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Application of the Miller cycle and turbo charging into a diesel engine to improve performance and decrease NO emissions
Energy 93 (2015) 795e800
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Application of the Miller cycle and turbo charging into a diesel engine to improve performance and decrease NO emissions _ Guven Gonca a, *, Bahri Sahin a, Adnan Parlak b, Vezir Ayhan c, Idris Cesur c, Sakip Koksal c a
Yildiz Technical University, Naval Arch. and Marine Eng. Depart, Besiktas, Istanbul, Turkey Yildiz Technical University, Marine Eng. Depar, Besiktas, Istanbul, Turkey c Sakarya University Mechanical Engineering Department, Sakarya, Turkey b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 November 2014 Received in revised form 12 August 2015 Accepted 14 August 2015 Available online xxx
The Miller cycle has been applied into the ICEs (internal combustion engines) to reduce NOx emissions, in the recent years. However, this method may decrease the engine power. The most common technique which improves the engine power is application of turbo charging. Thus, these two methods can be combined to make up for power loss and decrease emissions. In this study, the application of the Miller cycle and turbo charging methods into a single cylinder, four-stroke, DI (direct injection) diesel engine has been experimentally carried out. Two different versions of the Miller cycle, which provide 5 and 10 CA (crank angle) retarding compared to standard condition, are applied using two different camshafts. Turbo charging is applied at two different pressures, which are 1.1 and 1.2 bar, using a screw type compressor. In the results, the effective power and efficiency increased by 5.1% and 6.3%, NO, HC, CO and CO2 decreased by 27%, 28%, 55% and 10%, respectively. The results show that combination of the proposed methods may be applied into the diesel engines to minimize NO and improve engine performance. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Diesel engine Turbo charging Miller cycle Engine performance Emissions
1. Introduction Recently, engine researchers focused on the application of the Miller cycle into the ICEs (internal combustion engines) to reduce NOx emissions. However, a reduction is seen in engine torque and power due to reduction in volumetric efficiency [1e9]. Turbo charging systems are commonly used in the ICEs to improve specific power. Also, turbo charging decreases pollutant emissions [5e10]. Therefore, these two methods may be used together to decrease NOx emissions without power loss. Wang et al. [1,2] carried out experimental [1] and analytical [2] studies on the Miller cycle Otto engine with LIVC (late intake valve closing) version in order to reduce nitrogen oxides released from a petrol engine. Wang et al. [3] experimentally applied the Miller cycle into a diesel engine to reduce NOx emissions. Mikalsen et al. [4] examined the feasibility and potential advantages of the Miller cycle for an Otto cycle natural gas engine. The results showed that the SFC (specific fuel consumption) was reduced with the cost of a decreased power to weight ratio. Gonca et al. [5,6] numerically applied the Miller cycle into a diesel engine by using single-zone [5]
* Corresponding author. Tel.: þ90 212 383 2950; fax: þ90 212 383 2941. E-mail address: [email protected] (G. Gonca). http://dx.doi.org/10.1016/j.energy.2015.08.032 0360-5442/© 2015 Elsevier Ltd. All rights reserved.
and two-zone [6] combustion models to minimize NO emissions. Gonca et al. [7] parametrically derived performance maps of DualMiller cycle and also they [8] compared the performance of DualMiller cycle and the other gas cycle engines known in the literature. Gonca et al. [9] investigated the heat transfer effects on the performance of Dual-Miller cycle. In their studies, it was proved that the application of the Miller cycle into a diesel engine could abate the NO emissions and increase the effective efficiency. Kesgin [10] performed an experimental and theoretical study in order to examine the influence of the Miller cycle on the performance and emissions of a natural gas engine. Rinaldini et al. [11] performed an experimental and theoretical study to assess the potential and the limits of the Miller cycle application to a HSDI (High Speed Direct Injection) Diesel engine. The results demonstrated that NOx and soot emissions can be reduced up to 25% and 60%, respectively. Li et al. [12] experimentally examined the influences of the Miller cycle with LIVC and EIVC (early intake valve closing) versions on the SFC of a boosted DI (direct injection) gasoline engine. At the high load conditions, the fuel economy was improved up to 4.7% with LIVC, however, a remarkable change was not seen in the SFC with EIVC. At the low load conditions, SFC decreased up to 6.8% and 7.4% with LIVC and EIVC, respectively. Wu et al. [13] analyzed the performance of a supercharged Miller cycle Otto engine with EIVC
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G. Gonca et al. / Energy 93 (2015) 795e800
Nomenclature DI EIVC HSDI ICE IDI LIVC SIM SFC
direct injection early intake valve closing high speed direct injection internal combustion engines indirect injection late intake valve closing steam injection method specific fuel consumption
