Experimental investigation of flammability limits and flame characteristics of LPG–H₂ mixtures at various equivalence ratios via image processing techniques

Abstract

In combustion systems, determining the flammability limits of the fuel–air mixture to be used, or establishing the conditions that enable combustion within the desired limits, is of critical importance. By doing so, instabilities that may occur in the system can be minimized, and operational safety can be ensured. In the present study, the flammability limits and instantaneous flame images of premixed burners were experimentally investigated as a function of the amount of H₂ added to pure LPG. The H₂ content was increased up to 80%, while the swirl number and thermal power were kept constant at 1 and 4 kW, respectively, under all experimental conditions. Instantaneous flame images were taken at different equivalence ratios at 0.1 intervals below stoichiometric conditions and at 0.2 intervals above stoichiometric conditions. Flame brightness and RGB (red-green-blue) values were evaluated quantitatively in detail by image processing with HSV and grayscale detection methods using MATLAB. For 100% LPG, the stable flammability limits are ϕ=0.8–2.8, while with hydrogen enrichment the lower flammability limit expands to ϕ=0.4, and the upper flammability limit decreases to ϕ=2.0 (for 20% LPG–80% H₂). The results revealed that hydrogen addition significantly affects the LPG flame behavior, alters the stable flammability limits, and increases flame brightness up to ϕ=1.6.

Keywords

• LPG
• Hydrogen
• Flammability limits
• Instantaneous flame images
• MATLAB
• Image processing

Kaynakça

1. [1] Fosudo T, Kar T, Windom B, Olsen D. Low-carbon fuels for spark-ignited engines: A comparative study of compressed natural gas and liquefied petroleum gas on a CFR engine with exhaust gas recirculation. Fuel. 2024;360:130456.
2. [2] Talib Hashem G, Al-Dawody MF, Sarris IE. The characteristics of gasoline engines with the use of LPG: An experimental and numerical study. International Journal of Thermofluids. 2023;18:100316.
3. [3] Ianniello R, Di Blasio G, Marialto R, Beatrice C, Cardone M. Assessment of Direct Injected Liquefied Petroleum Gas-Diesel Blends for Ultra-Low Soot Combustion Engine Application. Applied Sciences. 2020;10(14):4949.
4. [4] Tira H, Herreros J, Tsolakis A, Wyszyński M. Characteristics of LPG-diesel dual fuelled engine operated with rapeseed methyl ester and gas-to-liquid diesel fuels. Energy. 2012;47:620-9.
5. [5] Tchato Yotchou GV, Issondj Banta NJ, Kabini Karanja S, Ngayihi Abbe CV. Experimental study on the effect of load and air+gas/fuel ratio on the performances, emissions and combustion characteristics of diesel–LPG fuelled single stationary ci engine. Engineering Reports. 2023;5(9):e12654.
6. [6] Dostiyarov AM, Umyshev DR, Aidymbayeva ZA, Yamanbekova AK, Duisenbek ZS, Kumargazina MB, et al. Comparative Study of the NOx, CO Emissions, and Stabilization Characteristics of H2-Enriched Liquefied Petroleum Gas in a Swirl Burner. Energies. 2024;17(23):6132.
7. [7] Dostiyarov AM, Umyshev DR, Kibarin AA, Yamanbekova AK, Tumanov ME, Koldassova GA, et al. Experimental Investigation of Non-Premixed Combustion Process in a Swirl Burner with LPG and Hydrogen Mixture. Energies. 2024;17(5):1012.
8. [8] Yangaz M, Özdemir MR, Şener R. Combustion performance of hydrogen-enriched fuels in a premixed burner. Environmental Technology. 2020;41:13-22.

