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Online Emissions from a Vibrating Roller Using an Ethanol-Diesel Blend during a Railway Construction O. Armas,*,† M. Lapuerta,† C. Mata,† and D. Pe´rez‡ Escuela Te´cnica Superior de Ingenieros Industriales, UniVersidad de Castilla-La Mancha, Edificio Polite´cnico, AV. Camilo Jose´ Cela s/n. 13071, Ciudad Real, Spain and AZVI, S.A. c/ Almendralejo, 5. 41019, SeVilla. Spain ReceiVed February 20, 2009. ReVised Manuscript ReceiVed April 7, 2009
The present work has been focused on the measurement and analysis of diesel emissions produced by a construction machinery (vibrating roller) fuelled with conventional fuel and an ethanol-diesel blend under the typical operations in railways construction. A commercial pure diesel fuel and a blend with 7.7% v/v of anhydrous ethanol (99.7%) were used as test fuels. The vibrating roller was equipped with a system HORIBA OBS 1300. The OBS system includes sensors for measurement of gaseous emissions, air-fuel ratio, exhaust gas flow, exhaust temperature and pressure, global positioning system (GPS), and inertial sensor. The last two sensors were used to determine the position and the velocity of the machine. Ambient conditions (temperature, pressure, and humidity) were measured using a sensor also coupled to the OBS system. A smoke meter Wager 6500 was used to measure the smoke opacity, and this signal was also registered by the OBS system. The properties of the test fuels and the time-recording of all the machine parameters were used for the analysis and interpretation of the results. The studied operation sequences were named: engine start on (S), idle operation (I), circulation (C), and work (W). The obtained results suggest that the use of the e-diesel blend is an interesting alternative for a significant reduction in smoke opacity during transient engine operation, the latter being a usual condition in this type of vehicles.
1. Introduction It is widely accepted that, similarly as many other oxygenated fuels, the use of ethanol-diesel fuels significantly reduces particulate emissions and smoke opacity.1-4 However, no unanimous position is taken with respect the effect of such blends on nitric oxides (NOx) and carbon monoxide (CO). Some published works show that ethanol-diesel blends (10% v/v without additives) increase NOx emissions at high load,1,2,5-7 or at low load,4,8 from engine tests under steady conditions. Other works under similar conditions show reductions in NOx * To whom correspondence should be addressed. Phone: +(34) 926 295 462; fax: +(34) 926 295 361; e-mail:
[email protected]. † Universidad de Castilla-La Mancha. ‡ AZVI. (1) De-gang, L.; Huang, Z.; Xingcai, L.; Wu-gao, Z.; Jian-guang, Y. Renewable Energy 2005, 30, 967–976. (2) Lapuerta, M.; Armas, O.; Herreros, J. M. Fuel 2008, 87, 25–31. (3) Armas, O.; Ca´rdenas, M. D.; Mata, C. Smoke Opacity and NOx Emissions from a Bioethanol-diesel Blend during Engine Transient Operation. SAE Paper 2007-24-0131; 2007. (4) Bang-Quan, H.; Shi-Jin, S.; Jian-Xin, W.; Hong, H. Atmos. EnViron. 2003, 23, 4965–4971. (5) Spreen, K. Evaluation of oxygenated diesel fuels. Final Report for Pure Energy Corporation; Southwest Research Institute: San Antonio, TX, 1999. (6) Xiaoyan, S.; Xiaobing, P.; Yujing, M. Atmos. EnViron. 2006, 40, 2567–2574. (7) Subramanian, K. A.; Singal, S. K.; Saxena, M.; Singhal, S. Biomass Bioenergy 2005, 29, 65-72. ¨ .; C¸elikten, I¨.; Usta, N. Energy ConVers. Manage. 2004, 45, (8) Can, O 2429–2440. (9) Xing-cai, L.; Jian-guang, Y.; Wu-gao, Z.; Zhen, H. Fuel 2004, 83, 2013–2020. (10) Kass, M. D.; Tomas, J. F.; Storey, J. M.; DomingoV; N.; Wade, J.; Kenreck, G. Emissions from a 5.9 Liter Diesel Engine Fuelled with Ethanol Diesel Blends. SAE Paper 2001-01-2018 (SP1632); 2001.
