Next Article in Journal
Engineering-Oriented Layout Optimization and Trade-Off Design of a 12U CubeSat with In-Orbit Validation
Previous Article in Journal
Aero-Structural Design Optimization of a Transonic Fan Rotor Using an Adaptive POD-Based Hybrid Surrogate Model
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Aerospace
Volume 12
Issue 6
10.3390/aerospace12060505
aerospace-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Surrogate Models and Related Combustion Reaction Mechanisms for a Coal-Derived Alternative Jet Fuel and Its Blends with a Traditional RP-3

by
Quan-De Wang
1,*,
Lan Du
2,
Bi-Yao Wang
2,*,
Qian Yao
3,
Jinhu Liang
4,
Ping Zeng
2 and
Zu-Xi Xia
2
1
Jiangsu Key Laboratory of Coal-Based Greenhouse Gas Control and Utilization, Carbon Neutrality Institute and School of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, China
2
Aviation Fuel and Chemical Airworthiness Certification Centre of CAAC, The Second Research Institute of CAAC, Chengdu 610041, China
3
College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
4
School of Environmental and Safety Engineering, North University of China, Taiyuan 030051, China
*
Authors to whom correspondence should be addressed.
Aerospace 2025, 12(6), 505; https://doi.org/10.3390/aerospace12060505
Submission received: 7 May 2025 / Revised: 30 May 2025 / Accepted: 30 May 2025 / Published: 3 June 2025
(This article belongs to the Topic Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion)
Browse Figures
Versions Notes

Abstract

Jet fuel from direct coal liquefaction (DCL) is an important alternative kerosene and represents a high-performance fuel for specific applications in civil applications. The study on its chemical positions and combustion properties is critical for the development of surrogate models and related combustion reaction mechanisms, which is valuable for promoting its usage in aeroengines. However, research on DCL-derived jet fuel is rather scarce. Herein, this work reports a systematic study on a DCL-derived jet fuel and its blends with traditional RP-3 jet fuel in two different ratios. Specifically, major physicochemical properties related to the aviation fuel airworthiness certification process are measured. Advanced two-dimensional gas chromatography (GC × GC) analysis is used to analyze the detailed chemical compositions on the DCL derived jet fuel and its blend with RP-3, which is then employed for surrogate model development. Moreover, ignition delay times (IDTs) are measured by using a heated shock-tube (ST) facility for the blended fuels over a wide range of conditions. Combustion reaction mechanisms based on the surrogate models are developed to predict the experimental measured IDTs. Finally, sensitivity analysis and rate-of-production analysis are carried out to identify the key chemical kinetics controlling the ignition characteristics. This work extends the understanding of the physicochemical properties and ignition characteristics of alternative jet fuels and should be valuable for the practical usage of DCL derived jet fuels.

1. Introduction

Petroleum-derived jet fuels are almost the only commercial aviation fuels that are used worldwide. However, considering the contiguous consumption and the uneven distribution of petroleum resources, alternative jet fuels, including sustainable jet fuels (SAFs), receive significant attention due to the rapid increase in aviation passengers and the demand for energy security. Alternative jet fuels can be synthesized via different techniques depending on the feedstock selection and production pathway [1,2]. Coal, natural gas, and biomass are representative feedstocks. As another major energy resource, the clean utilization of coal resources has become a major issue for many countries that are rich in coal but lack of petroleum/natural gas. The transformation of coal to liquid fuels has a long history and has also been widely used in many countries, i.e., Germany, South Africa, and China [3,4,5]. The conversion of coal to liquid fuels is generally performed through two production technical routes, i.e., indirect coal liquefaction (ICL) and direct coal liquefaction (DCL). The ICL technique is mainly achieved via the Fischer–Tropsch (FT) synthesis process, which converts the coal into syngas first, and then, the syngas is converted into long-chain hydrocarbons via catalytic process [5]. On the other hand, the DCL process uses the high-pressure hydrogenation process to break the chemical structure of coal and convert the unsaturated chemical bond to alkanes [3]. Due to the different technique routes, the chemical compositions of the liquid fuels from ICL and DCL are quite different. Specifically, iso-alkanes are major products from ICL [5,6], while polycyclic naphthenes with two or three rings are major products from DCL [3]. The usage of these fuels requires a comprehensive understanding of their combustion properties and related combustion chemistry, which is of critical importance for their airworthiness certification process.
During the past several decades, a series of research has been conducted on alternative jet fuels from different production routes. The corresponding chemical compositions and physiochemical and combustion properties of these fuels are studied and then used to develop and validate combustion reaction mechanisms that can be used for engine design [7]. For FT synthetic jet fuels, extensive efforts have been performed. Chemical kinetic mechanisms for two different FT fuels, i.e., Syntroleum S-8 and Shell GTL produced from natural gas, were constructed based on chemical composition analysis [8]. Dagaut et al. [9,10] also performed experimental and kinetic modeling study on a gas-to-liquid FT jet fuel. The chemical composition effects of FT jet fuels from Shell and Sasol on the autoignition behaviors were also experimentally studied [11]. In principle, the physiochemical and combustion properties of fuels are fundamentally determined by the chemical compositions and structures. Thus, advanced analytical methods [12,13] have been introduced to uncover the chemical compositions of jet fuels, which can promote more accurate surrogate models [14,15]. And this has been extended to study on alternative jet fuels [9,11,16,17,18,19,20,21,22]. Specifically, accurate two-dimensional gas chromatography (GC × GC) analysis has been employed for the determination of chemical compositions of FT jet fuels and SAF recently [23,24,25]. Compared with the extensive studies on FT jet fuels, fewer studies have been performed on DCL jet fuels [19,26,27]. The major reason may be due to the existence of few industrial projects because of the high cost of the high-pressure hydrogenation process. However, as the green hydrogen technology and catalytic technique continue to develop, the cost and technique problems of DCL have decreased. Further, due to the special process of DCL, the derived jet fuel represents a performance fuel with high energy density due to the ring structures [28]. Thus, a better understanding of the physicochemical and combustion properties of DCL-derived jet fuels is necessary to streamline the airworthiness certification process and design more efficient combustion chambers.
Based on the above considerations, this work contributes to the literature studies on DCL-derived jet fuels. Specifically, the detailed chemical compositions of a DCL-derived jet fuel and its blends with a traditional RP-3 jet fuel with two different ratios are systematically analyzed via two-dimensional gas chromatography (GC × GC) analysis. The major physicochemical properties related to airworthiness certification process are studied. Based on this, surrogate models for DCL-derived jet fuel and the blended fuels are developed, and two different kinds of combustion reaction mechanisms are constructed via detailed and decoupling methods. The ignition properties of the DCL-derived jet fuel with a traditional RP-3 jet fuel are experimentally studied and used to validate the developed mechanisms. Finally, sensitivity analysis and rate-of-production analysis are conducted to identify the key chemical kinetics controlling the ignition characteristics.

