Understanding ignition processes in spray-guided gasoline engines using high-speed imaging and the extended spark-ignition model SparkCIMM. Part A: Spark channel processes and the turbulent flame front propagation

2011 ◽  
Vol 158 (11) ◽  
pp. 2229-2244 ◽  
Author(s):  
Rainer N. Dahms ◽  
Michael C. Drake ◽  
Todd D. Fansler ◽  
T.-W. Kuo ◽  
N. Peters
Keyword(s):  
Flame Front ◽  
High Speed ◽  
Turbulent Flame ◽  
Front Propagation ◽  
Spark Ignition ◽  
High Speed Imaging ◽  
Channel Processes ◽  
Gasoline Engines ◽  
Spark Channel

Understanding ignition processes in spray-guided gasoline engines using high-speed imaging and the extended spark-ignition model SparkCIMM

2011 ◽  
Vol 158 (11) ◽  
pp. 2245-2260 ◽  
Author(s):  
Rainer N. Dahms ◽  
Michael C. Drake ◽  
Todd D. Fansler ◽  
T.-W. Kuo ◽  
N. Peters
Keyword(s):  
High Speed ◽  
Spark Ignition ◽  
High Speed Imaging ◽  
Gasoline Engines

The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence

2017 ◽  
Author(s):  
Sean D. Salusbury ◽  
Ehsan Abbasi-Atibeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Flame Front ◽  
Turbulence Intensity ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Turbulent Flame ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flames ◽  
Counter Flow

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities. These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.

The effect of the stroke-to-bore ratio on combustion, heat transfer and efficiency of a homogeneous charge spark ignition engine of given displacement

2000 ◽  
Vol 1 (2) ◽  
pp. 191-208 ◽  
Author(s):  
Z. S. Filipi ◽  
D. N. Assanis
Keyword(s):  
Heat Transfer ◽  
Flame Front ◽  
Turbulent Flame ◽  
Spark Ignition ◽  
Point Of View ◽  
Spark Ignition Engine ◽  
Combustion Heat ◽  
Geometric Point ◽  
Long Stroke ◽  
Homogeneous Charge

This study investigates how the selection of the stroke-to-bore (S/B) ratio affects combustion, heat transfer and overall efficiency in a homogeneous charge spark ignition (SI) engine of a given displacement. Initially, flame front area maps and wall areas in contact with burned gases are examined from a purely geometric point of view, for S/B ratios of 0.7, 1.0 and 1.3. Subsequently, a quasi-dimensional turbulent flame entrainment model is used to quantify the extent to which turbulence versus geometric factors are responsible for the observed combustion, heat transfer and cycle efficiency behaviour, as the S/B ratio varies. Calculations are performed for a range of engine speeds and loads, as well as for operation with 15 per cent exhaust gas recirculation (EGR). Results show that the S/B ratio has a significant effect on both turbulence levels and the geometric interaction of the flame front with the combustion chamber walls. In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss. These effects are non-linear, being more dramatic when the S/B ratio is increased from below unity than from above unity. The potential of the long-stroke engine for brake fuel economy improvement can be exploited to the fullest at low speeds, while friction losses gradually diminish it at higher speeds.

High-Speed Spectrally Resolved Imaging Studies of Spherically Expanding Natural Gas Flames Under Gas Turbine Operating Conditions

2019 ◽  
Author(s):  
Pradeep Parajuli ◽  
Tyler Paschal ◽  
Mattias A. Turner ◽  
Eric L. Petersen ◽  
Waruna D. Kulatilaka
Keyword(s):  
Natural Gas ◽  
Flame Front ◽  
Gas Turbines ◽  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Initial Pressure ◽  
Flame Speed ◽  
Operating Conditions ◽  
Important Species

