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Nissan reaches 50% engine efficiency in a hybrid powertrain

26 February 2021

Nissan announced it reached 50% thermal efficiency in a gasoline engine that is a part of the next generation hybrid e-POWER system. The engine has been optimized exclusively for use in the e-POWER system, which utilizes an on-board gasoline engine to provide electrical energy to the e-powertrain battery pack.

Conventional internal combustion engine (ICE) vehicles demand power and performance from an engine under a wide range of speeds and loads. This fundamental requirement means conventional engines cannot perform at their optimal efficiency at all times—there are restrictions on controlling the air-fuel mixture’s dilution level to respond to changing driving loads, with several trade-offs between various operating conditions, such as in-cylinder gas flow, ignition method, and compression ratio which can sacrifice efficiency for power output. Therefore, thermal efficiency in current commercial gasoline engines is typically limited to around 40%.

In contrast, a dedicated engine running at an optimal range of speed and load for electrical generation makes it possible to dramatically improve thermal efficiency. Nissan’s e-POWER system utilizes an on-board engine as a dedicated electricity generator for the system’s e-powertrain. Operation of the engine is limited to its most efficient range, appropriately managing the engine's electricity generation and the amount of electricity stored in the battery.

To achieve 50% thermal efficiency, Nissan developed a concept dubbed STARC (named after the keywords strong, tumble and appropriately stretched robust ignition channel). The concept enables improvement of thermal efficiency by strengthening in-cylinder gas flow and ignition, reliably burning a more diluted air-fuel mixture at a high compression ratio, Nissan said.

In internal testing with a multi-cylinder engine, Nissan achieved a thermal efficiency of 43% when using EGR dilution and of 46% when using lean combustion at λ = 2. A level of 50% was achieved by operating the engine at a fixed rpm and load combined with waste heat recovery technologies.

The e-POWER system was first introduced in Japan in 2016 with the Nissan Note. At its core is the same electric motor-driven technology used in the Nissan LEAF. The e-POWER system is comprised of a gasoline engine with a power generator, inverter, battery and electric motor. In December 2020, Nissan launched the all-new Note in Japan. The all-new Note, which comes exclusively with e-POWER, plays a key role in the Nissan NEXT global business transformation plan, the company said.

Source: Nissan