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.

Discharge Characteristics of Current Boosted Spark Events Under Flow Conditions

2017 ◽  
Author(s):  
Xiao Yu ◽  
Zhenyi Yang ◽  
Shui Yu ◽  
Mark Ives ◽  
Ming Zheng
Keyword(s):  
Flow Velocity ◽  
Discharge Current ◽  
Gas Flow ◽  
Spark Ignition ◽  
Current Level ◽  
Flow Conditions ◽  
Kernel Development ◽  
Flame Kernel ◽  
Spark Plasma ◽  
Gas Flow Velocity

With the advancement of spark ignition engines, lean or diluted in-cylinder charge is often used to improve the engine performance. Enhanced in-cylinder charge motion is widely applied under such conditions to promote the flame propagation, which raise challenges for the spark ignition system. In this work, the spark discharging process is investigated under different flow conditions via both optical diagnosis and electrical measurement. Results show that the spark plasma channel is stretched under flow conditions. A higher discharge current can maintain the stretched spark plasma for a longer duration. Re-strikes are observed when the spark plasma is stretched to a certain extent. The frequency of re-strikes increases with increased flow velocity and decreased discharge current level. The discharge duration reduces with the increased flow velocity. The effects of gas flow on the ignition and flame kernel development are studied in a constant volume optical combustion chamber with premixed lean and stoichiometric methane air mixture. Two spark strategies with low and high discharge current are used for the ignition. The flame propagation speed of both lean and stoichiometric mixtures increases with the increased gas flow velocity. A higher discharge current level retains a more stable spark channel and improves the flame kernel development for both lean and stoichiometric conditions, especially under the higher gas flow velocity of 20 m/s.

Ignition Dynamics in an Annular Combustor With Gyratory Flow Motion

2018 ◽  
Author(s):  
Chenran Ye ◽  
Gaofeng Wang ◽  
Yuanqi Fang ◽  
Chengbiao Ma ◽  
Liang Zhong ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Velocity Component ◽  
Thermal Power ◽  
Propagation Speed ◽  
Circumferential Velocity ◽  
Bulk Velocity ◽  
Ignition Process ◽  
Flow Motion ◽  
Annular Combustor ◽  
Flame Propagation Speed

In concepts of integrated design of combustor and turbine, an annular combustor model is developed and featured with multiple oblique-injecting swirling injectors to introduce gyratory flow motion in the combustion chamber. The ignition process is experimentally investigated to study the effects of introducing circumferential velocity component Uc to the light-round sequence. Experiments are carried out with premixed propane/air mixture in ambient conditions. The light-round sequence is recorded by a high-speed camera, which provides detailed flame azimuthal positions during the sequence and gives access to the light-round time τ and the circumferential flame propagation speed Sc. The results have also been compared with that obtained from a straight-injecting annular combustor. The effects of bulk velocity Ub, thermal power P and equivalence ratio Φ are also explored. Due to the gyratory flow motion induced by oblique injection, the flame fronts only propagate along the direction of circumferential flow. Both of the circumferential flame propagation speed increase with increasing bulk velocity in two injection types. It seems mainly to depend on bulk velocity, regardless of Φ, in oblique-injecting combustor when compared with the straight one. It indicates that the circumferential velocity component would play a dominant role in light-round sequence when it is sufficient higher than the displacement flame speed.

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.

Experimental determination of flame speed and flame stretch using an optically accessible, spark-ignition engine

2019 ◽  
pp. 146808741987771 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A Miers ◽  
Jeffrey D Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
Engine Speed ◽  
Spark Ignition ◽  
Flame Speed ◽  
Dominant Factor ◽  
Lean Mixture ◽  
Flame Stretch ◽  
Flame Development ◽  
The Rich

The current research experimentally studied flame speed and stretch under engine in-cylinder conditions. A direct-injection, spark-ignition, and optically accessible engine was utilized to image the flame propagation, and E10 was selected as the fuel. Also, three fuel–air mixtures (stoichiometric, lean, and rich) were examined. The flame front was located by processing high-speed images. This study introduces a novel approach for calculation of equivalent spherical flame radius for analysis of flame speed and stretch. Flame front propagation analysis showed that during the flame propagation period, the stretch decreased until the flame front touched the piston surface. This was a common trend for stoichiometric, lean, and rich mixtures, which occurred because the flame radius was the dominant factor in the stretch calculation. In addition, the rich fuel–air mixture showed a lower flame stretch compared to stoichiometric or lean mixture. This was the result of a lower Markstein number for the rich fuel–air mixture. To study the sensitivity of different fuel–air mixtures to the flame stretch, the trajectory of the flame centroid was tracked until the flame front touched the piston surface. The results showed that the end centroid for the lean mixture deviated from the start point more than those of the rich and stoichiometric mixtures because the lean mixture had a higher flame stretch and lower flame speed. Furthermore, comparing the flame stretch at three different engine speeds revealed that increasing the engine speed increased the flame stretch, especially during the early flame development period. According to previous studies which discussed flame stretch as a flame extinguishment mechanism, the probability of flame extinction is higher when the engine speed is higher. Also, uncertainty analysis was conducted to determine the effect of camera setting on the flame stretch. Results showed that a maximum relative uncertainty of 4.5% occurred during the early flame development.

