Cannot see a difference between normal mode and "accelerate" mode. I think it is placebo effect.

then ,how do i know it is boosting my download?

This is a shit, Azureus already has this functionalities:
- operable by system tray icon for quicker and easier use
· interface is pleasant and very easy to use
· clears downloaded and wrong files
· autoresumes paused downloads
· automatically searches for more sources at user-specified intervals
· saves configurations from last run and auto loads on start-up

Azureus Ultra
Accelerator 2.5.8 will help you by increasing download speed of large files, such as full albums, movies, TV shows,
games, and applications.