in front of 一般用来形容方位,位置
There is a tree in front of the house.
房子前面有一棵树.
ahead of 可指时间上的提前
ahead of time
I think the work can be completed ahead of time.
我认为这项工作能提前完成.
同时也有超过,先于的意思
He will be ahead of others in English.
他在英语方面将超过别人.