A NEW CONCEPT OF I.C. ENGINE WITH HOMOGENOUS COMBUSTION IN POROUS MEDIUM

                                                Abstract

                                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 efficiency. 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,. We 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 porous-medium (PM) combustion technology previously developed in the 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 efficiency 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. Verification 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.

                                                     Introduction

                        Gradually came the days when man started imagining huge & started striving for bringing his imagination to the day of light Today after having reached such heights of advancement we the human beings are still in thirst of technology indeed very desperately. One such field for current discussion and interest of brilliant brains is that how we developed such a engine which would give non-zero emission and as well as less fuel consumption to with stand under wild range of speed and load?  the answer to this question is homogeneous combustion in I.C. engine using porous medium Technology.

                        The process of mixture formation, ignition & combustion in conventional engine is not effective due to the lack of mechanisms for homogenous combustion process.

                        Two parameters will be required for future internal combustion engine i.e. non-zero emission level & low fuel consumption. These parameter is strongly dependant the process of mixture formation & combustion which are difficult to controlled in a conventional engine combustion system.                  

                        The question is remain unsolved is the method for realization of homogenous combustion in IC engine, specially if the variable engine operational conditions are considered.

                        So here porous medium concept is introduced in order to overcome above difficulty. PM utilize the special features of highly porous media to support and controlled the mixture formation and combustion process in IC engine.

                      Main requirements for future engine

                        Basic requirements for future clean internal combustion (I.C.) engine concern very low that is exhaust emissions level for both gaseous and particulate matter components under as low as possible fuel consumption. Internal combustion engine has to operate in a wide range of speeds and loads and should satisfy selected requirements under all operational conditions. For vehicle application, the following conditions are required for future engine:

                        Operation with a homogeneous stoichiometric charge for high power density  Operation with a homogeneous-lean charge for low specific fuel consumption

                        Realization of homogeneous combustion, for all mixture compositions for the lowest combustion emissions.

                        For significant reduction of specific fuel consumption and for a near-zero combustion emissions especially attractive would be realization of engine operating with a lean-homogeneous charge at part loads, assuming that the combustion process is homogeneous.                

                     HOMOGENEOUS COMBUSTION

                         Homogeneous combustion in an IC engine is defined as a process characterized by a 3D-ignition of the homogeneous charge with simultaneous-volumetric-combustion, hence, ensuring a homogeneous temperature field. According to the definition given above, three steps of the mixture formation and combustion may be selected that define the ability of a given combustion system to operate as a homogeneous combustion system

                        The PM has homogeneous surface temperature over the most of the PM-volume, higher than the ignition temperature. In this case the PM-volume defines the combustion chamber volume. Thermodynamically speaking, the porous medium is here characterized by a high heat capacity and by a large specific surface area. As a model, we could consider the 3D-structure of the porous medium as a large number of “hot spots” homogeneously distributed throughout the combustion chamber volume. Because of this feature a thermally controlled 3D-ignition can be achieved. Additionally, the porous medium controls the temperature level of the combustion chamber permitting the NOx level control almost independently of the engine load or of the (A/F) ratio

                                                                       

POROUS MEDIUM (PM) TECHNOLOGY

                        The porous medium technology for IC engines means here the utilization of specific features of a highly porous media for supporting and controlling the mixture formation and combustion processes in I.C. engines. The employed specific features of PM are directly related to a very effective heat transfer and very fast flame propagation within the PM. close view of a magnified 3D-structure of SiC ceramic foam is given in Figure

                                                                    

 Generally, the most important parameters of PM for application to engine combustion technology can be given as follows: heat capacity, specific surface area, heat transport properties, transparency for fluid flow, spray and flame propagation, pore sizes, pore density, pore structure, thermal resistance of the material, mechanical resistance and mechanical properties under heating and cooling conditions, PM material surface properties. For IC engine application, the thermal resistance of the porous medium is one of the most important parameter defining its applicability of a given material to combustion in engine. A view of the thermal test of SiC-reactors for engine application is shown in Fig.

                                                                                                                                       

New concept of mixture preparation for homogeneous combustion in engines using porous medium technology

                        Different R&D activities of the author using porous materials (highly porous 3D-structures) (see LSTM at University of Erlangen-Nürnberg and Promos GmbH in Erlangen) indicated unique features of this technology for mixture formation and combustion processes, also as applied to IC engines.

