**10. Two applications of PM technology**

#### **10.1. Internal combustion engines**

548 Numerical Simulation – From Theory to Industry

porous tube and oscillation occurs in value of it.

**Figure 10.** Temperature of solid phase in cross section x = 0 after a) t = 10 s b) t = 50s c) t= 100 s

Figs. 11, 12 show results for distribution of temperature in center line of PM tube in both phase of PM (solid and fluid) for different times versus axial direction. Heat transport is related to thermal properties of the solid material and fluid property. Flame core transports heat to incoming methane-air mixture with conduction and radiation, that its temperature is 300 K. At time t = 10 s maximum temperature in gas phase is about 1700 K. After 10 s flame moves to right with constant speed and maximum temperature of about 1600 K. After this time equilibrium between conduction, convection and radiation, causes to no change in maximum value of combustion. At the end of the tube temperature in all cases is about 325 K. In solid phase due to preheating of inlet mixture, at t = 10 s in inlet solid phase temperature is about 1450 K, in t = 50 s and t = 100 s, upstream temperature is about 850 K and 580 K, respectively and this temperature finally reach to 300 K approximately. Fig. 13 shows distribution of methane mass fraction from 10 to 100 s. Inlet mass fraction of methane is 0.016. Decrease in mass fraction of methane shows location of flame front. Flame location after 10 s is in location 3.8 cm and its thickness is thickness of 4 cm, after 50 s, is about 1.6 cm with the thickness 4.3 cm, and after 100 s is about 3.3 cm with the thickness 2.4 cm. From this Fig. inferred in 50 s and 100 s after simulation variation in flame thickness is very low value and the CH4 is almost completely consumed in this zone. Fig. 14 shows mass fraction of CO2 value in axial direction. Carbon dioxide is produced during combustion and its mass fraction reaches to highest value in x = 2.4, 5.5, 7.1 cm respectively to 0.036, 0.035, 0.024 mass fraction after 10, 50 and 100 s from simulation. Fig. 15 shows mass fraction of CO value in axial direction. Carbon monoxide is produced during combustion with entering of mixture and as an intermediate species produced and consumes gradually in axial direction. CO concentration reaches its highest value near the flame front at x = 1.8, 4.1, 6 cm respectively after 10, 50 and 100 s and gradually decreases at x = 4.8, 7.2 and 9.1 cm to approximately zero. With completeness of combustion and it oxidizes slowly and converted to CO2, because of enough accessible oxygen for converting CO to CO2. Fig. 16 shows mass fraction of CH3 value in axial direction. Methyl concentration reaches its highest value in x = 1.4, 3.6, 9.2 cm respectively 10, 50 and 100 s after simulation. But after 100s due to fluid flow, it disperses in The major target for further development of the current IC engines is to reduce their harmful emissions to environment. The most important difficulty with existing IC engines that currently exists is non-homogeneity of mixture formation within the combustion chamber which is the cause heterogeneous heat release and high temperature gradient in combustion chamber which is the main source of excess emissions such as NOx, unburned hydrocarbons (HC), carbon monoxide (CO), soot and suspended particles. At present, the IC engine exhaust gas emission could be reduced by catalyst, but these are costly, sensitive to fuel and with low efficiency. Another strategy has been initiated to avoid the temperature gradient in IC engines that is using homogeneous charge compression ignition (HCCI)

