RESEARCH ARTICLE

Yi REN, Ehab ABU-RAMADAN, Xianguo LI

Numerical simulation of biodiesel fuel combustion andemission characteristics in a direct injection diesel engine

© Higher Education Press and Springer-Verlag Berlin Heidelberg 2010

Abstract The effect of the physical and chemicalproperties of biodiesel fuels on the combustion processand pollutants formation in Direct Injection (DI) engine areinvestigated numerically by using multi-dimensionalComputational Fluid Dynamics (CFD) simulation. In thecurrent study, methyl butanoate (MB) and n-heptane areused as the surrogates for the biodiesel fuel and theconventional diesel fuel. Detailed kinetic chemicalmechanisms for MB and n-heptane are implemented tosimulate the combustion process. It is shown that thedifferences in the chemical properties between thebiodiesel fuel and the diesel fuel affect the wholecombustion process more significantly than the differencesin the physical properties. While the variations of both thechemical and the physical properties between the biodieseland diesel fuel influence the soot formation at theequivalent level, the variations in the chemical propertiesplay a crucial role in the NOx emissions formation.

Keywords biodiesel, diesel engine, CFD simulation,combustion, pollutant formation

1 Introduction

Replacing fossil fuels with renewable non-fossil biomassfuels presents a promising solution to the upcomingenergy crisis [1–5]. Due to the similarities betweenbiofuels and conventional diesel fuels in their energycontent and cetane number, most biofuels can be burnt inmodern direct injection (DI) diesel engines [6]. Biodieselfuels which are non-petroleum-based diesel fuels can

reduce the dependence on fossil fuels and can alsocontribute to the decrease of CO2 emission by 65%–90%compared with the conventional diesel fuel [7]. Variousexperimental studies have demonstrated that the applica-tion of biodiesel produce lower emissions of unburnedhydrocarbons, carbon monoxide, and particulate matter,but with a light increase in the NOx emissions in traditionaldiesel engines [8–12]. The sustainability and environ-mental advantages of bio-diesel fuels have resulted in aninterest in biodiesel fuels research. At present, many issuesstill need to be resolved to allow biodiesel fuels to be usedin highly efficient clean combustion automotive engines.Topically, the atomization process needs to be adjusted inthe conventional engine to accommodate the distinctlydifferent physical properties of biodiesel fuels [13,14],since variations of physical and chemical propertiesbetween biodiesel and diesel fuels are expected to alterthe atomization, ignition, combustion and pollutantformation processes [15–17].Previously biodiesel combustion and pollutant forma-

tion characteristics are identified numerically based on thecomparison with conventional diesel fuels, for providingdetailed understanding of the in-cylinder combustionprocess and emissions formation of DI engines fueledwith biodiesel fuels [18–23]. Since biodiesel molecules arelarge and long chain molecules containing extra oxygenatoms, the chemical reaction mechanism describing thecombustion of biodiesel fuels is distinctly different fromthe conventional diesel fuel combustion mechanism [24].To develop a reliable and detailed reaction mechanism forbiodiesel fuels, it is more practical to use a surrogate withsimple and well characterized structure, such as MB [25].Fisher et al. [26] have developed a detailed chemicalkinetic mechanism of MB containing 264 species and1219 reactions. The model has been further reduced to 41species and 150 reactions implemented in a multi-dimensional engine simulation study [27]. Herbinet et al[28] have developed a detailed chemical kinetic mechan-ism to study the oxidation of another surrogate of biodiesel

Received March 25, 2010; accepted April 26, 2010

Yi REN, Ehab ABU-RAMADAN, Xianguo LI (✉)Mechanical and Mechatronics Engineering Department, University ofWaterloo, Ontario N2L 3G1, CanadaE-mail: x6li@uwaterloo.ca

Front. Energy Power Eng. China 2010, 4(2): 252–261DOI 10.1007/s11708-010-0036-7

fuel, called methyl decanoate. Furthermore, the numericalstudies on the pollutants formation prediction have beenperformed in order to improve the predictive capability ofmodels for engine simulations. Boulanger et al. [29,30]have developed an improved phenomenological sootmodel for 3D multi-dimensional engine simulations. Guoet al. [31] have analyzed the interaction between soot andNOx formation, and the results show that the influence ofsoot on NO formation is caused by not only the radiation-induced thermal effect, but also the reaction-inducedchemical effect.Based on previous studies, the objective of the current

study is to clarify numerically the effects of the physicalproperties and the chemical structure of the biodiesel fuelon in-cylinder combustion process and pollutant forma-tion. The study is implemented by using ConvergeTM CFDcode. Moreover, MB and n-heptane are chosen to be thesurrogates of the biodiesel fuel and the conventional dieselfuel, respectively.

