Characteristics of Engine Emissions Using Biodiesel Blends in Low

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Characteristics of Engine Emissions Using Biodiesel Blends in Low-Temperature Combustion Regimes Prashanth K. Karra, Matthias K. Veltman, and Song-Charng Kong* Department of Mechanical Engineering, Iowa State UniVersity, 2025 Black Engineering Building, Ames, Iowa 50011 ReceiVed June 10, 2008. ReVised Manuscript ReceiVed August 21, 2008

Combustion and emissions of different biodiesel-diesel blends in a multicylinder diesel engine were investigated in this study. The engine used a modern common-rail fuel injection system that can achieve high injection pressures and multiple injections. The future diesel engines are likely to be operated in low-temperature combustion regimes to reduce exhaust emissions. Therefore, the performance of biodiesel in such operating conditions needs to be determined. The present results showed that biodiesel blends generally produced lower soot emissions and higher NOx emissions compared to regular diesel fuel. Results showed that the injection timing shift is not the reason for the NOx emissions increase using biodiesel. The increase in injection pressure will reduce soot emissions, while the use of exhaust gas recirculation will reduce the NOx emissions for all fuels. Reductions in NOx and soot emissions were achieved by using double injections with appropriate injection timings and fuel distributions. It was found that the use of pilot injection allowed late main injections for simultaneous soot and NOx reductions. In the low-temperature combustion regimes (i.e., late injection and/or high exhaust gas recirculation), the 20% biodiesel blend produced almost identical emissions as the regular diesel fuel, while 100% biodiesel still produced relatively higher NOx and lower soot emissions. Nonetheless, NOx emissions will not be a concern at low-temperature combustion conditions when 20% biodiesel blends are used.

1. Introduction Diesel engines are widely used in transportation and agricultural machinery. The exhaust emissions of diesel engines are of a major concern because of their impact on environment and human health. Rising prices and questions over future availability of crude-based diesel fuel has led to the interest in using renewable energy. Biodiesel is one of the renewable fuel alternatives to displace diesel fuel derived from crude oils. The advantageous features of biodiesel result from the fact that biodiesel has different physical and chemical properties than petroleum-based diesel fuel. Biodiesel has approximately 11% oxygen (by weight), which results in reduced soot, carbon monoxide (CO), and hydrocarbon (HC) emissions. Biodiesel is biodegradable and also has a higher cetane number, which leads to a shorter ignition delay. However, biodiesel has a higher viscosity, density, speed of sound, and bulk modulus that may cause injection system and combustion anomalies.1,2 Engine testing has shown that biodiesel produces lower exhaust emissions in CO, HC, and soot, compared to petroleumbased diesel fuel.3-6 Studies also revealed that biodiesel would * To whom correspondence should be addressed. Telephone: 515-2943244. Fax: 515-294-3261. E-mail: [email protected]. (1) Szybist, J. P.; Boehman, A. L. Behavior of a diesel injection system with biodiesel fuel. SAE Tech. Pap. Ser. 2003-01-1039, 2003. (2) Tat, M. E.; Van Gerpen, J. H.; Soylu, S.; Canakci, M.; Monyem, A.; Wormley, S. The speed of sound and isentropic bulk modulus of biodiesel at 21 °C from atmospheric pressure to 35 MPa. J. Am. Oil Chem. Soc. 2000, 77 (3), 285–289. (3) Sharp, C. A.; Howell, S.; Jobe, J. The effect of biodiesel fuels on transient emissions from modern diesel enginessPart 1: Regulated emissions and performance. SAE Tech. Pap. Ser. 2000-01-1967, 2000. (4) Graboski, S. M.; Ross, J. D.; McCormick, R. L. Transient emissions from No. 2 diesel and biodiesel blends in a DDC series 60 engine. SAE Tech. Pap. Ser. 961166, 1996.

