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Comparative analysis of a DI diesel engine fuelled with biodiesel blends during the European MVEG-A cycle: Preliminary study (I)
biomass and bioenergy 33 (2009) 941–947
Available at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Comparative analysis of a DI diesel engine fuelled with biodiesel blends during the European MVEG-A cycle: Preliminary study (I) J.M. Luja´n, B. Tormos*, F.J. Salvador, K. Gargar CMT-Motores Te´rmicos, Universidad Polite´cnica de Valencia, Valencia, Spain
article info
abstract
Article history:
The present work consists of introducing the tests and facilities used to perform
Received 19 February 2008
a comparative analysis of a diesel engine working with different blends of biodiesel fuel
Received in revised form
during the New European Driving Cycle. Furthermore, as a preliminary study, it was
31 January 2009
interesting to know the effects of biodiesel fuel on a common-rail high pressure injection
Accepted 10 February 2009
system, those more useful in modern light duty diesel engines, as a consequence of its
Published online 5 March 2009
different physicochemical properties compared with conventional diesel fuel. As the real goal of the study is to compare fairly performance and emissions from the engine, it was
Keywords:
essential to know any injection effects owed to fuel’s own characteristics that finally would
Biodiesel fuel
affect those parameters that will be evaluated.
Fuel characterization
A complete fuel characterization for diesel and biodiesel fuels, as the EN 590 and the EN
Injection rate
14214 standard specifications, was performed in order to quantify the differences between
Common-rail injection system
both fuels. A priori, it could be thought that viscosity and density values will be the most
New European driving cycle
significant parameters capable of altering the injection rate. As positive results, it was
Engine pollutant measurements
obtained that the common-rail high pressure injection system was totally blind in the
Engine performance
injection rate measurements, even the significant differences between both fuels, taking into account the counterbalancing effects generated by two parameters mentioned before. The second part of the study deals with engine performance and pollutant emissions on an unmodified common-rail turbocharged diesel engine running with biodiesel fuel blends during the New European Driving Cycle. ª 2009 Elsevier Ltd. All rights reserved.
1.
Introduction
As said in the European Commission [1], in spite of the actual high cost of biodiesel production, biofuels are now the only way to reduce our fossil fuel dependence in the transport field. Thus, biodiesel is emerging as a strong contender, and is becoming commercially available despite the fact that it is available in limited quantities and in a determined number of countries [2]. Besides, the production of biodiesel from vegetable oils can help to the reactivation of the agricultural sector
as another financial force. In the case of Mediterranean countries, where vegetable oil is widely consumed in cooking, the reutilization of the wasted oil to produce biodiesel can also contribute to make biodiesel more attractive from an environmental and financial point of view [3,4]. Its application is very effective in reducing harmful emissions and particularly CO2 emissions due to its carbon neutral cycle. A study from the CIEMAT in Spain (Centro de Investigaciones Energe´ticas, Medioambientales y Tecnolo´gicas) regarding CO2 emissions showed a reduction between a 75% and a 90% in the Fuel Life
* Corresponding author. Tel.: þ34 96 387 7650; fax: þ34 96 387 7659. E-mail address: [email protected] (B. Tormos). 0961-9534/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2009.02.004
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biomass and bioenergy 33 (2009) 941–947
Cycle Analysis using biodiesel fuel instead of conventional diesel fuel [5]. Another benefit of biodiesel fuels is to be an oxygenated fuel leading to a better and clean combustion [6]. Unfortunately, Murillo et al. stated that this content of oxygen and the lack of carbon and hydrogen content seem to be the reason why biodiesel presents such a lower heating value compared to diesel [7]. Other studies conclude after several tests that both torque and power outputs of biodiesel fuel are lower than those for diesel fuel throughout all engine speeds [8,9]; effects due to the lower heating value of the biodiesel. Main target of this work was to obtain a comparative analysis of performance and emissions of a commercial modern diesel engine under transient operation. In order to do this, an important experimental setup and detailed testing procedures are required. Furthermore, complete characterizations of fuels used on the test are also required in order to perform a clear comparison. Taking into account literature references about the effects of biodiesel blends on the classic mechanical injection systems, it was considered proper to perform a preliminary study to evaluate the effects on injection rate of using biodiesel blends in a modern common-rail injection system. In engines using mechanical injection systems controlled by a mechanical pump, the cyclic fuel delivery, pressure wave propagation time, average injection rate and maximum pressure during injection seemed to be significantly affected when pure biodiesel is used as said by Rosca et al. [10]. Kegl et al. also said that at the same initial design, the injection pressure and injection rate are higher and the needle opens earlier for neat biodiesel when using a mechanically controlled fuel injection system [11]. So the tests performed on the common-rail injection system were done in order to evaluate injection rate of diesel and biodiesel fuels for different injection pressure or injection time strategies.
2. Experimental facilities and test procedures The experimental facilities consists of a common-rail injection system test bed relating to the comparative study of injection rate measurements and a four cylinder diesel engine and specific engine test bed totally equipped to perform the measurements of engine’s performance and emissions. Facilities and test procedures are described in subsequent section.
2.1.
Common-rail injection system test bed
In order to evaluate injection rate differences between diesel and biodiesel fuel, a Bosch flowmeter was used to determine the injection rate using standard values of pressure and excitation time (Fig. 1). The Bosch method is based on the principle of pressure wave propagation in a column of liquid [12]. An injector is emptied directly in a very long tube of constant diameter filled with fuel. Then, the generated wave is propagated along the tube while the wave associated pressure is measured with a pressure sensor placed at the exit of the injector. Once arrived at the end of the tube, the wave is reflected and returned towards the injector. Tube’s length is
Fig. 1 – Bosch method measurement test bed.
calculated so that the considered wave can arrive at the pressure sensor only after the total emptying of the injector. The study was performed at 3 different injection pressures: 30, 80 and 160 MPa and at 3 different aperture times of the nozzle: 0.5, 0.1 and 2.0 ms. Latest engines generally work at very high injection pressure, but measuring the injection rate at 30 MPa contributes to evaluate the effect of biodiesel at low injection pressure where the differences could be more appreciable.
2.2.