2. Experimental Methods

2.1. GC × GC Analysis

Surrogate model approach usually selects several representative hydrocarbons with large fractions in real fuels to mimic their physicochemical properties. Thus, it strongly depends on the chemical composition analysis of the real fuels. But the real fuels usually consist of hundreds of different hydrocarbons; hence, accurate analysis of the fuel’s chemical compositions remain a great challenge for traditional established standardized techniques [12]. In recent years, a multidimensional separation technique to identify volatile and semi-volatile compounds in complex mixtures, GC × GC analysis, which is a universal method for the complete group-type to component-by-component analysis, has been introduced to perform chemical composition analysis of real fuels [12]. Herein, to gain insight into the chemical compositions of the DCL-derived jet fuel and its blends with RP-3, GC × GC analysis is employed to reveal their chemical compositions. The Shimadzu QP2010 GC × GC–MS/FID facility with two chromatographic columns, DB-17 (2.5 m × 0.10 mm × 0.10 μm) and DB-1 (30 m × 0.25 mm × 0.25 μm), is employed to separate the samples. The temperature at the injection port is set to be 548 K with a sample size of 1.0 μL. The initial temperature is 358 K and then gradually increased to 558 K with a rate of 1.5 K/min. The detection ranges of mass spectra (MS) in this work are 40–500 m/z (mass to charge ratio). Finally, the experimental results are processed by using GC × GC images, which are then matched with the NIST Mass Spectral Database to determine the quantitative compositions of the fuels.

2.2. Shock-Tube Experiment

Although the ignition characteristics of pure DCL-derived jet fuel have been experimentally studied, further work remains because it can only be used by blending with traditional jet fuels according to current airworthiness certification standards. Hence, this work performs experimental study on the ignition characteristics of DCL-derived jet fuel with traditional RP-3 with volume ratios of 30%/70% and 70%/30%. A high-pressure shock tube (HPST) at North University of China (NUC) is adopted to measure the IDTs. The experimental system has been described and validated previously [19,29,30,31]. Thus, only a brief description is introduced. The HPST contains a 3.0 m driver section and a 6.8 m driven section with inner diameter of 0.1 m, and they are connected through a 0.3 m double diaphragm section. Figure 1 shows the scheme of the shock-tube facility. Before the experiments, the reactant mixture is prepared in a gas distribution tank based on Dalton’s law of partial pressures, and it is maintained as static for 12 h for homogeneity. The detailed combustion conditions are listed in Table 1. Specifically, the descriptors, namely φ, x, Avg. P5, and T5, denote the equivalence ratio, concentrations of the corresponding species in the reactant mixtures, the reflected pressure and reflected temperature, respectively. The DCL-derived jet fuel is synthesized by CHN Energy Investment Group, while the RP-3 jet fuel is produced in Dalian West Pacific Petrochemical Company. They are provided by the Aviation Fuel and Chemical Airworthiness Certification Centre of CAAC. Helium with purity of 99.99% is used as the driven gas in HPST. The incident shock velocity is measured through five PCB113B26 piezoelectric transducers and is computed through a linear extrapolation of the four known velocities to the endwall. The pressure behind the reflected shock wave is recorded through a PCB 113B26 piezoelectric pressure sensor. The temperature and pressure behind the reflected shock wave is estimated by using the Gaseq program [32]. The definition of IDT is the time interval between the pressure increasing due to the arrival of the incident shock at the endwall and the maximum rate of increase in the pressure signal.
For the uncertainty of the experimental IDTs, it changes with the combustion conditions, i.e., pressure, temperature, equivalence ratio, and also the facility. Generally, the results from the present HPST facility are in good accordance with other related facilities [29,33,34], indicating the uncertainty should be consistent. Based on the literature analysis of the uncertainty analysis [33,35], the uncertainty of the measured IDTs can be controlled within 20%.

2.3. Kinetic Modeling Approach

The experimentally measured IDTs are simulated by using the Cantera software [36] by using the closed homogeneous batch reactor at constant volume, which has been confirmed to be accurate for shock-tube facility-derived IDTs from short test time experiments [37,38]. Figure 2 shows a conceptual diagram of the simulation procedure. Varying volume profiles are not considered because the shock attenuation ranges in the present experiments are minor. To obtain consistent results that can be compared with experiments, the IDT from the simulation is also defined as the extrapolation of the maximum dp/dt to the zero point. For the chemical kinetic analysis, sensitivity analysis is performed through the brute-force procedure [39], while rate-of-production (ROP) analysis is conducted by determining the contribution of each reaction to the net production or destruction rates of a species transiently during ignition simulations [24,25], which allows to quickly identify dominant reaction paths.

3. Results and Discussion

3.1. Physicochemical Properties

Although the aerospace engine operability is fundamentally influenced by the fuel’s ability to ignite and sustain a flame under demanding conditions [28], several critical physicochemical properties must be fulfilled according to airworthiness certification to ensure the fuel’s compatibility with existing engines and airport infrastructure. Table 2 lists the measured major physicochemical properties of the DCL-derived jet fuel and also the traditional RP-3 jet fuel associated with the specifications. It can be seen that all the measured physicochemical properties are comparable with the traditional RP-3 jet fuel and satisfy the specifications. Compared with the traditional RP-3, the DCL jet fuel is cleaner, as shown from the sulfur and naphthalene contents due to the restricted production routes. The other important physicochemical properties are very close between the DCL and RP-3 jet fuels, but larger differences exist for the aromatics and freezing point, which are significantly influenced by their chemical compositions, as discussed below. For some of the measured physicochemical properties of the blended fuels, it can be seen that they are also close to the pure DCL-derived jet fuel and RP-3.
Figure 3 shows the detailed chemical compositions, including the mass fractions of the different alkane types and the corresponding hydrocarbon species of the studied DCL jet fuel and its blends with RP-3 with volume ratios of 70/30 and 30/70 from GC × GC analysis. From Figure 3, the DCL-derived jet fuel is mainly composed of cyclic alkanes, which contributes 87.21% mass fraction of the total compositions. Of these, polycyclic alkanes account for nearly half of the total mass fraction of DCL-derived jet fuel, while n-alkanes and iso-alkanes account for only 11.59% of the compositions. It is also worth noting that aromatics hardly exist in the DCL-derived jet fuel due to the hydrogenation production process. On the contrary, the hydrocarbon types in the RP-3 fuel exhibit a more even distribution. The iso-alkanes contributes most to RP-3, but the mass fraction is only 31.47%, which is just slightly larger than that of n-alkanes and monocyclic alkanes. It is also noted that the polycyclic alkanes in RP-3 are significantly lower than that of monocyclic alkanes, which is quite different compared with the DCL-derived jet fuels. Moreover, the present RP-3 jet fuel contains a large mass fraction of aromatics. For the two blends of DCL-derived jet fuel and RP-3, it can be seen that the compositions of the hydrocarbon types fall generally between the two pure jet fuels, and the specific mass fractions tend to be close to the pure fuel with larger volume fractions.
For the carbon number distributions, the three fuels are primarily distributed within the C8–C15 range. Specifically, for the DCL-derived jet fuel, it can be seen that the main hydrocarbons of the polycyclic alkanes are C10–C12 hydrocarbons, while the main hydrocarbons of the monocyclic alkanes are C9–C12 hydrocarbons. The detailed compositions of the blended fuel with 70% DCL jet fuel also tend to show similar distributions. As the volume ratio of RP-3 increases to 70%, it can be seen that the hydrocarbon distributions become close to pure RP-3 [24]. The detailed compositions and related carbon number distributions provide fundamental information for surrogate model development.

