THE EFFECTS OF OXYGENATED ADDITIVE AND EGR IN A DIESEL ENGINE

Transcription

1 THE EFFECTS OF OXYGENATED ADDITIVE AND EGR IN A DIESEL ENGINE Seung-Hun, Choi Department of Automatic Mechanical Engineering, VISION University of Jeonju,Cheonjam-ro, Wansan-gu, Jeonju-si, Republic of Korea Abstract Potential possibility of the butyl ether (BE, oxygenates of di-ether group) was analyzed as an additives for a naturally aspirated direct injection diesel engine fuel. Engine performance and exhaust emission characteristics were analyzed by applying the commercial diesel fuel and oxygenates additives blended diesel fuels. Smoke emission decreased approximately 26% by applying the blended fuel (diesel fuel 8 vol-% + BE 2vol-%) at the engine speed of 25, rpm and with full engine load compared to the diesel fuel. There was none significant difference between the blended fuel and the diesel fuel on the power, torque, and brake specific energy consumption rate of the diesel engine. But, NOx emission from the blended fuel was higher than the commercial diesel fuel. As a counter plan, the EGR method was employed to reduce the NOx. Simultaneous reduction of the smoke and the NOx emission from the diesel engine was achieved by applying the BE blended fuel and the cooled EGR method. Keywords Oxygenated additive, Smoke, EGR(exhaust gas Recirculation), Engine, Reduction Ⅰ. INTRODUCTION Objectives of researches on the diesel engine could be classified broadly as accomplishment of the high output and low fuel mileage and the reduction of the exhaust gas. The goal of the former could be the reduction of the CO 2 emission and the later could be the reduction of the NOx and particulates. Methods for the reduction of the exhaust gas emission classified as a pre-treatment and a post-treatment method 1,2. The pretreatment method is a method to reduce the exhaust gas before it is emitted from the combustion chamber after the fuel combusted by modifying properties of the fuel and engine design technology. The post-treatment method is a method to treat the exhaust gas outside of the combustion chamber by using a catalyst system or the exhaust gas recirculation (EGR) method. As the pre-treatment method, blending the oxygenated fuel into the commercial diesel fuel, or using a reforming fuel, or applying the biomass group fuel are presented. The oxygenated fuels 3 are generally classified as a diether group (-o-), a mono ether group (-O-+-OH), a carbonate group (-O(C:O)O-), and a lower alcohol group (-OH). Major differences of these groups are the bonding status among atoms and the existence of active stage. Researches using these oxygenated fuels 4 have been carried out by many researchers but almost none of researches on the diether group of the butyl ether (BE) are carried out. The BE contained relatively small amount of the oxygen components as 12% compare to other oxygenated fuels. But the heating and the cetane value of the BE reached up to around 93% and 91% of the diesel fuel, respectively. These values are almost similar to the diesel fuel and the highest value among currently investigated oxygenated fuels and additives. (e.g. [1], [3]) This research analyzed variation of characteristics of the exhaust emission materials from the diesel engine at various engine speeds and loads by applying the commercial diesel fuel blended with the diether group oxygenated fuel, BE, up to 2 vol-%. Also, as a reduction method of the NOx, which was increased when using the oxygenated fuel, the cooled EGR method was applied in parallel to reduce the smoke and the NOx simultaneously. Ⅱ. EXPERIMENTAL APPARATUS AND METHODS An engine used for the experiment was single cylinder, water cooled, four strokes, direct injection diesel engine. Engine loads and speeds were arbitrary adjusted by using a dynamometer. Specification of the diesel engine and fuels used for the experiment is 78

