Energy Fuels 2010, 24, 2868–2874 Published on Web 04/14/2010
: DOI:10.1021/ef901317u
Influence of Biodiesel Addition to Fischer-Tropsch Fuel on Diesel Engine Performance and Exhaust Emissions Md. Nurun Nabi* and Johan Einar Hustad* Norwegian University of Science and Technology (NTNU ), 7491 Trondheim, Norway Received November 9, 2009. Revised Manuscript Received March 22, 2010
This paper reports on the influence of jatropha biodiesel (JBD) addition to Fischer-Tropsch (FT) fuel on diesel engine performance and exhaust emissions. JBD was produced from Jatropha Carcus oil and blended with FT fuel in volumetric ratios of 0:100, 25:75, 50:50, 75:25, and 100:0. The different JBD blends were termed as B0, B25, B50, B75, and B100. A six-cylinder, four-stroke, turbocharged, direct injection (DI) diesel engine was used in the experiments. The experimental results showed that without deteriorating engine performance, FT fuel produced less CO, THC, NOx, smoke, and PM emissions compared to diesel fuel (DF). The reduction in emissions was mainly due to extremely low amounts of or an absence of sulfur and aromatic compounds in FT fuel. Compared to FT fuel, JBD blends (B25, B50, B75, and B100) resulted in lower CO, THC, smoke, and PM emissions with higher NOx emissions. However, the engine thermal efficiency was slightly lower with higher JBD blends. On the basis of the engine performance and emission results, lower JBD blend, B25 for instance, may be one of the competitors for an environmentally friendly future alternative fuel.
Without modifying the engine, Huang et al.3 found lower CO, THC, NOx and smoke emissions relative to DF. Compared to DF, FT fuel reduced emissions, including benzene by 30-95%, toluene by 10-90%, o-xylene by 60-95%, and m-xylene by 30-90%.4 Another study reported lower or similar NOx emissions, lower CO2 emissions, and lower PM emissions with FT fuel.5 Like FT fuel, BD offers several benefits from diesel emissions. Most recently, there has been a growing interest in BD because of the following reasons: • BD is renewable in nature. • BD is biodegradable. • BD is nontoxic. • BD has a higher flash point and provides greater safety in transportation. • BD produces less emissions. • BD creates employment opportunities in rural areas.
1. Introduction As a result of the nonrenewable nature of fossil fuels, increasing worldwide demand for fuel and energy, and the price hike of fossil fuels in the 1980s, alternative renewable sources of fuels for internal combustion (IC) engines are needed to ensure the security and longevity of supply. For the last several decades, engine and fuel researchers devoted themselves to exploring alternative renewable fuels. In their efforts of exploring renewable alternative fuels for IC engines, Fischer-Tropsch (FT) fuel was found to be an effective alternative renewable fuel as it can be derived from coal, natural gas, or even biomass sources. FT is a process of converting a mixture of CO and hydrogen into liquid hydrocarbon. The liquid hydrocarbon is known as FT fuel. FT fuel is effective to reduce PM and NOx emissions. Like FT fuel, biodiesel (BD) was also found to be effective alternative fuel. BD is produced from plant oils, waste cooking oils, animal fats, or even yellow grease by a well-known transesterification process. Fuel and engine researchers are trying to reduce the exhaust emissions mainly three ways, such as replacing the fossil fuel with alternative fuel, improving the combustion chamber design, and exhaust after-treatment. Larsson et al.1 reported lower soot emissions with FT fuel as a negligible amount of aromatic contents in FT fuel. CO and THC emissions were lower due to the higher cetane number and lower densities of FT fuel. NOx emissions were also lower for FT fuel compared to diesel fuel (DF). McMillan et al.2 found lower NOx, CO, THC, and PM emissions with FT fuel.
Several reports6,7 elucidated lower exhaust emissions, including THC, CO, and smoke emissions fueling with BD. (3) Huang, Y.; Wang, S.; Zhou, L. Effects of Fischer-Tropsch diesel fuel on combustion and emissions of direct injection diesel engine. Front. Energy Power Eng. China 2008, 2 (3), 261–267 (DOI:10.1007/s11708-0080062-x). (4) Nord, K.; Haupt, D. Evaluating a Fischer- Tropsch Fuel, Eco-ParTM, in a Valmet Diesel Engine. SAE paper no. 2002-01-2726, 2002. (5) Cowart, J. S.; Sink, E. M.; Slye, P. G.; Caton, P. A.; Hamilton, L. J. Performance, Efficiency and Emissions Comparison of Diesel Fuel and a Fischer-Tropsch Synthetic Fuel in a CFR Single Cylinder Diesel Engine during High Load Operation. SAE paper no. 2008-012382, 2008. (6) Puhan, S.; Vedaraman, N.; Sankaranarayanan, G.; Rama, B. V. B. Performance and emission study of Mahua oil (madhuca indica oil) ethyl ester in a 4-stroke natural aspirated direct injection diesel engine. Renewable Energy 2005, 30, 1269–1278. (7) Puhan, S.; Vedaramana, N.; Rama, B. V. B.; Sankaranarayanan, G.; Jeychandran, K. Mahua oil (Madhuca Indica seed oil) methyl ester as biodiesel-preparation and emission characterstics. Biomass Bioenergy 2005, 28, 87–93.
