Performance Analysis of Turbocharged 2-Stroke Diesel Engine

Transcription

1 Performance Analysis of Turbocharged -Stroke Diesel Engine Ümit GÜNEŞ Yildiz Technical University, Naval Architecture and Marine Engineering, 34349, Beşiktaş, İstanbul, Turkey. Yasin ÜST Corresponding author: Yildiz Technical University, Naval Architecture and Marine Engineering, 34349, Beşiktaş, İstanbul, Turkey. A. Sinan ARAURT Yildiz Technical University, Naval Architecture and Marine Engineering, 34349, Beşiktaş, İstanbul, Turkey. Abstract Turbocharger systems are very important for vessels in terms of increasing energy efficiency and reducing green gas emissions. Ambient conditions (winter, ISO and summer) effect intake air temperature so do turbocharger efficiency. Engine load and fuel types that effect exhaust gas energy level are the other parameters for the turbocharger efficiency. In this study, a new numerical method is improved for enthalpy and entropy calculation based on exhaust gas components. Also two-stroke Diesel engine performance which operates various ambient conditions is analyzed in terms of thermal efficiency, engine load, specific fuel oil consumption (SFOC), exergy efficiency and exegetic performance coefficient (EPC). The results show that the highest thermal efficiency is obtained in winter ambient condition and turbocharger efficiency increases when fuel-oil quality is better. eywords: Ambient Condition, Two-Stroke Diesel Engine, Energetic Efficiency, Exegetic Performance Coefficient

2 ICENS International Conference on Engineering and Natural Science, May 015, Skopje, Macedonia 1. INTRODUCTION Waste heat recovery systems become important in recent years. While total efficiency is increasing, global warming effect is decreasing result of decreasing emissions by using waste heat recovery systems [1]. Combine systems, steam and gas cycle used together, are the most significant way to get more heat recover. In this system the efficiency can reach up to 60%. The result of this system, large scale of waste heat is recovered, EEDI gets better and the emissions decrease []. Figure 1. Net power and heat loses in a ship [3] Waste heat which is not used and T Diesel shown in figure 1. It is shown that not used exhaust gases and sent to environment has a significant ratio (5%). So it is the best way to increase the energy efficiency. Exhaust gas temperature after engine depends on many parameters. The most important ones are engine load and ambient condition. Air temperature changes with ambient conditions. The compression demanding power also changes with ambient condition to make air target pressure. Compressor gets the power from the turbocharger turbine. Exhaust gas temperature is effected the changing power demand. Vessels work in three ambient condition: [4]. ISO ambient condition Tropical ambient condition Winter ambient condition Properties ISO Tropical Winter Barometric Pressure (Bar) Turbocharger Air Intake Temperature ( o C) Charge Air Coolant Temperature ( o C) Relative Air Humidity (%) Ambient conditions and some properties belongs to them are shown in table 1. The most important factor for exhaust gases temperature is ambient condition. Figure. Turbocharger efficiency depending on engine load [5] Energy is transferred effectively from exhaust gas to the turbocharger turbine when the turbocharger efficiency is higher. High turbocharger efficiency makes the exhaust gas temperature lower because of more energy transfer from exhaust gas to the turbocharger.

3 Performance Analysis of Turbocharged -Stroke Diesel Engine, Ümit Güneş, Yasin Üst, A. Sinan arakurt Figure 3. Exhaust gas temperature after turbocharger outlet depending on engine load [6] The high efficiency leads to low exhaust gas temperature in figure 3. Also the lowest exhaust gas temperature occurs in 70-80% engine load. The highest exhaust gas temperature occurs in tropical ambient condition and the lowest exhaust gas temperature occurs in winter ambient condition. Figure 4. Exhaust gas temperature before turbocharger outlet depending on ambient condition [7] Hountalal et al [7] indicates that the effect of different ambient temperature on the exhaust gas temperature in figure 4. This figure is used for the equation of the temperature versus engine load. When turbine outlet temperature is known, turbine inlet temperature can be found by using these equations approximately. In this study turbine inlet temperature is calculated by using this approach. Figure 5. Engine efficiency depending on ambient condition The effect of air temperature takes from ambient on engine efficiency in figure 5. As this result when the air temperature decreases, the engine efficiency increase. Engine efficiency reaches highest value in winter ambient condition and lowest value in tropical ambient condition. Figure 6. SFOC depending on ambient condition The effect of air temperature takes from ambient on SFOC in figure 6 for MAN 798ME-C7-TII. As this result when the air temperature decreases, SFOC also decreases and the fuel oil consumption for producing same power also decreases so the engine efficiency increases. SFOC reaches highest value in tropical ambient

