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CFD analysis of biodiesel blends and combustion using Ansys Fluent
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
CFD analysis of biodiesel blends and combustion using Ansys Fluent Shivanshu Dixit a, Arvind Kumar b, Suraj Kumar c, Nitin Waghmare c, Harish C. Thakur b, Sabah Khan c,⇑ a
IIT Ropar, Rupnagar, Punjab 140001, India Gautam Buddha University, Greater Noida, UP 201310, India c Jamia Millia Islamia, New Delhi 110025, India b
a r t i c l e
i n f o
Article history: Received 20 November 2019 Accepted 27 December 2019 Available online xxxx Keywords: Biodiesel blend IC Engine Combustion analysis Ansys fluent CI Engine
a b s t r a c t Automobile sector heavily relies on burning of fossil fuels to meet its energy requirements. This continuous burning of fossil fuels generates harmful emissions which are hazardous for both environment and human being. To stare down these emissions levels, appropriate methods of emission reduction or a sustainable replacement to fossil fuels are desiderating of the current situation. An alternate solution to the stated concern is biodiesel, which is non-toxic, biodegradable, and renewable by its nature. Another advantage, where little or no modification to present compression ignition (CI) engines is boon for utilizing biodiesel. Biodiesel originates from organic matter, from animals and plants, via — a chemical process called transesterification. During the process, methyl or ethyl ester (biodiesel) are refined from animal fat or vegetable oil with other useful products like glycerin. The pure form of biodiesel, which is abbreviated as ‘BXX’- B100 (pure biodiesel), while blended with petroleum diesel in proportion are B2-2% biodiesel, B5-5% biodiesel, and B20-20% biodiesel. Biodiesel produced from plant origin like non-edible grade oil from Jatropha plant has promising potential as blending fuel. It has an economic aspect too, as blended petroleum products or pure biodiesel reduces the dependency of foreign petroleum imported by countries like India. This article is about CFD based combustion analysis of biodiesel fuel using Ansys FluentÓ and matched with the combustion of diesel fuel. Parameters like the temperature of combustion at various blend ratios of B0-B100 varies from 2100 K to 1100 K are recorded through contour plots. Results are compared with diesel fuel, and an appropriate blend ratio is given for biodiesel for having for maximum efficiency and the least emission in applications. Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization
1. Introduction Environmental pollution and the energy crisis are effecting life at a global level. Limited reservoirs of fossil fuel and emission due to the combustion of these fossil fuels are affecting the balance of our mother nature. Phenomena like global warming, climate change, and increase in Greenhouse Gases (GHG’s) are among such unbalances. The automobile sector is among those sectors which heavily rely on these fossil fuels for energy requirement. While pollution from these automobiles is among the primary reason behind the rapid increase in air pollution [1–5]. The by-product of combustion from automobiles engine exhaust consists of unburnt hydrocarbons, smoke, particulate matter, CO2, CO, NOx, which are affecting human being in particular and our environment in ⇑ Corresponding author. E-mail address: [email protected] (S. Khan).
general sense. With rapid economic growth and urbanization, this problem is becoming more severe in countries like India. The study from the various institution in India shows that air pollution is at an alarming level due to vehicular automobile pollutants [6–7]. The aforementioned concerns require attention and working towards alternative fuels [8–9]. One such solution is biodiesel, which is a suitable alternative as a fuel in CI engines. The main advantage of using such fuel are its renewability, biodegradable, non-toxic nature, and with little or no modification to CI engines [4]. Biodiesel is a clean-burning, renewable fuel made from vegetable oils, animal fats, and recycled cooking oil and greases. Biodiesel includes both animal fats and vegetable oils from plants like Palm, Jatropha, Mahua, Flax, Mustard, Rapeseed, Sunflower, and Algae, etc. It is produced from a chemical process called- transesterification shown in Fig. 1. (Fig. 1. (a) transesterifcation reaction and (b) life cycle of biodiesel production [11,12]). Chemically, it is methyl (or ethyl) esters while physically it is liquid in nature.
