Determination of performance degradation of a marine diesel engine by using curve based approach

Accepted Manuscript Determination of Performance Degradation of a Marine Diesel Engine by using Curve Based Approach Görkem Kökkülünk, Adnan Parlak, Hasan Hüseyin Erdem PII: DOI: Reference:

S1359-4311(16)31365-5 http://dx.doi.org/10.1016/j.applthermaleng.2016.08.019 ATE 8818

To appear in:

Applied Thermal Engineering

Received Date: Revised Date: Accepted Date:

28 March 2016 1 August 2016 2 August 2016

Please cite this article as: G. Kökkülünk, A. Parlak, H.H. Erdem, Determination of Performance Degradation of a Marine Diesel Engine by using Curve Based Approach, Applied Thermal Engineering (2016), doi: http://dx.doi.org/ 10.1016/j.applthermaleng.2016.08.019

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Determination of Performance Degradation of a Marine Diesel Engine by using Curve Based Approach

Görkem Kökkülünka1, Adnan Parlaka, Hasan Hüseyin Erdemb b

a Yildiz Technical University, Naval Arch.&Maritime Faculty, Marine Engineering Department Yildiz Technical University, Mechanical Engineering Faculty, Mechanical Engineering Department

Abstract Nowadays, energy efficiency measures on ships are the top priority topic for the maritime sector. One of the important key parameters of energy efficiency is to find the useful tool to improve the energy efficiency. There are two steps to improve the energy efficiency on ships: Measurement and Evaluation of performance of main fuel consumers. Performance evaluation is the method that evaluates how much the performance changes owing to engine component degradation which cause to reduce the performance due to wear, fouling, mechanical problems etc. In this study, zero dimensional two zone combustion model is developed and validated for two stroke marine diesel engine (MITSUI MAN B&W 6S50MC). The measurements are taken from a real ship named M/V Ince Inebolu by the research team during the normal operation of the main engine in the region of the Marmara Sea. To evaluate the performance, “Curve based method” is used to calculate the total performance degradation. These total degradation is classified as parameters of compression pressure, injection timing, injection pressure, scavenge air temperature and scavenge air pressure by means of developed mathematical model. In conclusion, the total degradation of the applied ship is found as 620 kW by power and 26.74 g/kWh by specific fuel consumption. Keywords: Degradation, Performance, Marine diesel engine, Two-Stroke, Mathematical model

1

Corresponding Author, [email protected]

1

1. Introduction The Energy Efficiency Operational Index (EEOI) that represents the comprehensive trading model of the vessel, obtains a numerical indicator of energy efficiency of a ship and fleet in operation, therefore, it might be considered as the primary monitoring tool [1,2]. To optimize the performance and decrease fuel consumption by means of performance monitoring is obviously important. There are many studies to investigate the ship energy efficiency and EEOI with regards to shipping performance. Yang et al. investigated the adaptability of marine dual fuel engine in terms of new regulations of MARPOL (International Convention for the Prevention of Pollution from Ships) as emissions and energy efficiency [3]. Tzannatos et al. examined the energy efficiency of domestic passenger shipping in Greece with respect to assessing the effect of fuel consumption upon the overall costs [4]. Xing et al. studied the operational energy efficiency for inland river ships in regard to greenhouse gas emissions and compared them with the performance of seagoing ships [5]. Schmid presented efficient propulsion for seagoing vessels from the point of consuming minimum amount of fuel, achieving a defined ship speed and generating minimum emissions [6]. Hasselaar investigated the ship service performance to reduce fuel consumption through propellerhull interaction [7]. In the other respect as the slow steaming for the shipping performance, Woo et al. investigated the effects of slow steaming on the environmental performance in liner shipping with respect to voyage speed, the amount of CO 2 emissions and operating costs on a loop [8]. Lindstad et al. analyzed the potential for reducing CO2 emissions and greenhouse gas emissions and cost by shipping at lower speeds [9]. Chang et al. discussed the energy conservation for international dry bulk carriers to examine emissions under economic speed and via vessel speed reductions of 10%, 20% and 30% [10]. Chang et al. also investigated the effects of ship speed that minimize costs and reduce the impact of shipping on the environment [11]. Norlund et al. examined how to reduce emissions from supply vessel operations by optimizing sailing speed in the supply vessel planning in the upstream supply chain to offshore installations [12]. The EEOI is not only concerning with hull performance as mentioned in the above literature, but also related to the machinery in the engine room. The large-scale two stroke