**Figure 11.** Mean temperature distribution in gas phase of PM versus axial direction

**Figure 12.** Mean mass fraction of methane versus axial direction

Numerical Simulation of Combustion in Porous Media 551

**Figure 16.** Mass fraction of CH3 value versus axial direction

engines but there still exist some challenges including, higher HC and CO emissions and control of ignition time and rate of heat release under variable engine operating condition. In such engines, lean mixture with high amount of exhaust gas recycled (EGR), could be used that increases amount of CO and soot. Also by increasing the load of HCCI engine, NOx formation and fuel consumption increases. It means that low compression ratio should be used for these engines, while in reality, the compression ratio must be high enough that temperature near the end of compression process, lead to self-ignition of mixture with reasonable time delay. Therefore, these engines are suitable for low and medium loads and it better for high loads the engine can change mode of operation to compression ignition. Also direct fuel injection engines generally have some unresolved problems due to lack of homogeneity of mixture formation and combustion. Several other technologies have been used to reduce emissions in engines, such as electronically controlled high pressure fuel injection systems, variable valve timing, EGR but still in these methods still could not solve the problem completely under all engine operating conditions. Could there be any other homogeneous combustion in IC engines to meet all operational conditions (various load and speed)? The demand target may be possible with homogeneous mixture formation and a 3D-ignition of a homogeneous charge to prevent formation of flame front that lead to temperature gradient in the entire combustion chamber which is ensuring a homogeneous temperature field. In conventional direct injection engines mechanisms also there is a lack of homogenization of combustion process. PM-engine is defined as an engine with homogeneous combustion process. The following distinct process of PM-engine is realized in PM volume: energy recirculation in cycle, fuel injection in PM, fuel vaporization for liquid fuels, perfect mixing with air, homogeneity of charge, 3D-thermal self-ignition, and homogeneous combustion. PM-engine may be classified as heat recuperation timing in an engine as: Engine with periodic contact between PM and cylinder is called closed PMchamber and Engine with permanent contact between PM and cylinder which is called open

**Figure 13.** Mass fraction of methane versus axial direction

**Figure 14.** Mass fraction of Carbone dioxide versus axial direction

**Figure 15.** Mass fraction of CO versus axial direction

**Figure 16.** Mass fraction of CH3 value versus axial direction

**Figure 13.** Mass fraction of methane versus axial direction

**Figure 14.** Mass fraction of Carbone dioxide versus axial direction

**Figure 15.** Mass fraction of CO versus axial direction

engines but there still exist some challenges including, higher HC and CO emissions and control of ignition time and rate of heat release under variable engine operating condition. In such engines, lean mixture with high amount of exhaust gas recycled (EGR), could be used that increases amount of CO and soot. Also by increasing the load of HCCI engine, NOx formation and fuel consumption increases. It means that low compression ratio should be used for these engines, while in reality, the compression ratio must be high enough that temperature near the end of compression process, lead to self-ignition of mixture with reasonable time delay. Therefore, these engines are suitable for low and medium loads and it better for high loads the engine can change mode of operation to compression ignition. Also direct fuel injection engines generally have some unresolved problems due to lack of homogeneity of mixture formation and combustion. Several other technologies have been used to reduce emissions in engines, such as electronically controlled high pressure fuel injection systems, variable valve timing, EGR but still in these methods still could not solve the problem completely under all engine operating conditions. Could there be any other homogeneous combustion in IC engines to meet all operational conditions (various load and speed)? The demand target may be possible with homogeneous mixture formation and a 3D-ignition of a homogeneous charge to prevent formation of flame front that lead to temperature gradient in the entire combustion chamber which is ensuring a homogeneous temperature field. In conventional direct injection engines mechanisms also there is a lack of homogenization of combustion process. PM-engine is defined as an engine with homogeneous combustion process. The following distinct process of PM-engine is realized in PM volume: energy recirculation in cycle, fuel injection in PM, fuel vaporization for liquid fuels, perfect mixing with air, homogeneity of charge, 3D-thermal self-ignition, and homogeneous combustion. PM-engine may be classified as heat recuperation timing in an engine as: Engine with periodic contact between PM and cylinder is called closed PMchamber and Engine with permanent contact between PM and cylinder which is called open