2 shown in table 1 and 2, respectively. Fig. 1 shows a schematic diagram of the experimental apparatus. Table 1 Specification of test engine Item Specification Injection method Direct injection Number of cylinder 1 Bore stroke(mm) Displacement(cc) 673 Compression ratio 18 Combustion chamber Toroidal Table 2 Properties of test fuels Diesel fuel In this experiment, the engine performance, the smoke, and the NOx were measured under various engine loads and the speeds by using the diesel fuel and the diesel fuel blended with the oxygenated fuel, BE, as - 2 vol-%. The smoke concentration was measured at 3 mm of downstream away from the engine using a smoke measurement system (Hesbon; Korea). A certain amount of the smoke was absorbed by a filter and measured the concentration on the filter. This test repeated three times at the same condition and a mean value was calculated. The NOx was measured by absorbing a certain amount of the exhaust gas with an exhaust gas analyzer (Motor branch; Korea) at 4 mm of downstream away from the manifold. The fuel consumption rate per unit time and unit output was calculated by measuring a time to consuming known amount of the fuel. Fig. 1 Experimental apparatus Butyl ether Molecular formula C 12H 26 C 12H 26O Density (15/4 C) LHV (MJ/kg) Cetane number Oxygen(wt%) Eq. (1) was used to calculate the EGR ratio as a reduction ratio of an amount of newly inlet air. (e.g. [2]-[8]) The other way to explain the EGR ratio is an amount of EGR to the total amount of inlet air. Here, V o (m 3 /h) is an amount of the inlet air without the EGR, and V a is an amount of the newly inlet air with the EGR. Also, among the EGR methods, cooled EGR method, which was known as more effective method, was employed for this experiment. Thus the temperature of the EGR gas was maintained as the ambient temperature as around 2 C. Also, particulates among the exhaust gas which is recycling into the inlet were eliminated using a smoke particulates elimination system before test. In this study, the EGR ratio is defined as: EGR(%) = (V EGR /V a ) X 1 (1) Where, V EGR is the recirculated exhaust gas mass flow rate, V a is the intake air mass flow rate for the case of no EGR. Ⅲ. RESULTS AND DISCUSSION Fig. 2 shows variations of the engine performance by applying the BE blended diesel fuel according to variations of the engine load at the engine speed of 2,5 rpm. By comparing the engine output by applying the diesel fuel only, the engine output showed difference as the blending ratio of the oxygenated fuel, BE, increased. The maximum output was Power [ KW ] BSEC [ MJ / kw-h ] rpm diesel 1% diesel 95% + BE 5% diesel 9% + BE 1% diesel 85% + BE 15% diesel 8% + BE 2% Engine Load [ % ] Fig. 2. Performance of power and BSEC 79

3 Fig. 3 Smoke and NOx variation rates obtained by applying the diesel fuel only. The brake specific energy consumption (below BSEC) was almost similar even though the blending ratio of the BE increased at each engine speed. At high engine speed of 2,5 rpm, the BSEC with the BE blended fuel increased very slightly compared to it with the diesel fuel only. The BSEC slightly got worse as the blending ratio of the BE increased. At the worst condition as the engine speed of 25 rpm and the full load, the difference of the engine output with the BE blended diesel fuel was very small compared to it with the diesel fuel. The engine output with the 5%, 1%, 15%, and 2% of the BE blended diesel fuel was about.3%,.8%, 1.5%, and 3%, respectively, lower than the engine output with the diesel fuel only. This was considered to be due to similar heating value of the BE as the diesel fuel even the blending ratio of the BE increased and the oxygenated components in the BE which increased the combustion efficiency. (e.g. [9]- [1]) Fig. 3 shows smoke and NOx variation ratios (%) of the direct injection diesel engine at the engine speed of 2,5 rpm according to the blending ratio of the BE to the diesel fuel. As shown in figure 3, there was significant difference of the smoke emission concentration between the diesel fuel and the diesel fuel blended with the diesel fuel. Even though the smoke emission from the diesel fuel shows the clear difference based on the engine load change throughout the engine speed, the smoke emission from the diesel fuel blended with the BE did not show big difference based on the engine load change as the blending ratio of the BE increased. The NOx emission increased up to 17% when 2% of the BE blended with the diesel fuel compared it with the diesel fuel only applied to the engine. This was considered to be due to the generation of the thermal NOx according to the temperature rising in the cylinder by oxygen components in the fuel at high engine load and speed. But, as shown in Fig. 3, the smoke reduction ratio was obtained with maximum of 42% when the BE was applied. Here, the smoke reduction effect was much higher than the NOx increasing ratio when the BE applied with the diesel fuel to the diesel engine. This could be a proof of an effect of the BE to the direct injection diesel engine. [e.g. [5], [7]] As results from above, when the BE blended diesel fuel was applied to the diesel engine, the smoke emission decreased significantly while the BSEC and the output of the diesel engine showed almost same effect. But the NOx, which was an uprising major regulatory subject on the diesel engine, increased steadily as the BE blending ration increased. To solve this problem, the EGR method 3 known as a NOx reduction method was applied at the same time. Specially, the cooled EGR method was applied for expansion of the volume effect. The blending ratio of the BE to the diesel fuel was selected as 15% for this test since it was considered to be an optimum blending ratio for the smoke reduction and the NOx increasing ratio point of view. Fig. 4 shows smoke emission variations at various engine speeds and loads according to application of the EGR ratio from to 2%. From Fig. 6, the smoke emission increased as the EGR ratio increased even the BE blended diesel fuel was applied. Specially, the smoke emission with the BE blended diesel fuel was higher than with the diesel fuel only when the EGR ratio of 2% applied. This was considered to be due to lack of the oxygen supply for sufficient combustion caused by recycled exhaust gas which reduced the oxygen in inlet air flown to the combustion chamber. From here, for the smoke reduction point of view, an optimum EGR ratio of the direct injection diesel engine by using the oxygenated fuel would be less than 15% and 1% at the mid low and the high engine load, respectively. 8

