Experimental investigation on soot reduction in city driving Diesel vehicles in comparison with EuroII standard

Transcription

1 Experimental investigation on soot reduction in city driving Diesel vehicles in comparison with EuroII standard M.Ghazikhani, Y. Kashi Torughi, M. Tuani and S.I. Mirzadeh Dep. O Mech. Engineering, Ferdowsi University o Mashhad, m_ghazikhani@yahoo.com Abstract Eectiveness o the particles issued rom diesel engines that are mainly soot, on human healthiness by international agency o cancer made in 988 has shown that, the Particulate Material (PM) will increase the probability o suering to cancer. In this work irst o all the naturally aspirated diesel engine o type OM34 rom city driving motorbus and truck vehicles (Khavar) has been introduced. Then it is converted to limited pressure turbocharged OM34 Diesel engine. At the inal stage the injectors pressure have been elevated rom 2 bars to 24 bars with the purpose o decreasing the soot emission. In each stage in order to investigate the soot contents, the engine has been tested under ECE-R49, 3 mode standard test. Results show that the naturally aspirated engine does not cover the standard Euro I. The turbocharged OM34 engine catches the Euro I standard with speciic soot emission 35% less then the naturally aspirated engine maybe due to reduction in ignition delay and better soot burnout process. The elevating o the injection pressure makes a better mixing o uel to and results an amount o speciic soot 2% less than Euro I, but it does not cover the Euro II standard. Keyword: Soot emission, Turbocharged Diesel engine, Nuzzle pressure. 35

2 Introduction Particles are generated rom a variety o sources, emissions rom the internal combustion engines are one o the major global sources o particulate matter (PM). PM is known to contribute to climate change, reduce visibility, and aect human health []. Diesel engines are extensively used in automotive systems due to their better uel economy compared to conventional gasoline engines as a result o their higher thermal eiciency. Despite these advantages diesel engines suer rom environmental drawbacks such as high levels o exhaust No x (oxide o nitrogen) and particulate matter [2]. With increasing concern on the eect o pollution on environment, animal and plant lie, particularly in the ield o road transport, vehicle exhaust emissions have in recent years, been subjected to increasingly stringent regulations. It is a matter o importance that diesel engines are an important source o particulate emissions and smoke. The particulate emission rom diesel engines amounts to about 5% o the total emissions, which consists primarily o soot with some additional absorbed hydrocarbon materials [3]. Nomenclature T engine torque (N.m) ρ uel density (kg/m 3 ) m o soot brake soot low rate (g/h) t time o 5 cc uel consumption (s) S soot speciic soot emission (g/kwh) Q o e volumetric low rate o exhaust(m 3 /s) P bm measured engine brake power (kw) ρ e exhaust density (kg/m 3 ) P bs standard engine brake power P e exhaust pressure (kpa) W weighting actor T e exhaust temperature (K) V velocity (m/s) PM particulate matter P oriice pressure drop (kpa) N engine speed (rpm) ρ density (kg/m 3 ) bsc brake speciic uel consumption (g/kwh) m o mass low rate o (kg/s) P s,d standard dry- absolute pressure (kpa) A o oriice inlet area (m 2 ) P m measured ambient- absolute pressure (kpa) C D discharge coeicient P ν,m measured ambient-water vapor partial pressure (kpa) ρ l liquid density o the manometer (kg/m 3 ) T m measured ambient temperature (K) g gravitational acceleration (m/s 2 ) T s Standard ambient temperature (K) H height dierence o manometer liquid(m) C power correction actor m o mass low rate o uel(kg/s) LIMP limited inlet maniold pressure 36

3 Reducing PM emissions to the levels required by stringent new regulations poses a signiicant challenge or engine manuacturers. In addition to the emissions challenge, soot ormation in diesel engines can also inluence engine perormance and have eedback eects on in-cylinder combustion and emission ormation processes [4]. Smoke, or particulate emissions, occurs when there is insuicient to completely burn the uel. One o the actors which the designers vary to provide low emission levels with high perormance and good uel economy is to use the turbocharger which is driven by exhaust gas rom the engine cylinder [5]. Increasing the intake pressure increases cylinder pressure, the amount o the charge entrained into the jet relative to the uel low at the lit o length and leads to a reduction in both in-cylinder soot and exhaust particulate [6]. This study, will investigate the soot emission level o the naturally aspirated OM34 type diesel engine rom city driving motorbus and truck vehicles (Khavar) and attempts to decrease it by using a turbocharger and elevating the injection pressure. In this research work soot emission is also compared with Euro II standard emission. Turbocharger The sole purpose, o which a turbocharger is used, is to improve the overall perormance o the engine [7]. In Fig. the turbocharger system o an engine is shown. The rated brake power output is obtained through an adjustment o the turbocharger waste gate. Fig.: Schematic o turbocharger with waste-gate Injection pressure In diesel engines, combustion and emission characteristics are greatly inluenced by quality o atomization and by the uel- mixture present in the combustion chamber [8]. Pressure is one o the most important parameters acting on the pulverization [8]. In present diesel engines uel injection systems are designed to obtain higher injection pressure. So it is aimed to decrease the exhaust emissions by increasing eiciency, when injection pressure is increased uel particle diameters will become small. Since ormation o mixing o uel to becomes better during ignition period, smoke level and CO emission will be less [9]. 37

