Effects of Methyl tert-Butyl Ether Addition to Base Gasoline on the

Energy & Fuels 2008, 22, 1341–1348

1341

Effects of Methyl tert-Butyl Ether Addition to Base Gasoline on the Performance and CO Emissions of a Spark Ignition Engine I˙smet Sezer* and Atilla Bilgin Mechanical Engineering Department, Faculty of Engineering, Karadeniz Technical UniVersity, 61080 Trabzon, Turkey ReceiVed October 6, 2007. ReVised Manuscript ReceiVed December 11, 2007

This study aims at investigating experimentally the effects of methyl tert-butyl ether (MTBE)-gasoline blends on the performance and CO emissions of a spark ignition engine. The blends are prepared by blending 5, 10, 15, and 20 vol % of MTBE with a specified amount of base gasoline. Base, leaded, and unleaded gasolines are also used in the study. The experiments were conducted under various engine speeds, spark timings, and compression ratios. The engine was operated under wide open throttle conditions. The results of the study show that a 10 vol % of MTBE addition to the base gasoline yields the best engine performance and the least CO emissions while the blend containing 15% MTBE and 85% base gasoline suggests the best performance in terms of the brake thermal efficiency.

1. Introduction The worldwide depletion of petroleum reserves, ever rising prices of crude oil, and growing environmental sensitivity have intensified the studies on alternative fuels.1–3 It has been expected that alternative fuels will decrease the dependency on petroleum based fuels and reduce the emitted harmful exhaust emissions. In that case, alternative fuels can either be replaced with the present fuels or be added to conventional fuels to improve the fuel properties and decrease their consumption.4 Oxygenates which contain oxygen in the molecular structure are a very suitable solution to improve the octane quality of gasoline and to ensure cleaner combustion.5–9 Essentially, the oxygenated compounds include a wide range of alcohols and ethers. However, the oxygenates used widely as gasoline additives are methanol, ethanol, and methyl tert-butyl ether * To whom correspondence should be addressed. Telephone: +90 462 377 29 50. Fax: +90 462 325 55 26. E-mail: [email protected]. (1) Kowalewicz, A.; Wojtyniak, M. Alternative fuels and their application to combustion engines. Proc. Inst. Mech. Eng., Part D 2005, 219 (1), 103–125. (2) Agarwal, A. K. Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines. Prog. Energy Combust. Sci. 2007, 33 (3), 233–271. (3) Bayraktar, H. Experimental and theoretical investigation of using gasoline-ethanol blends in spark-ignition engines. Renewable Energy 2005, 30 (11), 1733–1747. (4) Abu-Zaid, M.; Badran, O.; Yamin, J. Effect of methanol addition on the performance of spark ignition engines. Energy Fuels 2004, 18 (2), 312–315. (5) Nadim, F.; Zack, P.; Hoag, G. E.; Liu, S. United States experience with gasoline additives. Energy Policy 2001, 29 (1), 1–5. (6) Ancillotti, F.; Fattore, V. Oxygenate fuels: Market expansion and catalytic aspect of synthesis. Fuel Process. Technol. 1998, 57 (3), 163– 194. (7) Huang, Z.; Miao, H.; Zhou, L.; Jiang, D. Combustion characteristics and hydrocarbon emissions of a spark ignition engine fuelled with gasolineoxygenate blends. Proc. Inst. Mech. Eng., Part D 2000, 214 (3), 341–346. (8) Wang, C.-H.; Lin, S.-S.; Chang, H.-L. Effect of oxygenates on exhaust emissions from two-stroke motorcycles. J. EnViron. Sci. Health, Part A 2002, 37 (9), 1677–1685. (9) Iob, A.; Buenafe, R.; Abbas, N. M. Determination of oxygenates in gasoline by FTIR. Fuel 1998, 77 (15), 1861–1864.

