lable at ScienceDirect Renewable Energy 72 (2014) 236e242 Contents lists avai Renewable Energy journal homepage: www.elsevier .com/locate/renene Fuel economy and emissions of light-duty vehicles fueled with ethanolegasoline blends in a Mexican City Marcel Hernandez 1, Lizette Menchaca, Alberto Mendoza* Department of Chemical Engineering, Tecnologico de Monterrey, Campus Monterrey, Ave. Eugenio Garza Sada 2501, Monterrey, Nuevo Le�on, 64849, Mexico a r t i c l e i n f o Article history: Received 6 December 2013 Accepted 14 July 2014 Available online Keywords: Mobile sources Exhaust emissions Emission factor Air pollution Biofuels * Corresponding author. Tel.: þ52 81 8158 2091; fa E-mail addresses:
[email protected], A com (A. Mendoza). 1 Present address: Department of Biotechnology Tecnol�ogico de Monterrey, Campus Estado de M�exico, Km. 3.5, Atizap�an de Zaragoza, Estado de M�exico, 52 http://dx.doi.org/10.1016/j.renene.2014.07.018 0960-1481/© 2014 Elsevier Ltd. All rights reserved. a b s t r a c t The government of Mexico is mandating increased use of gasolineeethanol blends as a method for reducing air pollution. However, tests on light-duty vehicles have revealed mixed results in terms of fuel economy and emissions. In addition, little information on the performance of light-duty vehicles fueled by gasolineeethanol blends exists outside the conditions in Mexico City. Fuel economy and emission factors for commercial Regular (87 octane) and Premium (92 octane) gasoline were compared to cor- responding 5% v/v (E05R/E05P) and 15% v/v (E15R/E15P) ethanol blends under the conditions in Mon- terrey, Mexico, the third largest urban center in the country. Fuel economy was estimated under real- world driving conditions. CO2, CO, NOx, and unburned hydrocarbons (HC) emissions were measured for cold- and hot-start tests, as well as for constant-speed (40 km/h) real in-city driving. The highest fuel economy was achieved with pure gasoline, which decreased by as much as 4.4% when an E05R gasoline blend was used and as much as 9.9% when an E15R blend was evaluated. For the Premium blends, the fuel economy decrease was lower: 2.9% and 5.5%, respectively. Even more significantly, the newest ve- hicles tested experienced the lowest decrease in fuel economy. Overall, the Premium blends, and in particular the E15P blend, resulted in decreased CO, NOx, and HC emissions. However, mixed results for NOx emissions were obtained during the start tests. In addition, HC emissions were higher for the Premium blends compared to the corresponding Regular blends. CO2 emissions changes were not sig- nificant for the constant-speed tests. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction One of the most important arguments in favor of the use of ethanolegasoline blends in light-duty vehicles is the blends' po- tential for reducing air pollutant emissions. A significant percent- age of this decrease (on a mass basis) is related to the direct and indirect emission of greenhouse gases (mainly CO2). However, the actual overall life-cycle benefit of using biomass-derived ethanol in fuel blends is still unclear [1e3]. Emission co-benefits include the expected reduction of other air pollutants: unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx ¼ NO þ NO2), and fine particulate matter. However, there is disagreement on this issue [3]. Some, in fact, argue that in countries like Mexico, Tier 1 x: þ52 81 8328 4250. lberto.Mendoza.1971@gmail. and Chemical Engineering, Carretera Lago de Guadalupe 926, M�exico. and Tier 2 regulations should be favored since they provide significantly higher benefits compared to ethanolegasoline blends [4,5]. Ethanol, an oxygenate additive, has been studied extensively. Ethanol is an additive that increases octane [6,7] and has been proven to increase the Reid vapor pressure, which facilitate cold starts [8,9]. Higher thermal efficiency and pressure inside the cyl- inders have also been achieved for ethanol-oxygenated fuels [10]. This improved combustion performance counteracts the lower heating value of the fuel blends (provoked by the lower heating value of ethanol), increasing the fuel consumption only marginally and thus the direct CO2 emissions [11e13]. At the same time, a decrease in CO emissions has been observed while HC and NOx have had mixed results [10,12,14]. Data in the literature reveals a tendency, albeit inconsistent, for NOx emissions to increase when ethanol content increases [15]. This increase could be explained by the higher temperatures observed in the combustion chambers [10,14]. In addition, the emissions of other unregulated organic compounds are affected. Burning ethanolegasoline blends tends to increase the concentration of formaldehyde, acetaldehyde, acetone, Delta:1_- Delta:1_given name Delta:1_surname mailto:
