Analysis of injection spray patterns for common rail system
Date
2011-11-02
Authors
Alimia, Omid Iskander
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Abstract
The objective of this study was to investigate and compare the fuel spray characteristics of DME and
diesel fuel being injected through a common-rail fuel injection system into a constant volume pressure
vessel containing nitrogen gas. The fuel pressure and the chamber pressure were varied from 200-500bar
and 1-10bar respectively, all at room temperature conditions. Images of the spray were captured at a rate
of 7500fps utilizing a high speed camera, with a CMOS sensor, in conjunction with a schlieren optical
system. The images were then analyzed to determine quantitative aspects of the spray such as spray
penetration, cone angle and mean spray velocity and qualitative aspects like evaporation and flash boiling.
The fuel line pressure was also recorded and analysed to determine the effect that injection had on the
pressure in the line. For the same injection conditions it was found that the penetration of diesel was
greater than that of DME and the cone angle of diesel was greater than that of DME except at atmospheric
back pressure. The pressure oscillation in the DME fuel line was smaller in amplitude and longer in
duration than that of diesel. The DME spray exhibited signs of flash boiling and evaporation when
injected into an environment at atmospheric pressure and room temperature. As the chamber pressure was
increased the DME spray shape became increasingly similar to that of the diesel spray shape. The spray
boundaries, however, differed with DME exhibiting a more defined fuel-to-air barrier and diesel
exhibiting a fine mist at its boundary. The predicted spray penetrations of DME, using existing
correlations, were accurate for atmospheric back pressure conditions only.