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DI Diesel Engine Performance and Emissions from the Oxygen Enrichment of Fuels with Various Aromatic Content Theodoros C. Zannis† and Dimitrios T. Hountalas* Internal Combustion Engines Laboratory, Thermal Engineering Section, School of Mechanical Engineering, National Technical University of Athens, 9 Heroon Polytechniou Street, Zografou Campus, 157 80 Athens, Greece Received September 17, 2003. Revised Manuscript Received February 2, 2004
An experimental investigation was conducted on a direct injection diesel engine using conventional and oxygenated diesel fuels. The main scope is to examine the effect of fuel oxygen enhancement for fuels with various aromatic content on engine performance characteristics and, mainly, on pollutant emissions. A mixture of diethylene glycol dimethyl ether (diglyme) and diethylene glycol dibutyl ether (butyl-diglyme) of approximately 20% by mass were added to a high-paraffinics and two commercial diesel fuels of varying aromatic fractions. An experimental apparatus was installed and engine tests were carried out on a naturally aspirated DI diesel engine at various operating conditions. The measurements were comprised of cylinder pressure diagrams, fuel consumption, exhaust smokiness, and exhaust gas emissions (nitrogen oxides, unburned hydrocarbons, and carbon monoxides). According to the experimental findings, the addition of oxygenated agents results in earlier initiation of combustion and in an increase of maximum combustion pressure, mainly due to the increase of cetane number. Fuel oxygen enrichment results in an increase of brake specific consumption and a reduction of combustion duration. The addition of glycol ethers in the diesel fuels is accompanied by a significant decrease of soot opacity and a reduction of carbon monoxides and unburned hydrocarbons with a small penalty on nitrogen oxides. The relative change of diesel exhaust emissions and bsfc caused by the fuel oxygen enhancement depends almost entirely on the engine operating conditions without association with total aromatic percentage. Finally, the fuel oxygen addition appears to be more effective in the reduction of soot, CO, and HC emissions than is the decrease of fuel aromatic content.
Introduction The reduction of environmental pollutants from direct injection diesel engines is dictated by the continuously stringent environmental regulations. These mandates have directed the interest of diesel engine manufactures and the scientific community toward the development of clean-burning diesel fuels. A promising technique to reduce gaseous and particulate emissions from diesel engines is to optimize fuel chemical composition and physical properties.1,2 By this approach, significant improvements in the emission behavior not only of newly developed diesel engines but also of the existing vehicle fleet can be attained. The use of diesel fuels with suppressed aromatic content and the oxygenation of diesel fuels using oxygenated additives have been acknowledged as two efficient solutions for reducing mainly soot and particulate emissions.1-5
According to the literature, CO, HC, and aldehyde emissions depend on cetane number, NOx emissions are controlled by fuel density,and PAHs and smoke are directly related to the aromatic content.6 Prior studies have revealed that measured soot emissions from both direct and indirect injection diesel engines correlate well with the percentage of fuel-contained aromatics.1-4 These investigations showed that the increase of aromatic content negatively affects the NOx and CO emissions, while they demonstrated an interrelation between diaromatic content and HC emissions.1-5 A promising alternative to fuel reformulation with respect to reduction of diesel exhaust emissions is to increase the incylinder oxygen concentration. Earlier studies have revealed a significant decrease of particulate emissions with increasing oxygen molar concentration inside the intake air.7,8 However, this
* Author to whom correspondence should be addressed. Dimitrios T. Hountalas, Professor Assoc. for Internal Combustion Engines. Tel: (+30210) 772-1259. Fax: (+30210) 772-3475. E-mail: dx1961@ central.ntua.gr. † E-mail:
[email protected]. (1) Lepperhoff, G.; Baecker, H.; Pungs, A.; Petters, K.-D. 9th International Symposium for Transport and Air Pollution, Avignon, France, 2000. (2) Baecker, H.; Pungs, A.; Pischinger, S.; Petters, K.-D.; Lepperhoff, G. 3rd International Fuels Colloquium; Esslingen, Germany, 2001.
(3) Ladommatos, N.; Xiao, Z.; Zhao, H. Proc. Instn. Mech. Engrs. J. Automobile Eng. 2000, 214 (D), 779-794. (4) Kouremenos, D. A.; Hountalas, D. T.; Pariotis, E. G.; Papagiannakis, R. G. Society of Automotive Engineers, 2000; No. 2000-01-1172. (5) Xiao, Z.; Ladommatos, N.; Zhao, H. Proc. Instn. Mech. Engrs. J. Automobile Eng. 2000, 214 (D), 307-332. (6) Martin, B.; Aakko, P.; Beckman, D.; Del Giacomo, N.; Giavazzi, F. Society of Automotive Engineers, 1997; No. 972966. (7) Marr, W. W.; Sekar, D. E.; Cole, R. L.; Marciniak, T. J.; Longman, D. E. Society of Automotive Engineers, 1993; No. 932805.
