1. Introduction
In today’s world, the main parameter of sustainable economic development bounds up with energy. The diminishing of the energy sources due to fast consumption can cause detrimental effects on the environment [
1]. Aviation, one of the most energy consuming sectors, should be considered as per ecological threat to the world. Increases in CO
2 emissions and temperature cause climate change across the world. In this regard, many studies have been executed in order to eliminate the unfavorable effects of the emissions in aviation [
2,
3,
4,
5,
6]. Moreover, another challenge that must be considered is the diminution of fossil energy resources. In this context, these challenges led researchers to work on alternative energy resources. One of the most eco-friendly and least pollutant renewable source as well, known is hydrogen. In recent years, the studies on fuel cell-based energy systems have led liquefied hydrogen fuel to be considered as an important alternative fuel with feasible outcomes [
7,
8,
9,
10,
11,
12,
13,
14,
15], but the disadvantages that have been waiting to be solved still remain [
16,
17,
18,
19,
20,
21]. Hydrogen should be produced because it does not exist in nature by itself. The need for the large fuel tank size, preserving liquefied hydrogen approximately below 253 °C working conditions and the aerodynamic design challenges in terms of weight is counted to be the major problems [
22,
23,
24].
Beyond all this, the main concern is to design jet propulsion systems regarding exergetic efficiency in order to give the best feasible outcome regardless of the type of fuel used [
16,
17,
25,
26,
27]. It is known that aircraft gas turbine engines operate according to thermodynamic principles. The main criterion on performance evaluation of aircraft engines is to achieve maximum thrust with minimum fuel consumption [
28,
29]. On this aspect, energy and exergy performance assessments have been applied to aircraft engines based on thermodynamic rules [
30,
31,
32,
33,
34,
35,
36]. Thermodynamics’ second law analysis named exergy analysis can give a chance to evaluate the quality of energy, entropy production (irreversibility) and the capability of doing work. Exergy can deal with the quantity of the work by considering the system and its environment thanks to reversible processes. The entire performance in a gas turbine system can be determined by putting forth the irreversibilities [
37,
38,
39,
40,
41]. The whole performance of a system and its segments can be improved when the irreversibilities and the exergy destructions of the system are diminished [
42,
43]. Not only the destruction ratio but also the interplay of the segments in a system can give the researchers a better comprehension to evaluate the performance metrics in a gas turbine engine. Even though thermodynamic irreversibilities lead to inefficiencies, which can be examined through conventional exergy analysis, further investigation by examining the source of irreversibility and amelioration capacity can be achieved only via advanced exergy analysis [
44,
45,
46,
47,
48].
As opposed to prior researches, the comparative improved performance examination of J85-GE-5H turbojet engine (TJE), as considering advanced exergetic analyses with the utilization of H2 fuel, has not been detected during the literature review. The primary interest and the originality of this study lie in this view. The main objectives and typicalness of this study can be abstracted to:
Calculate the exergy destructions of TJE and its segments,
Compare the TJE exergetic efficiency with the improved exergetic efficiency at Military (MIL) and Afterburner (AB) process modes for JP-8 fuel and H2 fuel,
Determine advanced exergy destruction rates of TJE and its segments by dividing into endogenous/exogenous and avoidable/unavoidable parts,
Compare the advanced exergetic destruction rates with the usage of JP-8 fuel and H2 fuel and
Find out the segments in demand of recuperation.
4. Results and Discussion
In accordance with
Table 1, exergetic performance variables at MIL and AB process modes of the entire TJE are demonstrated in
Table 3 and
Table 4 for kerosene utilization, respectively. As per the results, the velocities of the combustion gases were measured as 782.7 and 992.5 m/s at MIL and AB process modes, respectively. The thrusts of the aircraft at MIL and AB process modes were 13.05 and 17.28 kN, respectively. While the specific fuel consumption (SFC) was calculated as 99.77 (kg/h)/kN at the MIL process mode, it was determined to be 229.78 (kg/h)/kN at the AB process mode. The product exergy rates of the entire engine known as the kinetic exergy of the combustion gases were calculated as 5106.21 and 8575.33 kW at MIL and AB process modes, respectively, while the fuel exergy rates were 16,553.58 and 50,494.99 kW. Thus, exergy consumption rates were calculated as 11,447.37 and 41,919.66 kW at MIL and AB process modes, respectively.
