自燃

例句：

1. 1. The fire started spontaneously in the forest.
   森林中的火是自发地开始的。
2. 2. The car caught fire after hitting a pothole.
   汽车在碰到一个坑后起火了。
3. 3. The oil tank on the truck ignited spontaneously.
   卡车上的油罐自发地起火了。