10.1021/ef0301598 CCC: $27.50 © 2004 American Chemical Society Published on Web 03/30/2004
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approach showed a considerable penalty in NOx emissions and failed to induct more oxygen in the fuel-rich areas of the jet to prevent formation of soot. On the other hand, it has been demonstrated that the use of methanol, ethanol, ethers, methylals, and carbonates as oxygenated fuel additives reduces considerable particulate and soot emissions.1-3,5-14 Studies in laminarpremixed flames have identified the profound influence of fuel-bounded oxygen on the reduction of the molar concentration of PAH species and soot.15 The decrease of exhaust smoke correlates quite well with increasing oxygen content and, according to some researchers, is not affected by changes in the additive type or blending ratio.12 Recent studies have demonstrated that the previous observation is valid for oxygenated compounds with low molecular weight and one or two oxygen atoms in their molecule.12,16 However, other studies have shown that the rate of decrease of soot emissions varies with engine type, operating conditions, and the type of additive used, especially in cases of fuels with complex molecular structure and multiple oxygen atoms.15-18 The addition of oxygen within fuel generally results in a decrease of particulates, smoke, CO, and HC emissions with small penalties in NOx emissions. In fact, smokeless operation has been reported in the literature with the use of pure dimethyl ether, diglyme, or tri-propylene glycol methyl ether.12,19-21 In the past, researchers doubted that it is possible to reduce soot and NOx emissions with only the use of oxygenated fuels and they have implied that it was necessary to use simultaneously oxygenated additives and high EGR ratios to obtain the desired results.22-24 However, the use of EGR weakens and, for high ratios, diminishes the effect of fuel quality on diesel exhaust emissions. In fact, there are reported cases where reductions in smoke, particulates, NOx, CO, and HC emissions with only the use of glycol ethers were (8) Donahue, R. J.; Foster, D. E. Society of Automotive Engineers, 2000; No. 2000-01-05. (9) Liotta, F. J., Jr.; Montalvo, D. M. Society of Automotive Engineers, 1993; No. 932734. (10) Ullman, T. L.; Spreen, K. B.; Mason, R. L. Society of Automotive Engineers, 1994; No. 941020. (11) Bertoli, C.; Del Giacomo, N.; Beatrice, C. Society of Automotive Engineers, 1997; No. 972972. (12) Miyamoto, N.; Ogawa, H.; Nurun, M. N.; Obata, K.; Arima, T. Society of Automotive Engineers, 1998; No. 980506. (13) Vertin, K. D.; Ohi, J. M.; Neageli, D. W.; Chldress, K. H.; Hagen, G. P.; McCarthy, C. I.; Cheng, A. S.; Dibble, R. W. Society of Automotive Engineers, 1999; No. 1999-01-1508. (14) Bertola, A.; Boulouchos, K. Society of Automotive Engineers, 2000; No. 2000-01-2885. (15) Inal, F.; Senkan, S. M. Combust. Sci. Technol. 2002, 174 (9), 1-19. (16) Choi, C. Y.; Reitz, R. D. Fuel 1999, 78, 1303-1317. (17) Beatrice, C.; Bertoli, C.; Del Giacomo, N.; Migliaccio, M. N. Society of Automotive Engineers, 1999; No. 1999-01-3595. (18) Mueller, C. J.; Martin, G. C. Society of Automotive Engineers, 2002; No. 2002-01-1631. (19) Sorenson, S. C.; Mikkelsen, S.-E. Society of Automotive Engineers, 1995; No. 950064. (20) Kajitani, S.; Chen, Z. L.; Konno, M.; Rhee, K. T. Society of Automotive Engineers, 1997; No. 972973. (21) Mueller, C. J.; Pickett, L. M.; Siebers, D. L.; Pitz, W. J.; Westbrook, C. K.; Martin, G. C. Society of Automotive Engineers, 2003; No. 2003-01-1791. (22) Murayama, T.; Zheng, M.; Chikahisa, T.; Oh, Y.-T.; Fujiwara, Y.; Tosaka, S.; Yamashita, M.; Yoshitake H. Society of Automotive Engineers, 1995; No. 952518. (23) Wang, H. W.; Huang, Z. H.; Zhou, L. B.; Jiang, D. M.; Yang, Z. L. Proc. Instn. Mech. Engrs. J. Automobile Eng. 2000, 214 (D), 503508. (24) Song, J.; Cheenkachorn, K.; Wang, J.; Perez, J.; Boehman, A. L.; Young, P.-J.; Waller, F. J. Energy Fuels 2002, 16, 294-301.
Zannis and Hountalas
attained.12,25 Studying the literature, a lack of information is witnessed concerning the effect of fuel aromatic composition in cases where oxygenated constituents were added to conventional diesel fuels to decrease exhaust smoke, CO, and HC emissions. In the present study, an attempt is made to investigate the effect of oxygen enrichment of diesel fuels with various aromatic percentages on DI diesel engine performance characteristics and exhaust emissions. Emphasis is given to examining the influence of the aromatic content of the basic blending compound (baseline fuel) on the emission behavior of the resulting oxygenated fuels. For this reason, an experimental apparatus comprised of a single cylinder direct injection diesel engine was installed at the authors’ laboratory, and tests were conducted at various operating conditions using three conventional and three oxygenated fuels. The three oxygenated fuels are the blending result of each one of the conventional fuels with a mixture of glycol ethers, all having an oxygen content of approximately 6% by mass and an increasing aromatic content ranging from