https://doi.org/10.1016/j.matpr.2019.12.362 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
2
S. Dixit et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 1. (a) Example of transesterification reaction with byproduct of biodiesel and glycerin [11]; (b) Life cycle comparison between diesel and biodiesel [12]
Biodiesels are replenishable, reduce carbon emissions, free from sulfur content, sustainable, and reduce dependence on foreign sources. Its physical and thermal properties are similar to diesel. Due to its lower energy content 5–10% as compared to diesel and high viscosity, a blending of 10–20% is used in CI engines. It can be used in pure which is B100 or blended form (in diesel). Most of the common blend includes B2 which is 2% biodiesel-98% diesel, B5, B20, B50, B90 and B100 are defined according to blend ratios [10]. Various literature is available for biodiesel in reports, experimental findings, computer simulations and, practical applications at a variety of platforms like CI engines, power plants, gas turbines, etc. Some among which are as follows: Klaus Becker and H.P.S. Makkar in the year 2008 investigated a Jatropha plant and its potential biodiesel as a source of energy for the future [17]. Rajesh Govindam, O.P. Jakhar, and Y.B. Mathur analyzed biodiesel blends in CI engine using Ansys Fluent. Their model predicted a higher in-cylinder pressure and temperature for the biodiesel blends during combustion as compared to pure diesel [18]. A.M. Indrodia, N.J. Chotai and B.M.Ramani investigated the effect of combustion chamber geometry [19]. Prem Kumar, M.P. Sharma, Gaurav Dwivedi analyzed the performance of the diesel engine along with B10 blended fuel. Notable conclusion of CO reduction, NOx increment and maximum power for B10 fuel are compared with conventional diesel fuel [20]. S. M. Palash and his group investigated that biodiesel as alternate fuel. They emphasis emission reduction through the use of biodiesel. They also addressed higher NOx emissions in biodiesel combustion with increasing engine load, and vice versa. Where NOx can be decreased using Exhaust Gas Recirculation [21]. Eugene S. Domalski calculated released heat after the combustion of fuels containing carbon, hydrogen, oxygen, nitrogen, and sulfur. [22]. CFD analysis under high ambient conditions and high pressure for biodiesel as well as combustion characteristics of Jatropha in CI engine are reported using Ansys FluentÓ [23 24]. In this article, we report theoretical combustion analysis and CFD simulation of biodiesel fuel using Ansys FluentÓ, and are compared with diesel combustion. The various blend ratios of B0, B15, B20, B50, B90, and B100 are studied using temperature contour plots. Results in comparison with diesel fuel are made, and an appropriate blend ratio is given for biodiesel for having maximum utility is studied. 1.1. Production process of biodiesel Biodiesel is a by-product of transesterification of oil from vegetable/animal, fats, and from sources like waste oil and tallow, etc. Potassium hydroxide (KOH) or sodium hydroxide (NaOH) is the catalyst used in the reaction. The reaction completes, and Biodiesel is formed as one of the products.
A typical molecular structure Biodiesel is shown in Fig. 2 below which is a long chain of carbon and hydrogen atom attached. This chain also consists of an ester functional group (shown with blue color) that differentiates it from regular diesel [13]. 2. Combustion analysis For the combustion analysis, it is required to have all thermal parameters used in combustion analysis shown in Table 1 [15]. When combustion of various elements occurs in the presence of O2, the basic equation goes like equations (1). For complete combustion, a generalized eddy-dissipation model is used to analyze the biodiesel-air combustion [14]. The chemical reaction equation of biodiesel is:-
C17 H34 O2 + 24.5O2 ! 17CO2 + 17H2 O + Heat
ð1Þ
There are 17 carbon, 34 hydrogen and 2 oxygen atoms, so molecular weight of Biodiesel = 12*17 + 34 + 2*16 = 270 (molecular weight calculated directly) and the empirical relation to calculate the average molecular weight of the Biodiesel i.e. MWi = 14.027C-2.016d + 31.998 = 14.027*17–2.016*1 + 31.9988 = 268.4578. Where, C = number of carbons; d = number of double bonds. 2.1. A/F ratio for the combustion of biodiesel In the combustion process, the stoichiometric combustion reaction in which the reactant from hydrocarbon from fuel (Biodiesel) must form CO2, H2O and heat as the product of combustion and the reaction is as follows in Fig. 3. Where z is known as the stoichiometric coefficient for the oxidizer (air) z = x + (y/4); z = 17 + (34/4) = 25.5 Biodiesel + 24.5 (O2 + 3.76 N2) ? 17 CO2 + 17H2O + 92.12 N2 Theoretical A/F ratio = mass of air/mass of fuel inlet = z*4.76*29/ (molecular mass of fuel* no. of moles) = 12.525 kg 12.53 kg of air is required for a complete combustion of 1 kg of biodiesel. 3. Modelling of the problem The cylindrical combustor considered is shown in Fig. 4. The flame in this analysis is considered as turbulent diffusion flame. Biodiesel enters the cylinder through a small nozzle placed at the center of the cylinder at 50 m/s while ambient air at 0.5 m/s coaxially. The equivalence ratio is around 0.76 (around 28% excess air). Since the injection speed is high for biodiesel, outer wall of cylinder offers less hindrance so it expands rapidly and mixes with air entering the cylinder.
