Cummins is leading global manufacturer of diesel and natural gas engines, engine-related component products, and electric power generation systems.

FORBES: CMI Ready To Rev Higher

The Green Book, produced by the American Council for an Energy-Efficient Economy (ACEEE), says that in evaluating plug-in hybrids, it considers both the emissions from the gas engine and from the power plants that feed the grid.

FORBES: Green car book disses the Chevy Volt, GM isn't too happy

PowerBox Concept hybrid, for example, shown at the L.A. show, looks a lot like a standard sports utility vehicle (SUV) but combines a supercharged V-6 engine that runs on compressed natural gas and an electric motor that provides added power for acceleration and passing.

FORBES: The Hybrids Are Coming

The rocket engine power plant runs at a 35% thermal efficiency, versus 55% for conventional gas-fired plants.

FORBES