4 ICENS International Conference on Engineering and Natural Science, May 015, Skopje, Macedonia condition and lowest value in winter ambient condition.. MATHEMATICAL METHOD.1. Component of Exhaust Gas Exhaust gas components changes depend on various factor. The most important ones are combustion efficiency and fuel specifications. T Diesel Engine generally use heavy fuel oil (HFO). General HFO fuel specifications and exhaust gas components is shown in figure 7. Figure 7. Some component which are occurs after HFO combustion [8] Three main components, air, fuel oil and lubrication oil, goes into the engine in combustion process. Air includes 1% Oxygen (O) and 79% Nitrogen (N ). Fuel oil includes 97% hydrocarbon (HC) groups and 3% sulfur (S).In combustion process some lubrication oil also is included but the rate of it is low. Lubrication oil includes %97 HC groups, %.5 CA groups and %0.5 sulfur. Exhaust gases of HFO includes 76.% N, % 14 O, 5.1 % H O and %4.5 CO. In this study it is assumed that exhaust gas has 4 main component (N, O, HO and CO) and all analyses are done for this assumption... Exhaust Gas temperature after Funnel SO X which is included in fuel react with water in low temperature. After this reaction sulphuric acid is occurs and it causes corrosion. So it is not possible for decreasing the exhaust gas temperature bellow the dew point of sulphuric acid. The rage of sulphuric acid is 3 % for HFO [9]. Figure 8. Dew point depending on sulfur ratio in fuel [8] Dew point of HFO which has 3% sulfur is 135 C in figure 8. Because of this result, the exhaust gas temperature for waste heat recovery cannot be lower than 145 C (135 C + pinch point for heat exchanger). When analyzed the real system, the exhaust gas temperature cannot decrease lower than 160 C [8]..3. Enthalpy Calculation of Exhaust Gas An Eq 1 was developed by Domingues et al [10] to calculate exhaust gas enthalpy value using experimental results. Specific heating value of exhaust gas is calculated in the Eq. 1 when the temperature range is 400 to ( ( ) ) ( ) C T T + 73 (1) P,E E E Enthalpy of exhaust gas is calculated by using temperature and specific heat in Eq.. he C P,E.TE ()

5 Performance Analysis of Turbocharged -Stroke Diesel Engine, Ümit Güneş, Yasin Üst, A. Sinan arakurt Figure 9 is drawn for enthalpy value versus various exhaust gas temperature by using Eq.. Figure 9. Enthalpy change of exhaust gas depending on temperature and pressure.4. Entropy Calculation of Exhaust Gas Entropy calculations of exhaust gases are more difficult than enthalpy calculations which calculate by formulas that given by Bejan [11]. Entropy values of all elements in the exhaust gas must be separately calculated and then total entropy value will be found. Every state points entropies can be calculated with Eq. 3 where S+, a, b, c and d values can be read from Table and also 3 y 10 T. Calculated entropy values from Eq. 3 are subjected to pressure correction in Eq.4. X P O k. sk sk Rln P 0 (3) where ( s O k ) is equal to Eq. 3, R is ideal gas constant, X k is mass ratio of respective component in the exhaust gases, P is exhaust pressure, P 0 is standard ambient pressure and ( s k ) refers to respective element entropy value. Entropy value of the exhaust gases can be calculated with Eq. 5 while summing every elements entropies. x s k k (4) k The constants required for entropy calculation depending on the elements of the exhaust gas are given in o Table and ( s ) is calculated in accordance with terms of reference value of 5 C temperature and 1 bar pressure. Table. Exhaust gases element entropy calculation constants [7] Element Formula % (x) S + a b c d Nitrogen N (g) Oxygen O (g) Carbon dioxide CO (g) Water H O(g) o sk Figure 10. Exhaust gases entropy changing depends on temperature and pressure [11] Exhaust gases entropy changing with temperature for three different pressures is given in figure 10 which shows that when pressure increases the exhaust gas entropy values decrease.

