The Influence of Biofuel on the Operational Characteristics of Small

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

The Influence of Biofuel on the Operational Characteristics of Small Experimental Jet Engine 1 K. Ratkovská1, a, M. Hocko2, b, J. Čerňan3, c, M. Cúttová3, d 1 – Department of Power System Engineering, Pilsen, 306 14, Czech Republic 2 – Department of Aviation Engineering, Kosice, 041 21, Slovakia 3 – Department of Aviation Technical Studies, Kosice, 041 21, Slovakia a – ratkovsk@zcu.kke.cz b – marian.hocko@tuke.sk c – jozef.cernan@tuke.sk d – miroslava.cuttova@tuke.sk DOI 10.2412/mmse.99.53.683 provided by Seo4U.link

Keywords: Fatty Acid Methyl Esters, jet engine, alternate fuel.

ABSTRACT. This paper investigates the results from experimental measurements made on a small experimental jet engine designated as MPM-20. The aim of these measurements is to evaluate the possibility of using a blend of the Fatty Acid Methyl Ester biofuel and Aviation turbine fuel for driving aircraft turbocompressor engines. The experiments were focused on evaluating the influence of different concentrations of mixtures both fuel types on fuel flow rate, change to revolutions and the thrust of the turbocompressor engine. A significant influence of the composition of the mixture on the process of the engine ignition was recorded. As the percentages of biofuel increased in the blend with aviation turbine fuel, the time taken to reach the engine operation mode was prolonged. More accurate data and results obtained from the measurements on the small jet engine are discussed in detail in this article.

Introduction. Since the introduction of jet engine aircraft in the early 1950s, world air transportation revenue traffic volume has experienced unprecedented growth. Today, air transportation accounts for about 10% of the passenger kilometres travelled by all major motorized modes, and for around 40% of the interregional transport of goods by value [1].

The historical growth in air transportation was entirely fuelled with petroleum-derived jet fuel. Unlike any other sector, air transportation heavily depends on this high-energy-density fuel. For nearly 100 years, the perennial fear of peak oil – point of time when half of the world‘s oil resources will have been depleted and prices therefore will arise to maximum – has also contributed to the search for alternatives to petroleum [2]. It follows that the aviation industry needs to find new organic alternatives to conventional fuels, which should be a full substitute for kerosene and jet fuel. The main reasons are the dependency of aviation fuels on petroleum and the increasing impact of air transport on the earth's atmosphere [3].

According to numerous studies [4, 5, 6] it is believed that some specific Fatty Acid Methyl Ester (FAME) blends, such as low carbon number saturated fatty acid esters, could be reconsidered as a possible aviation fuel blend component. However, at the present moment FAME is not approved as a jet fuel additive. The maximum allowable level is 50 ppm, which is the officially accepted functional definition of Identified Incidental Material [7]. All the accepted alternative jet fuels have a common drawback: they do not have any oxygen in their molecular structures since FAME are not approved additives. However, the presence of oxygen in a fuel has two main advantages: it reduces the carbon © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

content of the fuel, which in turn reduces its carbon footprint and reduces the soot formation (emission) of the fuel. Llamas et al. [8] make the point that based on smoke point testing, jet fuel containing oxygenates should give lower total particulate matter (PM) emissions than conventional jet fuel. According to numerous studies, emissions from planes at large airports are significant sources of local air pollution, including fine PM that can increase people´s risk of heart disease and asthma [9].

At present, there are many studies in progress with varying results. In one such study focused on alternatives to conventional diesel fuels it has been found that tall oil methyl ester–diesel fuel blends had the advantages of decreasing CO emissions (up to 38.9%), low sulphur content and higher cetane number [10]. However, the literature on the production and use of biodiesel for the aviation sector is still scarce and in some cases, contradictory. Dunn [11] studied the properties of a fuels obtained by blending 10-30% vol. of soybean FAME with JP-8 and JP-8+100. Dagaut and Gail [12] examined the oxidation behaviour of a blend of 20% vol. Rapeseed FAME with Jet-A1. This blend is important also for our research.

Experimental.

