When it comes to making the cars we drive more fuel efficient and environmentally friendly, many carmakers are focused on vehicles that replace traditional combustion engines with new hybrid or electric motors.

But a select few have set their sights on making the engines of old work just as efficiently as their contemporary counterparts.

Take, for instance, Audi, Ford and Mazda, each of which is responsible for one of 10 finalists for this year’s Green Car Journal’s Green Car Technology of the Year Award, which will be handed out later this month at the Washington Auto Show. All three of their inventions seek to improve the type of standard combustion engine that can be found in the majority of cars out on the road today.

Related: A look back at last year’s finalists and winner

Another, the finalist from Hyundai, looks beyond combustion, hybrid and electric cars, altogether. Instead, the South Korean automaker is bringing to market the first mass-produced vehicle that runs on hydrogen gas.

Check out our gallery above to learn more about each of the finalists, and check back to our coverage of the Washington Auto Show to see which takes home the award on Jan. 22.

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