PM-chamber. In this paper an open PM-chamber is studied. Permanent contact between working gas and PM-volume is shown schematically in Fig. 17. The PM is placed in cylinder head. During the intake stroke there is a not much influence from PM-heat capacitor with in-cylinder air thermodynamic conditions. Also during early stages of compression stroke only a small amount of air is in contact with hot porous medium. The heat transfer process (non-isentropic compression) increases during compression, and at TDC the air penetration is cut to the PM volume. At final stages of compression stroke the fuel is injected into PM volume and with liquid fuels rapid fuel vaporization and mixing with air occurs in 3Dstructure of PM-volume. A 3D-thermal self-ignition in PM-volume together with a volumetric combustion is characterized by a homogeneous temperature distribution. Therefore, all essential conditions exist for having homogeneous combustion in the PM engine. The initial idea to use PM in IC engines was proposed by Weclas. Their investigation was performed in a single-cylinder air-cooled PM Diesel engine without any catalyst. A Silicon Carbide (SiC) PM was mounted in the cylinder head between the intake and exhaust valves and fuel was injected through the PM volume. The implementation has improved engine thermal efficiency, reduced emissions and noise in comparison to the base engine. The mean cylinder temperature was about 2200 K for base engine without having any PM. The temperature reduces to about 1500 K when PM is used which is significantly even lower during combustion.

Numerical Simulation of Combustion in Porous Media 553

Porous regenerator as shown in Fig. 18 has the potential to improve fuel–air mixing and combustion. The porous insert is attached to a rod and moves in the cylinder, synchronized, but out of phase with the piston. During the regenerative heating stroke, the regenerator remains just beneath the cylinder head for most of the period and moves down to the piston (as it approaches the TDC position). During the regenerative cooling stroke, the regenerator moves up and remains in the original position until the next regenerative heating stroke. Following the combustion and expansion, the products of combustion (exhaust gases) retain an appreciable sensible heat. During the regenerative cooling stroke, the hot exhaust gas flows through the insert and stores part of this sensible heat by surface-convection heat transfer in the porous insert (with large surface area). For the proposed engine, a thermal efficiency of 53% was claimed, compared to 43% of the conventional Diesel engines. Macek and Polasek presented a finite volume based simulation of porous medium combustion for

**Figure 18.** Sequence of motion of the regenerator and physical of fuel injection and air blowing during

The application of a highly porous open cell structures to internal combustion engines for supporting mixture formation and combustion processes was introduced by Weclas. Novel concepts for internal combustion engines based on the application of PMC technology were presented and discussed. His study proved that gas flow, fuel injection and its spatial distribution, vaporization, mixture homogenization; ignition and combustion could be controlled or positively influenced with the use of porous media reactors. The key features of the highly porous medium for supporting the mixture formation, ignition and combustion in IC engines are illustrated in Fig. 19. A study on the use of PMC in direct injection (diesel or gasoline) IC engines was performed by Durst and Weclas. Polasek and Macek presented the simulation of properties of IC engine equipped with a PM to homogenize and stabilize the combustion of CI engines. The purpose of the PIM matrix use was to ensure reliable ignition of lean mixture and to limit maximum in-cylinder

reducing emissions from reciprocating internal combustion engines.

the regenerative heating stroke (Park and Kaviany, 2002)

temperature during combustion.

**Figure 17.** A permanent contact PM-engine in operation (Weclas, 2001)

The effect of SiC PM as a regenerator was simulated by Park and Kaviany. In their study a PM disk like shape was connected to a rod and was moving near piston within the cylinder of diesel engine. A two-zone thermodynamic model with single-step reaction for methaneair combustion is carried out. It is shown that the maximum cylinder pressure during combustion increases and more work is done during a full cycle, also engine efficiency increases, but due to high temperature of PM that its temperature is higher than adiabatic flame temperature of methane-air, the production of NOx is rather higher while as its soot decreases. Macek and Polasek simulated and studied a PM engine with methane and hydrogen respectively and its potential for practical application was shown. Weclas and Faltermeier investigated penetration of liquid-fuel injection into a PM (as arrangement of cylinders which were mounted on a flat plate with different diameters). The arrangement was changed to obtain optimum geometry which produces the best mixture formation.