increase NOx emissions. Performance and emissions of a turbocharged direct-injection diesel engine were compared using biodiesel and diesel fuel.5 In the study, NOx emissions increased by about 20% when biodiesel was used. The increase in NOx emissions by using biodiesel could vary significantly with different combustion systems and different injection strategies and operating conditions.6 The U.S. Environmental Protection Agency (EPA) reported that, on average, NOx increases by 2 and 10% for 20% biodiesel in diesel (B20) and 100% biodiesel (B100), respectively, in a heavy-duty on-highway diesel engine.7 There are numerous theories to explain the increase of NOx emissions. It has been observed in older engines that the increase in NOx emissions can be attributed to the earlier start of injection for biodiesel because of its higher bulk modulus of compressibility. It was also reported that actual fuel injection timing was advanced by 2.3 crank angle degrees (CAD) with 100% biodiesel, and this advancement was believed to cause an increase in NOx emissions.8 A recent study purposely used the same injection timing for both biodiesel and diesel, and the test results still showed an (5) Senatore, A.; Cardone, M.; Rocco, V.; Prati, M. V. A comparative analysis of combustion process in DI diesel engine fueled with biodiesel and diesel fuel. SAE Tech. Pap. Ser. 2000-01-0691, 2000. (6) Hribernick, A.; Kegl, B. Influence of biodiesel fuel on he combustion and emissions formation in a direct injection (DI) diesel engine. Energy Fuels 2007, (21), 1760–1767. (7) United States Environmental Protection Agency (EPA). A comprehensive analysis of biodiesel impacts on exhaust emissions. EPA 420-P02-001, 2002. (8) Monyem, A.; Van Gerpen, J. H.; Canakci, M. The effect of timing and oxidation on emissions from biodiesel-fueled engines. Trans. ASAE 2001, 44 (1), 35–42.

10.1021/ef8004493 CCC: $40.75  2008 American Chemical Society Published on Web 10/07/2008

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increase in NOx emissions for biodiesel.9 It was proposed that the lesser soot radiation in biodiesel combustion could cause a higher flame temperature, leading to an increase in NOx emissions. Another study speculated that the double bonds in biodiesel could contribute to the formation of certain hydrocarbon radicals that could result in higher prompt NO formation.10 Nonetheless, different strategies were evaluated for biodiesel NOx reductions.11 Low-Temperature Combustion. One of the diesel emission reduction technologies is to control the combustion to occur at low temperatures. Under conventional engine-operating conditions, the combustible mixture in the cylinder is highly heterogeneous and soot is formed at the fuel-rich regions. Additionally, the peak flame temperature is typically in the range of 2300-2600 K, which produce relatively high NOx emissions. Several approaches have been proposed to create a more homogeneous mixture and/or to reduce the local flame temperature for emission reduction. Low-temperature combustion can be achieved by using high exhaust gas recirculation (EGR) and/ or advanced fuel injection schemes, such as high injection pressure and multiple injections. Exhaust species, such as carbon dioxide and water, have higher specific heat than oxygen and nitrogen in fresh air. Thus, the combustion temperature can be reduced by displacing fresh air with exhaust gas if the same amount of fuel energy is released during combustion. This concept is referred to as low-temperature combustion, which is very effective in reducing NOx emissions. Because most of the work on biodiesel was previously performed on conventional engines with pump-line-nozzle fuel injection systems, there is an increasing need for the tests to be performed on a modern diesel engine equipped with a commonrail fuel injection system. Furthermore, the electronic control in modern engines can be exploited to optimize the engineoperating conditions for reducing exhaust emissions. A study investigated the impact of biodiesel on NOx emissions in a diesel engine using a common-rail injection system.12 Effects of different fuels on emissions were also studied in a transparent engine under mixing controlled conditions.13 Future diesel engines are likely to be operated under the low-temperature combustion conditions to meet the increasing demand for emission reduction. Strategies for emission reductions can include the use of exhaust gas recirculation (EGR), multiple injections, and late injection timings to achieve low-temperature combustion. EGR has been demonstrated to reduce NOx emissions by lowering combustion temperature. However, soot emissions increase as the amount of EGR is increased to a moderate level. It was found that soot emissions could be reduced if a high level of EGR was used.14 Low-temperature diesel combustion (9) Cheng, A. S.; Upatnieks, A.; Mueller, C. J. Investigation of the impact of biodiesel fueling on NOx emissions using an optical DI diesel engine. Int. J. Engine Res. 2006, (7), 297–318. (10) Miller, J. A.; Bowman, C. T. Mechanism and modeling of nitrogen chemistry in combustion. Prog. Energy Combust. Sci. 1989, (15), 287– 338. (11) Szybist, J. P.; Boehman, A. L.; Taylor, J. D.; McCormick, R. L. Evaluation of formulation strategies to eliminate the biodiesel NOx effect. Fuel Process. Technol. 2005, 86, 1109–1126. (12) Zhang, Y.; Boehman, A. L. Impact of biodiesel on NOx emission in a common rail direct injection diesel engine. Energy Fuels 2007, 21 (4), 2003–2012. (13) Cheng, A. S.; Upatnieks, A.; Mueller, C. J. Investigation of fuel effects on dilute, mixing-controlled combustion in an optical direct-injection diesel engine. Energy Fuels 2007, 21, 1989–2002. (14) Miles, P. C.; Choi, D.; Pickett, L. M.; Singh, I. P.; Henein, N.; Rempel Ewert, B. A.; Yun, H.; Reitz, R. D. Rate-limiting processes in lateinjection, low-temperature diesel combustion regimes. Proceedings of the THIESEL 2004 Conference, 2004; pp 429-447.