2

diesel engine which is the most fuel consuming machinery in comparison to the other machineries in the engine room is focused on the subject of energy efficiency challenges. In this respect, Kowalski investigated firstly emission and combustion characteristics of the marine diesel engine with fuel pump malfunctions such as fuel injection timing delay and fuel leakages [13] secondly malfunctions of marine engine cylinders, the air/exhaust gas exchange system and the high-pressure part of the fuel system by means of multidimensional diagnostic tool [14]. Sigurdsson et al. studied the scavenging process and convective heat transfer in a two-stroke marine diesel engine to determine the effective scavenging and low convective heat loss [15]. Scappin et al. examined the energy system performance and NOx emissions of marine low speed diesel engines with a zero dimensional two zone combustion model [16]. Baldi et al. analysed the propulsion system behavior of the ship for constant and variable engine speed operation with a combined mean value–zero dimensional model to find the most efficient ship operation strategies and quantifying the expected fuel savings [17]. Murphy et al. studied the thermodynamic simulation of marine diesel engine related with engine performance across the full range of operational conditions in engine speed and load [18]. Guan et al. investigated the turbocharger cut-out operation of two stroke marine diesel engine using a zero-dimensional combustion model to discuss the influence of engine operating strategies on the annual fuel savings for the container ship [19]. Basurko and Uriondo examined the condition-based maintenance model for marine diesel engines to determine fuel consumption and faulty conditions such as a polluted turbine, dirty air filter/compressor and dirty air cooler [20]. The performance of the engine which is directly related to the energy efficiency can be divided by performance monitoring and performance evaluation. Performance monitoring is the continuous monitoring of the performance of the engines and sub-systems by means of measuring devices. Performance evaluation is the method that evaluates how much the performance changes owing to equipment degradation which is described as the shortcoming in equipment performance originated from mechanical problems, wearing fouling etc. in engines or sub-systems such as heat exchangers, turbochargers. Performance changes can be classified as changes due to ambient conditions which are not defined as degradation and the changes sourced from degradation of the engine. Although some of the degradation of the engine can be utilized by planned maintenance, the others 3

cannot be recovered due to aging of the engine components. Consequently, the purpose of performance evaluation is to utilize these degradations of the engine and its equipment so as to assist the engineer operators how much the engine performance changes and what is its equipment contribution to this degradation [21]. In the literature, some scientist performed some studies on performance evaluations. Among them, Hountalas investigated the some parameters affecting the engine performance by using mathematical model which was developed for MAN-6S70MC engine. In his study, the changing of injection timing, injection pressure, compression pressure, the effect of air cooler fouling, turbocharger faults, exhaust port and pipe faults were examined [22]. In the other study performed by Lamaris et al. studied the important engine parameters on engine performance by using mathematical model for main propulsion and auxiliary diesel engines [23]. The study conducted by Medica et al. developed performance simulation of two stroke marine diesel engine with turbocharger under fault conditions with the numerical model implemented on the computer using the application Matlab Simulink [24]. In the above studies, even though the effects of parameters on performance are investigated, there is no study on performance degradation on marine diesel engines. In this study, theoretically and experimentally studies are conducted in a large two stroke marine diesel engine for determining the degradation. Zero dimensional two zone combustion model is developed in order to obtaining the performance curves of operating parameters and the model is validated for MITSUI MAN B&W 6S50MC engine. The measurements are taken from a real ship named M/V Ince Inebolu by the research team during the normal operation of the main engine in the region of the Marmara Sea. The performance evaluation model named “Curve Based Method” is performed for calculating the performance degradations depending on the variation of compression pressure, injection timing, injection pressure, scavenge air temperature and scavenge air pressure. 2. Methodology 2.1. Brief description of the mathematical model In the mathematical model of the two stroke marine diesel engine, combustion chamber is composed of two combustion zone, as burned and unburned (shown in Figure 1). General assumptions for the engine processed are homogeneous gas mixture, constant blow-by

4

rate, gas leakage and residual gas fraction and in-cylinder mixture property as an ideal gas [25-29].

