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Energy & Fuels 2007, 21, 3010-3016
Change in Operational Characteristics of Diesel Engines Running on RME Biodiesel Fuel Sergejus Lebedevas,† Andrius Vaicekauskas,*,† Galina Lebedeva,‡ Violeta Makareviciene,§ and Prutenis Janulis§ Department of Marine Engineering, Klaipeda UniVersity Maritime Institute, LT-92123 Klaipeda, Lithuania, Computer Science Department of Faculty of Natural Sciences and Mathematics of Klaipeda UniVersity, LT-92294, Klaipeda, Lithuania, and Laboratory of Chemical and Biochemical Research for EnVironmental Technology, Lithuanian UniVersity of Agriculture, LT-53361, Akademija, Kaunas r., Lithuania ReceiVed July 9, 2006. ReVised Manuscript ReceiVed June 6, 2007
Complex research into the change of parameters concerning the fuel economy, thrust, and harmful components of exhaust gases, namely, hydrocarbons (HC), carbon monoxide (CO), and nitric oxides (NOx), was carried out to evaluate the efficiency of fuel replacement; that is, mineral diesel fuel, which is normally used by diesel engine fleets of agricultural machinery in Lithuania, was replaced with biofuel (hereafter biodiesel), which is rapeseed oil methyl esters, hereafter RME. Diesel engine F2L511 and a single section of diesel engine A41 were chosen as models and tested within the above-mentioned research parameters. Fuel blends of mineral diesel fuel and RME-biodiesel fuel, and also pure RME, were tested as follows: BI0, in which the content of RME is 10%; B15 and B30, in which the contents of RME are 15% and 30% appropriately; and Bl00, which is pure RME. A nonlinear change of operational characteristics was determined depending on the loads of the diesel engine. According to its technical ecological parameters, B30-biodiesel fuel was acknowledged as the most convenient and reliable one being tested within a wide range of speed and load regimes. In the same range of speed and load regimes, the influence of technical conditions of the fuel injector on harmful emission parameters of diesel engine exhaust gases, while running on RME, was estimated by means of a failure simulation of the fuel injector, namely, gumming up the fuel injector nozzle. An improvement of all the ecological parameters was estimated by optimization of the diesel engine injection timing while running on RME.
1. Introduction The results of research into the production and use of rapeseed oil methyl esters (RME) in Lithuanian diesel engine fleets are presented in this article. The above joint research was performed by the Lithuanian Agricultural University, Klaipeda University, and supported by the Council of Science and Studies of Lithuania within the framework of International Project EUREKA, Project Acronym “BIOWASTEFUEL.E! 3234”. The aim of this basic research is the realization of a European Union policy concerning renewable sources of energy, according to Directive 2003/30/EC of the European Parliament, to promote the use of biofuels or other renewable ones in transport and to develop an efficiency of energy (European Commission Green PapersDoing More with Less). The solution of the problem concerning the replacement of mineral oil fuels with biofuels for diesel engines in Lithuania had several features enumerated below. The main part of the diesel engine fleet, which is still operating in Lithuania, consists of models designed and made in the late 1970s to early 1980s. The appropriate statistical data concerning the renovation of agricultural machinery in Lithuania are presented in Table 1. A large number of diesel engines which are still in use in Lithuania were made by the Minsk tractor plant. The main data of these engines are shown in Table 2. * Corresponding author. Tel./fax: +370 46 300101. E-mail address:
[email protected]. † Klaipeda University Maritime Institute. ‡ Computer Science Department of Faculty of Natural Sciences and Mathematics of Klaipeda University. § Lithuanian University of Agriculture.