(MTBE).10 The undesirable properties of alcohols that have dampened the interest for methanol and ethanol are as follows: high water solubility, which can cause phase separation problems; high Reid vapor pressure (RVP), which may lead the plugging of the fuel flow by increasing the vapor pressure;11 high volatility, which increases the volatile organic compounds emissions;12,13 high latent heat of vaporization, which brings about cold start and drivability matters;14 and low heating value.15 MTBE, on the other hand, retains all the benefits of methanol and ethanol without their drawbacks. In other words, MTBE blends with gasoline easily without any separation problem, gives high octane numbers, enhances the combustion of gasoline, and reduces the CO emissions.16,17 It is clearly evident that the addition of MTBE to gasoline is one of the most effective methods for the improvement of octane quality and the reduction of engine CO emissions. Therefore, there are numerous studies on the effects of MTBE–gasoline blends on a spark ignition (SI) engine performance and exhaust emissions.18–23 However, the number of studies performed with variable compression ratio (CR) engines is limited.19,22 As is well-known, (10) Al-Farayedhi, A. A.; Al-Dawood, A. M.; Gandhidasan, P. Experimental investigation of SI engine performance using oxygenated fuel. Trans. ASME: J. Eng. Gas Turbines Power 2004, 126 (1), 178–191. (11) da Silva, R.; Cataluna, R.; de Menezes, E. W.; Samios, D.; Piatnicki, C. M. S. Effect of additives on the antiknock properties and Reid vapor pressure of gasoline. Fuel 2005, 84 (7–8), 951–959. (12) de Menezes, E. W.; Cataluna, R.; Samios, D.; da Silva, R. Addition of an azeotropic ETBE/ethanol mixture in eurosuper-type gasolines. Fuel 2006, 85 (17–18), 2567–2577. (13) Pumphrey, J. A.; Brand, J. I.; Scheller, W. A. Vapour pressure measurements and predictions for alcohol-gasoline blends. Fuel 2000, 79 (11), 1405–1411. (14) Silva, N. R.; Sodre, J. R. Cold start and drivability characteristics of an ethanol-methyl-t-butyl ether blend fuelled vehicle. Proc. Inst. Mech. Eng., Part D 2001, 215 (5), 645–649. (15) Shenghua, L.; Clemente, E. R. C.; Tiegang, H.; Yanjv, W. Study of spark ignition engine fueled with methanol/gasoline fuel blends. Appl. Therm. Eng. 2007, 27 (11–12), 1904–1910. (16) Aboul-Fotouh, S. M. Production of antiknock additive in gasoline (Methyl Tert-Butyl Ether, MTBE) using zeolite catalysts. Acta Chim. SloV. 2004, 51 (2), 293–304. (17) Franklin, P. M.; Koshland, C. P.; Lucas, D.; Sawyer, R. F. Evaluation of combustion by-products of MTBE as a component of reformulated gasoline. Chemosphere 2001, 42 (5–7), 861–872.

10.1021/ef700592n CCC: $40.75  2008 American Chemical Society Published on Web 01/31/2008

1342 Energy & Fuels, Vol. 22, No. 2, 2008

Sezer and Bilgin

Table 1. Properties of the Fuels Used in This Study property chemical formula molecular weight (kg/kmol) oxygen percent (w %) density (kg/m3) boiling temperature (°C) Reid vapor pressure (psi) latent heat of vaporization (kJ/kg) lower heating value (kJ/kg) stoichiometric air-fuel ratio (AFRs) research octane number (RON) motor octane number (MON)

base

leaded

unleaded

MTBE

C6–8.3H13.1–18a 86–115a 710–740a

43075b 91a 80a

725–760a 26.7–225a 8–5 300–350a 42560b 14.5 95a 84a

C5H12O 88.15 18.2 758 55 7.8 340 35200 11.76 117 101

725–780a

41572b 95a 85a

a Obtained from a catalogue of the Turkish Petroleum Office Company. b Obtained from tests that were performed in a laboratory of the Department of Chemistry at KTU.

