Explosion

Day before yesterday while I was driving, I heard a loud boom and gray smoke was coming out the back of the truck. By the time I parked it there was a flame under the passenger dashboard and black smoke coming out of the hood. I jumped out and ran. Immediately it "exploded" again and did so about five or six times within a few minutes. The entire front end was engulfed in flames. Previously before this happened the truck had been "lacking power" and did not pick up speed as if it did not want to go; especially up hills. I really just want to know what could have possibly caused this as I am still terrified and want to prevent this from ever happening in any vehicle I drive.