浑然不知

wǒ hún rán bù zhī hé shí fā shēng shì gù

我浑然不知何时发生事故。

I was quite ignorant when the accident had happened.

qǐ chū tā hún rán bù zhī yǒu rén zài duì tā gǎo yīn móu

起初，他浑然不知有人在对他搞阴谋。

At first, he was completely unaware of the conspiracy against him.