1.   Yet a special air management system gives a cleaner burn.

2.   Ethanol, made from U.S. corn and Brazilian sugar, burns cleaner than gasoline.

3.   The theory is that delivering pressurized, more finely atomized fuel into the cylinders results in a cleaner burn for more power.

4.   Petrol and diesel burn cleaner with this method.

5.   China has been improving the quality of the coal it exports by using equipment to remove dust for a cleaner burn, it said.

6.   The fuel mixture is expected to burn much cleaner than diesel fuel alone.