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Outline
In order to meet the future emission regulations for diesel engines, dual-injection selective catalytic reduction(SCR) system has become an important means, in which the urea uniformity on the cross section of the close-coupled SCR(cc-SCR) is crucial for NOx conversion. A transparent after-treatment test bench was established and a particle image velocity(PIV) optical method was used to measure the urea droplet velocity field and droplet concentration distribution of the cc-SCR. A computing simulation of the urea distribution was also conducted and validated by the measurement. Results showed that, when the injection pulse width is less than 1.00s, there has no urea droplets on the cross section of the cc-SCR within 1.00s, which leads to a decrease of NOx conversion efficiency under the condition of low ammonia storage. The velocity field at different cross-sections presents double vortices. The simulation results are found to be consistent with the experimental results. In addition, different nozzles with different particle sizes were tested on the bench under the temperature of 215℃ and the air flow rate of 1250kg/h and 360kg/h, respectively. It is found that the distribution uniformity of urea droplet depends on the exhaust air flow rate. This phenomenon is also well explained through simulation results.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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