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Numerical investigation of exhaust gas emissions for a dual fuel engine configuration using diesel and pongamia oil
Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv
Numerical investigation of exhaust gas emissions for a dual fuel engine configuration using diesel and pongamia oil N.H. Mohamed Ibrahim n, M. Udayakumar Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, India
art ic l e i nf o
a b s t r a c t
Article history: Received 10 December 2014 Received in revised form 25 May 2015 Accepted 28 May 2015
The investigation presented in this paper focuses on determination of gaseous exhaust emissions by computational simulation during combustion in compression ignition engine with pongamia oil substitution. Combustion is modeled using Equilibrium Constants Method (ECM) with MATLAB program to calculate the mole fraction of 10 combustion products when pongamia oil is burnt along with diesel at variable equivalence ratio and blend ratio. It had been observed that pongamia oil substitution causes decrease in the CO emission and increase in the NOx emission as the blend ratio as well as equivalence ratio increases. & 2015 Elsevier Inc. All rights reserved.
Keywords: Equilibrium Constants Method (ECM) Equivalence ratio Pongamia oil JANAF table Combustion model Newton–Raphson iteration
1. Introduction Environmental concerns and the possible role of alternative renewable fuels are leading the first actions towards the production of sustainable fuel supply. Biofuels for diesel engine comprise vegetable oils and biodiesel, neat or blended with mineral diesel fuels (Pischinger et al., 1982). The concept of using biodiesel in diesel engine originated from the demonstration of first diesel engine by the inventor “Rudolf Diesel” at the world exhibition in Paris in 1900 by using peanut oil as a fuel. Due to abundant supply of petrol diesel, R&D activities on vegetable oils were not seriously pursued till 1970s (Last, 2012). Since the petroleum fuels are dwindling fast alternative and environmental friendly renewable substitute must be identified. Apart from the fuel depletion aspects diesel engines are the major sources of urban air pollution and particulate emission. Using alcohol fuels in diesel engine substantially increase the aldehyde emission and these could cause a significant pollutant when these fuels are used in large quantities compared to gasoline and diesel (Kumar et al., 2003). Hence biodiesel is good fuel substitute because biodiesels are free from carcinogenic, mutagenic, which decreases certain emissions like CO, unburned HC and particulate matters. Here pongamia oil blends with diesel is used as an alternative fuel. The oil is extracted from seed of legume tree Pongamia pinnata. The constituent of n
Corresponding author. E-mail address: [email protected] (N.H. Mohamed Ibrahim).
http://dx.doi.org/10.1016/j.ecoenv.2015.05.044 0147-6513/& 2015 Elsevier Inc. All rights reserved.
these seed is 3.8% of ash, 9.7% of sugar, 7.07% of protein, 24% of oil, 10.7% of free amino acids and 0.27% of fatty acids. Significant experimental research work has been done by Venkataraman (2008) for investigating the performance and emission characteristic of pongamia biodiesel in DICI and HCCI engine. In the present study, an effort is made by developing a combustion mathematical model to determine exhaust gas that causes serious effects on environment by using pongamia-diesel blend fuels. Based on Equilibrium Constant Method (ECM) (Turns, 2013), a computer program using MATLAB has been developed for the blended fuels to calculate the mole fractions of various emitted gases. ECM is based on thermodynamic measurements and empirical calculations. It is very accurate and precise in solving most of chemical kinetics problems. Thermodynamic data for elements, combustion products and many pollutants are available in a complication published by the National Bureau of Standards, called the JANAF (Joint Army–Navy–Air Force) tables.
2. Combustion model Governing equation for the reaction combustion equations were performed based on following assumption (Heywood, 2011) 1. 2. 3. 4.
All the gases are assumed to be perfect and homogenous. Range of equivalence ratio is 0.5–1.5. There is no delay time. Effect of convection, conduction and radiation is neglected.