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[email protected] http://crossmark.crossref.org/dialog/?doi=10.1016/j.renene.2014.07.018&domain=pdf www.sciencedirect.com/science/journal/09601481 http://www.elsevier.com/locate/renene http://dx.doi.org/10.1016/j.renene.2014.07.018 http://dx.doi.org/10.1016/j.renene.2014.07.018 http://dx.doi.org/10.1016/j.renene.2014.07.018 M. Hernandez et al. / Renewable Energy 72 (2014) 236e242 237 and acetic acid in combustion gases [16e21]. The maximum ben- efits, in terms of emissions decreases in the most abundant polluting species in exhaust gases (CO2, CO, HC, NOx), have been attained with 15 vol. % to 30 vol. % ethanolegasoline blends [7,9,12]. In Mexico, the federal government has made several efforts to reduce emissions from gasoline-powered vehicles. In the 1990s, unleaded gasoline blends with methyl tert-butyl ether (MTBE) as oxygenate and with limits set for benzene, total aromatics, olefin volatility, and sulfur content were introduced [21]. A limited number of studies were performed before, during, and after the new fuel was introduced; therefore, the effects were not precisely quantified [22,23]. Standards to limit the emission of CO, HC, and NOx for new vehicles were instituted in 2001 and, since then, have been revised. However, air pollution has remained a major envi- ronmental problem in the largest cities. The Law for the Promotion and Development of Biofuels is the most recent attempt by the Mexican government to improve air quality. The law requires a reformulation of gasoline using ethanol as oxygenate [5]. Few studies have assessed the direct potential benefits of using ethanolegasoline blends in Mexican vehicles, and all have been conducted for the prevailing conditions of Mexico City (19� 250 1000 N, 99� 80 4400 W; average elevation 2240 m above sea level [masl]) [5,24,25]. In this paper, we analyze the results for ethanol-gasoline fuel blends used in Monterrey, Mexico. Monterrey is located in northeastern Mexico (25� 400 1700 N, 100� 180 3100 W; average elevation 540 masl). It is the third largest metropolitan area of the country (3.93 million inhabitants) and the second largest industrial center in Mexico, with a vehicle fleet of more than 1.7 million units. Currently, Monterrey has some of the worst air quality in the country: The city is in non-attainment status for the 1-h Mexican Air Quality Standard for O3 and the air quality standards for sus- pended particulate matter with aerodynamic diameter of less than 10 microns. The possible effects on fuel economy and emissions during cold starts, hot starts, and constant-speed driving conditions in Monterrey were examined for ethanolegasoline blends. 2. Experimental methods 2.1. Fuel characterization Fuel economy and emission measurement experiments were performed for six different fuel types. Regular (87 octane, R) and Premium (92 octane, P) base gasoline was blended with reagent- grade anhydrous ethanol to produce the fuel blends tested. The E05R and E05P blends contained 95% vol. Regular or Premium gasoline, respectively, and 5% vol. ethanol, while E15R and E15P were 15% vol. ethanolegasoline blends. The results for these four blends were compared to commercial gasoline (i.e., commercial Regular and Premium gasoline). The ethanol content was selected based on the future content of Mexican gasoline [5] and an amount that has proven to give good results without the need to modify existing engines [26]. The blends were prepared using a three-necked glass vessel connected to three peristaltic pumps. The pumps fed the appro- priate amount of ethanol and gasoline into a container inwhich the mixture was blended. The outlet of the container was connected to a receptacle in which the reformulated fuel was collected. No ad- ditives were required to prevent phase separation [27]. The entire system was hermetically sealed to prevent humidity absorption by the anhydride ethanol. The physicochemical properties of the ethanol-free gasoline and E15 blends were evaluated. The E05 mixtures were not measured since their physicochemical properties do not vary significantly from the original corresponding commercial gasoline [28]. The following properties of the mixtures were measured: oxygenate content (ASTM D-5599), research and motor octane numbers (ASTM D-2699/ASTM D-2700), Reid vapor pressure (ASTMD-5191), distillation curve (ASTM D-86), oxidation stability (ASTM D 525), and density (ASTM-D-218). Each sample was analyzed in triplicate. All measurements were conducted by the Southwest Research Institute (San Antonio, Texas). Finally, the heating value was determined using an ignition calorimeter (PARR Model 6200) following the ASTM-D240-02(2007) method. 2.2. Fuel economy estimation To estimate fuel consumption (km/L), the fuel system, including the reservoir, pump, and tubing, was flushed before the tank was filled with a known volume. Real-world driving conditions were simulated using a circuit comprising freeway, arterial, and sec- ondary roads [29]. The complete circuit was 16.8 km long (Fig. 1). After the vehicle was driven in this cycle, the systemwas evacuated again to measure the amount of fuel left. The difference between the initial and final volumes was taken as the consumption. 