Browse Publications Technical Papers 2019-24-0015
2019-09-09

Experimental Validation of a Model-Based Water Injection Combustion Control System for On-Board Application 2019-24-0015

Water Injection (WI) has become a key technology for increasing combustion efficiency in modern GDI turbocharged engines. In fact, the addition of water mitigates significantly the occurrence of knock, reduces exhaust gas temperatures, and opens the possibility to reach optimum heat release phasing even at high load. This work presents the latest development of a model-based WI controller, and its experimental validation on a GDI TC engine. The controller is based on a novel approach that involves an analytic combustion model to define the SA required to reach a combustion phase target, considering injected water mass effects. The model has been expanded to directly consider air-to-fuel ratio variation effects on combustion phasing, and the same controller structure could integrate other variables that influence 50 percent of Mass Fraction Burned angular position (MFB50), such as EGR. The calibration and experimental validation of the proposed controller is shown in detail in the paper. At first, the focus is on the open-loop branch, to evaluate the performance of the combustion model and its ability to manage Spark Advance (SA) taking into account the phasing implications of WI, maintaining a pre-defined combustion phase target. Then the closed-loop (CL) chain is introduced, defining a structure that allows reaching the target while keeping knock intensity (KI) level under an established threshold using two different control levers (SA and WI). At the same time, the controller has been designed to minimize water consumption. The proposed controller has been implemented in a Rapid Control Prototyping environment, and the main results achieved at the test bench are shown in the paper. The closed-loop controller was initially based on in-cylinder pressure signals both for knock intensity and combustion phasing measurements. To allow the proposed controller implementation on actual engine management systems, a specific signal processing algorithm has been developed to extract heat release position from the accelerometric signals available on-board, and it has been validated with experimental data.

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