A little chemistry. Nitrogen is an inert gas. It does nothing to enhance combustion because it is inert. But it does increase the volume of the finished product. And since you brought up shell let me tell you a little story.
Shell, for years, hyped their gasoline as Shell with Platformate. Platforming is a process that uses a platinum based catalyst to alter the molecular structure of the gasoline thereby increasing the octane. Sounds great. Everyone else uses the same exact process. The call it reforming and the gasoline from the process is called reformate. Same exact stuff using the same exact catalyst from, you guessed it, the same exact manufacturers.