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 lowtemperature 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.

Macro-Cellular Silicon carbide Reactors for Nonstationary Combustion Under Piston Engine-Like Conditions

“…Realization of nonstationary flameless and clean combustion under pressure in porous structures includes a number of individual process such as high‐pressure fuel injection, fuel distribution in reactor volume, heat transfer, fuel vaporization, preignition reactions (cool‐ and blue‐flames), thermal ignition, and the combustion process itself 4,7,12,13 . A high‐temperature, high‐pressure, adiabatic, and constant‐volume combustion chamber was developed, which allows the examination of low‐ as well as high‐temperature oxidation behavior of the ligament structure specimens under conditions relevant for high‐pressure diesel injection 12,13 . A high‐pressure common‐rail diesel injection system with electronically controlled diesel injector was applied, which provides a multijet 4 .…”

“…The pressure and pressure gradient after diesel injection were measured as a function of time. Low‐temperature oxidation (cool‐ and blue‐flame reactions) as well as thermal auto‐ignition and high‐temperature oxidation (combustion) were analyzed 13 …”

Application of macro-cellular SiC reactor to diesel engine-like injection and combustion conditions

“…Application of a combustion porous reactor to engine allows realization of homogeneous and flameless combustion process characterized by a near-zero emissions level [1,2,9]. Internal heat recuperation in porous reactor may allow increase of engine-cycle efficiency resulting in reduction of CO 2 emissions and results in significantly lowered combustion temperature permitting nearly-zero NOx level.…”

“…For analysis of the reaction rate a slope of the reaction curve corresponding to the particular oxidation process is described by average pressure changes in time [bar/ms]. The heat release process in a macro-cellular reactor consists of steps similar to those defined for free volume combustion [8,9]. Just after starting of fuel injection process, the fuel partly vaporizes and the pressure changes to the negative range and is followed by lowtemperature oxidation (exothermic) reactions resulting in a positive change of pressure.…”

“…The former processes include Diesel-jet interaction with the highly porous structure described with reference to multi-jet splitting and fuel vaporization in a hot reactor [5][6][7]. Low-temperature oxidation processes include cool-and blue-flame reactions that occur just after injection begins during the ignition delay time period [8,9]. Thermal ignition and high-temperature oxidation (heat release) complete the investigated process.…”