Karra et al. Table 1. Specifications of the Test Engine engine bore and stroke (mm) total engine displacement (L) compression ratio valves per cylinder intake/exhaust firing order combustion system engine type aspiration injection system piston

John Deere 4045 HF475 4-cylinder 4-valve direct injection 106 × 127 4.5 17:1 2/2 1-3-4-2 direct injection in-line, 4-stroke turbocharged common rail bowl-in-piston

was achieved by using high EGR (up to 60%) for various engine loads (up to 50%) and injection timings.15 Low-temperature biodiesel combustion was also studied in both an experimental engine and a production engine.16,17 Injection pressure can play an important role in reducing soot emissions. Extremely high injection pressures were used along with EGR for simultaneous reductions of both soot and NOx.18 Multiple injection strategies were also tested for emission reduction at different operating conditions.19 It was reported that appropriate configurations could offer simultaneous soot and NOx reductions while maintaining a reasonable fuel economy. Multiple injection schemes were also used for the biodiesel combustion study at different load conditions.20,21 In this study, biodiesel combustion will be investigated with a focus on low-temperature combustion conditions. A mediumduty diesel engine will be used with various biodiesel/diesel blends. Strategies such as EGR, injection pressure, injection timing, and multiple injections will be applied to achieve lowtemperature combustion. Effects of these parameters on emissions and fuel efficiency will be discussed. 2. Experimental Setup In the present study, three fuels B0 (No. 2 diesel), B20 (20% biodiesel in No. 2 diesel), and B100 (100% biodiesel) were tested at various engine-operating conditions. The detailed engine parameters are given in Table 1. In all of the engine tests, the fuel injected was held constant at 50 mg/cylinder/stroke. The engine was operated at approximately 50% of the full load. The fuel injection conditions and EGR levels are listed in Table 2. Note that, in the doubleinjection conditions, the pilot injection consisted of 15% of the total fuel, with the injection timing varying from -35 to -15 ATDC. The main injection was set at +5 ATDC. The above injection conditions were found to give the most favorable emission results based on a previous study using the present engine.18 Two levels (15) Alriksson, M.; Denbratt, I. Low temperature combustion in a heavy duty diesel engine using high levels of EGR. SAE Tech. Pap. Ser. 200601-0075, 2006. (16) Fang, T.; Lin, Y. C.; Foong, T. M.; Lee, C. F. Spray and combustion visualization in an optical HSDI diesel engine operated in low-temperature combustion mode with bio-diesel and diesel fuels. SAE Tech. Pap. Ser. 2008-01-1390, 2008. (17) Zheng, M.; Mulenga, C.; Han, X.; Tan, Y.; Kobler, M.; Ko, S. J.; Wang, M.; Tjong, J. Low temperature combustion of neat biodiesel fuel on a common-rail diesel engine. SAE Tech. Pap. Ser. 2008-01-1396, 2008. (18) Karra, P.; Kong, S.-C. Diesel emission characteristics using high injection pressure with converging nozzles in a medium-duty engine. SAE Tech. Pap. Ser. 2008-01-1085, 2008. (19) Hardy, W. L.; Reitz, R. D. An experimental investigation of partially premixed combustion strategies using multiple injections in a heavy-duty diesel engine. SAE Tech. Pap. Ser. 2006-01-0917, 2006. (20) Reitz, R. D.; Choi, C. Y.; Bower, C. R. Effects of biodiesel blended fuels and multiple injections on DI diesel engines. SAE Tech. Pap. Ser. 970218, 1997. (21) Stringer, V.; Cheng, W. L.; Lee, C.-F; Hansen, A. Combustion and emissions of biodiesel and diesel fuels in direct injection compression ignition engines using multiple injection strategies. SAE Tech. Pap. Ser. 2008-01-1388, 2008.

