Physical and Chemical Properties of GTL−Diesel Fuel Blends and

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Energy & Fuels 2007, 21, 1908-1914

Physical and Chemical Properties of GTL-Diesel Fuel Blends and Their Effects on Performance and Emissions of a Multicylinder DI Compression Ignition Engine Tao Wu,* Zhen Huang, Wu-gao Zhang, Jun-hua Fang, and Qi Yin School of Mechanical and Power Engineering, Shanghai Jiao Tong UniVersity, Shanghai, People’s Republic of China ReceiVed December 21, 2006. ReVised Manuscript ReceiVed April 8, 2007

An analysis of physical and chemical properties of Fischer-Tropsch fuel gas-to-liquids (GTL) blends with a conventional diesel was conducted. Then, engine performance, combustion, and emission investigations were performed to better understand the differences in regulated emissions between diesel, GTL, and their blends using a six-cylinder turbocharged direct-injection compression ignition (DICI) engine at different load-speed conditions and pump timings. Most of the properties of blended fuels have a good linear relation with the GTL volume fraction in the blends. Density, sulfur, polyaromatics, and total aromatics of blends decrease, while the cetane number and lower heating value increase as the GTL fraction increases. Both the maximum combustion pressure and peak value of heat release rate for neat GTL are slightly lower, and the locations of the two peaks are slightly retarded versus those of the diesel. GTL blends, especially neat GTL, show improvements in fuel economy and thermal efficiency. GTL blends can reduce CO, HC, soot, particulate matter (PM), and NOx emissions simultaneously at different engine operating conditions. There is a trend that the magnitude of reductions in emissions increases with an increasing GTL proportion in blends. The use of retarding pump timings and GTL fuel instead of a conventional diesel on a DICI engine is an effective means to reduce NOx without significantly compromising PM emissions.

1. Introduction Synthetic ultraclean diesel-type fuels can be manufactured through the Fischer-Tropsch (F-T) process. The feedstock can be either natural gas (gas-to-liquids, GTL) or biomass (biomassto-liquids) or coal (coal-to-liquids).1-3 Shell’s Shell Middle Distillate Synthesis process can convert natural gas into GTL fuel via synthesis gas by combining a modern, improved F-T synthesis and a special hydroconversion process.4 The GTL fuel is characterized by a high cetane number (CN), being free of sulfur, and having an ultralow aromatics content, which are supposed to facilitate further reductions of engine-out emissions. Several papers have documented GTL behavior, and experiments have involved the study of engine and vehicle emissions running with GTL. A common trend observed in those studies was reductions in emissions using different kinds of GTL fuels compared to conventional fossil-based diesel fuel.5-8 Alleman and McCormick9 reviewed the Fischer-Tropsch diesel fuel’s properties and exhaust emissions then concluded that, in almost every case, NOx, CO, and particulate matter (PM) emissions were reduced with neat F-T diesel fuel; however, HC emissions were variable. Atkinson et al.10 * Corresponding author. Tel./Fax: +86(0)21 64078095. E-mail address: [email protected]. (1) Vosloo, A. Fuel Process. Technol. 2001, 71, 149-155. (2) Heng, H.; Idrus, S. J. Nat. Gas Chem. 2004, 13, 63-70. (3) Tijmensena, M.; Faaija, A.; Hamelincka, C.; Hardeveld, M. Biomass Bioenergy 2002, 23, 129-152. (4) Alleman, T.; Eudy, L; Miyasato, M.; Oshinuga, A.; Allison, S.; Corcoran, T.; Chatterjee, S.; Jacobs, T.; Cherrillo, R.; Clark, R.; Virrels, I.; Nine, R.; Wayne, S.; Lansing, R. SAE Tech. Pap. Ser. 2004, No. 200401-2959.

