Spectral Diagnostics of Diesel Flame Radiation in Gasifiers

2025-06-24

Flame Spontaneous Radiation Characteristics

Spontaneous radiation spectra provide critical insights into flame structure, combustion state, and temperature distribution without disturbing the flame. In hydrocarbon flames, discrete spectral radiation originates from excited radicals:

OH & CH**: Located at fuel burned/unburned interface
C₂: Marks flame boundaries
CO₂: Continuous background radiation

Flame height is defined by CH peak position along the axis, avoiding soot interference.*

Technical Challenges in Gasifier Monitoring

Complex Diesel Flame Properties

Under high-temperature/pressure conditions, diesel flame radiation combines:

Radical emission spectra (CH, OH) indicating reaction activity
Soot continuum radiation from incomplete combustion

Traditional methods struggle to decouple these overlapping signals for real-time analysis.

Industry Demands

Efficiency and emission regulations drive need for:

Combustion optimization to increase energy conversion
Pollution control through emission pathway analysis

Optosky Spectrometer Solutions

ATP5020 High sensitivity & resolution Cooling Spectrometer

ATL30007 Muti-channel Spectrometer for LIBS

Core Advantages

Instrument	ATP5020	ATL30007
Measurement	Non-contact	Multi-channel
Resolution	Standard	Ultra-high
Range	UV-Vis	190-1100nm

Key Capabilities:

Non-contact operation: Collects radiation through gasifier viewports
Radical detection: Resolves OH* (306.47 nm), CH* (431.42 nm), Na*/K* peaks despite soot interference
Multi-spectrometer stitching: Covers 200-950 nm with <0.1 nm resolution

Critical Parameters & Applications

Equivalence Ratio (Φ) Effects

Decreasing CH* intensity at Φ→1.0 indicates complete combustion
Higher Φ reduces soot radiation, enhancing radical detection

Flame Stability Metrics

Flame lift-off length (nozzle detachment distance) correlates with CH* intensity, providing:

Early instability detection
Operational parameter optimization benchmarks

Experimental Validation

Gasifier Setup

Schematic of Multi-Nozzle Opposed Entrained-Flow Gasifier

Fiber probe: 3mm diameter, 25° FOV positioned at refractory brick
Spectrometers: Quad-system covering 200-950 nm

Spectral Findings

Flame Spectral Radiation Lines in the 420-450 nm Band Spectral Radiation Lines of Diesel Flame

Condition	Key Observations
Φ=0.6	Strong soot continuum obscures CH* peak
Φ=0.3	Distinct OH/CH/Na/K/Ar* peaks
420-450 nm band	CH* peak clarity increases with Φ

The figure shows the radiation spectra of diesel flames measured by a fiber optic spectrometer in the central region of the combustion chamber under single-nozzle conditions at [O/C]e = 0.6 and [O/C]e = 1.3. Key observations include:

OH* radiative peaks at 306.47 nm and 309.12 nm,
A distinct CH* radiative peak at 431.42 nm,
Emission lines from alkali metals: Na* at 589.45 nm and K* at 766.91 nm and 770.06 nm. Argon was used as the purge gas during experiments, resulting in an Ar* peak at 670.74 nm. At [O/C]e = 0.6, incomplete combustion produced significant soot, leading to intense continuous blackbody radiation in the visible spectrum.

Excited radicals in flames form via thermal excitation (e.g., Na*, K*, Ar*) and chemical excitation (e.g., OH*, CH*). The CH* peak at 431.42 nm was isolated within the 420–450 nm range for detailed analysis. As the equivalence ratio ([O/C]e) increases:

Total radiative intensity decreases due to reduced soot (weaker blackbody radiation),
Background radiation shifts toward CO₂* contributions,
The CH* peak becomes less prominent and nearly vanishes in fuel-rich flames.Lower equivalence ratios strengthen background radiation, significantly interfering with radical peak detection.

This demonstrates that background radiation (e.g., from CO₂* or soot) critically impacts the visibility of CH* and other radical-specific emissions, particularly in fuel-lean conditions.

Industrial Applications