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
O OH NO ECM DICI HCCI HC JANAF
Nomenclature CO2 H2O N2 O2 CO H2 H
Carbon dioxide Water Nitrogen gas Oxygen Carbon monoxide Hydrogen gas Hydrogen atom
Φ
5. No chemical changes in diesel, biodiesel and are prior to the combustion. 6. All the properties are time dependent. The governing equations are prepared by assuming 10 combustion products and a system of equation appears and this can be solved by Newton–Raphson method prior to its implementation into MATLAB program. The combustion reaction is given by B(CaHbOc)þD(CαHβOχNδ)þ(as/Φ)(O2 þ3.76N2) -n1CO2 þn2H2O þn3N2 þn4O2 þ n5CO þn6H2 þ n7H þn8O þn9OH þn10NO (1)
Oxygen atom Hydroxide Nitrogen oxide Equilibrium Constant Method Direct Injection Compression Ignition Homogenous Charge Compression Ignition Hydrocarbon Joint Army–Navy Force Equivalence ratio
here Ki (i¼1–6) represents the equilibrium constants for the respective reactions and p represents the combustion pressure. The value of the equilibrium constant can be calculated using the formula
Ki = e (−ΔG °
Ti / RT comb)
(13)
Δ
G° where Ti , Tcomb, R represents Gibbs free energy, combustion temperature and gas constant respectively and these values are taken from JANAF table corresponds to combustion temperature. The equilibrium constants from the equation (7–12) are rearranged to express the mole fraction of emission product in terms of Xi
(
)
(
)
X1 = K6X5√p√X 4 = S6X5√X 4 , whereS6 = K6√p where B-mole fraction of pongamia biodiesel. D-mole fraction of diesel. as-stoichiometric air–fuel ratio. Φ-equivalence ratio. ni ¼(i¼ 1–10) no. of moles of each combustion emission product. Atomic balance of C, H, O and N leads to
C:B(a) + D(α ) = nt (x1 + x5)
(2)
H:B(b) + D(β ) = nt (2x2 + 2x6 + x7 + x 9)
(3)
X2 = K5X6 √p√X 4 , = S5X6 √X 4 , whereS5 = K5√p
N:D(δ ) + 3.76(2as/Φ) = nt (2x3 + x10)
(5)
)
(16)
(
)
(17)
(
)
(18)
X8 = K2√X 4 /√p = S2√p, whereS2 = K2/√p
X10 = K4√X 4 √X3 = S4√X 4 √X6 , (whereS4 = K4 )
(6)
where xi is the mole fraction of ith species of various combustion emission product and nt represents the total number of moles after combustion where xi ¼ ni/nt and nt ¼ Σni (i¼1–10). The dissociation reactions and the equilibrium constants associated are Stull and Prophets (1971)
(
)
(7)
(
)
(8)
1/2H2 ← → H, K1 = x7 √p /√x6
(
(
1/2H2 + 1/2O2 ← → OH, K3 = x 9 / √x6 √x4
(
)
(9)
)
(10)
(
)
(11)
(
)
(12)
1/2O2 + 1/2N2 ← → NO, K 4 =x10 / √x3√x4 H2 + 1/2O2 ← → H2 O, K 5 = x2 / x6 √x4 √p
CO + 1/2O2 ← → CO2 , K 6 = x1/ x5√x4 √p
)
2S5X6 √X6 + 2X6 + S1√X6 + S3√X 4 √X6 –Z1 S1X5√X 4 + X5 = 0
(20)
2S6X5√X 4 + S5X6 √X 4 + 2X 4 + X5 + S2√X 4 + S3√X 4 √X6
(
)
+ S4√X 4 √X3–Z2 S6X5√X 4 + √X5 = 0
(
)
2X3 + S4√X3√X 4 –Z3 S6X5√X 4 + √X5 = 0
(21) (22)
S6X5 √X 4 + S5X 6 √X 4 + X3 + X 4 + X5 + X 6 + S1√X 6 + S2√X 6 + S3√X 4 √X 6
(23)
+ S4√X 4 √X3 –1 = 0
1/2O2 ← → O, K2 = x8√p /√x4
(19)
To obtain the value of X3, X4, X5, and X6 Eqs. (3–6) is divided by equation and rearranged so that the equation we obtain contains four equation with four unknowns as follows:
Addition of all mole is given by
Σxi = 1(i = 1–10)
(15)
(
X7 = K1√X6 /√p = S1√X6 , whereS1 = K1/√p
X8 = K2√X 4 /√p = S2√p, whereS2 = K2/√p
O:B(c ) + D(χ ) + (2as/Φ) = nt (2x1 + x2 + 2x4 + x5 + x8 + x 9 + x10) (4)
(14)
where
Z1 = (Bb + Dβ )/(Bα + Dα )
(
)
Z2 = Bc + Dχ + 2(as /Φ) /(Bα + Dα )
(
)
Z3 = Dδ + (7.52as /Φ) /(Bα + Dα ) On solving above equation (20–23) we will get X3 X4 X5 X6 by substituting these values in the above mentioned equation (14–19) we will get the remaining mole fraction of combustion species.
