**4. Hot tests in aviation combustor.**

Hot tests were performed at the Central Institute of Aviation Motors using a combusting chamber test rig. Fire tests of a burner with the low-emission aviation combustion chamber compartment have been conducted. Combustion chamber starting was conducted only on one pilot channel of a burner. Fuel mass flow rate ranged from 1 to 5.7 g/s. The part of the air arriving in the flame tube front passed through air swirlers of the burner. Thus, the centrifugal– pneumatic spraying was carried out, and as shown in the previous section, provided the best droplet dispersity. The kerosene TS-1, ethanol, and kerosene-ethanol-castor oil mixture were used as fuel. The operation mode corresponded to the altitude of an order of 2 km. The fixation of flame starting and blowout was carried out with the help of digital camera through a window at the liner outlet.

Test results are given in Figs. 11-20. The epures of the combustor's blowout characteristics at different excess air coefficients αC and total air volume flow rates QC were obtained. Also the temperature fields behind an exit from the combustor in a pipe with a diameter of 110 mm have been taken out under various αC.

Here α<sup>C</sup> - the general excess air coefficient in the combustion chamber - the relation of total air mass flow rate passing through the chamber to the air flow rate was required theoretically for complete combustion of the fuel arriving at the same time in this chamber. Thus, α<sup>C</sup> < 1 means rich fuel-air mixture and αC > 1 means lean mixture. 1 Here αC - the general excess air coefficient in the combustion chamber - the relation of total 2 air mass flow rate passing through the chamber to the air flow rate was required

The received blowout boundary line shows, that for conventional fuel (Figs. 11, 12), the combustor steadily works (the area within the curve) in the coefficient of air excess αC range from 1 to 10 and till QC = 0,4 m3 /с. The area boundary reaches satisfactory values on αC, and comprehensible values on QC. The ignition domain (within the curve in Fig. 11) is sufficient on the square for assured firing of the combustion chamber. 1 Here αC - the general excess air coefficient in the combustion chamber - the relation of total 2 air mass flow rate passing through the chamber to the air flow rate was required 3 theoretically for complete combustion of the fuel arriving at the same time in this chamber. 4 Thus, αC < 1 means rich fuel-air mixture and αC > 1 means lean mixture. 5 The received blowout boundary line shows, that for conventional fuel (Figs. 11, 12), the 6 combustor steadily works (the area within the curve) in the coefficient of air excess αC range from 1 to 10 and till QC = 0,4 m<sup>3</sup> 7 /с. The area boundary reaches satisfactory values on αC, and 8 comprehensible values on QC. The ignition domain (within the curve in Fig. 11) is sufficient 3 theoretically for complete combustion of the fuel arriving at the same time in this chamber. 4 Thus, αC < 1 means rich fuel-air mixture and αC > 1 means lean mixture. 5 The received blowout boundary line shows, that for conventional fuel (Figs. 11, 12), the 6 combustor steadily works (the area within the curve) in the coefficient of air excess αC range from 1 to 10 and till QC = 0,4 m<sup>3</sup> 7 /с. The area boundary reaches satisfactory values on αC, and 8 comprehensible values on QC. The ignition domain (within the curve in Fig. 11) is sufficient

**Figure 11.**

13

10

0,1

0,2

0,3

0,4

0,5

13

0

Boundary lines of ignition and blowout in the combustion chamber compartment; fuel - ker‐ osene TS-1; ● – lean blowout; ■ –rich blowout 10 11 Figure 11. Boundary lines of ignition and blowout in the combustion chamber compartment; 12 fuel - kerosene TS-1; ● – lean blowout; ■ –rich blowout 0 2 4 6 8 10 12

11 Figure 11. Boundary lines of ignition and blowout in the combustion chamber compartment;

Figure. 12 Flame photos at various α<sup>C</sup> from wake-up to lean blowout(kerosene) 14 **Figure 12.** Flame photos at various αC from wake-up to lean blowout (kerosene)

12 fuel - kerosene TS-1; ● – lean blowout; ■ –rich blowout

9 on the square for assured firing of the combustion chamber.

