Energy Fuels 2009, 23, 6168–6180 Published on Web 09/16/2009
: DOI:10.1021/ef9006356
Biodiesel Emissions from a Baseline Engine Operated with Different Injection Systems and Exhaust Gas Recirculation (EGR) Strategies during Transient Sequences Octavio Armas,* Arantzazu G omez, and Marı´ a D. Cardenas Escuela T ecnica Superior de Ingenieros Industriales, Universidad de Castilla La Mancha, Edificio Polit ecnico, Av. Camilo Jos e Cela s/n. 13071, Ciudad Real, Spain Received June 23, 2009. Revised Manuscript Received August 28, 2009
This work is focused on the measurement and analysis of biodiesel emissions resulting from two commercial diesel engines derived from the same baseline engine. One of the engines was equipped with a rotary fuel injection pump electronically controlled. Another engine was equipped with a common-rail injection system. Both engines were tuned by the manufacturer with diesel fuel, and each of them was optimized with different exhaust gas recirculation (EGR) strategies. Both engines were tested under several transient conditions. A methyl ester obtained from unused sunflower oil was tested as diesel fuel, pure and blended with 30 and 70% of a commercial diesel fuel, which was also used pure. The engines were mounted in a test bench prepared for operating under transient conditions. An AVL 439 smoke meter and an Environnement gas analyzer allowed for the study of the effect of these fuels on the variations of the engine emissions with time. The consideration of the thermochemical properties of the tested fuels and the engine parameters, such as fuel/air ratio or EGR ratio, were used for the analysis of the results. The studied engine transient processes were (a) a load increase at constant engine speed and (b) an engine speed decrease at constant torque. The obtained results proved that the biodiesel effect on pollutant emissions during transient conditions depends upon the fuel injection system and EGR strategy used during the engine tuning. produced by diesel engines working in steady1-9 and transient conditions.10-14 Reviewing an important number of studies, Lapuerta et al.15 observed a great consensus when it affirms that the biodiesel fuel produces an important particulate matter (PM) emission decrease. In the case of nitrogen oxides (NOx) emissions, some researchers have not observed the effect produced by biodiesel, while other authors observe a slight increase of this emission when biodiesel fuel is used. In general, most of the studies reviewed by Lapuerta et al.15 show hydrocarbon (HC) emission decreases when the biodiesel fuel is used. The most important reasons that have been used to explain the reductions of PM emissions when biodiesel or biodiesel blends are used are the following: the oxygen content of the biodiesel molecule, which enables more complete combustion even in regions of the combustion chamber with fuel-rich diffusion flames16-18 and promotes the oxidation of the
Introduction During the past decade, an important number of experimental works have been published that have studied the effect of different biodiesels on performance and pollutant emissions *To whom correspondence should be addressed. E-mail: octavio.
