Engine performance and emissions of a compression ignition engine operating on the diesel methanol blends

Transcription

1 435 Engine performance and emissions of a compression ignition engine operating on the diesel methanol blends Z H Huang1,2*, H B Lu2, D M Jiang2, K Zeng2, B Liu2, J Q Zhang2 and X B Wang2 1State Key Laboratory of Multiphase Flow in Power Engineering, Xi an Jiaotong University, Xi an, People s Republic of China 2School of Energy and Power Engineering, Xi an Jiaotong University, Xi an, People s Republic of China Abstract: A stabilized diesel methanol blend was realized and a study on the performance and emissions of the diesel methanol blend was carried out in a compression ignition engine. The study showed that the engine thermal e ciency increases and the diesel equivalent b.s.f.c. decreases with increase in the oygen mass fraction (or methanol mass fraction) of the diesel methanol blends due to an increased fraction of premied combustion phase, oygen enrichment and improvement in the di usive combustion phase. Further increase in the fuel delivery advance angle will achieve a better engine thermal e ciency when the diesel engine is operated using the diesel methanol fuel blends. A marked reduction in the ehaust CO and smoke can be achieved when operating with the diesel methanol blend. There is not a large variation in the ehaust hydrocarbon with the addition of methanol in diesel fuel. NO increases with increase in the mass of methanol added; methanol addition to diesel fuel was found to have a strong in uence on the NO concentration at high engine loads rather than at low engine loads, and a at NO smoke trade-o curve eists when operating with the diesel methanol fuel blends. Keywords: performance, combustion, emission, diesel methanol blends, compression ignition engine NOTATION and Mikkelsen [ 3] have studied dimethyl ether (DME ) in the modi ed diesel engine, and their results showed b b.s.f.c. e H u lower heating value that the engine can achieve ultralow emission prospects without a fundamental change in combustion systems. Huang et al. [4] investigated the combustion and emission DME and found that DME engine has a high thermal g e ective thermal e ciency e e ciency, short premied combustion and fast di usion h fuel delivery advance angle before the top dead centre characteristics in a compression ignition engine with combustion; this gives the advantage of realizing lownoise smoke-free combustion. Kajitani et al. [ 5] studied 1 INTRODUCTION the DME engine with delaying the injection time to The reduction in engine emissions is a major research reduce both smoke and NO. aspect of engine development with increasing concern Practically, adding some oygenated compounds to about environmental protection and stringent ehaust fuels to reduce engine emissions without engine modi- gas regulation; it is di cult to reduce nitrogen oides cation seems to be more attractive. Huang et al. [6] (NO ) and smoke simultaneously in a normal diesel tested gasoline oygenated fuel blends in a spark-ignited engine due to the trade-o between NO and smoke. engine and obtained satisfactory results on emission One prospective method to solve this problem is to use reduction; Huang et al. [ 7] also investigated the comalternative oygenated fuels or to add the oygenated bustion and emission characteristics of diesel dimethyl fuels to diesel to provide more oygen during com- carbonate (DMC ) in a compression ignition engine. bustion. In the application of pure oygenated fuels, Murayama et al. [ 8] studied the emissions and com- Fleisch et al. [1], Kapus and Ofner [2] and Sorenson bustion with EGR and DMC. Ajav et al. [9] studied diesel ethanol blends for emission reduction, and Bertoli The MS was received on 16 June 2003 and was accepted after revision et al. [10], Miyamoto et al. [11] and Akasaka and for publication on 5 December Sakwai [12] also conducted research on diesel com- * Corresponding author: College of Energy and Power Engineering, Institute of Internal Combustion Engines, Xi an Jiaotong University, Xi an, , People s Republic of China. bustion improvement and emission reduction by the use of various oygenated fuel blends.

