Formation of Soot in Ethylene–Air Partially Premixed Flames Over a Wide Range of Premixedness

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Aritra Chakraborty ◽  
Satya R. Chakravarthy
Keyword(s):  
Flow Rate ◽  
Volume Fraction ◽  
Premixed Flames ◽  
Soot Volume Fraction ◽  
Premixed Flame ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Wide Range ◽  
Partially Premixed Flames ◽  
Partially Premixed

This paper reports an investigation of soot formation in ethylene–air partially premixed flames (PPFs) over a wide range of premixedness. An axisymmetric co-flow configuration is chosen to establish PPFs from the fully nonpremixed to fully premixed conditions. Reducing the fuel flow rate as a percentage of the maximum from the core stream and supplying the same to the annular stream leads to stratification of the reactant concentrations. The thermal power, overall equivalence ratio, and the average velocity in both the streams are maintained constant under all conditions. The soot volume fraction is estimated by light attenuation method, and laser-induced incandescence (LII) is performed to map the soot distribution in the flow field. The soot volume fraction is observed to exhibit an “S”-type trend as the conditions are traversed from near the premixed to the nonpremixed regimes. That is, when traversing from the nonpremixed to near-premixed regime, below 60% fuel flow rate in core, the soot volume fraction drops drastically. The onset of sooting in the PPFs is clearly seen to be at the tip of the rich-premixed flame (RPF) branch of their triple flame structure, which advances upstream toward the base of the flame as the premixing is reduced. The S-type variation is clearly the effect of partial premixing, more specifically due to the presence of the lean premixed flame (LPF) branch of the triple flame. LII intensities are insufficient to capture the upstream advance of the soot onset with decreased premixedness. So, a quick and inexpensive technique to isolate soot luminescence through flame imaging is presented in the paper involving quasi-simultaneous imaging with a 650 nm and a BG-3 filter using a normal color camera.

Formation of Soot in Ethylene-Air Partially Premixed Flames Over a Wide Range of Premixedness

2017 ◽  
Author(s):  
Aritra Chakraborty ◽  
Satya R. Chakravarthy
Keyword(s):  
Volume Fraction ◽  
Premixed Flames ◽  
Soot Volume Fraction ◽  
Premixed Flame ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Wide Range ◽  
Partially Premixed Flames ◽  
Laser Induced Incandescence ◽  
Partially Premixed

This paper reports an investigation of soot formation in ethylene-air partially premixed flames over a wide range of premixedness. An axisymmetric co-flow configuration is chosen to establish partially premixed flames from the fully non-premixed to fully premixed conditions. Reducing the fuel flow rate as a percentage of the maximum from the core stream and supplying the same to the annular stream leads to stratification of the reactant concentrations. The thermal power, overall equivalence ratio, and the average velocity in the both streams are maintained constant under all conditions. The soot volume fraction is estimated by light attenuation method, and laser induced incandescence is performed to map the soot distribution in the flow field. The soot volume fraction is observed to exhibit a ‘S’-type trend as the conditions are traversed from near the premixed to the non-premixed regimes. That is, when traversing from the non-premixed to near-premixed regime, below 60% fuel flow rate in core, the soot volume fraction drops drastically. The onset of sooting in the partially premixed flames is clearly seen to be at the tip of the rich-premixed flame branch of their triple flame structure, which advances upstream towards the base of the flame as the premixing is reduced. The ‘S’-type variation is clearly the effect of partial premixing, more specifically due to the presence of the lean premixed flame branch of the triple flame. Laser induced incandescence intensities are insufficient to capture the upstream advance of the soot onset with decreased premixedness. So, a quick and inexpensive technique to isolate soot luminescence through flame imaging is presented in the paper involving quasi-simultaneous imaging with a 650 nm and a BG-3 filter using a normal color camera.

Two-Dimensional Imaging of Soot Volume Fraction in Pulsed Diffusion Flames by Laser-Induced Incandescence

2006 ◽  
Author(s):  
H. Sapmaz ◽  
C. Ghenai
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Volume Fraction ◽  
Two Dimensional ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Laser Induced Incandescence ◽  
Pulsed Flames

Laser-Induced Incandescence (LII) is used in this study to measure soot volume fractions in steady and flickering ethylene diffusion flames burning at atmospheric pressure. Better understanding of flickering flame behavior also promises to improve understanding of turbulent combustion systems. A very-high-speed solenoid valve is used to force the fuel flow rate with frequencies between 10 Hz and 200 Hz with the same mean fuel flow rate of steady flame. Periodic flame flickers are captured by two-dimensional phase-locked emission and LII images for eight phases (0°–360°) covering each period. LII spectra scan for minimizing C2 swan band emission and broadband molecular florescence, a calibration procedure using extinction measurements, and corrections for laser extinction and LII signal trapping are carried out towards developing reliable LII for quantitative applications. A comparison between the steady and pulsed flames results and the effect of the oscillation frequency on soot volume fraction for the pulsed flames are presented.

