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Experimental and Numerical Investigation on Mixture Formation in a HDDI Diesel Engine With Different Combustion Chamber Geometries
Technical Paper
2005-24-055
ISSN: 0148-7191, e-ISSN: 2688-3627
Sector:
Language:
English
Abstract
One of the most important phases in the development of
direct-injected diesel engines is the optimization of the fuel
spray evolution within the combustion chamber, since it strongly
influences both the engine performance and the pollutant emissions.
Aim of the present paper is to provide information about mixture
formation within the combustion chamber of a heavy-duty direct
injection (HDDI) diesel engine for marine applications. Spray
evolution, in terms of tip penetration, is at first investigated
under quiescent conditions, both experimentally and numerically,
injecting the fuel in a vessel under ambient temperature and
controlled gas back-pressure. Results of penetration and images of
the spray from the optically accessible high-pressure vessel are
used to investigate the capabilities of some state-of-the-art spray
models within the STAR-CD software in correctly capturing spray
shape and propagation.
The experimental investigation is carried out using a mechanical
injection pump equipping a heavy-duty, eight-cylinder engine. Only
one of its plungers is activated, and the fuel is discharged
through a seven-hole nozzle, 0.40 mm in diameter, mounted on a
mechanical injector. Tests are carried out at two different load
fuel amounts, representing 50%, and 100% respectively, and results
are used as database for the CFD setup. CFD analyses of the intake
and compression strokes are at first performed in order to compare
two different combustion chambers and different jet orientations
with respect to the combustion chamber cavities, running the engine
under motored conditions and injecting 50% load fuel amount. Both
the two tested pistons show two-stage deep valve pockets hollowed
under the valve seats projections, but some relevant differences
exist in the piston outer region and in the squish area.
Subsequently, full CFD analyses of the intake, compression and
combustion processes are performed for the two different combustion
chambers and the previously optimized jet orientation, operating
the engine at full load, maximum revving speed. Numerical
predictions are used to assess the influence of both combustion
chamber shapes on the mixture formation effectiveness and the
engine-out emissions.