Diesel engines make very good use of the fuel they burn. They also make lots of torque (pronounced "tork"), or twisting power. An engine with a lot of torque will be able to spin its shaft even if it is very hard to do so. This makes a diesel engine a good choice in heavy equipment like trucks, trains and construction machines. The very big trucks on the road have diesel engines in them. So do train locomotives, unless they are electric or the old steam-powered kind. 