At present, the emissions of internal combustion engines can only be improved by catalytic treatments of the exhaust gases. Such treatments, however, result in high costs and relatively low conversion eYciency. This suggests that a new combustion technique should be developed to yield improved primary combustion processes inside the engine with drastically reduced exhaust gas emissions. In this paper, the authors report on such a technique that is applicable to direct injection, internal combustion engines, either diesel or gasoline fuelled. This technique is based on the porousmedium (PM ) combustion technology previously developed in the authors' laboratory for steady state household and industrial combustion processes.It is shown that the PM combustion technique can be applied to internal combustion engines, i.e. it is demonstrated that improvements obtained in steady state combustion are also realizable in unsteady combustion processes. Theoretical considerations are presented for internal combustion engines, indicating that an overall improvement in thermal eYciency can be achieved for the PM engine. This is explained and the general performance of the new PM engine is demonstrated for a single-cylinder, air-cooled, direct injection diesel engine. Veri cation experiments are described that were carried out as part of the present study. Initial results are presented and an outlook is given on how the present developments might continue in the future.

Strut lattice structures of reaction‐bonded silicon infiltrated silicon carbide ceramics (RB‐SiSiC) for air–fuel mixture formation and for nonstationary lean‐burn under pressure applications were fabricated. The lattice design with a high porosity >80% was shaped by indirect three‐dimensional printing. It was shown that pre‐ignition processes in the porous reactor are much faster than in a free combustion, especially at lower temperatures. Interaction of high velocity diesel jets with cylindrical strut ligaments of the SiSiC lattice structure offers a new possibility for quick and efficient fuel distribution (multi‐jet splitting) in space.

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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.

The paper summarizes the knowledge concerning porous media combustion techniques as applied in engines. One of most important reasons of this review is to introduce this still not well known technology to researchers doing with internal combustion engine processes, thermal engines, reactor thermodynamics, combustion, and material science. The paper gives an overview of possible applications of a highly porous open cell structures to in-cylinder processes. This application means utilization of unique features of porous media for supporting engine processes, especially fuel distribution in space, vaporization, mixing with air, heat recuperation, ignition and combustion. There are three ways for applying porous medium technology to engines: support of individual processes, support of homogeneous combustion process (catalytic and non-catalytic) with temperature control, and utilization of the porous structure as a heat capacitor only. In the first type of application, the porous structure may be utilized for fuel vaporization and improved fuel distribution in space making the mixture more homogeneous in the combustion chamber. Extension of these processes to mixture formation and ignition inside a combustion reactor allows the realization of a homogeneous and a nearly zero emissions level combustion characterized by a homogeneous temperature field at reduced temperature level.