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Table 2. Engine-Operating Conditions single injection double injection engine speed EGR injection pressure fuels BMEP at 150 MPa, 0% EGR, -5 ATDC SOI fuel injected injector

SOI ) -20 to 5 ATDC 15% pilot at SOI ) -30 to -15 ATDC; main SOI ) +5 ATDC 1400 rpm 0 and 30% 150 and 180 MPa B0 (No. 2 diesel) B20 (20% biodiesel in No. 2 diesel) B100 (100% biodiesel) 7.11 bar (B0) 6.85 bar (B20) 5.97 bar (B100) 50 mg/injection/cylinder, corresponding to 50% peak torque. 6-hole, 133 included spray angle, 148 µm nozzle hole diameter

of EGR (0 and 30%) were tested together with two different injection pressures, 150 and 180 MPa. Low-temperature combustion can be achieved by using high EGR and/or late injection timings. Gaseous emissions were measured using a HORIBA MEXA 7100DEGR emissions analyzer. The emission data recorded were CO, CO2, NOx, THC, O2, and EGR CO2. The smoke number was measured using an AVL 415S soot meter. The cylinder pressure was measured using a Kistler 6125B piezo-electric pressure transducer. The signal was amplified using a Kistler 5010 charge amplifier. The cylinder pressure was measured every 0.1 crank angle degree and averaged over 50 engine cycles. The exhaust gas is recirculated into the intake using the back pressure created by a valve in the exhaust pipe. The exhaust gas flows through a heat exchanger before entering the intake. The mixture enters the turbocharger and then goes through an intercooler for further cooling. The charge entering the cylinder was maintained at 23 °C for all of the EGR levels.

Figure 1. NOx emissions at 150 and 180 MPa injection pressures and 0% EGR for B20 and B100.

