The rotating injector as a tool for exploring DI diesel combustion and emissions formation processes

Sammanfattning: A diesel fuel injector has been modified to allow rotationaround its axis, driven by an electric motor. Injections at upto 6000 rpm from the rotating injector have been investigatedunder the influence of air swirl on one optical research engineand one optically accessible heavy-duty diesel engine.The experiments show that changing from a normal, staticinjection to a sweeping injection has profound effects on sprayformation, dispersion and penetration. This influences thefuel/air-mixing, autoignition, combustion rate and emissionsformation. The spray propagation is stronger influenced byinjector rotation than by air swirl.The air entrainment into the spray increases forcounter-swirl rotation of the injector and this speeds up thevaporization and decreases the formation of soot. In addition,the oxidation of soot is enhanced since the counter-swirlinjection forces the intense fuel-rich and soot containingspray core to penetrate into fresh air instead of replenishingthe rich regions in the head of the spray. Fuel accumulationalong the piston bowl wall decreases as an effect of thereduced penetration with counter-swirl injection. Altogether,this decreases the smoke emissions for low and intermediateengine loads.For the combustion system studied, counter-swirl rotation ofthe injector cannot decrease the smoke emissions at high engineload since the reduced spray penetration impairs the airutilization. Fast and efficient combustion at high loadrequires spray induced flame spread out into the squish region.Spray induced flow of cool fresh air from the bottom of thepiston bowl in towards the injector is also important for lowsoot formation rates.Co-swirl rotation of the injector reduces the airentrainment into the spray and increases the soot formation.The increased smoke and CO emissions with co-swirl injectionare also attributed to the excessively large fuel-rich regionsbuilt up against the piston bowl wall.Increased air swirl generally reduces smoke and COemissions. This is mainly an effect of enhanced burnout due tomore intense mixing after the end of fuel injection.Changes in smoke as an effect of injector rotation aregenerally accompanied with opposite, but relatively small,changes in NO. Fast and efficient burnout is important for lowsmoke emissions and this raises both the temperature andproduction of NO. NO production is strongly influenced by thein-cylinder conditions during the latter part of themixing-controlled combustion and in the beginning of theburnout.Keywords:diesel spray combustion, rotating injector,air swirl, air/fuel-mixing, soot, NO, CO, flame visualization,Chemkin modeling, soot deposition