A diesel engine satisfying China Ⅴ was tested at the altitudes of 1700m

2200m and 3000m with a removable engine test bench and on-board equipment. The results of the test without urea-SCR show that

with the increase of altitude

intake air decreases

combustion deteriorates

the highest combustion pressure decreases

fuel consumption and CO emission increase

and NOx emissions decreases; increased altitude has dual effects of raising combustion temperature and reducing oxygen content on engine emissions

of which the later has greater impact on emissions at high altitude. The results of the test with urea SCR show that NOx emissions still exceed China Ⅴ regulation limits

because the engine manufacturer reduces the amount of urea injection.