2.3. Emissions characterization A Flexible Gas Analyzer onboard instrument (Snap On®, model AL293-001; Kenosha, WI, USA) was used to sample three light-duty vehicles (Table 1). All vehicles had a fuel supply system consisting of a normally aspirated electronic-controlled sequential multiport fuel injection system. Five species are measured with the instru- ment: CO2, CO, HC, O2, and NOx (Table 2). Additionally, the analyzer can be connected to the OBD2 port of the on-board computer of the vehicle to record engine speed. The instrument was calibrated us- ing a standard CAM-97 mid-range mixture containing 3200 ppm HC (propane), 8% CO, 12% CO2, 3000 ppm NO, and nitrogen as the balance. Leak checks were performed before each test. Emission factors were estimated based on the emissions and operational conditions readings, and the duration of each test, as described elsewhere [30]. Briefly, the average emission factor of pollutant i, Ei, in terms of mass emitted per kilometer traveled can be expressed as: Ei ¼ 1 l Ztf to Q � yiP RT Mi � dt (1) where Q is the volumetric flow of the combustion gases in the exhaust, yi is the molar fraction of pollutant i in the exhaust, P is the pressure, T is the temperature, R is the universal ideal gas constant, Mi is the molecular weight of species i, and l is the distance traveled during the test. Equation (1) was integrated for the duration of the test (toetf) since the time interval for every measurement regis- tered by the gas analyzer was 1 s. For the cold- and hot-start tests, Equation (1) was modified eliminating the traveled distance term (l) so the units were mass emitted for the total duration of the test ðE0iÞ. When the concentration of any given species was below the analyzer's detection limit, one-half of the detection limit concen- tration was used for estimation purposes. Cold-start emissions were measured after the engine was shut down for 12 h; hot-start tests were performed 10 min after the engine was shut down. In each test, the vehicles were first started, and after the pipelinewas purged for 15 s, the exhaust was sampled for 180 s. In all cases, the engine speed was left to attain idle levels (approximately 800 rpm). Emissions were estimated for the first 90 s of the test since this represents the time period when most of the emissions in this mode occur [31]. On-road emissions were measured by a single driver at constant speed (40 km/h) under Fig. 1. On-road driving cycle followed in the downtown MMA. M. Hernandez et al. / Renewable Energy 72 (2014) 236e242238 controlled conditions on a circuit used by driving schools. The tests were conducted with no other vehicles on the circuit, and the ve- locity was kept constant for three full laps (approximately 1 km/ lap). Each test mode (cold start, hot start, constant-speed driving) was repeated five times for each fuel blend and vehicle. All tests were performed between May and August, under prescribed times to ensure similar ambient conditions. 3. Results and discussion The physicochemical properties of the commercial gasoline and E15 blends are given in Table 3. Adding ethanol increased the oc- tane number and decreased the heating value of the blends, as expected [32]. The relative increase in octane content was greater for the gasoline with the lower initial octane number, as has been observed by others [33]. The Reid vapor pressure decreased when ethanol was added to Regular gasoline but increased when ethanol was added to Premium gasoline. This non-ideal behavior of the blends as a function of the composition has been reported by others as well [28,32,34]. In general, the distillation curves shifted to lower temperatures with the presence of ethanol; the largest changes Table 1 Test vehicles' characteristics. Vehicle model Gearbox Mileage (km) Displacement (L) Power (hp@rpm) Compression ratio 2004 Nissan Tsuru Manual 54,000 1.6 132@6400 9.5:1 2005 VW Derby Manual 95,500 1.8 98@5500 9.0:1 2008 Jeep Compass Automatic 4500 2.4 172@5400 10.5:1 occurred for T50 (the temperature at which 50% of the mixture evaporates). The initial boiling point changed only marginally. Additional details on the properties of the derived fuel blends can be found in Castillo-Hern�andez et al.’s work [27]. The fuel economy for each of the three vehicles used during the study is given in Table 4. The results represent the average of the five trips made by each vehicle over the circuit for every fuel blend presented in Fig. 1. In every case, the vehicle with the lowest displacement (smallest engine) had the highest fuel economy (level of significance, a ¼ 0.01, p value ¼ 0.000). All ethanolegasoline blends had lower fuel economy (a ¼ 0.01, p value ¼ 0.000) compared to the corresponding commercial fuel. The magnitude of the fuel economy reduction is in line with what others have esti- mated [10,14]. In general, the fuel economy decrease was greater when the vehicles used the ethanol-Regular gasoline blends instead of the corresponding ethanolePremium blends. Using ethanol in the newest vehicle (model year 2008) had less impact on fuel economy than on the older