The radial temperature distribution at the combustor exit is shown in Fig. 13. The temperature field received has a symmetric appearance and a small non-uniformity on the value of the temperature - the minimum value differs from maximum on 50°C.

Test results are given in Figs. 11-20. The epures of the combustor's blowout characteristics at different excess air coefficients αC and total air volume flow rates QC were obtained. Also the temperature fields behind an exit from the combustor in a pipe with a diameter of 110 mm

Here α<sup>C</sup> - the general excess air coefficient in the combustion chamber - the relation of total air mass flow rate passing through the chamber to the air flow rate was required theoretically for complete combustion of the fuel arriving at the same time in this chamber. Thus, α<sup>C</sup> < 1 means

The received blowout boundary line shows, that for conventional fuel (Figs. 11, 12), the combustor steadily works (the area within the curve) in the coefficient of air excess αC range

1 Here αC - the general excess air coefficient in the combustion chamber - the relation of total 2 air mass flow rate passing through the chamber to the air flow rate was required 3 theoretically for complete combustion of the fuel arriving at the same time in this chamber.

1 Here αC - the general excess air coefficient in the combustion chamber - the relation of total 2 air mass flow rate passing through the chamber to the air flow rate was required 3 theoretically for complete combustion of the fuel arriving at the same time in this chamber.

5 The received blowout boundary line shows, that for conventional fuel (Figs. 11, 12), the 6 combustor steadily works (the area within the curve) in the coefficient of air excess αC range from 1 to 10 and till QC = 0,4 m<sup>3</sup> 7 /с. The area boundary reaches satisfactory values on αC, and 8 comprehensible values on QC. The ignition domain (within the curve in Fig. 11) is sufficient

5 The received blowout boundary line shows, that for conventional fuel (Figs. 11, 12), the 6 combustor steadily works (the area within the curve) in the coefficient of air excess αC range from 1 to 10 and till QC = 0,4 m<sup>3</sup> 7 /с. The area boundary reaches satisfactory values on αC, and 8 comprehensible values on QC. The ignition domain (within the curve in Fig. 11) is sufficient

11 Figure 11. Boundary lines of ignition and blowout in the combustion chamber compartment;

11 Figure 11. Boundary lines of ignition and blowout in the combustion chamber compartment;

0 2 4 6 8 10 12

Boundary lines of ignition and blowout in the combustion chamber compartment; fuel - ker‐

0 2 4 6 8 10 12

Figure. 12 Flame photos at various α<sup>C</sup> from wake-up to lean blowout(kerosene)

Figure. 12 Flame photos at various α<sup>C</sup> from wake-up to lean blowout(kerosene)

comprehensible values on QC. The ignition domain (within the curve in Fig. 11) is sufficient

/с. The area boundary reaches satisfactory values on αC, and

αc

αc

have been taken out under various αC.

from 1 to 10 and till QC = 0,4 m3

10

0,1

0,2

0,3

0,4

0,5

340 Biofuels - Status and Perspective

0

osene TS-1; ● – lean blowout; ■ –rich blowout

12 fuel - kerosene TS-1; ● – lean blowout; ■ –rich blowout

0,1

0,2

0,3

0,4

0,5

13

0

**Figure 11.**

10

13

14

14

rich fuel-air mixture and αC > 1 means lean mixture.

on the square for assured firing of the combustion chamber.

9 on the square for assured firing of the combustion chamber.

Qc, m<sup>3</sup>

12 fuel - kerosene TS-1; ● – lean blowout; ■ –rich blowout

**Figure 12.** Flame photos at various αC from wake-up to lean blowout (kerosene)

9 on the square for assured firing of the combustion chamber.

