This study investigates the impact of fuel structure and chemistry on the combustion dynamics of a high-pressure fuel spray under realistic diesel engine conditions. The focus of the research was to better understand the combustion characteristics of a bio-derived hydroreformed Navy diesel, HRD-76, which is populated with a higher percentage of paraffins and expected to exhibit more rapid ignition behavior in comparison to the conventional Navy diesel, F-76. Specific attention was paid to intermediate temperature ignition conditions, which are of particular interest due to unique ignition behavior and the potential for reducing common oxide pollutants in this region. Experiments were conducted in a constant pressure flow chamber using dry air at ambient temperatures of 800 K <= T <= 975 K under various compressed pressures within the standard engine operating envelope (20-95 bar), and under a moderate to high fuel loading condition when compared to realistic engine applications. The ignition delays, combustion duration, and ignition dwell of the fuels at various temperatures and pressures were measured utilizing a photodiode to capture the OH* emission signature. In addition, high-speed broadband chemiluminescence imaging and intensified high-speed OH* chemiluminescence imaging were utilized to understand the fuel's ignition behavior at frame-rates of 60 kHz. The optical diagnostics employed showed that the HRD-76 has a higher propensity to ignite in comparison to F-76 under the same ambient conditions. The results were correlated with shock tube data and chemical kinetic simulations to determine the impact of the fuels' physical delay time on the overall ignition delay. These results will supply fundamental combustion information for the use of alternative fuels in current and future engine technologies. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.