The design and performance parameters of these diesel engines were chosen by firms-producers and are applicable to fuels of mineral origin. Physical-chemical properties of said fuels, that is, mineral fuels and biofuels, are different, and this reason leads to the modification of the performance parameters of the diesel engine fuel system applicable to biodiesel fuel and, in turn, to better fuel consumption and lower harmful emissions of exhaust gases into the environment. Also, a diesel engine’s thrust characteristics should not worsen when being run on biofuels, and this matter is of great importance to researchers. Mainly, the content of this article is dedicated to consideration of this problem. For the same reason, a limited list of the biofuels’ properties was mentioned in the article. In this article, the authors give a list of physical-chemical properties of different fuels, which is necessary to analyze and comprehend the results obtained within the motor test of diesel engines. The above diesel engine designs can be considered out of date, obviously, as their range of main parameters, such as the rated brake mean effective pressure and specific fuel consumption, are 0.53-0.97 MPa and 220-245 g/kWh, respectively, and do not meet recent demands. Rapeseed is a basic raw material used to produce biodiesel fuel in Lithuania.1 The initial stage of research was performed to evaluate the change of diesel engine operational and ecological characteristics while running on RME diesel fuel and (1) Janulis, P.; Makareviciene¨, V. Biofuel and biooil application in Lithuania; Lithuania University of Agriculture: Kaunas, Lithuania, 2004; pp 1-71.
10.1021/ef060314t CCC: $37.00 © 2007 American Chemical Society Published on Web 08/09/2007
Operational Characteristics of Diesel Engines
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Table 1. Statistical Data Concerning the Renovation of Agricultural Machinery in Lithuania item purchased tractors which were produced in post Soviet Union countries: Minsk tractor plant Lipeck tractor plant Vladimirskij tractor plant purchased tractors produced in other countries total
total quantity, pcs
quantity of new modifications, pcs
2240
1240
1760 50 310 410 3410
1100 130 190 1730
Table 2. Main Technical Parameters of Diesel Engines Made by Minsk Tractor Plant type of diesel engine
number of cylinders, pcs
D120 D242 D243 D244 D245 260.2 TURBO D248 D65MI
2 4 4 4 4 6 4 4
cylinder diameter/ piston stroke length, cm 10.5/12 11/12.5 11/12.5 11/12.5 11/12.5 11/12.5 11/12.5 11/13
engine displacement, dm3 2.07 4.75 4.75 4.75 4.75 7.2 4.75 4.94
for further evaluation of new types of waste biodiesel fuel. The difference between physicochemical and thermodynamic properties of biodiesel fuel and those of a mineral one influences the indicator process in diesel engines and finally changes the operational and ecological parameters.3 It is important to determine the biodiesel fuel optimal concentration being mixed with mineral diesel fuel under different operational conditions to have a maximal effect in decreasing the exhaust gas emissions and a minimal influence on diesel engine technical-economical parameters and regulation as well. Mineral diesel fuel is replaced by biodiesel because of the desire to improve the harmful emission of exhaust gases but not worsen operational parameters and regulation as well. The aim of this performed research stage was an evaluation of operational and ecological qualitative parameter changes for diesel engines of agricultural machinery running on pure RME biodiesel fuel and on a mixture of the same with mineral diesel fuel. 2. Methodical Aspects of the Research High-speed, naturally aspirated F2L511 diesel engines (made by JSC “Oruva ir Ko”, Mazeikiai, Lithuania) and a single cylinder section 1A41 of diesel engine A41 (made by JSC “Altaiskij motornij zavod”, Barnaul, Russian Federation) were tested on an engine test bed. These objects of research were chosen as typical models of diesel engines in Lithuania because of their main parameters, which made it possible to extend the same research and evaluate the diesel engine fleet efficiency and reliability while running on biodiesel fuel. The main parameters of the tested diesel engines are given in Table 3. The types of tested fuels are as follows: mineral diesel fuel as per standard GOST 305; biodiesel fuel RME certified according to standard LST EN 14214 and refined by JSC “Rapsoila”, Mazeikiai, Lithuania; and mixtures of the above-mentioned fuels, namely, 90/10, B10; 85/15, B15; 70/30, B30; and pure biodiesel fuel, Bl00. The physicochemical characteristics of the tested fuels are presented in Table 4. Modeling of the diesel engine technical conditions of different types was an important aspect of this research. Within an experi(2) Canakci, M.; Van Gerpen, J. A pilot plant to produce biodiesel from high free fatty acid feedstocks. Trans. ASAE 2003, 46 (4), 945-954. (3) Schmidt, K.; Van Gerpen, J. The effect of biodiesel fuel composition on diesel combustion and emissions. Society of AutomotiVe Engineers paper no. 961086; SAE: Warrendale, PA, 1996.