version. Gonca et al. [14,15] applied the Miller cycle into a naturally aspirated, DI diesel engine [14] and steam injected DI diesel engine [15] to decrease NO emissions. So many studies on turbo charging have been carried out as it increases the performance of the ICE. Mostafavi and Agnew [16] examined the influences of pressure and temperature ratios on thermal efficiency and net work of a turbocharged diesel engine. Rakopoulos and Giakoumis [17] carried out the second-law analysis of a multi-cylinder, turbocharged, IDI (indirect injection) diesel engine using single-zone thermodynamic model. Tauzia et al. [18] presented a new heat release model for modern turbocharged heavy duty diesel engines. The model proposed was validated against experimental data. Serrano et al. [19,20] performed theoretical and experimental studies on a methodology which characterizes and simulates the combustion characteristics of a turbocharged diesel engine. They presented the study in two parts. In the first part, data acquisition and post-processing was obtained [19] and phenomenological combustion simulation was carried out in the second part [20]. Rakopoulos et al. [21] performed an experimental study in order to examine the formation mechanisms of smoke, NO and combustion noise radiation during hot starting for a turbocharged diesel engine fuelled with biodiesel-diesel and n-butanol-diesel blends. Zamboni and Capobianco [22,23] examined and compared the high and low pressure EGR (exhaust gas recirculation) systems with variable nozzle turbine control [22] and variable geometry turbine [23] fitted on an automotive turbocharged diesel engine. Boretti [24] used the water injection method in a turbocharged, DI, spark ignition engine fuelled with ethanol. Gonca et al. [25] carried out a theoretical analysis based on the thermodynamics to determine the optimum steam temperatures and mass ratios for the turbocharged ICEs. This study experimentally reports the influences of the Miller cycle and turbo charging applications on the performance and emissions of a single cylinder diesel engine. The performance parameters such as torque, effective power, effective efficiency, SFC and NO, CO, CO2, HC emissions have been experimentally obtained. In the literature, although the Miller cycle and turbo charging are well known there is no such a work investigating the effects of dual combination of turbo charging and Miller cycle with LIVC version on the performance and emissions of a diesel engine by experiments. Therefore, this work includes a good novelty and originality. 2. Material and method 2.1. Experimental set-up The experiments were performed with a single cylinder, fourstroke and DI diesel engine. Table 1 demonstrates the engine properties. The Miller cycles are provided by retarding the closing of intake valve as 5 and 10 CA. The original camshaft is camshaft 52 (STD) which means the intake valve is closed 52 CA after the BDC
Table 1 Engine properties [15]. Engine type
Antor
Bore [mm] Stroke [mm] Cylinder Number Stroke volume [dm3] Power, 2700 rpm [kW] Injection pressure [bar] Injecting timing [crank angle] Compression ratio Maximum speed [rpm] Cooling Injection
85 90 1 0.51 9 175 28 17.5 3000 Air Direct injection
(bottom dead center). 5 and 10 CA retarding are conducted with camshaft 57 (C57) and camshaft 62 (C62). In order to apply the Miller cycle into the diesel engine, two different camshafts were manufactured and mounted into the engine one by one. The picture of the camshafts and technical drawing are given in Fig. 1. In order to apply turbo charging into the diesel engine, a compressor taken from E 211 brand Mercedes-Benz truck was adapted to the engine. The compressor was mounted to suction line of the engine and then 1.1 bar (T1.1) and 1.2 bar (T1.2) pressures were applied by an electronic control unit. In order to measure brake torque, the engine was coupled with an electric dynamometer of 20 kW absorbing capacity using an “S” type load cell with the precision of 0.01 kg. In order to measure species of the exhaust emissions, MRU Spectra 1600 L type gas analyzer was used [14,15,26e29]. CO, CO2, NO, and HC emissions were obtained as unit of (%) and ppm. The experiments were performed at variable engine speeds from 1500 to 3000 rpm and full load condition. In order to compare, the compressor was mounted to the suction line of the engine and then standard camshaft and the other camshafts were mounted to the engine in order to obtain the experimental data for the Miller cycle and turbo charging conditions. The experiments were repeated three times for each camshaft and then performance and emission data were compared with each other. Total uncertainties of the measured parameters are substantial to verify the accuracy of the test results, so they are given in the Table 2. 3. Results and discussion Fig. 2 shows the engine torque and effective power with respect to change of engine speed for different camshafts and pressures. It is clear from the figures that the engine torque reduces and effective power increases with increasing engine speed. The highest torque is acquired at 1500 rpm and the maximum power is obtained at 3000 rpm. Also, the torque and effective power increase with increasing turbo charging pressure. C57 conditions give the maximum performance values. However, although C62 conditions provide the higher performance at low and medium engine speeds, they have lower performance at high engine speeds. At T1.1 conditions, the maximum increase rate is obtained with C57-T1.1, as 5.1% at 1500 rpm, the maximum decrease rate is acquired with C62T1.1, as 1.2% at 3000 rpm for the engine torque and effective power. However, the change rate is lower at T1.2 conditions. The maximum increase rate is attained with C57-T1.2, as 2.9% at 1500 rpm, the maximum decrease rate is seen with C62-T1.2, as 0.8% at 3000 rpm. The engine torque is depended on combustion duration, combustion temperatures and friction losses. Due to higher combustion duration, combustion temperatures and lower friction losses, the maximum torque values are seen at medium engine speeds. At the modified conditions, the maximum torque and maximum effective
G. Gonca et al. / Energy 93 (2015) 795e800
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Fig. 1. The picture and technical drawings of the original and modified camshafts in accordance with the Miller cycle [15].
