operation in the advanced combustion mode 1 the engine 39 s peak no x emission level is between about 5 to about 99 lower than the peak no x emission level generated by combustion of a reference gasoline under equivalent combustion conditions and 2 the engine cylinder optionally contains a small percentage by volume of egr prior to combustion of the gasoline alcohol blend in the cylinder in another embodiment of the methods described herein an advanced combustion engine 39 s operating envelope in an advanced combustion mode is expanded by supplying an engine cylinder during operation in the advanced combustion mode with a gasoline alcohol blend a that has a ron mon 2 value of between about 85 to about 100 and b that comprises between about 10 to about 30 by volume of an alcohol and about 70 to about 90 by volume of a gasoline in this embodiment during operation in the hcci advanced combustion mode 1 the engine 39 s peak no x emission level is between about 5 to about 99 lower than the peak no x emission level generated by combustion of a reference gasoline under equivalent combustion conditions and 2 the engine cylinder optionally contains a small percentage by volume of egr prior to combustion of the gasoline alcohol blend in the cylinder in another.