Porous regenerator as shown in Fig. 18 has the potential to improve fuel–air mixing and combustion. The porous insert is attached to a rod and moves in the cylinder, synchronized, but out of phase with the piston. During the regenerative heating stroke, the regenerator remains just beneath the cylinder head for most of the period and moves down to the piston (as it approaches the TDC position). During the regenerative cooling stroke, the regenerator moves up and remains in the original position until the next regenerative heating stroke. Following the combustion and expansion, the products of combustion (exhaust gases) retain an appreciable sensible heat. During the regenerative cooling stroke, the hot exhaust gas flows through the insert and stores part of this sensible heat by surface-convection heat transfer in the porous insert (with large surface area). For the proposed engine, a thermal efficiency of 53% was claimed, compared to 43% of the conventional Diesel engines. Macek and Polasek presented a finite volume based simulation of porous medium combustion for reducing emissions from reciprocating internal combustion engines.

552 Numerical Simulation – From Theory to Industry

during combustion.

**Figure 17.** A permanent contact PM-engine in operation (Weclas, 2001)

The effect of SiC PM as a regenerator was simulated by Park and Kaviany. In their study a PM disk like shape was connected to a rod and was moving near piston within the cylinder of diesel engine. A two-zone thermodynamic model with single-step reaction for methaneair combustion is carried out. It is shown that the maximum cylinder pressure during combustion increases and more work is done during a full cycle, also engine efficiency increases, but due to high temperature of PM that its temperature is higher than adiabatic flame temperature of methane-air, the production of NOx is rather higher while as its soot decreases. Macek and Polasek simulated and studied a PM engine with methane and hydrogen respectively and its potential for practical application was shown. Weclas and Faltermeier investigated penetration of liquid-fuel injection into a PM (as arrangement of cylinders which were mounted on a flat plate with different diameters). The arrangement was changed to obtain optimum geometry which produces the best mixture formation.

PM-chamber. In this paper an open PM-chamber is studied. Permanent contact between working gas and PM-volume is shown schematically in Fig. 17. The PM is placed in cylinder head. During the intake stroke there is a not much influence from PM-heat capacitor with in-cylinder air thermodynamic conditions. Also during early stages of compression stroke only a small amount of air is in contact with hot porous medium. The heat transfer process (non-isentropic compression) increases during compression, and at TDC the air penetration is cut to the PM volume. At final stages of compression stroke the fuel is injected into PM volume and with liquid fuels rapid fuel vaporization and mixing with air occurs in 3Dstructure of PM-volume. A 3D-thermal self-ignition in PM-volume together with a volumetric combustion is characterized by a homogeneous temperature distribution. Therefore, all essential conditions exist for having homogeneous combustion in the PM engine. The initial idea to use PM in IC engines was proposed by Weclas. Their investigation was performed in a single-cylinder air-cooled PM Diesel engine without any catalyst. A Silicon Carbide (SiC) PM was mounted in the cylinder head between the intake and exhaust valves and fuel was injected through the PM volume. The implementation has improved engine thermal efficiency, reduced emissions and noise in comparison to the base engine. The mean cylinder temperature was about 2200 K for base engine without having any PM. The temperature reduces to about 1500 K when PM is used which is significantly even lower

**Figure 18.** Sequence of motion of the regenerator and physical of fuel injection and air blowing during the regenerative heating stroke (Park and Kaviany, 2002)

The application of a highly porous open cell structures to internal combustion engines for supporting mixture formation and combustion processes was introduced by Weclas. Novel concepts for internal combustion engines based on the application of PMC technology were presented and discussed. His study proved that gas flow, fuel injection and its spatial distribution, vaporization, mixture homogenization; ignition and combustion could be controlled or positively influenced with the use of porous media reactors. The key features of the highly porous medium for supporting the mixture formation, ignition and combustion in IC engines are illustrated in Fig. 19. A study on the use of PMC in direct injection (diesel or gasoline) IC engines was performed by Durst and Weclas. Polasek and Macek presented the simulation of properties of IC engine equipped with a PM to homogenize and stabilize the combustion of CI engines. The purpose of the PIM matrix use was to ensure reliable ignition of lean mixture and to limit maximum in-cylinder temperature during combustion.