2 436 Z H HUANG, H B LU, D M JIANG, K ZENG, B LIU, J Q ZHANG AND X B WANG Methanol is regarded as one of the promising alternative fuels or oygen additives in diesel engines with its advantages of low price and high oygen fraction. However, owing to the di culty in forming a stabilized diesel methanol blend, very little research was found on this topic, and the previous work mainly concentrated on the application of diesel ethanol blends in a compression ignition engine [ 13, 14]. Therefore, much work is needed on the application of diesel methanol blends in a compression ignition engine to clarify the basic combustion and emission characteristics and to provide an approach for attaining a stabilized diesel methanol blend with some solvent; the study is epected to supply more information on engine combustion operating with oygenated fuels and to provide more practical measures for improvement in combustion and reduction in emissions. Based on the present authors previous study, the objectives of this study is to form a stabilized diesel methanol blend by adding a speci c solvent and then to investigate the performance and emissions of a compression ignition engine operating with the diesel methanol blends. diesel fuel, a solvent consisting of oleic acid and isobutanol was added to the diesel methanol blends to produce stabilized diesel methanol blends. The fuel properties and the fractions of three blends are given in Table 2, Table 3 and Fig. 1, and the oygen fraction in the fuel blends ranges from 5.87 to 11.1, as shown in Fig. 2. It can be seen that the oygen in the fuel blends mainly comes from the methanol addition although the mass fractions of methanol and solvent are the same; 2 TEST ENGINE AND FUEL PROPERTIES The speci cations of the test engine are listed in Table 1. Three fractions of diesel methanol blends were designated for study. Because of the low solubility of methanol in Fig. 1 Mass fraction of the fuel blends Table 1 Engine speci cations Bore (mm) 100 Stroke (mm) 115 Displacement (cm3) 903 Compression ratio 18 Combustion chamber w type Rated power; speed 11 kw; 2300 r/min Nozzle hole diameter (mm) 0.3 Number of nozzle hole 4 Fig. 2 Oygen mass fraction in the fuel blends Table 2 Fuel properties of diesel, methanol, solvents and blended fuel constitutions Solvents Base fuel, Blended fuel, diesel methanol Oleic acid Isobutanol Chemical formula C H CH OH C H O C H O Mole weight (g) Density (g/cm3) Lower heating value (MJ/kg) Heat of evaporation (kj/kg) Self-ignition temperature ( C) Cetane number Carbon mass fraction (wt %) Hydrogen mass fraction (wt %) Oygen mass fraction (wt %) Blended fuel 1 (wt %) Blended fuel 2 (wt %) Blended fuel 3 (wt %)

3 ENGINE PERFORMANCE AND EMISSIONS OF A CI ENGINE 437 Table 3 Fuel properties of the diesel methanol blended fuel 3 RESULTS AND DISCUSSION Blended Blended Blended fuel 1 fuel 2 fuel 3 The b.s.f.c. of the fuel blends at three fuel delivery advance angles are shown in Fig. 3, Fig. 4 and Fig. 5 Lower heating value (MJ/kg) respectively. In the case of the 1500 r/min engine speed, Heat of evaporation (kj/kg) Cetane number the b.s.f.c. increases with the increase in oygen mass Carbon mass fraction (wt %) fraction (or methanol mass fraction) in the fuel blends Hydrogen mass fraction (wt %) under high and low loads, and the variation in the Oygen mass fraction (wt %) b.s.f.c. with the oygen mass fraction presents the same behaviour at three settings of the fuel delivery advance angle. It is considered that the oygen available in the therefore it is reasonable to regard the in uence of fuel blends is helpful for improving the combustion, oygen on the fuel blends as the in uence of oygen which will bene t the reduction in the b.s.f.c. Mean- from the addition of methanol. The fuel properties show while, the cetane number of the diesel methanol blends that methanol has a high oygen content while the heat decreases with increase in the methanol mass fraction value is less and the cetane number is low compared with (oygen mass fraction) in the blends, and this would those of pure diesel fuel. In the eperiment, the above cause a long ignition delay for the diesel methanol three fuel blends with di erent methanol fractions were blends, where a long ignition delay causes more fuel to tested on the engine. Meanwhile, combustion characterin be burned in the premied burning phase and results istics and ehaust emissions were measured and analysed a high combustion pressure and an improvement in under the same b.m.e.p. Furthermore, a comparison of thermal e ciency. However, more cyclic fuel is needed these parameters was made with those of pure diesel to produce the same b.m.e.p. Consequently, the b.s.f.c. combustion in order to clarify the e ect of oygenated shows an increase with increase in the oygen mass fuel additives on combustion. A Horiba ehaust gas fraction (methanol mass fraction). In the case of the high analyser was used to measure the combustion products. engine speed (2000 r/min), it was found that the b.s.f.c. Fig. 3 B.s.f.c.s of the fuel blends at h = 17 C and before top dead centre (BTDC) Fig. 4 B.s.f.c.s of the fuel blends at h = 21 C and BTDC