Engine setup for transient mode measurements
The engine test bed is described in Fig. 2. A HSDI (High Speed Direct Injection) 4-cylinder, 1.6-l, turbo diesel engine with high pressure fuel injection common-rail system, oxidation catalyst and particulate filter meeting the EURO III regulations for light duty vehicles were employed [13]. The engine’s specifications are shown in Table 1. The engine is coupled with a Shenck–Pegasus dynamometer controlling online engine torque and speed. The software used is named as XONE, and is able to program the driving condition of the vehicle. By means of this software, the MVEG-A cycle is programmed as a time sequence for gears and vehicle speeds taking into account the vehicle features and current driver skills. In order to perform possible modifications of any of the engine’s parameters, its Engine Control Unit (ECU) is totally opened and the engine settings maps can be recalibrated with the ETAS INCA Software. The installation counts with a series of temperature, pressure and air mass flow sensors in order to precisely control the engine.
biomass and bioenergy 33 (2009) 941–947
Opacimeter AVL 439
Dynamometer
Data acquisition and control system ECU Exhaust gas analysers
VNT
Oxidation DPF Catalyst
Intake CO2 (NDIR) CO2 (NDIR) CO (NDIR) HC (HFID)
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necessary given the fact that the Diesel Particle Filter intake must be, at least at a distance of six times the diameter of the exhaust pipe from the turbine. Furthermore, measured emissions without the after-treatment system gave us information on the way biodiesel fuel affects engine’s neat emissions and allows us to extend our results to old vehicles, devoided of after-treatment system. Measuring emissions with the aftertreatment system was useful to evaluate biodiesel effects on the vehicle’s emissions. Finally, after comparing the two sets of results, a clear post-treatment system characterization, regarding the biodiesel content in the fuel was performed.
EGRv
NOx (CLA)
2.3.
Performance and emissions test procedure
Cooler
Fig. 2 – Engine test bed.
Fuel consumption is determined by a fuel gravimetric system, the AVL 733S Dynamic Fuel Meter. It consists of a measuring vessel filled with fuel suspended on a balance system. Fuel consumption values are then obtained by calculating the vessel’s time related weight loss. As the response time of this system was too long for the study, a calibration of the fuel consumption signal provided by the ECU was performed in steady state, so the ECU is also used as a second fuel consumption measuring system [14]. Related to emissions, Fig. 2 also shows a diagram of the layout of the equipment during the tests. Exhaust gases were analyzed with and without after-treatment devices. Emissions (CO, CO2, O2, THC and NOx) were directly measured in each location by engine exhaust gas analyzer – HORIBA MEXA 7100EGR. The exhaust line is directly joined to the equipment through a pipe in which the temperature is maintained at 191 C in order to avoid hydrocarbons’ condensation. The hydrocarbons are analyzed using a HFID (Heated Flame Ionisation Detector), the nitrogen oxides using a HCLD (Heated ChemiLuminiscent Detector), the carbon monoxide just as carbon dioxide using a NDIR detector (Non Dispersive InfraRed) and the AVL model 439 Opacimeter measured the opacity of the exhaust gases. All the instruments meet the requirements of European Union Directives and International Standards Organisation. Measuring with and without after-treatment system in spite of before and after the after-treatment system was
Table 1 – Diesel engine characteristics. Engine specifications Type Swept volume Cylinders Valves Bore stroke Compression ratio Turbocharger Fuel injection system Max. power Max. torque
HSDI 1.6 l 4 Cylinders 4 Valves/cylinder 75 88.3 mm 18:1 Variable geometry turbocharger Common rail 82 kW/4000 rpm 245 Nm/2000 rpm
Tests have been performed with different fuel compositions from pure petroleum diesel fuel to pure biodiesel fuel. In this sense, conventional diesel fuel, B30, B50 and B100 are the fuels tested in this study. Besides, the emission’s levels of key pollutants are measured with and without the oxidation catalyst and particulate filter. This allows identifying the effect of biodiesel in both engine raw emissions and the pollutants emitted by the vehicle. Emission certification of light duty engines in Europe takes place in a test bed reproducing a European cycle named MVEG-A (European Motor Vehicle Emission Group A) which simulates road load conditions. At the beginning of the test, the room, the engine coolant and the oil temperature should be between 20 and 30 C. The temperature chosen was 22 C approximately. The first part of the cycle is known as UDC (Urban Driving Cycle) consisting of four ECE-15 segments of 200 s each and where the objective is to simulate cold start and car conduction in a city. It represents low vehicle speed (max. 50 km h1), low engine load and low exhaust gas temperature. In order to simulate the car driving in highways, it has been added a second cycle after the fourth ECE-15 cycle: the EUDC (Extra Urban Driving Cycle) which is a 400 s segment where the car can reach 120 km h1 [15]. Usually, the New European Driving Cycle is performed on a chassis dynamometer with a real vehicle. In our case, the Driving Cycle is a simulation of the original test and is performed on an engine dynamometer where all the parameters of the vehicle (weight, geometry, aerodynamic coefficient, etc.) can be entered. It is important to note that the MVEG-A cycle specifies the vehicle speed and demanded gear, so, for a given vehicle, the time sequence of engine speed and torque is the same for any fuel used. Fig. 3 shows the engine torque evolution during the MVEG-A cycle. It can be observed that the torque curves coincide for any fuel used in the study. Therefore, tests have been carried out under iso-power conditions. While iso-power tests allow establishing comparisons in order to obtain the best fuel under the point of view of engine homologation, the analysis of the results becomes more difficult. Effectively, differences obtained in iso-power tests are not exclusively dependent on the fuel type since the injected quantities and control conditions between tests are not equal. Finally, it should be noted that this kind of tests require severe test schedule and procedures in order to reduce the influence of external factors on engine measurements, especially pollutant emission measurements. In this sense, of this study the test schedule and the data pre-processing method detailed in Refs. [14,16]
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biomass and bioenergy 33 (2009) 941–947
Diesel B30 B50 B100 Vehicle Speed
150
Torque (Nm)
80
50 0
40
-50
Vehicle Speed (km h-1)
100
120
0 0
200
400
600
800
1000
1200
Time (s)
Fig. 3 – Engine torque measurements during the MVEG-A cycle.
have been followed. In addition, some specific measures have been taken into account because of the particular properties of biodiesel. In order to prevent possible problems reported by other authors concerning plugging and gumming of filters,
lines and injectors [6,2], the engine fuelling system was completely emptied and fuel filters were replaced before performing tests with any fuel blend.
