scholarly journals Investigation of the Effect of Electrode Surface Roughness on Spark Ignition

2018 ◽  
Author(s):  
Mohammadrasool Morovatiyan ◽  
Martia Shahsavan ◽  
Mengyan Shen ◽  
John Hunter Mack
Keyword(s):  
Surface Roughness ◽  
Electrode Surface ◽  
High Speed ◽  
Fuel Efficiency ◽  
Spark Ignition ◽  
Ignition Process ◽  
Flammability Limit ◽  
Lean Burn ◽  
Flame Kernel ◽  
Spark Plug

Lean-burn engines are important due to their ability to reduce emissions, increase fuel efficiency, and mitigate engine knock. In this study, the surface roughness of spark plug electrodes is investigated as a potential avenue to extend the lean flammability limit of natural gas. A nano-/micro-morphology modification is applied on surface of the spark plug electrode to increase its surface roughness. High-speed Z-type Schlieren visualization is used to investigate the effect of the electrode surface roughness on the spark ignition process in a premixed methane-air charge at different lean equivalence ratios. In order to observe the onset of ignition and flame kernel behavior, experiments were conducted in an optically accessible constant volume combustion chamber at ambient pressures and temperatures. The results indicate that the lean flammability limit of spark-ignited methane can be lowered by modulating the surface roughness of the spark plug electrode.

Investigation of the Effect of Electrode Surface Roughness on Spark Ignition

2018 ◽  
Author(s):  
Mohammadrasool Morovatiyan ◽  
Martia Shahsavan ◽  
Mengyan Shen ◽  
J. Hunter Mack
Keyword(s):  
Surface Roughness ◽  
Electrode Surface ◽  
High Speed ◽  
Fuel Efficiency ◽  
Spark Ignition ◽  
Ignition Process ◽  
Flammability Limit ◽  
Lean Burn ◽  
Flame Kernel ◽  
Spark Plug

Lean-burn engines are important due to their ability to reduce emissions, increase fuel efficiency, and mitigate engine knock. In this study, the surface roughness of spark plug electrodes is investigated as a potential avenue to extend the lean flammability limit of natural gas. A nano-/micro-morphology modification is applied on surface of the spark plug electrode to increase its surface roughness. High-speed Z-type Schlieren visualization is used to investigate the effect of the electrode surface roughness on the spark ignition process in a premixed methane-air charge at different lean equivalence ratios. In order to observe the onset of ignition and flame kernel behavior, experiments were conducted in an optically accessible constant volume combustion chamber at ambient pressures and temperatures. The results indicate that the lean flammability limit of spark-ignited methane can be lowered by modulating the surface roughness of the spark plug electrode.

Spark Ignition of SPP Injector Under Sub-Atmospheric Conditions

2021 ◽  
Author(s):  
Qianpeng Zhao ◽  
Yong Mu ◽  
Jinhu Yang ◽  
Yulan Wang ◽  
Gang Xu
Keyword(s):  
High Speed ◽  
Spark Ignition ◽  
Test Facility ◽  
Propagation Mode ◽  
Inlet Temperature ◽  
Reacting Flow ◽  
Atmospheric Conditions ◽  
Flame Kernel ◽  
Flame Development ◽  
Initial Flame

Abstract The sub-atmospheric ignition performance of an SPP (Stratified Partially Premixed) injector and combustor is investigated experimentally on the high-altitude test facility. In order to explore the influence of sub-atmospheric pressure on reignition performance and flame propagation mode, experiments are conducted under different pressures ranging from 19 kPa to 101 kPa. The inlet temperature and pressure drop of the injector (ΔPsw/P3t) are kept constant at 303 K and 3% respectively. The transparent quartz window mounted on the sidewall of the model combustor provides optical access of flame signals. Ignition fuel-air ratio (FAR) under different inlet pressures are experimentally acquired. The spark ignition processes, including the formation of flame kernel, the flame development and stabilization are recorded by a high-speed camera at a rate of 5kHz. Experimental results indicate that the minimum ignition FAR grows rapidly as the inlet air pressure decreases. An algorithm is developed to track the trajectory of flame kernels within 25ms following the spark during its breakup and motion processes. Results show that the calculated trajectory provides a clear description of the flame evolution process. Under different inlet air pressures, the propagation trajectories of flame kernels share similarities in initial phase. It is pivotal for a successful ignition that the initial flame kernel keeps enough intensity and moves into CTRZ (Center-Toroidal Recirculation Zone) along radial direction. Finally, the time-averaged non-reacting flow field under inlet pressure of 54kPa and fuel mass flow of 8kg/h is simulated. The effects of flow structure and fuel spatial distribution on kernel propagation and flame evolution are analyzed.

