Diesel engine options are popular for heavy-duty trucks in the US thanks to their higher torque levels enabling higher towing capacities. But they are a dying breed in passenger cars thanks to their higher costs and the infamous Dieselgate scandal.

Hyundai and Kia, for example, has never offered diesel engines in the US market. It's a different story in Europe and South Korea, where the Korean automakers still offer oil-burners. The popular Hyundai Santa Fe, for example, is offered with a 2.2-liter turbocharged four-cylinder diesel producing 197 horsepower and 324 lb-ft of torque - but not for much longer. As part of its transition to environmentally-friendly fully electric and hydrogen fuel-cell cars, Korea Times reports that Hyundai is no longer developing new diesel engines.

In the short term, Hyundai will continue assembling diesel engines and refine its existing oil-burners, but these will be phased out in the future. As of late last year, the development of new Hyundai diesel engines has already stopped. "It is a global automotive trend to stop developing new diesel engines," a source at Hyundai said. "However, this does not mean that Hyundai will end diesel vehicle production immediately, and the group will release updated versions of existing engines for a while."

Hyundai currently offers four diesel engines for passenger vehicles with different designations: the U for the i30, R for the Santa Fe, A for the Starex and S for the Veracruz.

Phasing out diesel engines won't be easy, however, because Hyundai also develops three diesel units for commercial vehicles, which rely on the high torque and lower fuel prices of diesel engines. To make up for this, Hyundai is developing the XCIENT Fuel Cell, the world's first mass-produced heavy-duty fuel-cell truck with a range of around 250 miles.

In 2040, Hyundai will also stop selling combustion engine cars in the US, Europe, China, and other markets and will instead focus on EVs. Hyundai's embracement of electrification will shift up a gear this year with next month's debut of the Ioniq 5, Hyundai's first dedicated EV that will be sold under the automaker's new Ioniq EV sub-brand.