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
fraction X3, X4, X5, X6 act as input to obtain the remaining mole fraction such as X1, X2, X7, X8, X9 and X10.
Table 1 Input data to MATLAB program. Variables
Diesel
Pongamia oil
Combustion pressure (bar) Combustion temperature (K) Carbon atoms Hydrogen atoms Oxygen atoms Nitrogen atoms Stoichiometric air–fuel ratio Range of equivalence ratio
45 2500 12 23 0 0 20 0.5–1.5
45 2500 17 32 02 0 20 0.5–1.5
4. Result and discussion In this study, the effects of equivalence ratio in emission were analyzed based on developed combustion model. Here our main aim is to focus on the species that cause hazardous to environment for example CO, CO2 and NOx. Fig. 1 shows the variation of mole fraction of CO2 with equivalence ratio at constant pressure of
Fig. 1. Variation of [CO2] with equivalence eatio (Φ).
Fig. 2. Variation of [H2O] with equivalence ratio (Φ).
3. Simulation procedure A MATLAB simulation program is prepared using fsolve command for solving above simultaneous equation (20–23) with some initial guess. These program takes the input parameters such as number of carbon, hydrogen, oxygen, nitrogen atoms, equivalence ratio, stoichiometric air fuel ratio, combustion temperature, combustion pressure as displayed below to obtain the values of S1, S2, S3, S4, S5, S6, Z1, Z2 and Z3 ( Table 1). From these values thus we can obtain X3, X4, X5 and X6. Another MATLAB program is prepare were these above obtained mole
45 bar and temperature 2500 K. It is noted that if the fuel blend ratio varied and increase in equivalence ratio there is increase in CO2 emission indicate the complete combustion. The relationship between H2O emissions and equivalence ratio is depicted in Fig. 2. It is indicated that as pongamia blend ratio increases there is a decrease in the emission of H2O up to the equivalence ratio Φ ¼ 1 then it starts to decrease consequently. Since the depletion of H2O species after Φ ¼1.2 the temperature of the exhaust seems to increase significantly so there is chance of dissociation of species to occur. Fig. 3. Shows the same graphical trends for mole fraction of N2 with equivalence ratio, as a percentage of pongamia oil substitution
4
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Fig. 3. Variation of [N2] with equivalence ratio (Φ).
Fig. 4. Variation of [O2] with equivalence ratio (Φ).
Fig. 5. Variation of [CO] with equivalence ratio (Φ).
increases, N2 emission increases in the range of 0.50%. Fig. 4. Shows the mole fraction of O2 with respect to equivalence ratio. It shows that there is 0.1–0.7% increase in the O2 species for various blend ratio and it starts to decrease as the equivalence ratio varied. Fig. 5 depicts the variation of CO concentration with respect to blend ratio and equivalence ratio. It is noted that for any constant
blend ratio there is increase in the emission of CO is observed with increase in equivalence ratio Φ also it is found that there is decrease in the emission of CO emission for the blends varied from pure diesel to pure pongamia oil at a given equivalence ratio's. It is found that up to equivalence ratio of Φ ¼ 1 there is no significant changes seen in the CO emissions.
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
5
Fig. 6. Variation of [H2] with equivalence ratio (Φ).
Fig. 6 and Fig. 7 indicates the variation of H2 and H respectively. It has been noted from Fig. 6. That there is 0.01% of decrement of H2 species seen as the blend fraction of diesel decreases. Since the exhaust temperature due to low emission of H2O species the dissociation of H2 take place. As the blend ratio increase there is decrease in the H atom and with respect to equivalence ratio for a particular blend it is found that there is increase in the H atom and is shown in the Fig. 7. Due to high exhaust emission temperature. Similar to H atom there is a significant decrease in the O atom has been noted from Fig. 8. It is noted that as a blend ratio increases the emission of O atom decreases with respect to equivalence ratio. It also found that the dissociation of O atom contributes to 0.00001% among whole species. Fig. 9 sketches the variation of OH with respect to equivalence ratio and blend ratio. It has been noted that as the increase in the blend ratio there is increase in OH species and with respect to equivalence ratio there is a decrease in the OH emission by 0.01% is found. The main toxic gas NO, that causes hazards to environment is presented in Fig. 10. It is observed that for a given constant equivalence ratio there is an increase in the NO species emission by 0.20% as the blend fraction varied from pure diesel to pure pongamia oil. Again it is noted that for the constant blend ratio decrease in the emission of NO is found as the equivalence ratio increased from 0 to 1.5.
