Diesel engines are more efficient than their gasoline counterparts. There are several reasons for this; they burn a more energy-dense fuel, they’re run much higher compression ratios and there are fewer pumping losses since they have no throttle bodies. But what if you could take the best attributes of both powerplant types and combine them into one unit? That’s exactly what engineers at Hyundai are doing.
They’ve built a running gasoline engine that has no spark plugs. Like a diesel it’s compression-ignition. They call this powerplant Gasoline Direct Compression Ignition, GDCI for short.
Over the years various technologies have allowed gasoline and diesel engines to become more and more similar. For instance they can both have direct fuel injection and high compression ratios; in a way it’s almost like they’re converging into one.
Nayan Engineer (yes, that’s really his last name), a powertrain engineer with Hyundai said “We believe the technology (GDCI) we are pushing forward is a promising technology.”
What they’ve developed is a step beyond Homogenous Charge Compression Ignition (HCCI) technology other companies have been working on for many years. Engineer said “For decades people have been trying HCCI” and still it’s not commercially viable. Super-high in-cylinder pressures are a challenge and they can damage internal components.
High Compression Ratio
Hyundai’s GDCI system runs a very high 14.8-to-1 compression ratio. Additionally Engineer noted that it has “no spark plugs; (it’s) pure auto-ignition.” It’s essentially a diesel that runs on regular 87-octane gasoline, a fuel that’s usually considerably cheaper than diesel.
To make all of this work it features a two-part forced-induction system, with a supercharger providing boost at low speeds and a turbo for high-end performance. However, the engine doesn’t really spin all that fast; it’s more of a low-RPM torque monster. Redline is around 4,500.
A transmission with taller ratios takes advantage of all that off-idle twist. Overall with this entire package they’ve targeted a 25 percent fuel-economy gain. The engine has very comparable brake specific fuel consumption figures to a 2.0-liter diesel. This is especially impressive because it displaces almost the same amount. The basis for the engine was a FACTORY STOCK block from their Theata engine family.
A Cam Inside a Cam
Heat is needed to help the air-fuel mixture ignite under pressure and the GDCI engine does something very unique. It’s got fast-acting electronic cam phasers but beyond this high-tech upgrade it also features a special exhaust bump-stick; it’s essentially a cam inside a cam. This allows the exhaust valves to open slightly during the intake strokes, which sucks some of the hot gassed back into the cylinder. This heat bump helps facilitate compression ignition.
This combustion strategy may sound like it’d be terrible for emissions but as of right now the GDCI engine only needs standard after-treatment catalysts like any other gasoline engine, though this may change if it makes it into production. Additionally, since it essentially features a diesel combustion cycle it sounds like, surprise, surprise a diesel! But supposedly the clatter is kept to a minimum thanks to multiple fuel0-injection pulses per cycle.
But best of all Engineer said “it’s not that expensive,” noting that with the GDCI technology “we truly believe this is a game changer.” This powerplant was designed with production in mind meaning it’s not a fancy (and expensive) one-off engineering study.
Hyundai representatives wouldn’t give us a firm date but their GDCI engine could enter production in the not-too-distant future. Intriguingly Engineer noted that “possibly gasoline is the best fuel for diesel engines.” Who knows? He may just be right.
GALLERY: Hyundai GDCI Engine
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