NDLI: Computational and Experimental Analysis of Direct CNG Injection and Mixture Formation in a Spark Ignition Research Engine

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Baratta, Mirko Andrea, E. Catania Francesco, C. Pesce
Copyright Year	2010
Abstract	Direct injection (DI) of compressed natural gas (CNG) under high pressure conditions is a topic of great interest, owing to its potential for improving SI engine performance and fuel consumption. However, relevant technical difficulties have yet to be resolved in order to stabilize combustion process, especially for stratified engine operating conditions. The present paper is focused on experimental and numerical investigations of the jet formation and fuel-air mixing process in a research optical-access single-cylinder engine. The engine is based on the multi-cylinder engine under development within the European Community (EC) VII Framework Program (FP) InGAS Integrated Project, and features a centrally mounted poppet-valve injector on a pent-roof combustion chamber with a bowl in piston. Experimental investigations were made by means of the planar laser-induced fluorescence technique, and revealed a cycle-to-cycle jet shape variability. In particular, for specific cylinder pressure values at the start of injection, the jet can adhere to chamber walls for a relevant number of cycles, leading to an ‘umbrella-like’ shape. This can change the mixing capabilities of the combustion chamber and cause instabilities in the combustion process. The mentioned behaviour is strongly dependent not only on the injection and cylinder pressures, but also on important design parameters, such as needle cone angle and in-chamber injector protrusion. For this reason, in order to obtain a deep insight into the injected gas behaviour on an average cycle basis, the experimental investigation was supported by a numerical analysis. Simulations were carried out by an optimized variable-density finite-volume numerical model which was built within the Star-CD environment. A previously developed and validated ‘virtual injector’ model was implemented. The outcomes of the numerical model were compared to laser-induced fluorescence images, for both stratified- and homogeneous-charge engine operating conditions and a good agreement was obtained, substantiating the reliability of the applied computational model. Then, the effects of the injector protrusion in the combustion chamber and of injection timing were analyzed, and their impact on jet stability and mixture-formation process was analyzed.
Sponsorship	Internal Combustion Engine Division
Starting Page	777
Ending Page	793
Page Count	17
File Format	PDF
ISBN	9780791849446
DOI	10.1115/ICEF2010-35103
e-ISBN	9780791838822
Conference Proceedings	ASME 2010 Internal Combustion Engine Division Fall Technical Conference
Language	English
Publisher Date	2010-09-12
Publisher Place	San Antonio, Texas, USA
Access Restriction	Subscribed
Subject Keyword	Cycles Single-cylinder engines Spark-ignition engine Ignition Fluorescence Roofs Fuel consumption Valves Combustion Fuels Density Engines Design Pistons High pressure (physics) Lasers Ejectors Needles Shapes Engineering simulation Cylinders Stability Computer simulation Pressure Numerical analysis Simulation Experimental analysis Combustion chambers Performance Reliability Natural gas
Content Type	Text
Resource Type	Article

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