found that, at all operating conditions, when compared to D2 diesel, GTL yielded an approximately 14% shorter ignition delay, an average 3.4% lower peak combustion pressure t, and a 35% average lower maximum burn rate. Abu-Jrai et al.11 performed combustion and gas reforming experiments with GTL and ultralow sulfur diesel fuels and concluded that using GTL fuel could reduce NOx emission but increase smoke for the default injection timing, yet both NOx and smoke were reduced simultaneously by optimizing the injection timing. During exhaust-gas reforming, the use of GTL fuel increased fuel conversion, while producing more hydrogen and less methane. In this paper, effects of different GTL volume fractions on GTL-diesel blends’ properties are presented, and a comprehensive study on engine performance, combustion, and emission characteristics versus the GTL fraction, load, speed, and pump timing is conducted. The purpose of this work is to perform a comparative study between conventional fossil diesel and Fischer-Tropsch GTL (5) Schaberg, P.; Myburgh, I.; Botha, J.; Roets, P.; Viljoen, C.; Dancuart, L.; Starr, M. SAE Tech. Pap. Ser. 1997, No. 972898. (6) Clark, N.; Gautam, M.; Lyons, D.; Atkinson, C.; Xie, W.; Norton, P.; Vertin, K.; Goguen, S.; Eberhardt, J. SAE Tech. Pap. Ser. 1999, No. 1999-01-2251. (7) Stavinoha, L.; Alfaro, E.; Dobbs, H.; Villahermosa, L.; Heywood, J. SAE Tech. Pap. Ser. 2000, No. 2000-01-3422. (8) Kenney, T.; Gardner, T.; Low, S. SAE Tech. Pap. Ser. 2001, No. 2001-01-0151. (9) Alleman, T.; McCormick, R. SAE Tech. Pap. Ser. 2003, No. 200301-0763. (10) Atkinson, C.; Thompson, G.; Traver, M.; Clark, N. SAE Tech. Pap. Ser. 1999, No. 1999-01-1472. (11) Abu-Jrai, A.; Tsolakis, A.; Theinnoi, K.; Cracknell, R.; Megaritis, A.; Wyszynski, M.;Golunski, S. Energy Fuels 2006, 20, 2377-2384.

10.1021/ef0606512 CCC: $37.00 © 2007 American Chemical Society Published on Web 05/24/2007

Properties of GTL-Diesel Fuel Blends

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Table 1. Engine Specifications engine type configuration aspiration

D6114ZLQB inline 6 cylinders turbocharged, intercooled 114 × 135 8.27 18 184/2200 1000/1400 6, 9, 12 6 × 0.24

bore (mm) × stroke (mm) engine displacement (L) compression ratio rated power (kW)/speed (r/min) maximum torque (N m)/speed (r/min) pump timing (°CA BTDC) nozzle number × orifice diameter (mm) Table 2. Fuel Properties fuel analysis

method

diesel

G100

density at 15 °C cetane number sulfur (wt %) lower heating value (MJ/kg) total aromatics (wt %) polyaromatics (wt %) 50% distillation (°C) 90% distillation (°C) viscosity at 40°C (mm2/s) C (wt %) H (wt %)

ASTM D4052 ASTM D613 ASTM D2622 ASTM D4868 EN 12916 EN 12916 ASTM D86 ASTM D86 ASTM D445 SH/T 0656 SH/T 0656

839.2 51.7 0.0403 42.9 27.7 6.2 265.3 330.8 2.665 86.32 13.32

779.0 75 0.0003 43.6 1.4 0.4 275.7 310.1 2.74 84.9 15.1

(kg/m3)

Figure 1. Effect of GTL fraction on density of GTL-diesel blends.