3. Table 2 – Main fuels characteristics. Diesel fuel Biodiesel fuel (B100) Summarized formula Molecular weight [g mol1] Oxygen content [% w] Cetane number Density at 15 C [kg m3] Viscosity at 40 C [mm2 s1] Sulphur content [mg kg1] H/C ratio Lower heating value [MJ kg1] CFPP [ C]
C15.27 H27.33 210.96 0 51.52 843.0 2.847 27.9 1.79 42.834 7
C18.61 H35.65 O2 293.26 10.91 54.50 881.4 4.173 0.2 1.91 35.910 3
Fuel properties
Biodiesel fuel is the result of a transesterification process of a vegetable oil. This process consists of a catalyzed reaction between a triglyceride (vegetable oil) and an alcohol in order to produce glycerol and ester. In Europe, the biodiesel produced from the transesterification process should respect the EN 14214. A complete characterization, according to the EN 590 and the EN 14214, for diesel and biodiesel fuels respectively, was performed to the fuel involved in the test by an external laboratory. Additionally, measurements of the heating value and other parameters were done at the CMT-Motores Te´rmicos and are presented in Table 2 (the European Standard EN 14214 nor the EN 590 do not precise heating value as a characteristic value).
Table 3 – Biodiesel fuel full properties (EN 14214). Tests Ester content Flash point Carbon residue on 10% distillation residue Sulphated ash content Water content Total contamination Copper strip corrosion (3 h at 50 C) Oxidation stability at 110 C Acid value Iodine value Linolenic acid methyl ester Polyunsaturated (4 double Bonds) methyl ester Methanol content Monoglyceride content Diglyceride content Triglyceride content Free glycerol Total glycerol Group I metals (Na þ K) Group II metals (Ca þ Mg) Phosphorus content
Units
Test methods
Results
EN 14214 standard
% (m/m) C % (m/m) % (m/m) mg kg1 mg kg1 Rating h mgKOH/g – % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) mg kg1 mg kg1 mg kg1
EN ISO 14103:03 EN ISO 3679/04 EN ISO 10370/96 ISO 3987 EN ISO 12937:01 ISO 12662:1999 EN ISO 2160/99 EN 14112/03 EN 14104 EN 14111/03 EN 14103 — EN ISO 14110:03 EN ISO 14105:03 EN ISO 14105:03 EN ISO 14105:03 EN 14105/03 EN 14105/03 EN 14108/03 EN 14108/03 EN ISO 14107:03
99.3 165.0 <0.04 <0.007 352 5.1 1a 14.4 0.26 105 1.2 <1.0 <0.01 <0.25 <0.05 <0.05 0.02 <0.10 <0.5 <0.5 <0.5
96.5 min. 120 min. 0.30 max. 0.02 max. 500 max. 24 max. Class 1 6.0 min. 0.50 max. 120 max. 12.0 max. 1 max. 0.20 max. 0.80 max. 0.20 max. 0.20 max. 0.02 max. 0.25 max. 5.0 max. 5.0 max. 10.0 max.
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Table 4 – Diesel fuel full properties (EN 590). Tests
Units
Cetane index Polycyclic aromatic hydrocarbons Distillation Recovered at 65% Recovered at 85% Recovered at 95% Flash point Carbon residue on 10% distillation residue Lubricity Water content Total contamination Ash content Copper strip corrosion (3 h at 50 C) Oxidation stability, 110 C ASTM colour
– % (m/m)
EN ISO 4264/98 EN ISO 12916:00 EN ISO 3405:01
C C C C % (m/m) mm mg kg1 mg kg1 % (m/m) Rating g m3 Rating
The bibliography assumes a reduction of about 13–14% for biodiesel heating value compared with diesel (referred to mass units) due to its high oxygen content and its lower carbon and hydrogen content [17]. For this study, it was intentionally chosen a low heating-value biodiesel fuel coming from wasted oil in order to observe the results in the worst of the possible cases. Diesel fuel net heating value was about 42.83 MJ Kg1 compared with the one of biodiesel which was about 35.91 MJ Kg1 representing a 16% reduction. Complete fuels characterization can be seen in Tables 3 and 4. In general terms, biodiesel fuel presents lower sulphur content, higher flash point and lower total contamination values compared to diesel fuel [18]. This very low or zero content of sulphur lead to that sulphur pollutants (SO2) generated in biodiesel emissions are much lower than the emission of conventional fuels [19]. The biodiesel’s flash point is usually higher than diesel fuel, but besides this property, the European Standards limit its value to ensure that the manufacturer has correctly removed excess methanol used in the manufacturing process. Water and sediment content are important characteristics because of corrosion and microorganism development during storage. The engine fuel system has to be protected too, so the copper strip corrosion test is a limitation about prolonged contact between copper and bronze with biodiesel that could degrade the fuel and cause sediment formation. Carbon residue is an indication of the carbon-depositing tendency of the fuel. The acid number is an
Table 5 – Composition and concentration of fatty acids in biodiesel fuel. Fatty acids
Concentration
Triglyceride
Methyl ester
Oleic acid Linoleic acid Palmitic acid Stearic acid Myristic acidC18
40.10% 39.90% 11.70% 4.20% 2.30% 1.30% 0.5%
C18 C18 C16 C18 C14 C13 C19
C19 C19 C17 C19 C15 C14 C20
Total
100%
H34 O2 H32 O2 H32 O2 H36 O2 H28 O2 H26 O2 H38 O2
Test methods
H36 O2 H34 O2 H34 O2 H38 O2 H30 O2 H28 O2 H40 O2
ASTM D-93/02a EN ISO 10370/96 EN ISO 12156/01 EN ISO 12937:01 ISO 12662:1999 EN ISO 6245/03 EN ISO 2160:99 EN ISO 12205:96 ASTM D-1500/04a
Results
EN 590 Standard
49.6 3.4
46.0 min. 11 max.