emissions either at high load4,8-11 or at low load.1,9 Other studies made under transient sequences showed increases or decreases in NOx emissions depending on the sequence.3 In the case of CO emissions, some studies show increases,10,11 and others record decreases.7 However, the majority of the works state that the CO concentration is increased or reduced with respect to that observed with diesel fuel depending on the engine load.1,6,8,9 All the studies mentioned used blends with 10% ethanol v/v, except6 where ethanol-biodiesel-diesel blends (5% ethanol and 20% biodiesel) were used, and they all used small-cylinder engines. In all cases the engine was tested under steady or wellcontrolled transient conditions. By the contrary, very few studies are published presenting results from vehicles developing their usual duty. The use of ethanol-diesel blends requires the fulfilment of different technical and legal restrictions, which force the installation of specific equipment such as seals for fuel tanks, security valves on vehicle fuel tanks and on fuel station tanks, special systems for recovering of fuel vapors on vehicles and fuel stations, etc. These restrictions constitute a barrier for the massive use of the ethanol-diesel blends in private vehicles. By the contrary, such requirements are easier to accomplish by captive fleets, such as those of urban buses or public construction (11) Shaus, J. E.; McPartlin, P.; Cole, R. L.; Poola, R. B.; Sekar, R. Effect of Ethanol Fuel Additive on Diesel Emissions. Report for Illinois Department of Commerce and Community Affairs and US Department of Energy; Argonne National Laboratory: 2000. (12) Durbin, T. D.; Collins J. R.; Galdamez, H.; Norbeck, J. M.; Smith, M. R.; Evaluation of the effects of biodiesel fuel on emissions from heavyduty non road vehicles. Final Report by Center for EnVironmental Research and Technology; College of Engineering, University of California: 2000.
10.1021/ef900148c CCC: $40.75 2009 American Chemical Society Published on Web 05/01/2009
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and civil machinery. For this reason, a construction machine was selected, similarly as others researchers did in their studies.12,13 The construction machine selected and used in this work is classified as mobile nonroad machinery in the European legislation.14 This vehicle fleets were excluded from emission directives until recently. However, the new directives approved in the European Union impose different security and health requirements as well as emissions limitations to this machinery to be commercialized in the European countries. In 2004 the directive 2004/26/CE was published, restricting the pollutant emissions for the commercialization of the new machinery.15 Additionally, more regulations are planned for 2009 and beyond in the European Union to provide more stringent limitations to the emissions of this machinery. Similarly, regulations for the emissions from these machines started in 1998.13 Therefore, it can be foreseen in the future an increasing interest by manufacturers, on the one side, to develop lower-consuming and cleaner engines, and on the other side, to promote research on the study of the environmental effects of alternative fuels to be used in their engines and machinery. The present work intends to provide some information that may be useful for future control emissions actuations to be applied in the construction machinery. Various studies have been published during the last years trying to quantify the gaseous emissions from on-road vehicles.16-18 Owing to the low repeatability of the working cycles and to the complex combination of steady and transient sequences they are composed of, their authors often opt to enlarge the number of recorded experiments in order to improve the statistic significance of the results. This procedure increases the cost of the projects, and even then, an appropriate number of records may not be guaranteed in all cases for an adequate statistic analysis. The methodology used in this work was to compare the emissions obtained