2 Computational model

2.1 Governing equations and turbulence modeling

The dynamics of fluid flow in cylinder are governed by thecompressible equations for the conservation of mass,momentum, energy and species:Conservation of mass:

∂�∂t

þ ∂�ui∂xi

¼ S: (1)

Conservation of momentum:

∂�ui∂t

þ ∂�uiuj∂xj

¼ –∂p∂xi

þ ∂�ij∂xj

þ Si: (2)

Conservation of energy:

∂�e∂t

þ ∂uj�e∂xj

¼ –P∂uj∂xj

þ �ij∂ui∂xj

þ ∂∂xj

K∂T∂xj

� �

þ ∂∂xj

�DXm

hm∂Ym∂xj

!þ Se:

(3)

Conservation of species:

∂�m∂t

þ ∂uj�m∂xj

¼ ∂∂xj

�D∂Ym∂xj

� �þ Sm: (4)

Where S, Si, Se, and Sm represent the source terms, p ispressure, ρ is density, Ym denotes the mass fraction ofspecies m, D is the mass diffusion coefficient, e is the

specific internal energy, K is the conductivity, hm is thespecies enthalpy, T is the temperature, ρm is the density ofspecies, and σij is the stress tensor which is given as

�ij ¼ �∂ui∂xj

þ ∂uj∂xi

� �–2

3�∂uk∂xk

δij: (5)

in which δij is the Kronecker delta, μ is viscosity.For the turbulent flow, the conductivity, K, is replaced by

Kt expressed as Kt ¼ K þ cp�t=Pr, in which �t is theturbulent viscosity and Pr is the Prandtl number; theviscosity, μ, in the Eq. (5) is replaced by �# expressed as�# ¼ �þ �t in which μt is turbulent viscosity; the massdiffusion coefficient, D, is used by Dt given byDt ¼ �t=Sct, where Sct is the turbulent Schmidt number.Turbulence modeling is very important for in internal

combustion (IC) engines. Turbulence directly influencesinjection and atomization processes and spray character-istics, as well as mixing and combustion processes in aninternal combustion engine. The superiority of the rapiddistortion RNG k-ε model in comparison with the standardk-ε [32] and RNG k-ε models [33] has been demonstratedearlier in Ref. [34]. Hence, turbulence is simulated usingthe rapid distortion RNG k-εmodel developed by Han et al.[35] based on the RNG k-ε model through an isotropicrapid analysis.The equation for the turbulence kinetic energy, k, of the

rapid distortion RNG k-ε model developed by Han et al.[35] is given as

∂�κ∂t

þ ∂�uiκ∂xi

¼ τij∂ui∂xj

þ ∂∂xj

�t

Pr

∂κ∂xj

– �εþ Ss, (6)

where ui is the instant velocity and Ss is the source term.The Reynolds stress τij is given by

τij ¼ 2�tSij –2

3δij �κ þ �t$

∂~u∂x

� �, (7)

in which �t is the turbulent viscosity which is given as

�t ¼ C��κ2

ε

� �, (8)

where C� is a model constant. Sij is the mean strain ratetensor and given by

Sij ¼1

2

∂eui∂xj

þ ∂euj∂xi

� �, (9)

eui � �ui�

(10)

The dissipation of turbulence kinetic energy, ε, is givenby

.

Yi REN et al. Biodiesel fuel combustion and emission 253

∂�ε∂t

þ ∂ð�uiεÞ∂xi

¼ ∂∂xj

�

Pr$∂ε∂xj

� �–

2

3C1 –C3 þ

2

3

C�ηð1 – η=η0Þð1þ βη3Þ

κε∂uκ∂xκ

� �

$�ε∂ui∂xi

þ c1 –ηð1 – η=η0Þð1þ βη3Þ

� �∂ui∂xj

�ij – c2�εþ csSs

� �εκ,

(11)

where c1, c2, c3 and cs are model constants, Pr is thePrandtl number, and η is given by

η ¼ κε

� �$ Sij�� ��: (12)

2.2 Breakup model

The break-up procedure is simulated using the hybridKelvin–Helmholtz/Rayleigh–Taylor model (KH-RT) [36–40]. The break-up length in this model is defined by

Lb ¼ Cbld0

ffiffiffiffiffi�1�g

r, (13)

where ρl and ρg are the liquid and gas densities,respectively, and d0 is the diameter of the injected liquid“blob”, which is set to the diameter of the nozzle hole. InEq. (13), Cbl is the model constant that can be tunedfollowing the technique described by Senecal et al. [41] toincrease or decrease the spray break-up length.

