Model-based Control Development of a Tier 4 Locomotive Engine with Exhaust Gas Re-circulation

The Tier 4 emission standards for heavy duty diesel engines have a reduction of
$> 70\%$
in nitrous oxide (NOx) & particulate matter (PM) as compared to the Tier 3. Technology changes need to be introduced to meet these stringent norms. The paper discusses the model-based control development for a Tier 4 locomotive engine using Exhaust gas recirculation (EGR) wherein part of the exhaust gas is re-circulated into the cylinder to reduce NOx formation. Since emissions are predominantly functions of how good combustion takes place inside the cylinder and how the engine breathes i.e. the conditions of the air and fuel entering and exiting the cylinder, control of oxygen-based indicators like the oxygen fraction in the intake manifold will be critical to identify the emission. The oxygen-based metrics can in turn be mapped to the flows & pressures in the air handling path. To accurately control these parameters advanced control techniques, need to be developed. The aforementioned controls problem is a complex and intellectually challenging one for the following reasons: (i) multi-input multi-output system dynamics with coupled control loops, (ii) non-minimum phase behavior, and (iii) limited sensor measurements etc. This paper describes the details of the controls development process. Specifically, we discuss (i) single input single output control scheme keeping in mind simplicity for real-time implementation, (ii) decoupling technique to minimize the coupling between the interacting loops, (iii) virtual actuator coupling to aid in control design, and (iv) scheduling the control gains for optimal performance throughout the operating range.