with the two tested fuels during similar sequences in which the whole working cycle was divided. The defined sequences were identified as “engine start on”, “idle”, “circulation”, and “work”. Some other published studies used similar methodologies.12,13,19,20 2. Experimental Facilities A vibrating roller Lebrero Rahile 155TT was employed as the experimental unit. This construction machine was equipped with a 6-cylinder 4-stroke turbocharged, direct injection diesel engine, typical of those used during road and railway construction. The main engine characteristics are listed in Table 1. The vibrating roller was equipped with a system HORIBA OBS 1300 as shown in Figure 1. (13) Cocker, D. R.; Shah, S. D.; Johnson, K.; Miller, J. W.; Norbeck, J. M. EnViron. Sci. Technol. 2004, 38, 2182-2189. (14) Directive 97/68/CE; European Parliament and Council: Dec. 16, 1997. (15) Modifying Directive 97/68/CE. Directive 2004/26/CE; European Parliament and Council: Apr. 21 2004. (16) Kittelson, D. B.; Watts, W. F.; Johnson, J. P., J. Aerosol Sci. 2006, 37, 913-930. (17) Durbin, T. D.; Cocker, D. R.; Sawant, A. A.; Johnson, K.; Miller, J. W.; Holden, B. B.; Helgeson, N. L.; Jack, J. A.; Atmos. EnViron. 2007, 41, 5647-5658. (18) Ropkins K.; Quinn, R.; Beebe, J.; Li, H.; Daham, B.; Tate J.; Bell M.; Andrews, G. Sci. Total EnViron. 2007, 376, 267-284. (19) Durbin, T. D.; Johnson, K.; Miller, J. W.; Maldonado, H.; Chernich, D. Atmos. EnViron. 2008, 42, 4812-4821. (20) Chen, C; Huang, C; Jing, Q; Wang, H.; Pan, H.; Li, L.; Zhao, J.; Dai, Y.; Huang, H.; Schipper, L; Streets, D. G. Atmos. EnViron. 2007, 41, 5334-5344. (21) Lapuerta, M.; Armas, O.; Garcı´a-Contreras, R. Fuel 2007, 86, 1351– 1357.
Armas et al. Table 1. Main Engine Characteristics of the Lebrero Rahile 155TT Vibrating Roller model fuel injection system rated power highly intermittent rated torque cylinder arrangement bore (mm) stroke (mm) swept volume (L) compression ratio
Deutz FL6913 turbocharged Bosch in-line injection pump 109 kW (at 2500 min-1) 510 N m (at 1700 min-1) 6, in-line 102 125 6.128 15.5:1
The OBS system includes sensors for the measurement of gaseous emissions (among which only those of NOx are presented here), the relative air-fuel ratio (Fr), the exhaust gas flow (Vg), the exhaust temperature (Tg) and pressure, the vehicle velocity (V), and its position. The NOx emissions were measured with a MEXA 720 NOx analyzer equipped with a zirconium sensor. This sensor also measures the O2 concentration, which was used for the determination of the instantaneous equivalence ratio, which is considered here as the relative fuel-air ratio with respect to each fuel stoichiometry. The smoke opacity, which ranges from 0 to 100% and is proportional to the total light extinction across the exhaust gas stream, was determined by a smoke opacimeter, Wager 6500, with this measurement also being registered by the OBS system. The vehicle velocity and position were determined using a global positioning system (GPS) and an inertial sensor. For recording all the instantaneous vehicle parameters and emissions, a Data logger PC OBS-1000 was employed. The sampling frequency used by the OBS system was 1 Hz. Finally, the ambient conditions (temperature (Tamb), pressure, and humidity) were measured using a sensor coupled to the OBS system. Figure 2 shows an installation scheme of the different sensors used during the experimental work.
3. Fuels A low-sulfur diesel fuel was used as a reference for comparison (ref). A blend was made by blending 7.7% v/v ethanol (E) with reference diesel fuel, using a stabilizing additive (0.62%), and it was denoted as e-diesel fuel (ED7.7). The e-diesel fuel was supplied by Abengoa Bioenergy and O2Diesel companies. The ethanol volume content of the tested blend was determined attending to the results of the previous study.21 The main properties, either measured or calculated, of the tested fuels are presented in Table 2. Since the additive composition is not known, all the characteristics of the ED7.7 fuel derived from
Figure 1. A general view of the experimental installation.
