Study of droplet size and velocity of fuel containing CO2 spray by means of PDA

Injection of fuel containing CO2 has potential to reduce NOx and soot emissions in a diesel engine. This paper presents an experimental study on the spray charac-teristics of fuel containing CO2 as measured by phase dop-pler anemometry (PDA). Experiments were performed un-der atmospheric conditions on diesel hole-type nozzles at constant injection pressure. Effects of CO2 concentration in diesel fuel on the spray pattern, droplet size and velocity were measured. Experimental results show that fuel atomi-zation will improve greatly when the concentration of dis-solved CO2 in the fuel exceeds the critical value. The axial and radial velocity of the fuel spray containing CO2 is larger than that of conventional diesel fuel spray near the nozzle exit due to flash boiling phenomena. Downstream of the spray, the radial velocity and droplet size of fuel containing CO2 is much more uniform and smaller than that of pure diesel spray. It is attributed to the greatly enhanced liq-uid-gas mixing resulting from flash separation of CO2 from the liquid. New insight into the atomization of the fuel con-taining CO2 was obtained and a possible mechanism to ex-plain the phenomena was proposed. The method may be developed into a new technique for controlling diesel com-bustion and exhaust emissions.