Model-Based Precise Air-Fuel Ratio Control for Gaseous Fueled Engines

In this article, an adaptive state estimation algorithm for precise air-fuel ratio (AFR) control is presented. AFR control is a critical part of internal combustion engine (ICE) control, and tight AFR control delivers lower engine emissions, better engine fuel economy, and better engine transient performance. The proposed control algorithm significantly improves transient AFR control to eliminate and reduce the amplitude of the lean and rich spikes during transients. The new algorithm is first demonstrated in simulation (using Matlab/Simulink^TM and GT-Power^TM) and then verified on a test engine. The engine tests are conducted using the European Transient Cycle (ETC) with Horiba^TM double-ended dynamometer. The developed algorithm utilizes a nonlinear physics-based engine model in the observer and advanced control principles with modifications to solve real industrial control issues. This method dramatically reduces on-engine AFR transient calibration efforts, which was one of the objectives of this research. The developed algorithm is applicable for various fuel mixer configurations including pre-turbocharger, pre-throttle, and post-throttle. It also demonstrates robustness to engine to engine inconsistency. The novel algorithm is developed by following model-led design process. Woodward^TM natural gas engines and engine control modules are used for algorithm development and validation.