brake mean effective pressure, MPa 0.6/0.64 0.64 0.69 0.62 0.97 0.76 0.55 0.53
rated output, kW
rated speed, rpm
specific fuel consumption, g/kWh
18.4/22.1 46 60 42 77 96 44 44
1800-2000 1800 2200 1700 2000 2100 2000 2000
241-245 220 220 225 220 226 220 220
Table 3. Main Technical Parameters of Diesel Engines F2L511 and 1A41 parameter cylinder diameter, cm piston stroke length, cm engine displacement, dm3 compression ratio rated output, kW rated brake mean effective (indicated) pressure pme (pmi), MPa rated speed, rpm fuel injection type of combustion chamber
F2L511
1A41
10 10.5 1.65 17 25.7 0.62
13 14.0 1.115 16 14 (0.85)
3000 direct open
1750 direct open
ment, a failure of fuel injection was simulated in an allowable range of said conditions, and finally a wide and extensive data set which consisted of 87 regimes was compiled. The above data were made available to determine the efficiency of biodiesel fuel, which was used at a certain level within diesel engine operational conditions, and to draw a distinction between the “ideal technical conditions” and the “nonideal technical conditions” of diesel engines, that is, while injector nozzles were gumming up. The loads were regulated within the tests by means of a Zollner 20LLNE3N19A (limits: 0-200 N; a measurement error of ( 0.5% to be taken into account) hydraulic brake, which in turn was controlled by computer block FIPS-S486/66-FTFT-635-ES/AT-084SER/TM-PLU; fuel consumption was measured with a PLU 401115W/116HR feeding rate gauge (limits: 0,3-631/hr, measurement error ( 0.5%). The total exhaust gas emission was measured with a MIR9000 analyzer; namely, a harmful emission of exhaust gases was recorded continuously by the method of infrared spectroscopy and gas filter correlation. The scale divisions while measuring the harmful emission are as follows: carbon dioxide 0-10 ppm, 0-20 mg/m3; nitrogen monoxide (NO) 0-100 ppm, 0-200 mg/m3 (below in the text, nitric oxides are denoted as NOx); hydrocarbons 0-20 ppm, 0-25 mg/m. The accuracy of the measurement error was within the above scale divisions. Within the tests, the direct measure of particulate matter emissions was not carried out. The smoke emission of the exhaust gases was measured by a Bosch analyzer, with a measuring range of 0-10 Bosch units and a measurement accuracy of 0.1 Bosch units.
3. Change of Ecological Parameters while the Diesel Engine Was Run with RME The emission parameters of diesel engines F2L511 and A41, that is, harmful components CO, NOx, and smoke emission depending on the load while running on mineral diesel fuel,
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Table 4. Physicochemical Characteristics of Tested RME Biodiesel Fuels and Mineral Diesel Fuel fuel oils no.
items specification
mineral diesel fuel
B100
B10
B15
B30
1 2 3 4 5 6 6.1 6.2 6.3
density @ 20 deg. C, g/cm3 viscosity @ 40 deg. C, cSt cetane number net heat of combustion, kJ/kg stoichiometric ratio elementary composition carbon, % oxygen, % hydrogen, %
0.840 2.6 46 42 470 0.495
0.887 6.6 51.6 37 417 0.433
0.845 3.0 51.04 41 965 0.489
0.847 3.2 50.76 41 707 0.485
0.854 3.8 49.92 40 954 0.476
87.0 0.4 12.6
77.0 10.9 12.1
86.0 1.45 12.55
85.5 1.98 12.52
84.0 3.55 12.45
Table 5. Emission Parameters of Diesel Engines F2L511 and A41, That Is, Harmful Components CO, NOx, and Smoke Emissions, Depending on Load, while Running on Mineral Diesel Fuel brake mean effective pressure, MPa F2L511
1A41
no.
