Well 7 years later and Delphi has completed the 3rd iteration of it's GDCI engine and is moving onto the 4th generation. The fuel efficiency improvement was there but other issues have prevented the engines from going commercial such as higher costs, higher emissions, durability issues, etc.
04-09-2019 - the lead researcher for a long-running, Delphi Technologies-directed program to maximize the thermal efficiency of gasoline engines said the latest developments show promise for delivering a production-ready gasoline engine that approaches 50% thermal efficiency. The improvements to the Gen3X engine further enhance the GDCI concept that has been under development in the $9.8-million U.S. Dept. of Energy-funded research program that began in 2011 and produced two prior versions of the engine. “All these engines are now obsolete,” Sellnau said flatly. “None meet the requirements for commercial light-duty engines.” Sellnau said numerous revisions have reduced the cost and complexity of the latest Gen3X engine and enhanced performance, not to mention durability.
The existing Gen3X engine, coupled to an 8-speed automatic transmission and a 12-volt start-stop system and fitted in a midsize passenger car, demonstrated 61 mpg fuel economy in the highway cycle and 48 mpg on the city cycle. Sellnau said the Gen4X engine is expected to be capable of 68 mpg on the highway.
On to a fourth generation
But despite meaningful gains in performance, efficiency and emissions reductions, Sellnau indicates the continuing research already is looking to the Gen4X engine. The research indicates that the GDCI engine can markedly exceed the efficiency of today’s best spark-ignited gasoline engines and hybrid-electric vehicles, which he said also are heavier and more complex.
Engine researchers: 50% gasoline-engine efficiency in sightHyundai ran into similar issues:
December 14, 2016 - Well, at this year's Hyundai powertrain-tech shindig, I got an update from powertrain honcho John Juriga as to just whatever happened to GDCI. He explained that under compression-ignition operating conditions, the peak cylinder pressures were so great that the block and lower end (crank and bearings) needed to be strengthened to what is essentially diesel specifications, adding cost and mass. All direct-injected gas engines have some issues with particulate emissions, and these were even worse with the GDCI engine, requiring a particulate trap not unlike what Mercedes is fitting to many forthcoming S-Class engines, which eroded the hoped-for emissions aftertreatment savings. The GDCI combustion process required considerable exhaust-gas recirculation, some of which was handled by retaining said gasses in the chamber using elaborate variable valve-timing mechanisms that added cost to the top of the engine. Achieving sufficient cylinder pressures at lower engine speeds demanded fitment of a supercharger in addition to the planned turbocharger, which added still more cost (and Juriga added that electric superchargers don't represent much of a savings relative to mechanical ones).
This litany of cost overruns left a less expensive, lower pressure direct fuel injection system as about the only remaining cost savings relative to a diesel, so the program was deemed too risky and expensive. We suspect Mercedes and GM have come to the same conclusion, as all has gone pretty quiet on the HCCI front.
WHATEVER HAPPENED TO HYUNDAI’S HCCI ENGINE?Looks like Hyundai is trying again though:
Sep 24th 2018 - Hyundai said Monday it has won a grant worth $4.95 million from the U.S. Department of Energy to support research and development for an advanced, mixed-mode gasoline spark-compression engine, meaning the Korean automaker appears to be back at it in its quest to develop a fuel-efficient, low-emissions gasoline compression engine that can catch the likes of Mazda's Skyactiv-X.
Hyundai says the three-year grant will leverage existing work with advanced valve train and previous DOE-funded technologies. Hyundai previously was working on its own HCCI — short for homogeneous charge compression ignition — project, developing a Gasoline Direct-Injection Compression engine with help from Delphi that used supercharging and turbocharging, a high compression ratio and fully variable valve train. But it has never come to fruition, reportedly due in large part to added costs.
Hyundai spokeswoman Michele Tinson said the grant will support a new project for the automaker. "It's a departure from the past efforts forging a new direction forward for Hyundai where the fuel and engine combustion modes can be optimized to meet new targets." Tinson said the GDCI project is completing its third round of DOE funding.
Hyundai returns to spark-compression engines with $5 million grantMazda had to push back it's compression engine as well and the 2019 Mazda 3 has a more conventional engine. Apparently Mazda took the route of using the efficiency savings to produce an engine of equal power but smaller fuel consumption. This made sense when gasoline prices were expensive and US consumer were downsizing. However with cheap gasoline and the US consumer opting for larger vehicles, Mazda wants to tweak the engine to produce more power output as they feel the higher fuel efficiency alone is not enough of a selling point in the current market.
1/28/19 - I was pretty impressed with the short amount of time in the 2019 Mazda 3. But besides wondering when we’ll get the all-wheel drive hatchback with a manual, there was one huge question on my mind: “Where’s the ‘holy grail’ SkyActiv-X engine on this car?” So I asked around. While there’s no word on exactly when we’ll see the X engine make it into the new 3, Moro did clue us into what the hold-up could be about.
Mazda told Jalopnik the company is still exploring the SkyActiv-X technology for its full potential. As it stands, the initial excitement over the new technology was its improved and more reliable efficiency gains over the SkyActiv-G engines. But its efficiency in combustion also has the potential to produce more power compared to a normal gasoline engine of similar displacement.
This could be where Mazda’s focus for the engine is at now. Moro mentioned that the company is fine-tuning the engine in preparation for production, and that he believes the engine needs to do more than just get better fuel efficiency, since gas prices are low and it would be tougher to market it on fuel savings alone.
The suggestion is that Mazda is now working to tune as much performance out of the engine as possible, possibly even with turbocharging. When we previously drove a prototype back in September of 2017, the 2.0-liter SkyActiv-X could produce 187 horsepower—as much as the 2.5-liter SkyActiv-G engine in the 2019 Mazda 3. If Mazda can push that level of performance enhancement higher, then it has a new way of marketing its fancy new engine.
Here's Why the 2019 Mazda 3 Doesn't Have the 'Holy Grail' Skyactiv-X Engine Yet
The oil barrel is half-full.