Ignition Characteristics of Diesel Fuel in a Constant Volume Bomb under Diesel-Like Conditions. Effect of the Operation Parameters

Abstract

A constant volume chamber system was used to characterize the ignition and combustion of a diesel fuel. Fuel is injected in the chamber through a standard diesel common rail injection system. Injection parameters and initial chamber conditions were varied: fuel injection pressure (600 to 1000 bar), injection duration (500 to 3000 μs), initial temperature (808 to 923 K), initial pressures (6 to 21 bar), and oxygen mole fractions (15 to 30% diluted in nitrogen). Multiple measurements confirmed the repeatability of the measurements. Most of the experiments showed a two-stage combustion process, especially at low chamber pressure and highly premixed conditions. This is characteristic of large paraffinic hydrocarbons such as those composing around two-thirds of commercial diesel fuels. Combustion pressure data from diesel fuel have shown a moderate effect of injection pressure and injection duration on the ignition delays, especially when compared to the effect of other operation parameters. A strong effect of initial pressure and temperature was also observed. Increasing the initial pressure leads to nonlinear decreases in the ignition delay, this effect being especially strong at low pressures. Further, an increase in the oxygen mole fraction advances the onset of ignition, this effect being more intense at the lowest oxygen mole fraction in the oxidant. Two separate regions with different temperature-dependence functions were detected, indicating two different fuel oxidation chemistries. Arrhenius-type correlations were obtained for both regions, including the most influential parameters, to predict the first- and second-stage ignition delays.