4 438 Z H HUANG, H B LU, D M JIANG, K ZENG, B LIU, J Q ZHANG AND X B WANG Fig. 5 B.s.f.c.s of the fuel blends at h = 25 C and BTDC did not show an increase with increase in the oygen The thermal e ciency and the diesel equivalent b.s.f.c. mass fraction, and the variation in the b.s.f.c. versus the at three settings of fuel delivery advance angle h are oygen mass fraction of diesel methanol blends shows illustrated in Fig. 6, Fig. 7 and Fig. 8 respectively. Since a slight di erence at di erent fuel delivery advance the thermal e ciency g is inversely proportional to the e angles, and even a slight decrease in the b.s.f.c. with diesel equivalent b.s.f.c. b, as indicated in the formula e increase in the oygen mass fraction was observed at the g = /(H b ), they must re ect the same e u,diesel e high engine load (b.m.e.p., MPa). It is considered phenomenon but present opposite trends in their curves. that the high swirl intensity at the high engine speed The results show that the thermal e ciency increases would improve the miing process of the injection fuel, and the diesel equivalent b.s.f.c. decreases with increase and this improvement in combustion will tend to be in the oygen mass fraction (methanol mass fraction) of more obvious at the high engine load since the high diesel methanol blends at all engine loads (b.m.e.p.s), combustion temperature would make the combustion of all fuel delivery advance angles h and all engine speeds. methanol more e ective. This suggested that the combustion could be improved Fig. 6 Diesel equivalent b.s.f.c.s and thermal e ciencies of fuel blends at h = 17 C and BTDC

5 ENGINE PERFORMANCE AND EMISSIONS OF A CI ENGINE 439 Fig. 7 Diesel equivalent b.s.f.c.s and thermal e ciencies of fuel blends at h = 21 C and BTDC Fig. 8 Diesel equivalent b.s.f.c.s and thermal e ciencies of fuel blends at h = 25 C and BTDC

6 440 Z H HUANG, H B LU, D M JIANG, K ZENG, B LIU, J Q ZHANG AND X B WANG with the addition of methanol to diesel where the local phase combustion; this means a short di usive combustion oygen enrichment in the diesel methanol spray is considered duration could be realized for the oygenoygen to enhance the combustion due to the oygen containing fuel blends and it is also consistent with the available in the fuel blends. Meanwhile, the decrease in present authors previous results in a study of diesel cetane number of the fuel blends would also result in a DMC blends [ 7]. The results also show that better long ignition delay, which in turn causes a high combustion improvement in thermal e ciency and diesel equivalent rate in the premied burning phase and a high b.s.f.c. are presented at the high engine speed (2000 r/min), cylinder pressure due to the fast heat release rate. In and this is due to a better miing process of the fuel addition to this, the oygen available in the fuel blends spray with the surrounding air during the di usive combustion can also improve the combustion rate of the subsequently period in the presence of high swirl motion di usive burning phase. Thus, it was found at the high engine speed. It can be derived from the that the addition of oygen-containing fuel to diesel eperimental results that an average improvement in is bene cial to the improvement in the di usive com- the thermal e ciency at 1500 r/min was 5 per cent, and bustion process as oygen is a critical parameter for such in the case of 2000 r/min it would reach 10 per cent Fig. 9 Diesel equivalent b.s.f.c. versus fuel delivery advance angle