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Figure 2. Scheme of experimental installation on the vibrating roller: 1-personal computer, 2-data integration unit, 3-heated line for gas sampling, 4-tube, 5-high pressure sample outlet for flow rate measurement, 6-NOx sensor, 7-pitot probe, 8-pitot pipe, 9-smoke opacity sensor, 10-exhaust pressure sample outlet, 11-gas sampling toward heated line, 12-low pressure sample outlet for flow rate measurement. Table 2. Fuel Properties ref density (kg/m3)a kinematic viscosity (cSt)b gross heating value (MJ/kg) low heating value (MJ/kg)c %C (in weight)d %H (in weight)d %O (in weight)d % H2O (in weight)d %S (in weight)d C/H mass ratio stoichiometric fuel-air ratiod adiabatic flame temperaturee (K); initial conditions: relative fuel-air ratio ) 1; pressure ) 90 bar; temperature ) 900 K Distillation PI (°C) T10 (°C) T20 (°C) T50 (°C) T90 (°C)
ED7.7
E
834.9
831
792
2.718
2.408
1.1314
45.54
43.82
28.04
42.61
40.80
25.18
86.13
83.63
52.14
13.87
13.82
13.13
2.55
34.73
0.024
0.202
0.0057 0.0034f 6.209 1/14.67 2738
Figure 3. NOx emissions and relative fuel air ratio during the sequence W.
0 6.051 1/14.25 2736
3.970 1/9.00 2674
Table 3. Mean Values of Some Operation Parameters Obtained from the Data Measured during the Whole Sequence sequence
fuel
Fr
Tamb (°C)
Texh (°C)
Vg (L/min)
m ˙ fuel (g/s)
V (km/h)
S
ref ED7.7 ref ED7.7 ref ED7.7 ref ED7.7
0.259 0.240 0.186 0.181 0.308 0.312 0.528 0.471
3 6 7 2 9 0 2 3
157 84 162 154 243 238 387 348
3498 2871 3467 3470 5444 4025 5905 4638
0.794 0.750 0.563 0.574 1.221 0.950 1.750 1.340
0 0 0 0 7.6 6.6 6.7 3.5
I C W
182 204 220 266 348
78 79 205 257 347
78
a Measured at 15 °C. b Measured at 40 °C. c Calculated from composition and gross heating value. d Obtained from composition. e Calculated using homemade software. f Measured by supplier.
the fuel composition were determined using only diesel and ethanol fuels. 4. Experimental Procedures The analysis and comparison of the pollutant emissions recorded during the operation of a construction machine is very complex. For that reason, the study was divided in four categories or operation sequences: “engine start on” (S), measured during the first start in the day, “idle” (I), measured after the engine starting when the engine reached the typical refrigerant thermal conditions (80-90 °C), “circulation” (C), measured when the vehicle is moving from the parking station to the working area, and finally, the operation sequence “work” (W), measured when the vibrating roller is
compacting ground. All measurements were made trying cause the least possible disturbance to the daily machine operation. The above-mentioned engine parameters and pollutant emissions were measured four times during the selected operation sequences. The recording time for sequences I and C was 500 s. For sequence W the recording time was 1200 s. Due to the short duration of the engine start sequence (∼2-5 s) the data were registered during 130 s. This period of time was centered around the proper engine start, and additional subperiods of about 60 s were included before and after. The tests were carried out during different days. The reference diesel fuel was tested first, and some days later, after the filling with ED7.7 the tests were repeated. For a better understanding, the results are presented in two forms. First, the comparison of the average parameters obtained from all the registered data obtained from both fuels during each sequence tested. Second, a comparison along a time interval which was selected so that the characteristic vehicle parameters remained similar with both fuels (see time window in Figure 3, as an example corresponding to sequence “work”). As characteristic vehicle parameters, the following ones were selected: (a) the load, proportional to the engine relative fuel-air ratio (Fr), and/or (b) the
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Figure 4. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during the sequence S.
vehicle velocity, proportional to the engine speed. The vibrating roller was equipped with a mechanical transmission with only a gear to front and one to rear. j ) and their relative For fuel comparison, the mean values (M deviations (Dre) were calculated. The relative standard deviation of the sequence S was not calculated because the engine start was tested only once with each fuel.
