Nissan Announces a 'Major Breakthrough' in Thermal Efficiency With its New e-POWER Hybrid Technology

author: Eric Walz   

Automaker Nissan Motor Corp. announced what its calls a "major breakthrough" in engine thermal efficiency with it's e-POWER hybrid vehicle technology.

Unlike a conventional hybrid system, Nissan's e-POWER technology uses a small gasoline engine for electrical generation, separating the engine's output and the driving force at the wheels. The gas engine provides electrical energy to the e-powertrain battery pack to keep it charged.

With this setup, the gas-powered engine is not used to power the wheels like a traditional car, rather it serves as a "dedicated electricity generator" for the vehicle's electric motor. Operation of the gas engine is limited to its most efficient range by managing the engine's electricity generation and the amount of electricity stored in the battery.

With this design, Nissan has been able to improve thermal efficiency beyond current levels. 

Nissan e-POWER technology achieves a world-leading thermal efficiency of 50%, which represents around a 20% improvement over the current auto industry average. This increase in efficiency translates into a further reduction of harmful CO2 emissions. 

"In pursuit of carbon neutrality across our product lifecycle by 2050, Nissan aims to electrify all new models launched in major markets by the early 2030s," said Toshihiro Hirai, senior vice president of the powertrain and EV engineering division. "Nissan's electrification strategy promotes the development of e-powertrains and high-performance batteries for EVs, with e-POWER representing another important strategic pillar."

A diagram of Nissan's e-POWER

Nissan's STARC concept

To achieve this breakthrough of 50% thermal efficiency, Nissan developed a concept it calls "STARC" for its gas-powered engine. The term STARC is an acronym for "strong, tumble and appropriately stretched robust ignition channel." 

The concept improves thermal efficiency by controlling the flow of the air-fuel mixture that is pulled into the cylinder and the ignition to a spark plug, which results in burning a more diluted air-fuel mixture at a high compression ratio for maximum efficiency.

In a conventional internal combustion engine, there are restrictions on controlling the air-fuel mixture's dilution level to respond to varying engine loads, such as when traveling uphill. There are trade-offs between various operating conditions, such as in-cylinder gas flow, ignition method, and compression ratio which can sacrifice efficiency for greater power output, Nissan says.

However, using a dedicated engine running at an optimal range of speed and load for electrical generation makes it possible to dramatically improve thermal efficiency, according to Nissan.

In internal testing Nissan said it achieved a thermal efficiency of 43% when using the EGR dilution method and an efficiency of 46% when using lean combustion with a multi-cylinder gas engine. 

The EGR diluting method is commonly used in diesel engines. It reduces fuel consumption by introducing some engine exhaust gas into the intake air, which results in a diluted air/fuel mixture. 

A level of 50% was achieved by operating the engine at a fixed RPM and load, then combining it with additional waste heat recovery technologies.

Nissan's e-POWER technology was first introduced in Japan in 2016 with the Nissan Note, which uses the same 100% electric motor-driven technology as the popular Nissan LEAF. The system consists of a gasoline engine with a power generator, inverter, battery and electric motor.

In Dec 2020, Nissan launched the all-new Note in the Japan market, which comes exclusively with e-POWER.

Chinese Startup Li Auto Developed a Similar Technology

Nissan e-POWER technology is similar to that of Chinese automaker Li Auto, a new startup building "New Energy Vehicles" (NEVs) for the China market.

While most of China's automotive startups are following Tesla's lead and building fully-electric vehicles, Li Auto's technology allows drivers to charge the vehicle's battery pack with electricity or gas. 

Li Auto calls the design "EREV (extended range EV) technology" and its offered in the company's first vehicle, the Li One SUV.

Although the Li ONE is powered by its electric motors when cruising, the energy source for the electric motors comes from both its battery pack and range extension system that includes a dedicated, 1.2 liter turbo-charged internal combustion gas engine used to power a 100 kW electric generator. A component called a "speed reducer" used to connect the two power sources together. 

The electric propulsion portion of the Li ONE consists of a 140-kilowatt rear-drive electric motor powered by a 40.5-kilowatt-hour battery pack. The SUV also includes a 11.9 gallon fuel tank for the dedicated gas engine. 

While the combustion engine is used to generate electricity to charge the SUV's battery, it also helps to extend range. With this setup, the Li ONE delivers a NEDC range of 800 kilometers (497 miles) while still offering the instant acceleration and torque of an EV. The Li One SUV can accelerate from 0 to 62 mph in 6.5 seconds, according to Li Auto.

Li Auto cites limited access to EV charging infrastructure in China as one reason for designing its SUV with an internal combustion engine rather than building a fully-electric vehicle like most of China's startup automakers are doing.

While these new hybrid technologies are not considered to be "zero emissions", they do help to reduce harmful greenhouse gases and boost the range of EV powertrains, which is an important goal for the world's automakers. 

The hybrid technology also serves as a transitional method to reduce emissions as the auto industry works towards building more fully-electric vehicles.

Eric Walz

Originally hailing from New Jersey, Eric is a automotive & technology reporter covering the high-tech industry here in Silicon Valley. He has over 15 years of automotive experience and a bachelors degree in computer science. These skills, combined with technical writing and news reporting, allows him to fully understand and identify new and innovative technologies in the auto industry and beyond. He has worked at Uber on self-driving cars and as a technical writer, helping people to understand and work with technology.