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.
Highlights
Future internal combustion engines are to feature a clean combustion process
Heat release processes in porous reactors have been analyzed under Diesel engine-like conditions as simulated in a special combustion chamber with a common-rail Diesel injection system
The fuel was directly injected into the combustion chamber, and the processes of mixture formation in porous reactors and in free volume chambers have turned out to be different
Summary
Future internal combustion engines are to feature a clean combustion process. Clean process means a homogeneous combustion requiring simultaneous (volumetric) ignition of a homogeneous (preferably premixed) charge. Owing to these significant different thermodynamic conditions, one of the critical questions concerns timescale and the rate of oxidation processes in porous reactors and their applicability to internal combustion engine cycle conditions These aspects are discussed in the present paper, and the attention is paid to particular processes of mixture formation and combustion realized in a porous reactor volume. The focus of the present paper is to investigate the basic process behavior for typical engine variable conditions such as pressure and temperature at the moment of fuel injection, and for different reactor structures and architectures This is clear to the authors that it is still impossible to quantify the process data in detail with porous reactor structure, its porosity, heat capacity, specific surface area, and so forth. Along the direct fuel injection into reactor volume, spray interaction with structure wall junctions and heat transfer from the reactor to fuel for its vaporization are very complex and very sensitive to any changes in reactor parameters and remain still not well recognized or understood [13]
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