5. Results and Discussion 5.1. Instantaneous and Average Results from the Sequences. The mean values of some parameters (directly measured or derived from the measurements) are listed in Table 3. These mean values are indicative of the engine and/or vehicle operation such as: relative fuel-air ratio (Fr), ambient temperature (Tamb, °C), exhaust gas temperature (Tg, °C), exhaust gas ˙ fuel, g/s), and vehicle speed flow (Vg, L/min), fuel mass flow (m (V, km/h) for each operation sequence and fuel. Sequence “Start On” (S). Figure 4 shows the Fr, the smoke opacity (a), and the NOx concentration (b) during the engine start sequence with both fuels. As shown in the figure, the S sequence using e-diesel fuel occurred with a Fr signal whose peak value was lower than the peak value obtained when reference fuel was used. In addition, there were no significant instantaneous changes after the engine start as occurred with the reference fuel. The instantaneous Fr curve obtained from e-diesel fuel was always lower and smoother than that obtained from reference fuel. The oscillations presented in the reference case could be explained by the lower ambient temperature, which probably led to higher necessity of fuel energy to start the engine. Additionally, the presence of a low-volatility component in the fuel was probably helping the stabilization of the internal fuel-air mixing in the combustion chamber under cold conditions. NOx emissions and smoke opacity measured were consistent with the Fr behavior registered with each fuel. Figure 5 shows the mean values obtained from the instantaneous records. Compared to the reference fuel, a decrease in all emissions can be observed when e-diesel was used. This trend can be explained by the lower (7% in average) and lessoscillating Fr, which also led to reduced fuel consumption (5%). The mean exhaust gas temperature confirms the trend observed in the Fr. Sequence “Idle” (I). Figure 6 shows the Fr, the smoke opacity (a), and the concentration of NOx (b) during the engine idle operation sequence with both fuels. It can be observed that the engine idle operation occurred with lower instantaneous Fr using e-diesel fuel. Similarly as occurred during the engine start sequence, the smoke opacity measured was consistent with the Fr behavior of each fuel, respectively. Figure 7 shows the mean values obtained from the parameters presented in Figure 6.
Figure 5. Average values of Fr, smoke opacity, and NOx emissions from test fuels during the sequence S.
Compared to the reference fuel, this figure shows a sharp decrease of smoke opacity when the e-diesel fuel was used during the whole engine idle operation sequence. The mean smoke opacity from e-diesel decreased 36%. The Fr decrease (3% in average) can partly explain the smoke opacity decrease. The NOx emission was nearly the same with both fuels. In this sequence the fuel mass flow was 12% lower than the e-diesel fuel. Sequence “Circulation” (C). Figure 8 shows the Fr, the smoke opacity (a), and the concentration of NOx (b) during sequence C with both fuels. As observed, sequence “C” occurred with approximately the same instantaneous Fr using both fuels. Figure 9 shows the mean values obtained from the parameters presented in Figure 8. A sharp decrease of mean smoke opacity from e-diesel fuel can be observed even though the mean Fr was 1.3% higher. The slight decrease mean of NOx emission obtained from e-diesel fuel could be explained by the lower mean ambient temperature measured during the test with this fuel. In this sequence the diesel fuel mass flow was 22% higher than with e-diesel fuel. The increase in fuel mass flow was consistent with the exhaust gas flow measured during the test according to the higher mean vehicle speed. Sequence “Work” (W). Figure 10 shows the Fr, the smoke opacity (a), and the concentration of NOx (b) registered during sequence W with both fuels. Figure 11 shows the corresponding mean values. The instantaneous Fr from diesel fuel was higher than e-diesel during almost all the sequence. During this sequence, the mean Fr from e-diesel fuel was 11% lower than with diesel fuel. The emissions measured were consistent with the Fr of each fuel. The mean smoke opacity decreased 22%, whereas the mean NOx concentration decreased 17%.
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Figure 6. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during the sequence I.
Figure 7. Average values of Fr, smoke opacity, and NOx emissions from test fuels during the sequence I.
5.2. Instantaneous and Average Results from a Time Interval Selected from Each Sequence. Since the differences observed between Fr and vehicle speeds during the machine operation with both fuels was not negligible, a selection was made of time intervals of each sequence in which the mentioned parameters were almost the same, in order to be analyzed under more comparable conditions. The main selection criterion was the similarity in Fr, because the main objective of this work was to evaluate the effect of the fuel on the engine emissions. Even though, following this criterion did not guarantee that the selected intervals were fully comparable, since some differences were found in the vehicle velocity or in the power developed to roll grounds with different consistencies. Table 4 summarizes the mean values of Fr, ambient temperature, exhaust gas temperature, exhaust gas flow, fuel mass flow, and vehicle speed obtained from the data measured during the time interval selected from each sequence and fuel.
