Characteristics of Flameless Combustion in 3D Highly Porous Reactors under Diesel Injection Conditions

Abstract

The heat release process in a free volume combustion chamber and in porous reactors has been analyzed under Diesel engine-like conditions. The process has been investigated in a wide range of initial pressures and temperatures simulating engine conditions at the moment when fuel injection starts. The resulting pressure history in both porous reactors and in free volumes significantly depends on the initial pressure and temperature. At lower initial temperatures, the process in porous reactors is accelerated. Combustion in a porous reactor is characterized by heat accumulation in the solid phase of the porous structure and results in reduced pressure peaks and lowered combustion temperature. This depends on reactor heat capacity, pore density, specific surface area, pore structure, and heat transport properties. Characteristic modes of a heat release process in a two-dimensional field of initial pressure and temperature have been selected. There are three characteristic regions represented by a single- and multistep oxidation process (with two or three slopes in the reaction curve) and characteristic delay time distribution has been selected in five characteristic ranges. There is a clear qualitative similarity of characteristic modes of the heat release process in a free volume and in porous reactors. A quantitative influence of porous reactor features (heat capacity, pore density, pore structure, specific surface area, and fuel distribution in the reactor volume) has been clearly indicated.

Characteristics of the heat release in three-dimensional, highly porous reactors under engine-like conditions in comparison with free diesel injection conditions

“…By analogy, different configurations and thermal engines with heat recuperation in the porous structure have been previously considered. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The influence of the initial temperature on the heat release process and the corresponding temperature history at a constant initial pressure (p IB = 18 bar), a constant mass of injected fuel and various initial temperatures (T PM = T IB ) is shown in Figure 14. Under these conditions, the resulting excess air ratio decreases with increasing initial temperature (l = f(T IB )).…”

“…These fields represent the distribution of the characteristic combustion modes. 7,10,12 There are three characteristic areas (regions) selected in the two-dimensional plots in Figure 16.…”