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
S. Dixit et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Fig. 2. Molecular structure of Biodiesel [13]
Table 1 Comparison of properties between diesel and biodiesel [15 16]. Property name
Unit
Biodiesel (variety)
Diesel
Density Kinematics Viscosity Calorific value Cetane number Auto ignition Temp. Specific heat Stoichiometric air/fuel ratio Molecular weight Flash point Ignition delay
kg/m3 Cst kJ/kg – K J/kg-K –
845–900 4.8 (40 °C) 39340–43759.5 58.4 (47–60) 700 1900–2050 12.525
825 (15 °C) 3.6 (40 °C) 44,000 51.5 (40–60) 483 1750 15
– °C Angle to crankshaft MJ/kg
270 88–170 9.39
200 76 10.56
39.8
45
Calorific value
Fig. 3. Schematic of reaction along with input and output from combustion chamber.
Fig. 4. Schematic of cylinder combustor for analysis.
reaction and turbulent flow. The first analysis is done for the combustion reaction of diesel (B0). Outputs (temperature, exhaust gases and mass fraction) have taken, and same analysis is done for biodiesel. Different blends ratio as B15, B20, B50, B90, and B100 with diesel have analyzed. Analysis steps and boundary conditions are summaries in Table 2. 5. Results and discussion Biodiesel proves better in terms of less knocking, less emissions, ignition with less delay and complete combustion [26]. In the combustion of diesel, temperature profile varies between 1700 K and 2100 K, while in biodiesel, temperature varies from 1100 K to 1350 K. Fig. 5 shows the temperature profile in the combustion of Diesel and biodiesel. Temperature characteristics in the combustion of diesel is higher than that of biodiesel. Biodiesel does not produce so much of heat as compared to diesel, so its blending with diesel can be used for better output. In the combustion of Diesel, CO2 produced up to a range of 0.16–0.18 mass fractions while biodiesel produces CO2 up to a range of 0.11–0.125 mass fractions which are lesser than that of diesel fuel. Fig. 6 represents the mass fraction of CO2 in the combustion analysis of diesel and biodiesel. Which shows biodiesel is more eco-friendly than that of diesel fuel. NOx produced in the combustion of diesel are in range of 0.015 to 0.020 mass fraction while biodiesel produces are in range of 0.20 to 0.33 mass fraction. NOx produced are more in biodiesel than that of diesel during combustion. This is one of the drawback of for the biodiesel using as a fuel. Using Exhaust Gas Recirculation (EGR) in the exhaust system, we can control NOx up to a certain limit. Fig. 7 shows the NOx exhaust gas in the combustion of diesel and biodiesel fuel. To predicit the lubrication property of fuel, Fig. 8 represent the mass fraction C17H34O2 in diesel and biodiesel. Conventional diesel fuel is less viscous than biodiesel fuel. Biodiesel have a lubricating property so it flows smoothly in the combustion chamber as compared to that of diesel. Thus, engine life increases giving advantages to biodiesel applications.
4. CFD analysis of biodiesel blends using Ansys Fluent 5.1. Blending of biodiesel with diesel The problem is analyzed using Ansys Fluent [25], and design is imported. The whole domain is discretized using fine mesh generation on the geometry. Convection load is applied using boundary conditions. ST-Model is used in the analysis of any chemical reaction, and the eddy dissipation model is used for rapid
Biodiesel is blended with diesel as defined above and are studies different concentrations. B90 (90% biodiesel, 10% diesel) is analyzed for use. The greater the % blend of biodiesel in fuel, the more eco-friendly is the fuel. While B50 (50% biodiesel, 50% diesel)
Table 2 Consolidated analysis step and boundary condition. Analysis steps a) b) c) d) e) f) g) h) i)
Import the geometry in Ansys Fluent. Discretize the whole geometry into fine meshes. Select Energy and choose ON option. Select viscous model as k-e(2eqn) turbulence model. Transport the species using species transport. Select material and feed boundary condition. Solve the reaction for temperature and Exhaust output. NOx is selected again in Models for computing NOx. Solve it again for exhaust.
Boundary condition a) Fuel: 50 m/s from nozzle and at a temperature of 300 K b) Air: 0.5 m/s and at a temperature of 300 K and 0.76 species mass fraction. c) Walls: constant at 300 K.
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
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S. Dixit et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 5. (a) The static temperature profile in the combustion of diesel; (b) biodiesel.