power are obtained with C57-T1.2. The maximum torque is 45.3 Nm at 1500 rpm, the maximum effective power is 10.13 kW at 3000 rpm. The minimum torque and minimum effective power are attained with C62-T1.1. The minimum torque is 30.9 Nm at 3000 rpm, the minimum effective power is 6.5 kW. The change of the effective efficiency with respect to engine speed for different camshafts and pressures are illustrated in Fig. 3. It is obviously seen from the figures that the middle range of the engine speeds gives the maximum effective efficiency. At the lower and higher engine speeds, the effective efficiency decreases. The application of the Miller cycle and turbo charging together improves the effective efficiency. Effective efficiency is related to
engine performance. Therefore, it changes with respect to reasons which affect the engine torque and effective efficiency. At T1.1 conditions, the maximum increase rate is obtained with C57-T1.1, as 6.3% at 3000 rpm, the maximum reduction rate is seen with C62T1.1, as 1.1% at 3000 rpm. At T1.2 conditions, the maximum increase rate is acquired with C57-T1.2, as 6.8% at 1800 rpm, while the maximum reduction rate is attained with C62-T1.2, as 0.9% at 3000 rpm. The figure shows that the maximum effective efficiency is obtained with C57-T1.2, as 38.2% at 2100 rpm. The minimum effective efficiency is acquired with C62-T1.1, as 29.7% at 3000 rpm. Fig. 4 illustrates the variation of NO formation with respect to engine speed for different engine modes. The formation of NO
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G. Gonca et al. / Energy 93 (2015) 795e800 Table 2 The errors in parameters and total uncertainties [15]. Parameters
Systematic errors±
Load [N] Speed [rpm] Time [s] Temperature [ C] Fuel consumption [g] NOx [ppm] HC [ppm] CO [%] CO2 [%] SFC [g/kWh] Torque [Nm]
0.1 1.0 0.1 1.0 0.01 5% of 5% of 5% of 5% of 1.5 1.1
measured measured measured measured
value value value value
emission is very sensitive to combustion temperature and duration [14,15,26e29]. Also, the equivalence ratio affects the combustion temperature, the highest combustion temperatures are seen about stochiometric combustion conditions [30]. At the lower equivalence ratios, the formation of NO slows down. It can be observed from Fig. 4 that NO increases at the low engine speeds. However, NO abates with increasing engine speeds due to lower combustion duration, lower combustion temperature and leaner air-fuel mixtures. It is clear that NO emissions increase with increasing charge pressure and decreasing Miller cycle angle (retarding angle). At T1.1 conditions, the maximum and minimum NO reduction rates are seen as 27% with C62-T1.1 at 2700 rpm and as %5 with C57-T1.1 at 1800 rpm, respectively. At T1.2 conditions, the maximum and minimum NO reduction rates are obtained as 23% with C62-T1.2 at 2700 rpm and as %1 with C57-T1.2 at 3000 rpm, respectively. . The minimum and maximum NO are found as 470 ppm with C62-T1.1 at
Fig. 2. a) Torque and b) effective efficiency with respect to engine speed for different camshaft and turbo charge modes.
Fig. 3. Effective efficiency with respect to engine speed for different camshaft and turbo charge modes.
3000 rpm and 1204 ppm with C57-T1.2 at 1500 rpm, respectively, for the Miller cycle conditions. Fig. 5 demonstrates the variation of HC with respect to engine speed. HC formation rate decreases with increasing engine speeds due to leaner combustion conditions for all engine modes. Since turbo charging and the Miller cycle application lead to higher oxygen concentration and lower equivalence ratio, HC emission decreases considerably with the application of the Miller cycle. Higher turbo charging pressure. However, C57 condition is the optimum point for the minimization of HC. At higher the crank angles, there is an increase trend in HC, due to lower volumetric efficiency and charge loss. As expected, the lowest HC levels are seen with the C57-T1.2. At T1.1 conditions, the maximum and minimum reduction rates are 27% with C57-T1.1 at 1800 rpm and 7% with C62-T1.1 at 2100 rpm, respectively. At T1.2 conditions, the maximum and minimum reduction rates are 28% with C57-T1.2 at 1500 rpm and 1% with C62-T1.2 at 3000 rpm. The maximum HC is 65 ppm with C62-T.1.1 at 1500 rpm and the minimum HC is 35 ppm with C57T1.2 at 3000 rpm. Fig. 6 shows the variation of CO with respect to engine speed. The formation characteristics of CO is similar to those of HC emissions. The formation of CO and HC emissions strongly depends on oxygen concentration (equivalence ratio) of the cylinder charge, hence CO formation rate decreases with increasing engine speeds and the application of turbo charging and Miller cycle. However, it
Fig. 4. NO emissions with respect to engine speed for different camshaft and turbo charge modes.
G. Gonca et al. / Energy 93 (2015) 795e800
Fig. 5. HC emissions with respect to engine speed for different camshaft and turbo charge modes.
799
Fig. 7. CO2 emissions with respect to engine speed for different camshaft and turbo charge modes.
conditions, the maximum and minimum CO2 reduction rates are seen as 10% with C62-T1.1 at 3000 rpm and as %1 with C57-T1.1 at 1500 rpm. At the second turbo charge condition, they are 15% (with C62-T1.2 at 2700 rpm) and 1% (with C57-T1.2 at 1800 rpm). The minimum and maximum CO2 are found as 9.1% with C62-T1.2 at 3000 rpm and 11.7% with C57-T1.1 at 1500 rpm, respectively, for the modified conditions. The main purpose of this study is to decrease NO emission without power loss. C62-T1.1 condition gives the maximum NO reduction rates compared to other engine modes. 4. Conclusion
Fig. 6. CO emissions with respect to engine speed for different camshaft and turbo charge modes.