9. [9] Escofet-Martin D, Chien Y-C, Dunn-Rankin D. PLIF and chemiluminescence in a small laminar coflow methane-air diffusion flame at elevated pressures. Combustion and Flame. 2022;243:112067.
10. [10] Grauer SJ, Mohri K, Yu T, Liu H, Cai W. Volumetric emission tomography for combustion processes. Progress in Energy and Combustion Science. 2023;94:101024.
11. [11] Maes N, Meijer M, Dam N, Somers B, Toda H, Bruneaux G, et al. Characterization of Spray A flame structure for parametric variations in ECN constant-volume vessels using chemiluminescence and laser-induced fluorescence. Combustion and Flame. 2016;174:138-51.
12. [12] Swain W, Wang Y, Parajuli P, Hay M, Saylam A, Dreier T, et al. Characterization of a high-pressure flame facility using high-speed chemiluminescence and OH LIF imaging. Experiments in Fluids. 2023;64(4):71.
13. [13] Tagliante F, Nguyen TM, Dhanji MP, Sim HS, Pickett LM, Manin J, et al. The role of cool-flame fluctuations in high-pressure spray flames, studied using high-speed optical diagnostics and Large-Eddy Simulations. Proceedings of the Combustion Institute. 2023;39(4):4871-9.
14. [14] Tiwari P, Premchand C, Palies P. Ignition characteristics of fully premixed hydrogen/air and methane/air flames with high-speed chemiluminescence and schlieren imaging. Turbo Expo: Power for Land, Sea, and Air: American Society of Mechanical Engineers; 2024. p. V03BT4A074.
15. [15] Wang H, He Z, Tang T, Li F, Tian Y, Wan M, et al. Visualization of supersonic combustion using high-speed camera/dual-component planar laser-induced fluorescence simultaneous diagnostic technique. Physics of Fluids. 2023;35(9).
16. [16] Sellan D, Pillai SK, Murugan R, Balusamy S. Blending hydrogen with LPG and methane in premixed and stratified flames: an experimental study. Journal of Flow Visualization and Image Processing. 2024;31(3):21-36.
17. [17] Liang Y, Zhao Z, Song S, Wang J, Liu L, Bai J. Study on Flame Propagation of H2/LPG Premixed Gas in a Tube (Preprint). SSRN Electronic Journal. 2023.
18. [18] Elshimy M, Ibrahim S, Weeratunge W. Numerical Studies of Hydrogen and LPG Turbulent Premixed Flames (ICMFHT 129). Proceedings of the 7th World Congress on Momentum, Heat and Mass Transfer (MHMT'22). Lisbon, Portugal, 2022.
19. [19] Zhao Z, Liang Y, Guo B, Song S, Bai J. Explosion dynamics of premixed LPG/H2 fuel in a confined space. International Journal of Hydrogen Energy. 2023;48(92):36211-21.
20. [20] AbdulAmeer MT, Shahad H, Abdulhaleem S. Experimental Investigation of LPG/H2/Air Premixed Flame Stability Zone. Journal of Engineering and Technological Sciences. 2020;52:691-706.
21. [21] Sankar V, Jithin E, Mohammad A, Velamati RK. Effect of Hydrogen Addition on Laminar Burning Velocity of Liquefied Petroleum Gas Blends. Energy & Fuels. 2020;34:798-805.
22. [22] Ghazal RM, Akroot A, Abdul Wahhab HA. Flame Evolution Characteristics for Hydrogen/LPG Co-Combustion in a Counter-Burner. Applied Sciences. 2025;15(5):2503.
23. [23] Aravindan M, Praveen Kumar G, Arulanandam MK, Murali S, Sheoran N, Waykole N, et al. Multi-objective optimization and analysis of chemical kinetics properties: Exploring the impact of different hydrogen blending ratios on LPG and methane-air mixtures. Energy Conversion and Management: X. 2024;22:100532.
24. [24] Zhen HS, Cheung CS, Leung CW, Choy YS. Effects of hydrogen concentration on the emission and heat transfer of a premixed LPG-hydrogen flame. International Journal of Hydrogen Energy. 2012;37(7):6097-105.