the whole effect of MTBE on engine performance and exhaust emissions can be determined by examining the MTBE-gasoline blends in SI engines at several operating conditions. For this reason, this study is devoted to investigate experimentally the effects of MTBE–gasoline blends on an SI engine performance and CO emissions at various CRs. A systematic experimental study was conducted with various MTBE-base gasoline blended fuels over a wide range of operating conditions such as various engine speeds, spark timings (STs), and CRs at a wide open throttle (WOT) condition. MTBE has been added to base gasoline, and the results obtained with these blends have been compared to those of base, leaded, and unleaded gasoline to determine the effect of the MTBE ratio on engine performance and CO emissions. 2. Experimental Section 2.1. Properties of the Fuels. In this study, Merck pure grade MTBE having a purity of 99.9% was used. Blended fuels were prepared by adding 5, 10, 15, and 20 vol % of MTBE to a certain amount of base gasoline. The blends were prepared just before starting the experiments to obtain a homogeneous mixture. Properties of MTBE, base, leaded, and unleaded gasolines are given in Table 1. 2.2. Experimental Setup and Test Procedure. The test bed consisted of a test engine, the measurement instruments, and a control panel. A schematic layout of the test bed is shown in Figure 1. The engine used in the experiments is a single cylinder, variable compression, four-stroke engine which can operate as an SI engine or a compression ignition engine by replacing the engine head. The major specifications of the engine are given in Table 2. The test engine is coupled to an electrical dynamometer, which is used to load the engine and measure the engine output torque. A calibrated burette and stopwatch were used to measure the engine fuel consumption. The mass flow rate of air was measured by means of an orifice and an inclined manometer. The concentration of CO emissions was measured with a “Gossen CO-Tester AG 50/4” gas (18) Song, C.-L.; Zhang, W.-M.; Pei, Y.-Q.; Fan, G.-L.; Xu, G.-P. Comparative effects of MTBE and ethanol additions into gasoline on exhaust emissions. Atmos. EnViron. 2006, 40 (11), 1957–1970. (19) Popuri, S. S.; Bata, R. M. A Performance study of iso-butanol-, methanol-, and ethanol-gasoline blends using a single cylinder engine; SAE Paper 932953; Society of Automotive Engineering Inc.: 1993. (20) Al-Dawood, A. M. Effect of blending MTBE, methanol, or ethanol with gasoline on performance and exhaust emission of SI engines. MS Thesis, King Fahd University, Dhahran, Saudi Arabia, 1998. (21) Al-Farayedhi, A. A.; Al-Dawood, A. M.; Gandhidasan, P. Effects of blending MTBE with unleaded gasoline on exhaust emissions of SI engine. J. Energy Resour. Technol. 2000, 122 (4), 239–247. (22) Hamdan, M. A.; Al-Subaih, T. A. Improvement of locally produced gasoline and studying its effects on both the performance of the engine and the environment. Energy ConVers. Manage. 2002, 43, 1811–1820. (23) Poulopoulos, S.; Philippopoulos, C. Influence of MTBE addition into gasoline on automotive exhaust emissions. Atmos. EnViron. 2000, 34 (28), 4781–4786.

Figure 1. Schematic layout of the experimental setup. Table 2. Engine Specifications cycle cooling system number of cylinders bore × stroke displacement volume compression ratio

four stroke water cooled 1 90 mm × 120 mm 763.4 cm3 variable (7.5–24.5)

analyzer connected to the exhaust pipe outlet. The analyzer serves a CO measurement range of 0–10% on a volume basis with a

Effects of MTBE Addition to Base Gasoline

Energy & Fuels, Vol. 22, No. 2, 2008 1343

Figure 2. Variations of uncertainties with engine speed.

