Nissan Working on Engine With 50-Percent Thermal Efficiency (roadandtrack.com)

Nissan Says It's Working on an Engine With 50-Percent Thermal Efficiency

Achieving 50-percent thermal efficiency could prolong the life of the internal-combustion engine, but there's a catch.

BY CHRIS PERKINS

FEB 26, 2021

In the big scheme of things, gas-powered internal-combustion engines aren't all that efficient, as most of what they generate is waste heat. Toyota is believed to offer the most thermally efficient internal-combustion automotive engine in production today, a 2.0-liter naturally aspirated four-cylinder that achieves 41 percent thermal efficiency. In other words, 41-percent of that engine's work is converted to powering the car, 59 percent is just useless heat.

Nissan says it's achieved a breakthrough in internal-combustion thermal efficiency, developing an engine that achieves 50 percent thermal efficiency. But there's a big difference between this new Nissan engine and Toyota's four-cylinder—the former is only designed to operate within a very narrow range. Nissan is developing this engine as a generator for a series hybrid vehicle, where only an electric motor drives the wheels. The internal-combustion engine generates energy to charge a battery, and that battery powers the motor. There's no mechanical connection between the engine and the wheels.

An infographic from Nissan explaining how e-POWER differs from pure EVs and conventional hybrid cars.

NISSAN

This engine will be used in a future generation of Nissan's e-POWER system, which is currently employed in the Japanese-market Note. Nissan was able to achieve 50-percent thermal efficiency in testing by essentially tuning the engine to operate within a very specific range of speed and load. Because the engine doesn't drive the wheels, it doesn't have to work with such wide parameters.

"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," Nissan said in a press release. "However, a dedicated engine running at an optimal range of speed and load for electrical generation makes it possible to dramatically improve thermal efficiency."

NISSAN

The engine is tuned to work with a very diluted air-fuel mixture, and it operates with a high compression ratio. Nissan didn't give away much about the engine itself, declining to specify size, cylinder count, and compression ratio. Photos released by Nissan show a single-cylinder mockup engine on a test bench, so it seems that the company hasn't decided on the exact form this engine will take.

Nissan is aiming for 100-percent carbon neutrality by 2050 and to achieve that goal, it's investing big in battery-electric vehicles and cars that use its e-POWER system. This system seems like a great alternative to an EV, especially in places where charging infrastructure is lacking.

Right now, the only internal-combustion gas engine we're aware of that has over 50 percent thermal efficiency is the Mercedes-AMG 1.6-liter Formula 1 V-6. But that engine uses tech far too expensive and complicated for mass-market road cars. It's unclear when we'll see this new engine from Nissan, but, developments like this show that there may yet be life in internal combustion.