Not the person you were asking, but I did a double take on your question because I had thought growing up in the DRC that "mazut" was the French word for diesel. Turns out mazut is a separate thing. Also, it was definitely used in the local heavy trucks up to the last time I was there in 2011 - ones like this: https://farm6.staticflickr.com/5292/5509628757_f8219820b9_z....