6 ICENS International Conference on Engineering and Natural Science, May 015, Skopje, Macedonia.5. Turbocharger Pressure The aim of turbocharger system is to obtain more power from smaller size engine. According to this, higher engine inlet air pressure means more power can be derived from the engine. Moreover, increasing inlet air pressure at compressor increases the compressor power consumption. Figure 11. The compression power in turbocharger depending on compression ratio Power consumption of 7L60ME-C8-TII engine turbocharger system which depends on turbocharger air pressure is shown in figure 11. It is showed that increasing inlet air pressure increases the power linearly. m * m (5) The relationship between air flow rate in compressor and exhaust flow rate in gas turbine is given by Eq. 5 [1]. Accordingly, air flow rate is almost equal to the exhaust air flow. Required compressor power for compressing the air to a certain pressure will be provided from the gas turbine. The produced power in gas turbine that required for compressor can be found from figure 11 when certain air compression pressure is defined. If flow rates of compressor and gas turbine are same the temperature difference in gas turbine will be found in figure Energy and Exergy Analyses.6.1. Energy Analysis Energy and exergy definitions of thermodynamic model have to be studied before waste heat recovery systems. General energy equation is defined below for steady state open system V V Qi Wi m h gz Qo Wo m h+ + gz i o where ( Q i ) and ( Q o ) are inlet and outlet heat transfer rates, ( W i ) and ( o ) ( mh i ) and ( mh) (6) W are inlet and outlet powers o V V are inlet and outlet enthalpies, m i and m o are inlet and outlet kinetical m o gz are inlet and outlet potential energies. energy of system, ( m i gz ) and ( ).6.. Exergy Analysis Exergy values of every state points in steady state open system are calculated by Eq.7. F E m. ( h h ) T ( s s ) (7) i i 0 0 i 0 where ( F i ) is physical exergy, ( m ) is flow rate, ( h i ) is entalpy, ( s i ) is entropy and subscripts 0 is refer to ambient conditions. + E (8) i, i i, i y,i where ( i,i ) is exergy inlet, ( o,i ) is exergy outlet and ( y,i ) is exergy destruction in the processes. Exergy destruction of control volume in a steady state is defined as Eq. 9.

7 Performance Analysis of Turbocharged -Stroke Diesel Engine, Ümit Güneş, Yasin Üst, A. Sinan arakurt T0 T 0 y,i Q. 1 Q. 1 + ( W i W o) + ( i o) T T (9) i o where ( Q i ) and ( Q o ) are refer to inlet and outlet heat rates..7. Turbocharger System.7.1. Principles of turbocharger system Turbocharger system supports higher pressure and lower volume air than atmospheric conditions to engine by using exhaust gases energy which allows to design more power from lower size cylinder Figure 1. Turbocharger System General layout of a turbocharger system is shown in figure 1 which consists of turbine and compressors section. Turbine is on the exhaust section and compressor is on the suction section and a shaft connects turbıne to compressor. Exhaust gases waste heat energy converts to mechanical energy in turbine transfers via shaft to compressor to compress and support more air flow..7.. Thermodynamic model of turbocharger system Air compressor supports air at higher pressure and rate and also lower volume in turbocharger system Compressor power consumption is approximately equal to turbine power and real compressor power is found with the ratio of ideal compressor power to compressor efficiency (η,m ). ( k 1 ) k m. 1k.R.T1 P 1 1 k 1η P 1,M W (10) inetic energy of exhaust gases is converted to mechanical energy in the gas turbine whose power is obtained by Eq. 11. W m 3. CP,E. ( T3 Tη 4 ). (11) Chemical exergy of fuel is calculated with Eq. 1 [13]. e Y H O S H LHV C C C C where H, C, O and S are refer to hydrogen, carbon, oxygen and sulphur. It is suppose that fuel consist of 87.4% carbon, 9.5% hydrogen and 3% sulphur [14] and LHV is 4700 kj/kg for heavy fuel oil [15]. (1) Chemical exergy is very important however physical exergy is negligible for combustion processes. Flow rate and chemical exergy rate of fuel are calculated with Eq m m m (13) y E H E e.m Y Y y (14)

8 ICENS International Conference on Engineering and Natural Science, May 015, Skopje, Macedonia Table.3. General Formulations of Turbocharger System General Ex Des. EPC Ε y ç g EPC i 1 ç y εi 1 y i Compressor Y, 1 + W Gas Turbine Diesel Engine +DE system E E E W Y, 3 4 EPC y,i E ( ) 4 + W E E W Y,DM Y DM E + E + E Y,DM Y, Y, y,i E ( ) Y, 1+ W EPC y, W DM Y EPCDM 1 EPC sistem Y,DM Y,DM ( E4 + WDM ) ( Ey, + Ey, DM ) ε ε g g ( 4 + W ) DM εdm 1 Y 3 W E ( + W ) 4 DM ε Sistem ( + ) 1 Y Y,DM Y y y E y,i y,t Y, Y,T E Y, Y,T 3. RESULTS AND DISCUSSION Table 5-6 are calculated from component efficiencies (Table 4) and thermodynamic model for turbocharger system. Calculations have done at ISO ambient condition and 80% engine load for MAN 7L60ME-C8-TII engine. Table.4. Efficiency of Turbocharger Components Mechanical Efficiency (ηm) (%) 98 Isentropic Efficiency of Compressor (η,i) (%) 65 Isentropic Efficiency of Turbine (η C,i ) (%) 90 State properties are given at ISO ambient condition and 80% engine load in Table 5 State T ( o C) P (bar) Table.5. The Property of the states h ( kj kg ) s ( kj kg. ) E (kw) m. ( h1 h0) T0( s1 s0) m. ( h h0) T0( s s0) m 3 ( h3 h0) T0( s3 s0) m ( h h ) T ( s s ) E Exergetic performance parameters of the system components for ISO conditions and 80% engine load are shown in Table 6. The highest exergy destruction and also exergy destruction rate occurs in compressor beyond the diesel engine is seen from the result. Table.6. Exergetic Performance Coefficient of the System Component System Components E y (kw) EPC i ε i y i Diesel Engine Compressor GasTurbine Total

