Characterization of low- and high-temperature oxidation processes under non-premixed diesel-engine-like conditions

Abstract

Low- and high-temperature oxidation processes, including thermal auto-ignition under diesel-engine-like conditions (non-premixed mixtures), have been investigated. A special combustion chamber, characterized by constant volume and adiabatic conditions, has been used as an engine simulator. The investigated processes are very complex in nature, and depend significantly on the temperature and pressure. There are five characteristic regions of the process characterized by different delay times, reaction rates and number of recognizable oxidation reactions: region 1 corresponds to processes occurring at low initial pressures over a wide range of initial temperatures; region 2 corresponds to low initial temperatures over a wide range of initial pressures; region 3 corresponds to middle pressures and higher temperatures; region 4 corresponds to middle temperatures and higher pressures; and region 5 corresponds to high initial pressures and high temperatures. by analogy to a negative temperature coefficient (as discussed in the literature), a positive pressure coefficient has been introduced here. This indicates that in the selected range of pressures, the delay time of low-temperature oxidation processes is the shortest, and the rate of these reactions is the highest. Further increases in the pressure behind the positive pressure coefficient range increase the delay time and decrease the reaction rate. The positive pressure coefficient has been observed at lower temperatures (mostly corresponding to cool-flame reactions and transitions to blue flames). Generally, the ignition delay time reduces with increasing chamber temperature and pressure.