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Optical Characterization of Biodiesel and Diesel Fuel Sprays From a Cr Injection Apparatus
Technical Paper
2004-05-0399
Sector:
Language:
English
Abstract
The fuels from renewable resources have obtained an increasing
interest for transport application in the last decade because of
their biodegradability, potential improvements on exhaust emissions
and benefits on the virtuous CO2 cycle of the earth.
The different physic-chemical characteristics of the biofuel,
respect to diesel fuel, affect the combustion phenomenon in diesel
engines being different the droplets distribution in the combustion
chamber and, consequently, the air-fuel mixture preparation in the
ignition delay ready to be burned. The recent trend to enhance the
spray atomization, increasing the injection pressure and the hole
number in the nozzle to better distribute the fuel, imposes a deep
understatement of the spray characteristics in terms of tip
penetration, cone-angle, droplet velocity, fragmentation and
vaporization.
The modern Common-Rail (CR) injection apparatus enables a
management of injection strategy both in terms of injection
pressure and injection number and timing per cycle. They allow to
exploit all the potentiality of modulated combustion in engine for
NOx and noise reduction, acting on pilot and pre-injections, and
matter particulate using post and late injections.
In this paper a study of overall behavior of spray from rapeseed
methylester (RME) biofuel and diesel fuel has been carried out in
an optically accessible vessel filled with inert gas (N2) with
pressure ranging between 0.1 to 5.0 MPa. The injections were
obtained by a CR apparatus driven by a Programmable Electronic
Control Unit (PECU) enabling different strategies performances. The
injector mounted an axially disposed cylindrical single hole nozzle
(0.18 mm in diameter and 1.0 mm in thickness) and the investigated
injection pressures have been 60, 90 and 120 MPa. The sprays have
been lightened by a pulsed sheet (100 μm in thickness and 10 ns
in duration) generated by the second harmonic of an Nd-YAG laser
and matched at different instant from the start of injection. The
jet images have been captured by a CCD camera collecting the light
scattered at right angle and synchronized with the light sheet. A
digital pulser/delayer has allowed finely investigating the entire
spray duration (1.0 ms). The spray characteristics have been
extracted by a digital image processing software. Tip penetration
and spray cone angle have been strictly measured while droplet
velocities and nozzle discharge coefficient have been derived from
the data.
The diverse characteristics of the investigated fuels have
produced quite differences in sprays global performances in terms
of penetrations and cone angles. These differences have shown a
no-monotonic behavior during the spray duration and their
relationships with the injection pressure have been observed.