Examining evaporation characteristics of typical aviation fuels including JP-4, JP-5, JP-7, RT, Jet A-1 and TS-1

Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
 EXAMINING EVAPORATION CHARACTERISTICS OF 
 TYPICAL AVIATION FUELS INCLUDING JP-4, JP-5, JP-7, RT, 
 Jet A-1 AND TS-1 
 1 1
 Pham Vu Thanh Nam , Nguyen Trung Kien , 
 Pham Duc Canh2, Pham Xuan Phuong1,* 
 1Le Quy Don Technical University; 2Air Defence - Air Force Academy 
 Abstract 
 This work numerically studies the evaporation characteristics of 6 typical gas turbine fuels 
 (JP-4, JP-5, JP-7, RT, Jet A-1, and TS-1, respectively). In this work, the influence of 
 ambient temperature and liquid properties on the droplet lifetime is examined. At the same 
 initial conditions (e.g. fuel temperature Ts0 = 300 K, droplet diameter D0 = 1 mm and 
 atmospheric pressure p = 101.33 kPa) and low ambient temperature (e.g. 500 K), 
 significant differences in evaporation characteristics among these fuels are observed. 
 JP-4 has the longest droplet lifetime while JP-7’s is the shortest. However, at high ambient 
 temperature (e.g. 2000 K), the droplet lifetimes of the fuels are almost identical. 
 Under critical temperature, it is shown that the fuel properties remarkably impact the 
 evaporation rate. 
 Keywords: Aviation fuel; drop evaporation; drop evaporation rate; drop lifetime. 
1. Introduction 
 The evaporation process of liquid fuels comprises of simultaneous heat and mass 
transfer processes in which the heat for evaporation is transferred to the liquid surface 
by conduction and convection from the surrounding hot gas environment, and vapor is 
transferred by convection and diffusion back into the hot gas stream. Fuel evaporation 
characteristics significantly affect the fuel and air mixing quality. Improving 
evaporation processes can, therefore, directly enhance combustion efficiency, which is 
crucial for heat engines including aviation counterparts. In this work, drop evaporation 
is characterized for 6 different aviation liquid fuels including JP-4, JP-5, JP-7, RT, 
Jet A-1 and TS-1. These fuels are typically used in both civil and army aviation gas 
turbine engines in which TS-1 is commonly used in Vietnam Airforce. 
 Droplet evaporation is a fundamental phenomenon in nature and has implications 
in different industries and research areas, thus, this phenomenon has been intensively 
studied for decades [1, 2]. Compared to a monocomponent droplet, evaporation of a 
* Email: PhuongPham@lqdtu.edu.vn 
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 Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
multicomponent droplet is more practical and common but involves much more 
complicated mechanism. Therefore, scientists have been attracted to this area and 
efforts have been made to understand the underlying physical mechanisms of 
multicomponent droplet evaporation utilizing experimental and numerical methods [3]. 
 One of the earliest numerical studies on multicomponent droplets done by 
Newbold and Amundson [4] has characterized the evaporation processes for a 
multicomponent droplet under a temperature condition close to the drop boiling point. 
Later, a number of models based on different approaches, such as expanded diffusion 
limit model [5], distillation curve model [6], continuous distribution model [7], and 
continuous thermodynamics model [8], has been developed in order to describe and 
predict multicomponent droplet evaporation rate. Meanwhile, experimental studies have 
been carried out under different environmental conditions to understand the mechanism 
of multicomponent evaporation, including vaporization in an electric field [9], free 
falling in a temperature gradient field [10], sitting on heated or non-heated flat surface 
[11], evaporating in heated air flow [12] and at elevated pressure and temperature 
conditions [13]. 
 According to our knowledge, studies on comparison of multicomponent droplet 
evaporation for typical aviation fuels like the ones investigated here, are scarce. This 
paper adopted numerical approach developed earlier in [14] to predict droplet 
evaporation rate and droplet lifetime for six different commercial aviation fuels. 
Enhancing knowledge on the evaporation characteristics for these fuels may help to 
improve the evaporation quality and this in turn improves mixing and combustion 
processes for aviation engines. 
