Date of Award

2025

Document Type

Open Access Dissertation

Degree Name

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

Administrative Home Department

Department of Mechanical and Aerospace Engineering

Advisor 1

Youngchul Ra

Committee Member 1

Jeffrey D. Naber

Committee Member 2

Chunpei Cai

Committee Member 3

Kartik Iyer

Abstract

Future mobility is expected to rely on a broad spectrum of powertrain technologies, including battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), fuel cell electric vehicles (FCEVs) and traditional internal combustion engine (ICE) vehicles. Despite the shift toward electrification, internal combustion engines are projected to remain a key component of future powertrains, either as the primary power source or as range extenders to generate electricity in hybrid systems. As such, significant research efforts continue to focus on enhancing the efficiency and reducing the emissions of ICEs to meet increasingly stringent regulatory and environmental targets. Gasoline compression ignition (GCI) has been identified as a promising combustion strategy that can combine the high thermal efficiency of diesel engines with the potential for much lower nitrogen oxides (NOx) and particulate matter (PM) emissions. GCI takes advantage of the lower reactivity of gasoline to enable controlled autoignition at lower temperatures and pressures, which in turn reduces the formation of harmful pollutants. However, successful implementation of GCI technology depends not only on engine hardware but also on the chemical and physical properties of the fuel.

This research focuses on understanding the effects of gasoline fuel properties, specifically fuel reactivity on GCI combustion. A range of gasoline fuel formulations were considered, with research octane numbers (RON) from 60 to 90, in order to capture a broad spectrum of autoignition characteristics. In addition to these fuels, three oxygenated blends of ethanol (E36Gas) and isobutanol (iB25gas, iB51Gas) were also studied, along with a baseline RON 87 E10 gasoline, to assess the impact of fuel oxygenation on combustion and emissions. Numerical simulations were conducted using MTU-MRNT, an in-house multidimensional computational fluid dynamics (CFD) solver. The code was coupled with advanced physical sub-models and the Chemkin library to enable accurate modeling of combustion and emissions. Reduced chemical kinetics mechanisms, specifically developed for multicomponent gasoline surrogate fuels, were employed to simulate the oxidation behavior of both conventional and oxygenated fuels.

Initial validation of the fuel models was carried out in a constant volume combustion chamber (CVCC) configuration. The ignition delay and heat release trends observed in simulations closely matched those from experimental data, thereby confirming the model’s capability to predict ignition behavior. Subsequently, a series of parametric studies were performed to explore the sensitivity of ignition to variations in ambient gas density, ambient temperature, fuel injection pressure and oxygen concentration.

Following validation, the fuel models were applied to simulate low-load GCI engine operation at 5 bar brake mean effective pressure (BMEP). The simulation results showed that ignition characteristics, including ignition delay and combustion phasing, exhibited a strong correlation with the fuel's RON. Fuels with lower RONs (higher reactivity) ignited earlier, while higher-RON fuels demonstrated delayed autoignition. This trend aligns well with the experimental measurements.

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