4 Thus, αC < 1 means rich fuel-air mixture and αC > 1 means lean mixture.

Qc, m<sup>3</sup> /s

/s

4 Thus, αC < 1 means rich fuel-air mixture and αC > 1 means lean mixture.

When using the ethanol (Figs. 14 - 16), lean blowout limit falls to αC = 3, and the combustor demonstrates stable operation only at major fuel flow rate (approximately αC = 1.8). This is due to the fact that alcohol is more volatile than the other liquid fuel, and thus, it will only burn before it can spread to a larger volume of flame front. The temperature reaches its maximum value with 300°C at αC = 2.1. 1 The radial temperature distribution at the combustor exit is shown in Fig. 13. The 2 temperature field received has a symmetric appearance and a small non-uniformity on the 3 value of the temperature - the minimum value differs from maximum on 50°C. 4 When using the ethanol (Figs. 14 - 16), lean blowout limit falls to αC = 3, and the combustor

In view of the foregoing, the use of pure ethanol as an alternative type of aviation fuel is not possible, as a minimum, without the use of special fuel additives. 6 due to the fact that alcohol is more volatile than the other liquid fuel, and thus, it will only 7 burn before it can spread to a larger volume of flame front. The temperature reaches its 8 maximum value with 300°C at αC = 2.1.

5 demonstrates stable operation only at major fuel flow rate (approximately αC = 1.8). This is

9 In view of the foregoing, the use of pure ethanol as an alternative type of aviation fuel is not

10 possible, as a minimum, without the use of special fuel additives.

Figure 13 Temperature distributions along the height of the liner; - αC = 3.5, ■ - αC = 5, - αC = 6.3; fuel - kerosene TS-1; QC = 0.3 m<sup>3</sup>/s **Figure 13.** Temperature distributions along the height of the liner; ◆ - αC = 3.5, ■ - αC = 5, ▲ - αC = 6.3; fuel - kerosene TS-1; QC = 0.3 m3 /s

Figure 14. Boundary lines of ignition and blowout in the combustion chamber compartment; fuel - ethanol; ■ – blowout, - combustor works, - combustor **Figure 14.** Boundary lines of ignition and blowout in the combustion chamber compartment; fuel - ethanol; ■ – blow‐ out, ◆ - combustor works, ▲ - combustor does not work

Figure 15 Flame photos at various αC from wake-up to lean blowout(ethanol)

does not work

1

2

0,1

0,2

0,3

0,4

0,5

QC, m<sup>3</sup>

/S

1

2

1

does not work

Figure 14. Boundary lines of ignition and blowout in the combustion chamber compartment; fuel - ethanol; ■ – blowout, - combustor works, - combustor

αC

Figure 15 Flame photos at various αC from wake-up to lean blowout(ethanol) **Figure 15.** Flame photos at various αC from wake-up to lean blowout (ethanol)

Figure 16 Temperature distribution along the height of the liner; fuel - ethanol; αC = 2.1; QC =

0.21 m<sup>3</sup>/s **Figure 16.** Temperature distribution along the height of the liner; fuel - ethanol; αC = 2.1; QC = 0.21 m3 /s

2 When using blended fuel (kerosene-ethanol-castor oil mixture), the combustor works better 3 than at pure ethanol. Nevertheless, the lean blowout boundary is reduced from 10 to 6.5 at 4 maximum volume flow rate conservation in comparison with kerosene (Figs. 11 and 17). 5 The flame color (Fig. 18) changes while maintaining its overall structure due to the 6 reduction of combusting efficiency and flame temperature and the increasing soot 7 production. One can see from the comparison of Figs. 13 and 19 to 20 that when using 8 blended fuel, it is possible to reach a maximum outlet flame temperature of 290°C only by 9 increasing the mass of the injected fuel (αC changes from 3.5 to 2.6). 10 Thus, biofuel application results in poor combustion stability characteristics for aircraft 11 engines when compared with kerosene. For biofuel use, it is necessary to provide a number When using blended fuel (kerosene-ethanol-castor oil mixture), the combustor works better than at pure ethanol. Nevertheless, the lean blowout boundary is reduced from 10 to 6.5 at maximum volume flow rate conservation in comparison with kerosene (Figs. 11 and 17). The flame color (Fig. 18) changes while maintaining its overall structure due to the reduction of combusting efficiency and flame temperature and the increasing soot production. One can see from the comparison of Figs. 13 and 19 to 20 that when using blended fuel, it is possible to reach a maximum outlet flame temperature of 290°C only by increasing the mass of the injected fuel (αC changes from 3.5 to 2.6).

