Diesel Fuel is a liquid material containing adequate BTU content used for combustion in a diesel engine. The purpose of exhaust gas recirculation (EGR) is to reduce nitrogen oxide (NOx) emissions by returning a portion of the engine's exhaust gas back to the engine's combustion cylinders. This reduces the amount of heat in the cylinder. NOx formation progresses much faster at high temperatures, thus the EGR reduces the amount of NOx the combustion process generates. The EGR valve controls the amount of exhaust gases returned to the cylinders.