Fig. 6. (a) The contour profile for mass fraction of CO2 in diesel; (b) biodiesel.
Fig. 7. (a) The contour profile for mass fraction of NOx in diesel; (b) biodiesel.
Fig. 8. (a) The profile for mass fraction of in C17H34O2 in diesel; (b) biodiesel.
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
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S. Dixit et al. / Materials Today: Proceedings xxx (xxxx) xxx
b
c
d
e
f
Temperature (K)
a
2100 1800
1750
1600 1225
B0
B15
B20
B50
B90
1100
B100
% Blend
Fig. 9. the static temperature profile in the (a) B90; (b) B50; (c) B20; (d) B15; (e) B0 (f) graph of temperature in combustion of blend B0, B15, B20, B50, B90 and B100.
shows no difference in the serviceability compared to those fuelled with petroleum diesel fuel. Biodiesel as discussed above significantly reduces exhaust emissions. The complete burn of biodiesel fuel is results due naturally present oxygen in it. Depending on engine type and operating conditions NOx emissions can be handled. While B20 is widespread and have similar charaterstics as diesel fuel. B15 show a similarity with B20 with slight increase in combustion temperature. The emissions problem can be addresed using blended fuel due to their combustion support and lesser pollutant in exhaut. The contour profile and a temperature in the combustion of blend B0, B15, B20, B50, B90 and B100 are shown in Fig. 9. 6. Conclusion Biodiesel is a sustainable alternative to fossil fuel. Simulation results show that the temperature in the combustion of diesel (2100 K) is higher than that of biodiesel (1100 K). Due to less heat, less CO2 emission in biodiesel is less while NOx is high. These emissions can be reduced with the use of EGR and SCR systems. Biodiesel shows better lubrication property in comparison to the diesel counterpart. Blend diesel fuel shows a variety of properties, depending on % of the blend. A gradual decreasing temperature profile is observed from B0 to B100
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References [1] Sayyed Siraj, Renuka Kale, Swapnil Deshmukh, Effects of thermal, physical, and chemical properties of biodiesel and diesel blends, Am. J. Mech. Ind. Eng. 2 (1) (2017) 24–31, https://doi.org/10.11648/j.ajmie.20170201.14. [2] M. Mofijur et al., Effect of biodiesel-diesel blending on physico-chemical properties of biodiesel produced from Moringa oleifera, Procedia Eng. 105 (2015) 665–669. [3] Ritchie, Hannah, and Max Roser. Fossil fuels. Our World in Data (2017). [4] Digambar Singh, Dilip Sharma, S.L. Soni, Sumit Sharma, Pushpendra Kumar Sharma, Amit Jhalani, A review on feedstocks, production processes, and yield for different generations of biodiesel, Fuel 262 (2020) 116553. [5] L.C. Meher, D. Vidya Sagar, S.N. Naik, Technical aspects of biodiesel production by transesterification—a review, Renewable Sustainable Energy Rev. 10 (3) (2006) 248–268. [6] Centre for Science and Environment (CSE) ‘‘At the Crossroads: World Environment Day, https://www.cseindia.org/at-the-crossroads-worldenvironment-day-9463. [7] Pti. Pollution Worse in Indian Cities as Registered Vehicles up by 700 Times. https://www.livemint.com, Livemint, 12 June 2019, https://www. livemint.com/news/india/pollution-worse-in-indian-cities-as-registeredvehicles-up-by-700-times-since-1951-study-1560366478591.html. [8] Soo-Young No, Inedible vegetable oils and their derivatives for alternative diesel fuels in CI engines: a review, Renewable Sustainable Energy Rev. 15 (1) (2011) 131–149. [9] M. Gumus, S. Kasifoglu, Performance and emission evaluation of a compression ignition engine using a biodiesel (apricot seed kernel oil methyl ester) and its blends with diesel fuel, Biomass Bioenergy 34 (1) (2010) 134–139. [10] Robert L. McCormick, Steven R. Westbrook, Storage stability of biodiesel and biodiesel blends, Energy Fuels 24 (1) (2009) 690–698. [11] Lichtarowicz, Marek. Biofuels. Essential Chemical Industry Online, http://www. essentialchemicalindustry.org/materials-and-applications/biofuels.html. [12] Dr. Guido Reinhardt Screening Life Cycle Assessment of Jatropha Biodiesel Institute for Energy and Environmental Research Heidelberg GmbH, 2007. Link: https://www.ifeu.de/en/project/jatropha [13] The Chemistry of Biodiesel: Biodiesel Project: Goshen College. Academics, https://www.goshen.edu/academics/chemistry/biodiesel/chemistry-of. [14] J. Van Gerpen et al., Biodiesel analytical methods, Contract 303 (2004) 275– 3000. [15] P.K. Sahoo, L.M. Das, Combustion analysis of Jatropha, Karanja and Polanga based biodiesel as fuel in a diesel engine, Fuel 88 (6) (2009) 994–999. [16] G.B. Adebayo, O.M. Ameen, L.T. Abass, Physico-chemical properties of biodiesel produced from Jatropha curcas oil and fossil diesel, J. Microbiol. Biotech. Res 1 (1) (2011) 12–16.
