Various methods and systems are provided for controlling emissions and a likelihood of engine knock during combustion in a multi-fuel engine. A method for an engine includes mixing an amount of a first fuel and an amount of a second fuel to combust a fuel mixture having a fuel ratio of the first fuel relative to the second fuel, the first fuel having a faster combustion flame speed relative to the second fuel, the fuel mixture having an air-to-fuel ratio with an amount of air delivered to the engine. The method further includes controlling either or both of a speed of combustion and a stability of combustion of the fuel mixture with the amount of air delivered to the engine by changing at least one of the fuel ratio, the air-to-fuel ratio, or both of the fuel ratio and the air-to-fuel ratio.

Various methods and systems are provided for controlling emissions and a likelihood of engine knock during combustion in a multi-fuel engine. A method for an engine includes mixing an amount of a first fuel and an amount of a second fuel to combust a fuel mixture having a fuel ratio of the first fuel relative to the second fuel, the first fuel having a faster combustion flame speed relative to the second fuel, the fuel mixture having an air-to-fuel ratio with an amount of air delivered to the engine. The method further includes controlling either or both of a speed of combustion and a stability of combustion of the fuel mixture with the amount of air delivered to the engine by changing at least one of the fuel ratio, the air-to-fuel ratio, or both of the fuel ratio and the air-to-fuel ratio.

An evaporative emissions (EVAP) system and its method of control comprise commanding a three-way valve to fluidly connect an auxiliary vapor canister and a bottom portion of a fuel tank, controlling at least one of an engine of the vehicle and a purge pump of the EVAP system disposed between the engine, a separate primary vapor canister, and the auxiliary vapor canister to draws fuel vapor from the fuel tank into the auxiliary vapor canister for storage, commanding the three-way valve to fluidly connect the bottom portion of the fuel tank to an atmosphere outside of the EVAP system to generate additional fuel vapor in the fuel tank, commanding the three-way valve to fluidly connect the auxiliary vapor canister to the atmosphere, and controlling at least one of the engine and the purge pump to draw the fuel vapor from the auxiliary vapor canister into the engine.