Experiments were carried out for examination of how different concentrations of blends of Fatty Acid Methyl Ester (FAME) biofuels and aviation turbine fuel - Jet A-1 affect the operational characteristics of small jet engine. The concentration of FAME biofuel was varied from 0% to 40%. The methyl fatty acid esters of rapeseed are a biofuel, and the fuel is nontoxic, as it does not contain any heavy metals or any harmful substances. For experiments was used small experimental jet engine designated as MPM-20 shown on Fig. 1.

Fig. 1. Experimental jet engine MPM-20.

Small experimental jet engine marked as MPM-20 was made by constructional modification of the TS-20/21 turbo – starter. The MPM-20 jet engine is made up of following main components: a mixed (axial-radial) air intake system, a centrifugal compressor with a single sided impeller, an annular combustion chamber, a single stage axial uncooled gas turbine of the reaction type, an output system with the fixed outlet nozzle. Detailed constructional description has been already mentioned in our previous work [13].

An MPM-20 jet engine is equipped with sensors that continuously monitor the basic thermodynamic parameters of the engine and other selected parameters describing its activity. Principal schematics MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

of such system, providing controlling and monitoring function, is shown on Fig. 2. In the measuring chain were used analog and digital sensors, which are connected to the bus system of SCXI 1000 with transduction SCXI cards 1102 and 1303. The system was connected to a PC, where with the help of the program LabView environment is processed and displayed as a virtual dashboard for immediate endpoint all the measured parameters of the engine MPM20.

This system allows the monitoring of the engine during operation and also recording these parameters for the purpose of subsequent diagnosis of correct operation of the engine and its systems. Electronic management of engine MPM 20 improved characteristics of the engine and also the possibility of its regulation within the prescribed limits. The monitoring of conditions in real time allows safer operation of the engine and the protection of the parts before exceeding the safe operating temperature and pressure [17].

Fig. 2. Schematics of MPM-20 controlling and monitoring system.

During experiment the MPM-20 was set to the reduced operation mode (n = 46 700 min-1). The length of measurement cycles ranged from 45 ¹ 5 seconds. The short time operation cycles is necessary because the original Turbo-starter was constructed only for short operation suited for starting up more powerful jet engine. The long-term operation of the MPM-20 small turbojet engine causes an increase of the thermal stress of the hot engine parts, in particular the combustor liner, turbine stator vanes and rotor blades, turbine rotor disc, and the engine can be easily damaged. Most importantly, the turbine rotor disc dangerously changes its outer radius at high temperatures – there is a danger of destruction of the rotor blades by collision with the outer turbine ring [13].

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Fatty Acid Methyl Ester in rapeseed.

The fatty acid methyl esters of rapeseed are a biofuel. Biofuels can be defined as liquid fuels produced from biomass for either transport or burning purposes. They can be produced from agricultural and forest products, and the biodegradable portion of industrial and municipal waste [14, 15]. Methyl esters must meet the requirements of standard EN 14214, which strictly applies only to methyl esters made from rapeseed oil (FAME).

Although it is chemically different from petroleum products, its density, viscosity, calorific value and process of burning is very close to diesel fuel. In comparison with diesel fuel, it is characterized by much better parameters for CO2 and SO2 emissions, and has only slightly higher NOX emissions.

FAME is nontoxic, as it does not contain any heavy metals or any harmful substances [16]. When examining the possibility of blends of FAME biofuel and A-1 jet fuel, it was found that at all concentrations (from 0% to 90%) there was a homogeneous blend, without the formation of deposits or coagulants. The density of blends depended on the increasing proportion of FAME biofuel in the blend The physical properties of FAME (Fig. 3b) biofuel and fuel Jet A-1 (Fig. 3a) are shown in Table 1.

a)

b)

Fig. 3. a) Jet A -1, b) FAME [15].

Table 1. The physical properties of FAME biofuel and Jet A-1.

Parameter

Unit

Jet A–11

FAME2

Parameter

Density (15 °C)

kg.m-3

810

882

Density (15 °C)

Acid number

mgKOH/g

0.003

0.23

Acid number

Flashpoint

°C

64

168

Flashpoint

Sulphur content

mg.kg-1

0.01

0.1

Sulphur content

1

based on the standards STN 050100

2

based on the standards TSHV 08-001 a EN14214

Operational parameters of MPM-20 The experimental measurements were conducted on the MPM-20 jet engine operating in the reduced mode for 45 ± 5 seconds and the concentration of FAME biofuel was varied from 0% to 40% [17].