7 ENGINE PERFORMANCE AND EMISSIONS OF A CI ENGINE improvement in thermal e ciency when the oygen mass fraction in the diesel methanol blend increased to 10 wt %. Figure 9 shows the diesel equivalent b.s.f.c.s of diesel methanol blends at three fuel delivery advance angles. Generally speaking, the diesel equivalent b.s.f.c. of fuel blends decreases with increase in the fuel delivery advance angle at the high engine speed (2000 r/min) and all engine loads while it has a slight variation versus fuel delivery advance angle at 1500 r/min under high and medium engine loads; this suggested that methanol addition to diesel fuel has a strong in uence on the thermal e ciency under the high engine speed. At the high engine speed, an increase in the fuel delivery advance angle would cause a relatively long period of ignition delay and increase the amount of fuel consumed in the Fig premied combustion phase while decreasing the amount of fuel burned in the subsequently di usive combustion phase; moreover, as mentioned above, the oygencontaining fuel blend would improve the di usive phase combustion due to oygen enrichment. At an engine speed of 1500 r/min, the optimum fuel delivery advance angle of the fuel blends is observed at h = 21 C and BTDC, the same setting as the optimum delivery advance angle of the diesel engine. However, at an engine speed of 2000 r/min, a further increase in the fuel delivery advance angle is required to achieve better thermal e ciency (or diesel equivalent b.s.f.c.) for diesel methanol blends, and this is considered to be due to the decrease in cetane number and the increase in ignition delay. Thus, the results suggested that a further increase Ehaust NO concentrations of the fuel blends

8 442 Z H HUANG, H B LU, D M JIANG, K ZENG, B LIU, J Q ZHANG AND X B WANG in the fuel delivery advance angle should be implemented to achieve a better thermal e ciency when the diesel engine is operated using diesel methanol fuel blends. The NO concentration of diesel methanol blends at three settings of the fuel delivery advance angle is shown in Fig. 10. Similar to the behaviour of NO versus the fuel delivery advance angle in a diesel engine, the NO concentration of the fuel blends also shows an increase with increase in the fuel delivery advance angle. When the oygen mass fraction is less than 8 wt %, the NO concentration increases with increase in the methanol mass addition because more of fuel burns in the premied combustion phase, the combustion temperature is high and more oygen is available. However, a further Fig. 11 increase in the methanol mass addition would accompany a high temperature drop due to an increase in the heat of evaporation of the fuel blends; furthermore, an increase in the duration of fuel injection also contributes to the decrease in the NO concentration. The results revealed that methanol addition to diesel fuel has a strong in uence on the NO concentration at the high engine load while it has little in uence at the low engine load. Figure 11 shows the carbon monoide (CO) concentration of diesel methanol blends at three settings of the fuel delivery advance angle. At all settings of the fuel delivery advance angle and all engine speeds, the CO concentration shows a decrease with increase in the Ehaust CO concentrations of the fuel blends

9 ENGINE PERFORMANCE AND EMISSIONS OF A CI ENGINE oygen mass fraction (methanol mass fraction) of the diesel methanol fuel blends, and a marked decrease in CO with increase in the oygen mass fraction is presented at the high engine load, while a slight decrease is observed at the middle and low loads. This suggested that oygen-containing fuel blends could e ectively decrease the locally rich spray regions where CO is mainly formed, especially at the high engine load where a larger locally rich spray region will eist due to the high swirl intensity. In addition to this, the oygen enrichment can also improve the post- ame oidation of CO in the late engine epansion and ehaust processes, and a high load results in a high cylinder temperature and consequently a high degree of CO oidation. The results Fig also revealed the addition of 6 wt % oygen to diesel methanol blends could markedly reduce the engine ehaust CO and a further increase in the oygen mass fraction has a slight impact on the reduction of engine ehaust CO. The ehaust hydrocarbon (HC ) concentration of diesel methanol blends at three settings of the fuel delivery advance angle is illustrated in Fig. 12. Unlike the behaviours of NO and CO versus the oygen mass fraction of the fuel blends, the ehaust HC concentration does vary greatly with the addition of methanol to diesel fuel, although the HC concentration shows a slight di erence at di erent engine speeds and fuel delivery advance angles. The ehaust HC of a compression Ehaust HC concentrations of the fuel blends

