Experimental study on stoichiometric laminar flame velocities and Markstein lengths of methane and PRF95 dual fuels

Natural gas is one of the most promising alternative fuels. The main constituent of natural gas is methane. The slow burning velocity of methane poses significant challenges for its utilization in future energy efficient combustion applications. Methane-gasoline dual fuelling has the potential to improve methane’s combustion. The fundamental combustion characteristics of a methane-gasoline Dual Fuel (DF) blend needs further investigation. In the current experimental study, the relationship between laminar flame velocity and Markstein length, with the ratio of gas to liquid in a DF blend has been investigated using spherical flames in a constant volume combustion vessel. A binary blend of primary reference fuels (PRF95) was used as the liquid fuel. Methane was added to PRF95 in three different energy ratios 25%, 50% and 75%. Values of the stoichiometric laminar flame velocities and Markstein lengths are measured at pressures of 2.5, 5, 10 Bar and a temperature of 373 K. It has been found that with a 25% increase in the DF ratio, the Markstein length is reduced by 15%, 21%, 32% at a pressure of 2.5, 5 and 10 Bar respectively whereas at the same pressures the laminar flame velocity is reduced by 2%, 3% and 5%. The flame evolution at the early stages of combustion is found to be faster with an increase in the DF ratio, and gradually as the flame develops it becomes slower

Experimental investigation on the Laminar burning velocities and Markstein lengths of methane and PRF95 dual fuels

© 2016 American Chemical Society.Natural gas is a promising alternative fuel. The main constituent of natural gas is methane. The slow burning velocity of methane poses significant challenges for its utilization in future energy efficient combustion applications. The effects of methane addition to PRF95 on the fundamental combustion parameters, laminar burning velocity (Su0) and Markstein length (Lb), were experimentally investigated in a cylindrical combustion vessel at equivalence ratios of 0.8, 1, and 1.2, initial pressures of 2.5, 5, and 10 bar, and a constant temperature of 373 K. Methane was added to PRF95 in three different energy ratios 25%, 50%, and 75%. Spherically expanding flames were used to derive the flow-corrected flame velocities, from which the corresponding Lb and Su0 were obtained. The flame velocities were corrected for the motion of burned gas induced by the cylindrical confinement. It has been found that at stoichiometric conditions there is a linear decrease in Lb and Su0 with the dual fuel (DF) ratio in all investigated pressures. At rich conditions, all DFs resulted in having lower Su0 as compared to methane and to a larger extent PRF95. The values of Lb for all DFs were lower than methane and comparable to those of PRF95. At lean conditions, the values of Lb for all DFs are biased toward those of methane whereas the values of Su0 are found to be higher than those of PRF95 at pressures of 2.5 and 5 bar. At 10 bar both Lb and Su0 reduce with DF ratio although Su0 of all DFs converge to that of PRF95. The findings of the current study indicate a distinct synergy in the utilization of dual fueling in future lean burn energy efficient combustion applications

Experimental study on the burning rate of Methane and PRF95 dual fuels

Natural gas as an alternative fuel offers the potential of clean combustion and emits relatively low CO2 emissions. The main constitute of natural gas is methane. Historically, the slow burning speed of methane has been a major concern for automotive applications. Literature on experimental methane–gasoline Dual Fuel (DF) studies on research engines showed that the DF strategy is improving methane combustion, leading to an enhanced initial establishment of burning speed even compared to that of gasoline. The mechanism of such an effect remains unclear. In the present study, pure methane (representing natural gas) and PRF95 (representing gasoline) were supplied to a constant volume combustion vessel to produce a DF air mixture. Methane was added to PRF95 in three different energy ratios 25%, 50% and 75%. Experiments have been conducted at equivalence ratios of 0.8, 1, 1.2, initial pressures of 2.5, 5 and 10 bar and a temperature of 373K. At stoichiometric conditions, experiments in an SI engine have been also performed. It has been found that methane and all DFs have their fastest burning rate at stoichiometric conditions whereas PRF95 at rich conditions (Φ=1.2). At lean conditions (Φ=0.8), all DFs resulted in faster combustion than PRF95, whereas methane is the slowest of all. At rich conditions, DF75 and DF50 are slower than methane. The transition mechanism between the constant volume combustion experiments and those in the engine environment resulted in a larger increase in the burning speed of methane and all DFs in comparison to that of the liquid fuel