4 Experimental apparatus and test conditions - Experimental acilities In this work as Fig.2 shows a our-cylinder, our-stroke, direct injection,naturally aspirated diesel engine with a peak power o 63kW and peak torque o 235 N-m at 83 rpm was used. This was a 26 production engine Daimler OM34 with a compression ratio o 7 to, bore and stroke 97mm and 28mm and displacement volume o L. the engine was installed and operated on a 2kW DXF Heenan & Froude hydraulic dynamometer. An AVL 45 smart sampler was used to measure soot emission levels in the exhaust gas. An electrical speed meter was mounted on the engine lywheel to measure the engine speed. The temperatures o inlet and exhaust gases were recorded on PC utilizing K-type thermocouples attached to the engine while the pressure o the exhaust and the inlet maniold was measured using Bourdon pressure gauge. Relative humidity and atmospheric pressure are read or each mode o test. In table the instrumental resolution o the apparatus are indicated. Table : Instrumental resolution o the test bed apparatus Facility Instrumental resolution Smoke meter. mgr/kwh Speed meter rpm Torque meter N-m Pressure gauge. mmhg Thermocouple. oc Experimental procedure - Engine perormance test Internal combustion engines have upper and lower limits o torque and power published by manuacturers. Fig.2: schematic o the engine test bed Beore the engine was provided or the tests, its perormance was investigated to be in the permitted limitations. The maximum power o the engine was measured or dierent speeds. Fig.3 and 4 represent the actual engine perormance in comparison with the limits. 38

5 - The standard ECE-R49, 3 mode test. In this study soot emissions o the heavy duty diesel engine under the ECE R49 3 mode test cycle were analyzed. OM34 diesel engine was tested under ECE-R49 3 mode sample method. PM at the exhaust at every test mode was separately sampled. According to the equations coming in the ollowing, the brake speciic soot emission or 3 modes, ive modes o speed 83rpm (speed at maximum torque), ive modes o Speed 28 rpm (rated power speed) and three modes o speed 7 rpm (idle speed), were calculated. This cycle is not representative o the engine real use on road, but allows repeatable conditions, useul or comparative tests []. This test should be under steady state operational conditions and or heavy duty diesel engines at every mode the torque is varied rom % to % o the engine maximum torque at the speciied speed, according to the regulation []. The soot emissions are measured in g/kwh. Ater the test, or each mode, a value is deined which stands or weighting coeicient. Data processing - Brake speciic soot and bsc calculations The inal brake speciic soot level is obtained by Equation () []: 3 m soot = * W soot P bs S () Where, P bs stands or standard atmospheric brake power and W indicates the weighting actor. The pressure, humidity, and temperature o the ambient inducted into an engine, at a given engine speed; aect the mass low rate and the power output. Correction actors are used to adjust measured power output values to standard atmospheric power output. The torque exerted on the engine by the dynamometer gives the measured power output by the Equation (2). P bm = 2πNT (2) Relationship between measured power output and standard atmospheric power output can be expressed by Equation (3) P = C P (3) bs bm Where correction actor is given by Equation (4) [2]: 2 Ps, d T m C = (4) P m P m, v * Ts Where, P s,d, T m, T s, P m and P m,v represent standard dry- absolute pressure, ambient temperature, standard temperature, measured ambient absolute pressure and the measured partial water vapor pressure. Air mass low rate was measured by Bernoulli's method in this study. The velocity equation can be expressed as Equation (5). 2 P V = ρ Where, P and ρ represent pressure dierence inside and outside (5) 39