[email protected]. (1) Puhan, S.; Vedaraman, N.; Sankaranarayanan, G.; Bharat Ram, B. V. Performance and emission study of mahua oil (madhuca indica oil) ethyl ester in a 4-stroke natural aspirated direct injection diesel engine. Renewable Energy 2005, 30, 1269–1278. _ (2) Yucesu, H. S.; Ilkilic -, C. Effect of cotton seed oil methyl ester on the performance and exhaust emission of a diesel engine. Energy Sources, Part A 2006, 28, 389–398. (3) Cardone, M.; Prati, M. V.; Rocco, V.; Seggiani, M.; Senatore, A.; Vitolo, S. Brassica carinata as an alternative oil crop for the production of biodiesel in Italy: Engine performance and regulated and unregulated exhaust emissions. Environ. Sci. Technol. 2002, 36 (21), 4656–4662. (4) Ramadhas, A. S.; Muraleedharan, C.; Jayaraj, S. Performance and emission evaluation of a diesel engine fueled with methyl esters of rubber seed oil. Renewable Energy 2005, 30, 1789–1800. (5) Boehman, A. L.; Song, J.; Alam, M. Impact of biodiesel blending on diesel soot and the regeneration of particulate filters. Energy Fuels 2005, 19, 1857–1864. (6) Canakci, M. Performance and emissions characteristics of biodiesel from soybean oil. Proc. Inst. Mech. Eng., Part D 2005, 7, 915–922. (7) Lapuerta, M.; Rodrı´ guez-Fernandez, J.; Agudelo, J. R. Diesel particulate emissions from used cooking oil biodiesel. Bioresour. Technol. 2007, DOI: 10.1016/j.biortech.2007.01.033. (8) Shaheed, A.; Swain, E. Combustion analysis of coconut oil and its methyl esters in a diesel engine. Proc. Inst. Mech. Eng., Part A 1999, 213 (5), 417–425. (9) Lapuerta, M.; Armas, O.; Ballesteros, R.; Fernandez, J. Diesel emissions from biofuels derived from Spanish potential vegetable oils. Fuel 2005, 84, 773–780. (10) Graboski, M. S.; Ross, J. D.; McCormick, R. L. Transient emissions from no. 2 diesel and biodiesel blends in a DDC series 60 engine. SAE Tech. Pap. 961166. (11) Graboski, M. S.; McCormick, R. L.; Alleman, T. L.; Herring, A. M. The effect of biodiesel composition on engine emissions from a DDC series 60 diesel engine. National Renewable Energy Laboratory (NREL), Golden, CO, 2003; NREL/SR-510-31461. r 2009 American Chemical Society
(12) Martini, G.; Astorga, C.; Farfaletti, A. Effect of biodiesel fuels on pollutant emissions from LD diesel vehicles. Institute for Environment and Sustainability (IES), Ispra, Italy, 2005. (13) Turrio-Baldassarri, L.; Battistelli, C. L.; Conti, L.; Crebelli, R.; De Berardis, B.; Iamiceli, A. L.; Gambino, M.; Iannaccone, S. Emission comparison of urban bus engine fuelled with diesel oil and biodiesel blend. Sci. Total Environ. 2004, 327, 147–162. (14) Armas, O.; Hernandez, J. J.; Cardenas, M. D. Reduction of diesel smoke opacity from vegetable oil methyl esters during transient operation. Fuel 2006, 85, 2427–2438. (15) Lapuerta, M.; Armas, O.; Rodrı´ guez-Fernandez, J. Effect of biodiesel fuels on diesel engine emissions. Prog. Energy Combust. Sci. 2008, 34, 198–223. (16) Lapuerta, M.; Armas, O.; Ballesteros, R. Diesel particulate emissions from biofuels derived from Spanish vegetable oils. SAE Tech. Pap. 2002-01-1657, 2002. (17) Graboski, M. S.; McCormick, R. L. Combustion of fat and vegetable oil derived fuels in diesel engines. Prog. Energy Combust. Sci. 1998, 24, 125–164. (18) Wang, W. G.; Lyons, D. W.; Clark, N. N.; Gautam, M.; Norton, P. M. Emissions from nine heavy trucks fuelled by diesel and biodiesel blend without engine modification. Environ. Sci. Technol. 2000, 34 (6), 933–939.
