# Isopar-M spray flame forms smaller soot particles than Jet A-1 in laser incandescence tests

- Published: 2026-11-13 20:32 UTC
- Section: Sky & Space › Aviation
- Tags: laser-induced incandescence, soot particle size, Jet A-1 kerosene, Isopar-M surrogate, turbulent spray flames, soot volume fraction, alternative aviation fuel, LII diagnostics, Applied Physics B
- URL: https://realtech.media/news/rt-b17d6b47cf2411fdead48d64_isopar_m_spray/

**Authors measured soot in turbulent spray flames of Jet A-1 and the Isopar-M surrogate on a laboratory burner; Isopar-M showed weaker signals and limited particle growth.**

![Isopar-M spray flame forms smaller soot particles than Jet A-1 in laser incandescence tests](https://realtech.media/media/2026/11/ae61d80806d6371b.jpg)
*Arthur Jan Fijałkowski, Wikimedia Commons, CC BY-SA 3.0*

Researchers Brendan Gachot, Cornelia Irimiea, Renaud Jalain, Nicolas Fdida and Xavier Mercier compared soot formation in turbulent spray flames of Jet A-1 kerosene and Isopar-M, a laboratory surrogate for alternative aviation fuel. The work was published in Applied Physics B and used three laser-induced incandescence (LII) configurations: time-resolved, planar and spectral. [1] According to the authors, the Jet A-1 flame produced higher soot loads and longer signal decay times, while the Isopar-M flame gave weak signals. [1]

## Burner and measurement setup

Both flames were stabilized on a laboratory burner at atmospheric pressure with a nebulizer. Fuel flow was held at 100 grams per hour, atomized with 18 grams per hour of nitrogen, and the co-flowing air was 1500 grams per hour. The flames were about 270 millimeters tall. Isopar-M serves as a laboratory analog of alcohol-to-jet synthetic kerosene.

For LII, the team used a pulsed Nd:YAG laser at 532 nanometers with a fluence of 80 millijoules per square centimeter, below the soot sublimation threshold. Time-averaged planar images were compiled from 2000 instantaneous frames.

## Particle size, distribution and filaments

The decay time of the incandescence signal reflects primary particle size: a longer decay indicates larger particles. In the Jet A-1 flame, decay times ranged from 50 to 550 nanoseconds and peaked between 140 and 150 millimeters above the burner. In the Isopar-M flame they stayed between 50 and 150 nanoseconds with an essentially flat axial profile, which the authors interpret as limited particle growth. [1] Average incandescence intensity in Jet A-1 was roughly three times that of Isopar-M.

Planar images differed as well. The Jet A-1 flame showed a clear signal maximum between 110 and 140 millimeters. The Isopar-M signal was lower and more homogeneous, so locations where soot formation or oxidation dominates could not be distinguished. [1] Filament intermittency was assessed with statistical image-to-image metrics. Spectral measurements revealed interfering fluorescence and allowed the soot volume fraction in the Jet A-1 flame to be inferred. [1]

The authors conclude that soot formation in spray flames is complex and requires multi-scale, time-resolved measurements to characterize. [1]

## Sources

1. [Applied Physics B](https://doi.org/10.1007/s00340-026-08655-8)
2. [bioengineer.org](https://bioengineer.org/laser-diagnostics-reveal-alternative-aviation-fuel-yields-significantly-smaller-soot-particles)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-b17d6b47cf2411fdead48d64_isopar_m_spray/