294.5 329.2 357.0 66.5 <0.04 356 92 20 < 0.007 1a <1.0 0.5
250 min. 350 max. 360 max. 55 min. 0.30 max. 460 max. 200 max. 24 max. 0.01 max. Class 1 max. 25 max. 2 max.
indicator of free fatty acids and can be very high if the fuel is not properly manufactured. A higher acid number could reduce life of fuel pumps and filters. Free and total glycerine content informs about the presence of glycerine in the fuel as well as reflects the conversion degree of the oil into biodiesel [20]. In order to characterize the biodiesel fuel more precisely, it calculated the chemical formula using its content and composition in fatty acids. The fatty acid composition of biodiesel fuel is summarized in Table 5, leading to an estimation of its chemical formula: C18,61 H35,65 O2. Therefore, the stoichiometric fuel-to-air ratio was also determined as 1/12.50. Biodiesel fuel has a higher density than diesel, which means that for an equal volume, more mass is introduced. Nevertheless, the blends were made volumetrically.
4. Results and discussion of injection rate study The first step of this study consisted of the fact that biodiesel could have some effects on the engine’s injection system which could be a reason for admitting differences in the engine’s performance. Biodiesel has different physicochemical properties compared to diesel so its behaviour in the
Table 6 – Injection rate tests matrix. Injection pressure [MPa]
Injector energizing time [ms]
30
0.5 1.0 2.0 Multiple injection
80
0.5 1.0 2.0 Multiple injection
160
0.5 1.0 2.0 Multiple injection
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biomass and bioenergy 33 (2009) 941–947
Table 7 – Injection rate results for diesel, B30, B50 and B100. Injection pressure [MPa] Aperture time [ms] Diesel injection rate [mg/st] B30 injection rate [mg/st] B50 injection rate [mg/st] B100 injection rate [mg/st]
30 0.5 1.0 1.1 1.0 0.8
1.0 7.8 8.1 7.9 7.1
2.0 22.3 22.0 22.3 21.4
80 0.510 þ 2.420 27.6 28.0 27.8 27.6
0.5 8.4 8.2 8.2 8.3
1.0 26.0 26.2 25.5 25.9
2.0 47.7 47.3 48.1 48.2
160 0.337 þ 1.230 32.3 32.2 32.4 32.7
0.5 15.5 15.3 15.7 15.2
1.0 39.0 39.2 39.4 39.2
Fig. 4 – Injection rate for 160 MPa and 2.0 ms for all fuel blends.
Fig. 5 – Injection rate for 160 MPa and multiple injection times for all fuel blends.
2.0 71.9 71.5 71.8 71.7
0.220 þ 0.670 30.9 29.1 28.1 30.5
biomass and bioenergy 33 (2009) 941–947
system could affect diesel engines’ performance. In our case, we were interested in studying injection rate differences (amount and shape) between the fuels: related with if the demanded pressure rail could be maintained and if the injector could deliver the same amount of fuel for all 4 blends. Table 6 presents a summary of the tests performed and Table 7, the results of injection rate for each blend. Fig. 4 shows the results obtained for 160 MPa of injection pressure and 2.0 ms of energizing time and Fig. 5, results for multiple injection rate tests performed at 160 MPa. As it can be seen, there are no significant differences between the rail pressure and the injection rate for all 4 blends. Biodiesel fuel has a higher viscosity than diesel which tends to retard the fuel flow in the combustion chamber, so low quantity of biodiesel is injected. On the other hand, biodiesel fuel has higher density than diesel fuel which implies more fuel mass for the same volume injected. The counteracting effects of these two parameters could explain why there are no differences between both fuel injection rates in a high pressure common-rail system.
5.
Summary and conclusions
This study was done in order to evaluate the effects of biodiesel blends in a diesel engine without any modification and respecting the Euro III standards. Initially, a complete characterization of all the fuels used and a study about the engine’s common-rail injection system behaviour were performed. Main conclusions of this previous study are that: - From the point of view of the injection system, there are no significant differences between B30, B50, B100 and diesel fuel related neither to the shape nor to the quantity of fuel injected. - High pressure common-rail systems seem to be very appropriate for biodiesel fuel to minimize different behaviour associated to its different values of viscosity and density compared to diesel. - In the second part of the paper, the engine performance results (torque, power and fuel consumption) and contaminant emissions (NOx, CO, PM and THC) are presented using a diesel engine equipped with this same common-rail injection system fuelled with biodiesel blends. Knowing that the injection system is injecting the same quantity of fuel despite the blend used, the common-rail injection system can be considered as a neutral system in this study. So any differences occurring during the test could not be associated to this type of injection system.
Acknowledgments Thanks are due to BIONOR for supporting this work and for supplying the fuel. Authors also would like to thank Salvador Torro´ for his help in the experiments.