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[17] Klaus Becker, H.P.S. Makkar, Jatropha curcas: a potential source for tomorrow’s oil and biodiesel, Lipid Technol. 20 (5) (2008) 104–107. [18] Rajesh Govindan, O.P. Jakhar, Y.B. Mathur, Computational analysis of Thumba biodiesel-diesel blends combustion in CI engine using Ansys-fluent, IJCMS 3 (2014) 29–39. [19] Indrodia, A., N. Chotai, and B. Ramani. Investigation of Different Combustion Chamber Geometry on Diesel Engine using CFD Modelling of In-cylinder Flow for Improving the Performance of Engine. 5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014). 2014. [20] Prem Kumar, M.P. Sharma, Gaurav Dwivedi, Impact of biodiesel on combustion, performance and exhaust emissions of diesel engines, J. Integr. Sci. Technol. 2 (2) (2014) 57–63. [21] S.M. Palash et al., Impacts of biodiesel combustion on NOx emissions and their reduction approaches, Renewable Sustainable Energy Rev. 23 (2013) 473–490.
[22] Eugene S. Domalski, Selected values of heats of combustion and heats of formation of organic compounds containing the elements C, H, N, O, P, and S, J. Phys. Chem. Ref. Data 1 (2) (1972) 221–277. [23] Irwin Osmond Toppo, CFD Analysis of combustion characteristics of Jathropha in compression ignition engine, Inter. J. Eng. Res. Technol. IJERT 2 (10) (2013) 2278–10181. [24] Norrizam Jaat et al., Analysis of injection pressure and high ambient density of biodiesel spray using computational fluid dynamics, Combustion 11 (1) (2019) 28–39. [25] Fluent, A. N. S. Y. S. ANSYS fluent theory guide 15.0. ANSYS, Canonsburg, PA (2013). [26] O.C. Chukwuezie et al., Cetane number effect on engine performance and gas emission: a review, Am. J. Eng. Res. 6 (1) (2017) 56–67.
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
CFD analysis of biodiesel blends and combustion using Ansys Fluent Shivanshu Dixit a, Arvind Kumar b, Suraj Kumar c, Nitin Waghmare c, Harish C. Thakur b, Sabah Khan c,⇑ a
IIT Ropar, Rupnagar, Punjab 140001, India Gautam Buddha University, Greater Noida, UP 201310, India c Jamia Millia Islamia, New Delhi 110025, India b
a r t i c l e
i n f o
Article history: Received 20 November 2019 Accepted 27 December 2019 Available online xxxx Keywords: Biodiesel blend IC Engine Combustion analysis Ansys fluent CI Engine
a b s t r a c t Automobile sector heavily relies on burning of fossil fuels to meet its energy requirements. This continuous burning of fossil fuels generates harmful emissions which are hazardous for both environment and human being. To stare down these emissions levels, appropriate methods of emission reduction or a sustainable replacement to fossil fuels are desiderating of the current situation. An alternate solution to the stated concern is biodiesel, which is non-toxic, biodegradable, and renewable by its nature. Another advantage, where little or no modification to present compression ignition (CI) engines is boon for utilizing biodiesel. Biodiesel originates from organic matter, from animals and plants, via — a chemical process called transesterification. During the process, methyl or ethyl ester (biodiesel) are refined from animal fat or vegetable oil with other useful products like glycerin. The pure form of biodiesel, which is abbreviated as ‘BXX’- B100 (pure biodiesel), while blended with petroleum diesel in proportion are B2-2% biodiesel, B5-5% biodiesel, and B20-20% biodiesel. Biodiesel produced from plant origin like non-edible grade oil from Jatropha plant has promising potential as blending fuel. It has an economic aspect too, as blended petroleum products or pure biodiesel reduces the dependency of foreign petroleum imported by countries like India. This article is about CFD based combustion analysis of biodiesel fuel using Ansys FluentÓ and matched with the combustion of diesel fuel. Parameters like the temperature of combustion at various blend ratios of B0-B100 varies from 2100 K to 1100 K are recorded through contour plots. Results are compared with diesel fuel, and an appropriate blend ratio is given for biodiesel for having for maximum efficiency and the least emission in applications. Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization
1. Introduction Environmental pollution and the energy crisis are effecting life at a global level. Limited reservoirs of fossil fuel and emission due to the combustion of these fossil fuels are affecting the balance of our mother nature. Phenomena like global warming, climate change, and increase in Greenhouse Gases (GHG’s) are among such unbalances. The automobile sector is among those sectors which heavily rely on these fossil fuels for energy requirement. While pollution from these automobiles is among the primary reason behind the rapid increase in air pollution [1–5]. The by-product of combustion from automobiles engine exhaust consists of unburnt hydrocarbons, smoke, particulate matter, CO2, CO, NOx, which are affecting human being in particular and our environment in ⇑ Corresponding author. E-mail address: [email protected] (S. Khan).
