Abstract:

In order to study the performance of SCR at different altitudes， the performance and emission tests on a high?pressure common?rail diesel engine meeting the national?V emission regulation are conducted under 80、90 and 100 kPa atmospheric pressures respectively to study the effects of exhaust temperature， exhaust flow rate， and altitude on NO_x conversion rate and ammonia slip. The results show that under an exhaust flow rate of 350 kg/h， with the increase of exhaust temperature， the NO_x conversion rate exhibits a tendency of rises first and then falls， with the maximum difference of NO_x conversion rate of 43.4 percentage points at different exhaust temperatures； The ammonia slip by and large reduces with the rise in exhaust temperature， and the maximum difference of ammonia slip is 328×10^-6 at different temperatures. The NO_x conversion rate show a trend of rise first and then fall as the exhaust flow rate increases， with a maximum difference of NO_x conversion rate of 21.5 percentage points at different exhaust flow rates when the exhaust temperature is 250 ℃； The ammonia slip increases with the increase of exhaust flow rate， and the maximum difference of ammonia slip is 90.8×10^-6 at different exhaust flow rates when the exhaust temperature is 250 ℃. Under the same working conditions， the higher the altitude， the greater the NO_x conversion rate and the smaller the ammonia slip， and when the atmospheric pressure lowers from 100 kPa to 80 kPa， the maximum NO_x conversion rate rises by 20.1 percentage points and the maximum ammonia slip reduces by 54.6×10^-6.

Key words: diesel engine, altitude, SCR system, NO_x conversion rate, ammonia slip