fuel in terms of combustion and emission characteristics and to better understand the differences in regulated emissions between diesel, GTL, and their blends via an examination of fuel properties of GTL-diesel blends. 2. Experimental Section The engine experiment was carried out on a six-cylinder, fourstroke, turbocharged, intercooled direct injection compression ignition engine. The engine specifications are listed in Table 1. The engine remained unmodified in the experiment when operating on all test fuels. An AVL CEB gas emission analyzer was used to measure the concentration of NOx, total HC, and CO. The smoke density was tested using an opacimeter (AVL 439). The PM mass was tested using a PM emission analyzer model AVL 472 Smart Sampler PC. The in-cylinder pressure was obtained by a Kistler piezoelectric 6125A sensor; the output of the pressure transducer was amplified by a Kistler 5015A charge amplifier and then converted to digital signals and recorded by a Yokogawa GP-IB data acquisition apparatus. The signals of the crank angle were also recorded by the Yokogawa apparatus. After obtaining the in-cylinder pressure, the heat release rate (HRR) was calculated through the first law of thermodynamics and a zero-dimensional model.12 The test fuel GTL (labeled G100) used in this work was produced and provided by Shell International Gas Limited. The conventional diesel in this work is No. 0 diesel in the market. Blends of these two fuels, G10, G20, G30, G50, and G70, represent GTL fractions of 10%, 20%, 30%, 50%, and 70% by volume, respectively. Fuel properties of neat GTL and diesel fuels and the test methods used for GTL-diesel blend properties are listed in Table 2. As the diesel engine used in this study was equipped with a mechanically controlled pump-line-nozzle-type fuel injection system, the start of fuel injection can hardly be controlled directly, because it depends on sophisticated transport phenomena in the pump, high-pressure tubes, and the injector. However, the start of injection is closely related to the start of fuel pump delivery, which can be set easily to a desired value. In this paper, the start of the fuel pump delivery crank angle, namely, pump timing, was set at 6, 9, and 12 °CA (degree crank angle) before top dead center (BTDC) to examine the effect of different pump timings on GTLfueled engine performance. (12) Heywood, J. Internal Combustion Engine Fundamentals; McGrawHill: New York, 1988.

Figure 2. Effect of GTL fraction on viscosity of GTL-diesel blends.

Figure 3. Distillation curves of GTL-diesel blends.

3. Results and Discussion 3.1. GTL-diesel Blends Fuel Properties. 3.1.1. Density. With the GTL volume fraction increasing in the blends, the densities of GTL blends decrease gradually, as shown in Figure 1. The reason is that GTL is the mixture of normal and iso paraffins which have the lowest density of all hydrocarbons. The density of neat GTL is lower than that of diesel by 7.2%. 3.1.2. Viscosity. Figure 2 shows variation of the kinematic viscosity at 40 °C with a GTL volume fraction in the blends. The viscosity almost keeps constant when the GTL volume ratio is below 50%, yet it increases relatively fast when the ratio goes beyond 50%. The kinematic viscosity of neat GTL is higher than that of diesel by 2.8%. 3.1.3. Distillation. The distillation curves of neat diesel, G100, and blends from the initial boiling point to the final boiling point are shown in Figure 3. When the distillation percentage is below 70%, the distillation temperatures of GTL blends are

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Figure 4. Effect of GTL fractions on sulfur content of GTL-diesel blends.

Figure 5. Effect of GTL fractions on aromatics content of GTLdiesel blends.

higher than that of diesel. However, the distillation temperatures of blends become lower than that of diesel with the percentage beyond 70%. The T90 (90% distillation temperature) of GTL is lower than that of diesel by 6.3%, which indicates that GTL has less heavy distillation and is easier to evaporate and form into a more combustible air-fuel mixture. 3.1.4. Sulfur. Figure 4 displays variation of the sulfur content with the GTL volume fraction in blends. It can be seen that a higher proportion of GTL contributes to less sulfur content in the blends, since GTL has an ultralow sulfur content. In particular, the neat GTL has almost zero sulfur, at 0.0003% by mass, relatively lower than diesel by 99.3%. 3.1.5. Aromatics. The relation between aromatics, including total and polyaromatics, and the GTL fraction in the blends is illustrated in Figure 5. We can see that total and polyaromatics of the blended fuels decrease gradually when the GTL fraction increases in the blends. Total aromatics and polyaromatics of neat GTL are lower than those of diesel by 96% and 71.4%, respectively. 3.1.6. Cetane Number. Figure 6 presents a variation of CNs with the GTL volume fraction in the GTL-diesel blends. It can be clearly seen that the CN of blended fuels increases linearly with the GTL fraction increasing in the blends. 3.1.7. Lower Heating Value. Lower heating values (LHVs) of the GTL-diesel fuels rise with an increasing GTL fraction in the blends, as shown in Figure 7. Neat GTL has a 1.6% higher LHV than that of diesel. 3.2. Combustion. 3.2.1. Cylinder Pressure and Heat Release Rate. A comparison of combustion pressure in the cylinder and the HRR between diesel and GTL at the maximum torque point and 9 °CA pump timing is shown in Figure 8. It can be seen that the maximum combustion pressure and the peak value of