2.3 Reaction mechanism

Researchers at the Lawrence Livermore National Labora-tory (LLNL) have developed a detailed kinetic reactionmechanism containing 264 species and 1219 reactions forMB which has been proposed as a surrogate of biodiesel[26]. Brakora et al. [27] have developed and reduced theabove LLNL detailed mechanism to ERC-mb mechanismwhich consists of 41 species and 150 reactions and can beused for the 3D multi-dimensional diesel engine simula-tion. The current study implements the ERC-mb reaction tosimulate the biodiesel fuel combustion with ConvergeTM

CFD code. For n-heptane, the current study employs thereduced reaction mechanism developed by Amar et al.[42], which contains 29 species and 52 reactions. Themodel has been validated against a detailed mechanismconsisting of 179 species and 1642 reactions. Bothmechanisms produce comparable results. However,Amar’s mechanisms reduces the computing time by50%–70%.

2.4 Pollutant formation model

In this study, the extended Zel’dovich model and theHiroyasu-NSC oxidation soot model are applied to model

the formations of nitric oxide (NOx) and soot in thecombustion process. The extended Zel’dovich mechanismhas been presented by Heywood [43] and is given by thefollowing set of reactions:

Oþ N2 ¼ NOþ N, (14)

Nþ O2 ¼ NOþ O, (15)

Nþ OH ¼ NOþ H: (16)

Furthermore, in the soot formation model, as well as theHiroyasu-NSC oxidation soot model, the production ofsoot mass Ms is determined by

dMs

dt¼ Msf

$– Mso

$, (17)

where Msf

$is the soot mass formation rate and Mso

$is the

soot mass oxidation rate.

According to the Hiroyasu model [44], Msf

$is given as

Msf

$ ¼ AsfMformp0:5exp –

Esf

RuT

� �, (18)

where Asf is the Arrhenius pre-exponential factor; Mform isthe mass of the soot formation species, which is substitutedby C2H2 in the computational cell in this study since thedetailed combustion reaction mechanisms have beenimplemented; p is the cell pressure; Ru is the universalgas constant; T is the cell temperature; and Esf is theactivation energy.The soot mass oxidation rate is derived from the three

reaction equations in the Nagle–Strickland-Constableoxidation model [45], as given by

Mso

$ ¼ 6Mwc

�sDsRtotalMs, (19)

where Mwc is the molecular weight of carbon, Rtotal is thenet surface reaction rate, furthermore, ρs andDs are the sootdensity and the nominal soot particle diameter, respec-tively.

3 Computational fuels

MB is used as a surrogate for biodiesel fuels in thesimulation since it has the same ester functional group asthe components of biodiesel fuels. N-heptane is used as asurrogate for the conventional diesel fuel in the simulationsince it has similar properties to diesel fuel. In order tocompare the effects of physical properties and chemicalproperties of the biodiesel fuel on in-cylinder phenomenain a DI engine, two hypothetical fuels, A and B, aredesigned and implemented in the current study. Fuel A hasthe same physical properties as the MB and the same

254 Front. Energy Power Eng. China 2010, 4(2): 252–261

chemical properties as n-heptane. Fuel B has the samephysical properties as n-heptane and the same chemicalproperties as the biodiesel fuel. As the lower heating valuesof MB and heptane are 27 MJ/kg and 44.6 MJ/kg,respectively; thereby, those of Fuel A and Fuel B are44.6MJ/kg and 27MJ/kg as that of heptane and MB. Theproperties of the four fuel types; diesel, biodiesel, Fuel A,and Fuel B are summarized in Table 1.Comparisons of densities, viscosities, surface tensions

and latent heat of vaporizations between n-heptane andMB are plotted in Fig. 1. Temperature dependentcorrelations are obtained from Ref. [46]. As shown inFig. 1, both of the density and surface tension of MB arehigher than those of n-heptane. While MB viscosity ishigher at lower temperature, both fuels exhibit similarviscosities as the temperature exceeds 400 K. Slightdifferences in the latent heat of vaporization between the

two fuels are observed. Generally speaking, the higherdensities of MB could result in a higher initial momentumof MB spray, and consequently, a longer spray penetrationof MB. Since viscosity and surface tension are keyproperties for the droplet break-up process, longer break-up length and bigger size of liquid droplets are expected forMB spray.

