Date of Award

Summer 2019

Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

First Advisor

Allen, Casey M.

Second Advisor

Singer, Simcha

Third Advisor

Roy, Somesh


For over 40 years, researchers have been studying homogenous charge compression ignition (HCCI) as a combustion strategy to improve the efficiency and emissions of the internal combustion strategy. Although early results were promising, it has been since discovered that HCCI engines only operate to their potential over a narrow load band. To remedy this, introducing inhomogeneities has been suggested as a method of controlling HCCI combustion in such a way to improve its usefulness. One such inhomogeneity is referred to as fuel octane number stratification and consists of port injecting a low reactivity fuel, allowing it to become well mixed, and then direct injecting a high reactivity fuel to introduce local mixture stratifications. Reciprocating engine and computational studies have shown this to improve efficiency and emissions of compression ignition engines, however, there has been little work done to explore octane number stratification on a per stroke basis in well-controlled conditions. The objective of this study is to utilize fuel octane number stratification combustion strategy to optically observe the influence of the low-reactivity fuel, propane, on the dynamics of the reaction zone growth. To accomplish this, a rapid compression machine (RCM) was used to perform experiments in which combustion was captured by a high-speed camera. The RCM was outfitted with heaters and a polycarbonate window to control the temperature and optically access the cylinder. In addition, the mixture composition of propane to n-heptane was varied while keeping the global equivalence ratio constant at three unique initial temperatures. The results of this study showed that ignition time, reaction front start location, and reaction front speed was sensitive to the amount of propane in the mixture. As propane content was decreased the time for the mixture to ignite relative to the start of compression decreased. Furthermore, as propane content decreased, the origin of the reaction front(s) increased in height along the cylinder wall. Reaction front velocity also increased as propane content decreased. Finally, through this work it was also discovered that ignition time and the reaction front speed of some mixtures were sensitive to changes in initial and compressed temperature.

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Engineering Commons