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Figure 6. Effect of GTL fraction on cetane number of GTL-diesel blends.

Figure 7. Effect of GTL fractions on lower heating value of GTLdiesel blends.

HRR for G100 are lower than those of diesel by 2.9% and 2.8%, respectively. The main reason for this is the significantly high cetane number of GTL shortening the ignition delay period, during which less of the combustible mixture formed and the maximum combustion pressure dropped. Lower peak combustion pressures, resulting in a lower in-cylinder gas temperature, would contribute to reducing the NOx emission of GTL. It is worth noting from Figure 8 that the locations of the maximum pressure and HRR peak value for GTL are slightly later than those for diesel. It is believed that, using the pump-line-nozzle-type fuel injection system, GTL causes later fuel injection timings due to its different density and bulk modulus of compressibility compared to those of diesel.13,14 GTL with a lower density and bulk modulus is more compressible than diesel fuel, so the pressure in the fuel injection system develops slower; pressure waves propagate slower, leading to a later injection timing of GTL than diesel at the same nominal pump timing. As a corresponding result, later ignition for GTL causes later locations of the maximum pressure and HRR peak value. 3.2.2. Cylinder Pressure Rise Rate. A comparison of incylinder pressure rise rate (PRR) between diesel and GTL at the maximum torque point and 9 °CA pump timing is displayed in Figure 9. It can be clearly observed that the peak value of the PRR for G100 is lower than that for diesel. It indicates that GTL produces lower combustion noise when compared to diesel. (13) Boehman, A.; Morris, D.; Szybist, J.; Esen, E. Energy Fuels 2004, 18, 1877-1882. (14) Szybist, J.; Kirby, S.; Boehman, A. Energy Fuels 2005, 19, 14841492.

Properties of GTL-Diesel Fuel Blends

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Figure 8. Comparison of cylinder pressure and heat release rate between diesel and GTL at maximum torque point.

Figure 11. Variation of brake thermal efficiency with engine speed and volume fraction of the blends. Figure 9. Comparison of cylinder pressure rise rate between diesel fuel and GTL at maximum torque point.

presented in Figure 11. As can be seen, there is no significant difference in the BTE of all the fuels, and only G100 shows a slightly higher value by 1.2% compared to the diesel average at all engine operating conditions. The main reason for this is discussed below.

ηbt )

Figure 10. Variation of brake-specific fuel consumption with engine speed and volume fraction of the blends.

3.2.3. Brake-Specific Fuel Consumption. The brake-specific fuel consumption (BSFC) of GTL-diesel blends versus engine speed at 9 °CA and full load are plotted in Figure 10. It can be seen that the BSFCs of all GTL blends are generally lower than diesel at test conditions, and an improvement of fuel economy is seen as more significant at low speed than at mid-high speed. G100 shows the best fuel economy with a lower BSFC by 2.7% than diesel since GTL blends have higher lower heating values on a gravimetric basis than diesel (Figure 7). 3.2.4. Brake Thermal Efficiency. The results of brake thermal efficiency (BTE) for all blends at 9 °CA and full load are

3.6 × 106 × 100% be × Hu

(1)

