Numerical simulations of diesel reacting jets in a simulated engine environment were carried out to study the effect of oxygen concentration on the ignition delay time and lift-off length dynamics. A recently developed mechanism, direct integration of chemistry, and well established Lagrangian-Eulerian spray model were utilized for 3-D turbulent spray combustion simulation under engine like conditions. The simulations are able to provide a time-history of chemical species including formaldehyde CH2O intermediates and hydroxide OH radicals to facilitate development of auto-ignition and lift off length numerical diagnostics. A range of important operating points including variations in the oxygen concentration, rail pressure, and injection duration were examined. The purpose of conducting the parametric studies is to investigate the consistency of the results and provide a more comprehensive analysis than a single point condition. It is found that the kinetic sub-model adopted is able to capture the faster burning rates at the various oxygen concentrations and conditions. It also demonstrates the influence of higher injection pressure on the ignition and propagation combustion dynamics. The predicted behaviors are also in reasonable agreement with diesel fuel spray scaling laws and measurements. Fuel injection and combustion processes are highly relevant to air and terrestrial chemical propulsion applications of interest to the Army.