2. Mathematical Modeling 
 Mathematical modeling used to characterize droplet evaporation will be discussed 
in this section. In this model, a stationary drop is placed in a hot gaseous environment 
and the drop lifetime is to be estimated. This is based on theory earlier reported in [14] 
and this section will summarize the mathematical correlations. The following 
assumptions are made: 
 (i) The drop is spherical. 
 (ii) The fuel is a pure liquid having a well-defined boiling point. 
 (iii) Radiation heat transfer is negligible. 
 (iv) Lewis Number of unity is obtained (i.e. diffusivities of heat and mass ...  dt
where Ds0 is initial drop diameter (m); D is drop diameter at time t (m); λ is evaporation 
constant (m2/s); and t is time (s). In addition, the rate of evaporation could be 
calculated as: 
 D3 
 F d 
 dm d() V 6 d() D 2 
 m FFF D D  
 FFFdt dt dt4 dt 4
hence 
 4m
  F (20) 
 D F
 At the end of the evaporation process, drop diameter is assumed to be zero, 
substituting for D = 0 into Equation (18) gives: 
 2
 td D s0 and as such the droplet lifetime, td could be estimated: 
 D 2
 t s0 (21) 
 d 
where td is drop lifetime (s). 
3. Model Prediction 
3.1. Fuel selection 
 Six different aviation fuels have been selected in this study (TS-1, RT, JP-4, JP-5, 
Jet A-1 and JP-7). The evaporation rate of these fuels depends on their application area 
and supply. Both TS-1 and RT are adopted in Russia, TS-1 is typically used in military 
aircraft while RT is typical civil gas turbine engine fuel. Remaining fuels including 
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 Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
JP-4, JP-5, Jet A-1 and JP-7 are standard liquids used for specific purposes in America. 
The wide-cut JP-4 is the primary fuel that meets operational requirements and reflects a 
broad availability. The U.S. Navy, particularly for aircraft carrier safety, relies on JP-5, 
a high flash-point fuel. JP-7 is used by the Air Force for specific applications in which 
high thermal stability is required. And Jet A-1 is the primary commercial fuel outside 
the US. The more details about the selected fuels availability is directed to [19, 20]. 
 The important properties of the selected fuels are shown in Tab. 1 [19, 20]. Table 
1 also shows constants used in the mathematical model presented in previous section, 
they were calculated by using data from [19, 20]. As can be seen from the Tab. 1, the 
average number of C atoms contained in the fuels ranges from 7 to 12 and this may 
cover most of the fuels currently used in civil air crafts as well as military airforce. 
 Tab. 1. Fuel physical properties 
 Fuel TS-1 RT JP-4 JP-5 Jet A-1 JP-7 
 Approximate Formula C7.21H13.2936 C10.8H21.6 C8.5H17 C12H22 C12H21 C12H25 
 3
 Density ρF0 (kg/m ) 782.456 781.32 765.15 812.5 801.36 793.68 
 a in Equation (6) 19.02 18.18 17.32 21.75 18.87 21.75 
 b in Equation (6) 5605.02 5279.52 4204.5 7500.8 5978.6 7500.8 
 A in Equation (17) 34680.91 33510 36902.66 37218.31 36146.6 31208.69 
 B in Equation (17) 639.77 659.24 603.15 617.46 683.15 688.34 
3.2. Model validation 
 Fig. 1 shows the predictions and experimental results for Jet A-1 fuel. The 
theoretical graph shows a straight-line relationship between diminishing ratio of droplet 
diameter squared versus time. However, experimental inspection reveals that the slope 
 2
of the (D/D0) /t line is almost zero in the first stage of evaporation and then gradually 
increases with time until the drop attains its wet-bulb temperature, in which the 
 2
temperature inside the drop is uniformed and the slope of the (D/D0) /t line remains 
fairly constant throughout the remainder of the drop lifetime. Therefore, the 
vaporization process can roughly be separated into the transient or unsteady state and 
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Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
the steady state. Fuel drops finally reach their wet-bulb temperature asymptotically with 
time, and for almost fuels, the drop generally spends only a very small portion of its 
time in the unsteady state; thus in this work, we only considers the steady state. Also, as 
mentioned in assumption (vi) that heat-up stage is negligible in this model but this is not 
practically true. As such this is also a limitation of the model shown here and we will 
look up these issues in the future to consider the first stage of evaporation. As illustrated 
in Fig. 1, the slope of second part of experimental graph and that of theoretical line are 
almost identical and as such we are confident to use the model to predict the droplet 
lifetime. The discrepancy in droplet lifetime for the experimental case is formed 
because of inclusion unsteady state period. 