Figure 3 indicates the exergetic and improved exergetic efficiency of the TJE and its segments for the MIL and AB process modes, respectively, with the usage of JP-8 fuel hereinafter.
While the entire engine had 9108.99 kW exergy destruction rate and 2338.38 kW exergy loss rate at the MIL process mode, it had 28,595.47 kW exergy destruction rate and 13,324.19 kW exergy loss rate at the AB process mode. Even though the overall engine efficiency was detected at MIL and AB process modes with the ratios of 30.85% and 16.98%, respectively, it was determined to be 59.12% and 54.64% when taking into account the improved potential of the system. The exergy ratio and other variables for the system segments are given as undermentioned:
As per
Table 3 at the MIL process mode, the utmost exergy demolition took place in the CC segment, which had a rate of 7525.35 kW. The entire engine had a 7916.25 kW exergy improvement potential rate, which was detected in the CC as the highest ratio with a value of 3421.07 kW. The CC segment had the rock-bottom exergy efficiency with a ratio of 54.54%, while it was detected as 68.75% for the improved condition. Therewithal, the CC had the utmost relative exergy consumption ratio with 65.74%, the maximum fuel exergy depletion ratio with 45.46% and the maximum productivity exergy lack ratio with 147.38%.
As per
Table 4 at the AB process mode, the utmost exergy demolition occurred in the ABED segment, which had a rate of 19,727.84 kW. The entire engine had a 34,800.63 kW exergy improvement potential rate, which was detected in the ABED as the highest ratio, with a value of 9354.18 kW. The ABED had the rock-bottom exergy efficiency with a ratio of 52.58%, whereas it was detected 67.84% for the improved condition. At the same time, the ABED had the maximum relative exergy consumption ratio with 47.06%, the maximum fuel exergy depletion ratio of 39.07% and the maximum productivity exergy lack ratio with 230.05%.
In accordance with
Table 2, exergetic performance variables at MIL and AB process modes of the entire TJE are demonstrated in
Table 5 and
Table 6 for H
2 utilization, respectively. Since the research has been performed parametrically in terms of H
2 fuel usage similar to Ref. [
65], the velocities of the exhaust gases were assumed as 782.7 and 992.5 m/s at MIL and AB process modes, respectively. The thrusts of the A/C at MIL and AB process modes were 12.87 and 16.58 kN, respectively. While SFC was calculated 36.52 (kg/h)/kN at MIL process mode, it was calculated 86.46 (kg/h)/kN at the AB process mode. The product exergy rates of the entire engine known as the kinetic exergy of the exhaust gases were determined as 5035.44 and 8228.21 kW at MIL and AB process modes, respectively, while the fuel exergy rates were 17,594.04 kW and 53,668.79kW. Thus, exergy consumption rates were calculated as 12,558.60 and 45,440.58 kW at MIL and AB process modes, respectively.
Figure 4 illustrates the exergetic and improved exergetic efficiency of the TJE and its segments for the MIL and AB process modes, respectively, with the usage of H
2 fuel hereinafter.
While the entire engine had a 10,378.03 kW exergy destruction rate and 2180.57 kW exergy loss rate at the MIL process mode, it had a 33,113.43 kW exergy destruction rate and 12,327.15 kW exergy loss rate at the AB process mode. Even though the engine efficiency was detected at MIL and AB process modes with the ratios of 28.62% and 15.33%, respectively, it was determined 58.35% and 54.15% for the improved conditions. The exergy ratio and other variables were presented as follows:
As per
Table 5 at the MIL process mode, the utmost exergy demolition took place in the CC segment, which had a rate of 8474.61 kW. The entire engine had 8964.31 kW exergy improvement potential, which was in the CC as the highest ratio with the value of 4082.01 kW. The combustion chamber segment had the rock-bottom exergy efficiency by the ratio of 51.83%, while it was detected 67.49% for the improved condition. Therewithal, the CC had the utmost relative exergy consumption ratio with 67.48%, the maximum fuel exergy depletion ratio with 48.17% and the maximum productivity exergy lack ratio with 168.30%.
