Date of Award

5-14-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Ben Akih-Kumgeh

Subject Categories

Engineering

Abstract

This research investigates relative ignition behavior of some oxygenated fuels and their

blends with gasoline surrogates. It seeks to identify fuels with higher resistance to ignition

and validate tentative kinetic models intended to predict their combustion chemistry. It

also develops a method for simplified ignition delay time correlation that can allow for a

more rapid estimation of the ignition behavior of a given fuel at known thermodynamic

conditions.

The work is motivated by the fact that in spark-ignition (SI) engines, increasing energy

conversion efficiency through increasing the engine compression ratio is limited by the

phenomenon of undesired autoignition known as engine knock. This is controlled by the

chemical kinetics of the fuels which can be modified toward higher resistance using fuels of

higher ignition resistance. In this study, the ignition behavior of the representative fuels is

studied using both shock tube experiments and simulations of the kinetics of homogeneous

chemical reactors. Specifically, we study: 1) propanol isomers, which are alcohols with

three carbon atoms and promising alternative fuels for gasoline fuels; 2) MTBE and ETBE,

which are effective ignition-resistant fuel components; 3) blends of a gasoline with ETBE or

iso-propanol, to establish the kinetic interactions. The resulting experimental data are used

to validate current chemical kinetics models of the individual fuels. To further facilitate the use of fuel blends suggested by this study, combined chemical kinetic models are developed of iso-octane as a gasoline surrogate and each of ignition resistant fuels identified.

In order to reduce the computational cost of using the validated detailed models of the

fuels studied, reduced kinetic models are developed. These reduced versions are of two

kinds. The first uses the model reduction method known as Alternate Species Elimination

(ASE) to derive smaller versions of the detailed models. The second reduction approach

focuses on the prediction of the chemical time scale associated with ignition. Here a

generalized ignition format is developed and detailed model simulations are used to obtain

the constraining data. This makes it possible to predict ignition time scales based on

knowledge of temperature, pressure, and composition of the combustible mixture.

The work advances understanding of biofuels combustion by characterizing ignition

properties of promising fuel additives and the effects of fuel blend on ignition. The

resulting experimental data sets are useful for validating existing and future kinetic models.

The combined models will allow for better insight into the combustion chemistry of

ignition-resistant fuels formed from blending iso-octane with iso-propanol or ETBE.

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