Investigation of the spark ignition enhancement in a supersonic flow

2014 ◽  
Vol 28 (29) ◽  
pp. 1450226 ◽  
Author(s):  
Zun Cai ◽  
Zhen-Guo Wang ◽  
Ming-Bo Sun ◽  
Hong-Bo Wang ◽  
Jian-Han Liang
Keyword(s):  
Ignition Time ◽  
Spark Ignition ◽  
Dominant Factor ◽  
Ignition Process ◽  
Operation Condition ◽  
Flame Kernel ◽  
Operation Conditions ◽  
Key Factor ◽  
Lean Fuel ◽  
Spark Energy

Ethylene spark ignition experiments were conducted based on an variable energy igniter at the inflow conditions of Ma = 2.1 with stagnation state T0 = 846 K , P0 = 0.7 MPa . By comparing the spark energy and spark frequency of four typical operation conditions of the igniter, it is indicated that the spark energy determines the scale of the spark and the spark existing time. The spark frequency plays a role of sustaining flame and promoting the formation and propagation of the flame kernel, and it is also the dominant factor determining the ignition time compared with the spark energy. The spark power, which is the product of the spark energy and spark frequency, is the key factor affecting the ignition process. For a fixed spark power, the igniter operation condition of high spark frequency with low spark energy always exhibits a better ignition ability. As approaching the lean fuel limit, only the igniter operation condition (87 Hz and 3.0 J) could achieve a successful ignition, where the other typical operation conditions (26 Hz and 10.5 J, 247 Hz and 0.8 J, 150 Hz and 1.4 J) failed.

scholarly journals Ignition Probability and Lean Ignition Behaviour of a Swirled Premixed Bluff Body Stabilised Annular Combustor

2020 ◽  
Author(s):  
Roberto Ciardiello ◽  
Rohit S. Pathania ◽  
Patton M. Allison ◽  
Pedro M. de Oliveira ◽  
Epaminondas Mastorakos
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Ignition Process ◽  
High Speed Imaging ◽  
Ignition Probability ◽  
Flame Kernel ◽  
Annular Combustor ◽  
Initial Flame ◽  
Limiting Condition

Abstract An experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful propagation. The experiments are done at conditions that are close to the lean blow-off limit (LBO) and hence the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (ϕ) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2 mm gap, 10 sparks of 10 ms each) and “ignition” is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH* chemiluminescence. The lean ignition limits were evaluated and compared to the lean blow-off limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localised quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upwards. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ∼ 0 for most conditions, while Pign increased moving the spark away from the bluff-body or placing it between two burners and peaked to Pign ∼ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favourable conditions for achieving ignition in a complex multi-burner geometry and could help the design and optimisation of realistic gas turbine combustors.

Effect of Swirl Cup’s Venturi Shape on Spray Structure and Ignition Process

2014 ◽  
Author(s):  
Xiaofeng Wang ◽  
Yuzhen Lin ◽  
Haosheng Hu ◽  
Chi Zhang ◽  
Yao Kang
Keyword(s):  
Spatial Distribution ◽  
High Speed ◽  
Side Wall ◽  
Video Camera ◽  
Spark Ignition ◽  
Ignition Process ◽  
Turbine Engine ◽  
Fuel Droplets ◽  
Spray Structure ◽  
Air Stream

In a gas turbine engine combustor, combustion performance is tied to the spatial distribution of the fuel injected into the dome. Swirl cup, as an air blast atomizer, is widely used to provide a uniform presentation of fuel droplets to the combustor dome. In this paper, two swirl cups with different venturi angle have been studied: case 1 (with narrow venturi angle) and case 2 (with wide venturi angle). Kerosene is injected to the test domain through a simplex nozzle. The spatial distribution of droplet characteristics produced by the two swirl cups were measured using dual-phase Doppler anemometry (PDA). A single cup combustor has been built in order to characterize the swirl cups’ ignition phenomena. Spark ignition test has been performed for ground condition, two swirl cups’ lean ignition limits are obtained, and ignition sequences have been recorded by a high-speed video camera. Comparing the two swirl cups’ small droplets velocity, case 1 swirl cup produces a different velocity profile from typical swirl cup. The air stream outflowing from case 1 swirl cup just ran into the side wall. The droplet size around the spark plug of case 2 is smaller than case 1. Ignition test results show that case 2 swirl cup’s lean ignition limit is wider than case 1’s. Record of the ignition process deepened the understanding of spark ignition of the swirl diffusion flame. It takes some time for the kernel to anchor in swirl cup. The results demonstrate that swirl cup’s venturi shape strongly influence the spray structure. Thereby affect the combustor ignition performance.

Impacts of Spark Discharge Current and Duration on Flame Development of Lean Mixtures Under Flow Conditions

2018 ◽  
Author(s):  
Zhenyi Yang ◽  
Xiao Yu ◽  
Shui Yu ◽  
Jianming Chen ◽  
Guangyun Chen ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Discharge Current ◽  
Propagation Speed ◽  
Spark Ignition ◽  
Spark Discharge ◽  
Current Level ◽  
Ignition Process ◽  
Flame Kernel ◽  
Flame Development ◽  
Discharge Duration