general sense. With rapid economic growth and urbanization, this problem is becoming more severe in countries like India. The study from the various institution in India shows that air pollution is at an alarming level due to vehicular automobile pollutants [6–7]. The aforementioned concerns require attention and working towards alternative fuels [8–9]. One such solution is biodiesel, which is a suitable alternative as a fuel in CI engines. The main advantage of using such fuel are its renewability, biodegradable, non-toxic nature, and with little or no modification to CI engines [4]. Biodiesel is a clean-burning, renewable fuel made from vegetable oils, animal fats, and recycled cooking oil and greases. Biodiesel includes both animal fats and vegetable oils from plants like Palm, Jatropha, Mahua, Flax, Mustard, Rapeseed, Sunflower, and Algae, etc. It is produced from a chemical process called- transesterification shown in Fig. 1. (Fig. 1. (a) transesterifcation reaction and (b) life cycle of biodiesel production [11,12]). Chemically, it is methyl (or ethyl) esters while physically it is liquid in nature.
https://doi.org/10.1016/j.matpr.2019.12.362 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
2
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Fig. 1. (a) Example of transesterification reaction with byproduct of biodiesel and glycerin [11]; (b) Life cycle comparison between diesel and biodiesel [12]
Biodiesels are replenishable, reduce carbon emissions, free from sulfur content, sustainable, and reduce dependence on foreign sources. Its physical and thermal properties are similar to diesel. Due to its lower energy content 5–10% as compared to diesel and high viscosity, a blending of 10–20% is used in CI engines. It can be used in pure which is B100 or blended form (in diesel). Most of the common blend includes B2 which is 2% biodiesel-98% diesel, B5, B20, B50, B90 and B100 are defined according to blend ratios [10]. Various literature is available for biodiesel in reports, experimental findings, computer simulations and, practical applications at a variety of platforms like CI engines, power plants, gas turbines, etc. Some among which are as follows: Klaus Becker and H.P.S. Makkar in the year 2008 investigated a Jatropha plant and its potential biodiesel as a source of energy for the future [17]. Rajesh Govindam, O.P. Jakhar, and Y.B. Mathur analyzed biodiesel blends in CI engine using Ansys Fluent. Their model predicted a higher in-cylinder pressure and temperature for the biodiesel blends during combustion as compared to pure diesel [18]. A.M. Indrodia, N.J. Chotai and B.M.Ramani investigated the effect of combustion chamber geometry [19]. Prem Kumar, M.P. Sharma, Gaurav Dwivedi analyzed the performance of the diesel engine along with B10 blended fuel. Notable conclusion of CO reduction, NOx increment and maximum power for B10 fuel are compared with conventional diesel fuel [20]. S. M. Palash and his group investigated that biodiesel as alternate fuel. They emphasis emission reduction through the use of biodiesel. They also addressed higher NOx emissions in biodiesel combustion with increasing engine load, and vice versa. Where NOx can be decreased using Exhaust Gas Recirculation [21]. Eugene S. Domalski calculated released heat after the combustion of fuels containing carbon, hydrogen, oxygen, nitrogen, and sulfur. [22]. CFD analysis under high ambient conditions and high pressure for biodiesel as well as combustion characteristics of Jatropha in CI engine are reported using Ansys FluentÓ [23 24]. In this article, we report theoretical combustion analysis and CFD simulation of biodiesel fuel using Ansys FluentÓ, and are compared with diesel combustion. The various blend ratios of B0, B15, B20, B50, B90, and B100 are studied using temperature contour plots. Results in comparison with diesel fuel are made, and an appropriate blend ratio is given for biodiesel for having maximum utility is studied. 1.1. Production process of biodiesel Biodiesel is a by-product of transesterification of oil from vegetable/animal, fats, and from sources like waste oil and tallow, etc. Potassium hydroxide (KOH) or sodium hydroxide (NaOH) is the catalyst used in the reaction. The reaction completes, and Biodiesel is formed as one of the products.