Formulation 1 is BTE ηbt (%), where be is the BSFC (g/kW‚h) and Hu is the lower heating value of a fuel (kJ/kg). The Hu of neat GTL is higher by 1.6% than that of diesel, so GTL blends show benefits in mass fuel consumption. In terms of formulation 1, the combination of a lower be and a higher Hu of GTL results in small variations of brake thermal efficiency ηbt between diesel and GTL fuels. 3.3. Pollutant Emissions. 3.3.1. Load Effect on GTL Emissions. Figure 12 shows variation of the CO emissions with the volume fraction of GTL and engine load at an engine speed of 1400 rpm and a pump timing of 9° CA BTDC. A general trend is that CO emissions of all fuels are very low at low loads while the emission increases significantly at high loads. GTL blends produce lower CO emissions than diesel, especially at high loads. Obviously, G100 has the lowest CO emissions with a reduction of 26.7% compared to the diesel. Figure 13 presents variation of the HC emissions with the volume fraction of GTL and engine load at an engine speed of 1400 rpm and a pump timing of 9° CA BTDC. As shown in

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Figure 12. Comparison of CO emissions between GTL-diesel blends and neat diesel at different loads.

Figure 13. Comparison of HC emissions between GTL-diesel blends and neat diesel at different loads.

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Figure 15. Comparison of NOx emissions between GTL-diesel blends and neat diesel at different loads.

Figure 16. Comparison of CO emissions between GTL-diesel blends and neat diesel at different speeds.

Figure 14. Comparison of soot emissions between GTL-diesel blends and neat diesel at different loads.

Figure 17. Comparison of HC emissions between GTL-diesel blends and neat diesel at different speeds.

the figure, HC emissions of all fuels are at a very low level. Furthermore, HC emissions decrease with increasing GTL in the blends at all load conditions. The best G100 produces 20.2% less HC emissions than diesel. Figure 14 gives variation of the soot emission in terms of an extinction coefficient (unit, m-1) with the GTL fraction and an engine load at 1400 rpm and 9° CA BTDC. As can be seen, as the load increases, soot emissions of all test fuels increase gradually, and GTL fuels show benefits in reducing soot emissions, especially at high loads. GTL fuels G30, G70, and G100 on average at all test conditions reduce soot emissions by 4.8%, 12.2%, and 15.6%, respectively, in comparison with diesel. The variation of NOx emissions with the GTL volume fraction and an engine load at 1400 rpm and 9° CA BTDC is shown graphically in Figure 15. As shown, NOx emissions of GTL fuels as well as diesel increase gradually when the engine load increases. GTL blends reduce NOx in all cases; furthermore, a higher GTL volume fraction in blends leads to further reductions in the emission. GTL fuels G30, G70, and G100 offer

average reductions of 4.3%, 9.1%, and 12.1%, respectively, when compared to diesel. 3.3.2. Speed Effect on GTL Emissions. The variation of CO emissions with the GTL fraction and an engine speed at full load and a pump timing of 9° CA BTDC is displayed in Figure 16. It shows that, at lower speeds, CO emissions are very high for all of the fuels, yet CO emissions are at very low levels at mid-high speeds. Reductions in CO levels at lower speeds for GTL blends relative to diesel are larger than the reductions at higher speeds. Generally, G100 produces the best reductions in CO emissions by 38.6% on average in all cases compared to diesel. Figure 17 shows variation of the HC emissions with the GTL fraction and an engine speed at full load and a 9° CA BTDC pump timing. The result demonstrates that, at overall engine operating conditions, all fuels produce very low HC emissions, and the speeds have no significant effect on the emission. GTL fuels show lower emissions with the exception of several points. In general, G100 shows 9.9% less HC emissions than diesel.

Properties of GTL-Diesel Fuel Blends

Figure 18. Comparison of soot emissions between GTL-diesel blends and neat diesel at different speeds.

Figure 19. Comparison of NOx emissions between GTL-diesel blends and neat diesel at different speeds.

Figure 20. Specific CO emissions of GTL-diesel blends over ECE R49 13-mode cycles at different pump timings.