Figure 9. Average values of Fr, smoke opacity, and NOx emissions from test fuels during the sequence C.
Sequence S. Figure 12 shows the Fr, the smoke opacity (a), and NOx concentration (b) registered during the time interval selected from sequence “S” with both fuels. Figure 13 shows the mean values obtained from the emissions presented in Figure 12. The mean Fr obtained from e-diesel fuel during the time interval selected from sequence S was approximately 5.8% lower than that obtained from diesel fuel. During the time interval selected for comparison, the e-diesel fuel led to a reduction in fuel consumption next to 4%. The differences mentioned probably contributed to reductions in both NOx emissions (26%) and smoke opacity (44%) higher than expected. Sequence I. Figure 14 shows the Fr, the smoke opacity (a), and NOx emissions (b) registered during the time interval analyzed in sequence I with both fuels, and Figure 15 shows the mean values obtained from the parameters presented in Figure 14. The mean values of Fr obtained from both fuels
Figure 8. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during the sequence C.
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Figure 10. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during the sequence W.
Figure 11. Average values of Fr, smoke opacity, and NOx emissions from test fuels during the sequence W.
Figure 13. Average values of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence S.
Table 4. Mean Values of Operation Parameters Obtained from the Data Measured during the Time Interval Selected from Each Sequence
sequence “S”, the e-diesel led to an important reduction of NOx emissions (15%) and smoke opacity (23%). Under these comparable conditions the reductions observed on smoke opacity are quite in agreement with the results obtained in previous works by our group2,3 and by other authors7,9 and are slightly sharper in NOx, although very few of them were measured under idle conditions. Sequence C. Figure 16 shows the Fr, the smoke opacity (a), and NOx concentration (b) registered during the time interval selected from sequence C with both fuels, with their mean values presented in Figure 17. In this case, the mean values of Fr obtained from both fuels were similar. As occurred during sequences S and I, an important reduction of NOx concentration (20%) and smoke opacity (25%) was again observed with the e-diesel fuel. The smoke opacity decrease observed is comparable with that obtained by Subramanian et al.7 In this case, two factors may be contributing to provide reductions in NOx emissions higher than expected. On the one hand, the ambient
sequence
fuel
Fr
Tamb (°C)
Texh (°C)
Vg (L/min)
m ˙ fuel (g/s)
V (km/h)
S
ref ED7.7 ref ED7.7 ref ED7.7 ref ED7.7
0.257 0.242 0.178 0.180 0.301 0.301 0.518 0.515
3 6 7 2 9 0 2 3
163 87 208 129 240 247 387 356
3547 2896 3831 3265 5396 4024 7736 4816
0.788 0.756 0.537 0.570 1.191 0.901 2.251 1.504
0 0 0 0 6.5 4.6 4.9 4.1
I C W
during the time interval selected from sequence I were approximately the same (the difference was next to 1%), although slightly higher in the case of e-diesel fuel. During the time interval selected for comparison, the e-diesel fuel consumption was 6% higher than diesel fuel, according to the difference in volumetric energy content (4.8%). Such as occurred during
Figure 12. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence S.
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Figure 14. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence I.
Figure 15. Average values of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence I.
Figure 17. Average values of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence C.
