For about a decade, we have declared each year’s pool of nominees for Ward's 10 Best Engines more diverse than the last. 

Each year's assemblage of grunty V-8s, silky V-6s, punchy welterweight 4-cyl. turbos, fuel-sipping hybrids and zero-emission electric vehicles left us convinced the powertrain world was becoming a United Nations summit with no dominant superpower.

This year, we really mean it. 

Our pool of 38 nominees for 2015 includes internal-combustion engines powered by three, four, five, six and eight cylinders. We’re looking at five diesels, two hybrids, five electric vehicles, a boxer, a CNG flex-fuel V-6, an extended-range EV and a hydrogen-powered fuel cell – a first for Ward’s 10 Best Engines. Twenty-one engines are turbocharged while two employ supercharging.

If anyone needs evidence the auto industry is taking a big-tent approach to pressing fuel-economy challenges, look no further than our nominee pool, which illustrates the many directions engineers have been heading in recent years.

The Dodge Challenger SRT Hellcat’s supercharged Hemi V-8 makes an astonishing 707 hp and oozes testosterone in an old-school pushrod sort of way.

At the opposite end of the spectrum is the Hyundai Tucson fuel-cell vehicle, which runs on hydrogen and emits nothing but water vapor. The vehicle is available for lease only in California, where a limited hydrogen fueling infrastructure is taking shape.

But it’s included in this year’s competition in recognition of its far-reaching technology and because automakers may need FCVs to comply with future emissions standards. 

Honda, Toyota and General Motors plan to introduce FCVs in the future. New York is planning to build 100 hydrogen stations by 2020, and numerous other states and countries also are adding to the hydrogen infrastructure.