Numerical Study on Spark Ignition Characteristics of a Methane-Air Mixture Using Detailed Chemical Kinetics (Effect of Electrode Temperature and Energy Channel Length on Flame Propagation and Relationship between Minimum Ignition Energy and Equivalence Ratio)

Abstract

Spark ignition is considered one of the most difficult and complex problems because it involves complicated physical and chemical processes, and it has not yet been explained sufficiently. The minimum ignition energy (MIE) is an important parameter for judging the ignition ability of combustion systems. In the present study, the spark ignition characteristics of a methane-air mixture were investigated by numerical analysis using detailed chemical kinetics consisting of 53 species and 325 elementary reactions. Two different analytical models, with and without electrodes, were applied to research the effect of electrode temperature and energy channel length on flame propagation and the relationship between the MIE and equivalence ratio. The electrode temperature was set as 300 K, 1000 K, and 2000 K for analytical models with electrodes, and the energy channel length was set as 1 mm, 2 mm, and 3 mm for analytical models without electrodes. The obtained computational results showed good agreement with experimental results. We determined that with increasing electrode temperature, the minima of the curve indicating the relationship between the MIE and equivalence ratio move toward the leaner side, that a leaner mixture is more sensitive to heat loss to the cold surrounding gas, and that heat loss to the electrodes is an unignorable factor for the initial formation of the flame kernel.

Experimental study on the effects of the ignition parameters on the spark characteristics and the flame propagation of premixed methane–air mixtures

“…In the early stage of flame kernel development, the kernel becomes an approximate ellipsoid because a plasma channel is established between the electrodes after ignition and spread in the form of a shock wave more quickly in the radial direction than in the axial direction. 2,4 With development of the flame, the influences of the pressure, the temperature, etc., are far greater than that of the ignition energy. The kernel gradually grows into a quasi-sphere and spreads outwards from the burned zone to the unburned zone, while the effect of the ignition energy therefore can be ignored.…”

“…In a spark ignition engine, spark ignition is an important process because it affects the successful ignition of combustible mixtures, the formation of the flame kernel, the flame propagation and even the performance, the fuel economy and the emissions of the spark ignition engine. [1][2][3][4][5][6][7][8] The ignition process is composed of a series of complex physical and chemical processes affected by many factors such as the storage energy of the ignition system, the structure of the electrode, the species and concentration of the mixtures, the temperature and the humidity [9][10][11][12][13][14] ; of these, the storage energy of the ignition system and the structure of the electrode are the most important factors in controlling the ignition process. Ignition systems with control of the storage energy include inductive energy storage types, capacitive energy storage types and laser-induced ignition types.…”

“…Thiele et al, 2 Kravchik and Sher, 22 Nakaya et al, 23 Lian et al, 24 Yossefi et al 25 and Song and Sunwoo 26 constructed models by a numerical method to simulate spark ignition and investigated the development of the flame kernel. Lim et al 3 and Han et al 4 utilized detailed chemical kinetics to establish models to study the quenching distance, the effects of the electrode size and the ignition duration and equivalence ratio on the MIE. However, in these models, many simplifications and assumptions were introduced to solve these equations, e.g.…”

Effects of thermal and pressure loads on structural deformation of liquid oxygen/methane engine combustion chamber

“…The liquid oxygen (LOX)/methane rocket engine is regarded as an ideal candidate for the propulsion system of RLVs because that the propellant combination of LOX/methane has obvious advantages compared to traditional propellant combination, such as high-density specific impulse, non-toxic, cheap and easy to produce (Kobayashi et al,2007). In the past two decades, engineers and scholars have been working on the application of methane to rocket launches (Lin et al, 2013;Rahman et al, 2012;Han et al, 2009). As one of the critical components of the LOX/methane engine, the regenerative cooling combustion chamber (Xiang and Sun, 2018) consists of a nickel jacket and a copper alloy liner characterized by a high thermal conductivity.…”