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references
[1] Commission of the European Communities. Communication from the commission to the European Council and the European Parliament: an Energy Policy for Europe; 2007. [2] Babu AK, Devaradiane G. Vegetable oils and their derivatives as fuels for CI engines: an overview. SAE Paper 2003-01-0767; 2003. [3] Frondel M, Peters J. Biodiesel: a new Oildorado? Energy Policy, 2000;30:189–205. [4] Raneses AR, Glaser LK, Price JM, Duffield JA. Potential biodiesel markets and their economic effects on the agricultural sector of the United States. Industrial Crops and Products, 1999;9:151–62. [5] Lecho´n Y, Cabal H, de la Ru´a C, Lago C, Izquierdo L, Sa´ez RM, et al. Fase II: Ana´lisis de Ciclo de Vida Comparativo del Biodie´sel y del Die´sel. Energı´a y cambio clima´tico. CIEMAT/ASE/DJ – EO221/ 2. 1st ed. Madrid: Centro de publicaciones. Secretaria General Te´cnica Ministerio de Medio Ambiente; 2006. [6] Agarwal AK. Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines. Progress in Energy and Combustion Science, 2006;33:233–71. [7] Murillo S, Mı´guez JL, Portiro J, Granada E, Mora´n JC. Performance and exhaust emissions in the use of biodiesel in outboard diesel engines. Fuel, 2007;86:1765–71. [8] Kawano D, Ishii H, Goto Y, Noda A. Application of biodiesel fuel to modern diesel engine. National Traffic Safety and Environment Laboratory; 2006. SAE Paper 2006-01-0233. [9] Puhan S, Vedaraman N, Ram BVB. Mahua oil (Madhuca Indica seed oil) methyl ester as biodiesel-preparation and emission characteristics. Biomass and Bioenergy, 2004;28:87–93. [10] Rosca R, Rakosi E, Manolache G. Fuel and Injection characteristics for a biodiesel type fuel from waste cooking oil. SAE Paper 2005-01-3674. 2005. [11] Kegl B, Kegl M, Pehan S. Optimization of a fuel injection system for diesel and biodiesel usage. Energy and Fuels, 2008;22:1046–54. [12] Benajes J, Payri R, Molina S, Soare V. Investigation of the influence of injection rate shaping on the spray characteristics in a diesel common rail system equipped with a piston amplifier. Journal of Fluids Engineering – Transactions of the ASME, 2005;127:1102–10. [13] Dieselnet. Emissions standards. European union. Cars and light trucks, http://www.dieselnet.com/standards/eu/ld.php [accessed 07.01.09]. [14] Broatch A, Luja´n JM, Serrano JR, Pla B. Pollutants Instantaneous measurement and data analysis of engine-in-the-loop tests. THIESEL 2006 conference on thermo-and fluid dynamic processes in diesel engines. Valencia; September 2006. [15] Dieselnet. Emissions test cycles ECE 15 þ EUDC/NEDC, http://www.dieselnet.com/standards/cycles/ece_eudc.html [accessed 07.01.09]. [16] Arre`gle J, Bermu´dez V, Serrano JR, Fuentes E. Procedure for engine transient cycle emissions testing in real time. Experimental Thermal and Fluid Science, 2006;30:485–96. [17] Rodrı´guez Ferna´ndez J. Estudio Bibliogra´fico y experimental de las emisiones y prestaciones de un motor trabajando con biodiesel. PhD Dissertation. Departamento de Meca´nica Aplicada e Ingenierı´a de Proyectos. Castilla-La-Mancha University; 2007. [18] Lapuerta M, Agudelo JR. Utilizacio´n de combustibles alternativos en motores te´rmicos -Mo´dulo II. Servicio de publicaciones de la E.T.S.I.I. de la Universidad de Castilla-La-Mancha; 2004. [19] Bozbas K, Mah C, Sok H. Biodiesel as an alternative motor fuel: production and policies in the European Union. Renewable and Sustainable Energy Reviews, 2008;12:542–52. [20] Shaine Tyson K. Biodiesel handling and use guidelines. Golden, CO: The National Renewable Energy Laboratory of United States; 2001. NREL/TP-580–30004.
Available at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Comparative analysis of a DI diesel engine fuelled with biodiesel blends during the European MVEG-A cycle: Preliminary study (I) J.M. Luja´n, B. Tormos*, F.J. Salvador, K. Gargar CMT-Motores Te´rmicos, Universidad Polite´cnica de Valencia, Valencia, Spain
article info
abstract
Article history:
The present work consists of introducing the tests and facilities used to perform
Received 19 February 2008
a comparative analysis of a diesel engine working with different blends of biodiesel fuel
Received in revised form
during the New European Driving Cycle. Furthermore, as a preliminary study, it was
31 January 2009
interesting to know the effects of biodiesel fuel on a common-rail high pressure injection
Accepted 10 February 2009
system, those more useful in modern light duty diesel engines, as a consequence of its
Published online 5 March 2009
different physicochemical properties compared with conventional diesel fuel. As the real goal of the study is to compare fairly performance and emissions from the engine, it was
Keywords:
essential to know any injection effects owed to fuel’s own characteristics that finally would
Biodiesel fuel
affect those parameters that will be evaluated.
Fuel characterization
A complete fuel characterization for diesel and biodiesel fuels, as the EN 590 and the EN
Injection rate
14214 standard specifications, was performed in order to quantify the differences between
Common-rail injection system
both fuels. A priori, it could be thought that viscosity and density values will be the most
New European driving cycle
significant parameters capable of altering the injection rate. As positive results, it was
Engine pollutant measurements
obtained that the common-rail high pressure injection system was totally blind in the
Engine performance
injection rate measurements, even the significant differences between both fuels, taking into account the counterbalancing effects generated by two parameters mentioned before. The second part of the study deals with engine performance and pollutant emissions on an unmodified common-rail turbocharged diesel engine running with biodiesel fuel blends during the New European Driving Cycle. ª 2009 Elsevier Ltd. All rights reserved.
1.
Introduction
As said in the European Commission [1], in spite of the actual high cost of biodiesel production, biofuels are now the only way to reduce our fossil fuel dependence in the transport field. Thus, biodiesel is emerging as a strong contender, and is becoming commercially available despite the fact that it is available in limited quantities and in a determined number of countries [2]. Besides, the production of biodiesel from vegetable oils can help to the reactivation of the agricultural sector
as another financial force. In the case of Mediterranean countries, where vegetable oil is widely consumed in cooking, the reutilization of the wasted oil to produce biodiesel can also contribute to make biodiesel more attractive from an environmental and financial point of view [3,4]. Its application is very effective in reducing harmful emissions and particularly CO2 emissions due to its carbon neutral cycle. A study from the CIEMAT in Spain (Centro de Investigaciones Energe´ticas, Medioambientales y Tecnolo´gicas) regarding CO2 emissions showed a reduction between a 75% and a 90% in the Fuel Life
* Corresponding author. Tel.: þ34 96 387 7650; fax: þ34 96 387 7659. E-mail address: [email protected] (B. Tormos). 0961-9534/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2009.02.004
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Cycle Analysis using biodiesel fuel instead of conventional diesel fuel [5]. Another benefit of biodiesel fuels is to be an oxygenated fuel leading to a better and clean combustion [6]. Unfortunately, Murillo et al. stated that this content of oxygen and the lack of carbon and hydrogen content seem to be the reason why biodiesel presents such a lower heating value compared to diesel [7]. Other studies conclude after several tests that both torque and power outputs of biodiesel fuel are lower than those for diesel fuel throughout all engine speeds [8,9]; effects due to the lower heating value of the biodiesel. Main target of this work was to obtain a comparative analysis of performance and emissions of a commercial modern diesel engine under transient operation. In order to do this, an important experimental setup and detailed testing procedures are required. Furthermore, complete characterizations of fuels used on the test are also required in order to perform a clear comparison. Taking into account literature references about the effects of biodiesel blends on the classic mechanical injection systems, it was considered proper to perform a preliminary study to evaluate the effects on injection rate of using biodiesel blends in a modern common-rail injection system. In engines using mechanical injection systems controlled by a mechanical pump, the cyclic fuel delivery, pressure wave propagation time, average injection rate and maximum pressure during injection seemed to be significantly affected when pure biodiesel is used as said by Rosca et al. [10]. Kegl et al. also said that at the same initial design, the injection pressure and injection rate are higher and the needle opens earlier for neat biodiesel when using a mechanically controlled fuel injection system [11]. So the tests performed on the common-rail injection system were done in order to evaluate injection rate of diesel and biodiesel fuels for different injection pressure or injection time strategies.
