Effect of road gradient in highway tunnel on smoke emission of diesel vehicle

A engine bench test is carried out by means of exhaust gas recirculation, and a certain proportion of exhaust gas is mixed with inlet air to monitor the effect of the environment in the highway tunnel on smoke emission. The effect of road gradient on the smoke emission is modified. A road test is achieved at different gradient. The test results show that the smoke emission increases remarkably with the increasing of road gradient and vehicle speed, the smoke emission increases 70%~120% when gradient degree in highway tunnel raises 1%.