DOE currently has programs with Ford, General Motors, and Chrysler to demonstrate a 25 percent improvement in fuel economy while achieving Tier 2 Bin 2 emissions requirements with downsized, boosted engines and a variety of other technologies, including lean combustion, cooled EGR, advanced ignition systems, and friction reduction technologies. These programs are described here.
FORD/DOE ADVANCED GASOLINE TURBOCHARGED DIRECT INJECTION (GTDI) ENGINE DEVELOPMENT PROGRAM
DOE has a program with Ford, with support on advanced ignition concepts from Michigan Technological University, to demonstrate 25 percent fuel economy improvement in a mid-sized sedan using a downsized, advanced GTDI engine with no or limited degradation in vehicle level metrics. The vehicle is to demonstrate the capability of meeting Tier 2 Bin 2 emissions. The project includes aggressive downsizing from a large V6 engine to a small I4 engine, direct fuel injection, lean combustion with cooled EGR and advanced ignition, boosting systems with active and compounding components, cooling and aftertreatment systems, advanced friction reduction technologies, engine control strategies, and NVH countermeasures. Vehicle demonstration of greater than 25 percent weighted city/highway fuel economy and Tier 3 Bin 30 emissions on the FTP-75 test cycle is scheduled to be completed by September 30, 2015 (see Weaver 2014).
GENERAL MOTORS/DOE LEAN GASOLINE SYSTEM DEVELOPMENT FOR FUEL EFFICIENT SMALL CARS PROGRAM
DOE has a 39 month program with General Motors to demonstrate 25 percent vehicle fuel economy improvement while achieving Tier 2 Bin 2 emissions with an advanced, boosted lean gasoline combustion engine and aftertreatment system (Smith 2013). The subsystems and components that are being redesigned to support the integration of the boosted lean combustion system include new spark plugs, injector targeting changes, chamber smoothing modifications, cylinder pressure transducer provisions, split intake port cylinder head, intake port deactivation adapter assembly to provide high swirl mixture motion for increased lean dilution tolerance, and a close coupled catalyst exhaust system with cooled external EGR exhaust. General Motors has projected the following efficiency improvements for this program:
- 12.5 percent for lean dilute combustion with closely spaced multiple pulse injections and cooled EGR;
- 7.5 percent for downsizing from 2.4L PFI to 1.4L turbocharged DI engine; and
- 5 percent for vehicle integration which includes 12V stop/start and active thermal management.
The 1.4L boosted stoichiometric homogeneous engine was modified to enable lean stratified operation. A passive SCR lean aftertreatment system is being developed with efforts directed at overcoming the limitations of excess CO breakthrough during NH3 generation and insufficient NOx reduction during high thermal operating conditions. Because of the issues with the passive SCR system, an active urea lean aftertreatment system development is continuing. The active urea dosing system initially will utilize copper zeolite SCR technology. The active and passive systems are projected to support lean and stoichiometric operation. Active thermal management is expected to provide up to an additional 1.5 percent in fuel economy benefit.
The LDB (Lean Downsized Boost) engine with the 12V stop/start and active thermal management is projected to meet the 25 percent target based on engine dynamometer test results. At the conclusion of the project in 2013, the lean downsized boosted (LDB) engine demonstrated 21 percent fuel economy improvement over the PFI baseline. The LDB engine combined with 12-volt start/stop and thermal management demonstrated the project objective of 25 percent fuel economy improvement over the PFI baseline.
CHRYSLER DOWNSIZED, TURBOCHARGED ENGINE RESEARCH PROGRAM
Chrysler has a three year, $30 million program half-funded by DOE and half-funded by Chrysler and its technology and research partners including Argonne National Laboratory, Bosch, Delphi, Ohio State University, and FEV. The three-year program began in 2010 and has since had a nine-month extension to April 2014. The objective of the program is to demonstrate a 25 percent improvement in combined city/highway fuel efficiency in a mini-van while meeting Tier 2 Bin 2 emissions and with drivability comparable to a current production vehicle. The program will downsize the base 4.0L V6 engine to a 2.4L I4 engine. Key technologies applied to this program include a purpose designed combustion chamber, 12:1 compression ratio, spray-bore cylinder liners with laser-honed surfaces for reduced mass and friction, high-energy dual-plug ignition, two-stage turbocharging, cooled EGR, secondary air injection, and a belt starter-generator (BSG). Chrysler is also using diesel micro-pilot (DMP) ignition. This system uses carefully timed pilot injection of diesel fuel to enhance and extend the gasoline burn rates at high load, while assisting the spark ignition combustion in the transition zone between high and low loads. Chrysler has found that the DMP ignition functions within very small tolerances of EGR rates that may not be controllable. As an alternative, the program is also investigating a spark-ignition dual-fuel strategy using E85 and three spark plugs per chamber.
The BSG is an enabler for iDFSO (integrated Deceleration Fuel Shut Off) functionality from 15 mph to 0 mph that is projected to provide approximately 2 percent fuel savings potential on FTP cycle. With secondary air injection, the rich combustion products react with the air to create an exotherm in the exhaust runner to provide an exhaust temperature of 842°C (compared to 455°C without air injection), within 11 seconds from a cold start for rapid catalyst warm-up.
This program has demonstrated 25 percent improvement in combined FTP city and highway fuel economy in the powertrain test cell. Vehicle results are pending as of the June 2014 DOE Annual Merit Review (Reese II 2014).
Reese II, R.A. 2014. A MultiAir/MultiFuel Approach to Enhancing Engine System Efficiency. Project ID ACE062, DOE Annual Merit Review, June 19.
Smith, S. 2013. Lean Gasoline System Development for Fuel Efficient Small Car. U.S. DOE Merit Review and FY 2013 Progress Report for Advanced Combustion Engine Research and Development, Energy Efficiency and Renewable Energy. Vehicle Technologies Office.
Weaver, C.E. 2014. Advanced Gasoline Turbocharged Direct Injection (GTDI) Engine Development. Project ID ACE065, DOE Annual Merit Review, June 19.