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A diesel fuel injector has been modified to allow rotation around its axis, driven by an electric motor. This enables sweeping injections in a DI Diesel combustion system. It has earlier been shown that sweeping injection enhances the air entrainment into the spray. This is one reason for the reduced smoke level by counter-swirl rotation of the injector. The injected amount of fuel is small and this enables exploration of spray / wall interaction and the effects of reverse-squish. Flame visualization shows that normal, non-sweeping injection tends to build up fuel pockets where the sprays hit the piston bowl wall. This fuel burns quite slowly since it only to a limited extent benefits from the mixing effects of the reverse-squish flow. Increasing the air swirl ratio from 1.65 to 2.47 does not reduce the impact onto the piston bowl wall much. The decrease in smoke level with increasing swirl was attributed to enhanced mixing of the fuel that had accumulated under the piston bowl rim.

This work explores the potential of partial fuel stratification to smooth HCCI heat-release rates at high load. A combination of engine experiments and multi-zone chemical-kinetics modeling was used for this. The term “partial” is introduced to emphasize that care is taken to supply fuel to all parts of the in-cylinder charge, which is essential for reaching high power output. It was found that partial fuel stratification offers good potential to achieve a staged combustion event with reduced pressure-rise rates. Therefore, partial fuel stratification has the potential to increase the high-load limits for HCCI/SCCI operation. However, for the technique to be effective the crank-angle phasing of the “hot” ignition has to be sensitive to the local ϕ. Sufficient sensitivity was observed only for fuel blends that exhibit low-temperature heat release (like diesel fuel).

A diesel fuel injector has been modified to allow rotation around its axis, driven by an electric motor. The injector was operated up to 6,000 rpm in the current study with a naturally aspirated, optically accessible AVL research engine. The effects of injector rotation on the liquid penetration and dispersion of the spray have been investigated by imaging of Mie-scattered light and flame luminosity. Ambient gas conditions are indirectly controlled by choosing start of injection. Injection timing was set to -45° (premixed-mode), -13° and 4° ATDC. The images show that the spray development is profoundly affected when going from a normal static position of the injector to a rotating movement. Unique liquid cascading phenomena were observed. Injection during the compression stroke into air of low temperature and density shows that the liquid spray tip penetration is unaffected within the field of view (35 mm radius). Enhanced dispersion is obtained however.