A typical molecular structure Biodiesel is shown in Fig. 2 below which is a long chain of carbon and hydrogen atom attached. This chain also consists of an ester functional group (shown with blue color) that differentiates it from regular diesel [13]. 2. Combustion analysis For the combustion analysis, it is required to have all thermal parameters used in combustion analysis shown in Table 1 [15]. When combustion of various elements occurs in the presence of O2, the basic equation goes like equations (1). For complete combustion, a generalized eddy-dissipation model is used to analyze the biodiesel-air combustion [14]. The chemical reaction equation of biodiesel is:-
C17 H34 O2 + 24.5O2 ! 17CO2 + 17H2 O + Heat
ð1Þ
There are 17 carbon, 34 hydrogen and 2 oxygen atoms, so molecular weight of Biodiesel = 12*17 + 34 + 2*16 = 270 (molecular weight calculated directly) and the empirical relation to calculate the average molecular weight of the Biodiesel i.e. MWi = 14.027C-2.016d + 31.998 = 14.027*17–2.016*1 + 31.9988 = 268.4578. Where, C = number of carbons; d = number of double bonds. 2.1. A/F ratio for the combustion of biodiesel In the combustion process, the stoichiometric combustion reaction in which the reactant from hydrocarbon from fuel (Biodiesel) must form CO2, H2O and heat as the product of combustion and the reaction is as follows in Fig. 3. Where z is known as the stoichiometric coefficient for the oxidizer (air) z = x + (y/4); z = 17 + (34/4) = 25.5 Biodiesel + 24.5 (O2 + 3.76 N2) ? 17 CO2 + 17H2O + 92.12 N2 Theoretical A/F ratio = mass of air/mass of fuel inlet = z*4.76*29/ (molecular mass of fuel* no. of moles) = 12.525 kg 12.53 kg of air is required for a complete combustion of 1 kg of biodiesel. 3. Modelling of the problem The cylindrical combustor considered is shown in Fig. 4. The flame in this analysis is considered as turbulent diffusion flame. Biodiesel enters the cylinder through a small nozzle placed at the center of the cylinder at 50 m/s while ambient air at 0.5 m/s coaxially. The equivalence ratio is around 0.76 (around 28% excess air). Since the injection speed is high for biodiesel, outer wall of cylinder offers less hindrance so it expands rapidly and mixes with air entering the cylinder.
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Fig. 2. Molecular structure of Biodiesel [13]
Table 1 Comparison of properties between diesel and biodiesel [15 16]. Property name
Unit
Biodiesel (variety)
Diesel
Density Kinematics Viscosity Calorific value Cetane number Auto ignition Temp. Specific heat Stoichiometric air/fuel ratio Molecular weight Flash point Ignition delay
kg/m3 Cst kJ/kg – K J/kg-K –
845–900 4.8 (40 °C) 39340–43759.5 58.4 (47–60) 700 1900–2050 12.525
825 (15 °C) 3.6 (40 °C) 44,000 51.5 (40–60) 483 1750 15
– °C Angle to crankshaft MJ/kg
270 88–170 9.39
200 76 10.56
39.8
45
Calorific value
Fig. 3. Schematic of reaction along with input and output from combustion chamber.
Fig. 4. Schematic of cylinder combustor for analysis.
