  The need for improved engine efficiencies has motivated the development of
high-pressure combustion systems, in which operating conditions achieve and
exceed critical conditions. Associated with these conditions are strong
variations in thermo-transport properties as the fluid undergoes phase
transition, and two-stage ignition with low-temperature combustion. Accurately
simulating these physical phenomena at real-fluid environments remains a
challenge. By addressing this issue, a high-fidelity LES-modeling framework is
developed to conduct simulations of transcritical fuel spray mixing and
auto-ignition at high-pressure conditions. The simulation is based on a
recently developed diffused interface method that solves the compressible
multi-species conservation equations along with a Peng-Robinson state equation
and real-fluid transport properties. LES analysis is performed for non-reacting
and reacting spray conditions targeting the ECN Spray A configuration at
chamber conditions with a pressure of 60 bar and temperatures between 900 K and
1200 K to investigate effects of the real-fluid environment and low-temperature
chemistry. Comparisons with measurements in terms of global spray parameters
(i.e., liquid and vapor penetration lengths) are shown to be in good agreement.
Analysis of the mixture fraction distributions in the dispersed spray region
demonstrates the accuracy in modelling the turbulent mixing behavior. Good
agreement of the ignition delay time and the lift-off length is obtained from
simulation results at different ambient temperature conditions and the
formation of intermediate species is captured by the simulations, indicating
that the presented numerical framework adequately reproduces the corresponding
low- and high-temperature ignition processes under high-pressure conditions,
which are relevant to realistic diesel-fuel injection systems.