5. Conclusions The emission of compression ignition engine with pongamia oil substitution has been modeled by using Equilbrium Method. From the above analysis and discussion, the following conclusion are drawn: 1. Pongamia oil diesel blends causes decrease in the CO emission when blend fraction is varied from pure diesel to pure pongamia oil at constant equivalence ratio. 2. The emission of CO also increases as the equivalence ratio varied from 0 to 1.5 for a fixed blend ratio's. However for the CI engines operating range(Φ o1) the increase in CO is insignificant.
3. Pongamia oil subsitution causes increase in the emission of NO by varying blend ratio from pure diesel to pongamia oil at a fixed equivalence ratio. 4. The emision of NO decreases in the range of equivalence ratio 0–1.5 at constant blends ratio. 5. The emission of CO2 decreases with the variation of blend ratio from pure diesel to pongamia oil at fixed equivalence ratio. 6. The emission of CO2 also increases over the range of Φ ¼0.5 to Φ ¼1.5 for fixed blend ratio. 7. The model can also be applied for other biodiesels as well to predict the emission concentrations.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2015.05. 044.
References Heywood, John B., 2011. Internal Combustion Engines Fundamentals, Indian ed. Mc- Grawhill. Pischinger, G.H., Siekmann, R.W., Falcon, A.M., Fernandes, 1982. Fr, Methylesters of plant oils as diesel fuels, either straight or in blends. In: Proceedings of the International Conference on Plant and Vegetable Oils as Fuels, August 2–4, USSA, ASAE Publisher. Last, Robert J., kuger, Michael, Durnholz, Manfred, 2012. Emissions and performance characteristics of a 4 stroke direct injection diesel engine fueled with blends of biodiesel and low sulfur diesel fuel. SAE Trans. 950054, 1–13. Kumar, Senthil, Ramesh, A., Nagalingam, B., 2003. An experimental comparision of method to use methanol and jatropha oil in a compression ignition engine. Biomass and Bioenergy 25, 309–318 0961-9534/03. Turns, Stephen R., 2013. An Introduction to Combustion Concepts and Applications. Devaragjane Venkataraman, 2008. Experimantal investigation of a diesel engine in DICI and HCCI mode using blends of pongamia oil and diesel. Stull, D.R., Prophets, H., 1971. JANAF Thermodynamical Tables, 2nd ed. National Bureau of Standards, The 4th 216 edition is available from NIST.
Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv
Numerical investigation of exhaust gas emissions for a dual fuel engine configuration using diesel and pongamia oil N.H. Mohamed Ibrahim n, M. Udayakumar Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, India
art ic l e i nf o
a b s t r a c t
Article history: Received 10 December 2014 Received in revised form 25 May 2015 Accepted 28 May 2015
The investigation presented in this paper focuses on determination of gaseous exhaust emissions by computational simulation during combustion in compression ignition engine with pongamia oil substitution. Combustion is modeled using Equilibrium Constants Method (ECM) with MATLAB program to calculate the mole fraction of 10 combustion products when pongamia oil is burnt along with diesel at variable equivalence ratio and blend ratio. It had been observed that pongamia oil substitution causes decrease in the CO emission and increase in the NOx emission as the blend ratio as well as equivalence ratio increases. & 2015 Elsevier Inc. All rights reserved.