2. Experimental facilities and test procedures The experimental facilities consists of a common-rail injection system test bed relating to the comparative study of injection rate measurements and a four cylinder diesel engine and specific engine test bed totally equipped to perform the measurements of engine’s performance and emissions. Facilities and test procedures are described in subsequent section.
2.1.
Common-rail injection system test bed
In order to evaluate injection rate differences between diesel and biodiesel fuel, a Bosch flowmeter was used to determine the injection rate using standard values of pressure and excitation time (Fig. 1). The Bosch method is based on the principle of pressure wave propagation in a column of liquid [12]. An injector is emptied directly in a very long tube of constant diameter filled with fuel. Then, the generated wave is propagated along the tube while the wave associated pressure is measured with a pressure sensor placed at the exit of the injector. Once arrived at the end of the tube, the wave is reflected and returned towards the injector. Tube’s length is
Fig. 1 – Bosch method measurement test bed.
calculated so that the considered wave can arrive at the pressure sensor only after the total emptying of the injector. The study was performed at 3 different injection pressures: 30, 80 and 160 MPa and at 3 different aperture times of the nozzle: 0.5, 0.1 and 2.0 ms. Latest engines generally work at very high injection pressure, but measuring the injection rate at 30 MPa contributes to evaluate the effect of biodiesel at low injection pressure where the differences could be more appreciable.
2.2.
Engine setup for transient mode measurements
The engine test bed is described in Fig. 2. A HSDI (High Speed Direct Injection) 4-cylinder, 1.6-l, turbo diesel engine with high pressure fuel injection common-rail system, oxidation catalyst and particulate filter meeting the EURO III regulations for light duty vehicles were employed [13]. The engine’s specifications are shown in Table 1. The engine is coupled with a Shenck–Pegasus dynamometer controlling online engine torque and speed. The software used is named as XONE, and is able to program the driving condition of the vehicle. By means of this software, the MVEG-A cycle is programmed as a time sequence for gears and vehicle speeds taking into account the vehicle features and current driver skills. In order to perform possible modifications of any of the engine’s parameters, its Engine Control Unit (ECU) is totally opened and the engine settings maps can be recalibrated with the ETAS INCA Software. The installation counts with a series of temperature, pressure and air mass flow sensors in order to precisely control the engine.
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Opacimeter AVL 439
Dynamometer
Data acquisition and control system ECU Exhaust gas analysers
VNT
Oxidation DPF Catalyst
Intake CO2 (NDIR) CO2 (NDIR) CO (NDIR) HC (HFID)
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necessary given the fact that the Diesel Particle Filter intake must be, at least at a distance of six times the diameter of the exhaust pipe from the turbine. Furthermore, measured emissions without the after-treatment system gave us information on the way biodiesel fuel affects engine’s neat emissions and allows us to extend our results to old vehicles, devoided of after-treatment system. Measuring emissions with the aftertreatment system was useful to evaluate biodiesel effects on the vehicle’s emissions. Finally, after comparing the two sets of results, a clear post-treatment system characterization, regarding the biodiesel content in the fuel was performed.
EGRv
NOx (CLA)
2.3.
Performance and emissions test procedure
Cooler
Fig. 2 – Engine test bed.
Fuel consumption is determined by a fuel gravimetric system, the AVL 733S Dynamic Fuel Meter. It consists of a measuring vessel filled with fuel suspended on a balance system. Fuel consumption values are then obtained by calculating the vessel’s time related weight loss. As the response time of this system was too long for the study, a calibration of the fuel consumption signal provided by the ECU was performed in steady state, so the ECU is also used as a second fuel consumption measuring system [14]. Related to emissions, Fig. 2 also shows a diagram of the layout of the equipment during the tests. Exhaust gases were analyzed with and without after-treatment devices. Emissions (CO, CO2, O2, THC and NOx) were directly measured in each location by engine exhaust gas analyzer – HORIBA MEXA 7100EGR. The exhaust line is directly joined to the equipment through a pipe in which the temperature is maintained at 191 C in order to avoid hydrocarbons’ condensation. The hydrocarbons are analyzed using a HFID (Heated Flame Ionisation Detector), the nitrogen oxides using a HCLD (Heated ChemiLuminiscent Detector), the carbon monoxide just as carbon dioxide using a NDIR detector (Non Dispersive InfraRed) and the AVL model 439 Opacimeter measured the opacity of the exhaust gases. All the instruments meet the requirements of European Union Directives and International Standards Organisation. Measuring with and without after-treatment system in spite of before and after the after-treatment system was
Table 1 – Diesel engine characteristics. Engine specifications Type Swept volume Cylinders Valves Bore stroke Compression ratio Turbocharger Fuel injection system Max. power Max. torque
HSDI 1.6 l 4 Cylinders 4 Valves/cylinder 75 88.3 mm 18:1 Variable geometry turbocharger Common rail 82 kW/4000 rpm 245 Nm/2000 rpm
Tests have been performed with different fuel compositions from pure petroleum diesel fuel to pure biodiesel fuel. In this sense, conventional diesel fuel, B30, B50 and B100 are the fuels tested in this study. Besides, the emission’s levels of key pollutants are measured with and without the oxidation catalyst and particulate filter. This allows identifying the effect of biodiesel in both engine raw emissions and the pollutants emitted by the vehicle. Emission certification of light duty engines in Europe takes place in a test bed reproducing a European cycle named MVEG-A (European Motor Vehicle Emission Group A) which simulates road load conditions. At the beginning of the test, the room, the engine coolant and the oil temperature should be between 20 and 30 C. The temperature chosen was 22 C approximately. The first part of the cycle is known as UDC (Urban Driving Cycle) consisting of four ECE-15 segments of 200 s each and where the objective is to simulate cold start and car conduction in a city. It represents low vehicle speed (max. 50 km h1), low engine load and low exhaust gas temperature. In order to simulate the car driving in highways, it has been added a second cycle after the fourth ECE-15 cycle: the EUDC (Extra Urban Driving Cycle) which is a 400 s segment where the car can reach 120 km h1 [15]. Usually, the New European Driving Cycle is performed on a chassis dynamometer with a real vehicle. In our case, the Driving Cycle is a simulation of the original test and is performed on an engine dynamometer where all the parameters of the vehicle (weight, geometry, aerodynamic coefficient, etc.) can be entered. It is important to note that the MVEG-A cycle specifies the vehicle speed and demanded gear, so, for a given vehicle, the time sequence of engine speed and torque is the same for any fuel used. Fig. 3 shows the engine torque evolution during the MVEG-A cycle. It can be observed that the torque curves coincide for any fuel used in the study. Therefore, tests have been carried out under iso-power conditions. While iso-power tests allow establishing comparisons in order to obtain the best fuel under the point of view of engine homologation, the analysis of the results becomes more difficult. Effectively, differences obtained in iso-power tests are not exclusively dependent on the fuel type since the injected quantities and control conditions between tests are not equal. Finally, it should be noted that this kind of tests require severe test schedule and procedures in order to reduce the influence of external factors on engine measurements, especially pollutant emission measurements. In this sense, of this study the test schedule and the data pre-processing method detailed in Refs. [14,16]
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Diesel B30 B50 B100 Vehicle Speed
150
Torque (Nm)
80
50 0
40
-50
Vehicle Speed (km h-1)
100
120
0 0
200
400
600
800
1000
1200
Time (s)
Fig. 3 – Engine torque measurements during the MVEG-A cycle.