13 activities include the incorporation of artificial flame stabilizers into the design to preserve 14 the stability limits of the combustor and the optimization of fuel injection system for the 15 purpose of reducing fuel-air aerosol dispersity to maintain combustion efficiency. Thus, biofuel application results in poor combustion stability characteristics for aircraft engines when compared with kerosene. For biofuel use, it is necessary to provide a number of actions for the modernization of conventional aviation combustion chambers. Main activities include the incorporation of artificial flame stabilizers into the design to preserve the stability limits of the combustor and the optimization of fuel injection system for the purpose of reducing fuel-air aerosol dispersity to maintain combustion efficiency.

12 of actions for the modernization of conventional aviation combustion chambers. Main

Figure 14. Boundary lines of ignition and blowout in the combustion chamber compartment; fuel - ethanol; ■ – blowout, - combustor works, - combustor

αC

0 2 4 6 8 10 12

Figure 15 Flame photos at various αC from wake-up to lean blowout(ethanol)

Figure 16 Temperature distribution along the height of the liner; fuel - ethanol; αC = 2.1; QC =

When using blended fuel (kerosene-ethanol-castor oil mixture), the combustor works better than at pure ethanol. Nevertheless, the lean blowout boundary is reduced from 10 to 6.5 at maximum volume flow rate conservation in comparison with kerosene (Figs. 11 and 17). The flame color (Fig. 18) changes while maintaining its overall structure due to the reduction of combusting efficiency and flame temperature and the increasing soot production. One can see from the comparison of Figs. 13 and 19 to 20 that when using blended fuel, it is possible to reach a maximum outlet flame temperature of 290°C only by increasing the mass of the injected

0 50 100 150 200 250 300 350

T, °C

/s

2 When using blended fuel (kerosene-ethanol-castor oil mixture), the combustor works better 3 than at pure ethanol. Nevertheless, the lean blowout boundary is reduced from 10 to 6.5 at 4 maximum volume flow rate conservation in comparison with kerosene (Figs. 11 and 17). 5 The flame color (Fig. 18) changes while maintaining its overall structure due to the 6 reduction of combusting efficiency and flame temperature and the increasing soot 7 production. One can see from the comparison of Figs. 13 and 19 to 20 that when using 8 blended fuel, it is possible to reach a maximum outlet flame temperature of 290°C only by

**Figure 16.** Temperature distribution along the height of the liner; fuel - ethanol; αC = 2.1; QC = 0.21 m3

10 Thus, biofuel application results in poor combustion stability characteristics for aircraft 11 engines when compared with kerosene. For biofuel use, it is necessary to provide a number 12 of actions for the modernization of conventional aviation combustion chambers. Main 13 activities include the incorporation of artificial flame stabilizers into the design to preserve 14 the stability limits of the combustor and the optimization of fuel injection system for the

Thus, biofuel application results in poor combustion stability characteristics for aircraft engines when compared with kerosene. For biofuel use, it is necessary to provide a number of actions for the modernization of conventional aviation combustion chambers. Main activities include the incorporation of artificial flame stabilizers into the design to preserve the stability limits of the combustor and the optimization of fuel injection system for the purpose of

15 purpose of reducing fuel-air aerosol dispersity to maintain combustion efficiency.

9 increasing the mass of the injected fuel (αC changes from 3.5 to 2.6).

reducing fuel-air aerosol dispersity to maintain combustion efficiency.

**Figure 15.** Flame photos at various αC from wake-up to lean blowout (ethanol)

does not work

0.21 m<sup>3</sup>/s

fuel (αC changes from 3.5 to 2.6).

