Correlation Between Flame Pattern, Heat-Release and Emissions for a DI Diesel Engine with Rotating Injector and Variable Swirl 2001-01-2003
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 speeded up the burnout.
Counter-swirl rotation of the injector markedly reduces the impact onto the piston bowl wall. This led to faster combustion and lower smoke level. This shows that fuel located along the wall burns slowly and contribute preferentially to engine-out soot.