Nissan claims to have made a major efficiency breakthrough in efficiency for an internal-combustion in its e-Power hybrid system.
The automaker announced Friday that it had reached 50% thermal efficiency, which is the percentage of energy converted to work within the engine. That's a figure normally associated with Formula One racing engines; the most efficient current production engines are closer to 40% thermal efficiency.
Nissan achieved 50% thermal efficiency in a test engine using what it calls "STARC," an acronym for "Strong, Tumbler, and Appropriately-stretched Robust ignition Channel." That involved "strengthening" the air-fuel mixture going into each cylinder, and burning a more diluted mixture at a high compression ratio.
In testing, Nissan said it achieved 43% thermal efficiency just by diluting the mixture (using exhaust-gas recirculation), 46% when using lean combustion (meaning more air and less fuel), and 50% when operating the engine at a fixed rpm and load, with waste-heat recovery technologies.
It's not normally possible to operate a gasoline engine at a fixed rpm and load for long periods of time in real-world conditions, but since e-Power is a series-hybrid system that essentially uses the internal-combustion engine as an onboard generator, that's a scenario that's possible with this layout.
Nissan STARC combustion
While this highest level of efficiency has only been achieved in laboratory tests, the e-Power system is currently available on certain Nissan models, albeit not in the United States.
Nissan launched e-Power on the Japanese-market Note subcompact in 2016, and has since made the Note all-hybrid.
The hybrid system was due to arrive in the U.S. by now and, at least check, is still due be used extensively in the U.S. market in the future. We've been told that e-Power in the U.S. will aim for performance, not just mpg, though. It will also be used by Nissan's Infiniti luxury brand, which is aiming to make all of its models hybrid or all-electric over the next few years.
Infiniti QS Inspiration concept - on exhibit October 2019
Other automakers have shied away from series hybrids, opting for parallel hybrids instead. Honda's hybrid system comes close, but still has a clutch that engages the engine to the drive wheels, at a tall ratio, at highway speeds, because it says that a series-hybrid setup alone won't produce satisfactory efficiency in those conditions.
Series hybrids were once the next big thing—100 years ago. Will a new generation of internal-combustion tech, like what Nissan has demonstrated, help them finally be relevant?