vehicles (model years 2004 and 2005). Table 2 Specifications of the portable emissions testing device. Species Range Precision Resolution HC 0e30,000 ppm ±3% 1 ppm O2 0e25% ±5% 0.01 ppm CO 0e15% ±3% 0.01 ppm CO2 0e20% ±3% 0.01 ppm NOx 0e5000 ppm ±4% 1 ppm Table 3 Physical and chemical properties of the commercial gasoline blends and E15 fuel blends used in this study. Fuel property Commercial gasoline E15 blends Regular Premium E15R E15P Ethanol content EtOH, % wt Fig. 2. Chemical composition of the exhaust gases of the 2004 Tsuru (left panel) and the 2008 Compass (right panel) during one cold-start test using ethanolepremium blends. M .H ernandez et al./ Renew able Energy 72 (2014) 236 e 242 240 Fig. 3. Average mass emission for (a) cold-start and (b) hot-start tests (grams emitted during the duration of the test: 90 s). Error bars indicate 95% confidence intervals for the mean. Table 5 Average emission factors (g/km) for the constant-speed driving mode.a Fuel Pollutant CO HC NOx Regular 2.87 ± 4.07 0.035 ± 0.022 0.038 ± 0.035 E05R 1.86 ± 2.03 0.024 ± 0.014 0.035 ± 0.022 E15R 1.33 ± 1.53 0.024 ± 0.011 0.035 ± 0.018 Premium 2.86 ± 1.13 0.051 ± 0.017 0.030 ± 0.040 E05P 1.65 ± 0.64 0.038 ± 0.016 0.023 ± 0.031 E15P 0.77 ± 1.15 0.032 ± 0.007 0.017 ± 0.019 a Uncertainty values (i.e., ± values) represent the standard deviation obtained by propagating the standard deviations associated with themeans of the three vehicles since they are independent (i.e., Var[y] ¼ S(1/3)2 Var[xi], where Var is the variance). M. Hernandez et al. / Renewable Energy 72 (2014) 236e242 241 HC, and NOx emissions were lower for the E05 and E15 blends compared to commercial gasoline. Premium blends provided higher decreases in CO and NOx emissions, but the HC emissions were higher compared to the corresponding Regular blends. Overall, Premium blends gave the best results in terms of fuel economy and, with the exception of HC, emission reductions. Acknowledgments This work was supported by Tecnol�ogico de Monterrey through grant number CAT-186 and the Consejo Nacional de Ciencia y Tecnología (CONACYT, Mexico). Marcel Hernandez and Lizette Menchaca received additional support (scholarship) through CONACYT. Appendix A. Supplementary material Supplementary data related to this article can be found online at http://dx.doi.org/10.1016/j.renene.2014.07.018. References [1] Niven RK. Ethanol in gasoline: environmental impacts and sustainability re- view article. Renew Sust Energ Rev 2005;9:535e55. [2] Farrell AE, Plevin RJ, Turner BT, Jones AD, O'Hare M, Kammen DM. Ethanol can contribute to energy and environmental goals. Science 2006;311:506e8. [3] Jacobson MZ. Review of solutions to global warming, air pollution, and energy security. Energy Environ Sci 2009;2:148e73. [4] Garcia CA, Manzini F, Islas J. Air emissions scenarios from ethanol as a gasoline oxygenate in Mexico city metropolitan area. Renew Sust Energ Rev 2010;14: 3032e40. [5] Schifter I, Díaz L, Rodríguez R, Salazar L. Assessment of Mexico’s program to use ethanol as transportation fuel: impact of 6%ethanol-blended fuel on emissions of light-duty gasoline vehicles. Environ Monit Assess 2011;173: 343e60. [6] Rasskazchikova TV, Kapustin VM, Karpov SA. Ethanol as high-octane additive to automotive gasolines. Production and use in Russia and abroad. Chem Technol Fuel Oil 2004;40:203e10. [7] da Silva R, Catalu~na R, de Menezes EW, Samios D, Piatnicki CMS. Effect of additives on the antiknock properties and Reid vapor pressure of gasoline. Fuel 2005;84:951e9. [8] Liao SY, Jiang DM, Cheng Q, Huang ZH, Wei Q. Investigation of the cold-start combustion characteristics of ethanol-gasoline blends in a constant-volume chamber. Energy Fuels 2005;19:813e9. [9] Chen RH, Chiang LB, Chen CN. Cold-start emissions of an SI engine using ethanol-gasoline blended fuel. Appl Therm Eng 2011;31:1463e7. [10] Bayraktar H. Experimental and theoretical investigation of using gasoline- ethanol blends in spark-ignition engines. Renew Energ 2005;30:1733e47. [11] Al-Hasan M. Effect of ethanol-unleaded gasoline blends on engine perfor- mance and exhaust emissions. Energ Convers Manag 2003;44:1547e61. [12] Balaji D, Govindarajan P, Venkatesan J. Emission and combustion character- istics of Si engine working under gasoline blended with ethanol oxygenated organic compounds. Am J Environ Sci 2010;6:495e9. [13] Costa RC, Sodr�e JR. Hydrous ethanol vs. gasoline-ethanol blend: engine per- formance and emissions. Fuel 2010;89:287e93. [14] Roayei E, Taheri K. Test run evaluation of a blend of fuel-grade ethanol and regular commercial gasoline: its effect on engine efficiency and exhaust gas composition. Clean Technol Environ Policy 2009;11:385e9. [15] Durbin TD, Miller JW, Younglove T, Huai T, Cocker K. Effects of fuel ethanol content and volatility on regulated and unregulated exhaust emissions for the latest technology gasoline vehicles. Environ Sci Technol 2007;41:4059e64. [16] Zervas E, Montagne X, Lahaye J. The influence of gasoline formulation on specific pollutant emissions. J Air Waste Manag Assoc 