The powertrain pairs the Optima’s existing 1.7-litre CRDi turbo-diesel engine, paired with a small electric motor, powered by a 48V lead-carbon battery. The diesel-electric powertrain concept, which was previewed at the 2014 Geneva Motor Show, enables the Optima T-Hybrid show car to be driven in electric-only mode at low speeds and when cruising, with deceleration serving to recharge the battery pack.

The carmaker says that lead-carbon batteries were chosen for the mild hybrid powertrain as, unlike lithium-ion batteries, they require no active cooling and are easier to recycle at the end of the unit's lifecycle.

The vehicle features a zero-emissions stop-start system, and a new belt-driven starter generator replaces the conventional alternator, meaning the engine can restart with almost no noise or vibration.

Installing the powertrain in the Optima saloon has enabled engineers to fit a smaller vehicle battery and starter motor, enhancing weight distribution and handling.

The system also allows the installation of an electric supercharger for the CRDi engine, in addition to the conventional turbocharger, in particular helping to boost torque and engine response at low engine speeds.

Kia said the system is still under development with no plans confirmed yet for mass production. However it added that the T-Hybrid powertrain remains under consideration for new Kia models in the future, saying that any model equipped with the powertrain could see a significant reduction in CO2 tailpipe emissions and fuel consumption and a power increase of between 15 to 20% for any model. Currently, the Optima's 134bhp 1.7-litre engine produces CO2 emissions of 128g/km (when fitted with ISG stop-start).

Michael Cole, chief operating officer, Kia Motors Europe, said: ‘The new mild hybrid system is our flagship technology for improving the efficiency of our internal combustion-powered models. In future, technology such as this will help Kia further reduce fleet emissions in Europe.’