increases with the application of C62 compared to that of C57 condition, because C57 is optimum condition and CO increases at higher camshaft angles. The remarkable reduction rates are seen in the CO emissions with the application of turbo charging. The lowest CO levels are seen with the C57-T1.2. At T1.1 conditions, the maximum and minimum reduction rates are 55% with C57-T1.1 at 2700 rpm and 4% with C62-T1.1 at 1500 rpm, respectively. The maximum and minimum reduction rates are 53% with C57-T1.2 at 2700 rpm and 1% with C62-T1.2 at 1800 rpm for T1.2 conditions. The maximum CO is 1.8% with C62-T.1.1 at 1500 rpm and the minimum CO is 0.15% with C57-T1.2 at 3000 rpm for the modified conditions. The variation of CO2 with respect to engine speed is shown in Fig. 7. CO2 emissions are complete combustion products so CO2 increases with increasing oxygen concentration and combustion temperatures. It is obvious from the figure that CO2 decreases with increasing engine speeds, although equivalence ratio decreases and oxygen concentration increases, combustion temperatures decrease. The effect of lower combustion temperatures dominates the increase of oxygen concentration. Therefore, CO2 decreases as seen in the Fig. 7. If the Figs. 7 and 4 are investigated together, it can be said that the combustion temperatures increase at the lower engine speeds with higher oxygen concentration. The application of the Miller cycle decreases the oxygen concentration and combustion temperatures, therefore, CO2 formation reduces. At T1.1
In the present study, the application of the Miller cycle and turbo charging together into a diesel engine has been performed and the effects of this modification on the engine performance and emissions have been experimentally examined. The torque, effective power, effective efficiency are considerably improved by applying the modification. NO, HC, CO and CO2 emissions decreased at all engine speeds compared to the standard camshaft conditions. Even though C57-T1.2 gives the maximum performance values, C62-T1.1 gives the lowest NO values, therefore latter is determined optimum condition, as this study primarily aims to decrease NO emissions. It is known that the application of the Miller cycle into a ICE decreases NO with power loss [1e9]. The application of the turbo charging and the Miller cycle together increases the engine power and decreases the NO emissions at higher rates compared to standard camshaft conditions. The maximum reduction rates in NO are obtained with C62-T1.1 conditions. NO emissions decrease by 27% and the torque and effective efficiency increase up to 1%. At this condition, HC, CO and CO2 emissions decreased by 20%, 43% and 10% respectively. The application of this modification decreases NO emissions in substantial rates at high engine speeds. Thus, this combination may be used in the diesel engines running at constant engine speeds in order to obtain higher engine performance and lower emissions. Acknowledgment This study is a part of PhD thesis of the first author. The authors thank The Scientific and Technological Research Council of Turkey (TUBITAK- the project number is 111M065), Yildiz Technical University Scientific Research Projects Coordination Department (the project number is 2011-10-01-KAP03) and Turkish Academy of Sciences (TUBA) for their financial supporting.
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References [1] Wang Y, Lin L, Zeng S. Application of the Miller cycle to reduce NOx emissions from petrol engines. Appl Energy 2008;85:463e74. [2] Wang Y, Lin L, Roskilly AP. An analytic study of applying Miller cycle to reduce NOx emission from petrol engine. Appl Therm Eng 2007;27:1779e89. [3] Wang Y, Zeng S, Huang J. Experimental investigation of applying Miller cycle to reduce NOx emission from diesel engine. Proc IMechE Part A J Power Energy 2005;219:631e8. [4] Mikalsen R, Wang YD, Roskilly AP. A comparison of Miller and Otto cycle natural gas engines for small scale CHP applications. Appl Energy 2009;86:922e7. [5] Gonca G, Sahin B, Ust Y, Parlak A. A study on late intake valve closing miller cycled diesel engine. Arab J Sci Eng 2013;38:383e93. [6] Gonca G, Sahin B, Ust Y, Parlak A, Safa A. Comparison of steam injected diesel engine and Miller cycled diesel engine by using two zone combustion model. J Energy Inst 2015;88(1):43e52. [7] Gonca G, Sahin B, Ust Y. Performance maps for an air-standard irreversible Dual-Miller cycle (DMC) with late inlet valve closing (LIVC) version. Energy 2013;5:285e90. [8] Gonca G, Sahin B, Ust Y, Parlak A. Comprehensive performance analyses and optimization of the irreversible thermodynamic cycle engines (TCE) under maximum power (MP) and maximum power density (MPD) conditions. Appl Therm Eng 2015;85:9e20. [9] Gonca G, Sahin B, Ust Y. Investigation of heat transfer influences on performance of air-standard irreversible dual-miller cycle. J Thermophys Heat Transf 2015;29:678e83. [10] Kesgin U. Efficiency improvement and NOx emission reduction potentials of two-stage turbocharged Miller cycle for stationary natural gas engines. Int J Energy Res 2005;29:189e216. [11] Rinaldini CA, Mattarelli E, Golovitchev VI. Potential of the Miller cycle on a HSDI diesel automotive engine. Appl Energy 2013;112:102e19. [12] Li T, Gao Y, Wang J, Chen Z. The Miller cycle effects on improvement of fuel economy in a highly boosted, high compression ratio, direct-injection gasoline engine: EIVC vs LIVC. Energy Convers Manage 2014;79:59e65. [13] Wu C, Puzinauskas PV, Tsai JS. Performance analysis and optimization of a supercharged Miller cycle Otto engine. Appl Therm Eng 2003;23:511e21. [14] Gonca G, Sahin B, Parlak A, Ust Y, Ayhan V, Cesur I, et al. Theoretical and experimental investigation of the Miller cycle diesel engine in terms of performance and emission parameters. Appl Energy 2015;138:11e20. [15] Gonca G, Sahin B, Parlak A, Ust Y, Ayhan V, Cesur I, et al. The effects of steam injection on the performance and emission parameters of a Miller cycle diesel engine. Energy 2014;78:266e75. [16] Mostafavi M, Agnew B. Thermodynamic analysis of combined diesel engine and absorption unit-turbocharged engine. Appl Therm Eng 1996;16(10): 845e50.