10 444 Z H HUANG, H B LU, D M JIANG, K ZENG, B LIU, J Q ZHANG AND X B WANG ignition engine comes from both the rich spray region and the lean spray region; it is suggested that oygencontaining fuel blend would have a tendency to reduce the rich spray region and to increase lean spray region while an increase in the oygen mass fraction would be accompanied by an increase in injected fuel and a promotion of HC post- ame oidation. At the fuel delivery advance angle h = 21 C and BTDC and h = 25 C and BTDC, the ehaust HC concentration presents a slight increased trend with increase in the oygen mass fraction (or methanol mass fraction) of the diesel methanol fuel blends, especially at high and middle loads. It is considered that increasing the fuel delivery advance angle will increase the fraction of lean spray region due to an increase in ignition delay. Generally speaking, it can be considered that the addition of methanol to diesel fuel does not a ect the ehaust HC concentration of a compression ignition engine. The smoke and its reduction rate in diesel methanol blends at three settings of the fuel delivery advance angle are illustrated in Fig. 13, Fig. 14 and Fig. 15. The purpose of using the oygen-containing fuel blend is epected to decrease the engine smoke by supplying more oygen to make it burn completely. The results clearly showed that the engine smoke could be decreased markedly with the addition of methanol to diesel fuel at all engine speeds, engine loads and fuel delivery Fig. 13 advance angles, and this is reasonable since the oygencontaining fuel blends can reduce the rich spray region and increase the post- ame oidation of the formed soot. Ecept at h = 17 C and BTDC, the smoke reduction rate has a higher value at the high engine load than that at the low engine load in the case of the 2000 r/min engine speed. In contrast with this, the low load gives a higher smoke reduction rate than that of the high load in the case of the 1500 r/min engine speed. Thus, we can suggest that the high swirl intensity at the high engine speed would improve the fuel air miing process under the high engine load and reduce the ecessive rich spray region in the combustion chamber. The relationship between NO and smoke of diesel methanol fuel blends at three settings of fuel delivery advance angle is plotted in Fig. 16. Unlike the engine operating with pure diesel fuel, a at NO /smoke trade o curve is presented when operating with the diesel methanol fuel blends, and an even atter curve is observed at the low engine load; this is reasonable since the marked reduction in smoke is not accompanied by a high NO increase. Furthermore, a high methanol mass addition will realize the simultaneous reduction in both smoke and NO. Since it is an oygen-containing fuel blend, techniques such as ehaust gas recirculation can be introduced to make a further decrease in NO and to realize reduction in both NO and smoke. Smoke and its reduction rates in the fuel blends at h = 17 C and BTDC

11 ENGINE PERFORMANCE AND EMISSIONS OF A CI ENGINE Fig. 14 Smoke and its reduction rates in the fuel blends at h = 21 C and BTDC Fig. 15 Smoke and its reduction rates in the fuel blends at h = 25 C and BTDC 445

12 446 Z H HUANG, H B LU, D M JIANG, K ZENG, B LIU, J Q ZHANG AND X B WANG Fig Relationship between NO and smoke from the fuel blends CONCLUSIONS A stabilized diesel methanol blend was realized and a study on the performance and emissions of the diesel methanol blend was carried out in a compression ignition engine; the main results are summarized as follows: 1. The engine thermal e ciency increases and the diesel equivalent b.s.f.c. decreases with increase in the oygen mass fraction (methanol mass fraction) of the diesel methanol blends due to an increased fraction in the premied combustion phase, oygen enrichment and improvement in the di usive combustion phase. 2. Further increase in the fuel delivery advance angle will achieve better engine thermal e ciency when the diesel engine is operated using the diesel methanol fuel blends. 3. Marked reductions in the ehaust CO and smoke can be achieved when operating with the diesel methanol blend. Ehaust HC does not vary much on the addition of methanol to diesel fuel. NO increases with increase in methanol mass addition, and the methanol addition to diesel fuel was found to have a strong in uence on NO concentration at the high engine load rather than at the low engine load; a at NO /smoke trade-o curve eisted when operating with the diesel methanol fuel blends.

