Fuel oil pollution control and additional maintenance required after burning it often outweigh the low cost of the fuel. Burning fuel oil, particularly residual fuel oil, produces uniformly higher carbon dioxide emissions than natural gas. Heavy fuel oils continue to be used in the boiler "lighting up" facility in many coal-fired power plants. This use is approximately analogous to using kindling to start a fire. Without performing this act it is difficult to begin the large-scale combustion process. The chief drawback to residual fuel oil is its high initial viscosity, particularly in the case of No. 6 oil, which requires a correctly
Synthetic fuel synthetic ammonia, and nitric acid. Nearly one third of the Bergius production was produced by plants in Pölitz () and Leuna, with 1/3 more in five other plants (Ludwigshafen had a much smaller Bergius plant which improved "gasoline quality by dehydrogenation" using the DHD process). Synthetic fuel grades included "T.L. [jet] fuel", "first quality aviation gasoline", "aviation base gasoline", and "gasoline - middle oil"; and "producer gas" and diesel were synthesized for fuel as well (e.g., converted armored tanks used producer gas). By early 1944, German synthetic fuel production had reached more than from 25 plants, including 10 in the