scholarly journals Experimental Investigation of Oxygen Addition to Fuel on Soot Formation in Laminar Coflow Diffusion Flames of Ethylene and Propane

2006 ◽  
Author(s):  
Fengshan Liu ◽  
Kevin A. Thomson ◽  
Gregory J. Smallwood
Keyword(s):  
Flow Rate ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Soot Volume Fraction ◽  
Oxygen Flow Rate ◽  
Flame Height ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Oxygen Addition

Investigation of the effect of oxygen addition to fuel on the visible flame appearance and soot formation characteristics of laminar diffusion flames is important to gain comprehensive understanding of gas-phase combustion chemistry and its interaction with soot chemistry. This paper reports experimental results of oxygen addition to fuel on the visible flame height and soot volume fraction distributions in axisymmetric coflow laminar ethylene and propane diffusion flames at atmospheric flames. The carbon flow rate was maintained constant in all the experiments. Although many experimental studies have been conducted in the literature in this topic, the present investigation aimed at providing spatially resolved soot volume fraction distributions over the entire range of oxygen addition from no oxygen addition up to the point of flashback while keeping the carbon mass flow rate constant. The level of oxygen added to fuel right before flashback is about 45% (the percentage of oxygen addition is always by volume in this study) of the fuel flow rate in the ethylene flame and 300% of the fuel flow rate in the propane flame. As the added oxygen amount to ethylene increases, the visible flame height first increases. When the added oxygen flow rate is about 13% of the fuel flow rate, the flame becomes smoking, i.e., soot escapes from the flame tip. When the oxygen flow rate reaches about 42% of the fuel flow rate, the flame stops smoking. When oxygen was added to propane, the visible flame height linearly decreases with increasing the amount of oxygen. These very different effects of oxygen addition to ethylene and propane indicate that oxygen plays a drastically different role in the chemical pathways leading to soot formation in ethylene and propane flames. Distributions of soot volume fractions in these flames were measured using a 2D light attenuation technique coupled with the Abel inversion. The present study provides valuable experimental data for validating soot models.

Measurements of Soot Volume Fraction in Pulsed Diffusion Flames by Laser-Induced Incandescence

2006 ◽  
Author(s):  
H. Sapmaz ◽  
C. Ghenai
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Volume Fraction ◽  
Calibration Procedure ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Laser Induced Incandescence ◽  
Pulsed Flames

Laser-Induced Incandescence (LII) is used in this study to measure soot volume fractions in steady and flickering ethylene diffusion flames burning at atmospheric pressure. Better understanding of flickering flame behavior also promises to improve understanding of turbulent combustion systems. A very-high-speed solenoid valve is used to force the fuel flow rate with frequencies between 10 Hz and 200 Hz with the same mean fuel flow rate of steady flame. Periodic flame flickers are captured by two-dimensional phase-locked emission and LII images for eight phases (0° - 360°) covering each period. LII spectra scan for minimizing C2 swan band emission and broadband molecular florescence, a calibration procedure using extinction measurements, and corrections for laser extinction and LII signal trapping are carried out towards developing reliable LII for quantitative applications. A comparison between the steady and pulsed flames results and the effect of the oscillation frequency on soot volume fraction for the pulsed flames are presented.

Laminar Flame Characteristics of Partially Premixed Palm Methyl Ester Gas Flames

2013 ◽  
Author(s):  
Diego Romero ◽  
Ramkumar N. Parthasarathy ◽  
Subramanyam R. Gollahalli
Keyword(s):  
Methyl Ester ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Volume Fraction ◽  
Laminar Flame ◽  
Soot Volume Fraction ◽  
Fuel Flow ◽  
Combustion Properties ◽  
Emission Index ◽  
Palm Methyl Ester

Palm methyl ester (PME) is a renewable biofuel that is produced by the transesterification of palm oil; it is a popular alternative fuel used in the transportation sector. The objective of this investigation was to study the combustion characteristics of flames of pre-vaporized diesel and PME in a laminar flame environment at initial equivalence ratios of 2, 3 and 7 and to isolate the factors attributable to chemical structure of the fuel. The equivalence ratio was changed by altering the fuel flow rate, while maintaining the air flow rate constant. The global CO emission index of the PME flames was significantly lower than that of the diesel flames; however, the global NO emission index was comparable. The radiative fraction of heat release and the soot volume fraction were lower for the PME flames compared to the diesel flames. The peak temperatures were comparable at an equivalence ratio of 2, but at higher equivalence ratios, the peak temperatures in the PME flames were higher. The measurements highlight the differences in the combustion properties of biofuels and petroleum fuels and the coupling effects of equivalence ratio.