resolution of 0.01%. The ambient pressure and temperature of the test room were measured by using a barometer and a thermometer, respectively. The experiments have been performed for the CRs of 7.5, 8, and 8.5 and the STs of 7.5, 10, and 12.5° before top dead center (BTDC). The engine was operated at WOT, and engine speed was varied from 900 to 1600 rpm via load adjustment. The carburetor setting, which was initially adjusted for base gasoline, was not varied throughout the experiments. The experimental data was recorded after the engine had reached the steady operation conditions. The brake torque, the flow rate of fuel, the mass flow rate of air, and the CO emissions were measured during the experiments, and these measured parameters have been used to calculate the engine performance parameters. Additionally, the wet- and drybulb temperatures of the ambient air and the atmospheric pressure were also measured during each test. Finally, the engine performance parameters were corrected to the standard atmospheric conditions by taking into account the measured bulb temperatures, atmospheric pressure, and humidity of the ambient air. The experimental calculations are presented in the next section, and further details can be found in refs 24 and 25.

The quantities in eq 3 such as h′, c′, o′, s′, and w′ represent the mass fraction of carbon, hydrogen, oxygen, sulfur, and water per unit mass of fuel, respectively. The stoichiometric air-fuel ratio and LHV of the blends is determined in a different manner as AFRs,bl )

∑ x F AFR ∑xF i i

Ne,1 ) Mdω

(1)

where ω ) πn/30 is the angular speed of the crankshaft. The calculated brake power is converted to the standard atmospheric conditions by taking into account the humidity Xhum of air and the standard atmospheric conditions P0 and T0 as Ne ) Ne,1

0.1013 P0

T0 X 293 hum

(2)

The humidity correction factor Xhum in eq 2 is determined from the psychometric chart considering the dry and wet thermometer bulb temperatures. The lower heating value (LHV) of the fuels is determined by using the Mendeleyev formula as in ref 24 LHV ) 1000[33.91c′ + 125.6h′ - 10.89(o′ - s′) 2.51(9h′ - w′)] (3) (24) Bilgin, A.; Durgun, O.; S¸ahin, Z. The effects of diesel-ethanol blends on diesel engine performance. Energy Sources 2002, 24, 431–440. (25) Durgun, O. Experimental methods in engines; lecture notes (in Turkish); Karadeniz Technical University: Trabzon, Turkey, 1995.

(4)

i i

The LHV of any blend can also be calculated from the following formula LHVbl )

∑ x F LHV ∑xF i i

i

(5)

i i

where the subscript i refers to gasoline or MTBE. 3.2. Economic Analysis. In this study, an economic evaluation of the blends is performed considering the unit cost of each fuel and blend per hour and effective power as in ref 26.

3. Calculations 3.1. Calculation of the Performance Parameters. The brake effective power is calculated using the following formula

s,i

Fb )

Fbl )

fbbsfcb Fb

(6)

∑ x f bsfc i i

bl

Fbl

(7)

Therefore, variations in the cost of fuel are determined as ∆F Fbl - Fb ) 100 Fb Fb

(8)

Consequently, taking the current prices of base gasoline and Merck pure grade MTBE in Turkey as $2.3/L and $40/L, respectively, the increments in the cost of blends compared with base gasoline have been determined as 79.15%, 159.4%, 235.3%, and 320.6% for MTBE5, MTBE10, MTBE15, and MTBE20, respectively. 3.3. Uncertainty Analysis. The results of the experiments calculated from the several measured physical quantities generally have certain uncertainties. Therefore, the results have uncertainties due to the uncertainties in the primary measurements. The method used for estimating the uncertainties in this study was developed originally by Kline and McClintock.27,28 According to this method, if the result R is a function of the independent variables x1, x2, ..., xn, it can be expressed as


Sezer and Bilgin

Figure 3. Variations of AEC at various operating conditions.

