SwRI IRD 2009--Preliminary Investigation of Control Approaches for Active DPF Regeneration during Transient Conditions, 03-R8007

Preliminary Investigation of Control Approaches for Active DPF Regeneration during Transient Conditions, 03-R8007

Background - Diesel emission standards are becoming increasingly stringent. It is impossible to meet the emissions legislations merely by relying on the diesel engine technology itself in the United States. Exhaust aftertreatment components have become essential parts of new engine emission control technologies. Diesel particulate filters (DPFs) are the most effective control technology for PM reduction.

Filters physically capture diesel particulates to prevent their release to the atmosphere. However, soot accumulated inside the filters will increase engine backpressure and result in engine performance deterioration. Therefore, when soot accumulation reaches a certain level, removal of soot becomes necessary to maintain proper engine performance. The process of removing soot from the DPF is defined as "regeneration." In order to achieve reliable and robust filter regeneration, the aftertreatment system must have an active regeneration capability, which requires sophisticated control strategies. Controlling the DOC outlet temperature/DPF inlet temperature at a desired value during engine transient conditions is one of the most challenging tasks in the overall control strategies.

Approach - This project investigated control approaches to achieving satisfactory control performance of active regeneration temperature during transient engine operating conditions. Five representative engine test modes were selected to cover the operating scope of the engine and broad exhaust mass flow change range. Under the five respective modes the dynamics of the temperature control system were thoroughly analyzed and characterized. Two temperature control loops were included in the overall control architecture. The outer loop was designed to determine a target temperature and to control the temperature ramp rate from being too high. The inner loop, which included a closed-loop feedback controller and a feed-forward controller, was developed to control the DOC outlet temperature to follow the target temperature.

Accomplishments - FOTD models were found effective to represent the dynamics of the temperature control system. Nonlinear compensation and gain scheduling techniques were used in the feedback controller to enhance its transient response performance. The feed-forward controller was added with the feedback controller to speed up the temperature tracking performance and improve system control. A dSPACE MicroAutoBox was used as a rapid prototyping development tool. A transient control scheme was implemented in the platform and tested under speed-load transient cycles at the engine test cell. The DOC outlet temperature overshoot/undershoot rate was effectively controlled to about 10 percent under challenging transient processes.


Figure 1. Test Engine and its Exhaust Treatment System at Test Cell	Figure 2. DPF Regeneration Temperature Control during a Speed-Load Transient Cycle