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Experimental and Numerical Investigation on Mixture Formation in a HDDI Diesel Engine With Different Combustion Chamber Geometries
ISSN: 0148-7191, e-ISSN: 2688-3627
Published September 11, 2005 by Consiglio Nazionale delle Ricerche in Italy
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.