Numerička analiaza izgaranja smjese metan –vodik u cilindru za različita vremena bacanja iskre

In this study, numerical simulations of combustion characteristics using pure methane and 70 % CH4-30 % H2 blends were investigated in a spark ignition engine. The numerical calculations were performed using the finite volume CFD code FLUENT with standard k-ε model using the compression ratio and the engine speed are 10 and 2000 rpm respectively. Excess air ratios were selected as 1, 1.2 and 1.4. The spark timings were started at 45, 30 and 15 degree crank angle (CA) before top dead center (BTDC). The results of the combustion process were investigated as a function of crank angle. The maximum cylinder pressures and temperatures were obtained with 70 % CH4-30 % H2 mixture. It is observed that peak pressure values are decreased when the excess air ratio increased.U ovom se radu numerički simuliraju karakteristike izgaranja čistog metana i smjese 70 % CH4 i 30 % H2 kod motora paljenih sa svjećicom. Numerički proračuni su napravljeni koristeći kontrolni volumen CFD, kod FLUENT, sa standardnim k – ε modelom koristeći kompresijski omjer i brzinu motora 10 i 2000 min-1. Odabrani faktori pretička zraka su 1, 1.2 I 1.4. Vrijeme početka paljenja iskrom odgovaralo je 45, 30 i 15 stupnjeva koljenastog vratila prije gornje mrtve točke. Reultati procesa izgaranja su istraživani u ovisnosti o kutu pretpaljenja. Utvrđeni su maksimalni tlakovi u cilindru za smjesu 70 % CH4 i 30 % H2. Uočeno je da se smanjuju vrijednosti maksimalnog tlaka s povećavanjem faktora pretička zraka

Alternative Fuels for Internal Combustion Engines

Researchers have studied on alternative fuels that can be used with gasoline and diesel fuels. Alternative fuels such as hydrogen, acetylene, natural gas, ethanol and biofuels also uses in internal combustion engines. Hydrogen in the gas phase is about 14 times lighter than the air. Moreover, it is the cleanest fuel in the world. On the other hand because of its high ignition limit (4–75%), low ignition energy, needs special design to use as pure hydrogen in internal combustion engines. It is proved that hydrogen improves the combustion, emissions and performance, when is added as 20% to fuels. Natural gas is generally consisting of methane (85–96%) and it can be used in both petrol and diesel engines. Ethanol can be used as pure fuel or mixed with different fuels in internal combustion engines. In this section, the effects of natural gas, hydrogen, natural gas + hydrogen (HCNG), ethanol, ethanol + gasoline, ethanol + hydrogen, acetylene, acetylene + gasoline mixtures on engine performance and emissions have been examined

Heat transfers and pressure drops for porous-ring turbulators in a circular pipe

A numerical heat-transfer and pressure-drop analysis is presented for porous rings inserted in a pipe at a distance L apart. A constant heat-flux is applied to the outer surface of the pipe. Numerical calculations are conducted with the Fluent 6.1.22 code, using the shear-stress transport (SST) k-omega model. Air is the fluid. The heat-transfer increase is analyzed for Reynolds numbers from 3 x 10(3) to 45 x 10(3). The porous-ring height is taken as H = 1 or 2 mm. The distance between two porous rings is 0.5D, D or 2D where D is the inside diameter of the pipe. An increase in L/D caused a decrease in heat-transfer. High Nusselt numbers were obtained when H/D and L/D ratios were 0.4 and 0.5, respectively, for a Reynold number of 45,000. The maximum Nusselt number occurred when L/D = 1 if H/D is selected as 0.2. (C) 2005 Elsevier Ltd. All rights reserved

Neutronic analysis of Lithium Hydride (LiH) material in a (D, T) driven hybrid blanket