Numerical Simulation of Combustion in Porous Media 555

Weclas, M., (2001). Potential of porous medium combustion technology as applied to

Trim, D., Durst, F., (1996). Combustion in porous medium – advances and application,

Howell, J. R., Hall, M. J., Ellzey, J. L., (1996). Combustion of hydrocarbon fuels within porous inert media, *Progress in Energy and Combustion Science,* Vol. 22, Issue. 2, pp. 121–

Kamal, M. M., Mohamad, A. A., (2006). Combustion in porous media, a review, *Journal of* 

Innocentini, M. D. M., Tanabe, E. H., Aguiar, M. L., Courty, J. R., (2012). Filteration of gases in high pressure : Permeation behavior of fiber-based media used for natural gas

Monmont, F. B. J., Van-Odyck, D. E. A., Nikiforakis, N. (2012). Experimental and theoretical

Loukou, A., Frenzel, I., Klein, J., Trimis, D., (2012). Experimental study of hydrogen production and soot particulate matter emissions from methane rich-combustion in

Wood, S., Harris, A. T., (2008). Porous burners for lean-burn applications. *Progress in Energy* 

Mujeebu, A. A., Abdullah, M. Z., Mohammad, A. A., Bakar, M. Z. A., (2010). Trend in Modeling of Porous Media Combustion, *J. Progress in Energy and Combustion Science,*

Kamal, M. M., Mohamad, A. A., (2006). Development of a cylindrical porous-medium

Kamal, M. M., Mohamad, A. A., (2007). Investigation of liquid fuel combustion in a cross flow burner. Proceedings of the Institution of Mechanical Engineers: Part A – *Journal of* 

Rortveit, G. J., Stromman, A. H., Ditaranto, M., Hustad, J. E., (2005). Emissions from combustion of H2 and CH4 mixtures in catalytic burners for small-scale heat and power applications, *Clean Air: International Journal on Energy for a Clean Environment,* Vol. 6,

Contarin, F., Saveliev, A.V., Fridman, A. A., Kennedy, L. A., (2002). A reciprocal flow filtration combustor with embedded heat exchangers: numerical study, *International* 

Bingue, J. P., Saveliev, A.V., Fridman, A. A., Kennedy, L. A., (2002). Hydrogen production in ultra-rich filtration combustion of methane and hydrogen sulfide. *International Journal of* 

Bingue, J. P., Saveliev, A.V., Kennedy, L. A., (2004). Optimization of hydrogen production by filtration combustion of methane by oxygen enrichment and depletion. *International* 

Slimane, R. B., Lau, F. S., Khinkis, M., Bingue, J. P., Saveliev, A. V., Kennedy, L. A., (2004). Conversion of hydrogen sulfide to hydrogen by super adiabatic partial oxidation:

of the combustion of n-tridecane in porous media, *J. Fuel*, Vol. 93, pp. 28-36.

internal combustion engine, *MECA/AECC*, Nurnberg, Germany.

cleaning, *J. Chemical Engineering Science*, Vol. 74, pp. 38-48.

inert porous media, *Int. J. Hydrogen Energy*, Article in press.

burner*. Journal of Porous Media,* Vol. 9, Issue. 5, pp. 469–481.

*Journal of Heat and Mass Transfer,* Vol. 46, pp. 949–961.

*Hydrogen Energy,* Vol. 27, Issue. 6, pp. 643–649.

*Journal of Hydrogen Energy,* Vol. 29, pp. 1365–1370.

*and Combustion Science,* Vol. 34, pp. 667–684.

*Power and Energy,* 221, pp. 371–385.

*Combustion Sci. and Tech*., Vol 121, pp. 153-168.

*Power and Energy,* Vol. 5,pp. 487–508.

145.

Vol. 2, pp. 1-24.

Issue. 2, pp. 187–194.

**Figure 19.** Main feature of porous structure to be utilized to support engine process (Durst and Weclas, 2001)