An Experimental Investigation on the Combustion Process of a Simulated Turbocharged Spark Ignition Natural Gas Engine Operated on Stoichiometric Mixture

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Hailin Li ◽  
Timothy Gatts ◽  
Shiyu Liu ◽  
Scott Wayne ◽  
Nigel Clark ◽  
...  
Keyword(s):  
Natural Gas ◽  
Flame Propagation ◽  
Combustion Process ◽  
Propagation Speed ◽  
Spark Ignition ◽  
Boost Pressure ◽  
Stoichiometric Mixture ◽  
Process Data ◽  
Intake Pressure ◽  
Flame Propagation Speed

This research investigated the combustion process of an AVL Model LEF/Volvo 5312 single cylinder engine configured to simulate the operation of a heavy-duty spark ignition (SI) natural gas (NG) engine operated on stoichiometric mixture. The factors affecting the combustion process that were examined include intake pressure, spark timing (ST), and the addition of diluents including nitrogen (N2) and carbon dioxide (CO2) to the NG to simulate low British thermal unit (BTU) gases. The mixing of diluents with NG is able to slow down the flame propagation speed, suppress the onset of knock, and allow the engine to operate on higher boost pressure for higher power output. The addition of CO2 was more effective than N2 in suppressing the onset of knock and slowing down the flame propagation speed due to its high heat capacity. Boosting intake pressure significantly increased the heat release rate (HRR) evaluated on J/°CA basis which represents the rate of mass of fuel burning. However, its impact on the normalized HRR evaluated on %/°CA basis, representing the flame propagation rate, was relatively mild. Boosting the intake pressure from 1.0 to 1.8 bar without adding diluents increased the peak HRR to 1.96 times of that observed at 1.0 bar. The increase was due to the burning of more fuel (about 1.8 times), and the 12.9% increase in the normalized HRR. The latter was due to the shortened combustion duration from 23.6 to 18.2 °CA, a 22.9% reduction. The presence of 40% CO2 or N2 in their mixture with NG increased the peak cylinder pressure (PCP) limited brake mean effective pressure (BMEP) from 17.2 to about 20.2 bar. The combustion process of a turbocharged SI NG engine can be approximated by referring to the HRR measured under a naturally aspirated condition. This makes it convenient for researchers to numerically simulate the combustion process and the onset of knock of turbocharged SI NG engines using combustion process data measured under naturally aspirated conditions as a reference.

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.

Effect of Different Ignition Methods on Combustion Characteristics of a Turbocharging Lean Burn LPG Engine

2012 ◽  
Vol 443-444 ◽  
pp. 1026-1031
Author(s):  
Da Wei Qu ◽  
Jun Li ◽  
Ying Gao ◽  
Dong Qing Zhou ◽  
Lu Yan Fan ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Three Dimensional ◽  
Propagation Speed ◽  
Propagation Distance ◽  
Spark Ignition ◽  
Simulation Software ◽  
Combustion Model ◽  
Power Performance ◽  
Working Process ◽  
Lean Burn

A turbocharging lean burn LPG engine combustion model is set up by using three-dimensional simulation software. And the numerical simulation of the engine working process is done. Based on the model validation, the effect of the engine working process is calculated and analyzed by comparing with different ignition models (single spark ignition and dual spark ignition) and the simulation results are validated by experiments. The results show that: dual spark ignition (DSI) model as compared to single spark ignition (SSI) model can reduce flame propagation distance, form the stronger swirl rapidly, accelerate the flame propagation speed, reduce knock phenomena, reduce the emission temperature and improve the engine efficiency. Therefore, the engine has better power performance and fuel economy.

Effects of tumble and swirl flows on turbulence scale near top dead centre in a four-valve spark ignition engine

2003 ◽  
Vol 217 (7) ◽  
pp. 607-615 ◽  
Author(s):  
K H Lee ◽  
C S Lee
Keyword(s):  
Flame Propagation ◽  
Propagation Speed ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Turbulence Scale ◽  
Iccd Camera ◽  
Spark Plug ◽  
Swirl Flows ◽  
Initial Flame ◽  
Dead Centre

The in-cylinder flowfield and the turbulence scale at the ignition timing play an important role in enhancing the propagation speed of the initial flame and the engine combustion. The aim of this work is to investigate the effect of tumble and swirl flows on the turbulence scale near the top dead centre in a four-valve spark ignition (SI) engine by an experimental method. In this study, various flowfields such as tumble and swirl flows were generated by intake flow control valves. For investigation of the flowfields, the single-frame particle tracking velocimeter (PTV) and the twocolour particle image velocimeter (PIV) techniques were developed to clarify the in-cylinder flow pattern during the intake stroke and the turbulence intensity near the spark plug during the compression stroke respectively. In addition, the flame propagation was visualized by an ICCD camera, and its images were analysed to compare the flowfields. From these experimental results, the effects of tumble and swirl flows on the turbulence scale and the flame propagation speed were clarified.

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