Delphi projects that engines employing its coming third-generation gasoline direct-injection compression-ignition (GDCI) combustion system will attain a thermal efficiency of 42%, the company said at the 2017 SAE High-Efficiency IC Engines Symposium in Detroit. That thermal efficiency would top any current production-vehicle gasoline engine, the most efficient of which are claimed to have peak thermal efficiency of about 40%.
Mark Sellnau, engineering manager, Delphi Advanced Powertrain, said a gasoline engine using the third-generation GDCI system now under development is projected to have approximately 22% better thermal efficiency than a current conventional spark-ignited gasoline engine with direct fuel injection and 11% better than a 2L diesel engine. He said many of the initial engineering challenges for GDCI have been overcome and that the company believes it can make the low-temperature combustion system emissions-compliant at the EPA Tier 3, bin 30 level.
Major advances over Delphi’s second-generation GDCI system include “wetless” combustion, quicker cold-start operation and an optimized low-temperature exhaust aftertreatment that achieves roughly 90% carbon monoxide conversion in about 4s.
Sellnau said the third-generation system has increased the compression ratio to 16:1 (from 15:1) and its new longer stroke and increased top-dead-center piston clearance enable the wetless operation that sees fuel completely vaporized before it contacts cylinder or combustion-chamber surfaces. Advanced fuel injectors operate at 350 bar (5076 psi) and provide three injection events. The third injection, Sellnau said, is “what differentiates (GDCI) from HCCI (homogenous-charge compression ignition).”
Much of Delphi’s GDCI research is being conducted under the auspices of a four-year, $9.8-million program funded by the U.S. Department of Energy; Delphi’s partners in the project include Oak Ridge National Laboratory, Umicore and the University of Wisconsin-Madison.
The system will require a variety of emissions-reduction measures that, in addition to the newly-formulated low-temperature catalyst, include an intake-air heater, gasoline particulate filter and urea injection. But Sellnau was confident those measures, coupled with the combustion-related design advances of the third-generation system, will enable a production engine to be Tier 3, bin 30 compliant—a vital achievement to advance the system for production-vehicle readiness.
Moreover, he promised the latest GDCI will operate with gasoline at currently-available octane. “We really need to get to market with commercial gasoline,” he said.
Sellanu said the project team began gathering test results for the third-generation GDCI system in February 2017 and added, “I think we’re going to see a very efficient engine evolving and going into our vehicle program.” He did not, however, provide a projection on when the system might be fitted to a production-vehicle engine.