Figure 1. Energy flow of two-zone combustion model Governing equations concerning to zero dimensional engine model are given as follows; Firstly Energy equation is;

dU dQ dW dH f dH bb     d d d d d

(1)

Where rate of internal energy respect to crank angle (CA) is dU/dθ, rate of heat transfer respect to CA is dQ/dθ, rate of work respect to CA is dW/dθ, rate of heat release respect to CA is dHf/dθ and rate of blow-by gas enthalpy respect to CA is dHbb/dθ. In expanded form of the equation (1) is;

dm   dQb dQu  du u  m    d  d  d  d

dm dV dm f   h f  bb hbb P d d d 

(2)

Secondly, conservation of mass applied to cylinder is;

dm dma dm f   d d d

(3)

dma mbb  Cma   d 1   FAs 

(4)

dm f d



mbb FAs  m f  Cm f 1  mf    1   FAs  

(5) 5

Where rate of in cylinder air constant versus CA is dma/dθ, leaked cylinder mass is mbb and blow by rate constant is C. ω, ϕ and FAs are the dθ/dt, equivalence ratio and fuel air stoichiometric ratio. Heat release rate is coupled to the above equation as in the calculation of injected fuel rate.

m f  x.m f

(6)

m f   FAs 1  f r  ma

(7)

Where rate of fuel injected respect to time is ṁf, fractional heat release rate is ẋ and residual gas fraction is fr, utilizing empirical double wiebe function. Furthermore, Miyamoto et al. was expressed the heat release rate of combustion in diesel engine using double Wiebe function [30]. In this form of Wiebe function, the combustion process is expressed in two parts, premixed and diffusive processes.  m 1       pre m pre  a   v         Q   Qdif x  av  pre  m pre  1  e  pre   m  1     dif       pre    dif   dif  pre   

  

mdif

e

   av    dif 

   

 mdif 1

   (8)   

Where av is wiebe constant and m is form parameter. According to Miyamoto et al. mpre, mdif ve θpre parameters depend on engine design and av parameter is recommended as 6.9 [30]. Considering the above equations, conservation of energy and mass, pressure rate during engine processing can be expressed as;  C V  + 1 ω  m c pb Tb

 h     - h u    tr A cyl  x 1 Tbw  1  x Tuw 2    ωm  c pb Tb c pu Tu     1  dx 1 dV  1 V  dm  x h b  1  x  h u   H u  2  f   h b  h u    vb  vu       m  dθ  c pb Tb  dθ m dθ  m c pb Tb     ds dv du dv dv du dv  d  ds  d 1  x   1  Tu u  P u  u   u  2 u  u  x  1  P b  b   b  b d d d  d c pu d  d dP  c pb Tb   c pb Tb  d d  d  dθ  2 2 d         x  1  3   (1  x)  2  4   c pb Tb P   cpu Tu P     

 x - x   h 2

b







(9)

6

In the above equation, 1 , 2 , 3 and 4 are expressed as 1  3 

 ln v b  ln v u vb , 2  vu  ln Tb  ln Tu

 ln v b  ln v u v b and 4  v u , respectively. x is the integrated expression of the  ln P  ln P

double wiebe function ẋ. Cylinder volume;





  1   1 V    Vc 1  1  cos   1  1  2 sin 2     2    

(10)

The equation number (10) is derived as follows;

 dV  2  cos   b S sin  1  2  d 8 1   sin   

   

(11)

Cylinder heat loss term in conservation of energy equation is expressed as [31]; dQb htr  A d  cyl



x .Tbw





(12)



dQu htr  A  1  x .Tuw   d  cyl 

(13)

The heat transfer coefficient of Hohenberg [32] as below; htr  C1V 0.06 P0.8  xTb  1  x  Tu 

0.4

S

p

 C2 

0.8

Where C1=130, C2=1.4 and the mean piston velocity is

(14) (m/s).

To calculate the ignition delay, empirical Sitkei correlation function can be expressed as follows [33, 34];

 id  0.5  0.133P0.7 e

3930 T

 0.00463P 1.8e

3930 T

(15)

Fuel air mixture properties are calculated using FARG (Fuel Air Residual Gas) and ECP (Equilibrium Combustion Products) developed by Olikara and Borman [35] FARG is utilized reaction temperatures under 1000K resulting with 6 combustion product species (CO2, H2O, N2, O2, CO, H2). The chemical formula of the fuel (HFO) is chosen as C 19H30 7