[17] Rakopoulos CD, Giakoumis EG. Speed and load effects on the availability balances and irreversibilities production in a multi-cylinder turbocharged diesel engine. Appl Therm Eng 1997;17(3):299e313. [18] Tauzia X, Maiboom A, Chesse P, Thouvenel N. A new phenomenological heat release model for thermodynamical simulation of modern turbocharged heavy duty diesel engines. Appl Therm Eng 2006;26:1851e7. [19] Serrano JR, Climent H, Guardiola C, Piqueras P. Methodology for characterisation and simulation of turbocharged diesel engines combustion during transient operation. Part 1: data acquisition and post-processing. Appl Therm Eng 2009;29:142e9. [20] Serrano JR, Climent H, Guardiola C, Piqueras P. Methodology for characterisation and simulation of turbocharged diesel engines combustion during transient operation. Part 2: phenomenological combustion simulation. Appl Therm Eng 2009;29:150e8. [21] Rakopoulos CD, Dimaratos AM, Giakoumis EG, Rakopoulos DC. Study of turbocharged diesel engine operation, pollutant emissions and combustion noise radiation during starting with bio-diesel or n-butanol diesel fuel blends. Appl Energy 2011;88:3905e16. [22] Zamboni G, Capobianco M. Experimental study on the effects of HP and LP EGR in an automotive turbocharged diesel engine. Appl Energy 2012;94: 117e28. [23] Zamboni G, Capobianco M. Influence of high and low pressure EGR and VGT control on in-cylinder pressure diagrams and rate of heat release in an automotive turbocharged diesel engine. Appl Therm Eng 2013;51:586e96. [24] Boretti A. Water injection in directly injected turbocharged spark ignition engines. Appl Therm Eng 2013;52:62e8. [25] Gonca G, Sahin B, Ust Y, Parlak A. Determination of the optimum temperatures and mass ratios of steam injected into turbocharged internal combustion engines. J Renew Sustain Energy 2013;023119(5):1e13. http://dx.doi.org/ 10.1063/1.4798313. [26] Gonca G. Investigation of the effects of steam injection on performance and NO emissions of a diesel engine running with ethanolediesel blend. Energy Convers Manage 2014;77:450e7. [27] Kokkulunk G, Parlak A, Ayhan V, Cesur I, Gonca G, Boru B. Theoretical and experimental investigation of steam injected diesel engine with EGR. Energy 2014;74:331e9. [28] Cesur I, Parlak A, Ayhan A, Boru B, Gonca G. The effects of electronic controlled steam injection on spark ignition engine. Appl Therm Eng 2013;55:61e8. [29] Kokkulunk G, Gonca G, Ayhan V, Cesur I, Parlak A. Theoretical and experimental investigation of diesel engine with steam injection system on performance and emission parameters. Appl Therm Eng 2013;54:161e70. [30] Heywood JB. Internal combustion engine fundamentals. New York: McGrawHill Inc.; 1998.
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Application of the Miller cycle and turbo charging into a diesel engine to improve performance and decrease NO emissions _ Guven Gonca a, *, Bahri Sahin a, Adnan Parlak b, Vezir Ayhan c, Idris Cesur c, Sakip Koksal c a
Yildiz Technical University, Naval Arch. and Marine Eng. Depart, Besiktas, Istanbul, Turkey Yildiz Technical University, Marine Eng. Depar, Besiktas, Istanbul, Turkey c Sakarya University Mechanical Engineering Department, Sakarya, Turkey b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 November 2014 Received in revised form 12 August 2015 Accepted 14 August 2015 Available online xxx
The Miller cycle has been applied into the ICEs (internal combustion engines) to reduce NOx emissions, in the recent years. However, this method may decrease the engine power. The most common technique which improves the engine power is application of turbo charging. Thus, these two methods can be combined to make up for power loss and decrease emissions. In this study, the application of the Miller cycle and turbo charging methods into a single cylinder, four-stroke, DI (direct injection) diesel engine has been experimentally carried out. Two different versions of the Miller cycle, which provide 5 and 10 CA (crank angle) retarding compared to standard condition, are applied using two different camshafts. Turbo charging is applied at two different pressures, which are 1.1 and 1.2 bar, using a screw type compressor. In the results, the effective power and efficiency increased by 5.1% and 6.3%, NO, HC, CO and CO2 decreased by 27%, 28%, 55% and 10%, respectively. The results show that combination of the proposed methods may be applied into the diesel engines to minimize NO and improve engine performance. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Diesel engine Turbo charging Miller cycle Engine performance Emissions
1. Introduction Recently, engine researchers focused on the application of the Miller cycle into the ICEs (internal combustion engines) to reduce NOx emissions. However, a reduction is seen in engine torque and power due to reduction in volumetric efficiency [1e9]. Turbo charging systems are commonly used in the ICEs to improve specific power. Also, turbo charging decreases pollutant emissions [5e10]. Therefore, these two methods may be used together to decrease NOx emissions without power loss. Wang et al. [1,2] carried out experimental [1] and analytical [2] studies on the Miller cycle Otto engine with LIVC (late intake valve closing) version in order to reduce nitrogen oxides released from a petrol engine. Wang et al. [3] experimentally applied the Miller cycle into a diesel engine to reduce NOx emissions. Mikalsen et al. [4] examined the feasibility and potential advantages of the Miller cycle for an Otto cycle natural gas engine. The results showed that the SFC (specific fuel consumption) was reduced with the cost of a decreased power to weight ratio. Gonca et al. [5,6] numerically applied the Miller cycle into a diesel engine by using single-zone [5]
* Corresponding author. Tel.: þ90 212 383 2950; fax: þ90 212 383 2941. E-mail address: [email protected] (G. Gonca). http://dx.doi.org/10.1016/j.energy.2015.08.032 0360-5442/© 2015 Elsevier Ltd. All rights reserved.
