I met this guy in Iowa one day when i was passing through. He was talking about how he ran his diesel truck on veggi oil and made his regular car powered by a fuel cell. Which he said was made of pvc pipes. And when one thinks about it it becomes easy. Just use an electrolyser. Run an electrical current thru water to split it into hydrogen and oxygen. Run the car on hydrogen and release oxygen into the air. We mad an electrolyser in my science class.