9 Performance Analysis of Turbocharged -Stroke Diesel Engine, Ümit Güneş, Yasin Üst, A. Sinan arakurt Figure 13. Compressor Power of MAN 7L60ME-C8-TII Engine for ambient conditions and engine load Compressor inlet power in the turbocharger system for different ambient conditions and different engine loads are shown in figure 13. Compressor needs more power because of increasing compressed air flow rate at higher engine load and the lowest power consumption is seen at tropical conditions. 4. CONCLUSIONS Performance of two-stroke Diesel engine operating various ambient conditions have been analyzed with respect to thermal efficiency, engine load, specific fuel oil consumption (SFOC), exergy efficiency and exegetic performance coefficient (EPC). The results show that the highest thermal efficiency is obtained in winter ambient condition and turbocharger efficiency increases when fuel-oil quality is better. A new numerical method is also improved for enthalpy and entropy calculation according to exhaust gas components. The compressor of turbocahger system needs more power at higher engine load and the lowest power consumption is obtained at tropical conditions. Acknowledgments The authors are thankful to Yildiz Technical University Institute of Science and Technology for providing opportunity to study on this subject. References [1] E. H. Wang, H. G. Zhang, B. Y. Fan, M. G. Ouyang, Y. Zhao, and Q. H. Mu, Study of working fluid selection of organic Rankine cycle (ORC) for engine waste heat recovery, Energy, vol. 36, no. 5, pp , May 011. [] D. Marek, On the possible increasing of efficiency of ship power plant with the system combined of marine diesel engine, gas turbine and steam turbine, at the main engine - steam turbine mode of cooperation, Pol. Marit. Res., vol. 16, no. 59, pp. 47 5, 009. [3] Bent Ørndrup Nielsen, Waste Heat Recovery System, 07-Jan-011. [4] MAN Diesel & Turbo, Influence of Ambient Temperature Conditions Main engine operation of MAN B&W two-stroke engines.. [5] Volkmar Galke, Turbo Compound System with Power Turbine and Generator, 8-Jul-011. [6] MAN Diesel & Turbo, Engine room and performance data for 7S80MC-C8.-TII with x MAN TCA77-1 and high load tuning. MAN Diesel & Turbo, 5-Jun-013. [7] Dimitrios T. Hountalal, Antonis. Antonopoulos, Nikolaos F. Sakellaridis, Georgios N. Zovanos, Efthimios G. Pariotis, and Roussos G. Papagiannakis, Computational Investigation of the Effect of Ambient Conditions on the Performance of Turbocharged Large Scale Marine Diesel Engines, presented at the The 5th international conference on efficiency, cost, optimization, simulatıon and environmental impact of energy systems, Perugia, Italy, 01. [8] MAN Diesel & Turbo, Soot Deposits and Fires in Exhaust gas Boilers.. [9] MAN Diesel & Turbo, MAN B&W S70ME-C8-TII Project Guide Electronically Controlled Two-stroke Engines, 1st Edition. MAN Diesel & Turbo, 010. [10] A. Domingues, H. Santos, and M. Costa, Analysis of vehicle exhaust waste heat recovery potential using a Rankine cycle, Energy, vol. 49, pp , Jan [11] A. Bejan, G. Tsatsaronis, and M. Moran, Thermal Design and Optimization, 1st ed. Wiley-Interscience, [1] MAN Diesel & Turbo, MAN B&W L60ME-C8-TII Project Guide Electronically Controlled Two-stroke Engines, 1st Edition. MAN Diesel & Turbo, 010. [13] Perihan Sekmen and Zeki Yılbaşı, Application of Energy and Exergy Analyses To A CI EngineUsing Biodiesel Fuel, Math. Comput. Appl., vol. 16, no. 4, pp , 011. [14]. D. Bartle, J. M. Jones, A. R. Lea-Langton, M. Pourkashanian, A. B. Ross, J. S. Thillaimuthu, P. R. Waller, and A. Williams, The combustion of droplets of high-asphaltene heavy oils, Fuel, vol. 103, pp , Jan [15] MAN Diesel & Turbo, MAN B&W S35ME-B9-TII Project Guide Electronically Controlled Two-stroke Engines, 1st Edition. MAN Diesel & Turbo, 010.