Air-to-Fuel and Dual-Fuel Ratio Control of an Internal Combustion Engine

Air-to-fuel (A/F) ratio is the mass ratio of the air-to-fuel mixture trapped inside a cylinder before combustion begins, and it affects engine emissions, fuel economy, and other performances. Using an A/F ratio and dualfuel ratio control oriented engine model, a multi-inputmulti-output (MIMO) sliding mode control scheme is used to simultaneously control the mass flow rate of both port fuel injection (PFI) and direct injection (DI) systems. The control target is to regulate the A/F ratio at a desired level (e.g., at stoichiometric) and fuel ratio (ratio of PFI fueling vs. total fueling) to any desired level between zero and one. A MIMO sliding mode controller was designed with guaranteed stability to drive the system A/F and fuel ratios to the desired target under various air flow disturbances. The performance of the sliding mode controller was compared with a baseline multi-loop PID (Proportional-Integral-Derivative) controller through simulations and showed improvements over the baseline controller. Finally, the engine model and proposed sliding mode controller are implemented into a Hardware-In-the-Loop (HIL) simulator and a target engine control module, and HIL simulation is conducted to validate the developed controller for potential implementation in an automotive engine. INTRODUCTION Increasing concerns about global climate changes and ever-increasing demands on fossil fuel capacity call for reduced emissions and improved fuel economy. Vehicles equipped with DI fuel systems have been introduced to markets globally. In order to improve DI engine full load performance at high speed, Toyota introduced an engine with a stoichiometric injection system with two fuel injectors for each cylinder, see [1]. One is a DI injector generating a dual-fan-shaped spray with wide dispersion, while the other is a port injector. The dual-fuel system introduces one additional degree of freedom for engine combustion optimization to reduce emissions with improved fuel economy. Using gasoline PFI and ethanol DI dual-fuel system to substantially increase gasoline engine efficiency is described in [2]. The main idea is to use a highly boosted small turbocharged engine to match the performance of a much larger engine. Direct injection of ethanol is used to suppress engine knock at high engine load due to its substantial air charge cooling resulting from its high heat of vaporization. The control of A/F ratio is an increasingly important control problem due to federal and state emission regulations. Operating the spark ignited internal combustion engines at a desired A/F ratio is due to the fact that the highest conversion efficiency of a three-way catalyst occurs around stoichiometric A/F ratio. There have been several fuel control strategies developed for internal combustion engines to improve the efficiency and to reduce exhaust emissions. A key development in the evolution was the introduction of a closed-loop fuel injection control algorithm [3], followed by a linear quadratic control method [4], and an optimal control and Kalman filtering design [5]. Specific applications of A/F ratio control based on observer measurements in the intake manifold were developed in 1991 [6]. Another approach was based on measurements of exhaust gases by an oxygen sensor and the throttle position [7]. Hedrick also developed a nonlinear sliding mode control of A/F ratio based upon the oxygen sensor feedback [8]. The conventional A/F ratio control for automobiles uses both closed-loop Copyright © 2009 SAE International SAE Int. J. Engines | Volume 2 | Issue 2 245 Downloaded from SAE International by Brought To You Michigan State Univ, Thursday, April 02, 2015