Dilution and Suppression of Partially Premixed Flames in Normal and Microgravity for Different Fuels

2006 ◽  
Author(s):  
Andrew J. Lock ◽  
Alejandro Briones ◽  
Suresh K. Aggarwal ◽  
Ishwar K. Puri ◽  
Uday G. Hegde
Keyword(s):  
Volume Fraction ◽  
Premixed Flames ◽  
Dilution Effect ◽  
Critical Volume ◽  
Area Of Interest ◽  
Air Stream ◽  
Partially Premixed Flames ◽  
Critical Volume Fraction ◽  
Partially Premixed ◽  
Fuel Stream

The suppression of fires and flames is an important area of interest for both terrestrial and space based applications. In this investigation we elucidate the relative efficacy of fuel and air stream inert diluents for suppressing laminar partially premixed flames. A comparison of the effects of fuel and air stream dilution are also made with other fuels. Both counterflow and coflow flames are investigated, with both normal and zerogravity conditions considered for coflow flames. Simulations are conducted for both the counterflow and coflow flames, while experimental observations are made on the coflowing flames. With fuel or air stream dilution, coflow flames are observed to move downstream from the burner after overcoming initial heat transfer coupling. Further increases in diluent result in increases in the flame liftoff height until blow off occurs. The flame liftoff height and the critical volume fraction of extinguishing agent at blow out vary with both equivalence ratio and with the stream in which diluents are introduced. Nonpremixed methane-air flames are more difficult to extinguish than partially premixed flames with fuel stream dilution; whereas, partially premixed methane-air flames are more resistant to extinction than nonpremixed flames with air stream dilution. This difference in efficacy of the fuel and air stream dilution is attributed to the action of the diluent. In leaner partially premixed flames with fuel stream dilution and richer partially premixed flames with air stream dilution the effect of the diluent is to replace the deficient reactant in the system, thus starving the flame. In leaner partially premixed flames with air stream dilution and richer partially premixed flames with fuel stream dilution the effect of the diluent is purely thermal in that it absorbs heat from the flame, until combustion may no longer be sustained. The dilution effect is more effective than the thermal effect. When gravity is eliminated from the 2-D flame the liftoff height decreases and the critical volume fraction of diluent for blow off is also decreased.

Laminar Partially Premixed Flames of Blends of Pre-Vaporized Jet-A Fuel and Palm Methyl Ester

2014 ◽  
Author(s):  
Arun Balakrishnan ◽  
Ramkumar N. Parthasarathy ◽  
Subramanyam R. Gollahalli
Keyword(s):  
Methyl Ester ◽  
Flow Rate ◽  
Volume Fraction ◽  
Air Flow ◽  
Soot Volume Fraction ◽  
Flame Length ◽  
Phase Reaction ◽  
Combustion Properties ◽  
Partially Premixed ◽  
Palm Methyl Ester

Biofuels, such as palm methyl ester (PME), are attractive alternates to petroleum fuels. In order to isolate the effects of fuel chemistry on the combustion properties, laminar partially premixed pre-vaporized flames of blends of Jet-A and PME (volume concentrations of 25%, 50%, 75% PME) were studied. A stainless steel circular tube (ID of 9.5 mm) served as the burner. The liquid fuel was supplied with a syringe pump into a high temperature (390°C) air flow to vaporize it completely without coking. The fuel flow rate was maintained constant and the air flow rate adjusted to obtain burner-exit equivalence ratios of 2, 3 and 7. The global flame properties including flame length, CO and NO emission indices, radiative heat fraction and in-flame properties including gas concentration (CO, CO2, NO, O2), temperature and soot volume fraction were measured. The near-burner homogeneous gas-phase reaction zone increased in length with the addition of PME at all equivalence ratios. The concentration and global emission measurements highlight the non-monotonic variation of properties with the volume concentration of PME in the fuel. The fuel-bound oxygen of PME affected the combustion properties significantly.

An Experimental Investigation of HCCI Combustion Stability Using N-Heptane

2007 ◽  
Author(s):  
Hailin Li ◽  
W. Stuart Neill ◽  
Wally Chippior ◽  
Joshua D. Taylor
Keyword(s):  
Heat Release ◽  
Flow Rate ◽  
Combustion Process ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Air Temperatures ◽  
Wide Range ◽  
Cyclic Variations

In this paper, cyclic variations in the combustion process of a single-cylinder HCCI engine operated with n-heptane were measured over a range of intake air temperatures and pressures, compression ratios, air/fuel ratios, and exhaust gas recirculation (EGR) rates. The operating conditions produced a wide range of combustion timings from overly advanced combustion where knocking occurred to retarded combustion where incomplete combustion was detected. Cycle-to-cycle variations were shown to depend strongly on the crank angle phasing of 50% heat release and fuel flow rate. Combustion instability increased significantly with retarded combustion phasing especially when the fuel flow rate was low. Retarded combustion phasing can be tolerated when the fuel flow rate is high. It was also concluded that the cyclic variations in imep are primarily due to the variations in the total heat released from cycle-to-cycle. The completeness of the combustion process in one cycle affects the in-cylinder conditions and resultant heat release in the next engine cycle.

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