Autoignition study of ULSD#2 and FD9A diesel blends

Autoignition study of two well-characterized reference diesel fuels with similar cetane ratings but different compositional characteristics has been conducted using a heated rapid compression machine (RCM). The two diesel blends used in the current study were a commercial grade ultra-low-sulfur diesel (ULSD) #2 reference fuel, ULSD#2, and Fuels for Advanced Combustion Engines (FACE) research diesel, FD9A. Ignition delay time measurements were conducted at compressed pressures of 10 bar, 15 bar, and 20 bar covering low-to-intermediate temperatures between 678 K and 938 K. In addition, experiments were carried out with diesel/O2/N2 mixtures at varying equivalence ratios of ϕ = 0.5, 0.69, and 1.02. Equivalence ratio was varied by changing the oxygen mole percentage while keeping the fuel mole percentage fixed at 0.514%. Therefore, the present ignition delay time measurements illustrate the effect of oxygen concentration on diesel autoignition. The experimental results showed that diesel blends with similar cetane ratings and different compositional makeups exhibited varying ignition propensities in different temperature regimes, thereby demonstrating the effect of molecular composition on autoignition characteristics. In particular, the difference in ignition propensities was observed at temperatures at which the low temperature branching reactions are active. Furthermore, the ignition delay time measurements from the current RCM study were found to complement well with the existing shock tube data in the literature, and hence this investigation provides additional experimental database of diesel blends needed for development and validation of diesel surrogate models.