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This study was visualized by experimental and numerical analysis for the unknown injected droplet phenomena with the multi-phase flow in the Urea-SCR dosing system. Visualization experiments were conducted on the droplet behavior inside the pipe with simulated urea SCR injection system. Although the total number of droplets decreases at gas temperatures of 150°C and 200°C, a significant number of injected droplets remained at the position corresponding to the SCR catalyst. That is physical kinetic energy was found to dominate over thermal evaporation. However, the impingement of droplets into the pipe wall had occurred complex behavior by physical/thermal evaporation, and these droplets weren't on gas airflow at the lower part of the pipe. Furthermore, these actual phenomena were reflected in experimental coefficients for new reduction model analysis instead of CFD.

Diesel engines as power sources ranging in size from small to large have been extensively used worldwide. However, further improvement in the complicated urea-SCR systems is required to meet the stricter NOx regulations on exhaust gas. This study shows that the behavior of the entire gas/injected droplet can be verified using visualization equipment. Valuable gas-liquid multiphase flow PIV results using the DDM were obtained. In addition, the detachment droplet behavior from the liquid film was visualized as unknown droplet behavior. These validations are considered to be useful for establishing the PIV-DDM for the flow characteristic estimation in the exhaust pipe of the urea-SCR system.

As a result of WNTE regulations and the introduction of close-coupled aftertreatment systems, exhaust purification at high temperatures in commercial vehicles has become increasingly important in recent years. In this report, we improve the prediction accuracy for NOx conversion at high temperatures in the kinetic model of conventional Cu-selective catalytic reduction (Cu-SCR). Reaction rate analysis indicated that the rate of NH3 oxidation was extremely low compared to the rate of standard SCR. We found that NOx concentration-dependent NH3 oxidations (termed NOx-assisted NH3 oxidations) were key to the rate of NH3 oxidation. The output of the improved Cu-SCR kinetic model was in agreed with experimental results obtained from the synthetic gas bench and engine dynamometer bench. We analyzed the contribution of each reaction to NH3 consumption during Cu-SCR. Under NH3 + NO + O2, standard SCR was dominant at low temperature.

Application of pre-mixed compression ignition (PCI) combustion for multi cylinder DI diesel engine has been reported in a previous paper [1]. On the FTP75 vehicle test cycle, application of the PCI combustion demonstrated a 50% decrease in the NOx level without any deterioration in fuel economy. In this study, PCI combustion properties were investigated under the condition of enhanced heat exchange capability of EGR cooler on multi cylinder DI diesel engine. Test results showed that the exhaust emissions and performance of PCI combustion were improved by increasing heat exchange on EGR cooler and PCI combustion region was expanded to higher load. However, few issues were encountered using higher heat exchange EGR cooler.

Tier 2 Emission standards enacted by the U.S. Environmental Protection Agency (EPA) require substantial emission reductions for new vehicles, including those with diesel engines. The standards are fuel neutral, and all light duty vehicles must eventually meet a fleet averaged emission level of Bin 5. To improve the emission capability for diesel engines, several advanced technologies have been investigated. These technologies include: common rail FIE with multi-injection capability, enhanced cooled EGR system with increased flow capability, variable geometry turbo charger, and a lower compression ratio piston. A new combustion approach using premixed diesel combustion was applied in the low load area for improving NOx and soot emissions significantly in the FTP-75 test cycle. Applying these technologies, engine out NOx was substantially reduced while maintaining similar soot levels.

Control of NOx and PM from diesel engines is a key for enlarging its application in transportation field. To achieve this, many improvements have been done, for instance, the introduction of highly flexible common-rail injection system and cooled EGR system with advanced control strategy. In order to meet more stringent emission regulations in near future, research and development activities have been carried out energetically in the world. In this paper, a low emission combustion strategy is realized by combination of common-rail and cooled EGR. First of all, low soot combustion is approached by optimizing pilot and main injection, in which pilot is controlled to eliminate hot flame. Then, once low soot combustion achieved, higher EGR can be used to reduce NOx.

The behavior of air-entrainment in a Diesel fuel spray was studied by analyzing the air movement around a free non-evaporated Diesel fuel spray in a pressurized vessel. To measure the air movement around the spray. The density difference in the air near the surface of spray was measured as a tracer of the moving air. This was accomplished heating a stainless steel (SUS) wire with large current. The movement of air caused by the air-entrainment into the spray was recorded by a high speed camera system. By analyzing the recorded air movement, the air-entrainment was obtained. The effects of nozzle hole diameter, injection velocity and ambient gas density on the air-entrainment behavior were investigated. Some discussions were added to help considering the complex phenomena of air-entrainment into a Diesel spray, based on comparing the averaged air/fuel ratio inside the spray with both values of measurement and predicted by momentum theory.

The effects of fuel injection velocity and ambient gas pressure on the spray formation and atomization process for a non-evaporating diesel spray were observed and analyzed with greatly magnified photographs illuminated by a pulsed ruby laser light sheet. Individual fuel droplets were distinguishable at the peripheral regions of the spray in these photographs. The spray width became narrower with an increase in injection velocity, and the spray spread out further with increase in ambient gas pressure. The branch-like structure in the spray originated from local high and low fuel particle number density regions and the difference in number density between these two regions increased with higher injection velocity. The ruby laser was double-pulsed to enable fuel particle velocity vectors to be characterized at the peripheral regions of the fuel spray. The vorticity scale was smaller and vorticity magnitude grew higher with increase of injection velocity.

This paper presents the results of engine experiments and spray observations on a VCO nozzle. Two types of VCO nozzles having different hole shapes were investigated. One had a straight step hole (the VCO-S) and the other had a tapered step hole (the VCO-T). Both VCO nozzles could greatly reduce HC emissions in comparison to a standard nozzle. The VCO-S nozzle could reduce NOx emissions more than the VCO-T nozzle, and its spray penetration was shorter than that of the VCO-T.