Abstract Natural gas is a major fuel source for many industrial and power-generation applications. The primary constituent of natural gas is methane (CH4), while smaller quantities of higher order hydrocarbons such as ethane (C2H6) and propane (C3H8) can also be present. Detailed understanding of natural gas combustion is important to obtain the highest possible combustion efficiency with minimal environmental impact in devices such as gas turbines and industrial furnaces. For a better understanding the combustion performance of natural gas, several important parameters to study are the flame temperature, heat release zone, flame front evolution, and laminar flame speed as a function of flame equivalence ratio. Spectrally and temporally resolved, high-speed chemiluminescence imaging can provide direct measurements of some of these parameters under controlled laboratory conditions. A series of experiments were performed on premixed methane/ethane-air flames at different equivalence ratios inside a closed flame speed vessel that allows the direct observation of the spherically expanding flame front. The vessel was filled with the mixtures of CH4 and C2H6 along with respective partial pressures of O2 and N2, to obtain the desired equivalence ratios at 1 atm initial pressure. A high-speed camera coupled with an image intensifier system was used to capture the chemiluminescence emitted by the excited hydroxyl (OH*) and methylidyne (CH*) radicals, which are two of the most important species present in the natural gas flames. The calculated laminar flame speeds for an 80/20 methane/ethane blend based on high-speed chemiluminescence images agreed well with the previously conducted Z-type schlieren imaging-based measurements. A high-pressure test, conducted at 5 atm initial pressure, produced wrinkles in the flame and decreased flame propagation rate. In comparison to the spherically expanding laminar flames, subsequent turbulent flame studies showed the sporadic nature of the flame resulting from multiple flame fronts that were evolved discontinuously and independently with the time. This paper documents some of the first results of quantitative spherical flame speed experiments using high-speed chemiluminescence imaging.

Experimental Study of Flame Stretch Under Engine-Like Conditions

2017 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A. Miers ◽  
Jeffrey D. Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Speed ◽  
Combustion Engine ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Flame Velocity ◽  
Turbulent Flame Speed ◽  
Stretch Rate ◽  
Flame Stretch

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

Assessment of elliptic flame front propagation characteristics of hydrogen in an optically accessible spark ignition engine

2013 ◽  
Vol 38 (35) ◽  
pp. 15452-15468 ◽  
Author(s):  
Balazs Ihracska ◽  
Dongsheng Wen ◽  
Shahid Imran ◽  
David R. Emberson ◽  
Lina María Ruiz ◽  
...  
Keyword(s):  
Flame Front ◽  
Front Propagation ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Propagation Characteristics

Characterization of the turbulent flame front surface in spark ignition engines during spark ignition operation to identify controlled auto-ignition and abnormal combustion

2020 ◽  
pp. 146808742093378
Author(s):  
Vicente Macián ◽  
J. Javier López ◽  
Jaime Martín ◽  
Jorge Valero-Marco
Keyword(s):  
Heat Release ◽  
Flame Front ◽  
Combustion Velocity ◽  
Turbulent Flame ◽  
Front Surface ◽  
Spark Ignition ◽  
Operating Point ◽  
Combustion Modes ◽  
Auto Ignition ◽  
Si Engines

The combustion diagnostics and subsequent analysis are standardized tools based on the estimation of the heat release law (HRL). From this estimation, the different combustion parameters can be obtained: combustion phasing and duration, heat release rate, and so on. This analysis might be usually enough to study traditional spark ignition (SI) engines. However, with the new upcoming SI engines, this is probably not the case anymore, since different combustion modes can be operated in the same engine, as for instance a combination of SI and controlled auto-ignition (CAI) combustion modes. When different combustion modes are combined, it seems interesting to study in more depth the HRL, trying to get more data and to study the differences among the diverse combustion modes. Toward this end, a methodology to go deeper in the study of the HRL is proposed in this work, consisting of, mainly quantifying and taking into account the most relevant influencing parameters: the fuel properties (mainly its lower heating value), the in-cylinder oxygen content, the density of the burned and unburned zones, the laminar combustion speed, and the turbulence effect. With the proposed methodology, a standard SI combustion, developed by a flame front, can be characterized at any given operating point. This would allow to predict which the combustion developement would be, at this operating point, assuming it to be developed by a flame front. Subsequently, this SI combustion prediction can be compared to the one obtained experimentally, making it possible to identify and analyze abnormal combustion phenomena, as well as to study the differences between a combustion developed by a flame front (SI) and by auto-ignition (CAI). Derived from this work, an alternative equation to experimentally characterize the laminar combustion velocity has also been proposed, in order to improve its applicability in a wider range of fuel/air ratios and dilution degrees.

Sign in / Sign up

Export Citation Format

Share Document