3.2. Ignition Properties of the Blends

Figure 4 shows the experimentally measured IDTs of the studied blended jet fuel of DCL with RP-3 in volume ratios of 30/70 and 70/30, and the effect from temperature and equivalence ratio is clarified. From Figure 4, the temperature demonstrates a typical Arrhenius relationship on the IDTs under the studied high-temperature combustion conditions, and the results can be linearly fitted. Under the studied temperature ranges, the effect of the equivalence ratio for the two blends with different ratios is also similar. Generally, the IDTs decrease as equivalence ratio increases, and this is more distinct at a temperature below 1250 K. As the temperature further increases, the IDTs become convergent, as shown from the fitted results. The controlling combustion chemical kinetics should be the major reason for the effect of the equivalence ratio on the IDTs. At the relatively lower temperature, the IDTs of the reactant mixture can be shortened due to the increase in fuel concentration because the chemistry of the fuel radicals dominates and has the largest effect on the ignition process. To be more specific, ignition at this stage is mainly affected by the fuel chemistry related to the two reactions, i.e., fuel + HO2 = radical + H2O2 and the subsequent H2O2 (+M) = OH + OH (+M) that will generate two reactive OH radicals, which can decrease the IDTs [40,41]. As temperature increases, the chain branching reaction, H + O2 = OH + O, begins to control the ignition process. But the reaction of the fuel with H atoms will still compete with this reaction. Consequently, the effect of the equivalence ratio will converge and then demonstrate an opposite trend compared with the lower temperature condition. From Figure 4, the IDTs of the two blended fuels with different volume ratios do not exhibit a large difference. At lower temperature conditions (lower than 1200 K), the IDTs of the two blended fuels have very close equivalence ratios of 0.5 and 1.0, and the blended jet fuel with the small RP-3 component can ignite a little faster. However, at a temperature larger than 1200 K, the blended jet fuel with a large RP-3 component generally shows longer IDTs irrespective of the equivalence ratio. Overall, the difference between the two volumes is small.
Figure 5 further compares the IDTs of pure DCL [19] and RP-3 [24] and their blends with different ratios at 10 bar under different equivalence ratio conditions. Generally, the IDTs of the four fuels show similar reactivity trends at different equivalence ratio conditions. Under a typical equivalence ratio condition, the IDTs of the pure DCL fuel are shorter compared with the other three fuels at temperatures approximately above 1100 K, and the IDTs of the four fuels become convergent at around 1100 K. The two blends of DCL with RP-3 at different volume ratios are close to the IDTs of RP-3 jet fuel, and the increment of RP-3 composition (the DCL/RP-3 mixture with volume ratio of 30/70) makes the IDTs closer to the RP-3 jet fuel. It is also worth noting that the DCL/RP-3 in a volume ratio of 70/30 with a large DCL component demonstrates the longest IDTs at high temperature conditions, which should be caused by the composition changes due to the small amounts of RP-3 additions.

3.3. Surrogate Models and Combustion Reaction Mechanism

Based on GC × GC analysis, surrogate models for DCL-derived jet fuel, RP-3, and their blends are proposed. Table 3 shows the surrogate models and the corresponding mole fractions of the surrogate components. Herein, a new version that is different from the literature model of RP-3 [24] is proposed. Specifically, decalin is also considered as a surrogate component considering the existence of about 5% polycyclic alkanes. For n-alkanes, n-undecane is selected as the surrogate component due to the largest amount of mass fractions, and the combustion reaction mechanisms are also widely studied. For iso-alkanes, it can be seen that the carbon number distributions are rather evenly distributed in the range from C9 to C13. However, studies on iso-alkanes are few and mainly focused on iso-dodecane. Hence, this study represents the iso-alkanes. For monocyclic alkanes, the most abundant species is C10 hydrocarbons, followed by the C11 and C9 hydrocarbons. Herein, n-butyl cyclohexane is proposed to mimic the monocyclic alkanes in the jet fuels. Decalin is employed to represent polycyclic alkanes because it is the simplest polycyclic alkanes and has been studied extensively. Larger polycyclic alkanes are studied very rarely. Moreover, it can be seen that polycyclic alkanes are mainly composed of C10 and C11 species, indicating decalin should be a major component in the studied fuels. Aromatic hydrocarbons in the studied fuels are usually distributed from C9 to C14. Herein, n-propyl benzene is adopted because previous studied revealed that the alkyl length effect on the ignition properties of aromatics is small, especially at high-temperature conditions [42]. Through a transformation and normalization process of the measured mass fraction of the species distributions, the mole fractions of the surrogate components are derived as shown in Table 3. The detailed mechanism is mainly based on previous studies on different jet fuels [24,25], comprising a sub-mechanism of these surrogate components that has been extensively validated. To be more specific, a detailed mechanism provided as supplementary materials is developed based on the comprehensively validated hierarchical NUIG mechanism [24,25,43,44,45] with the sub-mechanisms of decalin [46], iso-dodecane [47], n-butyl cyclohexane [48], and n-propyl benzene [49]. Using the surrogate models shown in Table 3, the adiabatic flame temperature, with initial temperature of 300 K and pressure of 1 bar with an equivalence ratio of 1.0, is estimated from chemical equilibrium calculations. The computed temperatures of DCL, DCL/RP-3 = 30/70, DCL/RP-3 = 70/30, and RP-3 are 2286, 2286, 2287, and 2289 K, respectively. Thus, the differences between the four jet fuels are very minor. The flame temperature can significantly affect the laminar flame properties, while it has small effect on the IDTs. From the computed flame temperature, it can be anticipated that the flame speed between these fuels could be small.