temperature registered during the test with e-diesel fuel was 9 °C lower than during the diesel tests. On the other hand, the vehicle velocity was 29% lower, and thus the fuel consumption (as well as the exhaust gas flow) was also lower (24%). Sequence W. Figure 18 shows the Fr, the smoke opacity (a), and NOx emissions (b) registered during the time interval selected from sequence C with both fuels, and its mean emission values are shown in Figure 19. The mean values of Fr obtained from both fuels during the time interval selected from sequence W were almost the same. Once more, both the NOx emissions and the smoke opacity were reduced when the e-diesel was used (8 and 27% respectively). The NOx and smoke opacity decreases observed in this case are in agreement with those presented in refs 3, 4, 7, and 9. In this case, the ambient temperature during the tests with both fuels was similar, but the e-diesel fuel consumption was 33% lower than that of diesel fuel, and so it was the volumetric gas flow (38%). This can be explained because the vibrating roller was packing down more consistent ground when using diesel than when using e-diesel. This difference, together with the lower vehicle
velocity (16%) could partly explain the observed differences in opacity and NOx emissions. Figure 20 shows a summary of the mean NOx concentrations and the smoke opacity obtained from the time interval analyzed for each sequence and fuel in front of their Fr. In general, increases in both NOx concentration and smoke opacity with increasing Fr are shown for both fuels. However, when the Fr remains below 0.25, (I and S sequences) increasing emissions are observed for decreasing fuel-air ratios probably as a consequence of increasingly poor fuel-air mixing. Similar trends can be observed in Figure 21. This figure shows the NOx emissions obtained in g/kg-fuel for all sequences tested. These results have been obtained from the time interval analyzed (results presented in Section 5.2). For translating the NOx concentration results to mass emissions results, the presented values have been corrected with the ambient temperature and humidity following the procedure described in ref 22. Figure 21 shows decreases in NOx emissions (g/kg-fuel) around 25% during the start-on sequence, 17% during the idle sequence, 21% during the circulation
Figure 16. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence C.
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Figure 18. Instantaneous results of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence C.
Figure 19. Average values of Fr, smoke opacity, and NOx emissions from test fuels during a time interval analyzed in the sequence C.
Figure 20. Summarized mean values of NOx concentration and smoke opacity obtained from the time interval analyzed for each sequence and fuel.
sequence, and 11% during the work sequence when the e-diesel fuel was used. As confirmed in both Figures 20 and 21, the maximum reductions in both NOx emissions and smoke opacity were obtained during the S sequence, where the ethanol content provided a stabilizing effect under cold conditions as a consequence of its higher volatility. 6. Conclusions Comparisons were made from operating sequences corresponding to engine start-on, idle, vehicle circulation, and vibrating roller work. The first conclusion was that online measurements are very difficult to compare, since the number of uncertainties associated with the daily vehicle operation is too many. When the mean emission values along the whole sequences were considered, differences in some vehicle or engine parameters can always be found disabling an appropriate comparison. These uncertainties could not be removed by statistic treatment, as they did not
Figure 21. Summarized mean values of specific NOx emissions obtained from the time interval analyzed for each sequence and fuel.
necessarily appear randomly (weather, ground, consistency, etc.). The only relevant conclusion from this part of the study is that the presence of ethanol in the fuel contributes to stabilize the Fr during the engine start-on under cold weather conditions (as observed in Figure 4), thus leading to additional benefits in emissions, apart from those derived from the increased molecular oxygen content and the reduced content of aromatic compounds. A better comparison was possible from the results obtained during the selected time intervals. The selection was made trying to maintain the Fr as similar as possible with both fuels. However, in some cases, other parameters remained different. During the engine operation working with the same engine speed and Fr such as was observed at the sequence I, the e-diesel fuel consumption increased approximately 6% as compared to diesel fuel. This difference was consistent with the difference in volumetric energy content in the fuels. The results obtained have shown that during the tests keeping constant the engine load (and thus the Fr) the e-diesel fuel led to decreases in smoke opacity around 24-27%, and to decreases in NOx emissions around 8-20% (and to around 11-25% when emissions were referred to fuel consumption), independently of the sequence tested. Acknowledgment. The authors gratefully acknowledge the financial support provided by the Castilla-La Mancha government (research project PAI 06-160, COMEDIA), by the Spanish CDTI (research project CENIT 2007-1031, I+DEA), and by the company Abengoa Bioenergy S.A. The company O2Diesel is also acknowledged for their technical support. Finally, the student Miguel Angel Angulo is also acknowledged for his thorough work.
EF900148C (22) Heavy duty engines - Measurements of gaseous emissions from raw exhaust gas and of particulate emissions using partial flow dilution systems under transient test conditions. ISO/FDIS 16183. 2001-08-06.