4 Numerical implementation

The engine used in the current study is similar to the oneexperimentally tested by Cheng et al. [47]. Comparisonwith already established experimental data is essential forvalidation purpose. Cheng et al. have performed theexperiment on an optical direct injection biodiesel-fueledengine, named the Sandia compression-ignition optical

Table 1 Physical and chemical properties of computational fuels

Fuel A diesel (n-heptane) Fuel B biodiesel (MB)

physical properties Phy.mb Phy.heptane Phy.heptane Phy.mb*

chemical properties Chem.heptane Chem.heptane Chem.mb Chem.mb

* The physical properties of the biodiesel fuel used in this study are calculated. The computational method of calculation has been presented in Ref. [46]

Fig. 1 Variations of MB and n-heptane liquid properties with temperature(a) Density; (b) viscosity; (c) surface tension; (d) latent heat of vaporization

Yi REN et al. Biodiesel fuel combustion and emission 255

research engine (SCORE). The specifications of the testengine and its injection system are given in Tables 2 and 3,respectively. It is modified from the Caterpillar 3176heavy-duty engine with a plat bottom piston bowl foroptical access via the piston bottom. Such modificationsresults in a reduction of the compression ratio from 16∶1 to11.3∶1. Similar to the experimental study, the intakepressure and temperature are reset in the current numericalanalysis to simulate a compression ratio of 16∶1. Since noactual injection rate shape is provided by previousliterature, the simple top hat shape is applied in the currentstudy.

Computations are performed on a 60° sector of thecombustion chamber of the SCORE test engine asillustrated in Fig. 2(a). The computational domainconsiders the fuel injector with 6 holes. Adaptive grid

embedding (AGE) with an original grid resolution of2.5 mm�2.5 mm is implemented to reduce the computa-tional cost while ensuring the required mesh resolution.The minimum embedded grid resolution is set to0.625 mm�0.625 mm. During the simulation, the variationof the velocity, temperature, species, and passives in a cellare referred to in determining the time when the cell isembedded and when the embedding is removed [48]. AGEis set to start at the beginning of the injection timing inorder to save computing time. The result of the embeddingis presented in Fig. 2(b).Similar to the experiment in Ref. [47], the current study

examines 5 engine load cases varying between 800 and1600 kPa (MEP) with 200 kPa increment. The injectiontiming is set to – 1.1° ATDC, and the injection pressure of150MPa is performed for all cases. Table 4 gives thesimulating conditions of all cases in the study.

5 Results and discussion

The in-cylinder pressure and heat release rate of the 4 fueltypes are shown in Fig. 3. It can be seen that the initialcombustion phase of the biodiesel (MB) and Fuel A aredelayed significantly, and the diffusive combustion frac-tion of biodiesel is higher than that of the diesel fuel (n-heptane). This can be explained by the fact that theinjection durations of the biodiesel fuel (MB) and Fuel Bare longer than those of the diesel fuel and Fuel A becausemore fuels should be injected into the cylinder in order toobtain the same power out due to the lower heating valuesof the biodiesel fuel and Fuel B compared to the diesel fueland Fuel A. Thereby, less energy was injected into thecylinder in the same period in the cases with the biodieselfuel and Fuel B compared to the cases of the diesel fuel andFuel A which has the same chemical properties as thediesel fuel, leading to the increase in the diffusivecombustion phase fraction of the biodiesel fuel.Furthermore, the results also show that the differences in

the chemical properties between the biodiesel fuel and theconventional diesel fuel have more significant effects oncombustion and heat release processes than the differences

Table 2 Specifications of test engine

items specifications

engine type one cylinder Caterpillar 3176

cycle four-stroke CIDI

valves per cylinder four

bore/mm 125

stroke/mm 140

IVO/(°) ATDC – 32

IVC/(°) ATDC – 153

EVO/(°) ATDC 116

EVC/(°) ATDC 11

connecting rod length/mm 225

piston bowl diameter/mm 90

piston bowl depth/mm 16.4

Displacement/L 1.72

compression ratio* 11.3∶1 (16.0∶1)

* The modification of piston bowl increases the clearance volume and decreasesthe compression ratio to 11.3∶1. Simulated compression ratio matches 16∶1 inoptical engine by preheating and boosting intake pressure.

Table 3 Specifications of fuel injection system

items specifications

injection type Caterpillar HEUI A

injection model HIA-450

nozzle style single-guided VCO

number of orifices 6

hydro-erosion/% 13

orifice L/D/(°) 8.0

included spray angle 140

oil rail pressure/MPa 20.8

max. fuel injection pressure/MPa 142

pressure intensification ratio 6.85∶1

valve opening pressure/MPa 31

Table 4 Simulated operating conditions for all load cases

items specifications

engine speed/(r%min–1) 800

engine loads(MEP)/MPa 0.8, 1.0, 1.2, 1.4, 1.6

time of injection – 1.1 CAD

fuel injection strategy Tophat

initial pressure/kPa 240

initial temperature/K 404

cylinder wall temperature/K 425

cylinder head temperature/K 425

piston temperature/K 500

256 Front. Energy Power Eng. China 2010, 4(2): 252–261

in the physical properties. As shown in Fig. 3(b), thediffusive combustion of Fuel B has a significant high heatrelease rate and a short duration compared to Fuel A and n-heptane due to more oxygen available in the biodiesel fuel.Comparisons of Sauter mean diameter (SMD) and spray