reaction and turbulent flow. The first analysis is done for the combustion reaction of diesel (B0). Outputs (temperature, exhaust gases and mass fraction) have taken, and same analysis is done for biodiesel. Different blends ratio as B15, B20, B50, B90, and B100 with diesel have analyzed. Analysis steps and boundary conditions are summaries in Table 2. 5. Results and discussion Biodiesel proves better in terms of less knocking, less emissions, ignition with less delay and complete combustion [26]. In the combustion of diesel, temperature profile varies between 1700 K and 2100 K, while in biodiesel, temperature varies from 1100 K to 1350 K. Fig. 5 shows the temperature profile in the combustion of Diesel and biodiesel. Temperature characteristics in the combustion of diesel is higher than that of biodiesel. Biodiesel does not produce so much of heat as compared to diesel, so its blending with diesel can be used for better output. In the combustion of Diesel, CO2 produced up to a range of 0.16–0.18 mass fractions while biodiesel produces CO2 up to a range of 0.11–0.125 mass fractions which are lesser than that of diesel fuel. Fig. 6 represents the mass fraction of CO2 in the combustion analysis of diesel and biodiesel. Which shows biodiesel is more eco-friendly than that of diesel fuel. NOx produced in the combustion of diesel are in range of 0.015 to 0.020 mass fraction while biodiesel produces are in range of 0.20 to 0.33 mass fraction. NOx produced are more in biodiesel than that of diesel during combustion. This is one of the drawback of for the biodiesel using as a fuel. Using Exhaust Gas Recirculation (EGR) in the exhaust system, we can control NOx up to a certain limit. Fig. 7 shows the NOx exhaust gas in the combustion of diesel and biodiesel fuel. To predicit the lubrication property of fuel, Fig. 8 represent the mass fraction C17H34O2 in diesel and biodiesel. Conventional diesel fuel is less viscous than biodiesel fuel. Biodiesel have a lubricating property so it flows smoothly in the combustion chamber as compared to that of diesel. Thus, engine life increases giving advantages to biodiesel applications.
4. CFD analysis of biodiesel blends using Ansys Fluent 5.1. Blending of biodiesel with diesel The problem is analyzed using Ansys Fluent [25], and design is imported. The whole domain is discretized using fine mesh generation on the geometry. Convection load is applied using boundary conditions. ST-Model is used in the analysis of any chemical reaction, and the eddy dissipation model is used for rapid
Biodiesel is blended with diesel as defined above and are studies different concentrations. B90 (90% biodiesel, 10% diesel) is analyzed for use. The greater the % blend of biodiesel in fuel, the more eco-friendly is the fuel. While B50 (50% biodiesel, 50% diesel)
Table 2 Consolidated analysis step and boundary condition. Analysis steps a) b) c) d) e) f) g) h) i)
Import the geometry in Ansys Fluent. Discretize the whole geometry into fine meshes. Select Energy and choose ON option. Select viscous model as k-e(2eqn) turbulence model. Transport the species using species transport. Select material and feed boundary condition. Solve the reaction for temperature and Exhaust output. NOx is selected again in Models for computing NOx. Solve it again for exhaust.
Boundary condition a) Fuel: 50 m/s from nozzle and at a temperature of 300 K b) Air: 0.5 m/s and at a temperature of 300 K and 0.76 species mass fraction. c) Walls: constant at 300 K.
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Fig. 5. (a) The static temperature profile in the combustion of diesel; (b) biodiesel.
Fig. 6. (a) The contour profile for mass fraction of CO2 in diesel; (b) biodiesel.
Fig. 7. (a) The contour profile for mass fraction of NOx in diesel; (b) biodiesel.
Fig. 8. (a) The profile for mass fraction of in C17H34O2 in diesel; (b) biodiesel.
Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362
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b
c
d
e
f
Temperature (K)
a
2100 1800
1750
1600 1225
B0
B15
B20
B50
B90
1100
B100
% Blend
Fig. 9. the static temperature profile in the (a) B90; (b) B50; (c) B20; (d) B15; (e) B0 (f) graph of temperature in combustion of blend B0, B15, B20, B50, B90 and B100.
shows no difference in the serviceability compared to those fuelled with petroleum diesel fuel. Biodiesel as discussed above significantly reduces exhaust emissions. The complete burn of biodiesel fuel is results due naturally present oxygen in it. Depending on engine type and operating conditions NOx emissions can be handled. While B20 is widespread and have similar charaterstics as diesel fuel. B15 show a similarity with B20 with slight increase in combustion temperature. The emissions problem can be addresed using blended fuel due to their combustion support and lesser pollutant in exhaut. The contour profile and a temperature in the combustion of blend B0, B15, B20, B50, B90 and B100 are shown in Fig. 9. 6. Conclusion Biodiesel is a sustainable alternative to fossil fuel. Simulation results show that the temperature in the combustion of diesel (2100 K) is higher than that of biodiesel (1100 K). Due to less heat, less CO2 emission in biodiesel is less while NOx is high. These emissions can be reduced with the use of EGR and SCR systems. Biodiesel shows better lubrication property in comparison to the diesel counterpart. Blend diesel fuel shows a variety of properties, depending on % of the blend. A gradual decreasing temperature profile is observed from B0 to B100
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Please cite this article as: S. Dixit, A. Kumar, S. Kumar et al., CFD analysis of biodiesel blends and combustion using Ansys Fluent, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.362