3.4. Kinetic Modeling Results

Figure 6 compares the simulated IDTs with the experimentally measured results of the two blended fuels with different ratios from DCL and RP-3 in the present work together with the literature IDTs for DCL-derived jet fuel [19] and RP-3 [24]. From Figure 6, it can be seen that the detailed mechanism can predict the experimental results for the four fuels with reasonable accuracy. The variations of IDTs as a function of temperature and equivalence ratio can be reflected. Additionally, the relative reactivity from the IDTs of the four fuels can also be predicted by the detailed mechanism. Compared with experimental results, the predicted IDTs of DCL are also faster than the other three fuels, while the IDTs of the other three fuels are very close. However, it is also worth noting that at high-temperature conditions, the predicted IDTs are generally faster than the experimental results at an equivalence ratio of 0.5. Overall, the reactivity can be well reflected by the detailed mechanism and the surrogate models. To further reveal the combustion chemical kinetics of the four fuels, rate-of-production (ROP) and sensitivity analysis are conducted.
It is widely recognized that the high-temperature combustion properties of large hydrocarbons are mainly controlled by the small C0–C4 intermediates formed through the pyrolysis process [39,50]. Thus, to reveal the different combustion properties of the four jet fuels, ROP is conducted, and Figure 7 and Figure 8 show the time histories of major intermediates as a function of time during the ignition processes of the four fuels at 10 bar and an equivalence ratio of 1.0, with temperature at 1100 K and 1450 K, respectively. From Figure 7 and Figure 8, the major intermediates formed during the ignition processes of the four fuels are quite different, indicating the chemical compositions and molecular structures show significant influence on the intermediates that further affects the IDTs of the fuels. Additionally, it can also be seen that the temperature demonstrates an important effect on the evolution of the species concentrations as a function of time, especially on the alkenes, i.e., ethylene (C2H4), propene (C3H6), 1,3-butadiene (C4H6), and iso-butene (IC4H8). This could be induced by the temperature effect on the reactions leading to the formation of these species. At high-temperature conditions, the β-scission reactions leading to the formation of these intermediates can be facilitated and can continuously produce these species. In addition, the greater importance of hydrogen chemistry at high-temperature conditions decreases the consumption of these species, resulting in more gradual tendencies of these species compared with conditions at lower temperatures whose concentrations demonstrate sudden changes approaching zero.
For the formed intermediates from different fuels, it can be seen that the relative quantities of the intermediates from the four fuels at 1100 and 1450 K are quite similar. Specifically, the quantities of H2 and CH4 from RP-3 are larger than that from DCL, and the two blends with different ratios lie between them. This could be induced by the lower H/C ratio of DCL compared with RP-3 due to the large amounts of cyclic alkanes. For C2H4, the quantities from the four fuels do not exhibit a large difference because it is mainly formed through the first-step β-scissions of the fuel radicals from the abstraction reactions, and the total molecular mass of the fuels is very close for the four fuels. For C2H6 and C3H6, the existence of linear alkanes in RP-3 tends to form these intermediates compared with cyclic alkanes, which leads to the quantity tendencies of the two intermediates. The large amounts of cyclic alkanes in DCL makes the formed 1,3-butadiene and benzene (C6H6) larger than that from RP-3 due to the dehydrogenation reactions and ring-opening reactions of cyclic alkanes. For iso-butene, the formation is mainly affected through the iso-alkanes in the fuels; thus, the quantity from RP-3 is larger than that from DCL. For acetylene (C2H2), it can be seen that its production from RP-3 is larger than that from DCL. Generally, acetylene is usually formed through the reactions of C2H3 with H, i.e., C2H2 + H (+M) = C2H3 (+M) and C2H3 + H = C2H2 + H2. Considering the similar production tendency of C2H4, the formation of acetylene could be related to the decomposition reaction of propene to the formation of C2H3 and CH3 radicals. Overall, from the above-detailed analysis, the major intermediates formed from different fuels are directly affected by the chemical compositions and molecular structures of the fuels.
Figure 9 shows the top 10 reactions with corresponding positive and negative sensitivity coefficients for the IDTs of the studied four fuels at 10 bar, 1100, and 1450 K with an equivalence ratio of 1.0. From the definition of the brute-force sensitivity coefficients, a negative sensitivity coefficient denotes that the IDTs are shortened when the reaction rate constant is doubled. Hence, the reactivity of the reactant system is increased and vice versa. From Figure 9, both the chemical compositions and temperature exhibit a large effect on the sensitivity analysis results of the four fuels. Firstly, the most sensitive reactions of the four fuels are strongly affected by their compositions, more specifically the surrogate models. The most influential reactions of the four fuels are rather different. Specifically, for DCL compared with the other three fuels, it can be seen that the most important reaction with a negative sensitivity coefficient is the decomposition reaction of hydrogen peroxide (H2O2) to the formation of two reactive hydroxy radicals from Figure 9. The major reason for this difference can be attributed to the large number of polycyclic alkanes in the real DCL. In the mechanism, decalin is employed to represent this kind of hydrocarbon. The results for DCL are in good accordance with the literature studies on decalin [51,52]: the chain-branching reaction H2O2(M) = 2OH + (M) demonstrates most important promoting effect on the IDTs in high-temperature combustion conditions because this reaction can generate two reactive OH radicals by consuming only one relatively unreactive HO2 radical. Furthermore, besides reactions involving small C0–C4 species, the reactions of decalin with H2O2 also demonstrate a reactivity-promoting effect on the IDTs because the H-atom abstraction reaction by HO2 radical plays an increasingly important role in the high-temperature combustion conditions [51]. As the DCL is blended with RP-3, the effect from decalin-related reactions and the chain-branching reaction H2O2(M) = 2OH + (M) on the IDTs becomes less important, especially at high-temperature conditions. At 1100 K for RP-3, it can be seen that the reactions related to decalin hardly affect the IDTs due to its composition in the surrogate model, and the reactions related to toluene and benzyl radical show a large effect, which is in good agreement with previous studies on traditional jet fuels [39].
Secondly, the temperature effect on the sensitivity analysis results shows a large dependence on the fuels. For DCL, it can be seen that the sensitive reactions at 1100 K and 1450 K do not exhibit a large difference. However, the sensitive reactions for the blended fuels are significantly affected from temperature 1100 K to 1450 K. For the blended fuels, the reactions related to decalin show little effect, while the decomposition reactions of n-butyl cyclohexane to cyclohexyl and n-butyl show some effect on the IDTs. Besides this, the dominant reactions with large, sensitive coefficients are mainly related to C0–C4 species. However, for RP-3, the sensitivity results are generally consistent at 1100 K and 1450 K, and a major difference is that some reactions related to propene and small species become important at 1450 K. Except for these differences in the sensitivity analysis results of the four fuels, there are still some consistent observations from the sensitivity analysis results. Generally, the most influential reactions with an ignition-promoting effect are the chain-branching reactions that can generate reactive radicals H2O2(M) = 2OH + (M) and H + O2 = OH+ H. The relative importance of the two reactions depends on the fuel types. On the other hand, the chain-termination reaction, CH3 + HO2 = CH4 + O2, which is competitive with another reactive channel, CH3 + HO2 = CH3O + OH, demonstrates the greatest ignition-inhibiting effect for most cases. Further, it can be concluded that under the studied high-temperature conditions, the abstraction and decomposition reactions directly related to the polycyclic alkanes, monocyclic alkanes, and aromatic hydrocarbons in the fuels can demonstrate a large effect on the IDTs compared with the n-alkanes and iso-alkanes.