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Measured values of the basic parameters (0% FAME) of the MPM-20, as the thermodynamic parameters, engine revolutions, fuel flow rate and thrust is given in Table 2. Comparing with these values it is possible to analyse the influence of a particular concentration of a blend FAME biofuel and Jet A-1 fuel on the operational characteristics in steady state mode and the transition modes of the engine. For each concentration of biofuel blends of FAME and Jet A-1 were performed at least three measurements, which have been selected for the evaluation of a representative graph.

Table 2. Change in MPM–20 basic parameters and the operational characteristics.

Parameter

20 sec.

30 sec.

40 sec.

45 sec.

T0 [°C]

25.5

25.5

25.5

29.1

T2t [°C]

107.1

123.5

105.4

70.5

T3t [°C]

943.1

992.8

1007.9

456.9

T4t [°C]

620.8

652.8

666.6

361.6

p2t [Pa]

263645.8

262923.1

260784.9

-

p3t [Pa]

192083.9

190688.5

188005.8

-

Qf[l.min-1]

1.233

1.221

1.204

-

n [RPM]

46 808.7

46 820.9

46 424.9

15 068.9

FN [N]

448.7

451.3

444.9

4.18

Engine revolutions. The change in engine revolutions of MPM-20 – Fig. 4 during its operation is controlled by a regulatory management system of the engine, which is set to maintain a constant speed on the operating mode n = nmax. The aforementioned regulating law depends on the needs of the original turbine starter TS-20, from which the MPM-20 was created. For this reason, the flow rate of fuel mixture Qf was changed. To maintain constant revolutions of the operating mode it was necessary for the individual blend of FAME biofuel and fuel Jet A-1 to ensure the required energy value, which required increased delivery of the blend of FAME biofuel, and fuel Jet A-1. In the range of operation of the MPM-20 from 25 seconds to 40 seconds, the maximum revolutions difference is Δnmax = 60.6 RPM which represents a deviation of 0.129% relative to the maximum engine revolutions.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 1. Behavior of engine revolutions.

Table 3. Change of engine revolutions – n [RPM x103].

Blend Jet A1/FAME

20 sec.

25 sec.

30 sec.

35 sec.

40 sec.

100 %

46.8

46.81

46.82

46.83

46.42

90 % / 10%

46.82

46.8

46.77

46.7

46.71

80 % / 20%

42.22

46.77

46.7

46.79

46.65

70 % / 30%

46.96

46.85

46.68

46.66

46.58

60 % / 40%

46.94

46.82

46.82

46.72

46.67

Fuel flow rate The course of changes in the supply of different blends of FAME biofuels and fuel Jet A-1 at startup of the engine corresponds to the startup of the MPM-20. After reaching the operating mode of MPM20, the flow rate of the fuel blend stabilizes and it only minimally falls by about 0.002 l.min. -1 (60% Jet A-1 and 40% FAME) to 0.052 l.min.-1 (80% Jet A-1 and 20% FAME). The biggest difference in the rate of flow of fuel ΔQf = 0.071 l.min.-1 between fuel Jet A-1 (1.204 l.min.-1) and a blend of 60% of fuel Jet A-1 and 40% FAME biofuel (1.277 l.min.-1) occurred in the 40th second.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 2. Behavior of fuel flow rate.

Table 4. Change of fuel flow rate - Qf [l.min-1].

Blend Jet A1/FAME

20 sec.

25 sec.

30 sec.

35 sec.

40 sec.

100 %

1.233

1.218

1.221

1.218

1.204

90 % / 10%

1.245

1.226

1.230

1.225

1.221

80 % / 20%

1.164

1.299

1.264

1.261

1.247

70 % / 30%

1.288

1.273

1.259

1.271

1.255

60 % / 40%

1.288

1.277

1.278

1.278

1.275

Thrust The change in the thrust of the experimental engine MPM-20 depends on the composition of the blend of the fuel Jet A-1 and FAME biofuel. In operation mode, the change is relatively low and is not proportional to the proportion of the FAME biofuel in the fuel blend. The MPM-20 achieves the highest thrust with a blend containing 20% FAME biofuel. From 20 seconds to 35 seconds the maximum deviation of thrust is 37.5 N (20 seconds) and the minimum deviation of thrust is 15.8 N (35 seconds), which is a deviation of 8.3%. The measured values of the thrust from the MPM-20 correspond to the calculated value.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 3. Behavior of thrust.

