Ford’s next-generation EcoBoost engine technology will likely feature some combination of aggressive cooled EGR, further advancements in valvetrain and turbocharger control, and engine downspeeding, with the goal of improving vehicle fuel economy by 25%, according to a recent presentation by Eric Curtis, Technical Leader and Manager of Engine and Powertrain Systems.
Curtis also indicated that an optimized stratified charge combustion regime may be employed on the EcoBoost (turbocharged, direct-injected gasoline) units, if the system can be configured to meet the proposed California LEV3 standards. “Lean combustion is very challenging in the context of LEV3 emissions,” he noted during the 2012 SAE High Efficiency IC Engines Symposium in Detroit.
Curtis noted that meeting dramatically higher (54.5 mpg) U.S. fleet fuel efficiency, with more stringent exhaust emission standards, will be tough indeed. “With LEV3, North American emission standards will remain the most challenging in the world,” he told the SAE audience.
Curtis believes potentially up to 40% brake thermal efficiency (BTE) can be achieved in stoichiometric gasoline engines “at moderate cost,” which is key to Ford’s “democratized technology” product mantra noted by Raj Nair, Ford’s new Group Vice President of Global Product Development, in a recent AEI interview. (See AEI print edition, 5 June 2012). Curtis’ optimism comes from progress made in an advanced technology development program with support from Michigan Technological University, called "Advanced Gasoline Turbocharged Direct Injection (GTDI) Engine Development."
Launched in October 2010, the four-year program is co-funded by Ford and the U.S. Department of Energy, each of which invested $15 million. Ford’s objectives for the Advanced GTDI program are to demonstrate 25% fuel-economy improvement in a midsize sedan using a downsized GTDI engine (compared to a baseline naturally aspirated PFI engine), with no or limited degradation in vehicle level metrics, and to demonstrate the vehicle is capable of meeting Tier 2 Bin 2 emissions on the FTP-75 cycle.
The primary technologies being investigated in the 2010-14 project include: advanced dilute combustion with cooled EGR and advanced ignition; advanced lean combustion with DI and advanced ignition; advanced boosting systems that include turbocompounding; and advanced cooling and aftertreatment systems.
Friction-reduction technologies and advanced engine control strategies are expected to provide additional fuel economy improvement, Curtis reported.
Cooled EGR up to 15%
Engine-displacement downsizing will be a substantial contribution to the 25% improvement target. Downspeeding is complementary to downsizing, as it helps shift the “good” brake-specific fuel consumption (BSFC) map toward the area of higher utilization.
Curtis added that pumping losses rapidly decrease as load increases. Cylinder size and bore/stroke ratio also effect thermal losses and engine knock, which impact engine efficiency. Undersquare dimensions can help to improve thermal efficiency in downsized and boosted applications, Curtis noted during the Q&A session.
Optimized stratified charge (lean burn) with cooled EGR and advanced aftertreatment pathways are being investigated with ignition system support from Michigan Tech, Curtis said. He said 10-15% cooled-EGR rates “would give good benefit.” The project is exploring both high- and low-pressure loop EGR systems.
Curtis told the SAE symposium audience, which included top engineers from major turbocharger suppliers including BorgWarner and Honeywell, that Ford (and the industry) needs new turbo systems that provide a greater range of boost capability. He outlined the benefits and trade-offs of various turbocharger types, including radial, mixed-flow, and axial-flow systems, which will require equally advanced valvetrains to deliver their full potential. He also said new fuels more amenable to high load regimens would be welcome.