3. Results and Discussion Many parameters were investigated in this study. The following results are presented in such a way that the effects of individual parameters are isolated and discussed. More results on high EGR (i.e., 30%) are presented to assess biodiesel performance under low-temperature combustion conditions. All of the results presented in the following sections used single fuel injection unless mentioned otherwise. Additionally, soot and NOx are the major emissions from the diesel engine. The emission results shown in this paper are mainly for soot and NOx. Additional results on HC and CO emissions are shown in the Appendix. Effects of Injection Pressure. Engine-out NOx emissions at 150 and 180 MPa injection pressures and 0% EGR for B20 and B100 are presented in Figure 1. NOx levels increased with the injection pressure for both fuels. A high injection pressure creates better atomization and vaporization, which, in turn, increases the premixed burn fraction and local combustion temperature, thus leading to higher NOx emissions. NOx emissions decreased as the SOI was retarded because of the lower combustion temperature in the cylinder. However, as the injection timing was retarded past top dead center, the ignition delay can increase and result in slightly higher NOx emissions because of more premixed burn, although the difference is small. The same phenomena were also observed in other studies.22 Soot emissions at 150 and 180 MPa injection pressures at 0% EGR for B20 and B100 are shown in Figure 2. Soot emissions decreased with the increase in injection pressure (22) Kong, S. C.; Sun, Y.; Reitz, R. D. Modeling diesel spray flame lift-off, sooting tendency and NOx emissions using detailed chemistry with phenomenological soot model. J. Eng. Gas Turbines Power 2007, 129, 245– 251.

Figure 2. Soot emissions at 150 and 180 MPa injection pressures and 0% EGR for B20 and B100.

because of better atomization and mixing. However, the effect of injection pressure diminished for SOI near TDC. At late injection timing (e.g., 0 and 5 ATDC), both NOx and soot emissions decreased, which is the characteristic of lowtemperature combustion. Figure 3 shows the brake-specific fuel consumption (BSFC) using 150 and 180 MPa injection pressures at 0% EGR for B20 and B100. Higher BSFC was noted at high injection pressures. This was mostly due to the higher pump work required by the engine to maintain a high pressure at the fuel rail. It should also be noted that the shift in combustion phasing will have effects on BSFC when a high injection pressure is used. In addition, B100 had a higher BSFC than B20 because of the lesser energy content in biodiesel.

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Figure 3. BSFC at 150 and 180 MPa injection pressures and 0% EGR for B100 and B20.

Figure 4. Cylinder pressure and heat release rate for B20 fuel at 150 and 180 MPa injection pressures, 0% EGR, and SOI ) 0 ATDC.

Figure 4 shows the cylinder pressure and heat release rate data for B20 at 150 and 180 MPa injection pressures for 0% EGR. The peak cylinder pressure was higher for 180 MPa injection pressure. This can be attributed to the better atomization associated with high injection pressures, which leads to more premixed burn. It can be noted that, while the SOI for both injection pressures remained the same, the premixed burn peak shifted to the left by about two crank angle degrees at high injection pressures. Such shifts in combustion phasing can also have effects on emission trends. Further analysis can be performed to correlate fuel performance and emissions with combustion phasing. Effect of Fuel. NOx emissions for the three fuels at 180 MPa injection pressure and 30% EGR are shown in Figure 5. As can be seen, the difference in NOx emissions between B0 and

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Figure 5. NOx emissions for B0, B20, and B100 at 180 MPa injection pressure and 30% EGR.

Figure 6. Crank angle at the end of fuel injection for B0, B20, and B100 at 150 and 180 MPa injection pressures and 30% EGR.

B100 was reduced as the SOI was retarded. As expected, NOx emissions increased with an increase in the biodiesel content in the fuel. The increase in NOx emissions was very little between B0 and B20 blends. The results indicate that NOx emissions of B20 may not be a concern at high EGR levels. The difference in NOx emissions for B0 and B100 did not change linearly with respect to SOI. This difference is thought to be due to the difference in combustion patterns of the fuels (oxygen content and amount of premixed burn). The present results are consistent with the finding of a recent study, which also indicated that the NOx emissions using B0 and B20 were comparable.23 It should be noted that, under traditional operational conditions, such as 0% EGR in Figure 1, the increase in NOx is about 15-20% using B100. Although the percentage increase in NOx

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Figure 7. Soot emissions for B0, B20, and B100 at 180 MPa injection pressure and 30% EGR.

