Hyundai today revealed that it is currently testing a new compression-ignition gasoline engine that is expected to be more efficient than an equivalent diesel. The new Hyundai 1.8-liter inline-four engine has both a supercharger and a turbocharger -- but no spark plugs.
The goal of Hyundai's engine technology, which the company calls Gasoline Direct Injection Compression Ignition (GDCI), is to return the fuel economy of a diesel but with the higher performance, cheaper build cost, cheaper fuel, and lower particulate emissions of a gasoline engine. It uses a high 14.8:1 compression ratio and injects fuel directly into a small bowl in the top of the piston just after the piston passes top dead center. The high compression ratio and the heat already in the cylinder ignite the air-fuel mixture without using a spark plug, just like in a diesel engine.
Several other automakers, including General Motors, have experimented with compression-ignition gasoline engines, but none are currently on the market.
Hyundai engineer Nayan Engineer (yes, that's really his name) says the GDCI engine could be 25 percent more fuel-efficient than a standard spark-ignition gasoline engine. And because it will run on 87-octane gasoline, which is cheaper than diesel, customers will see a greater savings at the pump than if they switched to a turbodiesel car.
There are several limitations to this technology. Hyundai uses a supercharger to provide more low-end power because the GDCI engine doesn't produce enough exhaust flow to spool-up a turbocharger at low RPMs. At higher speed, the supercharger is bypassed and the engine instead uses the turbocharger to produce extra power. Maximum engine speed is currently a diesel-like 4500 rpm, but Hyundai would counter that relatively low redline by choosing transmission gear ratios to match.
Another problem is that the compression-ignition system needs heat in the cylinder in order to work. Hyundai solves this by directing as much as 40 percent of the exhaust-gas recirculation flow (EGR) back into the intake tract, and by "popping" the exhaust valve open for a brief period during the intake stroke. However, Engineer says the current prototype will only start at room temperature -- figure 70 degrees or warmer -- and says that the GDCI engine might need glow plugs or an intake heater (as used in diesels) to operate in cold weather.
The Hyundai engine, which is being developed in partnership with Delphi, is currently running in four engine-test cells at the company's technical center in southeast Michigan. Officials say it sounds like a "muted" diesel engine. Because it is less complicated and requires less strengthening of the engine block than a traditional diesel, Hyundai believes its GDCI engine would also be considerably cheaper than a diesel. The prototype engine announced today is based on a series-production "Theta" engine block (and used in cars like the Santa Fe, Tucson, and Sonata) with some minor strength improvements.
As for when we might see it in a production car, Engineer notes that the 1.8-liter prototype will fit into a Sonata-like vehicle and says that the GDCI engine will arrive in the "not too distant future."
"The technology is very promising and we believe it will be a game-changer," said Hyundai powertrain engineering director John Juriga.