瞬时条件 meaning in English

instantaneous conditions
transient condition

Reciprocating internal combustion engines - exhaust emission measurement - part 9 : test cycles and test procedures for test - bed measurement of exhaust gas smoke emissions from compression ignition engines operating under transient conditions
往复式内燃机.废气排放测量.第9部分:瞬时条件下工作的压缩点燃装置的废气烟雾排放的试验床测量的试验循环和试验过程