[36-39]. ECP is used at combustion reaction temperatures over 1000K resulting with 10 combustion product species (CO2, H2O, N2, O2, CO, H2, H, O, OH, NO) [40]. The developed FORTRAN Code are used to execute the simulation and the Ordinary Differential Equations (ODE) are solved. Furthermore, the submodels/subroutines in the equation systems i.e. ignition delay are expressed in the code. FORTRAN built in Library function named DIVMRK was used to solve during calculation iterations as initial value problem for ordinary differential equations using Runge-Kutta pairs of various order. 2.2. Performance Evaluation There are two kinds of performance evaluation method. Curve Based Method and Model Based Performance Evaluation [21]. Firstly, the main concept for curve based method is to collect a set of performance curves that illustrate the variation in a specific equipment performance parameter (such as power, SFC) when one of the operating conditions changes. The total equipment performance fractional change is calculated by multiplying with the fractional changes for each operating condition where each multiplying factor is generated using a separate correction curve [21]. Secondly, for model based approach, the correction curves that equipment producer supply to operators are based on physically based computer models of the equipment performance evaluation. Computer models may conduct wide variations in environmental parameters and operational modes for which curves do not exist. Particularly, as conditions change over in a broad range, the interactions between environmental parameters become more and more important and computer codes are often built specifically to handle these interactions [21]. In this study, both curve based method and model based approach have been used to evaluate the performance. The total power and SFC degradations have been calculated via “Curve Based Method”. Degradations are classified by means of “Model Based Approach, developed mathematical model”. Degradation is a performance evaluation method which is described as the reduction in equipment performance originated from mechanical problems, aging etc. in engine or a system such as wear, fouling etc. in these components occurring over time based. To calculate the degradation of the engine, the engine power and SFC are measured via high 8

accuracy measuring devices. The corrected performance values are found by eliminating the ambient conditions, which are not controlled by operators, and then the “Actual Performance” curve is formed. Figure 2 shows the analogy of calculating degradation of the engine. In the Figure, the degradation is divided into three sections: repairable in operation, repairable with planning maintenance and repairable with rehabilitation. The former two degradations can be remedied by repairing in operation and by maintenance planning but the last part of the degradation cannot be remedied in a short period as it is required component replacement such as cylinder liner, piston due to wearing.

Figure 2. The explanation of performance change and degradation 3. Test cases of a large scale two stroke marine diesel engine In this study, Littlefuse Selco EngineEye (E5000) Cylinder pressure analyzer (Sensor accuracy: ±0.2%) was used in order to measure the in-cylinder pressure and analyze the performance of the two stroke marine diesel engine. The measurements were taken for the five cycles and these five measurements were averaged for each cylinder. The measurements data were imported from the measurement unit to a PC. The analyzer has a software displaying such as Mean Indicated Pressure (MIP) and cylinder indicated power. The software has a Top Dead Center (TDC) correction algorithm. The software recalculates indicated power after TDC correction. The TDC 9

correction is to adjust the area under the graph from when ignition occurs and until Bottom Dead Center (BDC) with the help of derivative curves. This area describes the work done by the cylinder and therefore influences the indicated power. TDC correction is required to compensate for inaccuracies in the measuring system (e.g. the indicator valve tubing and the flexing of the crank shaft etc.) [41-45]. The fuel measurements were taken with the Nitto Seiko Rotary Flowmeter (accuracy ±0.5%) to calculate the specific fuel consumption (SFC) and evaluate the performance degradation of the Main Engine. Aforementioned Two Stroke Marine Diesel Engine specification is illustrated in Table 1. Table 1. Technical data of the two stroke marine diesel engine Type Number of cylinders Bore, mm Stroke, mm Engine Power @115.6 rpm, kW Mean Piston Speed (MCO), m/s Fuel Type Specific Gravity of Fuel, @15 °C LCV, kJ/kg

MITSUI MAN B&W 6S50MC 6 500 1910 6570 7.39 HFO 0.9666 40775

Furthermore, the measurements were attained from the research team during the normal operation of the main engine in the region of the Marmara Sea. While measuring, the sea and weather conditions were stable and the rudder was fixed in such a case that the performance of the Main Engine was not affected. 4. Validation of the mathematical model In this study, the MAN B&W 6S50MC two-stroke marine diesel engine was investigated using the developed zero-dimensional two zone engine mathematical combustion model. In order to test the validation of the developed mathematical model, the data of developed model was compared with those of sea trial in which the data was received from marine diesel engine in exact operating conditions. It was shown that the theoretical model provides good agreement with pressure values, power and SFC (Figure 3-4).

