The advantages of homogeneous combustion in internal combustion (I.C.) engines are well known and many research groups all over the world are working on its practical realization. Recently, a new combustion concept that fulfils all requirements to perform homogeneous combustion in I.C. engines using the Porous Medium Combustion Engine, called “PM-engine”. This is an I.C. engine with the following processes realized in a porous medium - internal heat recuperation, fuel injection and vaporization, mixing with air, homogenization, 3D-thermal self-ignition followed by a homogeneous combustion.
The main features of the PM-engine are the following: 1)Very low emissions level due to homogeneous combustion and controlled temperature in the PM-combustion zone 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.
The main aim of this contribution is to present the better homogeneous combustion in IC engines which makes the IC engine very efficient. As a first step in the direction, homogeneous combustion, porous medium technology and its principle ,P.M. engine with open chamber and closed chamber is presented. Secondly, thermodynamics, practical realization, first results and potential of P.M engine is carried out. The paper concludes with the necessity of P.M. engine rather than diesel engine.
The nature of the mixture formation and the followed combustion processes realized in a direct injection engines, indicate a lack of mechanisms for controlling the mixture formation and homogenization of the sequence of process and, hence, do not allow homogeneous combustion. The entire homogenization, however, is necessary for significant reductions of engine emissions in primary combustion [1,2]. There is also no doubt today, that the future trend of development means homogenizations of the combustion process with a goal to develop such combustion systems that could operate under part to full loads with a homogeneous combustion. It has not only been studied theoretically but has been technically realized.
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: Homogenisation of charge. Ignition conditions. Combustion process and temperature field. Four different ignition techniques may be selected: Local ignition Thermal self-ignition (e.g. compression ignition). Controlled auto-ignition , 3D-thermal PM-self-ignition .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. 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. Let us consider four possible combustion modes of a homogeneous charge.