Phase-field model for grain boundary grooving in multi-component thin films

Polycrystalline thin films can be unstable with respect to island formation (agglomeration) through grooving where grain boundaries intersect the free surface and/or thin film-substrate interface. We develop a phase-field model to study the evolution of the phases, composition, microstructure and morphology of such thin films. The phase-field model is quite general, describing compounds and solid solution alloys with sufficient freedom to choose solubilities, grain boundary and interface energies, and heats of segregation to all interfaces. We present analytical results which describe the interface profiles, with and without segregation, and confirm them using numerical simulations. We demonstrate that the present model accurately reproduces the theoretical grain boundary groove angles both at and far from equilibrium. As an example, we apply the phase-field model to the special case of a Ni(Pt)Si (Ni/Pt silicide) thin film on an initially flat silicon substrate.Comment: 12 pages, 5 figures, submitted to Modelling Simulation Mater. Sci. En

Experimental Investigation on the Laminar Burning Velocities and Markstein Lengths of Methane and PRF95 Dual Fuels

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Energy and Fuels, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.energyfuels.6b00644© 2016 American Chemical Society.Natural gas is a promising alternative fuel. The main constituent of natural gas is methane. The slow burning velocity of methane poses significant challenges for its utilization in future energy efficient combustion applications. The effects of methane addition to PRF95 on the fundamental combustion parameters, laminar burning velocity (Su0) and Markstein length (Lb), were experimentally investigated in a cylindrical combustion vessel at equivalence ratios of 0.8, 1, and 1.2, initial pressures of 2.5, 5, and 10 bar, and a constant temperature of 373 K. Methane was added to PRF95 in three different energy ratios 25%, 50%, and 75%. Spherically expanding flames were used to derive the flow-corrected flame velocities, from which the corresponding Lb and Su0 were obtained. The flame velocities were corrected for the motion of burned gas induced by the cylindrical confinement. It has been found that at stoichiometric conditions there is a linear decrease in Lb and Su0 with the dual fuel (DF) ratio in all investigated pressures. At rich conditions, all DFs resulted in having lower Su0 as compared to methane and to a larger extent PRF95. The values of Lb for all DFs were lower than methane and comparable to those of PRF95. At lean conditions, the values of Lb for all DFs are biased toward those of methane whereas the values of Su0 are found to be higher than those of PRF95 at pressures of 2.5 and 5 bar. At 10 bar both Lb and Su0 reduce with DF ratio although Su0 of all DFs converge to that of PRF95. The findings of the current study indicate a distinct synergy in the utilization of dual fueling in future lean burn energy efficient combustion applications

Turbulent flame propagation with pressure oscillation in the end gas region of confined combustion chamber equipped with different perforated plates

Experiments were conducted in a newly designed constant volume combustion chamber with a perforated plate by varying the initial conditions. Hydrogen-air mixtures were used and the turbulent flame, shock wave, and the processes of flame-shock interactions were tracked via high-speed Schlieren photography. The effects of hole size and porosities on flame and shock wave propagation, intensity of the shock wave and pressure oscillation in closed combustion chamber were analyzed in detail. The effect of interactions between the turbulent flame and reflected shock or acoustic wave on the turbulent flame propagation was comprehensively studied during the present experiment. The results demonstrated that flame front propagation velocity and pressure oscillation strongly depend on the hole size and porosities of the perforated plate. The flame front propagation velocity in the end gas region increases as hole size increases and porosity decreases. The flame front propagation intensity in the end region of a confined space is strongly relevant to two competing effects: the initial turbulent formation and turbulent flame development. The experimental results indicated that an oscillating flame is associated with both the reflected shock wave and the acoustic wave. Meanwhile, different turbulent flame propagations and combustion modes were observed