6 o the surge tank and density, respectively. The mass low rate can be expressed by the Equation (6) m = ρ V A o C D Where, C D and A represent the coeicient o discharge, veriied by, and the area o the oriice. By summarizing the above equations, = C A D o m 2 P ρ (7) (6) In this work the pressure drop is investigated by use o a manometer mounted on the surge tank oriice, P = ρ L g H (8) Where, ρ L, g and H represent density o monometer liquid, the gravitational acceleration and the height dierence o liquid suraces o the manometer. From Equations (7) and (8) the mass low rate is given by m = C D A o 2 gρ Hρ (9) L A calibrated burette and a stopwatch were used to measure the mass low rate o uel consumption. This measuring system is based on the time needed or consumption o speciic volume o uel. The equation can be expressed as m ρ = t * 5 * 6 Where ρ and t represent the density o diesel uel, 3, and the time o 5 cc uel consumption. In the Equation () in order to measure the speciic soot pollution, m o soot is obtained rom Equation() 3 m soot = ρ soot * * Q e* 36 () Where, ρ soot and Q o e represent the soot density, which is obtained rom the smoke meter, and the volume low rate o the exhaust. The ollowing equations complete the correlations, m + m a e = (2) ρ e Q P 87 T e ρ e = (3) e Brake speciic uel consumption is calculated by Equation (4) m + 5 bsc = * 36 * (4) ( C * ) Pbm () 4

7 Results and discussion - Naturally Aspirated OM34 Diesel Engine Engine actories publish graphs which mention the upper and lower limits o the maximum engine operation conditions. In this work the maximum torque and brake power o the engine was obtained or every operating point. Torque and brake power output versus engine speed graphs with upper and lower limits and test engine are given in Fig.3. Brake speciic uel consumption versus engine speed with upper and lower limits, recommended by the actory, and the engine under test are given in Fig.4. Fig.3 and Fig.4 show, the actual perormance (operating characteristics) o OM34 diesel engine results. These results indicate that the natural aspirated engine is in an acceptable operating condition. The steady state 3 mode cycle, ECE-R49 test was perormed on the engine. The tests were conducted three times in order to examine the sensitivity o the test, and the averages o these 3 consecutive test results represents as the actual test result. Fig. 5 shows the three brake speciic soot results o the tests on the naturally aspirated OM34 diesel engine. The comparison o the engine soot emission and the standards Euro I and Euro II are given in Fig. 6. This result indicates that the naturally aspirated OM34 diesel engine does not cover the Euro standard level, as Pirouzpanah et al mentioned in re. [3] torque N M 8 6 I.D.E.M upper limits 4 engine under test I.D.E.M lower limits engine speed rpm power(kw) Fig.3: torque and brake power output vs. engine speed 4

8 - Eect o turbocharger The engine is turbocharged without any change in compression ratio, uel injection and valves overlap, aiming to a decrease in speciic soot emission levels; it is called the limited inlet maniold pressure turbocharged engine (LIMP turbocharged engine). bsc (gr/kwh) bsc max bsc act. bsc min engine speed (rpm) Fig.4: Engine bsc vs. Engine speed.2 S so ot (g /kw h ) irst 6/6/85 second 7/6/85 third8/6/85 Fig.5: Brake speciic soot emission at three ECE-R49 test results or natural aspirated OM34 diesel engine.2 Ssoot (g/kwh) OM34 naturally aspirated engine Euro I Euro II Fig.6: A comparison between soot levels o the naturally aspirated engine with Euro standards In cooperation with Ferdowsi University o Mashhad, the Borg Warner turbo charger producing company in Germany proposed the suitable turbocharger, according to the data provided by the Ferdowsi University [4]. In the LIMP turbo-charging method although higher eiciency is obtained, as the uel consumption is the same as naturally aspirated, there is no signiicant change in the engine power and torque. Thus ECE-R49 3 modes test, under steady-state cycle do not vary. It should also be mentioned 42

9 that due to exhaust back-pressure proposed by the turbocharger, the temperature o the cylinder will increase and thereby, the exhaust valve and upper ring o the piston would be exposed to more deterioration than beore turbo-charging. With regards to the sensitivity o the test, at this stage, the test is also repeated or three times as shown in Fig. 7. The comparison o the soot levels are shown in Fig. 8 or naturally aspirated, turbocharged engine and Euro standard levels. The results show that the soot emission decreases with increasing the inlet maniold pressure. This reduction may be due to increasing the intake- temperature which results in reduction o ignition delay that prolongs the late combustion phase. This improves the soot burnout process..2 Ssoot (g/kwh) 24/8/85 25/8/85 25/8/85 Fig.7: Brake speciic soot emission at three ECE-R49 test results or turbocharged OM34 diesel engine - Eect o pressurizing The Fuel Injection in Turbocharged Engine In order to investigate the eect o uel injection pressure on brake speciic soot emission level, the injector pressure is adjusted or optimum value o 24 bars [5]. Washer(s) has been used or the adjustment o the injector, that according to the experiments each o them makes a bars increase in pressure, and then tested by the test apparatus. Ssoot (g/kwh).2 OM34 naturally aspirated engine turbocharged Euro I Euro II Fig.8: A comparison between soot levels o the turbocharged engine with Euro standards Ater pressurizing, due to loss in uel low, because o the pressure drop, the injection pump is readjusted according to Bocsh standard table. As the engine maximum power and torque do not vary, the 3 modes o the test do not alter and the test is perormed just like previous stages. Fig. 9 and show the three results o the test and the comparison between the results o three stages o the study, respectively. 43

