A study on the influence of ignition energy on ignition delay time and laminar burning velocity of lean methane/air mixture in a constant volume combustion chamber

This study presents the effect of ignition energy (Eig) on ignition delay time (tdelay) and uncertainty of laminar burning velocity (Su0) measurement of lean methane/air mixture in a constant volume combustion chamber. The mixture at an equivalence ratio of 0.6 is ignited using a pair of electrodes at the 2-mm spark gap. Eig is measured by integrating the product of voltage V(t) and current I(t) signals during a discharge period. The in-chamber pressure profiles are analyzed using the pressure-rise method to obtain tdelay and Su0. Su0 approximates 8.0 cm/s. Furthermore, the increasing Eig could shorten tdelay, leading to a faster combustion process. However, when Eig is greater than a critical value, called minimum reliable ignition energy (MRIE), the additional elevating Eig has the marginal effect on tdelay and Su0. The existence of MRIE supports to optimize the ignition systems and partly explains why extreme-high Eig>> MRIE has less contribution to engine performance.

Effect of Turbulence On Forced Ignition of Jet-A/Air Mixtures

Consistent ignition of reactive mixtures in turbulent conditions continues to be a challenge, particularly for large, multi-component fuels. Prior work has shown that turbulence can affect ignition parameters such as flame speed, mixture temperature, and minimum ignition energy. However, these works have primarily considered small, single-component fuels. This work studies the effect of turbulence on forced ignition of jet-A/air mixtures with f between 0.3 and 0.7. The ignition probability of these mixtures was measured for bulk velocities between 5 and 7 m/s and turbulence intensities between 3% and 9%. A FLIR SC6700 infrared camera was used to measure the radiation intensity emitted by the flame kernels. Increases in turbulence intensity between 3% and 4% cause the probability of ignition to generally increase. This increase is attributed to the negative flame stretch that develops as a result of the turbulence. This observation is significant because it shows that turbulence can facilitate ignition for jet-A/air mixtures. In contrast, increasing turbulence beyond 5% causes ignition probabilities to decrease. This reduction occurs due to the increased role of heat diffusion and the associated reduction in kernel temperature. The sensitivities of ignition behavior to turbulence intensity and fuel chemistry are reasonably captured using the Peclet number. Further agreement in ignition behavior is achieved by considering Pe/TI2. Ignition probability data for two additional fuels were compared using Pe/TI2. Reasonable agreement within a 95% confidence interval was observed for CH4 mixtures but not for C3H8 mixtures.

Experimental Study on Ignition Characteristics of RP-3 Jet Fuel Using Nanosecond Pulsed Plasma Discharge

A study on forced ignition characteristics of RP-3 jet fuel-air mixture was conducted around a constant volume combustion vessel and a nanosecond pulsed plasma discharge power supply. Experiments were carried out at different initial pressures (pu = 0.2, 0.3, 0.5 atm), equivalence ratios (ϕ = 0.7, 0.8, 1.1), steam concentrations (ZH2O = 0%, 10%, 15%) and oxygen concentrations (ZO2 = 13.5%, 16%, 21%). The relationship between ignition probability and ignition energy is investigated. The experimental results show that the decrease in pressure, equivalence ratio, oxygen concentration and the increase in steam concentration all lead to an increase in minimum ignition energy (MIE). In order to further analyze the experimental data, one existing fitting equation is reformed with the initial conditions taken into account. Multivariate fitting is carried out for different conditions, and the fitting results of ignition probability are in good agreement with the experiments. The MIE results under different experimental conditions are figured out with the new fitting equation. The impact indexes, which stand for the effects of different factors, are also calculated and compared in present work.

Research on Ignition Energy Characteristics and Explosion Propagation Law of Coal Dust Cloud under Different Conditions

To study the ignition energy characteristics and explosion propagation law of coal dust cloud, a kind of coal dust cloud is studied through experiment and numerical simulation under different conditions. The result indicated that ignition delay time and dust spray pressure have obvious effects on the minimum ignition energy of coal dust cloud. CFD theory is used to simulate the explosion flame propagation. It is found that the simulation error of flame propagation distance is acceptable and the simulation result is consistent with the experimental result. When the spray pressure is 0.06 MPa, the flame propagation distance is the farthest, indicating that the turbulence of coal dust cloud is the largest at this condition. As the ignition temperature increases, the flame propagation distance continues to increase, proving that ignition temperature has an obvious effect on the flame propagation process of coal dust cloud explosion.

Study on ignition performance of tantalum nitride film energy exchangers based on new bridge area

In order to reduce the ignition energy of the tantalum nitride film transducer, a new type of energy exchangers bridge area was designed in this paper, and it was fabricated by MEMS technology. The parameters of ignition voltage, ignition energy, as well as action time were tested. The experimental results showed that in terms of ignition voltage, ignition energy, and action time, the value of the energy exchangers element of the new bridge area was lower than the value of the energy exchangers element of the conventional bridge area. In addition, ignition performance can be reduced by many energy exchangers in the new bridge area.