Figure 8. BSFC for B0, B20, and B100 at 180 MPa injection pressure and 30% EGR.

emissions using B100 is high (Figure 5), under low-temperature combustion conditions, the absolute magnitude is small. To further investigate the cause for the increase of biodiesel NOx, Figure 6 shows the fuel injection duration of the present engine for three fuels at 150 and 180 MPa injection pressures and 30% EGR. The start of injection was at 0 ATDC. It can be seen that the injection parameters remained nearly the same. Although the present common-rail system can eliminate the injection timing shift, NOx emissions were still significantly higher for B100. The small difference in durations shown in Figure 6 is thought to be due to the measurement uncertainty. Thus, the increase in biodiesel NOx emissions using the present common-rail system is not likely due to the injection timing shift as indicated in a previous study.8

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Figure 9. NOx emissions for B100 at 150 and 180 MPa injection pressures with different EGR levels.

Figure 10. Soot emissions for B100 at 150 and 180 MPa injection pressures with different EGR levels.

The corresponding soot emissions are given in Figure 7. Soot emissions decreased as the amount of biodiesel in the fuel blend increased. Soot emissions were relatively low when B100 was used, particularly, for both early and late injection conditions. The oxygen content in biodiesel clearly helps with soot reduction even at high EGR conditions. Figure 8 compares the BSFC values for three fuels. BSFC increased steadily as the amount of biodiesel in the fuel blend was increased because of the lower energy content in biodiesel. Effects of EGR. NOx emissions for B100 at 150 and 180 MPa injection pressures at 0 and 30% EGR are shown in Figure 9. At both injection pressures, the use of EGR resulted in lowcombustion temperatures and therefore NOx emissions. Effects of injection pressure on NOx emissions were less significant at high EGR levels, where NOx emissions were already low. This

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Figure 11. BSFC for B100 at 150 and 180 MPa injection pressures with different EGR levels.

Figure 12. Cylinder pressure for B100 at 150 MPa injection, 0 ATDC SOI, and 0 and 30% EGR.

feature can enable high injection pressure to be used together with high EGR to reduce soot and NOx emissions simultaneously. The corresponding soot emissions are presented in Figure 10. The increase in EGR consistently increased soot emissions. Considerable differences in soot emissions were observed between 150 and 180 MPa injection pressure cases under conventional injection timing (e.g., -15 and -5 ATDC). Note that combustion was not sustainable for the injection timing past TDC in 30% EGR cases because of the longer ignition delay and low in-cylinder gas temperatures. Figure 11 shows the BSFC values for the corresponding conditions. Effects of EGR on BSFC varied depending upon the injection timing. Figure 12 shows the cylinder pressure at 150 MPa injection and 0 and 30% EGR levels. The start of injection was at 0

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Figure 13. NOx emissions for B0, B20, and B100 with single and double injections at 180 MPa injection pressure and 30% EGR.

Figure 14. Soot emissions for B0, B20, and B100 with single and double injections at 180 MPa injection pressure and 30% EGR.

ATDC. From the cylinder pressure data, it can be seen that the 0% EGR case had higher peak cylinder pressure compared to the 30% EGR case because EGR would decrease the combustion temperature. In addition, EGR also delayed the ignition and resulted in a slower combustion rate. Effects of Double Injection. Figure 13 gives the comparisons of NOx emissions for single and double injections at 180 MPa injection pressure and 30% EGR. The SOI data for doubleinjection cases are the pilot injection timing. The main injection was fixed at 5 ATDC for all of the double-injection cases. The pilot injection consisted of 15% of total fuel. Such doubleinjection configuration was shown to benefit soot and NOx emissions reductions in the present engine in a previous study.18

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Figure 15. BSFC emissions for B0, B20, and B100 with single and double injections at 180 MPa injection pressure and 30% EGR.