Table 5. Change of thrust – FN [N].

Blend Jet A1/FAME

20 sec.

25 sec.

30 sec.

35 sec.

40 sec.

100 %

448.7

444.9

451.3

451.3

444.9

90 % / 10%

441.3

440.5

444.8

438.9

438.8

80 % / 20%

418.7

460.9

460.8

454.7

456.4

70 % / 30%

456.2

448.9

448.8

448.9

442.8

60 % / 40%

450.1

446.1

441.9

439.9

439.9

Summary. The measurements confirmed that due to small differences in the calorific values of Jet A-1 fuel and FAME biofuel, different concentrations of the blends have only a small effect on the measured parameters (thrust, engine revolutions, fuel flow rate) of the MPM-20 experimental engine.

The operating mode of the engine control law had a major impact, which ensures maintain constant revolutions nmax. = const.

The composition of the mixture of Jet A-1 and FAME biofuel has a substantial effect on the startup of the MPM-20. Increasing the percentages of FAME biofuel in Jet A-1 fuel prolonged the time taken to reach operating mode. After exceeding 40% of FAME biofuel mixed with Jet A-1 fuel the startup process failed. The reason for the unsuccessful ignition of the mixture was the evaporation of an insufficient amount of atomizing fuel mixture in the fuel nozzle, which was designed to dispense Jet A-1 fuel. The ignitor for the fuel-air mixture is only an electric discharge spark plug, which is not enough to ignite a mixture with a composition different from pure Jet A-1 fuel. When re-starting the heated MPM-20 engine after the previous operation, startup was successful with a mixture of 60% Jet A-1 and 40% biofuel. The evaporation of this mixture was caused by heat radiating from the heated parts of the MPM-20. The delayed start of the MPM-20 using a blend of 80% Jet A-1 and 20% biofuels was atypical. The largest deviation was measured with this composition. But this deviation was determined mainly by different temperature of the engine at the beginning of the test.

Acknowledgments The authors would like to take this opportunity to thank the staff of the Laboratory of Intelligent Control Systems of Jet Engine. The presented work was financially supported by the Ministry of Education, Youth and Sport Czech Republic Project LQ1603 (Research for SUSEN). This work has MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

been realized within the SUSEN Project (established in the framework of the European Regional Development Fund (ERDF) in project CZ.1.05/2.1.00/03.0108).

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[11] Dagaut P., Gail S. Kinetics of gas turbine liquid fuels combustion: jet A1 and biokerosene, Proceedings of ASME Turbo Expo Vol. 2 (2007), pp. 93-101 [12] Ratkovská K., Čerňan, J., Cúttová, M. Semrád, K.: The Analyses for the Casing Improvements of the MPM-20 Engine, In: Proceeding of ASME TurboExpo Vol. 8. (2015)., pp. 1-9. ISBN: 978-07918-5679-6 [13] Jiricek I., Rabl V. Energy from Biomass / Energie z biomasy, (AZE 04/2005) Available on: http://www.vscht.cz/ktt/zdrene/5.0_Energie_z_biomasy.pdf [14] Ratkovská, K. – Hocko, M.: The influence of the blend of FAME biofuel and jet fuel on the thermodynamic parameters of an MPM – 20 engine, Experimental fluid mechanics 2016, Mariánske Lázne, Czech Republic [15] A. Dufey, Biofuels production, trade and sustainable development: emerging issues (2006) ISBN: 978-1-84369-643-8 Available on: http://pubs.iied.org/pdfs/15504IIED.pdf [16] Fözö L., Andoga R., Madarász L. Mathematical model of a small Turbojet Engine MPM-20. In: Studies in Computational Intelligence. Vol. 313 (2010), pp. 313-322. - ISSN 1860-949X.

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