have been followed. In addition, some specific measures have been taken into account because of the particular properties of biodiesel. In order to prevent possible problems reported by other authors concerning plugging and gumming of filters,
lines and injectors [6,2], the engine fuelling system was completely emptied and fuel filters were replaced before performing tests with any fuel blend.
3. Table 2 – Main fuels characteristics. Diesel fuel Biodiesel fuel (B100) Summarized formula Molecular weight [g mol1] Oxygen content [% w] Cetane number Density at 15 C [kg m3] Viscosity at 40 C [mm2 s1] Sulphur content [mg kg1] H/C ratio Lower heating value [MJ kg1] CFPP [ C]
C15.27 H27.33 210.96 0 51.52 843.0 2.847 27.9 1.79 42.834 7
C18.61 H35.65 O2 293.26 10.91 54.50 881.4 4.173 0.2 1.91 35.910 3
Fuel properties
Biodiesel fuel is the result of a transesterification process of a vegetable oil. This process consists of a catalyzed reaction between a triglyceride (vegetable oil) and an alcohol in order to produce glycerol and ester. In Europe, the biodiesel produced from the transesterification process should respect the EN 14214. A complete characterization, according to the EN 590 and the EN 14214, for diesel and biodiesel fuels respectively, was performed to the fuel involved in the test by an external laboratory. Additionally, measurements of the heating value and other parameters were done at the CMT-Motores Te´rmicos and are presented in Table 2 (the European Standard EN 14214 nor the EN 590 do not precise heating value as a characteristic value).
Table 3 – Biodiesel fuel full properties (EN 14214). Tests Ester content Flash point Carbon residue on 10% distillation residue Sulphated ash content Water content Total contamination Copper strip corrosion (3 h at 50 C) Oxidation stability at 110 C Acid value Iodine value Linolenic acid methyl ester Polyunsaturated (4 double Bonds) methyl ester Methanol content Monoglyceride content Diglyceride content Triglyceride content Free glycerol Total glycerol Group I metals (Na þ K) Group II metals (Ca þ Mg) Phosphorus content
Units
Test methods
Results
EN 14214 standard
% (m/m) C % (m/m) % (m/m) mg kg1 mg kg1 Rating h mgKOH/g – % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) % (m/m) mg kg1 mg kg1 mg kg1
EN ISO 14103:03 EN ISO 3679/04 EN ISO 10370/96 ISO 3987 EN ISO 12937:01 ISO 12662:1999 EN ISO 2160/99 EN 14112/03 EN 14104 EN 14111/03 EN 14103 — EN ISO 14110:03 EN ISO 14105:03 EN ISO 14105:03 EN ISO 14105:03 EN 14105/03 EN 14105/03 EN 14108/03 EN 14108/03 EN ISO 14107:03
99.3 165.0 <0.04 <0.007 352 5.1 1a 14.4 0.26 105 1.2 <1.0 <0.01 <0.25 <0.05 <0.05 0.02 <0.10 <0.5 <0.5 <0.5
96.5 min. 120 min. 0.30 max. 0.02 max. 500 max. 24 max. Class 1 6.0 min. 0.50 max. 120 max. 12.0 max. 1 max. 0.20 max. 0.80 max. 0.20 max. 0.20 max. 0.02 max. 0.25 max. 5.0 max. 5.0 max. 10.0 max.