The trend in NOx emissions with respect to the fuel blend is the same as that in single-injection conditions. The start of the pilot injection did not have a significant impact on NOx emissions because a majority of emissions are believed to be produced during the main combustion. NOx emissions for double injections were lower than those for single-injection cases under the present operating conditions. This is believed to be due to the phased combustion provided by two injections. Figure 14 shows soot emissions for the same conditions mentioned above. As can be seen, the use of biodiesel reduced soot significantly for both single- and double-injection cases. Note that B20 produced significantly less soot emissions than B0 in double-injection conditions, unlike the single-injection cases. On the other hand, the penalty in B20 NOx emissions is negligible for double-injection conditions. It is worth noting that the U.S. EPA Tier 4 standards effective 2014 for the present off-road engine class (56-130 kW) are 0.4 g/kWh for NOx and 0.02 g/kWh for soot. At the operating conditions tested in this study, B100 using 30% EGR and the double-injection scheme with pilot SOI at -20 and -15 ATDC was able to meet the emissions requirements. The BSFC results for the conditions mentioned above are presented in Figure 15. The BSFC of the double-injection cases were comparable to those of single-injection cases. The BSFC increased significantly with the increase in biodiesel content in the fuel. This increase is primarily due to the lower energy content of biodiesel. Cylinder pressure comparisons for single- and doubleinjection cases are given in Figure 16 for 180 MPa injection pressure and 30% EGR. The start of injection for the singleinjection case was 0 ATDC, while for the double-injection case, the pilot SOI was -20 ATDC and the main SOI was 5 ATDC. The combustion of the pilot fuel led to a high cylinder pressure early in the engine cycle, and the late injection of the main fuel (23) Eckerle, W. A.; Lyford-Pike, E. J.; Stanton, D.; Wall, J.; LaPointe, L.; Whitacre, S. Effects of methyl-ester biodiesel blends on NOx production. SAE Tech. Pap. Ser. 2008-01-0078, 2008.

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Figure 16. Cylinder pressure and HRR for B100 with single and double injections at 180 MPa injection pressure and 30% EGR.

resulted in a lower peak pressure as compared to the singleinjection conditions. 4. Conclusions A medium-duty diesel engine with a common-rail fuel injection system was used to investigate the effect of biodiesel on emissions. Effects of the injection pressure, fuel blend, EGR, and injection scheme on combustion and emissions were evaluated. Biodiesel (B100) consistently produced higher NOx emissions compared to the other fuel (B0 and B20) blends. Soot emissions for B100 were the lowest compared to the other two fuels. The emissions using B0 and B20 were comparable under the conditions studied. The results presented are for a single engine operational regime rpm, and the results could vary at different engine speeds and loads. The increase in injection pressure resulted in an increase in NOx and a decrease in soot regardless of the fuel type. The effect of injection pressure on NOx emissions was less significant at high EGR conditions. The use of EGR helped achieve lowtemperature combustion for low NOx emissions. Doubleinjection schemes with small pilot fuel (i.e., 15%) were shown to have the potential for reducing both NOx and soot emissions simultaneously. Additionally, the increase in NOx emissions at low-temperature combustion regimes is not a concern when B20 is used. The present electronically controlled common-rail injection system produced practically the same injection conditions for different fuel blends. Thus, the increase in NOx emissions by using B100 is not likely due to the variation in the fuel injection conditions. Acknowledgment. The authors acknowledge the financial support from Central State Air Resources Agencies Association (Cen SARA), Iowa Department of Natural Resources, and John Deere.

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Appendix

Figure A3. CO emissions for B0, B20, and B100 with single and double injections at 180 MPa injection pressure and 30% EGR. Figure A1. CO for B100 at 150 and 180 MPa injection pressures with different EGR levels.

Figure A2. HC for B100 at 150 and 180 MPa injection pressures with different EGR levels.

Figure A4. HC emissions for B0, B20, and B100 with single and double injections at 180 MPa injection pressure and 30% EGR. EF8004493