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Optical measurement techniques are very valuable tools for spray and
combustion diagnostics. In order to observe non-luminous events in
the cylinder, such as spray and flow field, schlieren/ shadowgraph
techniques are used because these techniques are sensitive to
density changes. ERL has the state-of-the-art optical diagnosis
techniques, which has been used for fundamental research. In ERL, we
have high speed CCD camera and Constant Volume Spray chambers (CVSCs).
Macroscopic spray characteristics studies have been performed at
both atmospheric and elevated pressure conditions. We employ natural
luminosity technique to capture the combustion flames with high
speed camera and optically accessible engines (SCRE for CI and GDI
for SI) for fundamental combustion research. We have also modified
and developed a small L-head single cylinder carburated engine for
optical access. For combustion visualisation in commercial engines,
Endoscopy is a novel technique. Endoscopy provides in cylinder
optical access to a metallic engine without substantial
modification. A Kirlosker made agricultural diesel engine has been
modified for endoscopic study. The SCRE also has the facility to
accommodate endoscope. Widely recognized as a major step forward in
quantitative spray measurements, phase Doppler interferometry (PDI)
relies on light scattered from two intersecting, coherent laser
beams. The scattered light interferes at three detectors placed at
carefully designed locations to generate sinusoidal Doppler burst
signals whose frequency is proportional to droplet velocity and
whose phase (for spherical scatters) is related by Mie scattering
theory to droplet diameter. In our Lab, atomisation characteristics
of different fuels have been tested under varying ambient
conditions. In cylinder spray droplets behaviour has been
investigated in a GDI engine and compared with the results of CVSC
study. Particle Image Velocimetry is a non-intrusive technique which
is capable of characterizing instantaneous velocity fields in a
fluid flow and is being used in our laboratory. High energy Nd:YLF
laser is used to generate a light sheet inside the cylinder which is
optically accessible and tracer particles (graphite particles) are
used to seed the air flow. The light sheet illuminates the tracer
particles. Images are captured by using high speed cameras in double
exposure mode. The images are then processed by using Davis software
(LaVision) to generate velocity fields of the air flow. |
