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Nissan reaches 50% thermal efficiency with next-generation e-POWER system; STARC

Nissan announced a breakthrough in engine efficiency, reaching 50% thermal efficiency with its in-development, next-generation e-POWER system.

Nissan’s e-POWER system utilizes an on-board gasoline engine to provide electrical energy to the e-powertrain battery pack. Nissan’s latest approach to engine development has raised the bar to world-leading levels, accelerating past the current auto industry average range of 40% thermal efficiency, making it possible to even further reduce vehicle 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. Nissan’s electrification strategy promotes the development of e-powertrains and high-performance batteries for EVs, with e-POWER representing another important strategic pillar.

—Toshihiro Hirai, senior vice president of the powertrain and EV engineering division

Conventional internal combustion engine (ICE) vehicles demand power and performance from an engine under a wide range of speeds (RPMs) and loads. This fundamental requirement means conventional engines cannot perform at their optimal efficiency at all times.

However, 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.

With this dedicated approach, and the evolution of battery technology and energy management techniques, Nissan has been able to improve thermal efficiency beyond current levels. Development of the next generation e-POWER system continues this path of efficiency through Nissan’s design and development of an engine exclusively for e-POWER.

The STARC concept. To achieve 50% thermal efficiency, Nissan developed a concept called “STARC”—named after the key words strong, tumble and appropriately stretched robust ignition channel. The concept enables improvement of thermal efficiency by strengthening in-cylinder gas flow (the flow of the air-fuel mixture that is pulled into the cylinder) and ignition, reliably burning a more diluted air-fuel mixture at a high compression ratio.

In a conventional engine, 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.

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

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

The Nissan e-POWER System. e-POWER was first introduced in Japan in 2016 with the Nissan Note. At its core is the same 100% electric motor-driven technology used in the Nissan LEAF to deliver instant torque, power, efficiency and excitement. The system comprises a gasoline engine with a power generator, inverter, battery and electric motor.

Unlike a conventional hybrid system, e-POWER enables exclusive use of the on-board engine for electrical generation by separating the engine’s output and the driving force at the wheels.

In late December 2020, Nissan launched the all-new Note in the Japan market. The all-new Note comes exclusively with e-POWER and has already gained more than 20,000 orders. As the company’s best-selling model in its home market, the Note plays a key role in the Nissan NEXT global business transformation plan.

Comments

Prashanta Dhakal

This is unbelievable! I think almost nobody expected we'd see road-legal cars with 50% thermally efficient engines. Toyota's Dynamic Force engine and their Atkinson-cycle engine used in the Prius sit around 40%, and are industry leaders. This would represent a 20% reduction in CO2 emissions, compared to those engines, all else equal.

Thomas Pedersen

Dear Nissan,

Please begin making hundreds of thousands of these engines to all other car manufacturers.

Love,
Thomas

There is no information on power output, but I suppose 50 hp would be plenty for class C/D cars with a suitably large battery, like the coming generation of Mercedes C class. This car, however, sports a complicated, powerful 200 hp gasoline engine.

A modern aerodynamic car with low cooling demands (due to having only a small, efficient ICE) should be able to do >100 mph with 50 hp, and significantly more in peak bursts from the battery.

Another fabulous aspect of this is the fact that with such high efficiency, a just 10-20 litre gasoline tank would be able to deliver sufficient range between stops and not encroach on trunk space. This is the engine the BMW i3 REX should have had.

Albert E Short

A lightweight genset good enough for a pure electric-drive hybrid was a Holy Grail back in the day. Jaguar built a supercar using a pair of 35kW Bladon jets for the purpose, and I was fond of the MSU Wave Disc concept - https://www.nextbigfuture.com/2009/10/wave-disc-engines.html . Since the engines only had to charge the battery ergo could spin at a single optimized speed, turbines suggested themselves. These days, this would seem like a 'plan B' bet against fast charging solid-state batteries. Without range anxiety, what's the market for a range extender? TBT, I'm a happy owner of a Honda Clarity PHEV.

Paroway

Lowering the emissions by 20% is not eliminating the emissions, and then there is the continued complexity of all the moving parts. As battery prices continue to drop, EVs will become more and more economical than the hybrids that will only get more expensive to buy and to operate.

gryf

This is the third new Nissan IC engine introduced in the past two years (PR25DD I4 2.5 L Direct injection, the Variable Compression Turbo I4, and this one)!
The Qashquai Crossover SUV has a standard model with a 138 hp 1.3L DIG-T turbo and can be upgraded to a variable compression ratio 1.5L turbocharged gasoline engine with an electric motor that delivers a total of 184bhp and 330Nm of torque (in front-wheel-drive only).
What Nissan needs to do is take this new engine and add the Mitsubishi AWD PHEV system with > 200hp. BTW, my everyday drive is a 40 mile range Nissan Leaf (don't worry it was free and takes care of 90% of my driving).

TonyD

This system would be good for class 8 trucks.
A petrol engine maybe 5-6 liters optimized to run at 2500rpm using hcci or similar . No pm and little nox.
2 electric axles 1000 ftlbs each.
500kwh battery buffer.
soc < 30% engine turns on.
soc >80% engine tuns off.
Use subsides to make it cheaper than re powered gliders being sold that do not meet current diesel standards.

SJC

Good idea Tony, I would make it FFV for cars.

Nirmalkumar

What is kms per litre efficiency. This will be most important criteria.

Nirmalkumar

what is kms per litre?

Prashanta Dhakal

km/l will depend very much on the size and shape of the vehicle. Along with transmission and efficiency of the hybrid drivetrain. It's reasonable to expect e-POWER hybrid to be one of the most fuel efficient vehicles in its class.

yoatmon

It's truly amazing what engineering skills manage to achieve just to keep a stone age relict alive.

SJC

a dedicated engine running at an optimal range of speed and load...
Obvious reality.

Engineer-Poet

Been saying for many years that the electric side of the system allows the ICE side to be ruthlessly optimized for efficiency, because you don't have to worry about transient response and especially emissions control during transients.

Now, how does this compare with the Achates engine?

yoatmon

Back in 1975, during the second oil crisis, I'd suggested a serial hybrid and was scoffed and ridiculed and was informed that something like that would never work.

Prashanta Dhakal

yoatmon: Those that ridiculed you were almost right! But you were more right.

Engineer-Poet

I found a reference at Next Big Future to a 53% thermal efficiency for the Achates engine.  Given the differences in form factor between a conventional and opposed-piston engine, this is probably not a significant distinction.

yoatmon

Personally, I prefer the free floating piston design (FKLG) from Fraunhofer because its ideally suited for a serial hybrid drive with an overall efficiency over 50%. No connecting rods and no crankshaft just "gas springs" at each end; it runs on H2 and is also adaptable to various fossil fuels.
https://www.youtube.com/watch?v=_pBPw33ceoQ

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