EGR-VGT equipped heavy duty diesel engine calibration and air path control for optimized nitric oxide (NO_x) emissions

Efficient exhaust emissions control of diesel engines is a prime concern for the auto-mobile industry. Evolving emission standards set by authorities have resulted in development of different emission control technologies over past decades. Exhaust gas recirculation (EGR) and variable geometry turbochargers (VGT) have been introduced as hardware solutions intended to minimize harmful emissions. The EGR path recirculates exhaust gases into the cylinders which dilutes the fresh air. The exhaust gas recirculation is achieved by regulation of EGR-VGT valves at certain set-points by using sophisticated control techniques. Customary industrial practices employ exhaustive search and tests cell dynamo operations to calculate set-points for calibration. In this paper, steady state maximization of an objective function is used to calculate calibration set-points. The objective of the maximization is to increase EGR fraction recirculation into the intake manifold and thereby force the engine to operate with reduced nitric oxide emissions in the exhaust outflow. The set points are regulated using a higher order sliding mode control (HOSM) scheme to achieve the control objectives and feasible set-points. The regulation performed using the HOSM controller forces EGR and VGT actuators to be positioned for maximized EGR gas fraction in the intake manifold. The HOSM scheme implements the super-twisting algorithm to overcome chattering phenomenon. To avoid the complexity due to components like EGR and VGT, a reduced order model is used for controller design. The simulations performed using the calculated set-points show feasibility of the set-points and reduced NO_x emissions in the exhaust.