# Synergistic Effects of Fuel Components on Aromatics Formation in Combustion: A Review
## 5 Conclusions and Perspectives  
Carcinogenic polycyclic aromatic hydrocarbons are produced during the combustion process., with their formation contingent upon the fuel type and reaction conditions. Fuel blends play a pivotal role in shaping the composition of PAH formation. Given the diverse and intricate nature of PAHs, numerous reactions have been delineated and consolidated in this review, delineating different pathways for PAH formation. However, ongoing research may uncover new mechanisms that contribute to a deeper understanding of PAH formation.  
The review offers a comprehensive analysis of the synergistic effect on both mono-aromatic and PAH formation during the combustion process, drawing from a combination of experimental and simulation studies. It emphasized the significant influence of temperature and pressure on the interaction between fuel components, such as 1,3-butadiene/propyne, propane/ethylene, and ethane/ethylene, leading to the formation of mono-aromatic hydrocarbons. Conversely, the addition of dimethyl ether and ethanol to ethylene exhibited a synergistic effect at low concentrations but diminished at higher concentrations of oxygenated fuel components. Furthermore, the review summarizes findings related to synergistic effects in the formation of indene, naphthalene, and higher polyaromatic hydrocarbon formation in various mixtures. Mechanisms such as hydrogen abstraction and acetylene addition (HACA) were found to significantly influence indene and naphthalene formation, while reactions involving resonantly stabilized indenyl radicals and cyclopentadienyl radical reactions contributed to phenanthrene and pyrene formation.  
A further key development for understanding the synergistic effects on aromatic formation is the identification of more critical reactions, especially for larger PAHs. Additional reaction pathways have been uncovered, contributing to PAH formation in various contexts, such as sustainable aviation fuel combustion and the interstellar medium. These advancements encompass more comprehensive measurements of PAHs in both premixed and non-premixed flames, flow reactors, and jet-stirred reactors, as well as quantum chemical computational calculations aimed at enhancing our understanding of the key reactions involved in synergistic effects on aromatic formation. Furthermore, the understanding of  
Figure 24: Measured and simulated PAH mole fractions in the (**a**) propane/ethylene counterflow flame and (**b**) benzene/ethylene/propane counterflow flame (reprinted from [PERSON] et al., 2013) [115].  
synergistic effects on soot formation will be facilitated by the use of diagnostic methods and numerical simulations.  
Conceptualization, Y.L. and B.H.; formal analysis, B.H.; investigation, B.H. and Q.F.; writing--original draft preparation, B.H.; writing--review and editing, W.L.; funding acquisition, W.L. and Y.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (52206164), the Science Center for Gas Turbine Project (P2022-B-II-017-001) and the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University (SL2022 ZD104).  
Not applicable.  
Data Availability Statement: Data will be made available on request.  
The authors declare no conflicts of interest.