10

140 The Model

120

Sea Trial 100 Pressure, bar

80 60 40 20 0

-150

-100

-50

0 Crank Angle, °CA

50

100

Figure 3. Validation of developed mathematical model with sea trial

Figure 4. Validation of developed mathematical model with power and SFC 5. Correction of Values According to ISO 3046 Standards [46] In this part of study, “Power and SFC Adjustment Factors” are calculated by means of ISO 3046-1:2002 for ambient temperature, ambient pressure and sea water temperature to eliminate the effects of ambient conditions which cannot be controlled by operators. Firstly, ratio of indicated power is shown as “k”;

 P k  o P  ref

m

  Tref   Tsw,ref          To   Tsw  n

s

(16) 11

Where Po, To and T sw are expressed as ambient pressure, ambient temperature and sea water temperature, respectively. “ref” subscript means the reference values. “m, n and s” superscripts differ according to engine type, fuel type, conditions as turbocharged with or without air cooler and low, high or medium speed engines. Power adjustment factor is defined as;  1

  1  m 

  k  0, 7  1  k   

(17)

Where ηm is mechanical efficiency. SFC adjustment factor is expressed as; 

k

(18)



The effects of ambient temperature on power and SFC are shown in Figure 5. Power and SFC adjustment factors are stated as the multiplier value in order to correct the measured data. The Power and SFC factors are 1.000 for the ISO reference value 25 °C ambient temperature. As can be seen from the figure that power adjustment factor reduces with the increase of ambient temperature and SFC adjustment factor increases with increasing of ambient temperature.

1.010

SFC Adj. Factor, β

Power Adj. Factor, α

1.015

1.005 1.000 0.995 0.990 0.985

0

10 20 30 40 Ambient Temperature, °C

50

1.005 1.004 1.003 1.002 1.001 1.000 0.999 0.998 0.997 0.996 0

10 20 30 40 50 Ambient Temperature, °C

Figure 5. The effects of ambient temperature on power and SFC Power and SCF Adjusting Factors depending on ambient pressure are calculated via referred formulas given ISO 3046 Standards. The effects of ambient pressure on power and SFC are shown in Figure 6. The Power and SFC factors are 1.000 for the ISO

12

reference value 1000 mbar ambient pressure. As can be seen from the figure that SFC adjustment factor reduces with the increase of ambient pressure and power adjustment factor increases with increasing of ambient pressure.

SFC Adj. Factor, β

Power Adj. Factor, α

1.007 1.006 1.005 1.004 1.003 1.002 1.001 1.000 0.999 990

1.0001 1.0000 0.9999 0.9998 0.9997 0.9996 0.9995 0.9994 0.9993 990

1000 1010 1020 1030 Ambient Pressure, mbar

1010 1030 Ambient Pressure, mbar

Figure 6. The effects of ambient pressure on power and SFC Power and SCF Adjusting Factors depending on sea water temperature are also calculated by using formulas given ISO 3046 Standards. The effects of sea water temperature on power and SFC are shown in Figure 7. The Power and SFC factors are 1.000 for the ISO reference value 25 °C sea water temperature. As can be seen from the figure that power adjustment factor reduces with the increase of sea water temperature and SFC adjustment factor increases with increasing of sea water temperature. 1.025 SFC Adj. Factor, β

Power Adj. Factor, α

1.06 1.04 1.02 1.00 0.98 0.96

0.94

1.015

1.005 0.995 0.985 0.975

5

15 25 35 Sea Water Temperature, °C

45

5

15 25 35 45 Sea Water Temperature, °C

Figure 7. The effects of sea water temperature on power and SFC 6. The Effects of Parameters on SFC and Power Factors The performance of the marine diesel engine has two measures; Power and SFC. The effects of changes in parameter values such as scavenge air temperature and pressure, 13

timing etc. on performance (power and SFC) during factory or sea trial tests are not given by producer company comprehensively. For instance, the factory or sea trial tests are done with only for single scavenge air temperature and pressure for the same loads. However, the changings of scavenge air temperature and pressure, timing, etc. are quite difficult to determine the effects on performance while operating conditions. Because of this, the developed and validated mathematical model are used to determine the effects of various injection timing, compression pressure, injection pressure and scavenge air temperature and pressure values. The total power and SFC degradations of the equipment are calculated as [21];   Performancerated  Performanceexp ected    Pambient ,Tambient ,Tsea water  Multiplier Factor 

(19)

  Performancecorrected  Performancemeasured    Pambient ,Tambient ,Tsea water  Multiplier Factor 

(20)

Total Degradation  Performancerated  Performancecorrected

(21)