*To whom correspondence should be addressed. E-mail: nurun.
[email protected];
[email protected]. (1) Larsson, M.; Denbratt, I. An Experimental Investigation of Fischer-Tropsch Fuels in a Light-Duty Diesel Engine. SAE paper no. 2007.01-0030, 2007. (2) McMillan, M. H.; Goutam, M. Combustion and Emission Characteristics of Fischer-Tropsch and Standard Diesel Fuel in a SingleCylinder Diesel Engine. SAE paper no. 2001-01-3517. r 2010 American Chemical Society
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Energy Fuels 2010, 24, 2868–2874
: DOI:10.1021/ef901317u
Nabi and Hustad
the dilution ratio of 20. The in-cylinder gas pressure data were recorded with a pressure transducer (PCB-M112B11). In the current investigation, the engine loads were varied from 50 N-m to 1450 N-m. 50 N-m corresponds to 3% of the rated load; 400 N-m corresponds to 23%; 800 N-m corresponds to 46%; 1200 N-m corresponds to 69%; and 1450 N-m corresponds to 83% of the rated load. A range of 3-23% was considered as low loads, 46% was considered as a medium load, and 69-83% was considered as high loads.
Table 1. Specifications of the Tested Engine engine type compression ratio bore stroke number of cylinders firing sequence Maximum torque maximum power injection system size and number of holes needle opening pressure
Scania DC 1102 18:1 127 140 mm 6 1-5-3-6-2-4 1750 @ 1080-1500 rpm 280 kW @ 1800 rpm unit injector φ 0.216 mm 8 220 bar
3. Results and Discussion
However, NOx emissions were reportedly higher or lower with BD. Knothe et al.8 reported lower PM, THC, and CO emissions with BD compared to neat diesel, but NOx emissions were slightly increased with commercial BD and technical grade methyl oleate, while methyl laurate and methyl palmitate as well as dodecane and hexadecane led to a slight decrease of NOx compared to the base fuel. In this work, engine performance and exhaust emissions with neat DF, FT fuel, and different jatropha biodiesel (JBD) blends were investigated. Unlike other edible oils like soybean and rapeseed, jatropha oil is an inedible vegetable oil, which was chosen to avoid the food versus fuel conflict. JBD was blended with FT fuel at volumetric ratios of 0, 25, 50, 75, and 100%. In the text, the term FT is used with reference to EcoPar AB. The purposes of this work are as follows:
Exhaust Emissions. THC Emissions. Figure 1 shows the THC emissions of DF, FT fuel, and JBD (B25, B50, B75, and B100) blends for a wide operating load range. It is widely accepted that the THC is formed mainly due to over lean or over rich mixture. THC emissions were found to be lower with FT fuel compared to DF. At low to high load conditions (5-1450 N-m), the reductions in THC emissions with FT fuel ranged from 5 to 20%. Higher cetane number and lower density of FT fuel may be the reasons of lower THC emissions with FT fuel. Lower THC and CO emissions with FT fuel were also reported by Larsson et al.1 Compared to FT fuel, JBD blends reduced THC emissions significantly throughout the load range. Shorter ignition delay due to higher cetane number (Figures 8 and 9) and oxygen content in the JBD blends were the reasons for lower THC emissions. For a high load condition (1450 N-m), the reductions with B25, B50, B75, and B100 (JBD blends) were found to be 16, 56, 60, and 64%, respectively. CO Emissions. The variation in the CO emissions for the different fuels is shown in Figure 2. It is generally believed that CO emissions result from incomplete combustion from fuel rich regions. Compared to DF, FT fuel combustion resulted in lower CO emissions at high loads and slightly higher emissions at low loads as can be seen from Figure 2. The reductions in CO emissions with FT fuel were found to be 15% at a load of 1450 N-m. It has been reported earlier that FT fuel reduces CO emissions.10,11 Compared to FT fuel, JBD blends (B25, B50, B75, and B100) produced significantly lower CO emissions at high loads. However, CO emissions at low loads were approximately the same as those of FT fuel. At high load condition (1450 N-m), the reductions in CO emissions with B25 blend were 7%, while 24% lower CO emissions were realized with B50 blend. Reductions in CO emissions of 26 and 34% were observed with B75 and B100, respectively. The reductions in CO emissions with JBD blends were mainly due to the presence of oxygen in the blended fuels. The additional oxygen in JBD blends caused more complete combustion. Lower CO emissions were realized with oxygenated fuels as reported by Miyamoto et al.,12 Beatrice et al.,13 and Zhu et al.14