 - Experimental 
 * - Theoretical 
 2
 Fig. 1. Comparison between the predictions and experimental findings [21] for the (D/D0) 
 versus time for Jet A-1 fuel. Initial conditions: T∞ = 800 K, Ts0 = 300 K, 
 D0 = 100 µm and p = 101.33 kPa. 
3.3. Influence of fuel properties on evaporation process 
 Variations of diminishing ratio of droplet diameter squared with time for several 
gas turbine fuels are illustrated in Fig. 2. The figure clearly shows the influence of fuel 
properties on droplet lifetime. JP-4 shows its longest lifetime while JP-7’s evaporates 
quickest. The difference amongst the fuels tested here may due to the differences in 
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 Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
their physical and thermal properties as shown in Tab. 1. The influence of fuel 
properties on evaporation will be discussed further in this section. 
 2 
 Fig. 2. Variation of (D/D0) with time during evaporation process for several fuel. 
 Initial conditions: T∞ = 800 K, Ts0 = 300 K, D0 = 1000 µm and p = 101.33 kPa. 
 Influence of initial fuel temperature on evaporation process is shown in Fig. 3 
for TS-1 and JP-4 fuel at ambient temperature T∞ = 1000 K (bigger than TS-1 and 
JP-4 critical temperature: Tcr for TS-1 = 639 K, and for JP-4 = 603 K). As the fuel 
temperature rises, the fuel vapor formed at the drop surface has two impacts: (1) part 
of the heat transferred to the drop is needed to furnish the heat of vaporization of the 
liquid and (2) the outward flow of fuel vapor impedes the rate of heat transfer to the 
drop. This tends to diminish the rate of increase of the surface temperature, so there 
is a part of the graphs (where initial temperature is smaller than fuel normal boiling 
temperature) drop lifetime grows up according to the increase of fuel temperature. 
When initial temperature nearly attains normal boiling point (Tbn for TS-1 = 431 K, 
for JP-4 = 372 K) which corresponds to distillation temperature 50% recovery, the 
influence of the outward flow decreases. Eventually, droplet lifetime is diminished 
with increasing initial fuel temperature from Tbn to Tcr. This figure also reveals that 
as the fuel asymptotically reachs its critical temperature, the droplet lifetime 
approaches to zero. 
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Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
 Fig. 3. Influence of initial fuel temperature on drop lifetime for TS-1 and JP-4 fuel. 
 Initial conditions: T∞ = 1000 K, D0 = 1 mm and p = 101.33 kPa. 
 The variation of the fuel temperature also affects liquid properties such as: heat of 
evaporation, density, and specific heat. Fig. 4 correlates the heat of evaporation and 
droplet lifetime as the initial fuel temperature rises from Tbn to Tcr for several fuels. This 
figure reveals that heat of evaporation and droplet lifetime become zero at Tcr, and for 
this condition drop lifetime grows up according to increasing direction of L. 
 Fig. 4. Influence of heat of evaporation on droplet lifetime as the initial fuel temperature 
 rises from Tbn to Tcr for several fuels. Initial conditions: T∞ = 1,000 K, 
 D0 = 1 mm, and p = 101.33 kPa. 
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3.4. Influence of ambient temperature on evaporation process 
 Fig. 5 shows drop lifetime versus ambient temperature. The figure clearly 
indicates that the time decreases remarkably with an increase in ambient temperature. 
