Date of Award


Document Type

Open 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

Committee Member 1

Scott A. Miers

Committee Member 2

Jeremy J. Worm

Committee Member 3

Kuilin Zhang


Recent fuel economy and emission regulations are the major concern of the research and development of modern internal combustion engine. Such technologies include variable valve timing (VVT), direct injection (DI), turbocharging, downsizing, and over-expanded cycle are used by many manufacturers to improve engine fuel economy or increase power density.

Current Atkinson cycle technology in the production engine is mainly realized by an advanced valvetrain system to reduce the effective compression ratio while maintaining the same expansion ratio. Another approach to realize over-expanded cycle engine is to utilize a multi-link cranktrain mechanism. Although the Atkinson cycle was originally patented in the 1880s, the research of the over-expanded cycle engine realized by a multi-link cranktrain design is incomplete. This study focuses on the investigation of over-expanded engine realized by a cranktrain with a multi-link mechanism. The multi-link mechanism of cranktrain was developed and simulated with the constraints of packaging and match the same specification as the baseline engine including compression ratio, bore, and intake/compression stroke. This study also discusses adapting the cam profiles, cam phasing, and spark timing to compensate for the geometric characteristics difference between an Atkinson cycle engine and a conventional engine.

The 1-D engine model was developed and calibrated in the commercial engine program, GT-Suite/GT-Power, based on the experimental results from a production four-cylinder spark-ignited engine (not over-expanded). The simulations of multi-link over-expanded engine and high compression engine were realized by substituting the new cranktrain for the baseline cranktrain

In this study, the investigation of the multi-link over-expanded engine included a series of operating conditions from light load to high load. The results were compared at the optimized condition between the baseline engine, multi-link over-expand engine, and high compression engine. At the light load condition, it was observed that the net indicated efficiency of the over-expanded engine was slightly improved based on the adjustment method.

This study also investigated the operating condition of the baseline engine with knock constrained and exhaust temperature constrained conditions at medium to high load. With the optimization, the over-expanded cycle engine is less constrained than the baseline engine due to the reduced knock propensity and exhaust gas temperature resulting in the further improvement of net indicated efficiency.

The study of the multi-link over-expanded cycle engine includes the comparison with the latest production high compression ratio engine, representing state-of-the-art high efficiency engine technologies. The net indicated efficiency of multi-link over-expanded engine is even better than the peak efficiency point of the high compression engine.