4 Smoke [%] NOx [ppm] rpm 2rpm 25rpm diesel fuel 1% diesel fuel 85% + BE 15% diesel fuel 85% + BE 15%, EGR 5% diesel fuel 85% + BE 15%, EGR 1% diesel fuel 85% + BE 15%, EGR 15% diesel fuel 85% + BE 15%, EGR 2% Load [%] Fig. 4 Smoke emission at various EGR rates 1rpm 2rpm 25rpm diesel fuel 1% diesel fuel 85% + BE 15% diesel fuel 85% + BE 15%, EGR 5% diesel fuel 85% + BE 15%, EGR 1% diesel fuel 85% + BE 15%, EGR 15% diesel fuel 85% + BE 15%, EGR 2% Load [%] Fig. 5. NOx emission at various EGR rates Fig. 5 shows the NOx emission variation according to EGR ratios at the same condition as Fig. 6. The NOx significantly decreased as the EGR ratio increased. By applying 1% of the EGR, the NOx emission was almost same as application of the diesel fuel only. And, by applying over 15% of the EGR, the NOx reduced in overall relative to application of the dieselfuel only. In overall NOx emission point of view, the NOx significantly reduced as the EGR ratio increased. By application of the EGR ratio was over 2%, the smoke emission with the BE blended diesel fuel was higher than the smoke emission with the diesel fuel only. Meanwhile, the NOx emission was similar to the diesel fuel only application when 1% of the EGR applied. Thus, when applying 15% of the BE blended diesel fuel, an optimum EGR ratio would be 1 15% for simultaneous reduction of the smoke and the NOx. Ⅳ. CONCLUSION This research analyzed the engine performance and the exhaust emission materials of the water cooled, single cylinder, four strokes, and direct injection diesel engine by applying the diesel fuel and the butyl ether blended as volumetric ratio with the diesel fuel. Also the cooled EGR method was employed for reduction of the NOx to compensate shortcoming of the butyl ether application to the diesel engine. Following is summarized results obtained from this research. (a) The engine output and BSEC with the butyl ether did not show the significant difference compared to the engine output and BSEC with the diesel fuel only. The BSEC slightly deteriorated as the oxygen components in the fuel increased. But application possibility of the butyl ether to the direct injection diesel engine was confirmed based on less than 3% of difference with 2% of the blending ratio of the butyl ether. (b) The smoke reduction ratio increased as the butyl ether ratio in the fuel increased when the butyl ether blended fuel was applied to the diesel engine. The smoke reduction effect with the maximum blending ratio of 2% of the butyl ether was 42% and 3% with the load free and the full load condition, respectively, and at the engine speed of 2,5 rpm relative to with the diesel fuel only. (c) The NOx emission with the butyl ether blended fuel increased as the butyl ether blending ratio, which is the amount of the oxygen in the fuel, increased. But overall NOx increasing ratio was lower than the smoke reduction ratio at the same condition. (d) By comparing the diesel fuel only application, simultaneous reduction of the smoke and the NOx was achieved by applying the 15 vol-% of the butyl ether blended diesel fuel and the 1 15% of the EGR to the diesel engine at the same time. 81

5 Ⅴ. REFERENCES [1] S. H. Choi and Y. T. Oh, Experimental study on emission characteristics and analysis by various oxygenated fuels in a DI diesel engine, Int. J. of Automotive Technology, Vol.6, No.3, pp , 25. [2] Y. Akasaka and Y. Sakurai, Effects of oxygenated fuel and cetane improver on exhaust emissions from heavy-duty DI diesel engine, SAE paper, No.94223, [3] S. H. Choi and Y. T. Oh, Characteristics of performance and exhaust emission of diesel engines by changes in fuel properties and application of EGR, Int. J. of Automotive Technology, Vol.8, No.2, pp , 27. [4] S. H. Choi and Y. T. Oh, The emission effects by the use of biodiesel fuel, Inter. J. of modern physics B, Vol.25-6 & 7, pp , 26. [5] Wall, J. C. and Hoekman, S. K., Fuel Composition Effects on Heavy-Duty Particulate Emissions, SAE Paper No , [6] Ulman, T.L., Investigation of Effects of Fuel Composition on Heavy-Duty Diesel Engine Emissions, SAE Paper No , [7] Ulman, T. L., Lobert, L. M. and Daniel, A. M., Diesel Fuel Aromatic and Cetane Number Effects on Combustion and Emissions from a 1991 Prototype Heavy-Duty Diesel Engine, SAE Paper No , 199. [8] Manuch, N., Development of the First CARB Certified California Alternative Diesel Fuel, SAE Paper No , [9] Richard, A. G., Patrick, B. C., Peter, R. C., Philip, N. C. and Venkatesh, R., Emission Effects of Shell Low NOx Fuel on a Model Year Heavy-Duty Diesel Engine, SAE Paper No , [1] Gao, Z and Schreiber, W., The Effects of EGR and Split Fuel Injection on Diesel Engine Emission, Int. J. of Automotive Technology, Vol. 2, No.4/6, pp ,21. 82