Transient Control Strategies for an Engine with an Exhaust Treatment System to Meet Future Emissions Standards, 03-9526

Principal Investigators
Yiqun Huang
Qilong Lu

Inclusive Dates:  01/01/05 – Current

Background - Manufacturers of diesel-powered, light-duty vehicles in the United States and Europe face stringent emissions regulations in the future. A lean NO_x trap (LNT) is the likely exhaust treatment device for NO_x control in the U.S., while diesel particulate filters (DPF) are a certainty for particulate matter (PM) control. LNTs must be regenerated periodically to purge the nitrate emissions stored under lean operation. The regeneration process requires the diesel engine to be run richer than stoichiometric conditions. Regeneration under relatively steady-state conditions is a common practice in development efforts even though steady-state conditions are not common in the real-world driving practice.

Approach - The objectives of this project are to develop and demonstrate combustion technology and control strategies to accommodate transient operation of a diesel engine that uses a lean NO_x trap (LNT)-based four-way catalyst system with a specific focus on the following:

1. Successful LNT regeneration during transients, as opposed to delaying or aborting the regeneration until a more convenient condition occurs.
    
2. Thermal management of the entire four-way catalyst system during transients because the performance of one component cannot be sacrificed for the other components.
    
3. Achieving rapid warm-up of the exhaust treatment system during cold-start using in-cylinder controls and exhaust treatment configuration.

A Renault G9T-600, a modern diesel engine that complies with the Euro-IV European emissions regulations, is used in this project. This 2.2-liter engine was instrumented and installed in an SwRI emissions laboratory, and an SwRI-designed rapid prototyping electronic control system (RPECS®) is used to replace the production electronic control unit. Strategies for obtaining rich operation before and during a transient event have been proposed.

Accomplishments - The following objectives have been accomplished in this project.

1. This engine was converted with dual-loop EGR system to realize SwRI’s alternative combustion concepts for low emissions.
    
2. A simplified transient operating cycle was determined based on the survey results of the transient characteristics of light-duty diesel vehicle under the FTP-75 driving cycle as well as US06 driving cycle.
    
3. A patent-pending cold-start, fast warm-up engine control strategy was demonstrated, which consisted of highly reduced intake manifold pressure combined with highly premixed combustion.
    
4. A patent-pending flexible four-way catalyst exhaust aftertreatment system was tested, as shown in the top illustration, to achieve effective thermal management of the aftertreatment system during both steady-state and transient engine operations. The bottom graph shows that the LNT warm-up time was significantly reduced during the first phase of FTP-75 driving cycle when the LNT was valved in the close-coupled position by the flexible aftertreatment configuration system.

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