penetration between Fuel A and the diesel fuel arepresented in Fig. 4, which reveal that the SMD in thecase of Fuel A has a higher value and a longer lifetime thanthat in the case of the diesel fuel. The higher viscosities andsurface tensions of Fuel A, whose physical properties arethe same as biodiesel fuel (MB), can be used to account forits higher SMD, and the longer injection duration in thecase of biodiesel fuel (MB) leads to the longer break-uphistory. It can also be seen from Fig. 4(a) that there exists apeak of SMD. The reason for this is that the diameter of theinitial droplet size out of the nozzle has been set to be thesame size as the diameter of the nozzle. Moreover, theresults indicate that the spray penetration of Fuel A islonger than that of the diesel fuel due to the higher densityof Fuel A compared to diesel fuel. Since the physicalproperties of diesel fuel do better than those of biodieselfuel to improve the spray break-up process, as well as theconsequent mixture formation process, the total combus-tion duration is shortened by using the physical propertiesof the diesel fuel as shown in Fig. 4(b).

The distribution of the turbulent kinetic energy of the in-cylinder flow is given in Fig. 5. The results reveal that thein-cylinder flow of Fuel B has a lower turbulent kineticenergy than that of Fuel A and n-heptane in the initialcombustion phase, as shown in Fig. 5(a). On the contrary,in the diffusive combustion phase, as shown in Fig. 5(b),the case of Fuel B shows a higher predicted flow turbulentkinetic energy compared to Fuel A and n-heptane.Moreover, Fuel A and n-heptane have the similardistribution of the flow turbulent kinetic energy, whichcan be explained by the fact that the delay in the initialcombustion of Fuel B using the chemical properties ofbiodiesel fuel results in a lower heat release rate than FuelA and n-heptane, which leads to a lower turbulent kineticenergy, while the higher heat release rate of Fuel B in thediffusive combustion phase causes a higher turbulentkinetic energy.Figure 6 gives the images of the in-cylinder equivalence

ratio for Fuel A, n-heptane and Fuel B at the crank angle of2° ATDC for IMEP = 1.2MPa. It can be observed that thepenetration of Fuel A is significantly larger. than those ofFuel B and heptane, however, Fuel A and n-heptane havethe similar equivalence ratio distribution that is morewidespread than that of Fuel B. This indicates that thedifference in the chemical properties between biodiesel

Fig. 2 Computational domain(a) Original mesh; (b) adapted mesh (temperature distribution is shown in (b))

Fig. 3 Comparisons of in-cylinder pressure and heat release rate (HRR) among four kinds of fuels(a) In-cylinder pressure; (b) heat release rate (HRR)

Yi REN et al. Biodiesel fuel combustion and emission 257

fuel and diesel fuel results in a greater influence on mixtureformation process compared to the physical properties. Thereason for this behavior is that the flow turbulenceinfluences the mixture formation significantly. Thereby,

the higher flow turbulent kinetic energy for Fuel A and n-heptane is, the more mixture will be formed.Indicated efficiencies for the four kinds of fuels under

different engine loads are illustrated in Fig.7(a). The

Fig. 4 Comparisons of droplet-Sauter Mean Diameter (SMD) and spray penetration between Fuel A and diesel fuel(a) Droplet-Sauter Mean Diameter (SMD); (b) spray penetration

Fig. 5 Turbulent kinetic energy of the in-cylinder flow (unit for the numerical value given in the color legend is J/kg); IMEP = 1.2Mpa(a) Crank angle = 2° ATDC; (b) crank angle = 21° ATDC

Fig. 6 In-cylinder equivalence ratio at the crank angle of 2° ATDC; IMEP = 1.2MPa

258 Front. Energy Power Eng. China 2010, 4(2): 252–261

indicated efficiency can be expressed as ηf ¼ Qw=Qf , inwhichQw is the indicated work output per cycle, and theQf

is the total injected energy into cylinder per cycle. Theresults show that the diesel fuel has a higher indicatedefficiency than the biodiesel fuel at the same engineoperating condition. Furthermore, the absolute differencesin the indicated efficiencies for Fuel A relative to dieselfuel and Fuel B relative to diesel fuel, as well as Δηphy andΔηchem, are given in Fig. 7(b). In detail, Δηphy and Δηchemcan be defined as Δηphy ¼ ηdiesel – ηFuelAj j; Δηchem¼ ηdiesel – ηFuelBj j. The results reveal that the differencesin the physical properties between the biodiesel fuel andthe diesel fuel basically make a slight variation in theindicated efficiency, while the differences in chemicalproperties between the biodiesel fuel and the diesel fuelhave a significant effect on the indicated efficiency. Thissuggests that the chemical properties of fuels play a moreimportant role than the physical properties in fuel energy