25. [25] Sharma D, Singh AS, Alsulami R, Lee BJ, Dash SK, Reddy VM. Numerical investigations on tri-fuel chemical kinetics of hydrogen + Methane +LPG/air mixtures using reduced skeletal mechanism. International Journal of Hydrogen Energy. 2022;47(54):23038-59.
26. [26] Li Z, Chen J, Liu Z, Li Y, Chu Y, Chen Y, et al. Free-radical fluorescence emissions induced by 1,030 nm femtosecond laser filamentation in ethanol flame. Frontiers in Physics. 2022;10:1029954.
27. [27] Sadeghi SS, Tabejamaat S, Ghahremani A, Asl SN. A novel Swiss-roll counterflow micro-combustor: Experimental investigation of flame dynamic characteristics by spectroscopy and RGB image processing methods. Energy. 2024;299:131495.
28. [28] Omiotek Z, Kotyra A. Flame Image Processing and Classification Using a Pre-Trained VGG16 Model in Combustion Diagnosis. Sensors. 2021;21(2):500.
29. [29] Ryu J, Kwak D. Flame Detection Using Appearance-Based Pre-Processing and Convolutional Neural Network. Applied Sciences. 2021;11(11):5138.
30. [30] Ryu J-K, Kwak D-K. Flame Detection Based on Deep Learning Using HSV Color Model and Corner Detection Algorithm. Fire Sci Eng. 2021;35(2):108-14.
31. [31] Sun M, Han W. Flame Image Segmentation Method Based on Color Features. 2023 5th International Academic Exchange Conference on Science and Technology Innovation (IAECST). 2023:734-7.
32. [32] Turns SR. Introduction to combustion: McGraw-Hill Companies New York, NY, USA, 1996.
33. [33] Jones DR, Al-Masry WA, Dunnill CW. Hydrogen-enriched natural gas as a domestic fuel: an analysis based on flash-back and blow-off limits for domestic natural gas appliances within the UK. Sustainable Energy & Fuels. 2018;2(4):710-23.
34. [34] Lieuwen T, McDonell V, Santavicca D, Sattelmayer T. Burner development and operability issues associated with steady flowing syngas fired combustors. Combustion Science and Technology. 2008;180(6):1169-92.
35. [35] Liñán A, Vera M, Sánchez AL. Ignition, liftoff, and extinction of gaseous diffusion flames. Annual Review of Fluid Mechanics. 2015;47(1):293-314.
36. [36] Zhang Y, Wu J, Ishizuka S. Hydrogen addition effect on laminar burning velocity, flame temperature and flame stability of a planar and a curved CH4–H2–air premixed flame. international journal of hydrogen energy. 2009;34(1):519-27.
37. [37] Cheng Q, Ahmad Z, Kaario O, Vuorinen V, Larmi M. Effect of Hydrogen Enhancement on Natural Flame Luminosity of Tri-Fuel Combustion in an Optical Engine. Energies. 2022;15(23):9080.
38. [38] Choi J, Rajasegar R, Lee W, Lee T, Yoo J. Hydrogen enhancement on a mesoscale swirl stabilized burner array. International Journal of Hydrogen Energy. 2021;46(46):23906-15.
39. [39] Cheng Q, Karimkashi S, Ahmad Z, Kaario O, Vuorinen V, Larmi M. Hyperspectral image reconstruction from colored natural flame luminosity imaging in a tri-fuel optical engine. Scientific Reports. 2023;13(1):2445.
40. [40] Portilla J, Cruz J, Escudero F, Demarco R, Fuentes A, Carvajal G. A generalized neural network for accurate estimation of soot temperature in laminar flames using a single RGB image. Journal of the Energy Institute. 2025;119:102001.
41. [41] Yamamoto K, Sawada W. Measurements of C2 and CH chemiluminescence of CH4/H2 flames by a digital camera. Journal of Thermal Science and Technology. 2024;19(1):23-00587.
42. [42] WebBook NC. Heat Values of Various Fuels. World Nuclear Association; 2025.
43. [43] Lin Y-C, Lin S-L, Jhang S-R, Chen K-S, Su C-W, Huang C-E. Energy saving and pollutant emission reduction by adding hydrogen in a gasoline-fueled engine. Aerosol and Air Quality Research. 2022;22(11):220259.
44. [44] Shadidi B, Najafi G, Yusaf T. A review of hydrogen as a fuel in internal combustion engines. Energies. 2021;14(19):6209.