R ) R(x1, x2, ... , xn)

(9)

Then, the uncertainty in the result UR can be calculated by using the following root-sum-of-the-squares rules UR ) √UR,12 + UR,22 + · · · + UR,n2 )

∑ n

UR,i2

(10)

i)1

The UR,i values in the above equation, corresponding to the uncertainties of each measured quantity xi, are determined as follows: UR,i )

| |

∂R U ; (1 e i e n) ∂xi i

the brake thermal efficiency (bte), and 0.89–1.42% for the brake specific fuel consumption. Variations of these uncertainties with respect to engine speed are also given in Figure 2. It should be noted that the calculated uncertainties in the main engine characteristics do not have noticeable influences on the variation of the engine characteristics.

(11)

The above approximation is also called as partial uncertainty in the result because of the dependence on a measured quantity xi and its uncertainty Ui. The uncertainty in the torque, for example, comes from the measured force and the length of the moment arm, which have uncertainties of (0.5 N and (1 mm, respectively. Considering these uncertainties, the calculated uncertainty in the brake torque becomes 0.005% for the speed range of the test engine. The other uncertainties for the calculated engine characteristics are in the range of 0.44–0.46% for the effective power, 0.60–0.62% for the brake mean effective pressure (bmep), 0.91–1.52% for

4. Results and Discussion Figure 3 shows the variations of the air excess coefficient (AEC) with various operating parameters. Figure 3a shows the effect of engine speed on AEC for a CR of 8 and an ST of 10° BTDC. As seen from the figure, the AEC increases with increasing MTBE ratio up to 15%, so the maximum AEC value is obtained with the MTBE15 blend. The MTBE20 blend gives less AEC than the MTBE15 blend, and also the blends generally have higher AEC than pure gasolines. The leaded gasoline gives (26) Sezer, I˙. Experimental investigation of the effects of blending methanol and MTBE with regular gasoline on performance and exhaust emissions of SI engines. MS Thesis, Karadeniz Technical University, Trabzon, Turkey, 2002. (27) Holman, J. P. Experimental Methods for Engineers, 7th ed.; McGraw-Hill: New York, 2001. (28) Kostic, M. Unleashing Error or Uncertainty Analysis of Measurement Results. Presented at the NASA 2003 Faculty Fellowship program lecture series, Ohio Aerospace Institute, Cleveland, OH, Aug 1, 2003.



Figure 4. Variations of bmep at various operating conditions.

the top AEC values among the pure fuels while the unleaded gasoline has the lowest. The dependency of AEC on MTBE percentage is more clearly shown in Figure 3b for the same operating conditions as in Figure 3a and at an engine speed of 1400 rpm. The increase in AEC with increasing MTBE percentage can be attributed to a “leaning” effect of MTBE. As seen in Table 1, MTBE has a lower AFRs than gasoline because of the oxygen content in its basic form. Therefore, the addition of MTBE to base gasoline results in a reduction in AFRs for the blends compared to that for base gasoline. This means that the AFRa for the blend becomes higher relative to AFRs, which gives a higher AEC. Variations of AEC as a function of CR and ST are also given in parts c and d of Figure 3, respectively. Results of bmep at various operating conditions are given in Figure 4. In this study, the bmep is preferred as an engine output parameter because it enables one to compare the results without considering the engine dimensions. Figure 4a shows the variations of bmep with engine speed for a CR of 8 and an ST of 10° BTDC. The blends give slightly higher bmep values than the pure gasolines, especially at engine speeds lower than 1400 rpm. The effect of the MTBE ratio on bmep is given in Figure 4b, for the same operating conditions as in Figure 4a and at an engine speed of 1400 rpm. As can be seen from the figure, bmep increases with increasing MTBE ratio up to 10% and then it

