fuel是油，fire是火焰，add fuel to the fire的意思是“ 火上浇油，让情况变得更糟”。

【例句】
The discovery that the government was aware of the cover-up has really added fuel to the fire.
人们发现政府对这起隐瞒事件早已知情，这真是火上浇油。

If you add fuel to the fire, you do something to make a bad situation even worse.
如果你火上浇油，就表示你做了一些使原本的情况变得更糟的事。