                   Energy recirculation in engine cycle in the form of hot burned gases recirculation or combustion energy:- This may significantly influence thermodynamic properties of the charge in the cylinder and may control its ignitability (activity). This energy recirculation may be performed under different pressures and temperatures during the engine cycle. Additionally, this heat recuperation may be used for controlling the combustion temperature level.

                   Fuel injection in PM-volume:- Especially unique features of liquid jet distribution and homogenization throughout the PM-volume

Fuel vaporization in PM-volume:- Cmbination of large heat capacity of the PM-material, large specific surface area with excellent heat transfer in PM volume make the liquid fuel vaporization very fast and complete.

                   Mixing and homogenization in PM-volume:- Unique features of the flow properties inside 3D-structures allow very effective mixing and homogenization in PM-volume.

                   3D-thermal-PM-ignition:- (if PM temperature is at least equal to ignition temperature under certain thermodynamic properties and mixture composition): there is a new kind of ignition, especially effective if the PM-volume creates the combustion chamber volume.

                   Heat release in PM-volume:- Under controlled combustion temperature that permits homogeneous combustion conditions almost independently of the engine load with possibility of controlling the combustion temperature level.

                                   PRINCIPLE OF THE PM-ENGINE

                                The PM-engine is here defined as an internal combustion engine with the following processes realized in a porous medium: internal heat recuperation, fuel injection, fuel vaporization, mixing with air, homogenization of charge, 3D-thermal self-ignition followed by a homogeneous combustion. PM-Engine may be classified with respect to the heat recuperation.

                        One of the most interesting features of PM-engine is its multifuel performance. Independently of the fuel used, this engine is a self-ignition engine characterized by its 3D-thermal ignition in porous medium. Finally, the PM-engine concept may be applied to both two- and four-stroke cycles. Owing to the differences in thermodynamic conditions, the PM-engine cycle has to be separately analyzed for closed and open chambers

PM-engine with closed chamber

                        Let us start an analysis of the PM-engine cycle with a case of closed PM chamber, i.e. engine with a periodic contact between working gas and PM-heat recuperator. At the end of the expansion stroke the valve controlling timing of the PM-chamber closes and fuel is injected in the PM-volume. This volume represents in thermodynamic sense a low pressure chamber and a long time is available for fuel injection and its vaporization in the PM. These processes may continue through exhaust, intake and compression strokes (see Fig.)

Near the TDC of compression the valve in PM-chamber opens and the compressed air flows from the cylinder into the hot PM volume containing fuel vaporous. Very fast mixing of the gaseous charge occurs and the resulting mixture is ignited in the whole PM volume. The resulting heat release process performs simultaneously in the whole PM volume. The three essential conditions for a homogeneous combustion are here fulfilled: homogenization of charge in PM-volume, 3D-thermal self-ignition in PM and volumetric combustion with a homogeneous temperature field in PM-volume. Additionally, the PM-material deals as a heat capacitor and, hence, controls the combustion temperature. 

                           Advantages of PM Technology

1)Very low emissions level due to homogeneous combustion and controlled           temperature in the PM-combustion zone (e.g. NOx between 100 and 300mg/kWh for the (A/F) ratio from 1 to 5;. CO can be reduced by several times; (almost) eliminated soot formation).

            2) Theoretically higher cycle efficiency due to similarity to the Carnot cycle.

            3) Very low combustion noise due to significantly reduced pressure peaks.

4) Nearly constant and homogeneous combustion temperature field in the PM-       volume.

            5) Very fast combustion.

            6) Multi-fuel system.

7) May operate with homogeneous charge: from stoichiometric to very lean mixture  compositions.

            8) Weak effect of in-cylinder flow structure, turbulence or spray atomization              

                                              Conclusion

                        There is no doubt that the future of internal combustion engine is related to the homogeneous combustion process in a wide range of engine operational conditions.

This technique shows potential for a near-zero combustion emissions (especially NOx and soot) as well as high cycle efficiency (low fuel consumption). Moreover, this kind of combustion system is less fuel specific. However, the realization of homogeneous combustion in IC engine under variable loads and speeds will probably require new concepts for mixture formation and controlled ignition conditions under different engine loads. The future engine operating with a homogeneous combustion process in a wide range of load and speed will require variable temperature history during the compression stroke, variable TDC compression temperature, completely vaporized fuel prior the ignition process, variable mixture composition (A/F ratio), variable reactivity (ignitability) of the charge, homogeneity of the charge, volumetric ignition conditions, variable heat capacity of the cylinder content. But the research has been carried out to make this process more & more economical.