Date of Award

2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeffrey D. Naber

Advisor 2

Mahdi Shahbakhti

Committee Member 1

Bo Chen

Committee Member 2

David D. Wanless

Abstract

The in-cylinder trapped air, residual gas, and temperature are important dynamic parameters in Gasoline Direct Injection (GDI) Spark Ignition (SI) engines for fuel and combustion control. However, their real-time prediction for transient engine operations is complicated, especially when concerning variable valve timing. A dynamic cycle-by-cycle control-oriented discrete nonlinear model is proposed and developed in this thesis to estimate the in-cylinder mixture temperature and the mass of trapped air, and residual gas at the point of Intake Valve Closing (IVC). The developed model uses in-cylinder, intake, and exhaust pressures as the primary inputs. The exhaust gas backflow into the cylinder is estimated using a compressible ideal gas model that is designed for engines equipped with Variable Valve Timing (VVT). The designed model is integrated into a rapid-prototype control system for real-time operation. The model's dynamic behavior is validated using an engine dynamometer transient test cycle under real-time conditions.

The cold crank-start phase significantly contributes to total engine-out emissions during the US Federal Test Procedure (FTP). The first three engine cycles of the cold crank-start for a Gasoline Direct Injection (GDI) engine in Hybrid Electric Vehicle (HEV) elevated cranking speed is investigated at 20°C. To this end, the impact of the operating strategy on the individual-cylinder engine-out emissions is analyzed quantitatively. For this purpose, a new dynamic method was developed to translate the engine-out emissions concentration measured at the exhaust manifold outlet to mass per cycle per cylinder. The HEV elevated cranking speed provides valve timing control, throttling, and increased fuel injection pressure from the first firings. This study concentrates on analyzing the cranking speed, spark timing, valve timing, and fuel injection strategy, and parameter effects on engine-out emissions. Design of Experiment (DOE) method is used to create a two-step multi-level fractional-factorial test plan with a minimum number of test points to evaluate the significant parameters affecting engine-out emissions during cold crank-start. The split injection parameters, including the Start of the first Injection (SOI), End of the second injection (EOI), and split ratio, in addition to the first cycle additive fuel factor, are investigated. Results show that using the high cranking speed with stabilized low intake Manifold Absolute Pressure (MAP), highly-retarded spark timing, high valve overlap, late intake first injection, 30 CAD bTDC firing EOI, and low first cycle fuel factor reduces the average first three cycles HC emission by 94\%.

Available for download on Saturday, August 06, 2022

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