In this part of study, after validation of the mathematical model, SFC and power are found by using the model based approach for various injection timing, compression pressure, injection pressure and scavenge air temperature and pressure values. 6.1. Effects of Scavenge Air Temperature Marine Diesel Engines which are used as a propulsion system are commonly slow speed two stroke diesel engines. Furthermore, they have scavenge ports to intake air and exhaust valve to exhaust the burnt gases. Three basic methods are in use for scavenging; the cross flow, the loop and the uniflow. Marine diesel engines as propulsion systems use the uniflow scavenging system with a cylinder-head exhaust valve. The effects of scavenge air temperature on power and SFC are shown in Figure 8. Power and SFC Factors are 1.00 for the temperature as for 38 °C is the test condition (Sea Trial) value of the engine. As can be seen from the figure notwithstanding the power factor is reducing, SFC factor shows deterioration with the increasing of scavenge air temperature.

14

1.025 1.020

SFC Factor

Power Factor

1.005 1.000 0.995 0.990 0.985 0.980 0.975 0.970 0.965 0.960

1.015 1.010 1.005 1.000 0.995

35 40 45 50 55 Scavenge Air Inlet Temperature, °C

35 40 45 50 55 Scavenge Air Inlet Temperature, °C

Figure 8. The effects of scavenge air temperature on power and SFC 6.2. Effects of Scavenge Air Pressure The effects of scavenge air pressure on power and SFC are shown in Figure 9. Power and SFC Factors are 1.00 for as for 2.8 bar is the test condition (Sea Trial) value of the engine. As can be seen from the figure that though the power factor is decreasing, SFC factor deteriorates with the reduction of scavenge air temperature. 1.01

1.040 1.035 1.030 1.025 1.020 1.015 1.010 1.005 1.000 0.995

0.99

SFC Factor

Power Factor

1.00 0.98 0.97 0.96 0.95 0.94 2.4

2.5 2.6 2.7 2.8 2.9 Scavenge Air Inlet Pressure, bar

2.4

2.5 2.6 2.7 2.8 2.9 Scavenge Air Inlet Pressure, bar

Figure 9. The effects of scavenge air pressure on power and SFC 6.3. Effects of Injection Timing The injection timing is the time in which fuel is injected before top dead center and maximum torque is obtained for defined engine speeds. Changing the injection timing from the optimum point causes the engine produced less power and more fuel consumption.

15

The effects of timing on power and SFC are shown in Figure 10. As can be seen from the figure that even though the power factor is enhancing, SFC factor is decreasing with the increase of injection timing. 1.04 SFC Factor

Power Factor

1.02 1.00 0.98 0.96 0.94 0.92 0

2 4 Timing, (-)°CA

1.030 1.025 1.020 1.015 1.010 1.005 1.000 0.995 0.990 0.985

6

0

2 4 Timing, (-)°CA

6

Figure 10. The effects of timing on power and SFC 6.4. Effects of Compression Pressure The effects of compression pressure on power and SFC are shown in Figure 11. The Figure shows that although the power factor increases with the increase of compression

1.01 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0.93

1.10 1.08 SFC Factor

Power Factor

pressure, the increase in compression pressure adversely affects the SFC factor.

1.06 1.04

1.02 1.00 0.98

70

80 90 100 Compression Pressure, bar

70

80 90 100 Compression Pressure, bar

Figure 11. The effects of compression pressure on power and SFC 6.5. Effects of Injection Pressure The effects of injection pressure on power and SFC are shown in Figure 12. The Figures show that even though the power factor is enhancing, SFC factor is decreasing with the increase of injection pressure.

16

1.12

1.00

1.10 SFC Factor

Power Factor

1.02

0.98 0.96 0.94 0.92

1.08 1.06

1.04 1.02 1.00

0.90

0.98 255

265 275 285 295 Injection Pressure, bar

305

255

265 275 285 295 Injection Pressure, bar

305

Figure 12. The effects of compression pressure on power and SFC 7. Results and Discussion In this study, the developed mathematical model is firstly validated with sea trial condition measured parameters. Secondly, power and specific fuel consumption values of the points on expected and actual performance curves are corrected according to ISO 3046 Standards as ambient temperature, ambient pressure and sea water temperature. Thirdly, the total degradation for SFC and power are calculated via curve based method. After that the effects of important engine parameters such as scavenge air temperature and pressure, compression pressure, injection pressure and injection timing are investigated from the effective power and SFC point of view by using developed mathematical model. Lastly, the degradations of main engine of the ship named M/V Ince Inebolu are calculated depending on the variations of five parameters.

