Transient Control Strategies for an Engine with an Exhaust Treatment System to Meet Future Emissions Standards, 03-R9526

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Principal Investigators
Yiqun Huang
Qilong Lu

Inclusive Dates:  01/01/05 – 01/01/07

Background - Manufacturers of diesel-powered light-duty vehicles in the United States and Europe face stringent emissions regulations in the future. A lean NOx trap (LNT) is the likely exhaust treatment device for NOx 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 real-world driving.

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 NOx trap (LNT)-based, four-way catalyst system with a specific focus on the following:

  • Successful LNT regeneration during transients, as opposed to delaying or aborting the regeneration until a more convenient condition occurs.
  • Thermal management of the entire four-way catalyst system during transients because the performance of one component cannot be sacrificed for the other components.
  • 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.

  • The engine was converted with a dual-loop EGR system to realize SwRI’s alternative combustion concepts for low emissions.
  • 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.
  • A patent-pending, cold start fast warm-up engine control strategy has been demonstrated, which consists of highly reduced intake manifold pressure combined with highly premixed combustion.
  • A patent-pending flexible four-way catalyst exhaust aftertreatment system has been implemented and tested. The flexible system is designed to achieve effective thermal management of the aftertreatment system during both steady-state and transient engine operations. The LNT warm-up time is significantly reduced during the first phase of the FTP-75 driving cycle when the LNT is switched to close-coupled by the flexible aftertreatment configuration system.

Figure 1. Flexible exhaust treatment system at the test cell.

Figure 2. Temperature profiles of DPF and LNT during the first phase of FTP-75 with LNT close-coupled.

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