Albert Biermann, head of high performance development at Hyundai and Kia, has told Autocar that although the "research project [into a diesel-electric hybrid drivetrain] is still going on", there are doubts as to whether it's worth pressing on in light of ever tougher emissions regulations and the negative impact of the Volkswagen Group's Dieselgate scandal.
Biermann noted that the cost of the electric motors and batteries required for a hybrid drivetrain is "already significant", and that adding an expensive diesel engine into the mix might be a bridge too far.
He hinted that if the Kia did decide to end development of its diesel hybrid drivetrain, it could reuse much of the research and development for a new petrol hybrid system.
Above: Diesel hybrid drivetrain of the 2014 Kia Optima T-Hybrid concept.
Kia publicly introduced a prototype diesel-electric hybrid drivetrain in 2014 with the Optima T-Hybrid concept at the 2014 Paris motor show.
That setup featured the Korean car maker's 1.7-litre diesel engine. Similar to the recently launched Audi SQ7, this diesel motor is boosted by an 'electric supercharger' working off a 48V electrical system.
In Kia's design, though, the 48V electrical system used a lead-carbon battery. Kia's mild-hybrid concept drivetrain also featured an electric starter/generator that allowed the car to run in electric-only mode at low speeds or when cruising.
At the time, Kia claimed fuel economy, power, and torque improvements of between 15 to 20 per cent over the production 1.7-litre turbo-diesel.
MORE: Kia news and reviews