Keywords: Equilibrium Constants Method (ECM) Equivalence ratio Pongamia oil JANAF table Combustion model Newton–Raphson iteration
1. Introduction Environmental concerns and the possible role of alternative renewable fuels are leading the first actions towards the production of sustainable fuel supply. Biofuels for diesel engine comprise vegetable oils and biodiesel, neat or blended with mineral diesel fuels (Pischinger et al., 1982). The concept of using biodiesel in diesel engine originated from the demonstration of first diesel engine by the inventor “Rudolf Diesel” at the world exhibition in Paris in 1900 by using peanut oil as a fuel. Due to abundant supply of petrol diesel, R&D activities on vegetable oils were not seriously pursued till 1970s (Last, 2012). Since the petroleum fuels are dwindling fast alternative and environmental friendly renewable substitute must be identified. Apart from the fuel depletion aspects diesel engines are the major sources of urban air pollution and particulate emission. Using alcohol fuels in diesel engine substantially increase the aldehyde emission and these could cause a significant pollutant when these fuels are used in large quantities compared to gasoline and diesel (Kumar et al., 2003). Hence biodiesel is good fuel substitute because biodiesels are free from carcinogenic, mutagenic, which decreases certain emissions like CO, unburned HC and particulate matters. Here pongamia oil blends with diesel is used as an alternative fuel. The oil is extracted from seed of legume tree Pongamia pinnata. The constituent of n
Corresponding author. E-mail address: [email protected] (N.H. Mohamed Ibrahim).
http://dx.doi.org/10.1016/j.ecoenv.2015.05.044 0147-6513/& 2015 Elsevier Inc. All rights reserved.
these seed is 3.8% of ash, 9.7% of sugar, 7.07% of protein, 24% of oil, 10.7% of free amino acids and 0.27% of fatty acids. Significant experimental research work has been done by Venkataraman (2008) for investigating the performance and emission characteristic of pongamia biodiesel in DICI and HCCI engine. In the present study, an effort is made by developing a combustion mathematical model to determine exhaust gas that causes serious effects on environment by using pongamia-diesel blend fuels. Based on Equilibrium Constant Method (ECM) (Turns, 2013), a computer program using MATLAB has been developed for the blended fuels to calculate the mole fractions of various emitted gases. ECM is based on thermodynamic measurements and empirical calculations. It is very accurate and precise in solving most of chemical kinetics problems. Thermodynamic data for elements, combustion products and many pollutants are available in a complication published by the National Bureau of Standards, called the JANAF (Joint Army–Navy–Air Force) tables.
2. Combustion model Governing equation for the reaction combustion equations were performed based on following assumption (Heywood, 2011) 1. 2. 3. 4.
All the gases are assumed to be perfect and homogenous. Range of equivalence ratio is 0.5–1.5. There is no delay time. Effect of convection, conduction and radiation is neglected.
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
O OH NO ECM DICI HCCI HC JANAF
Nomenclature CO2 H2O N2 O2 CO H2 H
Carbon dioxide Water Nitrogen gas Oxygen Carbon monoxide Hydrogen gas Hydrogen atom
Φ
5. No chemical changes in diesel, biodiesel and are prior to the combustion. 6. All the properties are time dependent. The governing equations are prepared by assuming 10 combustion products and a system of equation appears and this can be solved by Newton–Raphson method prior to its implementation into MATLAB program. The combustion reaction is given by B(CaHbOc)þD(CαHβOχNδ)þ(as/Φ)(O2 þ3.76N2) -n1CO2 þn2H2O þn3N2 þn4O2 þ n5CO þn6H2 þ n7H þn8O þn9OH þn10NO (1)