and two-zone [6] combustion models to minimize NO emissions. Gonca et al. [7] parametrically derived performance maps of DualMiller cycle and also they [8] compared the performance of DualMiller cycle and the other gas cycle engines known in the literature. Gonca et al. [9] investigated the heat transfer effects on the performance of Dual-Miller cycle. In their studies, it was proved that the application of the Miller cycle into a diesel engine could abate the NO emissions and increase the effective efficiency. Kesgin [10] performed an experimental and theoretical study in order to examine the influence of the Miller cycle on the performance and emissions of a natural gas engine. Rinaldini et al. [11] performed an experimental and theoretical study to assess the potential and the limits of the Miller cycle application to a HSDI (High Speed Direct Injection) Diesel engine. The results demonstrated that NOx and soot emissions can be reduced up to 25% and 60%, respectively. Li et al. [12] experimentally examined the influences of the Miller cycle with LIVC and EIVC (early intake valve closing) versions on the SFC of a boosted DI (direct injection) gasoline engine. At the high load conditions, the fuel economy was improved up to 4.7% with LIVC, however, a remarkable change was not seen in the SFC with EIVC. At the low load conditions, SFC decreased up to 6.8% and 7.4% with LIVC and EIVC, respectively. Wu et al. [13] analyzed the performance of a supercharged Miller cycle Otto engine with EIVC
796
G. Gonca et al. / Energy 93 (2015) 795e800
Nomenclature DI EIVC HSDI ICE IDI LIVC SIM SFC
direct injection early intake valve closing high speed direct injection internal combustion engines indirect injection late intake valve closing steam injection method specific fuel consumption
version. Gonca et al. [14,15] applied the Miller cycle into a naturally aspirated, DI diesel engine [14] and steam injected DI diesel engine [15] to decrease NO emissions. So many studies on turbo charging have been carried out as it increases the performance of the ICE. Mostafavi and Agnew [16] examined the influences of pressure and temperature ratios on thermal efficiency and net work of a turbocharged diesel engine. Rakopoulos and Giakoumis [17] carried out the second-law analysis of a multi-cylinder, turbocharged, IDI (indirect injection) diesel engine using single-zone thermodynamic model. Tauzia et al. [18] presented a new heat release model for modern turbocharged heavy duty diesel engines. The model proposed was validated against experimental data. Serrano et al. [19,20] performed theoretical and experimental studies on a methodology which characterizes and simulates the combustion characteristics of a turbocharged diesel engine. They presented the study in two parts. In the first part, data acquisition and post-processing was obtained [19] and phenomenological combustion simulation was carried out in the second part [20]. Rakopoulos et al. [21] performed an experimental study in order to examine the formation mechanisms of smoke, NO and combustion noise radiation during hot starting for a turbocharged diesel engine fuelled with biodiesel-diesel and n-butanol-diesel blends. Zamboni and Capobianco [22,23] examined and compared the high and low pressure EGR (exhaust gas recirculation) systems with variable nozzle turbine control [22] and variable geometry turbine [23] fitted on an automotive turbocharged diesel engine. Boretti [24] used the water injection method in a turbocharged, DI, spark ignition engine fuelled with ethanol. Gonca et al. [25] carried out a theoretical analysis based on the thermodynamics to determine the optimum steam temperatures and mass ratios for the turbocharged ICEs. This study experimentally reports the influences of the Miller cycle and turbo charging applications on the performance and emissions of a single cylinder diesel engine. The performance parameters such as torque, effective power, effective efficiency, SFC and NO, CO, CO2, HC emissions have been experimentally obtained. In the literature, although the Miller cycle and turbo charging are well known there is no such a work investigating the effects of dual combination of turbo charging and Miller cycle with LIVC version on the performance and emissions of a diesel engine by experiments. Therefore, this work includes a good novelty and originality. 2. Material and method 2.1. Experimental set-up The experiments were performed with a single cylinder, fourstroke and DI diesel engine. Table 1 demonstrates the engine properties. The Miller cycles are provided by retarding the closing of intake valve as 5 and 10 CA. The original camshaft is camshaft 52 (STD) which means the intake valve is closed 52 CA after the BDC
Table 1 Engine properties [15]. Engine type
Antor
Bore [mm] Stroke [mm] Cylinder Number Stroke volume [dm3] Power, 2700 rpm [kW] Injection pressure [bar] Injecting timing [crank angle] Compression ratio Maximum speed [rpm] Cooling Injection
85 90 1 0.51 9 175 28 17.5 3000 Air Direct injection