13 ENGINE PERFORMANCE AND EMISSIONS OF A CI ENGINE ACKNOWLEDGEMENTS This study was supported by the National Science Fund for Distinguished Young Scholars from the National Natural Science Foundation of China (Grant ), the Ford-China Research and Development Fund (Grant ), the National Basic Research Program (Grant 2001CB209208) and the Key Project of the National Natural Science Fund (Grant ). The authors acknowledge the students of Xi an Jiaotong University for their help with the eperiment. The authors also epress their thanks to colleagues at Xi an Jiaotong University for their helpful comments and advice during the manuscript preparation. REFERENCES 1 Fleisch, T., McCarthy, C. and Basu, A. A new clean diesel technology: demonstration of ULEV emissions on a Navistar diesel engine fueled with dimethyl ether. SAE Trans., 1995, 104(4), Kapus, P. and Ofner, H. Development of fuel injection equipment and combustion system for DI diesels operated on dimethyl ether. SAE Trans., 1995, 104(4), Sorenson, S. C. and Mikkelsen, S. E. Performance and emissions of a liter direct injection diesel engine fueled with neat dimethyl ether. SAE Trans., 1995, 104(4), Huang, Z. H., Wang, H. W. and Chen, H. Y. Study on combustion characteristics of a compression ignition engine fueled with dimethyl ether. Proc. Instn Mech. Engrs, Part D: J. Automobile Engineering, 1999, 213(D6), Kajitani, Z., Chen, L. and Konno, M. Engine performance and ehaust characteristics of direct-injection diesel engine operated with DME. SAE Trans., 1997, 106(4), Huang, Z., Miao, H., Zhou, L. and Jiang, D. Combustion characteristics and hydrocarbon emissions of a spark ignition engine fuelled with gasoline-oygenate blends. Proc. Instn Mech. Engrs, Part D: J. Automobile Engineering, 2000, 214(D3), Huang, Z. H., Jiang, D. M., Zeng, K., Liu, B. and Yang, Z. K. Combustion characteristics and heat release analysis of a DI compression ignition engine fueled with diesel-dimethyl carbonate blends. Proc. Instn Mech. Engrs, Part D: J. Automobile Engineering, 2003, 217(D7), Murayama, T., Zheng, M. and Chikahisa, T. Simultaneous reduction of smoke and NO from a DI diesel engine with EGR and dimethyl carbonate. SAE paper , Ajav, E. A., Singh, B. and Bhattacharya, T. K. Eperimental study of some performance parameters of a constant speed stationary diesel engine using ethanol-diesel blend as fuel. Biomass Bioenergy, 1999, 17, Bertoii, C., Giacomo, N. D. and Beatrice, C. Diesel combustion improvements by the use of oygenated synthetic fuels. SAE Trans., 1997, 106(4), Miyamoto, N., Ogawa, H. and Obata, K. Improvements of diesel combustion and emissions by addition of oygenated agents to diesel fuels: in uence of properties of diesel fuels and kinds of oygenated agents. JSAE Rev., 1998, 19(2), Akasaka, Y. and Sakurai, Y. E ect of oygenated fuel on ehaust emission from DI diesel engines. Trans. Japan Soc. Mech. Engrs, Ser. B, 1996, 63(609), Satge de Caro, P., Mouloungui, E., Vaitilingom, G. and Berge, J. C. Interest of combining an additive with dieselethanol blends for use in diesel engines. Fuel, 2001, 80, Ali, Y., Hanna, M. A. and Borg, J. E. Optimization of diesel, methyl tallowate and ethanol blend for reducing emissions from diesel engine. Bioresource Technol., 1995, 52,

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