Moreover, at low ambient temperature, difference in drop lifetime amongst the fuels 
studied here is significant but the difference is smaller with high temperature and the 
drop lifetime is almost identical amongst the fuels studied here at 2,000 K. 
 Fig. 5. Influence of ambient temperature on fuel evaporation process. 
 Initial conditions: Ts0 = 300 K, D0 = 1mm, and p = 101.33 kPa. 
 Fig. 6. Influence of initial fuel temperature to drop lifetime at varied ambient temperature 
 for fuel TS-1. Initial conditions: D0 = 1000 µm, and p = 101.33 kPa. 
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Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
 It is shown earlier in Fig. 3 that with an increase in initial fuel temperature to Tcr 
drop lifetime reduces to zero. However, this thing only corresponds to predetermined 
condition, in which ambient temperature is greater than the fuel critical temperature, Tcr. 
 Fig. 6 shows the influence of initial fuel temperature to drop lifetime at varied 
ambient temperature for fuel TS-1. At ambient temperature higher than fuel critical 
temperature Tcr (for TS-1 Tcr = 639 K), when initial fuel temperature approaches to Tcr, 
drop lifetime reduces to zero; whereas at ambient temperature smaller than fuel critical 
temperature, as initial fuel temperature approaches to Tcr, drop lifetime increases 
to infinite. 
4. Conclusion 
 In this paper, evaporation of different aviation fuels has been succesfully 
investigated. The influence of fuel properties and ambient temperature on evaporation is 
examined. It is observed that the fuel properties significantly affect the evaporation 
characteristics. All of fuel evaporation processes are remarkably affected by ambient 
temperature and initial fuel temperature. At the same initial conditions (Ts0 = 300 K, 
D0 = 1 mm and p = 101.33 kPa) and low ambient temperature (500 K), difference in 
evaporation rates amongst those fuels tested here is significant. JP-4 has the longest 
droplet lifetime while JP-7 shows its fastest evaporation time. However, under a high 
ambient temperature condition (2000 K), these values are almost identical. As fuels’ 
temperature approaches to their critical values, the evaporation is strongly affected by 
the fuel properties. 
Acknowledgements 
 This research is financially supported by National Foundation for Science and 
Technology Development (NAFOSTED) under grant number 107.01-2018.310. 
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Journal of Science and Technique - N.203 (11-2019) - Le Quy Don Technical University 
NGHIÊN CỨU ĐẶC TRƯNG BAY HƠI CỦA CÁC LOẠI NHIÊN LIỆU 
 HÀNG KHÔNG BAO GỒM JP-4, JP-5, JP-7, RT, Jet A-1 VÀ TS-1 
 Tóm tắt: Bài báo nghiên cứu đặc tính bay hơi của 6 loại nhiên liệu tua bin khí điển hình 
bao gồm JP-4, JP-5, JP-7, RT, Jet A-1 và TS-1. Bài báo tập trung đánh giá ảnh hưởng của nhiệt 
độ môi trường và đặc tính nhiên liệu đến tốc độ và thời gian hóa hơi. Ở cùng điều kiện ban đầu 
(ví dụ: nhiệt độ nhiên liệu là Ts0 = 300 K, đường kính hạt D0 = 1 mm, áp suất khí quyển 
p = 101.33 kPa) tại nhiệt độ môi trường thấp (khoảng 500 K), sự khác biệt về tốc độ bay hơi 
giữa các nhiên liệu là rất rõ ràng, trong đó JP-4 có thời gian hóa hơi dài nhất trong khi thời 
gian hóa hơi JP-7 là ngắn nhất. Tuy nhiên, ở môi trường nhiệt độ cao (2000 K) những giá trị 
này lại xấp xỉ gần như nhau. Khi nhiệt độ môi trường tiến đến giá trị tới hạn, tốc độ bay hơi của 
nhiên liệu phụ thuộc lớn vào đặc tính nhiên liệu. 
 Từ khóa: Nhiên liệu hàng không; quá trình bay hơi; tốc độ bay hơi; thời gian bay hơi giọt nhiên liệu. 
 Received: 22/01/2019; Revised: 18/10/2019; Accepted for publication: 22/11/2019 
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