4. Conclusions

This work reports extensive experimental and modeling studies on an alternative jet fuel from DCL and its blends with traditional RP-3 jet fuel. The major conclusions are summarized as follows.
  • Advanced physicochemical analysis and chemical compositions were carried out for the DCL jet fuel and its blends with RP-3. Generally, the major physicochemical properties of the DCL jet fuel satisfied most of the airworthiness certification standards, and it is cleaner, with a lower freezing point (−66.0 °C compared with that of −52.5 °C of RP-3);
  • Advanced GC × GC analysis revealed that the DCL jet fuel is mainly composed of cyclic alkanes (87.21% mass fraction) with a small number of n/iso-alkanes (11.59%), and the carbon numbers are primarily distributed within the C9–C14 range;
  • The IDTs of the blended fuels of DCL and RP-3 with different volume ratios do not exhibit a large difference, and they tend to be close to the IDTs of RP-3 within the studied combustion conditions, i.e., equivalence ratios of 0.5, 1.0, and 2.0 and temperature ranges 1030–1530 K, with pressure at approximately 10 bar;
  • ROP analysis indicated that major intermediates, including 1,3-butadiene and benzene, can be largely formed due to the dehydrogenation and ring-opening reactions of cyclic alkanes during the ignition process of DCL, while the quantities of other intermediates, including hydrogen, methane, propene, acetylene, iso-butene, ethylene, and ethane, increase as the volume ratios of RP-3 increase;
  • Sensitivity analysis results highlighted that the ignition properties of the studied jet fuels are significantly affected by the chemical compositions and molecular structures of the jet fuels. Future studies on more accurate chemical composition analysis and other combustion properties, including laminar flame speeds and soot, should be conducted for surrogate model and mechanism optimization, which is critical for airworthiness certification and large-scale commercial applications of the DCL jet fuels.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/aerospace12060505/s1. Detailed_mech.THERM.txt: The thermochemical data file; Detailed_mech.MECH.txt: The combustion mechanism file.

Author Contributions

Q.-D.W., conceptualization, formal analysis, funding acquisition, supervision, and writing—review and editing; L.D., data curation, formal analysis, and investigation; B.-Y.W., methodology, investigation, and writing—original draft; Q.Y., data curation, formal analysis, and validation; J.L., data curation, formal analysis, investigation, and methodology; P.Z., data curation and validation; Z.-X.X., conceptualization, funding acquisition, and resources. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Joint Research Fund from National Natural Science Foundation of China and Civil Aviation Administration of China, grant number U2133215; National Natural Science Foundation of China, grant number 12172335; Advanced Aerospace Power Innovation Workstation, grant number HKCX2024-01-021; and Sichuan Science and Technology Program, grant number 2023ZYD0138.

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
DCLDirect coal liquefaction
GC × GCTwo-dimensional gas chromatography
HPSTHigh-pressure shock tube
IDTIgnition delay time

