10-04-2017, 08:06 PM
seminor ppt on new concept of homogeneous combustion in i c engines using the porous medium combustion engine
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.Homogeneous combustion in reciprocating internal combustion engines (ICE) may be realized not only in free gas (e.g.,
homogeneous mixture compression ignition HCCI) but also using porous medium (PM) combustion. This concept has
proven its advantages at steady-flame burners. It uses very porous grid of ceramic foam or metal wires heated by the
flame and stabilizing so lean mixture flame at temperatures that limits significantly NOx formation.
Its use in ICEs is not without problems due to heat transfer during compression, limited maximum temperature and
possibiliy of delayed heat supply to expansion. A simple tool for cycle parameter assessment using computerized T-s
diagram was developed and presented earlier. The preliminary results of it are promising.
As the further step, a CFD model has been developed for an evaluation of a PM combustion potential and its future
optimization. A simulation method based on a moveable-grid, Runge-Kutta finite volume (FV) 2.5-D model has
required the introduction of new source terms concerning spatially distributed heat transfer and momentum sink due to
drag in a PM domain. The geometry of a PM insert is characterized using a filament model of its matrix characterized
in 3 main directions. The temperature of a PM insert surface is solved using the Fourier equation with estimated
effective thermal conductivity of a solid phase. A combustion model uses momentum and specie sources near to a fuel
entry to a PM insert accompanied by very fast heat release for a part of fuel covered by oxygen available and complex
chemical kinetics.
The detailed FVM model has provided preliminary results as a base for sensitivity analysis, cycle optimization and
engine lay-out changes. Steep temperature gradients may occur in a PM domain due to a gradual transport of cylinder
charge into a PM and a compression or combustion of pre-heated gas. NOx formation might be limited only if high
temperature occurs in the zone of a rich mixture. Concerning efficiency, a premature heat supply to gas from a PM
during compression is disadvantageous as well as an intensive heat transfer during combustion. The model will be used
in a future optimization of the PM combustion process.