conversion process at the same engine operating condition.In order to compare the effects of the chemical properties

and the physical properties of the biodiesel fuel onpollutants formation, the percentage changes in soot andNOx emissions for the variations from Fuel A relativeto the diesel fuel and Fuel B relative to diesel fuel areplotted in Fig. 8, where Δsoot½phy:� represents thepercentage change in the soot emission derived from thevariation of the physical properties, which can be expressedas Δsoot½phy:� ¼ soot½diesel� – soot½fuelA�j j=soot½diesel�;Δsoot½chem:� represents the percentage change in thesoot emission derived from the variation of thechemical properties, which can be expressed asΔsoot½chem:� ¼ soot½diesel� – soot½fuelB�j j=soot½diesel�;and ΔNOx½phy:� and ΔNOx½chem:� are determined simi-larly.The results shown in Fig. 8(a) indicate that differences in

the physical properties and the chemical properties of

Fig. 7 Indicated efficiencies and their difference derived from the variation of physical propertiesand the variation of chemical properties

(a) Indicated efficiencies; (b) difference in conversion efficiency

Fig. 8 Percentage changes in soot and NOx emissions derived from the variation of physical properties and chemical properties betweenbiodiesel fuel and diesel fuel

(a) Percentage changes in soot; (b) NOx emissions

Yi REN et al. Biodiesel fuel combustion and emission 259

biodiesel fuel relative to diesel fuel produce the same levelof effect on the soot emission formation. Moreover, thereexist distinct trends in Δsoot½phy:� and Δsoot½chem:� withthe increase of the engine load. It can be seen that thedifferences in the physical properties of the biodiesel fuelrelative to the diesel fuel affect increasingly the sootformation with the increase of the engine load. The reasonfor this behavior is that the differences in the physicalproperties influence between the biodiesel fuel and thediesel fuel decrease with the increase in temperature asgiven in Fig. 2. As a result, the effects of the differences inthe physical properties on spray, mixture formation andpollutants formation processes will reveal a decreasingtrend with the increase in temperature. On the contrary,since the chemical reaction rate is the function oftemperature and pressure, the chemical properties havemore significant effects on the combustion and pollutantsformation processes at high temperature. In addition, theresults in Fig. 8(b) show that the percentage changes inNOx emissions decrease obviously with the increase of theengine load. And the differences in the chemical propertiesbetween biodiesel fuel and diesel fuel result in a higherinfluence on NOx emissions compared to the differences inthe physical properties between them.

6 Conclusions

In this study, methyl butanoate and n-heptane are chosen tobe the surrogate fuels for the biodiesel fuel and theconventional diesel fuel, respectively. Detailed kineticchemical mechanisms for MB and n-heptane are used toinvestigate numerically the effects of the physical andchemical properties of the biodiesel fuel on the combustionand emissions formation processes. The results show that:1) The differences in the physical properties of the

biodiesel fuel relative to the diesel fuel affect mainly thespray and atomization processes as well as the diffusivecombustion phase, while the variations in the chemicalproperties result in the differences in the whole combustionprocess.2) The differences in the chemical properties of biodiesel

fuel relative to diesel fuel have a significant effect on theindicated efficiency. The effect of the variation in thephysical properties of the biodiesel fuel relative to thediesel fuel on the indicated efficiency can be neglected.3) Both the physical and chemical properties affect soot

formation. As the engine load increases, soot formationpercentage changes derived from the variations in thephysical properties decrease, while soot formation percen-tage changes derived from the variations in the chemicalproperties increase. Chemical properties are found to havea great impact on NOx formation.

Acknowledgements The financial support from the Ontario ResearchFund-Research Excellence (ORF-RE) program via contract #RE-02-019 is

greatly appreciated. Convergent Science is gratefully acknowledged forproviding their ConvergeTM CFD code for the present study.