Oxygen atom Hydroxide Nitrogen oxide Equilibrium Constant Method Direct Injection Compression Ignition Homogenous Charge Compression Ignition Hydrocarbon Joint Army–Navy Force Equivalence ratio
here Ki (i¼1–6) represents the equilibrium constants for the respective reactions and p represents the combustion pressure. The value of the equilibrium constant can be calculated using the formula
Ki = e (−ΔG °
Ti / RT comb)
(13)
Δ
G° where Ti , Tcomb, R represents Gibbs free energy, combustion temperature and gas constant respectively and these values are taken from JANAF table corresponds to combustion temperature. The equilibrium constants from the equation (7–12) are rearranged to express the mole fraction of emission product in terms of Xi
(
)
(
)
X1 = K6X5√p√X 4 = S6X5√X 4 , whereS6 = K6√p where B-mole fraction of pongamia biodiesel. D-mole fraction of diesel. as-stoichiometric air–fuel ratio. Φ-equivalence ratio. ni ¼(i¼ 1–10) no. of moles of each combustion emission product. Atomic balance of C, H, O and N leads to
C:B(a) + D(α ) = nt (x1 + x5)
(2)
H:B(b) + D(β ) = nt (2x2 + 2x6 + x7 + x 9)
(3)
X2 = K5X6 √p√X 4 , = S5X6 √X 4 , whereS5 = K5√p
N:D(δ ) + 3.76(2as/Φ) = nt (2x3 + x10)
(5)
)
(16)
(
)
(17)
(
)
(18)
X8 = K2√X 4 /√p = S2√p, whereS2 = K2/√p
X10 = K4√X 4 √X3 = S4√X 4 √X6 , (whereS4 = K4 )
(6)
where xi is the mole fraction of ith species of various combustion emission product and nt represents the total number of moles after combustion where xi ¼ ni/nt and nt ¼ Σni (i¼1–10). The dissociation reactions and the equilibrium constants associated are Stull and Prophets (1971)
(
)
(7)
(
)
(8)
1/2H2 ← → H, K1 = x7 √p /√x6
(
(
1/2H2 + 1/2O2 ← → OH, K3 = x 9 / √x6 √x4
(
)
(9)
)
(10)
(
)
(11)
(
)
(12)
1/2O2 + 1/2N2 ← → NO, K 4 =x10 / √x3√x4 H2 + 1/2O2 ← → H2 O, K 5 = x2 / x6 √x4 √p
CO + 1/2O2 ← → CO2 , K 6 = x1/ x5√x4 √p
)
2S5X6 √X6 + 2X6 + S1√X6 + S3√X 4 √X6 –Z1 S1X5√X 4 + X5 = 0
(20)
2S6X5√X 4 + S5X6 √X 4 + 2X 4 + X5 + S2√X 4 + S3√X 4 √X6
(
)
+ S4√X 4 √X3–Z2 S6X5√X 4 + √X5 = 0
(
)
2X3 + S4√X3√X 4 –Z3 S6X5√X 4 + √X5 = 0
(21) (22)
S6X5 √X 4 + S5X 6 √X 4 + X3 + X 4 + X5 + X 6 + S1√X 6 + S2√X 6 + S3√X 4 √X 6
(23)
+ S4√X 4 √X3 –1 = 0
1/2O2 ← → O, K2 = x8√p /√x4
(19)
To obtain the value of X3, X4, X5, and X6 Eqs. (3–6) is divided by equation and rearranged so that the equation we obtain contains four equation with four unknowns as follows:
Addition of all mole is given by
Σxi = 1(i = 1–10)
(15)
(
X7 = K1√X6 /√p = S1√X6 , whereS1 = K1/√p
X8 = K2√X 4 /√p = S2√p, whereS2 = K2/√p
O:B(c ) + D(χ ) + (2as/Φ) = nt (2x1 + x2 + 2x4 + x5 + x8 + x 9 + x10) (4)
(14)
where
Z1 = (Bb + Dβ )/(Bα + Dα )
(
)
Z2 = Bc + Dχ + 2(as /Φ) /(Bα + Dα )
(
)
Z3 = Dδ + (7.52as /Φ) /(Bα + Dα ) On solving above equation (20–23) we will get X3 X4 X5 X6 by substituting these values in the above mentioned equation (14–19) we will get the remaining mole fraction of combustion species.
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
fraction X3, X4, X5, X6 act as input to obtain the remaining mole fraction such as X1, X2, X7, X8, X9 and X10.
Table 1 Input data to MATLAB program. Variables
Diesel
Pongamia oil
Combustion pressure (bar) Combustion temperature (K) Carbon atoms Hydrogen atoms Oxygen atoms Nitrogen atoms Stoichiometric air–fuel ratio Range of equivalence ratio
45 2500 12 23 0 0 20 0.5–1.5
45 2500 17 32 02 0 20 0.5–1.5
4. Result and discussion In this study, the effects of equivalence ratio in emission were analyzed based on developed combustion model. Here our main aim is to focus on the species that cause hazardous to environment for example CO, CO2 and NOx. Fig. 1 shows the variation of mole fraction of CO2 with equivalence ratio at constant pressure of
Fig. 1. Variation of [CO2] with equivalence eatio (Φ).
Fig. 2. Variation of [H2O] with equivalence ratio (Φ).
