Can a gasoline-fueled passenger-car engine achieve diesel levels of efficiency and torque, with lower emissions and cost—in real-world operation? Delphi and Hyundai are close to finding out. The two companies, in collaboration with the University of Wisconsin-Madison’s Engine Research Consultants (WERC) and Wayne State University, are in the final phase of a four-year, $15 million program to develop and demonstrate a 1.8-L GDCI (gasoline direct-injection compression ignition) engine installed in a Hyundai Sonata. Final testing is slated for 1Q2014.

Launched in October 2010, the Ultra Fuel Efficient Vehicle (UFEV) Program is targeting efficiency improvements of 25-40%, compared with a baseline stock vehicle, according to lead engineers at Delphi (which devised the combustion system) and Hyundai. The program incorporates two development phases. Phase 1, now completed, aimed at reducing friction and parasitic losses, according to Kevin Quinlan, Delphi Powertrain’s Vice President of Gasoline Engine Management Systems.

Phase 2, nearing completion, targets improved thermal efficiency from advanced low temperature combustion with GDCI. Sometimes referred to as PPCI—partial premixed compression ignition—GDCI is a “globally stratified but locally stoichiometric” combustion regime that Quinlan describes as being between the Otto and Diesel cycles. Since January the UFEV Sonata has been running on dyno rolls at Delphi’s Troy, MI, technical center, with “limited real road testing on public roads” to begin soon, according to Jim Zizelman, Delphi Director of Engineering, Gas EMS. A second engine has been accumulating steady-state testbed hours at the Hyundai-Kia America Technical Center (HATCI) in Ann Arbor, MI.

The partially premixed combustion is enabled by a multi-late injection strategy using Delphi centrally mounted fuel injectors. The GDI-like units feature a unique decoupled-armature design and operate at 4350 psi (300 bar). To optimize thermal efficiency, the GDCI engine runs a 14.8:1 compression ratio. Boost is provided by an Eaton TVS supercharger in combination with a variable-geometry turbocharger.

The engineers are quick to point out that GDCI differs from homogeneous charge compression ignition (HCCI), which generally requires spark ignition under certain load and temperature conditions.

“The big reason HCCI has its problems is because its pressure-rise rates are phenomenal. Our rise rates and pressure curves are significantly lower than HCCI,” explained Nayan Engineer, Manager of Engine Design and Testing at HATCI.

He said unique piston-crown geometry and intake tract design, along with EGR (exhaust gas recirculation) rates of 25-40%, enable the GDCI to avoid any HCCI-like uncontrolled combustion.

“We have several ‘knobs’ we can play with, but we still have to address how we ignite at -40°F—perhaps with [intake] heating. Once the initial ignition takes place we operate fully in GDCI mode. We don’t jump from spark ignition back to compression ignition as with HCCI,” Engineer said. “The transients will be easier because of that.”

Delphi’s Zizelman credits a combination of fully variable valve train and fast-acting electronically controlled cam phasers with more precise EGR control. The variable valve actuation uses an extra cam lobe to enable a brief moment of valve overlap (opening the exhaust valve on the intake stroke) during warm up.

The engine also uses electronically controlled oil jets for piston cooling that can be deactivated during cold starts.

Early single-cylinder engine tests at Delphi showed the GDCI’s indicated specific fuel consumption (mass-based), thermal efficiency, and CO₂ emissions to be significantly improved over a diesel baseline. Engineers are hopeful the low engine-out NOx levels will help reduce aftertreatment costs.

“Once we get into transient testing we’ll do some step changes,” HATCI’s Engineer told Automotive Engineering in late 2013. “Our NOx levels are below 0.2 g/kW. And at this point our smoke levels are extremely low, under 0.1.” All testing is done with 87 RON fuel with either E-zero or E10.

The program is being funded 50% by Delphi and Hyundai, with the U.S. Department of Energy covering the remaining half.