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: DOI:10.1021/ef9006356
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already formed soot, the lower stoichiometric need of air in the case of biodiesel combustion,16,19 which reduces the probability of fuel-rich regions in the non-uniform fuel/air mixture, the absence of aromatics in biodiesel fuels, with those being considered soot precursors,16,18 the combustion advance derived from the use of biodiesel, which enlarges the residence time of soot particles in a high-temperature atmosphere and, in the presence of oxygen, promotes further oxidation,20,21 the different structure of soot particles between biodiesel and diesel fuels, which may also favor the oxidation of soot from biodiesel,22 the nil sulfur content of most biodiesel fuels, which prevents sulfate formation, with this being a significant component of typical diesel PM,16,18 and the scrubbing effect, by which sulfur becomes an active center for hydrocarbon adsorption on the soot surface,23 and finally, the usually lower final boiling point of biodiesel, despite its higher average distillation temperature, providing a lower probability of soot or tar from being formed from heavy hydrocarbon fractions unable to vaporize.16 Concerning NOx emissions, the most important arguments used in the literature to explain the observed increases when using biodiesel fuels are the followings: the advance of the start of injection20,24 explained by different reasons, the higher flame temperature of biodiesel fuel,16,17 the characteristics of the injected fuel, which may have some influence on the delay time, on the premixed/diffusion combustion ratio and, in consequence, on the nitric oxide (NO) formation, the reactions governing the prompt mechanism of NO formation that are sensitive to the concentration of radicals, which could be higher during the combustion of biodiesel, and the reduced soot formation, which could eliminate the reactions between carbon and nitric oxide. The most important reasons used in the literature to explain the observed HC emissions decreases when using biodiesel fuels are the followings: the oxygen content in the biodiesel molecule, which leads to a more complete and cleaner combustion,25,26 the higher cetane number of biodiesel,26,27 which reduces the combustion delay and, subsequently, has been
the higher distillarelated to decreases in HC emissions, tion temperature for final fuel fractions that have been reported for diesel fuel,30,31 which may not be completely vaporized and burnt, thereby increasing HC emissions, the advanced injection and combustion timing when using biodiesel,32 the possibility of a flame ionization detector (FID) conventionally used for measuring these emissions to have a lower sensibility detecting oxygenated compounds, such as the ones that might be present in the exhaust gas when using an oxygenated fuel-like biodiesel,26 and finally, the possibility that the temperature sampling line temperature (usually 190 °C) between the exhaust pipe and the measuring instrument may not be high enough to avoid the HC condensation;21,26 therefore, these hydrocarbons could condensate and not reach the FID. Several studies have analyzed the effect on emissions of different technological changes in a diesel engine using fossil diesel fuel. A lower compression ratio has been related to higher HC emissions and lower NOx emissions, because of lower maximum pressure in the combustion chamber.33-36 The exhaust gas recirculation (EGR) has been a widely used method for reducing NOx emissions by its effect on the reduction of the combustion temperature, although this technique produces higher PM emissions.36-38 The high injection pressures and low nozzle diameters, characteristic of the last generations of common-rail systems, have improved the quality of the air-fuel mixture and combustion process and, in consequence, reduced PM, NOx, and HC emissions and improved fuel economy.36,37 Additionally, different injection strategies, such as split injection or optimized timing, can reduce diesel emissions.37-39 For these reasons, when biodiesel and its blends are used as diesel fuel, the different engine configurations and strategies provoke different behavior on pollutant emissions. Graboski and McCormick,17 analyzing results from other works, observed that NOx and PM emissions varied in a range between þ10 and -65%, respectively, (29) Abd-Alla, G. H.; Soliman, H. A.; Badr, O. A.; Abd-Rabbo, M. F. Effects of diluent admissions and intake air temperature in exhaust gas recirculation on the emissions of an indirect injection dual fuel engine. Energy Convers. Manage. 2001, 42, 1033–1045. (30) Murillo, S.; Mı´ guez, J. L.; Porteiro, J.; Granada, E.; Moran, J. C. Performance and exhaust emissions in the use of biodiesel in outboard diesel engines. Fuel 2007, DOI: 10.1016/j.fuel.2006.11.031. (31) Turrio-Baldassarri, L.; Battistelli, C. L.; Conti, L.; Crebelli, R.; De Berardis, B.; Iamiceli, A. L.; Gambino, M.; Iannaccone, S. Emission comparison of urban bus engine fuelled with diesel oil and biodiesel blend. Sci. Total Environ. 2004, 327, 147–162. (32) Storey, J. M.; Lewis, S. A.; West, B. H.; Huff, S. A.; Slucer, C. S.; Wagner, R. M.; Domingo N.; Thomas, J.; Kass, M. Hydrocarbon species in the exhaust of diesel engines equipped with advanced emissions control devices. CRC Project AVFL-10b-2, 2005. (33) Tsukahara, M.; Yoshimoto, Y. Reduction of NOx, smoke, BSFC, and maximum combustion pressure by low compression ratios on a diesel engine fuelled by emulsified fuel. SAE Tech. Pap. 920464. (34) Sobotowski, R. A.; Porter, B. C.; Pilley, A. D. The development of a novel variable compression ratio, direct injection diesel engine. SAE Tech. Pap. 910484. (35) Kohketsu, S.; Mori, K.; Kato, T.; Sakai, K. Technology for low emission, combustion noise and fuel consumption on diesel engine. SAE Tech. Pap. 940672. (36) Akmadza, F. Status of the Euro 5/6 legislation and impact on passenger cars engine development and after treatment technology. Diesel Emissions Conference, Frankfurt, Germany, 2007. (37) Pierpont, D. A.; Montgomery, D. T.; Reitz, R. D. Reducing particulate and NOx using multiple injections and EGR in a DI diesel. SAE Tech. Pap. 950217. (38) Hikosaka, N. A view of the future of automotive diesel engines. SAE Tech. Pap. 972682. (39) Kastner, O.; Atzler, F.; Muller, A.; Weigand, A.; Wenzlawski, K.; Zellbeck, H. Multiple injection strategies and their effect on pollutant emission in passanger car diesel engines. THIESEL, 2006.