In this study, neutronic performance of Lithium Hydride (LiH) material is analyzed in a D-T driven hybrid blanket cooled by flibe (Li2BeF4). The hybrid blanket is fuelled by UO2 from LWR fuel rod, LWR spent fuel rods and CANDU spent fuel rods. Energy production, tritium breeding, neutron leakage and fissile fuel breeding are considered. Volume fractions are selected as 1, 2, 3, 4 and 5. LiH thickness is increased from 0 to 80 cm. The number of rows is selected as 10 to 20. When the volume fractions increase, TBR values decrease. When the LiH thickness reaches 50 cm, TBR values reach the point of saturation. At this thickness, TBR values of Model-II (P. 4) are higher than those of Model-I (P. 4). The M energy multiplication factor has nearly the same tendency in both models. Neutron leakage values of Model-II (for DRLiH=50 cm) are lower than that Model-I. Although the fissile fuel breeding rate values of Model-I and Model-II are almost the same, the values of Model-I are a little higher than Model-II. Therefore, it is concluded that LiH material is,suitable for using, when neutronic behaviour is considered

Heat transfers and pressure drops for porous-ring turbulators in a circular pipe

A numerical heat-transfer and pressure-drop analysis is presented for porous rings inserted in a pipe at a distance L apart. A constant heat-flux is applied to the outer surface of the pipe. Numerical calculations are conducted with the Fluent 6.1.22 code, using the shear-stress transport (SST) k-[omega] model. Air is the fluid. The heat-transfer increase is analyzed for Reynolds numbers from 3 x 103 to 45 x 103. The porous-ring height is taken as H = 1 or 2 mm. The distance between two porous rings is 0.5D, D or 2D where D is the inside diameter of the pipe. An increase in L/D caused a decrease in heat-transfer. High Nusselt numbers were obtained when H/D and L/D ratios were 0.4 and 0.5, respectively, for a Reynold number of 45,000. The maximum Nusselt number occurred when L/D = 1 if H/D is selected as 0.2.Heat-transfer enhancement Porous ring Turbulent flow

Neutronic and thermal analysis of a peaceful nuclear explosion reactor

Thermal and neutronic behavior of a peaceful nuclear explosion reactor (PACER) producing approximate to1.2 GWe electrical-power from fusion explosions in a cylindrical explosion chamber (radius = 30 m, height = 75 m) are analyzed. For determination of flibe mass (m) required for safe operation temperatures and pressures with enough tritium breeding ratio (TBR) and high M (fusion energy absorption ratio), neutronic calculations are carried out for different coolant zone positions (DR) and coolant zone thicknesses (DRc) Inlet pressure and temperatures (T-in) of flibe are 1 atm, and 823 and 1540 K

NUMERICAL INVESTIGATION OF THE EFFECT OF FINNED OBSTACLE ON HEAT TRANSFER CHARACTERISTICS IN A RECTANGULAR CHANNEL

Nowadays, with the development of technology and science, heat transfer holds an important place in engineering applications. In industrial areas, heat increases give rise to overheating, causing system errors. Passive techniques are frequently used to prevent from such disruptions. In this work, fins which are passive techniques which provide heat transfer development with high efficiency and low cost were investigated. To improve heat transfer, finned structures should be well optimized. On the other hand, the designer can prevent mixing the incoming air with the heated air with a bad design, which may cause a negative effect rather than improve heat transfer. In this work, in contrast to previous works that is smooth tube and 0 degree rectangular finned tube, four fin structures were designed and flow and heat-transfer characteristics numerically analyzed. These are crescent finned tube, 20 degree symmetrical imperforated rectangular finned tube, 20 degree asymmetrical imperforated rectangular finned tube and 20 degree symmetrical perforated rectangular finned tube banks with six rows. In this investigation, the geometric parameters were not changed and their effects on flow and heat transfer properties in different Reynolds numbers on these models were examined. The results indicate that the symmetrical structure has better heat transferability and higher friction loss compared to the asymmetrical structure and the perforated fin is higher than imperforated fin but the overall performance is not always superior. Therefore, both symmetrical and perforated finned tube is designed and analyzed with the highest heat transfer potential, it is seen that in terms of heat transferability this model is better than other designs