decreases. Thus, the best performance is acquired with the MTBE10 blend. This variation in bmep with MTBE ratio can be attributed to both the oxygen content and the lower calorific value of MTBE than that of gasoline. Oxygen presence in MTBE assists to homogenize the fuel-air mixture in the cylinder and therefore to improve combustion efficiency which makes contribution to the increase in bmep by 10% with MTBE ratio. On the other hand, further addition of MTBE beyond 10% causes the decrease in energy content of the blend and therefore results in a decrease in bmep because of the domination of the lower calorific value of MTBE over the gain of improved combustion efficiency. The effects of the CR on bmep are given in Figure 4c. As expected, increases in CR result in the increases in bmep for the blends and gasolines except for the base gasoline. The lower octane rating of base gasoline compared to other gasolines and the blends results in knocking combustion as CR increases. It is known that knocking combustion in an SI engine causes a very high rate of energy release and excessive temperatures and pressures inside the cylinder and, therefore, adversely affects performance and efficiency of the engine. Variation of bmep with respect to ST is given in Figure 4d. As shown in this figure, base gasoline gives the best performance for the lower spark advances in contrast to the leaded and unleaded fuels. On the other hand, the blended fuels give the best performance for the mid values of ST for a selected spark


Sezer and Bilgin

Figure 5. Variations of bte at various operating conditions.

advance range. The noticeable result that can be concluded from Figure 4 is that the MTBE10 blend gives the best bmep values for the operating conditions manifest in the figure. This blending ratio is supported by the finding in ref 22. The increments in bmep obtained with the MTBE10 blend are about 0.7%, 1.37%, and 2.13% in comparison with those of the base, leaded, and unleaded gasolines for the mentioned operating conditions, respectively. Variations of bte with engine speed, MTBE percentage, CR, and ST are given in Figure 5a-d, respectively. As shown in Figure 5a, unleaded gasoline is the best performer among the blends and fuels for the tested engine speeds while the blends have higher bte values than leaded and base gasolines. On the other hand, the maximum bte values among the blends were obtained with the MTBE15 blend. The dependency of the bte to MTBE ratio is more clearly shown in Figure 5b for a CR of 8 and an ST of 10° BTDC at 1400 rpm. As can be seen from the figure, increases in MTBE ratio up to 15% result in an increase of bte and then it slightly decreases for the MTBE20 blend. This variation outcome on the improving combustion efficiency is due to the presence of oxygen in MTBE as mentioned above. However, it is considered that the MTBE addition further than 15% worsens combustion and decreases bte. Variations of bte values with respect to CR are given in Figure 5c. As expected, bte values increase with increasing CR for the blends and gasolines except for the base gasoline. The

lower knock tendency of base gasoline compared to other gasolines and blends causes the reduction of bte as a result of the knocking combustion, as mentioned above. The blends give higher bte with increasing CR because of the improving fuel octane rating. The leaded and unleaded gasolines also provide improvements in bte because of their high octane rating. Variations of bte values with ST are given in Figure 5d for the fuels and fuel blends. As is known, increases in ST beyond an optimum value lead to knocking combustion gradually. In this study, this tendency is observed for regular gasoline at 12.5° BTDC spark advance. For this reason, bte sharply decreases when regular gasoline is used with ST of 12.5° BTDC, while there are no important reductions in bte values obtained with the blends and other gasolines. It is also observed from Figure 5 that the maximum increment in bte is gained with the MTBE15 blend. The increments in bte obtained with the MTBE15 blend are about 5.4 and 4.3% compared to those for base and leaded gasolines, respectively, and the reduction is around 3.2% compared with that for unleaded gasoline. Figure 6 shows the variations of CO emissions for the same conditions as in the previous figures. The variation of CO emissions with engine speed is given in Figure 6a. As shown in this figure, CO emissions slightly increase with increasing engine speed. Unleaded gasoline is the best performer among neat gasolines. Leaded gasoline gives lower CO emissions than those of base gasoline. On the other hand, increasing the MTBE



Figure 6. Variations of carbon monoxide emissions at various operating conditions.

