1 3 J Braz. Soc. Mech. Sci. Eng. (2017) 39:2395–2403 DOI 10.1007/s40430-017-0808-7 TECHNICAL PAPER The impact of C/H on the radiative and thermal behavior of liquid fuel flames and pollutant emissions Mehdi Boghrati 1 · Mohammad Moghiman 1 · Seyed Hadi Pourhoseini 2 Received: 17 January 2017 / Accepted: 6 May 2017 / Published online: 11 May 2017 © The Brazilian Society of Mechanical Sciences and Engineering 2017 radiation of the flame. The flame luminosity was increased by 66% when the C/H was increased from 5.47 to 5.68, whereas the flame thermal radiation increased by 26%. In addition, a new correlation is proposed to predict the lin- ear relation of the increase in the thermal radiation and the increase in the luminosity of the flame as a function of C/H. Keywords Flame thermal radiation · Luminosity · Liquid fuels · C/H · Pollutant emissions 1 Introduction Carbon-to-hydrogen mass ratio (C/H) of hydrocarbon fuel molecules is a principal factor in the interpretation of flame characteristics, e.g., sooting characteristics, cracking per- formance, coking reactivity, and ignition probability [1–5]. Besides, the C/H determines the molecule chain length in hydrocarbon fuels. A larger hydrocarbon molecule chain length causes a greater yellow region in the flame (lumi- nous region) [6]. Luminosity contributes considerably to total flame radiation that is the dominant mode of heat transfer in diffusion flames [7]. On that account, flame luminosity and flame radiation heat transfer have been increased by preheating the fuel, adding solid carbon to the fuel, and changing the air-to-fuel flow rate [8–10]. Despite the significant effect of C/H on flame luminosity, it has not been fully investigated yet to the best of our knowledge. The effects of liquid hydrocarbon fuels and biodiesels on flame radiation have been studied by several researchers. Koseki [11] measured radiative fraction, i.e., radiation heat flux to lower heating value, of various hydrocarbon fuels for a variety of C/H mass ratios. He found that increas- ing the C/H value results in an elevated radiative fraction. In another study, Love et al. [12] investigated pollutant Abstract The present experimental study is performed to document the effects of carbon-to-hydrogen mass ratio (C/H) in liquid hydrocarbon fuels, on the luminosity, ther- mal radiation rate, and temperature of flame. Furthermore, extraction of the thermal and radiative characteristics of flame, and measurement of exhaust gases including CO, CO 2 , and NO x have been carried out. The CHNS elemental analyzer system was employed to ascertain fuel composi- tion. The thermopile sensor and the lux meter were utilized to measure the flame thermal radiation and luminosity. The measured flame radiation spectrum included all pos- sible wavelengths (i.e., flame thermal radiation) and vis- ible wavelengths (i.e., luminosity). The flame photography technique, as a non-intrusive method, depicted the flame visible radiation, IR spectral emittance, and high tempera- ture zone. The results revealed that the luminosity and ther- mal radiation of the flame increased as we increase C/H. A rise in C/H made the temperature along the flame axis more uniform. The NO x emissions were within standard levels (i.e., under 200 ppm). It was also shown that the C/H variation has a greater effect on luminosity than thermal Technical Editor: Fernando Marcelo Pereira. * Mohammad Moghiman moghiman@um.ac.ir Mehdi Boghrati mehdi.boghrati@mail.um.ac.ir Seyed Hadi Pourhoseini hadipoorhoseini@gmail.com 1 Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran 2 Department of Mechanical Engineering, Faculty of Engineering, University of Gonabad, Gonabad, Iran