Experimental investigation of turbulent flame propagation and pressure oscillation in a constant volume chamber equipped with an orifice plate

In this work, the main contribution is an understanding of different combustion phenomena involving flame acceleration, flame propagation, and the pressure oscillation resulting from flame-shock interactions. These physical phenomena were experimentally studied using a newly developed confined combustion chamber equipped with one or two orifice plates. The results showed that there are five stages of flame propagation when a laminar flame passes through the orifice plate in a confined space. These include the deceleration of the laminar flame, jet flame formation and rapid acceleration, deceleration of the flame, turbulent flame formation and acceleration, and turbulent flame propagation in the end-gas region. Flame acceleration and pressure oscillation were found to be strongly related to the aperture size of the orifice plate. The high amplitudes of pressure oscillations were found to be the results of two combustion mechanisms: the end gas auto-ignition and the interactions between the accelerated turbulent flame and shock wave. To further accelerate the flame and promote stronger disturbance in the end gas, another identical orifice plate was employed. Subsequently, strong flame-shock interaction caused end-gas auto-ignition with an extremely high-amplitude pressure oscillation. Eventually, the maximum amplitude of pressure oscillation exceeded 8 MPa as end-gas auto-ignition occurred in the end region of the combustion chamber

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

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 investigation of turbulent flame propagation and pressure oscillation in a constant volume chamber equipped with an orifice plate

In this work, the main contribution is an understanding of different combustion phenomena involving flame acceleration, flame propagation, and the pressure oscillation resulting from flame-shock interactions. These physical phenomena were experimentally studied using a newly developed confined combustion chamber equipped with one or two orifice plates. The results showed that there are five stages of flame propagation when a laminar flame passes through the orifice plate in a confined space. These include the deceleration of the laminar flame, jet flame formation and rapid acceleration, deceleration of the flame, turbulent flame formation and acceleration, and turbulent flame propagation in the end-gas region. Flame acceleration and pressure oscillation were found to be strongly related to the aperture size of the orifice plate. The high amplitudes of pressure oscillations were found to be the results of two combustion mechanisms: the end gas auto-ignition and the interactions between the accelerated turbulent flame and shock wave. To further accelerate the flame and promote stronger disturbance in the end gas, another identical orifice plate was employed. Subsequently, strong flame-shock interaction caused end-gas auto-ignition with an extremely high-amplitude pressure oscillation. Eventually, the maximum amplitude of pressure oscillation exceeded 8 MPa as end-gas auto-ignition occurred in the end region of the combustion chamber

Different combustion modes caused by flame-shock interactions in a confined chamber with a perforated plate

© 2017 The Combustion InstituteThe present work investigates the interaction of the turbulent flame and shock wave as well as the end-gas autoignition in a newly designed constant volume combustion chamber equipped with a perforated plate using a stoichiometric hydrogen-air mixture. Detailed high speed schlieren photography is used to track the turbulent flame fronts and shock waves which are generated by the laminar flame passing through the perforated plate. The different propagation speeds of the turbulent flames and shock waves can be obtained by controlling the initial pressures and the hole size of the perforated plate. In this work, three combustion modes were obtained clearly by experiment, depending on the interactions of the turbulent flame and shock wave, such as normal combustion, oscillating combustion and end-gas autoignition. The normal combustion is a weak turbulent flame propagation without an obvious shock wave in the confined chamber. The oscillating flame propagation is generated by the interaction of the reflected shock wave and flame front and this process can be clearly visualized in the present work. The end-gas autoignition is induced by the combined effect of the supersonic flame and the shock waves. The accelerating combustion in the confined chamber could produce the primary shock wave and the subsequent secondary shock wave is induced by the secondary flame occurring between the primary flame and primary shock wave. It is found that the secondary shock wave with speed of 780 m/s is faster than the primary one, which is the source of the end-gas autoignition. It is also observed that quasi-detonation wave produced by the end-gas autoignition can reach the speed of 1700 m/s. This wave is accompanied by a strong pressure oscillation which can explain the mechanism of engine knock