7.1. Degradations in Marine Diesel Engine In the calculation of degradation, the two performance curves are used as shown in Figure 13-14. While lower curve shows the actual performance, the upper one shows the expected performance. There are two points on the actual performance curves named “measured” and “corrected”. There are also two points on the expected performance curve named as “expected” and “rated”. Both “measured” and “expected” values on the curves are corrected according to ISO 3046 standards for finding “corrected” and “rated” values. Thus, the difference between these values on each curves can’t be considered as a total degradation since the environmental conditions affecting the performance can’t be controlled by the operators.

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In this study, “Expected Performance Curve” was obtained from a sea trial data of engine in order to find how the engine performance changes with the variation of operating parameters, “Actual Performance Curve” was obtained from actual measuring test data during operation. As can be seen from the Figure 13-14 the difference between the rated performance values on expected performance curve and the corrected performance values on the actual performance curve give the degradation of the engine depending on the operation parameters. This method which is the simplest and reliable method to calculate the engine performance changes over time is called “Curve Based Method” [21]. The measuring value of Main Engine Power and SFC, which were conducted by the research team, are found as 5921 kW and 205.92 g/kWh, respectively. After the measured values are corrected with regards to ISO 3046, the Power and SFC are found respectively 6014kW and 204.04 g/kWh. The rated power and SFC values are 6634 kW and 177.3 g/kWh respectively after the expected value of the Main Engine performance were corrected according to ISO 3046 standards. Thus, the power and the SFC degradations of the main engine of the M/V Ince Inebolu are calculated as 620 kW and 26.74 g/kWh by subtracting the rated values from the corrected values.

Figure 13. The main engine degradation of M/V Ince Inebolu on power

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Figure 14. The main engine degradation of M/V Ince Inebolu on SFC The effect of scavenge air temperature and pressure, injection timing, injection pressure and compression pressure on degradation of main engine performance can be repaired during operation and by maintenance planning. It is formidable to find out the causes of the rest of the degradation as it grows up gradually in long periods. When examining the reasons of these degradations, it can be explained from physical problem (wearing, fatigue) associated to aging, deterioration and mechanical problems. The sea trial and present measured data of pressure vs crank angle diagram is illustrated in the Figure 15. As can be seen from the figure that maximum pressure (Pmax) and compression pressure (Pcomp) of present measurement decreases in comparison to sea trial measurement. Moreover, present pressure curve shows that the power in the cycle reduced due to degradations.

19

140 120 Measured

100

Pressure, bar

Sea Trial 80

60 40 20 0

-150

-100

-50

0 Crank Angle, °CA

50

100

Figure 15. The measured and sea trial data of pressure vs crank angle diagram Table 2 illustrates the calculated degradation values depending on parameters of repairable in operation and repairable with rehabilitation. It can be said that repairable with operation has 526 kW and 21.14 g/kWh power and SFC degradation and repairable with rehabilitation has 94 kW and 5.60 g/kWh power and SFC degradation of total degradation. Table 2. Calculated degradation values depending on parameters Power Factor

Degradation (kW)

SFC Factor

Degradation (g/kWh)

Sea Trial Value

Measu red Value

Scav. Air Temp., °C

38

50

0.9762

-141

1.0121

+2.49

Scav. Air Pres., bar

2.8

2.7

0.9851

-88

1.0112

+2.32

Injection Timing, CA

-3.5

-1.5

0.9864

-81

1.0182

+3.76

Compression Pres., bar

98.3

89.2

0.9782

-129

1.0374

+7.72

Injection Pres.

300

290

0.9853

-87

1.0235

+4.85

Degradation Parameters

Pmeasured=5921 kW

SFCmeasured=205.92g/kWh

The Others (Aging, wearing, etc)