1999;49:1304e14. [17] Zervas E, Montagne X, Lahaye J. C1-C5 organic acid emissions from an SI engine: influence of fuel and air/fuel equivalence ratio. Environ Sci Technol 2001;35:2746e51. [18] Ban-Weiss GA, McLaughlin JP, Harley RA, Kean AJ, Grosjean E, Grosjean D. Carbonyl and nitrogen dioxide emissions from gasoline- and diesel-powered motor vehicles. Environ Sci Technol 2008;42:3944e50. [19] Pang X, Mu Y, Yuan J, He H. Carbonyls emission from ethanol-blended gaso- line and biodiesel-ethanol-diesel used in engines. Atmos Environ 2008;42: 1349e58. [20] Fayyad SM, Momani W, Abu-Ein SQ, Juditawy O, Abu-Rahmeh T. Experimental investigation of using fuel additives e alcohol. Res J Appl Sci Eng Technol 2010;2:164e9. [21] Schifter I, Diaz L, Avalos S, Vera M, Barrera A, Lopez-Salinas E. Effect of methyl tertiary butyl ether concentrations on exhaust emissions from gasoline used in the metropolitan area of Mexico city. J Air Waste Manag Assoc 2000;50: 488e94. [22] Bravo HA, Torres RJ. The usefulness of air quality monitoring and air quality impact studies before the introduction of reformulated gasolines in devel- oping countries. Mexico City, a real case study. Atmos Environ 2000;34: 499e506. [23] Bravo AH, Camacho RC, Roy-Ocotla GR, Sosa RE, Torres RJ. Analysis of the change in atmospheric urban formaldehyde and photochemistry activity as a result of using methyl-t-butyl-ether (MTBE) as an additive in gasolines of the metropolitan area of Mexico City. Atmos Environ 1991;25:285e8. [24] Schifter I, Vera M, Diaz L, Guzman E, Ramos F, Lopez-Salinas E. Environmental implications on the oxygenation of gasoline with ethanol in the metropolitan area of Mexico City. Environ Sci Technol 2001;35:1893e901. [25] Schifter I, Díaz L, Rodríguez R, Salazar L. Oxygenated transportation fuels. Evaluation of properties and emission performance in light-duty vehicles in Mexico. Fuel 2011;90:779e88. [26] Andersen VF, Anderson JE, Wallington TJ, Mueller SA, Nielsen OJ. Vapor pressures of alcohol-gasoline blends. Energy Fuels 2010;24:3647e54. [27] Castillo-Hern�andez P, Mendoza-Domínguez A, Caballero-Mata P. Analysis of physicochemical properties of Mexican gasoline and diesel reformulated with ethanol. Ing Invest Technol 2012;13:293e306. [28] Hatzioannidis I, Voutsas EC, Lois E, Tassios DP. Measurement and prediction of Reid vapor pressure of gasoline in the presence of additives. J Chem Eng Data 1998;43:386e92. [29] Frey HC, Unal A, Rouphail NM, Colyar JD. On-road measurement of vehicle tailpipe emissions using a portable instrument. J Air Waste Manag Assoc 2003;53:992e1002. http://dx.doi.org/10.1016/j.renene.2014.07.018 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref1 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref1 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref1 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref2 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref2 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref2 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref3 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref3 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref3 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref4 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref4 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref4 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref4 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref5 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref5 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref5 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http://refhub.elsevier.com/S0960-1481(14)00404-2/sref14 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref15 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref15 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref15 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref15 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref16 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref16 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref16 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref17 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref17 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref17 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref17 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref18 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref18 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref18 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref18 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref19 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref19 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref19 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref19 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref20 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref20 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref20 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref20 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref20 