A relationship of soot emissions with the engine speed for GTL blends at a full engine load is given in Figure 18. It shows that, with speed increasing, soot emissions decrease generally. GTL blends exhibit benefits in soot emissions at most test conditions, except an engine speed of 1000 rpm. G30, G70, and G100 present the respective reductions of 9.7%, 12.8%, and 15.4% on average in all cases when compared to diesel. Figure 19 gives a relation of NOx emission with the engine speed for GTL blends at a full engine load. Generally, NOx emissions decrease as the engine speed increases. There is a trend that more GTL in blends contributes to a greater NOx emissions reduction. GTL fuels G30, G70, and G100 on average reduce NOx by 1.1%, 3.5%, and 8.4%, respectively, compared with diesel. 3.3.3. Pump Timing Effect on GTL Emissions. Figure 20 shows the effect of pump timing on CO emissions over ECE R49 13-mode cycles. As the pump timing delays, specific CO emissions decrease gradually. In the case of 6° CA BTDC, GTL-diesel fuels produce the lowest CO emissions among three pump timings, and typically, G100 emits lower CO emissions by 22.6% and 42.5% than at 9° CA and 12° CA, respectively.

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Figure 21. Specific HC emissions of GTL-diesel blends over ECE R49 13-mode cycles at different pump timings.

Figure 22. Specific PM emissions of GTL-diesel blends over ECE R49 13-mode cycles at different pump timings.

Figure 23. Specific NOx emissions of GTL-diesel blends over ECE R49 13-mode cycles at different pump timings.

Figure 21 shows the effect of pump timing on specific HC emissions over ECE R49 13-mode cycles. As can be seen, the specific HC emissions are at very low levels for three pump timings due to use of the turbocharged diesel engine. The pump timing seems to have no significant influence on the absolute values of specific HC emissions. For 6° CA BTDC, the best G100 emits lower HC emissions only by 3.4% and 8% than at 9 °CA and 12 °CA, respectively. An effect of pump timing on specific PM emissions over ECE R49 13-mode cycles is shown in Figure 22. There is a general trend that, as pump timing advances from 6 to 12 °CA BTDC, PM emissions decrease slightly. G100 produces lower PM emissions by 3.4% and 5.5% at 9 °CA and 12 °CA than that at 6° CA BTDC, respectively. This is due to a more relative homogeneous mixture of air and fuel formation at the earlier pump timing of 12 °CA. The effect of pump timing on specific NOx emissions over ECE R49 13-mode cycles is described in Figure 23. It can be obviously observed that, when the pump timing retards from

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12 to 6 °CA BTDC, NOx emissions decrease gradually. In the case of 6° CA pump timing, G100 produces lower NOx emissions by 25.7% and 42.5% than at 9 °CA and 12 °CA, respectively. It is believed that a later pump timing leads to a later injection timing, resulting in a shorter premixed period, during which less NOx emissions are produced. Therefore, it is an effective means to reduce NOx using retarding pump timings and GTL fuel for conventional diesel engines without greatly compromising PM emissions, with slight increases of 3.5% and 5.8% at advanced 9 and 12 °CA BTDC, respectively, than at a 6 °CA pump timing (Figure 22). 3.3.4. GTL Fraction Effect on GTL-diesel Blends Emissions. In order to identify the influence of the GTL fraction on pollutant emissions, the specific emission experiments were conducted using seven more GTL-diesel blends over ECE R49 13-mode cycles at a 6 °CA BTDC pump timing. The results of specific CO, HC, NOx, and PM emissions are presented in Figures 2023. It is apparent that, compared to diesel, GTL blends offer reductions in the four regulated pollutant emissions simultaneously. Trend lines indicate that there is a strong linear correlation between the magnitude of reductions in emissions and the amount of GTL in the blends. The main reason for this is due to a good linear relation between most properties of GTL blends and the GTL fraction in blends, described in section 3.1. Typically, neat GTL (G100) offers a significantly greatest reduction of 12.9% in HC, 16.6% in CO, 23.7% in NOx, and 27.6% in PM in comparison with diesel over ECE R49 13mode cycles at a 6 °CA BTDC pump timing. From the emission results above, it can be clearly observed that GTL fuels can reduce CO, HC, soot, PM, and NOx emissions simultaneously at most test engine operating conditions. Although diesel engines have low CO and HC emissions, in this study, GTL fuels still show some improvements. The reductions possibly are attributable to a high cetane rating and extremely low aromatics. A lower T90 of GTL (Figure 3) than that of diesel indicates that GTL has less heavy distillation, which suggests that GTL is easy to evaporate and to mix with air, forming a more combustible charge. Therefore, reductions in HC and CO emissions are partially attributed to the lower T90 of GTL. The higher H/C ratio of GTL than that of diesel (Table 2) facilitates GTL completed combustion, resulting in less CO and HC emissions being produced. The higher cetane number of GTL indicates a shorter ignition delay and premixed combustion period, which leads to a less combustible mixture and a lower maximum temperature, hindering the formation of more NOx. Furthermore, there is a good linear correlation between total aromatics and NOx emission,15 so lower NOx emission is also owing to a lower aromatics content of GTL. Reductions in PM are mainly due to the zero sulfur content, which eliminates the sulfate contribution to PM, and an ultralow aromatic content, which reduces the soot contribution to PM. (15) Nylund, N.; Aakko, P.; Mikkonen, S.; Niemi, A. SAE Tech. Pap. Ser. 1997, No. 972997.