parameter
0.2
0.4
0.5
0.62
0.09
0.29
0.41
0.49
1 2 3
emission of nitrogen oxides NOx, g/kWh emission of carbon monoxide CO, g/kWh smoke emission, Bosch units
11.9 4.3 0.3
12 1.8 0.6
11.9 2.3 1.75
11.9 7.4 3.5
5.8 4.0
7.0 2.2
8.5 1.7
9.2 2.0
are given in Table 5. The diesel engine emissions of CO and HC and smoke change were characterized by comparatively low levels while running at low and medium loads, that is, 5060% of the rated output, and by an intensive 5- to 6-fold increase while running at rated and maximal loads (see Figure 1). The NOx emission level practically remained unchanged independent of the loads. As expected, the technical condition of the fuel injection equipment, namely, the fuel injector, significantly influenced the ecological parameters of emission. Then, an increase of F2L511 diesel engine harmful emission parameters was obtained while running on different mineral and biodiesel fuel mixtures: increment in CO ∼ 65%; increment in CH ∼ 150%; increment in NOx ∼ 25%; increment in smoke
Figure 1. The ecological parameters relative change of diesel engines F2L511 and 1A41 while running biodiesel fuel: (-b-) B100 (F2L511, n ) 3000 rpm, nonideal technical conditions); (-b-) B100 (1A41, n ) 1750 rpm); (-4-) B30 (F2L511, n ) 3000 rpm, nonideal technical conditions); (-O-) B30 (F2L511, n ) 2000 rpm, nonideal technical conditions); (s) B30 (F2L511, n ) 3000 rpm, ideal technical conditions); (-4-) B30 (1A41, n ) 1750 rpm); (-2-) B10 (F2L511, n ) 3000 rpm, nonideal technical conditions).
emission ∼ 15%, appropriately. The determined level of harmful emission in exhaust gases well correlates with results obtained simultaneously as test data and analytical calculations. An increase of oxygen content in the composition of biodiesel fuel from 1% up to 12%, in comparison tomineral diesel fuel,4 influences a decrease of the stoichiometric ratio of air to fuel and an excess of air in the cylinder ratio. Better characteristics of biodiesel fuel ignition quality, namely, the cetane number of pure biodiesel fuel, 51.9, and that of mineral fuel, 46.0,5 positively influence a decrease in the intensity of heat extraction in the primary kinetic timing of the combustion process characterized by the formation of incomplete combustion products. The increase of heat extraction within the main timing of combustion, namely, diffusion combustion, was maintained by a higher excess of air ratio and was connected with the oxygen content in the fuel during the entire process of combustion. Diffusion combustion timing was characterized by afterburning of the incomplete combustion products formed within the above kinetic combustion timing regime and, finally, the intensity of subsequent hydrocarbons and carbon monoxide formation and its afterburning within the main combustion timing regime. Diffusion combustion decreases greatly harmful emissions while running on biodiesel fuel. NOx emissions increase up to 10-13% and, being of thermal origin, depend on the nitrogen and oxygen concentration and temperature in the combustion zone.8 Also an analogous change of harmful emission increments can be seen for both diesel engines tested at partial workloads independent of the technical condition of the fuel supply equipment. The experimental data curves’ divergence from the generalized curves is about (3-5%. The obtained results made (4) Schumacher, L.; Chellappa, A.; Wetherell, W.; Russel, M. D. The physical & chemical characterization of biodiesel low sulfur diesel fuel blends; Final Report, National Biodiesel Board, University of Missouri: Columbia, MO, 1995. (5) Van Gerpen, J. Cetane number testing of biodiesel. Liquid fuels and industrial products from renewable resources - proceedings of the third liquid fuels conference, Nashville, TN, Sept 15-17, 1996. (6) Schumacher, L. The physical and chemical characterization of biodiesel/low sulfur diesel blends; National Biodiesel Board: Jefferson City, MO, 1995; NBB # 52019-1. (7) ComprehensiVe Analysis of Biodiesel Impacts on Exhaust Emissions; EPA-Draft Technical Report, EPA420-P-02-001, Enviromental Protection Agency: Washington, DC, 2002. (8) Zeldovich, J. The Oxidation of Nitrogen in Combustion and Explosions. Acta Physiochim. URSS 1946, 21 (4), 577-628.
