A premixing device includes an air inlet, at least one fuel inlet slot having a wall profile configured to form a fuel boundary layer along a portion of a wall of the premixing device, a mixing chamber, and at least one diverging fuel injection slot jet disposed inside the at least one fuel inlet slot, the slot jet being configured to create a flow separation region in a diverging portion thereof to generate mixing turbulence at an outlet of the slot jet to aerodynamically enhance a mixing of the fuel from the boundary layer with compressed air without causing a boundary layer flow separation and a flame holding in the mixing chamber. Low-emission combustors, gas turbine combustors, methods for premixing a fuel and an oxidizer in a combustion system, a gas turbine, and a gas to liquid system using the premixing device are also disclosed.