ratio in the blend up to 10% reduces the CO emissions at all engine speeds. Thus, the MTBE10 blend gives the minimum CO emissions while the base gasoline gives the maximum CO emission values. The variation of CO emissions with MTBE ratio can be apparently seen in Figure 6b, which has the same operating condition in Figure 6a and an engine speed of 1400 rpm. These variations in CO emissions can be attributed to the explanations about bte variations. In other words, MTBE addition to base gasoline up to a certain level improves the combustion quality and decreases CO emissions, and further addition of MTBE causes drawbacks in combustion as declared in ref 22. Variations of CO emissions with CR and ST are shown in parts c and d of Figure 6, respectively. As shown in the figure, the minimum CO emissions are generally obtained for the operating conditions of a CR of 8 and an ST of 10° BTDC. Figure 6clearly points out that the MTBE10 blend yields the most reduction in CO emissions. The decrements in CO emissions obtained with the MTBE10 blend are about 67%, 50%, and 25% compared to those of the base, leaded, and unleaded gasolines, respectively. 5. Conclusions From the results of the outlined study, the following conclusions can be drawn.

1. The blending of MTBE with base gasoline results in an increase in the AEC and makes leaner the inducted fuel-air mixture. 2. MTBE-gasoline blends give higher bmep values compared to those of base, leaded, and unleaded gasolines, especially at lower engine speeds. The maximum improvement in bmep is obtained with addition of 10% MTBE to base gasoline for a CR of 8 and an ST of 10° BTDC at a 1400 rpm engine speed. 3. MTBE addition to base gasoline improves bte up to a 15% blending ratio, but further addition of MTBE results in slight decreases in bte. Thus, in the present study, the maximum bte is obtained with a 15% addition of MTBE for all tested conditions among the blended fuels. The best performer among the pure fuels and blends is unleaded gasoline. 4. MTBE addition to base gasoline results in a considerable reduction in the CO emissions. However, further addition of MTBE beyond 10% results in little increments in emission values. Thus, the lowest CO emissions are obtained with the MTBE10 blend while the base gasoline gives the maximum CO emissions. 5. Finally, the blend that consists of 15% MTBE and 85% base gasoline (MTBE15) is recommended as the best blend in view of the fuel economy, engine performance, and CO emissions. This blend leads to the best improvement in bte, and


Sezer and Bilgin

it is also the best performer immediately following the MTBE10 blend in terms of engine performance and CO emissions. Acknowledgment. The present study was supported by the Research Fund of Karadeniz Technical University.

Nomenclature AEC ) air excess coefficient (dimensionless) AFR ) air-fuel ratio (kg air/kg fuel) bmep ) brake mean effective pressure (kPa) bsfc ) brake specific fuel consumption (kg fuel/(kW h)) bte ) brake thermal efficiency (%) BTDC ) before top dead center CAD ) crank angle (deg) CR ) compression ratio (dimensionless) LHV ) lower heating value (kJ/kg) Md ) brake torque (N m) MTBE5 ) a blend consisting of 5 vol % MTBE and 95% gasoline MTBE10 ) a blend consisting of 10 vol % MTBE and 90% gasoline MTBE15 ) a blend consisting of 15 vol % MTBE and 85% gasoline MTBE20 ) a blend consisting of 20 vol % MTBE and 80% gasoline

n ) engine speed (rpm) Ne ) brake power (kW) P0 ) ambient pressure (MPa) ST ) spark timing T0 ) ambient temperature (K) U ) uncertainty (%) V ) volume (cm3) Vh ) swept volume (cm3) x ) volume percent of fuel in the blend (%) Xhum ) humidity correction factor (dimensionless) z ) number of cylinder Greek Letters F ) density (kg m-3) ω ) angular speed (s-1)

base base base base

Subscripts a ) actual b ) base fuel bl ) blend hum ) humidity i ) base gasoline or MTBE s ) stoichiometric tot ) total EF700592N

Effects of Methyl tert-Butyl Ether Addition to Base Gasoline on the

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