As per
Table 6 at the AB process mode, the utmost exergy demolition was due to the ABED segment, which had a rate of 23,065.79 kW. The entire engine had 38,473.87 kW exergy improvement potential, which was detected in the ABED as the highest ratio, with a value of 12,203.64 kW. The ABED had the rock-bottom exergy efficiency by the ratio of 47.09%, whereas it was detected as 65.40% for the improved condition. At the same time, the ABED has the maximum relative exergy consumption ratio with 50.76%, the maximum fuel exergy depletion ratio with 42.98% and the maximum productivity exergy lack ratio with 280.33%.
When comparing the exergetic efficiency results acquired from the present study with the outcome of J69-T-25A TJE study [
65], one can write as follows:
The exergetic efficiency of the whole J69 engine was determined 15.40% with kerosene fuel usage while it was reckoned 14.33% with hydrogen fuel utilization. The percentage change of J69 engine’s exergetic efficiency calculated as 6.95% was not only lower than the MIL process mode exergy efficiency percentage change 7.23% of the J85-GE-5H TJE but also lower than the AB process mode exergy efficiency percentage change 9.73%. Although these findings have indicated that the use of hydrogen fuel caused more exergy destruction in J85 engine, the overall engine efficiency was more efficient than J69 engine in both process modes. On the other hand, as per Ref. [
31], the efficiency of (J85-GE-CAN-15) TJE determined 31.64% and 24.18% at the MIL and AB process modes, respectively, was detected more efficient than the ones in this article.
In order to verify the exergy analyses consequences, the advanced exergy analysis results were taken into account for further performance assessment of TJE and its segments. Turbojet engine and its segments’ advanced exergy destructions are shown for MIL and AB process modes in
Table 7 and
Table 8 for JP-8 usage.
As per
Table 7 at the MIL process mode, the total avoidable exergy destruction rate
of the TJE was 650.18 kW. The largest part of this ratio occurred in the CC with a rate of 207.71 kW. The utmost unavoidable exergy destruction rate was due to
in the CC with a value of 7317.64 kW. This rate was equal to 86.51% of the total unavoidable exergy destruction rate (8458.81 kW), which is 80.33% of the total exergy destruction rate (9108.99 kW). As per
Figure 5, the unavoidable demolition part of the CC was the sum of
the rate of 6643.88 kW and
with a rate of 673.76 kW. The unavoidable parts cannot be diminished via uplift in the efficiency of the system due to manufacturing restrictions.
On the other hand, the utmost endogenous exergy destruction rate
took place in the CC with a rate of 6835.25 kW. Since the great endogenous exergy destruction rate, being due to the CC, the amount of the endogenous part of the exergy destruction therein the entire engine was extremely greater than that of the exogenous part. The percentage of endogenous exergy destruction therein the CC was 83.24% of the total endogenous exergy destruction rate (8211.69 kW) and the 75.04% of the total exergy destruction rate. The TJE engine had an aggregate exogenous exergy demolition rate of 897.30 kW. The major fragments of this rate given in
Table 7 were determined 690.10 kW in the CC, 132.24 kW in the AC, 33.06 kW in the ABED and 25.98 kW in the FED. The exogenous exergy destruction was brought about in the
n-th segment by the irreversibilities that occurred in the downstream segments. One could have a chance to understand the reciprocal interplay between engine segments by separating the demolitions into the exogenous parts. With respect to
Table 7, the CC had a striking influence on the AC segment based on the inefficiencies. At the same time, the AC had the same influence on the CC segment too. Moreover, the AC and the CC segments’ inefficiencies caused the exergy destructions of the downstream segments.
One could have a better understanding by analyzing the dispersion of the exergy demolition as per
Table 7. The avoidable-exogenous exergy demolition
rates were calculated 20.01 and 16.34 kW in the AC and CC segments, respectively. The
could be diminished uplift in the form of the entire system or uplift in the efficiency of the downstream system segments. The
section could be diminished by uplifting the efficiency of the searched segment. According to the obtained results, while the CC segment had the utmost avoidable demolition value with the ratio of 31.95% at the MIL process mode, the ABED segment had the utmost avoidable demolition value with the ratio of 66.99% at the AB process mode.