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Table 4 – Diesel fuel full properties (EN 590). Tests
Units
Cetane index Polycyclic aromatic hydrocarbons Distillation Recovered at 65% Recovered at 85% Recovered at 95% Flash point Carbon residue on 10% distillation residue Lubricity Water content Total contamination Ash content Copper strip corrosion (3 h at 50 C) Oxidation stability, 110 C ASTM colour
– % (m/m)
EN ISO 4264/98 EN ISO 12916:00 EN ISO 3405:01
C C C C % (m/m) mm mg kg1 mg kg1 % (m/m) Rating g m3 Rating
The bibliography assumes a reduction of about 13–14% for biodiesel heating value compared with diesel (referred to mass units) due to its high oxygen content and its lower carbon and hydrogen content [17]. For this study, it was intentionally chosen a low heating-value biodiesel fuel coming from wasted oil in order to observe the results in the worst of the possible cases. Diesel fuel net heating value was about 42.83 MJ Kg1 compared with the one of biodiesel which was about 35.91 MJ Kg1 representing a 16% reduction. Complete fuels characterization can be seen in Tables 3 and 4. In general terms, biodiesel fuel presents lower sulphur content, higher flash point and lower total contamination values compared to diesel fuel [18]. This very low or zero content of sulphur lead to that sulphur pollutants (SO2) generated in biodiesel emissions are much lower than the emission of conventional fuels [19]. The biodiesel’s flash point is usually higher than diesel fuel, but besides this property, the European Standards limit its value to ensure that the manufacturer has correctly removed excess methanol used in the manufacturing process. Water and sediment content are important characteristics because of corrosion and microorganism development during storage. The engine fuel system has to be protected too, so the copper strip corrosion test is a limitation about prolonged contact between copper and bronze with biodiesel that could degrade the fuel and cause sediment formation. Carbon residue is an indication of the carbon-depositing tendency of the fuel. The acid number is an
Table 5 – Composition and concentration of fatty acids in biodiesel fuel. Fatty acids
Concentration
Triglyceride
Methyl ester
Oleic acid Linoleic acid Palmitic acid Stearic acid Myristic acid
40.10% 39.90% 11.70% 4.20% 2.30% 1.30% 0.5%
C18 C18 C16 C18 C14 C13 C19
C19 C19 C17 C19 C15 C14 C20
Total
100%
H34 O2 H32 O2 H32 O2 H36 O2 H28 O2 H26 O2 H38 O2
Test methods
H36 O2 H34 O2 H34 O2 H38 O2 H30 O2 H28 O2 H40 O2
ASTM D-93/02a EN ISO 10370/96 EN ISO 12156/01 EN ISO 12937:01 ISO 12662:1999 EN ISO 6245/03 EN ISO 2160:99 EN ISO 12205:96 ASTM D-1500/04a
Results
EN 590 Standard
49.6 3.4
46.0 min. 11 max.
294.5 329.2 357.0 66.5 <0.04 356 92 20 < 0.007 1a <1.0 0.5
250 min. 350 max. 360 max. 55 min. 0.30 max. 460 max. 200 max. 24 max. 0.01 max. Class 1 max. 25 max. 2 max.
indicator of free fatty acids and can be very high if the fuel is not properly manufactured. A higher acid number could reduce life of fuel pumps and filters. Free and total glycerine content informs about the presence of glycerine in the fuel as well as reflects the conversion degree of the oil into biodiesel [20]. In order to characterize the biodiesel fuel more precisely, it calculated the chemical formula using its content and composition in fatty acids. The fatty acid composition of biodiesel fuel is summarized in Table 5, leading to an estimation of its chemical formula: C18,61 H35,65 O2. Therefore, the stoichiometric fuel-to-air ratio was also determined as 1/12.50. Biodiesel fuel has a higher density than diesel, which means that for an equal volume, more mass is introduced. Nevertheless, the blends were made volumetrically.
4. Results and discussion of injection rate study The first step of this study consisted of the fact that biodiesel could have some effects on the engine’s injection system which could be a reason for admitting differences in the engine’s performance. Biodiesel has different physicochemical properties compared to diesel so its behaviour in the
Table 6 – Injection rate tests matrix. Injection pressure [MPa]
Injector energizing time [ms]
30
0.5 1.0 2.0 Multiple injection
80
0.5 1.0 2.0 Multiple injection
160
0.5 1.0 2.0 Multiple injection
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Table 7 – Injection rate results for diesel, B30, B50 and B100. Injection pressure [MPa] Aperture time [ms] Diesel injection rate [mg/st] B30 injection rate [mg/st] B50 injection rate [mg/st] B100 injection rate [mg/st]
30 0.5 1.0 1.1 1.0 0.8
1.0 7.8 8.1 7.9 7.1
2.0 22.3 22.0 22.3 21.4
80 0.510 þ 2.420 27.6 28.0 27.8 27.6
0.5 8.4 8.2 8.2 8.3
1.0 26.0 26.2 25.5 25.9
2.0 47.7 47.3 48.1 48.2
160 0.337 þ 1.230 32.3 32.2 32.4 32.7
0.5 15.5 15.3 15.7 15.2
1.0 39.0 39.2 39.4 39.2
Fig. 4 – Injection rate for 160 MPa and 2.0 ms for all fuel blends.
Fig. 5 – Injection rate for 160 MPa and multiple injection times for all fuel blends.
2.0 71.9 71.5 71.8 71.7
0.220 þ 0.670 30.9 29.1 28.1 30.5
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system could affect diesel engines’ performance. In our case, we were interested in studying injection rate differences (amount and shape) between the fuels: related with if the demanded pressure rail could be maintained and if the injector could deliver the same amount of fuel for all 4 blends. Table 6 presents a summary of the tests performed and Table 7, the results of injection rate for each blend. Fig. 4 shows the results obtained for 160 MPa of injection pressure and 2.0 ms of energizing time and Fig. 5, results for multiple injection rate tests performed at 160 MPa. As it can be seen, there are no significant differences between the rail pressure and the injection rate for all 4 blends. Biodiesel fuel has a higher viscosity than diesel which tends to retard the fuel flow in the combustion chamber, so low quantity of biodiesel is injected. On the other hand, biodiesel fuel has higher density than diesel fuel which implies more fuel mass for the same volume injected. The counteracting effects of these two parameters could explain why there are no differences between both fuel injection rates in a high pressure common-rail system.
5.
Summary and conclusions
This study was done in order to evaluate the effects of biodiesel blends in a diesel engine without any modification and respecting the Euro III standards. Initially, a complete characterization of all the fuels used and a study about the engine’s common-rail injection system behaviour were performed. Main conclusions of this previous study are that: - From the point of view of the injection system, there are no significant differences between B30, B50, B100 and diesel fuel related neither to the shape nor to the quantity of fuel injected. - High pressure common-rail systems seem to be very appropriate for biodiesel fuel to minimize different behaviour associated to its different values of viscosity and density compared to diesel. - In the second part of the paper, the engine performance results (torque, power and fuel consumption) and contaminant emissions (NOx, CO, PM and THC) are presented using a diesel engine equipped with this same common-rail injection system fuelled with biodiesel blends. Knowing that the injection system is injecting the same quantity of fuel despite the blend used, the common-rail injection system can be considered as a neutral system in this study. So any differences occurring during the test could not be associated to this type of injection system.
Acknowledgments Thanks are due to BIONOR for supporting this work and for supplying the fuel. Authors also would like to thank Salvador Torro´ for his help in the experiments.
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