuel jet which differs considerably from that of diesel fueled compression ignition (CI) and spark ignition (SI) engines. In diesel-CNG dual fuel engine, the performance of the engine is influence significantly by the quality of the diesel fuel sprays and CNG jet propagation. Those characteristics can be classified into two basic categories: Macroscopic and microscopic. The first one, which involves spray tip penetration, spray cone-angle, and their derivatives and the second, involves droplet velocity, droplet size, size distribution and air fuel ratio [6]. Improvement of the diesel-CNG dual fuel jet characteristics such as jet tip penetration, jet cone angle and jet velocity in turn determine the diesel-CNG dual fuel combustion process and the associated formation of pollutants. In addition, these characteristics not only aim to improve the engine efficiency, but also assist the understanding of parameters used to judge fuel spray performance [7]. For example, the spray penetration length must neither be too long nor short in a combustion chamber. If too long, impingement could occur resulting in wetting of cylinder walls and/or piston crown [8]. Spray-wall impingement can be characterized into radial penetration along the wall and jet height. Improvement of those characteristics leads to enhance the mixture formation as well as the combustion process. The present work investigates the jet propagation of jets created by CNG and diesel injectors with aid of flow visualization. Based on the previous studies, it is well known that the injection strategy and the atomization play an important role for the diesel Materials, Mechanics and Manufacturing, Vol. 3, No. 3, August 2015 spray, and the mixture formation is largely dependent upon the droplet distribution and evaporation [9]. In contrast with diesel spray, natural gas does not have droplets and evapor...

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