(bottom dead center). 5 and 10 CA retarding are conducted with camshaft 57 (C57) and camshaft 62 (C62). In order to apply the Miller cycle into the diesel engine, two different camshafts were manufactured and mounted into the engine one by one. The picture of the camshafts and technical drawing are given in Fig. 1. In order to apply turbo charging into the diesel engine, a compressor taken from E 211 brand Mercedes-Benz truck was adapted to the engine. The compressor was mounted to suction line of the engine and then 1.1 bar (T1.1) and 1.2 bar (T1.2) pressures were applied by an electronic control unit. In order to measure brake torque, the engine was coupled with an electric dynamometer of 20 kW absorbing capacity using an “S” type load cell with the precision of 0.01 kg. In order to measure species of the exhaust emissions, MRU Spectra 1600 L type gas analyzer was used [14,15,26e29]. CO, CO2, NO, and HC emissions were obtained as unit of (%) and ppm. The experiments were performed at variable engine speeds from 1500 to 3000 rpm and full load condition. In order to compare, the compressor was mounted to the suction line of the engine and then standard camshaft and the other camshafts were mounted to the engine in order to obtain the experimental data for the Miller cycle and turbo charging conditions. The experiments were repeated three times for each camshaft and then performance and emission data were compared with each other. Total uncertainties of the measured parameters are substantial to verify the accuracy of the test results, so they are given in the Table 2. 3. Results and discussion Fig. 2 shows the engine torque and effective power with respect to change of engine speed for different camshafts and pressures. It is clear from the figures that the engine torque reduces and effective power increases with increasing engine speed. The highest torque is acquired at 1500 rpm and the maximum power is obtained at 3000 rpm. Also, the torque and effective power increase with increasing turbo charging pressure. C57 conditions give the maximum performance values. However, although C62 conditions provide the higher performance at low and medium engine speeds, they have lower performance at high engine speeds. At T1.1 conditions, the maximum increase rate is obtained with C57-T1.1, as 5.1% at 1500 rpm, the maximum decrease rate is acquired with C62T1.1, as 1.2% at 3000 rpm for the engine torque and effective power. However, the change rate is lower at T1.2 conditions. The maximum increase rate is attained with C57-T1.2, as 2.9% at 1500 rpm, the maximum decrease rate is seen with C62-T1.2, as 0.8% at 3000 rpm. The engine torque is depended on combustion duration, combustion temperatures and friction losses. Due to higher combustion duration, combustion temperatures and lower friction losses, the maximum torque values are seen at medium engine speeds. At the modified conditions, the maximum torque and maximum effective
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Fig. 1. The picture and technical drawings of the original and modified camshafts in accordance with the Miller cycle [15].
power are obtained with C57-T1.2. The maximum torque is 45.3 Nm at 1500 rpm, the maximum effective power is 10.13 kW at 3000 rpm. The minimum torque and minimum effective power are attained with C62-T1.1. The minimum torque is 30.9 Nm at 3000 rpm, the minimum effective power is 6.5 kW. The change of the effective efficiency with respect to engine speed for different camshafts and pressures are illustrated in Fig. 3. It is obviously seen from the figures that the middle range of the engine speeds gives the maximum effective efficiency. At the lower and higher engine speeds, the effective efficiency decreases. The application of the Miller cycle and turbo charging together improves the effective efficiency. Effective efficiency is related to
engine performance. Therefore, it changes with respect to reasons which affect the engine torque and effective efficiency. At T1.1 conditions, the maximum increase rate is obtained with C57-T1.1, as 6.3% at 3000 rpm, the maximum reduction rate is seen with C62T1.1, as 1.1% at 3000 rpm. At T1.2 conditions, the maximum increase rate is acquired with C57-T1.2, as 6.8% at 1800 rpm, while the maximum reduction rate is attained with C62-T1.2, as 0.9% at 3000 rpm. The figure shows that the maximum effective efficiency is obtained with C57-T1.2, as 38.2% at 2100 rpm. The minimum effective efficiency is acquired with C62-T1.1, as 29.7% at 3000 rpm. Fig. 4 illustrates the variation of NO formation with respect to engine speed for different engine modes. The formation of NO
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G. Gonca et al. / Energy 93 (2015) 795e800 Table 2 The errors in parameters and total uncertainties [15]. Parameters
Systematic errors±
Load [N] Speed [rpm] Time [s] Temperature [ C] Fuel consumption [g] NOx [ppm] HC [ppm] CO [%] CO2 [%] SFC [g/kWh] Torque [Nm]
0.1 1.0 0.1 1.0 0.01 5% of 5% of 5% of 5% of 1.5 1.1
measured measured measured measured
value value value value
emission is very sensitive to combustion temperature and duration [14,15,26e29]. Also, the equivalence ratio affects the combustion temperature, the highest combustion temperatures are seen about stochiometric combustion conditions [30]. At the lower equivalence ratios, the formation of NO slows down. It can be observed from Fig. 4 that NO increases at the low engine speeds. However, NO abates with increasing engine speeds due to lower combustion duration, lower combustion temperature and leaner air-fuel mixtures. It is clear that NO emissions increase with increasing charge pressure and decreasing Miller cycle angle (retarding angle). At T1.1 conditions, the maximum and minimum NO reduction rates are seen as 27% with C62-T1.1 at 2700 rpm and as %5 with C57-T1.1 at 1800 rpm, respectively. At T1.2 conditions, the maximum and minimum NO reduction rates are obtained as 23% with C62-T1.2 at 2700 rpm and as %1 with C57-T1.2 at 3000 rpm, respectively. . The minimum and maximum NO are found as 470 ppm with C62-T1.1 at
Fig. 2. a) Torque and b) effective efficiency with respect to engine speed for different camshaft and turbo charge modes.
Fig. 3. Effective efficiency with respect to engine speed for different camshaft and turbo charge modes.
