The spray-induced mixing characteristics and thermal decomposition of aqueous urea solution into ammonia have been studied to design optimum sizes and geometries of the mixing chamber in SCR (Selective Catalytic Reduction) system. The cold flow tests about the urea-injection nozzle were performed to clarify the parameters of spray mixing characteristics such as mean diameter and velocity of drops and spray width determined from the interactions between incoming air and injected drops. Discrete particle model in Fluent code was adopted to simulate spray-induced mixing process and the experimental results on the spray characteristics were used as input data of numerical calculations. The simulation results on the spray-induced mixing were verified by comparing the spray width extracted from the digital images with the simulated particle tracks of injected drops. The single kinetic model was adopted to predict thermal decomposition of urea solution into ammonia and solved simultaneously along with the verified spray model. The hot air generator was designed to match the flow rate and temperature of the exhaust gas of the real engines. The measured ammonia productions in the hot air generator were compared with the numerical predictions and the comparison results showed good agreements. Finally, we concluded that the design capabilities for sizing optimum mixing chamber were established.

Prediction of the ROHR (rate of heat release) and NOx production in medium-speed marine diesel engines was investigated. The subject of this paper is qualitative and quantitative evaluation of the numerical results. FIRE code v8.1 was used to examine the behavior of spray and combustion phenomena in diesel engine. Wave breakup and Zeldovich models were adopted to describe the atomization characteristics and NOx formation. The spray visualization was performed experimentally in the constant-volume high-pressure chamber to clarify numerical results on the spray characteristics of the spray angle and penetration. Time-resolved spray behaviors were captured by high-speed digital camera. The simulation results were tested with the experimental data of the real engine. Finally, with adjustment of some model constants, reasonable agreements between experimental and simulated results on the ROHR and NOx were shown.

Mtmerical simulations and erperimentshave been carried out to investigate the etilect ofjuel itv'ection nozales on the combustion and NOx formation processes in medium-speed marine diesel engines. SPray and combustion phenomena were examined numerically usingFl/RE code. PPZive breakup and Zeldovich modlels were adopted to describe the atomization characteristics and IVCix formation processes. spray visualization erperiment was pecformed in the constant-volume highpressure chamber to verCtv the numerical results on the spray characteristics such as spray angie and spray tip penetration. nme-resolved spray behaviors were captured by high-speed digital camera and analyzed to extract the injbrmation on the spray parameters. Mtmerical analysis oj' juel injection system was also pet:formed to get theprqfiles ctLfitel itv'ection rate, which should be given as an imput datafor the combustion analysis.IVItmerical results were verijied with experitnental clata such as cylinderpressure, R()HR (ZRate ofHleat Releasel and NOx emission. FinalCM the efiZicts qifitel injection nozzles on the enginepel;ibrmance were investigatednumerically to ,find the optimum nozzleparameters such as.fiiel injection angle, nozzle hole diameter and number qf-nozzle holes. From this stuciji the optimumjuel injection nozzle (}iozzle hole diameter, O.32 mm, number ofnozzle holes, 8 andjuel injection angle. 148 Y wasseleeted to reduce beth the.fbel consumption and IVOx emission. 7he reasonfor this selection could be explained.fi'omthe highestjuei-air mixing in the earlyphase ofinjection due to the longest spray tippenetration and the highest heat release rate oj}er j9O A 1:DC due to the increased injection duration.