References

1. Huang Z H, Wang H W, Chen H Y. Study on combustion

characteristics of a compression ignition engine fueled with

dimethyl ether. Proc Inst Mech Eng, Part D, J Automobile Eng,

1999, 213(D6): 647–652

2. Huang Z H, Jiang D M, Zeng K, Liu B, Yang Z L. Combustion

characteristics and heat release analysis of a DI compression ignition

engine fueled with Diesel-dimethyl carbonate blends. Proc Inst

Mech Eng, Part D, J Automobile Eng, 2003, 217(D7): 595–606

3. Beatrice C, Capaldi P, Del N. Giacomo, Analysis of impact of diesel

fuel/biodiesel blends on a modern diesel combustion system

performance by means of injection test rig, optical and real SC

engine experiments. SAE paper 2009–01–0484, 2009

4. Murugesan A, Umarani C, Subramanian R, Nedunchezhian N. Bio-

diesel as an alternative fuel for diesel engines- A review. Renewable

and Sustainable Energy Reviews, 2009, 13(3): 653–662

5. Graboski M S, McCormik R L. Combustion of fat and vegetable oil

derived fuels in diesel engines. Prog Energy Combust Sci, 1998, 24

(2): 125–164

6. Knothe G, Krahl J, Van G J. The Biodiesel Handbook. New York:

AOCS Press, 2005, 76

7. Chakravarthy K, McFarlane J, Daw S. Physical properties of bio-

diesel and implications for use of bio-diesel in diesel engines. SAE

2007–01–4030, 2007

8. Sharp C A, Howell S A, Jobe J. The effect of biodiesel fuels on

transient emissions from modern diesel engines. Part I: Regulated

emissions and performance. SAE paper 2000–01–1967, 2000

9. Sharp C A, Howell S A, Jobe J. The effect of biodiesel fuels on

transient emissions from modern diesel engines. Part II: Regulated

emissions and performance. SAE paper 2000–01–1968, 2000

10. Rakopoulos C D, Rakopoulos D C, Hountalas D T, Giakoumis E G,

Andritsakis E C. Performance and emissions of bus engine using

blends of diesel fuel with bio-diesel of sunflower or cottonseed oils

derived from Greek feedstock. Fuel, 2008, 87(2): 147–157

11. Rakopoulos C D, Antonopoulos K A, Rakopoulos D C, Hountalas D

T, Giakoumis E G. Comparative performance and emissions study

of a direct injection Diesel engine using blends of Diesel fuel with

vegetable oils or bio-diesels of various origins. Energy Conversion

and Management, 2006, 47(18,19): 3272–3287

12. Bannister C D, Hawley J G, Ali H M, Chuck C J, Price P, Brown A

J, Pickford W. Quantifying the effects of biodiesel blend ratio, at

varying ambient temperatures, on vehicle performance and emis-

sions. SAE paper 2009–01–1893, 2009

13. Fang T, Lee C F. Bio-diesel effects on combustion processes in an

HSDI diesel engine using advanced injection strategies. Proceedings

of the Combustion Institute, 2009, 32(2): 2785–2792

14. Zhao F, Asmus T W, Assanis D N, Dec J E, Eng J A, Najit P M.

Homogeneous Charge Compression Ignition (HCCI) Engines: Key

Research and Development Issues. Warrendale, USA: SAE

International, 2003, 11–12

15. Pogoreve P, Kegl B, Skerget L. Diesel and biodiesel fuel spray

260 Front. Energy Power Eng. China 2010, 4(2): 252–261

simulations. Energy & Fuels, 2008, 22(2): 1266–1274

16. Choi C Y, Bower G R, Reitz R D. Effects of biodiesel blended fuels

and multiple injections on D. I. diesel engine emissions. SAE paper

970218, 1997

17. Lee C S, Park S W, Kwon S I. An experimental study on the

atomization and combustion characteristics of biodiesel-blended

fuels. Energy & Fuels, 2005, 19(5): 2201–2208

18. Szybist J P, Mcfarlane J, Bruce G B. Combustion of simulated and

experimental combustion of biodiesel blends in a single cylinder

diesel HCCI engine. SAE paper 2007–01–4010, 2007

19. Mao G, Wang Z, Yang D, Yuan Y. Numerical simulation and

experimental research on the free spray characteristics of bio-diesel

fuel. SAE paper 2008–01–1598, 2008

20. Park S H, Kim H J, Suh H, K, Lee C S. Experimental and numerical

analysis of spray-atomization characteristics of biodiesel fuel in

various fuel and ambient temperatures conditions. International

Journal of Heat and Fluid Flow, 2009, 30(5): 960–970

21. Pogorev P, Kegl B, Skerget L. Diesel and biodiesel fuel spray

simulations. Energy & Fuels, 2008, 22(2): 1266–1274

22. Stringer V L, Cheng W L, Lee C F, Hansen A C. Comparing the

operation of an HSDI engine using multiple injection schemes with

soybean biodiesel, diesel and their blends. SAE paper 2009–01–

0719, 2009

23. Ra Y, Retiz R D, Mcfarlane J, Daw C S. Effects of fuel physical

properties on diesel engine combustion using diesel and bio-diesel

fuels. SAE paper 2008–01–1379, 2008

24. Golovitchev V I, Yang J. Construction of combustion models for

rapeseed methyl ester bio-diesel fuel for internal combustion engine

applications. Biotechnology Advances, 2009, 27(5): 641–655

25. Gaïl S, Sarathy S M, Thomson M J, Diévart P, Dagaut P.

Experimental and chemical kinetic modeling study of small methyl

esters oxidation: methyl (E)-2-butenoate and methyl butanoate.