3000 rpm and 1204 ppm with C57-T1.2 at 1500 rpm, respectively, for the Miller cycle conditions. Fig. 5 demonstrates the variation of HC with respect to engine speed. HC formation rate decreases with increasing engine speeds due to leaner combustion conditions for all engine modes. Since turbo charging and the Miller cycle application lead to higher oxygen concentration and lower equivalence ratio, HC emission decreases considerably with the application of the Miller cycle. Higher turbo charging pressure. However, C57 condition is the optimum point for the minimization of HC. At higher the crank angles, there is an increase trend in HC, due to lower volumetric efficiency and charge loss. As expected, the lowest HC levels are seen with the C57-T1.2. At T1.1 conditions, the maximum and minimum reduction rates are 27% with C57-T1.1 at 1800 rpm and 7% with C62-T1.1 at 2100 rpm, respectively. At T1.2 conditions, the maximum and minimum reduction rates are 28% with C57-T1.2 at 1500 rpm and 1% with C62-T1.2 at 3000 rpm. The maximum HC is 65 ppm with C62-T.1.1 at 1500 rpm and the minimum HC is 35 ppm with C57T1.2 at 3000 rpm. Fig. 6 shows the variation of CO with respect to engine speed. The formation characteristics of CO is similar to those of HC emissions. The formation of CO and HC emissions strongly depends on oxygen concentration (equivalence ratio) of the cylinder charge, hence CO formation rate decreases with increasing engine speeds and the application of turbo charging and Miller cycle. However, it
Fig. 4. NO emissions with respect to engine speed for different camshaft and turbo charge modes.
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Fig. 5. HC emissions with respect to engine speed for different camshaft and turbo charge modes.
799
Fig. 7. CO2 emissions with respect to engine speed for different camshaft and turbo charge modes.
conditions, the maximum and minimum CO2 reduction rates are seen as 10% with C62-T1.1 at 3000 rpm and as %1 with C57-T1.1 at 1500 rpm. At the second turbo charge condition, they are 15% (with C62-T1.2 at 2700 rpm) and 1% (with C57-T1.2 at 1800 rpm). The minimum and maximum CO2 are found as 9.1% with C62-T1.2 at 3000 rpm and 11.7% with C57-T1.1 at 1500 rpm, respectively, for the modified conditions. The main purpose of this study is to decrease NO emission without power loss. C62-T1.1 condition gives the maximum NO reduction rates compared to other engine modes. 4. Conclusion
Fig. 6. CO emissions with respect to engine speed for different camshaft and turbo charge modes.
increases with the application of C62 compared to that of C57 condition, because C57 is optimum condition and CO increases at higher camshaft angles. The remarkable reduction rates are seen in the CO emissions with the application of turbo charging. The lowest CO levels are seen with the C57-T1.2. At T1.1 conditions, the maximum and minimum reduction rates are 55% with C57-T1.1 at 2700 rpm and 4% with C62-T1.1 at 1500 rpm, respectively. The maximum and minimum reduction rates are 53% with C57-T1.2 at 2700 rpm and 1% with C62-T1.2 at 1800 rpm for T1.2 conditions. The maximum CO is 1.8% with C62-T.1.1 at 1500 rpm and the minimum CO is 0.15% with C57-T1.2 at 3000 rpm for the modified conditions. The variation of CO2 with respect to engine speed is shown in Fig. 7. CO2 emissions are complete combustion products so CO2 increases with increasing oxygen concentration and combustion temperatures. It is obvious from the figure that CO2 decreases with increasing engine speeds, although equivalence ratio decreases and oxygen concentration increases, combustion temperatures decrease. The effect of lower combustion temperatures dominates the increase of oxygen concentration. Therefore, CO2 decreases as seen in the Fig. 7. If the Figs. 7 and 4 are investigated together, it can be said that the combustion temperatures increase at the lower engine speeds with higher oxygen concentration. The application of the Miller cycle decreases the oxygen concentration and combustion temperatures, therefore, CO2 formation reduces. At T1.1
In the present study, the application of the Miller cycle and turbo charging together into a diesel engine has been performed and the effects of this modification on the engine performance and emissions have been experimentally examined. The torque, effective power, effective efficiency are considerably improved by applying the modification. NO, HC, CO and CO2 emissions decreased at all engine speeds compared to the standard camshaft conditions. Even though C57-T1.2 gives the maximum performance values, C62-T1.1 gives the lowest NO values, therefore latter is determined optimum condition, as this study primarily aims to decrease NO emissions. It is known that the application of the Miller cycle into a ICE decreases NO with power loss [1e9]. The application of the turbo charging and the Miller cycle together increases the engine power and decreases the NO emissions at higher rates compared to standard camshaft conditions. The maximum reduction rates in NO are obtained with C62-T1.1 conditions. NO emissions decrease by 27% and the torque and effective efficiency increase up to 1%. At this condition, HC, CO and CO2 emissions decreased by 20%, 43% and 10% respectively. The application of this modification decreases NO emissions in substantial rates at high engine speeds. Thus, this combination may be used in the diesel engines running at constant engine speeds in order to obtain higher engine performance and lower emissions. Acknowledgment This study is a part of PhD thesis of the first author. The authors thank The Scientific and Technological Research Council of Turkey (TUBITAK- the project number is 111M065), Yildiz Technical University Scientific Research Projects Coordination Department (the project number is 2011-10-01-KAP03) and Turkish Academy of Sciences (TUBA) for their financial supporting.
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