As per
Table 8 at the AB process mode, the total avoidable exergy destruction rate
of the TJE was 3543.88 kW. The great section of this ratio occurred in the ABED segment with a value of 3001.05 kW. The irreversibilities took place in the downstream segments led to exogenous exergy demolition in the
n-th segment. The TJE engine had an aggregate exogenous exergy demolition rate of 4192.77 kW. The major fragments of this rate were 3328.53 kW in the ABED, followed by 690.10 kW in the CC and 132.24 kW in the AC. The supreme
was in the ABED with a rate of 16,726.80 kW, being equal to 66.77% of total unavoidable exergy destruction rate (25,051.59 kW) and 58.49% of total exergy destruction rate (28,595.47 kW). As per
Figure 6, the unavoidable demolition part of the ABED was the sum of
the rate of 13,867.49 kW and
with a rate of 2859.31 kW. In addition, the supreme endogenous exergy destruction rate
was determined in the ABED with a rate of 16,399.32 kW. This ratio equaled to 83.13% of the ABED exergy destruction rate (19,727.85 kW) and 67.20% of the total endogenous exergy destruction rate (24,402.70 kW). As per
Table 8, the ABED segment had the utmost
with the rate of 469.22 kW. The rate of the
equaled to 1.82% of the total exergy destruction rate in the TJE at the AB process mode while it was reckoned 0.7% at the MIL process mode.
On the other hand, the turbojet engine and its segments’ advanced exergy destructions are shown in
Table 9 and
Table 10 at MIL and AB process modes for H
2 usage hereinafter:
According to
Table 9 at the MIL process mode, the total avoidable exergy destruction rate
of the TJE was 860.40 kW. The great section of this ratio occurred in the CC with a rate of 300.33 kW. The utmost unavoidable exergy destruction rate took place
in the CC with a rate of 8174.28 kW, being equal to 85.89% of the total unavoidable exergy destruction rate (9517.63 kW) and 78.77% of the total exergy destruction (10,378.03 kW). As per
Figure 7, the unavoidable demolition part of the CC was the sum of
the rate of 7348.78 kW and
with a rate of 825.50 kW.
The utmost endogenous exergy destruction rate
occurred in the CC with a rate of 7613.87 kW. According to the obtained results, endogenous exergy destruction rates of the entire engine were greater than the exogenous destruction rates. The percentage of endogenous exergy destruction in the CC was 82.15% of the total endogenous exergy destruction (9268.47 kW) and 73.37% of the total exergy destruction in the TJE. The TJE engine had an aggregate exogenous exergy demolition rate of 1109.56 kW. The major fragments of this rate given in
Table 9 were 860.74 kW in the CC, 119.75 kW in the AC, 49.74 kW in the GT and 43.50 kW in the ABED. As per
Table 9, the influences of the CC and AC segments on each other not only caused their exergy destructions but also the exergy destructions of other engine segments. According to the results, while the CC segment had the utmost avoidable demolition value with a ratio of 34.91% at the MIL process mode, the ABED segment had the utmost avoidable demolition value with the ratio of 70.36% at the AB process mode. The results for endogenous, exogenous, unavoidable and avoidable exergy demolition of TJE and segments in advanced exergy evaluation at AB process mode for H
2 utilization are shown in
Table 10.
As per
Table 10 at the AB process mode, the total avoidable exergy destruction rate
of the TJE was 4694.19 kW. The great section of this ratio occurred in the ABED segment with a value of 3982.38 kW. The TJE engine had an aggregate exogenous exergy demolition rate of 5363.32 kW. The major fragments of this rate were 4297.26 kW in the ABED and 860.74 kW in the CC.
The supreme took place in the ABED with a rate of 19,083.41 kW, which was equal to 67.15% of the total unavoidable exergy destruction rate (28,419.23 kW) and 61.33% of the total exergy destruction rate (33,113.43 kW).
As per
Figure 8, the unavoidable demolition part of the ABED was the sum of
with a rate of 15,469.09 kW and
with a rate of 3614.32 kW. In addition, the supreme
occurred in the ABED with a rate of 18,768.53 kW, being equal to 81.37% of the ABED exergy destruction rate (23,065.79 kW) and 67.63% of the total endogenous exergy destruction rate (27,750.11kW). As per
Table 10,
rates were calculated as 682.94 kW in the ABED and 35.24 kW in the CC. The rate of the
equaled to about 2.3% of the total exergy destruction in the TJE at the AB process mode while it was reckoned approximately 0.9% at the MIL process mode.