A method for reducing the exhaust pollution emissions in a two-stroke sliding vane internal combustion engine. First, fresh air is inducted into a vane cell, and fuel is injected into the cell at an ultra-lean fuel-air equivalence ratio less than about 0.65. The fuel is injected at a location such that a circumferential distance at mid-cell-height to the stator site at the onset of combustion is at least about 4 times a vane cell height at intake. The ultra-lean fuel-air combination is then compressed and thoroughly premixed prior to combustion to a dimensionless concentration fluctuation fraction below about 0.25. The ultra-lean, thoroughly premixed fuel-air combination is then combusted. The combusted fuel-air combination is purged after an expansion cycle. The premixing step prior to combustion may use inclined airfoils within the intake duct to produce counter-rotating mixing vortices.