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4. Conclusions An analysis of the physical and chemical properties of GTLdiesel blends was conducted. Then, engine performance, combustion, and emission characteristics of a turbocharged direct-injection compression ignition engine using several GTLdiesel blends at different load-speed conditions and pump timings were deduced, and these were also compared to those of conventional diesel fuel. On the basis of the results, the conclusions of this study can be summarized as follows: (1) Most properties of blended fuels have a good linear relationship with the GTL volume fraction in the blends. Density, sulfur, polyaromatics, and total aromatics of blends decrease while the cetane number and lower heating value increase as the GTL fraction increases. (2) The viscosity almost keeps constant when the GTL volume ratio is below 50% yet increases relatively fast when the ratio goes beyond 50%. When the distillation percentage is below 70%, the distillation temperatures of GTL blends are higher than that of diesel. However, the temperatures of blends become lower than that of diesel with the percentage beyond 70%. (3) The maximum combustion pressure and the peak value of HRR for neat GTL are lower than diesel by 2.9% and 2.8%, respectively. The locations of the two peak values are slightly retarded when compared to diesel. (4) The BSFCs of all GTL blends are lower than those of diesel, and the improvement in the fuel economy is shown to be more significant at low speed than at mid-high speeds. GTL improves the fuel economy by 2.7% versus that with diesel because of its higher calorific values on a gravimetric basis compared to those of diesel. There is no significant difference in the brake thermal efficiency for all the fuels, and only G100 shows a slightly higher value, by 1.2%, compared to diesel. (5) The pump timing does not have a significant effect on specific HC and PM emissions, yet it has great influence on CO and NOx emissions over ECE R49 13-mode cycles. Therefore, the use of retarding pump timings and GTL fuel instead of a conventional diesel is an effective means to reduce NOx without significantly compromising PM emissions. (6) At most test conditions, all GTL blends can reduce CO, HC, soot, PM, and NOx emissions simultaneously. There is a good relation between the magnitude of reductions in emissions and the amount of GTL in blends due to the linear variations of most main properties of GTL-diesel blends with the GTL fraction. Neat GTL has the greatest improvement in emissions with reductions of 12.9% in HC, 16.6% in CO, 27.6% in PM, and 23.7% in NOx compared to those of diesel over ECE R49 13-mode cycles at a 6 °CA BTDC pump timing. Acknowledgment. The authors thank the Shanghai Science & Technology Commission (Contract No. 043012015) and Shell International Gas Limited for financial support for this study. Shell also provided the GTL fuel. Shell and SGS companies supplied the property data of all fuels. EF0606512