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Effect of Injection Rate and Gas Density on Ambient Gas Entrainment of Non-evaporating Transient Diesel Spray from Common-Rail Injection System  

Kong, Jang-Sik (Department of Mechanical Engineering, KAIST)
Choi, Wook (Department of Mechanical Engineering, KAIST)
Bae, Choong-Sik (Department of Mechanical Engineering, KAIST)
Kang, Jin-Suk (Powertrain Research, Hyundai-Motor)
Publication Information
Transactions of the Korean Society of Automotive Engineers / v.12, no.5, 2004 , pp. 19-24 More about this Journal
Abstract
Entrainment of ambient gas into a transient diesel spray is a crucial factor affecting the following preparation of combustible mixture. In this study, the entrainment characteristics of ambient gas for a non-evaporating transient diesel were investigated using a common-rail injection system. The effects of ambient gas density and nozzle hole geometry were assessed with entrainment coefficient. Laser Doppler Velocimetry (LDV) technique was introduced to measure the entrainment speed of ambient gas into a spray. There appeared a region where the entrainment coefficients remained almost constant while injection rates were still changing. The effect of common-rail pressure, which altered the slope of injection rate curve, was hardly noticed at this region. Entrainment coefficient increased with ambient gas density, that is, the effect of ambient gas density was greater than that of turbulent jet whose entrainment coefficient remained constant. The non-dimensional distance was defined to reflect the effect of nozzle hole diameter and ambient gas density together. The mean value of entrainment coefficient was found to increase with non-dimensional distance from the nozzle tip, which would be suggested as the guideline for the nozzle design.
Keywords
Common-rail injection system; Injection rate; Entrainment; Entrainment coefficient;
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