Operational Characteristics of Diesel Engines
it possible to accurately extrapolate test data of the biodiesel fuel and mixtures of the same with mineral diesel fuel to expected results concerning similar diesel engine operating processes and to solve consequent technical reliability problems. Functional dependences of the percent change of emissions on the rated brake mean pressure are of the “S” form; fuel injection incrementation changes the emission a little at low and medium loads, that is, up to 40-50% of the rated output; at loads above 50% of the rated output, namely, 90-100%, it is increased intensively and then stabilized. CO Emission. The use of biodiesel fuel B30 decreases the CO emissions in exhaust gases by 8-12% within the researched loads up to 50%; the change in CO emissions intensively increases up to 30-37% at loads above 50% of the nominal load. The dependence of the change in the CO emission on the rated brake mean effective pressure remains the same also for pure biodiesel fuel B100, and the curves (see Figure 1) equidistantly move toward the greater values of CO emission decrease. Values of the change of CO emission for identical operating regimes made it possible to state that increasing the content of the biodiesel fuel in the mixture with mineral diesel fuel influences a decrease in CO emission, and the above-mentioned dependence is nonlinear. The decrease in B100 CO emissions is 1.51.6 times more than that of B30, while the RME concentration is increased therefore more. This proportion remains constant in the whole researched range of brake mean effective pressures. HC Emission. The decrease in HC emissions is about 20% when using B30 and up to 50% at the rated load. HC emissions are decreased up to 65% when using B100 within the entire researched range of loads and 1.2-1.5 times more than those of B30. Smoke Emission. The decrease in smoke emissions conforms approximately with the change in CO and HC emissions while biodiesel fuel is in use. The dependence of the change in smoke emissions on the rated brake mean effective pressure is of the “U” form, having a maximum at medium load. B30-biodiesel fuel’s smoke emissions in exhaust gases decrease up to 5055% at medium load and are 25-30% at low and rated loads. The maximal effect of the decrease of B100 smoke emissions is 75%; the difference in the smoke emissions of B100 and B30 is l.5-l.8. It should be noted that the smoke emissions’ absolute decrease is at the rated load, or in other words, the greater the load, the less the smoke emissions. NOx Emission. NOx emissions connected by a relation with the rated brake mean effective pressure are analogous to CO and CH emissions relations, excluding the NOx emission increase in the case of biodiesel fuel use. The character of the function of change of the NOx emissions on the rated brake mean effective pressure should be taken into account, namely, the absolute and relative increase of NOx emissions can be seen at rated or lesser loads, that is, 85-100% of the rated output, and its value can reach 15-17% with B100. The intensity of the change in NOx emissions is decreased while running on biodiesel fuel at a medium load, but at low loads, the emission content approximately equals the emission content of the mineral diesel fuel. The measure of change in the NOx emissions when using B100 and B30 at medium and rated loads is 1.3-1.4. 4. Complex Improvement of NOx Emissions by Fuel Injection Timing Optimization To ensure improvement in all of the ecological parameters, the use of biofuel should be maintained by some additional specific means, for example, motor methods and so forth. The motor methods to decrease nitric oxides emissions are as
Energy & Fuels, Vol. 21, No. 5, 2007 3013