Combustion and Flame, 2008, 155(4): 635–650

26. Fisher EM, Pitz W J, Curran H J, Westbrook C K. Detailed chemical

kinetic mechanisms for combustion of oxygenated fuels. Proceed-

ings of the Combustion Institute, 2000, 28: 1579–1586

27. Brakora J L, Ra Y, Retiz R D, Mcfarlane J, Daw C S. Development

and validation of a reduced reaction mechanism for biodiesel-fueled

engine simulation. SAE paper 2008–01–1378, 2008

28. Herbinet O, Pitz W J, Westbrook C K. Detailed chemical kinetic

oxidation mechanism for a biodiesel surrogate. Combustion and

Flame, 2008, 154(3): 507–528

29. Boulanger J, Neill W S, Liu F, Smallwood G J. An improved

phenomenological soot formation submodel for three-dimensional

diesel engine simulations: extension to agglomeration of particles

into clusters. Journal of Engineering for Gas Turbines and Power,

2008, 130(6): 062808–062814

30. Boulanger J, Liu F, Neill W S, Smallwood G J. An improved soot

formation model for 3D diesel engine simulations. Journal of

Engineering for Gas Turbines and Power, 2007, 129(3): 877–884

31. Guo H, Smallwood G J. The interaction between soot and NO

formation in a laminar axisymmetric coflow ethylene/air diffusion

flame. Combustion and Flame, 2007, 149(1–2): 225–233

32. Launder B E, Spalding D B. Mathematical Models of Turbulence.

London: Academic Press, 1972

33. Yakhot V, Smith L M. The renormalization group, the ε-expansion

and Derivation of turbulence models. Journal of Scientific

Computing, 1992, 7(1): 35–61

34. Ren Y, Li X G. Numerical study on combustion and emissions

characteristics of a direct injection (DI) diesel engine. Proceedings

of Combustion Institute–Canadian Section, 2009, 18–23

35. Han Z, Reitz R D. Turbulence modeling of internal combustion

engines using RNG k-ε models. Combust Sci and Tech, 1995, 106

(4–6): 267–295

36. Reitz R D. Modeling atomization processes in high-pressure

vaporizing sprays. Atomization and Spray Technology, 1987, 3

(4): 309–337

37. Reitz R D. Atomization and other breakup regimes of a liquid jet.

Dissertation for the Doctoral Degree. Princeton University, 1978

38. Reitz R D, Bracco F V. Mechanism of atomization of a liquid jet.

The Physics of Fluids, 1982, 25: 1730–1742

39. Reitz R D, Bracco F V. Mechanism of breakup of round liquid jets.

In: Cheremisnoff N ed. The Encyclopedia of Fluid Mechanics,

Houston, TX: Gulf Publishing, 1986, 233–249

40. Taylor G I. The instability of liquid surfaces when accelerated in a

direction perpendicular to their planes. Proceedings of the Royal

Society of London. Series A, Mathematical and Physical Sciences,

1950, 201(1065): 192–196

41. Senecal P K. Development of a methodology for internal

combustion engine design using multi-dimensional modeling with

validation through experiments. Dissertation for the Doctoral

Degree. Department of Mechanical Engineering, University of

Wisconsin-Madison, 2000

42. Patel A, Kong S C, Reitz R D. Development and validation of a

reduced reaction mechanism for HCCI engine simulations. SAE

paper 2004–01–0558, 2004

43. Heywood J B. Internal Combustion Engine Fundamentals. New

York: McGraw Hill, Inc., 1988

44. Hiroyasu H, Kadota T. Models for combustion and formation of

nitric oxide and soot in DI diesel engines. SAE Paper 760129, 1976

45. Nagle J, Strickland-Constable R F. Oxidation of carbon between

1000–2000°C. Proc of the Fifth Carbon Conf 1, Oxford: Pergamon

Press, 1962, 154

46. Yaws C L. Chemical properties handbook: physical, thermody-

namic, environmental, transport, safety, and health related proper-

ties for organic and inorganic chemicals.New York: McGraw-Hill,

1999

47. Cheng A S, Upatnieks A, Mueller C J. Investigation of the impact of

biodiesel fuelling on NOx emissions using an optical direct injection

diesel engine. International Journal of Engine Research, 2006, 7(4):

297–318

48. Senecal P K, Richard K J, Pomraning E. A new parallel cut-cell

cartesian CFD code for rapid grid generation applied to in-cylinder

diesel engine simulations. SAE Paper 2007–01–0159, 2007

Yi REN et al. Biodiesel fuel combustion and emission 261