-94

+5.60

TOTAL

-620 kW

+26.74 g/kWh

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8. Conclusion In this article, zero dimensional two zone combustion model has been developed and validated for a large two stroke marine diesel engine. The measurements are taken from a real ship named M/V Ince Inebolu by the research team during the normal operation of the main engine in the region of the Marmara Sea. After taking measurements, the effects of ambient conditions are eliminated by using the formulas given in ISO 3046-1:2002 Standard [46] to find the performance degradations. “The Power and SFC Adjustment Factors” are calculated by means of ISO 3046-1:2002 for ambient temperature, ambient pressure and sea water temperature to eliminate the effects of ambient conditions which cannot be controlled by operators. But, “the Power and SFC Factors” are calculated via developed mathematical model. To evaluate the performance, “Curve Based Method” has been used to calculate the total performance degradations and it has been classified depending on the variation of compression pressure, injection timing, injection pressure, scavenge air temperature and scavenge air pressure by using developed mathematical model. It is observed from the results that two stroke marine diesel engine has a power degradation of 620 kW and SFC degradation of 26.74 g/kWh totally. This means that the engine has been producing less power with a more fuel consumption. The degradations which is caused by the deviation from standard values of compression pressure, injection timing, injection pressure, scavenge air temperature and scavenge air pressure are found as 526 kW and 21.14 g/kWh, respectively. The rest of the degradation which are difficult to find out the exact reason are found as 94 kW and 5.6 g/kWh power and SFC degradation of total degradation. There is a complex interactions between engine components affecting the performance. When examining the reasons of these degradations, it can be explained from physical problem (wearing, fatigue) associated to aging, deterioration and mechanical problems. The ratio of indirectly found degradation are %15.1 and %20.9 of total degradation. This can be reduced by rearranging the period of maintenance planning with the help of economic effects on the degradations. Acknowledgements This study was done by means of the first author (Görkem KÖKKÜLÜNK) PhD Thesis. The authors wish to express their appreciation to Ince Shipping Trading Co. Inc., especially, to DPA/Technical Manager A. Yaşar Canca for their kindly help and contributions in this study.

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Nomenclature Definitions/Abbreviations m In cylinder mass, kg Q Heat transfer, J P Pressure, N/m2 V Cylinder volume, m3 U Internal energy, J W Work output, J H Enthalpy, J C Blow by rate constant FAs Fuel Air stoichiometric ratio fr Residual gas fraction mpre,dif Form parameter, premixed/diffusive av Wiebe constant ẋ Fractional heat release rate cp specific heat at constant pressure, kJ/kg K A Heat transfer area, m2 htr Heat transfer coefficient T Temperature, K s specific entropy, kJ/kg K Vc Clearance volume, m3 r Crank shaft radius, m b Bore, m S Stroke, m Mean piston velocity, m/s

Greek Letters θ ω ϕ τ Ψ ε

Crank angle, degree Angular speed, rad/s Equivalence ratio Time, s Half stroke to rod length ratio Compression ratio

Subscripts u b f bb a pre dif cyl w id

Unburned Burned Fuel Blow-by Air Combustion phase, premixed Combustion phase, diffusive Cylinder Cylinder walls Ignition delay

Acronyms FARG ECP SFC MCO HFO LCV

Fuel Air Residual Gas Equilibrium Combustion Products Specific Fuel Consumption Maximum Continuous Output Heavy Fuel Oil Lower Calorific Value

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[46] ISO 3046-1:2002 Incorporating corrigendum, April 2008, Reciprocating internal combustion engines-Performance, Part 1: Declarations of power, fuel and lubricating oil consumptions, and test methods - Additional requirements for engines for general use.

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Figure Captions Figure 1. Energy flow of two-zone combustion model Figure 2. The explanation of performance change and degradation Figure 3. Validation of developed mathematical model with real condition Figure 4. Validation of developed mathematical model with power and SFC Figure 5. The effects of ambient temperature on power and SFC Figure 6. The effects of ambient pressure on power and SFC Figure 7. The effects of sea water temperature on power and SFC Figure 8. The effects of scavenge air temperature on power and SFC Figure 9. The effects of scavenge air pressure on power and SFC Figure 10. The effects of timing on power and SFC Figure 11. The effects of compression pressure on power and SFC Figure 12. The effects of compression pressure on power and SFC Figure 13. The main engine degradation of M/V Ince Inebolu on power Figure 14. The main engine degradation of M/V Ince Inebolu on SFC Figure 15. The measured and sea trial data of pressure vs crank angle diagram

Table Captions Table 1. Technical data of the two stroke marine diesel engine Table 2. Calculated degradation values depending on parameters

28

Highlights 

Mathematical model was developed for a marine diesel engine.



Measurements were taken from Main Engine of M/V Ince Inebolu.



The model was validated for the marine diesel engine.



Curve Based Method was performed to evaluate the performance.



Degradation values of a marine diesel engine were found for power and SFC.

29