• To investigate the engine performance, combustion, and emissions with DF, FT fuel, and BD blends • To compare engine performance, combustion, and emissions among DF, FT fuel, and different BD blends • To suggest alternative fuel for a diesel engine 2. Experimental Setup and Procedure of Experimentation The experiments were performed with a six-cylinder, fourstroke, direct injection (DI), turbocharged diesel engine. The specifications of the engine are shown in Table 1. The engine speed was kept constant at 1450 rpm. The speed was optimized with respect to thermal efficiency.9 The dynamic fuel injection timing was set at 20 °CA BTDC. The properties of the tested fuels are shown in Table 2. The JBD was made by a well-known transesterification process. The transesterification process is the conversion of triglycerides of oils or fats to produce esters and glycerol. In the process, triglycerides of oils or fats were reacted with an alcohol in the presence of a catalyst. Methanol or ethanol can be used as an alcohol, and KOH or NaOH can be used as a catalyst. If methanol is used the ester is termed as methyl ester (BD), or it is termed as ethyl ester (BD) if ethanol is used. The exhaust emissions including NOx concentrations were measured with a chemiluminescence detector (CLD) (Horiba PG-250), the THC emissions were measured with a heated flame ionization detector (FID) (JUM 3-200), and the filter smoke number (FSN) was measured with an AVL 415S smoke meter. The CO and CO2 concentrations were measured with a nondispersive infrared detector (NDIR) and O2 concentrations were measured with a paramagnetic detector. An electrical low pressure impactor (ELPI), Dekati, Finland, was used for determining fine particle number and mass emissions in this investigation. The size of the fine particle can be measured within the range of 42-8400 nm. For measuring the numbers and masses of fine particle, the engine operating conditions were engine speed of 1450 rpm, dynamic fuel injection timing of 20 °CA BTDC, and
(10) Schaberg, P. W.; Zarling, D. D.; Waytulonis, R. W.; Kittelson, D. B. Exhaust Particle Number and Size Distributions with Conventional and Fischer-Tropsch Diesel Fuels. SAE paper no. 2002-01-2727, 2002. (11) Schaberg, P. W.; Myburgh, I. S.; Botha, J. J.; Khalek, I. A. Comparative Emissions Performance of Sasol Fischer-Tropsch Diesel Fuel in Current and Older Technology Heavy-Duty Engines. SAE paper no. 2000-01-1912, 2000. (12) Miyamoto, N.; Ogawa, H.; Nabi, M. N.; Obata, K.; Arima, T. Smokeless, low NOx, high thermal efficiency and low noise diesel combustion with oxygenated agents as main fuel. SAE paper no. 980506, 1998. (13) Beatrice, C.; Bertoli, C.; Del Giacomo, N.; Migliaccio, M. na. Potentiality of Oxygenated Synthetic Fuel and Reformulated Fuel on Emissions from a Modern DI Diesel Engine. SAE paper no. 1999-013595, 1999.
(8) Knothe, G.; Sharp, C. A.; Ryan, T. W. Exhaust emissions of biodiesel, petrodiesel, neat methyl esters, and alkanes in a new technology engine. Energy Fuels 2006, 20, 403–408. (9) Nabi, M. N.; Kannan, D. Hustad, J. E. Experimental investigation of diesel combustion and exhaust emissions fuelled with FischerTropsch-biodiesel blends: Part-I. SAE paper no. 2009-01-2721, 2009.
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Energy Fuels 2010, 24, 2868–2874
: DOI:10.1021/ef901317u
Nabi and Hustad
Table 2. Properties of the Tested Fuels tested fuels properties
unit
BD specification EN14214
Method
viscosity (kinematic) @40 °C density @15 °C carbon hydrogen oxygen distillation 90% flash point content of sulfur ash (sulfated) oxidation stability cetane number higher calorific value lower calorific value cold filter plug point (cfpp) neutral value ester monoaromatic hydrocarbon diaromatic hydrocarbon polyaromatic hydrocarbon methanol content free glycerol monoglyceride diglyceride triglyceride iodine number
cSt kg/m3 % w/w % w/w % w/w °C °C mg/kg wt % 3 h/110 °C MJ/kg MJ/kg °C mg/KOH % w/w % v/v % v/v % v/v % w/w % w/w % w/w % w/w % w/w
3.5-5.0 860-900
0.5 max 96.5 min
EN 3104 EN 3675 ASTM D3176 ASTM D3176 ASTM D3176 ASTM D86 EN 3679 EN 20846 EN 3987 EN 14112 ASTM D613 ASTM D240 ASTM D4529 EN 116 EN 14104 EN 14103
0.2 max 0.02max 0.8 max 0.2 max 0.2 max 120 max
EN 14110 EN 14105 EN 14105 EN 14105 EN 14105 EN 14111
360 max 120 min 10 max 0.02 6 min 51 min
DF
FT fuel
2.58 840 85.95 14.05 0 324 65.2 2.78