References

  1. Pires, A.P.P.; Han, Y.L.; Kramlich, J.; Garcia-Perez, M. Chemical Composition and Fuel Properties of Alternative Jet Fuels. Bioresources 2018, 13, 2632–2657. [Google Scholar] [CrossRef]
  2. Zhang, C.; Hui, X.; Lin, Y.Z.; Sung, C.J. Recent development in studies of alternative jet fuel combustion: Progress, challenges, and opportunities. Renew. Sustain. Energy Rev. 2016, 54, 120–138. [Google Scholar] [CrossRef]
  3. Mochida, I.; Okuma, O.; Yoon, S.H. Chemicals from Direct Coal Liquefaction. Chem. Rev. 2014, 114, 1637–1672. [Google Scholar] [CrossRef] [PubMed]
  4. Huang, Y.; Rolfe, A.; Rezvani, S.; Herrador, J.M.H.; Franco, F.; Pinto, F.; Snape, C.; Hewitt, N. Converting brown coal to synthetic liquid fuels through direct coal liquefaction technology:Techno-economicevaluation. Int. J. Energy Res. 2020, 44, 11827–11839. [Google Scholar] [CrossRef]
  5. Khodakov, A.Y.; Chu, W.; Fongarland, P. Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels. Chem. Rev. 2007, 107, 1692–1744. [Google Scholar] [CrossRef] [PubMed]
  6. Li, J.; He, Y.; Tan, L.; Zhang, P.; Peng, X.; Oruganti, A.; Yang, G.; Abe, H.; Wang, Y.; Tsubaki, N. Integrated tuneable synthesis of liquid fuels via Fischer–Tropsch technology. Nat. Catal. 2018, 1, 787–793. [Google Scholar] [CrossRef]
  7. Sankaran, V. Research and development needs in combustion modeling. Appl. Energy Combust. Sci. 2025, 21, 100307. [Google Scholar] [CrossRef]
  8. Naik, C.V.; Puduppakkam, K.V.; Modak, A.; Meeks, E.; Wang, Y.L.; Feng, Q.Y.; Tsotsis, T.T. Detailed chemical kinetic mechanism for surrogates of alternative jet fuels. Combust. Flame 2011, 158, 434–445. [Google Scholar] [CrossRef]
  9. Dagaut, P.; Karsenty, F.; Dayma, G.; Dievart, P.; Hadj-Ali, K.; Mze-Ahmed, A.; Braun-Unkhoff, M.; Herzler, J.; Kathrotia, T.; Kick, T.; et al. Experimental and detailed kinetic model for the oxidation of a Gas to Liquid (GtL) jet fuel. Combust. Flame 2014, 161, 835–847. [Google Scholar] [CrossRef]
  10. Dagaut, P.; Dievart, P. Combustion of synthetic jet fuels: Naphthenic cut and blend with a gas-to-liquid (GtL) jet fuel. Proc. Combust. Inst. 2017, 36, 433–440. [Google Scholar] [CrossRef]
  11. Valco, D.; Gentz, G.; Allen, C.; Colket, M.; Edwards, T.; Gowdagiri, S.; Oehlschlaeger, M.A.; Toulson, E.; Lee, T. Autoignition behavior of synthetic alternative jet fuels: An examination of chemical composition effects on ignition delays at low to intermediate temperatures. Proc. Combust. Inst. 2015, 35, 2983–2991. [Google Scholar] [CrossRef]
  12. Melder, J.; Zinsmeister, J.; Grein, T.; Jürgens, S.; Köhler, M.; Oßwald, P. Comprehensive Two-Dimensional Gas Chromatography: A Universal Method for Composition-Based Prediction of Emission Characteristics of Complex Fuels. Energy Fuels 2023, 37, 4580–4595. [Google Scholar] [CrossRef]
  13. Heyne, J.; Bell, D.; Feldhausen, J.; Yang, Z.; Boehm, R. Towards fuel composition and properties from Two-dimensional gas chromatography with flame ionization and vacuum ultraviolet spectroscopy. Fuel 2022, 312, 122709. [Google Scholar] [CrossRef]
  14. Wu, Z.; Mao, Y.; Raza, M.; Zhu, J.; Feng, Y.; Wang, S.; Qian, Y.; Yu, L.; Lu, X. Surrogate fuels for RP-3 kerosene formulated by emulating molecular structures, functional groups, physical and chemical properties. Combust. Flame 2019, 208, 388–401. [Google Scholar] [CrossRef]
  15. Dooley, S.; Won, S.H.; Chaos, M.; Heyne, J.; Ju, Y.; Dryer, F.L.; Kumar, K.; Sung, C.-J.; Wang, H.; Oehlschlaeger, M.A.; et al. A jet fuel surrogate formulated by real fuel properties. Combust. Flame 2010, 157, 2333–2339. [Google Scholar] [CrossRef]
  16. Kim, D.; Martz, J.; Abdul-Nour, A.; Yu, X.; Jansons, M.; Violi, A. A six-component surrogate for emulating the physical and chemical characteristics of conventional and alternative jet fuels and their blends. Combust. Flame 2017, 179, 86–94. [Google Scholar] [CrossRef]
  17. Kathrotia, T.; Oßwald, P.; Naumann, C.; Richter, S.; Köhler, M. Combustion kinetics of alternative jet fuels, Part-II: Reaction model for fuel surrogate. Fuel 2021, 302, 120736. [Google Scholar] [CrossRef]
  18. Kathrotia, T.; Oßwald, P.; Zinsmeister, J.; Methling, T.; Köhler, M. Combustion kinetics of alternative jet fuels, Part-III: Fuel modeling and surrogate strategy. Fuel 2021, 302, 120737. [Google Scholar] [CrossRef]
  19. Yang, Z.-Y.; Zeng, P.; Wang, B.-Y.; Jia, W.; Xia, Z.-X.; Liang, J.; Wang, Q.-D. Ignition characteristics of an alternative kerosene from direct coal liquefaction and its blends with conventional RP-3 jet fuel. Fuel 2021, 291, 120258. [Google Scholar] [CrossRef]
  20. Richter, S.; Kukkadapu, G.; Westbrook, C.K.; Braun-Unkhoff, M.; Naumann, C.; Köhler, M.; Riedel, U. A combined experimental and modeling study of combustion properties of an isoparaffinic alcohol-to-jet fuel. Combust. Flame 2022, 240, 111994. [Google Scholar] [CrossRef]
  21. Abi Nurazaq, W.; Wang, W.-C.; Lin, J.-K. The properties of sustainable aviation fuel II: Laminar flame speed. Energy 2024, 294, 130946. [Google Scholar] [CrossRef]
  22. Guzman, J.; Brezinsky, K. Experimental and modeling study of the oxidation of F-24 jet fuel, and its mixture with an iso-paraffinic synthetic jet fuel, ATJ. Combust. Flame 2021, 224, 108–125. [Google Scholar] [CrossRef]
  23. Yang, Z.; Kosir, S.; Stachler, R.; Shafer, L.; Anderson, C.; Heyne, J.S. A GC × GC Tier α combustor operability prescreening method for sustainable aviation fuel candidates. Fuel 2021, 292, 120345. [Google Scholar] [CrossRef]
  24. Wang, Q.-D.; Wang, B.-Y.; Yao, Q.; Liang, J.; Zeng, P.; Liu, J.-G.; Xia, Z.-X. An experimental and kinetic modeling study on the ignition property of an alternative gas to liquid jet fuel. Combust. Flame 2025, 271, 113805. [Google Scholar] [CrossRef]
  25. Wang, Q.-D.; Zeng, P.; Yao, Q.; Liang, J.; Wang, B.-Y.; Huang, F.; Liu, J.-G.; Xia, Z.-X. An experimental and kinetic modeling study on the ignition kinetics of a sustainable aviation fuel and its blends with a traditional RP-3 jet fuel. Fuel 2025, 380, 133191. [Google Scholar] [CrossRef]
  26. Wang, B.-Y.; Zeng, P.; He, R.; Li, F.; Yang, Z.-Y.; Xia, Z.-X.; Liang, J.; Wang, Q.-D. Single-Pulse Shock Tube Experimental and Kinetic Modeling Study on Pyrolysis of a Direct Coal Liquefaction-Derived Jet Fuel and Its Blends with the Traditional RP-3 Jet Fuel. ACS Omega 2021, 6, 18442–18450. [Google Scholar] [CrossRef]
  27. Fang, X.Y.; Huang, X.Y.; Chen, W.K.; Qiao, X.Q.; Ju, D.H. Development of a skeletal surrogate mechanism for emulating combustion characteristics of diesel from direct coal liquefaction. Combust. Flame 2020, 218, 84–97. [Google Scholar] [CrossRef]
  28. Wang, F.; Rijal, D. Sustainable Aviation Fuels for Clean Skies: Exploring the Potential and Perspectives of Strained Hydrocarbons. Energy Fuels 2024, 38, 4904–4920. [Google Scholar] [CrossRef]