follows: exhaust gas recirculation, the use of water injection or the injection of water-in-oil (fuel) emulsions, and the optimization of fuel injection timing as well. The fuel injection timing optimization was carried out in this research as it is the most simple method to use in practice. Fuel injection timing regulation carried out under operating conditions is not complicated and can be considered as one of the real means to improve efficiency while running on biodiesel fuel. The influence of fuel injection timing on ecological parameters was tested by running the 1A41 engine on different fuels such as mineral diesel fuel, B30, and B100; test conditions were as follows: desired speed, n ) 1750 rpm; brake mean indicated pressure, 0.8 of the rated level. The alteration of fuel injection timing was tested in the range of 24-30° before top dead center (TDC). It should be noted that, as usual, the above-mentioned diesel engine injection timing is 27° before TDC (see Figure 2). A reduction in fuel injection timing in turn reduces the intensity of combustion within the primary kinetic timing and shifts it toward the expansion stroke, thus improving the process of combustion while running on biodiesel fuel. This positively influences the reduction of NOx emissions, which mostly forms within kinetic combustion timing before the moment when the maximum pressure of the cycle is reached.10 On the contrary, the emissions of incomplete combustion products are increased, but this increase as a whole is much less than the decrease in emissions if the mineral diesel fuel is in use. The linear character of harmful emissions changes can be seen in Figure 2, namely, the emissions CO and NOx. The increase in CO emissions was calculated for injection timing changed by 1° of the crank angle. It was determined for mineral diesel fuel, B30, to be 3% and for Bl00 to be 2%. At the same time, reduction of the NOx emission is 3-4-fold as much as that mentioned above, namely, for mineral diesel fuel and Bl00 it was 8% and for B30, it was 11%, when calculated for an injection timing change of 1° of the crank angle. Thus, the main task of injection timing optimization was done; that is, the decrease in NOx emissions is more than the increase in CO emissions. For instance, the decrease of fuel injection timing by 2° of the crank angle fully compensates the increase in NOx emissions while the diesel engine is run on B30. The expected increase in CO emissions is only 6%; thus, the whole positive result of B30 is obtained. Simultaneously, Bl00 NOx emissions are decreased down to 12%, and those of B30 are decreased down to 20%. The reduction of fuel injection timing also positively influences the maximum pressure reduction within the cycle and, consequently, the mechanical load reduction on the cylinder liner assembly. Such an increase is an important parameter, as brake-specific fuel consumption is only 2%. As expected, the positive effect of fuel injection timing reduction remains the same for both low and medium loads related with the characteristics of change of CO, HC, NOx, and smoke emissions. 5. Fuel Consumption Change of the Diesel Engine Running on Biodiesel Fuel The change in diesel engine fuel consumption while running on biodiesel fuel was analyzed with regard to two aspects: the change in fuel consumption and the efficiency index of heat conversion into mechanical work (see Figure 3). The RME net (9) Chang, Y. Z. D.; Van Gerpen, J. H.; Lee, I.; Johnson, L. A.; Hammond, E. G.; Marley, S. J. Fuel Properties and Emissions of Soybean Oil Esters as Diesel Fuel. J. Am. Oil Chem. Soc. 1996, 73 (11), 1549-1555. (10) Smailys, V.; Bykov, V. Optimization of economical and ecological parameters of diesel ChN21/21 boosting it by rated brake mean effective pressure. DVigatelestrojenije 1990, 4, 44-46.
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Figure 2. Influence of fuel injection timing on ecological parameters while diesel engine 1A41 runs on different fuels (n ) 1750 rpm): (-O-) mineral diesel fuel; (-4-) biodiesel B30; (-b-) biodiesel B100.