Lean or diluted combustion has been considered as an effective strategy to improve the thermal efficiency of spark ignition engines. Under lean or diluted conditions, the combustion speed is reduced by the diluting gas. In order to speed up the combustion, in-cylinder flow is intentionally enhanced to promote the flame propagation. However, it is observed that the flow may make the spark ignition process more challenging due to the shortened discharge duration, the frequent re-strikes of spark plasma and the more complicated interactions between the flow and the flame. In this research, the effects of spark discharge current level and discharge duration on flame kernel development and flame propagation of lean methane air mixture are investigated under flow velocity of about 25 m/s and background pressure of 4 bar abs in an optical combustion chamber. A dual coil ignition system and an in-house developed current management module are used to create different discharge current levels. The average discharge current levels range from 55 mA, 190 mA, up to 250 mA. Detached flame kernel is observed under some test conditions. The flame propagation speed with the detached flame is generally slower than the flame developed from a flame kernel attached to the spark plug. The flame detachment is related to both the discharge current level and the discharge duration. When the discharge current level is high at 250 mA, the detached flame is observed at shorter discharge duration of 0.8 ms, while when the discharge current is low at 190 mA, detached flame can happen at longer discharge duration of 1.3 ms. Various discharge current and discharge durations are adopted to initiate the combustion in a single-cylinder engine operating with lean gasoline air mixture. It is shown from the results that a higher discharge current level and longer discharge duration are beneficial for controlling the combustion phasing and improving the operation stability of the engine.

Large Eddy Simulation of the Ignition Performance in a Lean Burn Combustor

2015 ◽  
Author(s):  
Yingjie Qiao ◽  
Ronghai Mao ◽  
Yuzhen Lin
Keyword(s):  
Large Eddy Simulation ◽  
Flame Propagation ◽  
Bluff Body ◽  
Mixture Fraction ◽  
Ignition Process ◽  
Lean Burn ◽  
Flamelet Model ◽  
Flame Kernel ◽  
Eddy Simulation ◽  
Large Eddy

The ignition performance is a crucial issue for combustor design, especially when lean burn technologies are employed to reduce the NOx emission. Ignition is the initiation of a flame kernel followed by flame propagation and global establishment. The initiation of flame kernel is beyond the scope of this paper because it involves plasma formation process. The present investigation is mainly focused on flame front propagation which is modeled by solving a transport equation of reaction progress variable. Large eddy simulation (LES) with flamelet model has been employed to study the effect of various spark location under engine start condition. The numerical approach is validated by ignition experiments with turbulent bluff-body burner conducted by Ahmed and Mastorakos in Cambridge University. Mean and transient characteristics of velocity, mixture fraction and flame structures are compared with experimental data, to assess the accuracy of simulation in terms of flow structure, turbulent mixing and combustion performances. The validated LES model is then applied to study a series of physical locations of the spark plug in a single dome combustor. Successful and unsuccessful ignition sequences, time evolution of velocity and fuel/air ratio (FAR) of selected spots are recorded. Comparing the unsuccessful ignition with the successful ones, whether flame kernel enters into the CRZ and ignites the flammable mixture is a critical process which determines successful ignition. The evolution of flame kernel is correlated to flow field and fuel/air distribution to further analyze their effects on the ignition process. Since the process is highly transient, successful ignition is not only determined by parameters of spark location, but also influenced by the parameters throughout the flow path during flame propagation.

Chemical effects of plasma gases on flame kernel development

1988 ◽  
Vol 418 (1855) ◽  
pp. 313-329 ◽  
Keyword(s):  
Combustion Chamber ◽  
Active Regions ◽  
Ignition Process ◽  
Flammability Limit ◽  
Kernel Development ◽  
Flame Kernel ◽  
Chemical Effects ◽  
Initial Plasma ◽  
Dimensional Distribution ◽  
Approach To Steady State

A study of the plasma jet ignition of lean methane-air mixtures was conducted to determine the effect of different plasma gases on flame kernel development. A plasma igniter, incorporating a shutter that separated the gases in the igniter from the reactant gases in a combustion chamber before discharge, allowed any combination of gases to be used without mixing. Measurements of the two-dimensional distribution of OH concentration by laser-induced fluorescence in a diametral plane above the igniter yielded information on the ignition process and the subsequent flame kernel development. The methane-air mixtures chosen for study had equivalence ratios, ϕ , near the lean flammability limit of ϕ ═ 0.53. To differentiate OH formation in the initial plasma from that generated during mixing and reaction with gas in the combustion chamber, experiments were conducted using the following combinations of plasma media and reactant gases: H 2 and 2H 2 + O 2 plasmas into air; Ar, N 2 , H 2 and 2H 2 + O 2 plasmas into ϕ ═ 0.50 CH 4 -air; and 2H 2 + O 2 plasma into ϕ ═ 0.65 CH 4 -air. In addition to OH measurements, the pressure in the combustion chamber was measured, and Schlieren photographs were taken. Results indicated relatively small, chemically active regions, generally off-axis and often associated with vortices. Measurements in lean mixtures that are known to discriminate strongly between plasma of different effectiveness confirm the higher incendivity, for the same total energy, of chemically active plasmas and demonstrate the higher concentration and longer persistence of OH during the approach to steady state flame conditions. Such chemically active plasmas promote combustion for hundreds of milliseconds in normally non-flammable sub-limit mixtures.

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