10 .2 S soot (g/kw h) /7/85 /7/85 /7/85 Fig.9: Brake speciic soot emission at three ECE-R49 test results or turbocharged diesel engine with pressurized injection The result indicates that higher injection pressure makes the uel particle diameters to be smaller. Since ormation o mixing o uel to becomes better during ignition period, Smoke level will be less..2 Ssoot (g/kwh) OM34 naturally aspirated turbo charger elevated injection pressure Euro I Euro II Fig.: A comparison between soot level o the turbocharged engine with elevated injection pressure with Euro standards Conclusions In the present study, special investigation has been conducted on the soot emission level on an OM34 DI diesel engine. During the tests the engine was operated at three dierent conditions, naturally aspirated, LIMP turbocharged and elevated injection pressure. It was observed that the naturally aspirated engine had acceptable perormance characteristics but needed urgent attention in view o the soot emission levels. LIMP turbocharged engine had reduced the soot emission level to the extent o 35% because o the higher pressure and temperature o intake- and reduction o ignition delay which improves the soot burnout process, due to a prolong in the late combustion phase. When the injection pressure was elevated, it was observed that the speciic soot pollution decreased about 26% less than the turbocharged engine, and that was because smaller uel particles diameter and better ormation o mixing uel to. Also it is observed that the soot emission level o the engine was 2% less than the Euro I standard level but it does not match with the Euro II standard level. 44

11 Acknowledgements The authors acknowledge Mr. G.R. Shahi or his assistance and valuable suggestions during the tests. Environmental protection institute o Khorasane Razavi highly acknowledged or inancial support and Engineering aculty o Ferdowsi University o Mashhad highly acknowledged or providing the test instrumentations in the laboratory. Reerences []. Jonathan P.R. Symonds, Diesel soot mass calculation in real-time with a dierent mobility spectrometer, aerosol science 38(27) [2]. Sam George, Samantha Balla, Eect o diesel soot on lubricant oil viscosity Tribology international 4(27) [3]. N.K. Miller Jothi, Experimental studies on homogeneous charge CI engine ueled with LPG using DEE as an ignition enhancer, Renewable Energy, Volume 32, Issue 9, pages , July 27. [4]. Lyle M. Pickett, Soot in diesel uel jets: eects o ambient temperature, ambient density, and injection pressure, Combustion and Flame 38 (24), [5]. Steve Arnold, Kelvin Sulpski, Mark Groskreutz, Gary Vrbas, Rob candle, S.M. Shahed, Advanced turbo-charging technologies or heavy-duty diesel engines, SAE paper [6]. Dale R. Tree, Soot processes in compression ignition engines, progress in energy and combustion science 33 (27) [7]. K.S. Peat, A.J. Torregrosa, An investigation into the passive acoustic eect o the turbine in an automotive turbocharger, journal o sound and vibration 295 (26) [8]. E. Delacourt, Characterization o very high pressure diesel sprays using digital impinging techniques, Fuel 84 (25) [9]. Ismet Celikten, An experimental investigation o the eect o the injection pressure on engine perormance and exhaust emission in direct injection diesel engines, Applied Thermal Engineering 23 (23) []. Luigi Turrio-Baldassarri, Emission comparison o urban bus engine ueled with diesel oil and bio-diesel blend, Science o the Total Environment 327 (24) []. dieselnet.com/standards/eu/hd.htm [2]. John.B.Heywood, Internal Com- bustion Engine Fundamentals, Mc Graw-Hill Book company 988. [3]. V. Piroupanah, M. Mirsalim, M. Aghahi and Y. Jeihouni, Converting OM-34 Diesel engine to Dual-Fuel (Diesel+Gas) Engine,Journal o engine research, Techno-Engineering Quarterly Vol, No.6,Summer 25. [4]. Ali Sabazadeh, Eect o supercharging and variation o maniold pressure on soot ormation and OM34 engine parameters, thesis o master o science, mechanical engineering, supervised by M. Ghazikhani, Ferdowsi University o mashad, 23. [5] M. Ghazikhani, A. Darbandi, Eect o engine parameters on turbocharger second law eiciency in turbocharged diesel engines, ISME