H, mm

1

0

342 Biofuels - Status and Perspective

0,1

0,2

0,3

0,4

0,5

QC, m<sup>3</sup>

/S

1

2

Figure 17 Boundary lines of ignition and blowout in the combustion chamber compartment; mixed fuel (the embodiment 3 from Table 2); ● – lean blowout; ■ –rich blowout **Figure 17.** Boundary lines of ignition and blowout in the combustion chamber compartment; mixed fuel (the embodi‐ ment 3 from Table 2); ● – lean blowout; ■ –rich blowout Figure 17 Boundary lines of ignition and blowout in the combustion chamber compartment; mixed fuel (the embodiment 3 from Table 2); ● – lean blowout; ■ –rich blowout

2 Figure. 18 Flame photos at various αC mixed fuel from wake-up to lean blowout; mixed fuel (the embodiment 3 from Table 2) **Figure 18.** Flame photos at various αC mixed fuel from wake-up to lean blowout; mixed fuel (the embodiment 3 from Table 2)

1

0

0,1

0,2

0,3

0,4

Qc, m<sup>3</sup>

/s

0,5

1 2

Figure 19 Temperature distribution along the height of the liner; αC = 3.6; mixed fuel (the embodiment 3 from Table 2); QC = 0.29 m<sup>3</sup>/s 1 **Figure 19.** Temperature distribution along the height of the liner; α<sup>C</sup> = 3.6; mixed fuel (the embodiment 3 from Table 2); QC = 0.29 m3 /s

Figure 20 The dependence of axis temperature behind the combustor on excess air

2 3 4 5 6 7

α<sup>C</sup>

coefficient; mixed fuel (the embodiment 3 from Table 2)

0

50

100

150

200

250

300

Т, °С

1

H, mm

Figure 19 Temperature distribution along the height of the liner; αC = 3.6; mixed fuel (the

T, °С

embodiment 3 from Table 2); QC = 0.29 m<sup>3</sup>/s

Figure 20 The dependence of axis temperature behind the combustor on excess air coefficient; mixed fuel (the embodiment 3 from Table 2) **Figure 20.** The dependence of axis temperature behind the combustor on excess air coefficient; mixed fuel (the embodi‐ ment 3 from Table 2)

### **5. Summary**

An experimental study of the peculiarities of atomization of liquid fuels with different physical properties has been carried out. It has been shown that the spray angle upon hydraulic spraying is mainly determined by fluid viscosity, while remoteness of the point of the film decay from the exit section of the nozzle is determined by the surface tension coefficient. The effect of the properties of the liquid on the aerosol dispersity depends on the method of fluid crushing into droplets. In the case of the hydraulic atomization method without air supply, viscosity exerts the greatest impact on the dispersity of droplets. In the case of the centrifugalpneumatic method (with the same order of magnitude of the velocity of liquid and air), the greatest impact is from the surface tension. In the pneumatic method of spraying, when the injection velocity of the fluid is lower than the velocity of air, the linear size of droplets is mainly determined by the air flow irrespective of the properties of the liquid, whereas Sauter's mean diameter depends also on the surface tension coefficient.

In the case of low gas-turbine engine operating modes and high viscosity fuels like biodiesel or biokerosene, the centrifugal-pneumatic atomization method is optimal, while the pneumatic method is optimal for high operating modes.

For conducting of hot tests in aviation combustor, 11 embodiments of mixed liquid fuels were proved. The mixture in a proportion of 40% of aviation kerosene, 20% of castor oil, 40% of ethanol had been chosen for the tests as the most uniform and well mixed, without deposition and stratification.

Fire tests of the compartment of aviation combustion chamber with fossil fuel (kerosene TS-1) have shown comprehensible characteristics. In particular, wide side-altars of the stable combustion, assured firing of the combustion chamber, with uniform enough field of gas temperature on exit.

The application of blended fuel (kerosene-ethanol-castor oil mixture) results in worse com‐ bustion stability characteristics for aircraft engines when compared with kerosene. For biofuel use, it is necessary to provide a number of actions for the modernization of conventional aviation combustion chambers.
