Diesel or diesel fuel (IPA: ; voiced āsā because of its eponym) is a specific fractional distillate of fuel oil (mostly petroleum) that is used as fuel in a diesel engine invented by German engineer Rudolf Diesel. The term typically refers to fuel that has been processed from petroleum, but increasingly, alternatives such as biodiesel or biomass to liquid (BTL) or gas to liquid (GTL) diesel that are not derived from petroleum are being developed and adopted. Rudolph Diesel was not first to invent the diesel engine. His patent was filed in 1893. However Herbert Akroyd Stuart, built the first compression-ignition oil engine in Bletchley, England in 1891. He leased the rights to Richard Hornsby & Sons in July 1892, five years before Diesel's prototype was built.