3. Simulation procedure A MATLAB simulation program is prepared using fsolve command for solving above simultaneous equation (20–23) with some initial guess. These program takes the input parameters such as number of carbon, hydrogen, oxygen, nitrogen atoms, equivalence ratio, stoichiometric air fuel ratio, combustion temperature, combustion pressure as displayed below to obtain the values of S1, S2, S3, S4, S5, S6, Z1, Z2 and Z3 ( Table 1). From these values thus we can obtain X3, X4, X5 and X6. Another MATLAB program is prepare were these above obtained mole
45 bar and temperature 2500 K. It is noted that if the fuel blend ratio varied and increase in equivalence ratio there is increase in CO2 emission indicate the complete combustion. The relationship between H2O emissions and equivalence ratio is depicted in Fig. 2. It is indicated that as pongamia blend ratio increases there is a decrease in the emission of H2O up to the equivalence ratio Φ ¼ 1 then it starts to decrease consequently. Since the depletion of H2O species after Φ ¼1.2 the temperature of the exhaust seems to increase significantly so there is chance of dissociation of species to occur. Fig. 3. Shows the same graphical trends for mole fraction of N2 with equivalence ratio, as a percentage of pongamia oil substitution
4
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Fig. 3. Variation of [N2] with equivalence ratio (Φ).
Fig. 4. Variation of [O2] with equivalence ratio (Φ).
Fig. 5. Variation of [CO] with equivalence ratio (Φ).
increases, N2 emission increases in the range of 0.50%. Fig. 4. Shows the mole fraction of O2 with respect to equivalence ratio. It shows that there is 0.1–0.7% increase in the O2 species for various blend ratio and it starts to decrease as the equivalence ratio varied. Fig. 5 depicts the variation of CO concentration with respect to blend ratio and equivalence ratio. It is noted that for any constant
blend ratio there is increase in the emission of CO is observed with increase in equivalence ratio Φ also it is found that there is decrease in the emission of CO emission for the blends varied from pure diesel to pure pongamia oil at a given equivalence ratio's. It is found that up to equivalence ratio of Φ ¼ 1 there is no significant changes seen in the CO emissions.
N.H. Mohamed Ibrahim, M. Udayakumar / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Fig. 6. Variation of [H2] with equivalence ratio (Φ).
Fig. 6 and Fig. 7 indicates the variation of H2 and H respectively. It has been noted from Fig. 6. That there is 0.01% of decrement of H2 species seen as the blend fraction of diesel decreases. Since the exhaust temperature due to low emission of H2O species the dissociation of H2 take place. As the blend ratio increase there is decrease in the H atom and with respect to equivalence ratio for a particular blend it is found that there is increase in the H atom and is shown in the Fig. 7. Due to high exhaust emission temperature. Similar to H atom there is a significant decrease in the O atom has been noted from Fig. 8. It is noted that as a blend ratio increases the emission of O atom decreases with respect to equivalence ratio. It also found that the dissociation of O atom contributes to 0.00001% among whole species. Fig. 9 sketches the variation of OH with respect to equivalence ratio and blend ratio. It has been noted that as the increase in the blend ratio there is increase in OH species and with respect to equivalence ratio there is a decrease in the OH emission by 0.01% is found. The main toxic gas NO, that causes hazards to environment is presented in Fig. 10. It is observed that for a given constant equivalence ratio there is an increase in the NO species emission by 0.20% as the blend fraction varied from pure diesel to pure pongamia oil. Again it is noted that for the constant blend ratio decrease in the emission of NO is found as the equivalence ratio increased from 0 to 1.5.
5. Conclusions The emission of compression ignition engine with pongamia oil substitution has been modeled by using Equilbrium Method. From the above analysis and discussion, the following conclusion are drawn: 1. Pongamia oil diesel blends causes decrease in the CO emission when blend fraction is varied from pure diesel to pure pongamia oil at constant equivalence ratio. 2. The emission of CO also increases as the equivalence ratio varied from 0 to 1.5 for a fixed blend ratio's. However for the CI engines operating range(Φ o1) the increase in CO is insignificant.
3. Pongamia oil subsitution causes increase in the emission of NO by varying blend ratio from pure diesel to pongamia oil at a fixed equivalence ratio. 4. The emision of NO decreases in the range of equivalence ratio 0–1.5 at constant blends ratio. 5. The emission of CO2 decreases with the variation of blend ratio from pure diesel to pongamia oil at fixed equivalence ratio. 6. The emission of CO2 also increases over the range of Φ ¼0.5 to Φ ¼1.5 for fixed blend ratio. 7. The model can also be applied for other biodiesels as well to predict the emission concentrations.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2015.05. 044.
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