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Date of Award


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

Youngchul Ra

Committee Member 1

Seong-Young Lee

Committee Member 2

Song-Lin Yang

Committee Member 3

Pradeep Agrawal


This research aims to computationally develop a novel six-stroke gasoline compression ignition (GCI) engine cycle to improve the combustion performance and extend the operability of the existing four-stroke GCI engine at low loads. An in-house 3D CFD code, called MTU-KIVA, is used for this numerical work. As described in Chapter 2 of this document, this code includes high-fidelity physical sub-models coupled with the CHEMKIN library in combination with skeletal chemical kinetics mechanisms for gasoline surrogate fuels.

Chapter 3 introduces the proposed six-stroke engine cycle and describes the effects of two additional strokes on the charge mixtures' thermal and chemical composition conditions that affect ignition, combustion, and energy recovery processes. Chapter 4 investigates all the major operating parameters affecting in-cylinder combustion behavior and emission formation/oxidation under highly diluted, low-temperature combustion (LTC) conditions. The parameters include valve timing, injection, spray targeting, engine cylinder design attributes, and charge thermal and chemical composition conditions. It is uniquely found that the charge mixtures can burn in three different combustion modes in the additional two strokes, namely, kinetically-controlled mode of combustion (KCM), mixing-controlled mode of combustion (MCM), and kinetically-ignited mixing-controlled mode of combustion (K-MCM).

The underlying physics of combustion regime change is well understood, and strategies for combustion mode control are devised in Chapter 5. This chapter focuses on identifying the high thermal efficiency engine operation principles and formulating engine operation maps across injection strategy parameters adhering to the constraints of combustion, thermal efficiencies, and maximum pressure rise rate (MPRR).

The overall results indicated the likely trends of improving the engine performance and extending the operability limit of conventional 4S-GCI engine cycle by governing local mixture composition and thermal stratification of charge mixtures during the additional two strokes of a 6S-GCI engine cycle. However, achieving high thermal efficiency is limited by high MPRR and nitrogen oxide emissions.