heat of combustion is about 12.5% less than that of mineral diesel fuel.11 Two indices were used to characterize the saving of fuel, that is, brake-specific fuel consumption, be, and equivalent fuel consumption, beeqv, recalculated from brake-specific fuel consumption by a diesel fuel thermal equivalent (note that mineral diesel fuel be ) beeqv). This approach is used in power engineering for the comparative estimation of different sorts of fuels. The use of parameter beeqv, which as a matter of fact is an analog of the indicated efficiency factor, makes it possible to evaluate the relative overall efficiency factor within operating conditions and by an admissible method. The indicated overall efficiency factor can be determined by the following formula:
ηi )
3600Pi HuGf
(1)
where Pi is the indicated power in kilowatts, leaving outmechanical losses, and Gf is the fuel consumption per hour in kilograms per hour. As indicated, the specific fuel consumption bi ) Gf/Pi from the first equation can be transformed into
3600 Hubi
(2)
3600 Hubeηm
(3)
ηi ) and then
ηi )
In the formulas below, index “D” means diesel fuel and “B” means biofuel:
ηi )
3600 HDu bBe ηBm
(4)
ηi )
3600 HBu bBe ηBm
(5)
where ηm is the overall mechanical efficiency factor. By substituting bBeeqv, eqs 4 and 5 transform into
ηBi ηDi
)
bDe bBeeqv
(6)
Both relative changes, namely, beeqv and ηi, are identical, and this fact confirms the use of beeqv to evaluate the efficiency of different fuels while the heat of combustion converts into mechanical work. The results of both diesel engines’ experimental research were qualitatively identical; that is, the fuel consumption, taking into account the measurement error, remained practically unchanged for B10 and B15 and increased by 2-2.5% for B30 and by 10 ( 2 % for B100. A concentration of biodiesel fuel up to and equal to 30% in the mixture with mineral diesel fuel is optimawith respect to fuel consumption change and the effect of ecological parameters improvement. The specific fuel consumption deterioration was as follows: B30 by 2-2.5% and B100 by 9-12% within the whole researched range of loads. Ecological parameters were changed from 30% up to 55%, and a maximal possible ecological parameters improvement effect of 70% was obtained when B100 was used. It should be noted that ecological parameters improvement is accompanied by intensive fuel deterioration, when diesel engines are run on biodiesel fuel where the content of biocomponents is 30% or more. These results were obtained while the fuel feeding system was regulated continuously. The efficiency of the use of biodiesel fuel by operating diesel engines would be increased by main parameters optimization which in turn would be regulated continuously as well, depending on the concentrations of both components, that is, bio- and mineral diesel fuels, in its mixture. In a case of a lack of accurate experimental data, namely, diesel engine indicator process characteristics, one of many ways to derive results is an analysis of the ηi graphical relation within certain parameters of the working cycle, that is, (11) Freedman, B.; Bagby, M. O. Heats of combustion of fatty esters and triglycerides. J. Am. Oil Chem. Soc. 1989, 66 (11), 1601-1605.
Operational Characteristics of Diesel Engines
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Figure 3. Diesel engines F2L511 and 1A41 fuel consumption changes while running different fuels: (-O-) mineral diesel fuel ([| | | | |], summary of 87 regimes); (-4-) biodiesel B30 ([/ / / / /], summary of 87 regimes); (-×-) biodiesel B10 (1A41, B15); (-b-) biodiesel B100; (-‚-‚-‚-) B100 B30 beekv ; (-‚‚-‚‚-) beekv .
the excess of the air ratio, compression ratio, and pressure increase ratio.12 To evaluate the efficiency of heat conversion into mechanical work, specific efficient equivalent fuel consumption beeqv may be used. The use of B30 biodiesel fuel increases the efficiency of heat energy by approximately 2%, compared to that with mineral diesel fuel for both diesel engines (see Figure l). Additionally, the use of B100 decreases bB100 eeqv by only 1-2% when used by the 1A41 diesel engine, in comparison with bB30 eeqv while the biodiesel fuel content in the fuel mixture is 3-fold B30 more. The decrease of bB100 eeqv in comparison with beeqv is not determined entirely for the F2L511 diesel engine. 6. Thrust Characteristics of the Diesel Engine Running on Biodiesel Fuel From a conventional viewpoint, thrust characteristics are understood as a relation of torque Mt (brake mean effective pressure) to the diesel engine speed by a maximum quantity of the fuel portion, qcycle, within a fuel cycle. The cycle portion of (12) Ivancenko, N.; Krasovskij, O.; Sokolov, S. High turbocharging of diesel engines; Masinostroenije: Leningrad, 1983; pp 1-198.