(19) Armas, O.; Rodrı´ guez, J.; Cardenas, M. D.; Agudelo, A. F. Efecto del biodiesel procedente de aceites vegetales usados sobre las emisiones y prestaciones de un motor diesel. Anales del XVI Congreso Nacional de Ingenierı´ a Mecanica, Le on, Spain, 2004 (in Spanish). (20) Cardone, M.; Prati, M. V.; Rocco, V.; Seggiani, M.; Senatore, A.; Vitolo, S. Brassica carinata as an alternative oil crop for the production of biodiesel in Italy: Engine performance and regulated and unregulated exhaust emissions. Environ. Sci. Technol. 2002, 36 (21), 4656–4662. (21) Schmidt, K.; Van Gerpen, J. H. The effect of biodiesel fuel composition on diesel combustion and emissions. SAE Tech. Pap. 961086. (22) Boehman, A. L.; Song, J.; Alam, M. Impact of biodiesel blending on diesel soot and the regeneration of particulate filters. Energy Fuels 2005, 19, 1857–1864. (23) Dur an, A.; Monteagudo, J. M.; Armas, O.; Hernandez, J. J. Scrubbing effect on diesel particulate matter from transesterified waste oils blends. Fuel 2006, 85, 923–928. (24) Tat, M. E.; Van Gerpen, J. H. Measurement of biodiesel speed of sound and its impact on injection timing. National Renewable Energy Laboratory (NREL), Golden, CO, 2003; NREL/SR-510-31462. (25) Handbook of biodiesel: Emissions reductions with biodiesel, 1999 (available online at http://www.cytoculture.com/Biodiesel%20Handbook.htm). (26) Pinto, A. C.; Guarieiro, L. L. N.; Rezende, J. C.; Ribeiro, N. M.; Torres, E. A.; Lopes, E. A.; Pereira, P. A. P.; Andrade, J. B. Biodiesel: An overview. J. Braz. Chem. Soc. 2005, 16 (6B), 1313–1330. (27) Hansen, K. F.; Jensen, M. G. Chemical and biological characteristics of exhaust emissions from a DI diesel engine fuelled with rapeseed oil methyl ester (RME). SAE Tech. Pap. 971689. (28) Monyem, A.; Van Gerpen, J. H.; Canakci, M. The effect of timing and oxidation on emissions from biodiesel-fueled engines. Trans. ASAE 2001, 44 (1), 35–42.
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: DOI:10.1021/ef9006356
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Figure 1. Scheme of the experimental facilities. Table 1. Main Specifications of the Tested Engines engine code emission normative fuel injection system injection pressure number and relative position of injections EGR system maximum EGR ratio (%) maximum-rated power (kW) maximum-rated torque (N m) cylinders bore (mm) stroke (mm) swept volume (L) compression ratio a
1
2
Euro 2 rotary pump electronically managed 200 bar at idle (at 750 min-1) 1100 bar at full load (at 2000 min-1) 1 main injection after TDCa