  29. Panigrahy, S.; Liang, J.; Ghosh, M.K.; Wang, Q.-D.; Zuo, Z.; Nagaraja, S.; Mohamed, A.A.E.-S.; Kim, G.; Vasu, S.S.; Curran, H.J. An experimental and detailed kinetic modeling study of the pyrolysis and oxidation of allene and propyne over a wide range of conditions. Combust. Flame 2021, 233, 111578. [Google Scholar] [CrossRef]
  30. Liang, J.; Zhao, C.; Zhao, Z.; Wang, X.; Jia, M.-X.; Wang, Q.-D.; Zhang, Y.; Zhao, F. An experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine. Combust. Flame 2023, 252, 112769. [Google Scholar] [CrossRef]
  31. Wang, Q.-D.; Sun, Y.; Zhao, Z.; Zhang, Y.; Zhao, F.; Li, Y.; Liang, J. Ignition kinetics of nitrocyclohexane behind reflected shock waves in inert and air environments. Combust. Flame 2023, 255, 112865. [Google Scholar] [CrossRef]
  32. Morley, C. Gaseq: A Chemical Equilibrium Program for Windows, 0.79. 2005. Available online: http://www.gaseq.co.uk/ (accessed on 17 September 2010).
  33. Petersen, E.L.; Rickard, M.J.A.; Crofton, M.W.; Abbey, E.D.; Traum, M.J.; Kalitan, D.M. A facility for gas- and condensed-phase measurements behind shock waves. Meas. Sci. Technol. 2005, 16, 1716–1729. [Google Scholar] [CrossRef]
  34. Guzman, J.; Kukkadapu, G.; Brezinsky, K.; Westbrook, C. Experimental and modeling study of the pyrolysis and oxidation of an iso-paraffinic alcohol-to-jet fuel. Combust. Flame 2019, 201, 57–64. [Google Scholar] [CrossRef]
  35. Baigmohammadi, M.; Patel, V.; Nagaraja, S.; Ramalingam, A.; Martinez, S.; Panigrahy, S.; Mohamed, A.A.E.-S.; Somers, K.P.; Burke, U.; Heufer, K.A.; et al. Comprehensive Experimental and Simulation Study of the Ignition Delay Time Characteristics of Binary Blended Methane, Ethane, and Ethylene over a Wide Range of Temperature, Pressure, Equivalence Ratio, and Dilution. Energy Fuels 2020, 34, 8808–8823. [Google Scholar] [CrossRef]
  36. Goodwin, D.G.; Speth, R.L.; Moffat, H.K.; Weber, B.W. Cantera: An Object-oriented Software Toolkit for Chemical Kinetics, Thermodynamics, and Transport Processes; Version 2.4.0; Cantera: Tulsa, OK, USA, 2018. [Google Scholar]
  37. Davidson, D.F.; Hanson, R.K. Recent advances in shock tube/laser diagnostic methods for improved chemical kinetics measurements. Shock Waves 2009, 19, 271–283. [Google Scholar] [CrossRef]
  38. Sung, C.J.; Curran, H.J. Using rapid compression machines for chemical kinetics studies. Prog. Energy Combust. Sci. 2014, 44, 1–18. [Google Scholar] [CrossRef]
  39. Wang, Q.-D.; Fang, Y.-M.; Wang, F.; Li, X.-Y. Systematic analysis and reduction of combustion mechanisms for ignition of multi-component kerosene surrogate. Proc. Combust. Inst. 2013, 34, 187–195. [Google Scholar] [CrossRef]
  40. Curran, H.J. Developing detailed chemical kinetic mechanisms for fuel combustion. Proc. Combust. Inst. 2019, 37, 57–81. [Google Scholar] [CrossRef]
  41. Bugler, J.; Marks, B.; Mathieu, O.; Archuleta, R.; Camou, A.; Gregoire, C.; Heufer, K.A.; Petersen, E.L.; Curran, H.J. An ignition delay time and chemical kinetic modeling study of the pentane isomers. Combust. Flame 2016, 163, 138–156. [Google Scholar] [CrossRef]
  42. Darcy, D.; Tobin, C.J.; Yasunaga, K.; Simmie, J.M.; Wurmel, J.; Metcalfe, W.K.; Niass, T.; Ahmed, S.S.; Westbrook, C.K.; Curran, H.J. A high pressure shock tube study of n-propylbenzene oxidation and its comparison with n-butylbenzene. Combust. Flame 2012, 159, 2219–2232. [Google Scholar] [CrossRef]
  43. El-Sabor Mohamed, A.A.; Sahu, A.B.; Panigrahy, S.; Baigmohammadi, M.; Bourque, G.; Curran, H. The effect of the addition of nitrogen oxides on the oxidation of propane: An experimental and modeling study. Combust. Flame 2022, 245, 112306. [Google Scholar] [CrossRef]
  44. Wang, Q.-D.; Panigrahy, S.; Yang, S.; Martinez, S.; Liang, J.; Curran, H.J. Development of Multipurpose Skeletal Core Combustion Chemical Kinetic Mechanisms. Energy Fuels 2021, 35, 6921–6927. [Google Scholar] [CrossRef]
  45. Dong, S.; Wagnon, S.W.; Pratali Maffei, L.; Kukkadapu, G.; Nobili, A.; Mao, Q.; Pelucchi, M.; Cai, L.; Zhang, K.; Raju, M.; et al. A new detailed kinetic model for surrogate fuels: C3MechV3.3. Appl. Energy Combust. Sci. 2022, 9, 100043. [Google Scholar] [CrossRef]
  46. Zeng, M.R.; Li, Y.Y.; Yuan, W.H.; Li, T.Y.; Wang, Y.Z.; Zhou, Z.Y.; Zhang, L.D.; Qi, F. Experimental and kinetic modeling study of laminar premixed decalin flames. Proc. Combust. Inst. 2017, 36, 1193–1202. [Google Scholar] [CrossRef]
  47. Fang, R.; Kukkadapu, G.; Wang, M.; Wagnon, S.W.; Zhang, K.; Mehl, M.; Westbrook, C.K.; Pitz, W.J.; Sung, C.-J. Fuel molecular structure effect on autoignition of highly branched iso-alkanes at low-to-intermediate temperatures: Iso-octane versus iso-dodecane. Combust. Flame 2020, 214, 152–166. [Google Scholar] [CrossRef]
  48. Wang, H.; Dames, E.; Sirjean, B.; Sheen, D.A.; Tangko, R.; Violi, A.; Lai, J.Y.W.; Egolfopoulos, F.N.; Davidson, D.F.; Hanson, R.K.; et al. JetSurF II: A High Temperature Chemical Kinetic Model of n-Alkane (up to n-Dodecane), Cyclohexane, and Methyl-, Ethyl-, n-Propyl and n-Butyl-Cyclohexane Oxidation at High Temperatures. Available online: https://web.stanford.edu/group/haiwanglab/JetSurF/JetSurF2.0/ (accessed on 17 September 2010).
  49. Liu, Y.-X.; Richter, S.; Naumann, C.; Braun-Unkhoff, M.; Tian, Z.-Y. Combustion study of a surrogate jet fuel. Combust. Flame 2019, 202, 252–261. [Google Scholar] [CrossRef]
  50. Wang, H.; Xu, R.; Wang, K.; Bowman, C.T.; Hanson, R.K.; Davidson, D.F.; Brezinsky, K.; Egolfopoulos, F.N. A physics-based approach to modeling real-fuel combustion chemistry—I. Evidence from experiments, and thermodynamic, chemical kinetic and statistical considerations. Combust. Flame 2018, 193, 502–519. [Google Scholar] [CrossRef]
  51. Yu, L.; Wu, Z.Y.; Qiu, Y.; Qian, Y.; Mao, Y.B.; Lu, X.C. Ignition delay times of decalin over low-to-intermediate temperature ranges: Rapid compression machine measurement and modeling study. Combust. Flame 2018, 196, 160–173. [Google Scholar] [CrossRef]
  52. Kukkadapu, G.; Whitesides, R.; Wang, M.; Wagnon, S.W.; Mehl, M.; Westbrook, C.K.; McCormick, R.; Sung, C.-J.; Pitz, W.J. Development of a diesel surrogate for improved autoignition prediction: Methodology and detailed chemical kinetic modeling. Appl. Energy Combust. Sci. 2023, 16, 100216. [Google Scholar] [CrossRef]
Aerospace 12 00505 g001
Figure 1. Scheme of the shock-tube experimental facility used in the present work.
Figure 1. Scheme of the shock-tube experimental facility used in the present work.
Aerospace 12 00505 g001
Aerospace 12 00505 g002
Figure 2. The conceptual diagram of the Cantera software used in this work.
Figure 2. The conceptual diagram of the Cantera software used in this work.