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref21 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref21 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref21 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref21 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref21 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref22 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref22 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref22 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref22 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref22 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref23 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref23 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref23 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref23 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref23 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref24 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref24 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref24 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref24 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref25 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref25 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref25 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref25 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref26 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref26 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref26 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref27 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref27 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref27 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref27 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref27 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref28 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref28 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref28 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref28 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref29 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref29 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref29 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref29 M. Hernandez et al. / Renewable Energy 72 (2014) 236e242242 [30] Menchaca-Torre HL, Mendoza-Dominguez A. Desempe~no de un vehículo híbrido y su contraparte de combusti�on interna bajo condiciones de manejo de una ciudad mexicana. Rev Int Contam Ambie 2013;29:219e30. [31] Graham LA, Noseworthy L, Fugler D, O'Leary K, Karman D, Grande C. Contri- bution of vehicle emissions from an attached garage to residential indoor air pollution levels. J Air Waste Manag Assoc 2004;54:563e84. [32] Ardenson JE, Kramer U, Mueller SA, Wallington TJ. Octane numbers of ethanol- and methanol-gasoline blends estimated from molar concentrations. Energy Fuels 2010;24:6576e85. [33] Keller JL. Alcohols as motor fuel? Hydrocarb Process 1979;58:127e38. [34] American Petroleum Institute. Alcohols and ethers: a technical assessment of their application as fuels and fuel components. 3rd ed. Washington, DC: API publication 4261; 2001. [35] Topgül T, Yücesu HS, Çinar C, Koca A. The effects of ethanol-unleaded gasoline blends and ignition timing on engine performance and exhaust emissions. Renew Energ 2006;31:2534e42. http://refhub.elsevier.com/S0960-1481(14)00404-2/sref30 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref30 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref30 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref30 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref30 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref30 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref31 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref31 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref31 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref31 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref32 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref32 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref32 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref32 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref33 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref33 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref34 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref34 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref34 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref35 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref35 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref35 http://refhub.elsevier.com/S0960-1481(14)00404-2/sref35 Fuel economy and emissions of light-duty vehicles fueled with ethanol–gasoline blends in a Mexican City 1 Introduction 2 Experimental methods 2.1 Fuel characterization 2.2 Fuel economy estimation 2.3 Emissions characterization 3 Results and discussion 4 Conclusions Acknowledgments Appendix A Supplementary material References