the fuel, which is delivered by a plunger and distributional highpressure fuel pumps (excluding accumulative fuel supply systems), is determined by the working stroke of the plunger and the density of the fuel. Biodiesel fuels are characterized by higher density, and this reason makes it possible to compensate for a partial loss of diesel engine power while running biodiesel fuels having a lower net heat of combustion. Engine torque, while the diesel engine speed is maintained as constant, is determined by the quantity of fuel delivered by the high-pressure fuel pump, and the efficiency of heat energy converted into mechanical work is evaluated by effective overall efficiency factor ηe. In the case where ηm ) idem, when the speed of the engine and the brake mean effective pressure are constant, the above can be evaluated by indicated overall efficiency factor ηi. Relative divergence of the brake mean effective pressure, torque, can be evaluated by the following formula:
δpme ) 1 -
pBme pDme
)1-
ηBi qBcycleHBu ηDi qDcycleHDu
)1-
bDe bBe
×
qBcycle qDcycle
(7)
The quantity of fuel delivered by the plunger within the cycle qcycle = pxVcycle. If Vcycle ) idem,
3016 Energy & Fuels, Vol. 21, No. 5, 2007
qDcycle qBcycle
≈
FD FB
LebedeVas et al.
(8)
Equations 7 and 8, being solved simultaneously, are transformed into the final form:
δpme ) 1 -
bDe bBe
×
FB FD
(9)
The reduction of brake mean effective pressure of naturally aspirated diesel engines within the range of boost does not exceed 1% when using B30. The use of B100 by the diesel engine is characterized by a reduction of the brake mean effective pressure by 5-6% and involved the regulation of the high-pressure fuel pump, increasing the cycle quantity of fuel, qcycle. There is no necessity to regulate qcycle and the injection timing while running B30. Optimal parameters remain constant for both fuelssmineral and B30 biodiesel fuels. 7. Conclusions The qualitative identical “S” forms of CO, HC, and NOx and the change in harmful emissions connected by a relation to the load were determined for all biodiesel and mineral diesel fuel mixtures and for different technical conditions of the fuel system equipment, namely, injectors (for instance, gumming of the injectors). An appreciable improvement in the ecological parameters can be seen at loads above 40-50% of the rated loads. The maximum effect of increment of the emissions was determined at loads of 90% of the rated output and rated loads as well. The use of B30 biodiesel fuel was determined as the technically reliable optimum within a wide range of speed and load regimes in respect to ecological and technical economical parameters: (1) The reduction of exhaust gas emissions by increasing the biofuel content in the fuel mixture up to 30% is as follows: CO by 30-37%, HC by 20-50%, and smoke emission by 50-55%; this composes about 70% of the total
maximum effect when compared with the possible improvement in ecological parameters if B100 is used. (2) The increase in NOx emissions while running biodiesel fuels is as follows: B30 by 10-12% and Bl00 by 17%. (3) The deterioration of fuel consumption and the decrease of thrust characteristics (depending on biofuel content in fuel mixture) are as follows: B30 by 2-2.5% and Bl00 by 10 ( 2 %. A reduction of fuel injection timing by 2° of the crank angle makes it possible to obtain a complex reduction of all the harmful emission parameters including NOx while running biodiesel fuel, that is, RME. The above was confirmed experimentally, and moreover, any noticeable loss of fuel savings cannot be seen. For instance, the use of biodiesel fuel, namely, B30, by diesel engine A41 makes it possible to reduce harmful emission components in comparison with mineral fuels as follows: CO, 33%; NOx, 10%. The above-mentioned reduction was obtained by decreasing the crank angle from 27° to 25° before TDC, and this involves, in turn, the consequent reduction of fuel injection timing. The diesel engine indicator process, while running biodiesel fuel, is characterized by a higher value of the indicated overall efficiency factor ηi in comparison with mineral diesel fuel. The increase of ηi expressed by equivalent fuel consumption bBeeqv ) bBe HBu /HDu is 2% for B100 biodiesel fuels. The obtained results can be used as a basis to evaluate the ecological parameter improvement of diesel engines, which are still in use in Lithuania, when running biodiesel fuel. Objects of further research are the consequent determination and comparative analysis of the generalized relation of ηi to the main parameters of the diesel engine working process while running biodiesel and mineral diesel fuels.13 Acknowledgment. The research work was carried out within the framework of the EUREKA program. The authors are thankful to the Lithuanian Science and Studies Foundation for Support. EF060314T (13) Lebedev, S.; Nechaev, L. Indices improVement of standard size high speed diesel engines; Russian Federation Transport Academy Press: Barnaul, Russia, 1999; pp 1-112.