Aerospace 12 00505 g002
Aerospace 12 00505 g003
Figure 3. Detailed compositions of the studied DCL-derived jet fuel and its blends with RP-3 with volume ratios of 70/30 and 30/70 from GC × GC analysis. The results in (a) for RP-3 are adopted from [24]. Figures (b–d) display the carbon number distributions of the studied DCL, and its blends with RP-3 with volume ratios of 70/30 and 30/70, respectively.
Figure 3. Detailed compositions of the studied DCL-derived jet fuel and its blends with RP-3 with volume ratios of 70/30 and 30/70 from GC × GC analysis. The results in (a) for RP-3 are adopted from [24]. Figures (b–d) display the carbon number distributions of the studied DCL, and its blends with RP-3 with volume ratios of 70/30 and 30/70, respectively.
Aerospace 12 00505 g003
Aerospace 12 00505 g004
Figure 4. IDTs from ST experimental measurements of the studied blend jet fuel of DCL with RP-3 in volume ratios of 30/70 and 70/30.
Figure 4. IDTs from ST experimental measurements of the studied blend jet fuel of DCL with RP-3 in volume ratios of 30/70 and 70/30.
Aerospace 12 00505 g004
Aerospace 12 00505 g005
Figure 5. IDTs from ST experimental measurements of the studied blend jet fuel of DCL with RP-3 in volume ratios of 30/70 and 70/30 together with literature studies of pure DCL [19] and RP-3 [24] jet fuels. Figures (a–c) represent the experimental results at pressure of ~ 10.0 bar with equivalence ratios of 0.5, 1.0, and 2.0, respectively.
Figure 5. IDTs from ST experimental measurements of the studied blend jet fuel of DCL with RP-3 in volume ratios of 30/70 and 70/30 together with literature studies of pure DCL [19] and RP-3 [24] jet fuels. Figures (a–c) represent the experimental results at pressure of ~ 10.0 bar with equivalence ratios of 0.5, 1.0, and 2.0, respectively.
Aerospace 12 00505 g005
Aerospace 12 00505 g006
Figure 6. Predicted IDTs of the present experimental results by using the detailed (solid line) and decoupling (dashed line) mechanisms for the four fuels at pressure of ~10.0 bar with equivalence ratios of 0.5 (a), 1.0 (b), and 2.0 (c), respectively.
Figure 6. Predicted IDTs of the present experimental results by using the detailed (solid line) and decoupling (dashed line) mechanisms for the four fuels at pressure of ~10.0 bar with equivalence ratios of 0.5 (a), 1.0 (b), and 2.0 (c), respectively.
Aerospace 12 00505 g006
Aerospace 12 00505 g007
Figure 7. Species profiles of the major intermediates from ROP analysis during the ignition processes of the studied four fuels at 10 bar, 1100 K, and an equivalence ratio of 1.0.
Figure 7. Species profiles of the major intermediates from ROP analysis during the ignition processes of the studied four fuels at 10 bar, 1100 K, and an equivalence ratio of 1.0.
Aerospace 12 00505 g007
Aerospace 12 00505 g008
Figure 8. Species profiles of the major intermediates from ROP analysis during the ignition processes of the studied four fuels at 10 bar, 1450 K, and an equivalence ratio of 1.0.
Figure 8. Species profiles of the major intermediates from ROP analysis during the ignition processes of the studied four fuels at 10 bar, 1450 K, and an equivalence ratio of 1.0.
Aerospace 12 00505 g008
Aerospace 12 00505 g009
Figure 9. The most influential reactions on the IDT of the four fuels at 10 bar, 1100, and 1450 K with an equivalence ratio of 1.0.
Figure 9. The most influential reactions on the IDT of the four fuels at 10 bar, 1100, and 1450 K with an equivalence ratio of 1.0.
Aerospace 12 00505 g009
Table 1. HPST experimental conditions in this work.
Table 1. HPST experimental conditions in this work.
Fuel (DCL/RP-3 Blends)φxFuel (mol%)xO2 (mol%)xN2 (mol%)Avg. P5 (bar)T5 Range (K)
30/70 blends in volume0.50.6420.8778.5010.021110–1530
1.01.2720.7378.009.941060–1450
2.02.5020.4877.0310.231030–1490
70/30 blends in volume0.50.6420.8778.5010.031090–1510
1.01.2720.7378.0010.161070–1520
2.02.5020.4877.0310.131080–1500
Table 2. Physicochemical properties of the DCL and comparisons with RP-3. The standard refers to the airworthiness certification standards for jet fuels enacted by the American Society for Testing Materials (ASTM).
Table 2. Physicochemical properties of the DCL and comparisons with RP-3. The standard refers to the airworthiness certification standards for jet fuels enacted by the American Society for Testing Materials (ASTM).
PropertyDCLDCL/RP-3RP-3Standard
30/7070/30
Acidity (mg KOH/g)0.002——0.002ASTM D3242, ≤0.015
aromatics (% vol)0.9——16.8ASTM D1319, ≤25
sulfur (mass %)<0.0001——0.066ASTM D5453, ≤0.3
sulfur, mercaptan (mass %)<0.0003——0.0012ASTM D3227, ≤0.003
flash point (°C)45.5——47.5ASTM D1655, ≥38
density 15 °C (kg/m3)827.4——799.7ASTM D4052, 775–840
freezing point (°C)−66.0——−52.5ASTM D5972, ≤−47
viscosity, −20 °C (mm2/s)4.5284.3954.2424.230ASTM D445, ≤8.0
Net heat of combustion (MJ/kg)42.99243.25743.36243.296ASTM D3338, ≥42.8
smoke point (mm)25.226.127.626.6ASTM D1332, ≥25.0
naphthalene (vol %)0.00910.720.340.81ASTM D1840, ≤3.0
Table 3. Surrogate models for DCL derived jet fuel, RP-3, and the blends. The compositions are in mole fraction (%).
Table 3. Surrogate models for DCL derived jet fuel, RP-3, and the blends. The compositions are in mole fraction (%).
Surrogate ComponentDCLDCL/RP-3 = 30/70DCL/RP-3 = 70/30RP-3
n-Undecane6.8516.1110.4722.60
Iso-dodecane3.4619.119.7228.76
n-Butyl cyclohexane38.0832.2135.4622.90
Decalin51.6126.7039.655.28
n-Propyl benzene0.005.874.7020.46
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Wang, Q.-D.; Du, L.; Wang, B.-Y.; Yao, Q.; Liang, J.; Zeng, P.; Xia, Z.-X. Surrogate Models and Related Combustion Reaction Mechanisms for a Coal-Derived Alternative Jet Fuel and Its Blends with a Traditional RP-3. Aerospace 2025, 12, 505. https://doi.org/10.3390/aerospace12060505

AMA Style

Wang Q-D, Du L, Wang B-Y, Yao Q, Liang J, Zeng P, Xia Z-X. Surrogate Models and Related Combustion Reaction Mechanisms for a Coal-Derived Alternative Jet Fuel and Its Blends with a Traditional RP-3. Aerospace. 2025; 12(6):505. https://doi.org/10.3390/aerospace12060505

Chicago/Turabian Style

Wang, Quan-De, Lan Du, Bi-Yao Wang, Qian Yao, Jinhu Liang, Ping Zeng, and Zu-Xi Xia. 2025. "Surrogate Models and Related Combustion Reaction Mechanisms for a Coal-Derived Alternative Jet Fuel and Its Blends with a Traditional RP-3" Aerospace 12, no. 6: 505. https://doi.org/10.3390/aerospace12060505

APA Style

Wang, Q.-D., Du, L., Wang, B.-Y., Yao, Q., Liang, J., Zeng, P., & Xia, Z.-X. (2025). Surrogate Models and Related Combustion Reaction Mechanisms for a Coal-Derived Alternative Jet Fuel and Its Blends with a Traditional RP-3. Aerospace, 12(6), 505. https://doi.org/10.3390/aerospace12060505

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop