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International Review of Mechanical Engineering (I.RE.M.E.), Vol. 7, no. 7

Effect of Charge Air Temperature on Specific Fuel Consumption in Intercooled Direct Injection Diesel Engines used for Power Generation G. A. Kahandagamage1, N. S. Senanayake2, T.S.S. Jatunarachchi 3 Abstract – This paper presents the results of a study carried out to determine the variations of Specific Fuel Consumption (SFC) and fuel efficiency in day time and night time operation of an intercooled direct injection diesel engine of 17MW used for electrical power generation. In the study pressure development curves for 18 cylinders were obtained and the Mean Indicated Pressure (MIP) and crank positions for the Peak Pressure, Kinetic Burning (KB), and Diffusive Burning (DB) points were analyzed. The results showed a reduction of 1.9% in SFC in the night time operation in which the charge air temperature was lower and relative humidity was higher than those of day time. The reasons for changes in SFC are explained with the changes in the incylinder pressure curves. Further, the fuel efficiency was found to be increased in the night time by 0.8%. Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved.

Keywords: Specific fuel consumption, Diesel engines, Mean Indicated Pressure

I.

Introduction

Many studies have been carried out to determine the effects of charge air and fuel properties on the performance of diesel engines. These studies aimed to identify the factors that would optimize the combustion process so that Specific Fuel Consumption (SFC) is reduced. The SFC of engines depends on various factors such as heating value of the fuel, fuel density, engine condition and the charge air condition. According to preliminary investigations carried out at the Heladhanavi Thermal Power Plant in Puttalum District in Sri Lnaka, it has been observed that SFC has a positive relationship with the charged air or the ambient air temperature as shown in Fig.1. Heladhanavi Power Plant is a 100MW thermal power plant, consisting of six Wartsila 18V46 turbocharged, intercooled direct injection diesel engines each with a capacity of 17MW.

SFC (g/kWh)

204 202 200 198 196 22

26

30

34

38

Ambient temperature (deg. C)

Fig.1. Variation of SFC with ambient air temperature

The present study was carried out to analyse the shape of the pressure develpoment cuve, Mean Indicated Pressure (MIP), Peak Pressure (PP), and the SFC when the diesel engine was operated during the day time and night time, which provided different charge air temperature and humidity. Also actual fuel consumption and the electrical energy output were measured to assess the differences in fuel consumption and the fuel efficiency in the night compared to day time operation of the engine.

II.

Literature Review

The effect of charge air properties on diesel engines have been reported in many literature.These studies focussed maily on the effect of charge air temperature on the performance, SFC and emission characteristics [1 -5], and some studies also focussed on the effect from the moisture in the charge or fuel on the diesel engine performance [6]. Lin and Jeng (1996) reported finding of a study on the effect of humidity and temperature of intake air on the performance and the emission characteristics of diesel engines. According this stduy air consuption rate, brake torque, and nitrogen oxide in the exhust decreased, while specific fuel consumption, carbon monxide and sulphur dioxide increased with both the temperature and the humidity of charge air [7]. Inlet air temperature and the air-to-fuel ratio also have a significant effect on the maximum in-cylinder pressures and its position relative to the top dead center, the shape of the pressure rise curve, and the heat relese rates [8]. In a study carried out by Maiboom (2008) the charegd air temperature in a diesel engine was varied from 20 oC to 38oC and found that increase in charge air temperature at constant boost pressure resulted in a slight decrease in rate of heat release (ROHR). The increase of inlet

Copyright © 2013 Praise Worthy Prize S.r.l. - All rights reserved

G. A. Kahandagamage, N. S. Senanayake, T.S.S. Jatunarachchi

temperature with exhaust gas recirculation (EGR) has contrary effects on combustion and emissions, for example, the reduction of NOx emissions with increased inlet temperature [9]. In diesel engines four stages of combsution can be identified namely, Ignition delay period, Kinetic burning period (premixed burning), Diffusive burning period, and Diffusive and end burning [10]. During the ignition delay period, the injected diesel fuel undergoes both physical and chemical processes. Physical process include the atomization into fine fuel droplets, the heating and evaporation of the fuel droplets, and entrainment of surrounding air into the spray and mixing with it to form a flammable mixture, which initiates combustion. During the chemical process autoaccelerating chemical reaction takes place at the same time. Once the reaction rate reaches the explosive stage, combustion takes place. Noticeable pressure rise on the cylinder pressure appears. The length of the delay period depends on both physical and chemical processes. For the physical process, temperature and injected fuel droplet size have the greatest effect. For the chemical process, temperature at the time of injection and fuel quality (cetane number) affect the delay period [10]. Many of the research in the analysis of the effect of charge air prioperties on the peformance of diesel engines have been done for the automotive diesel engines. The present study was caaried out for a high capacity diesel engine of power rating 17MW that is used for electrical power generation.

III.

Method

A Wartsila 18V46 turbocharged, intercooled engine that consists of 18 cylinders was used for the experiments. This was a recently 48,000 running hour maintenance completed engine at 54,890 rhs. All the injector pumps and injector nozzles were in good condition. Cylinder head, piston and liner maintenances have been done recently. The load of the engine was set at 17MW. The measurements were taken during the day time and the night time in order to change the ambient conditions (temperature and humidity). Time of running during which all measurements were taken was four hours in each of day time and night time. During the running periods the following were measured. Pressure development in the cylinder Charge air temperature Charge air relative humidity Fuel consumption Electrical energy meter readings All the cylinders were analyzed using the “Lemag Premat XL analyzer” to study the pressure development inside the cylinders. The analyzer was connected to the combustion chamber through the indicator cock on the cylinder head and pressures inside were recorded for four


cycles. Then the recorded values were fed into the computer. The pressure curves and (dp/da) curves versus the crank angle after TDC were plotted by using Premet software v 4.12. The fuel consumption measurement was carried out during the same time periods. The readings of the individual fuel racks of the engine were recorded with a marking on the rack to see the amount of fuel injected in to the engine. .

Fig.2. Layout of the engine

Also during the four hour periods in day time and night time experiments the ambient and charged air properties (temperature and humidity) were measured in 1 hour intervals. The exported electrical energy was recorded during the day and the night time operation using energy meters installed in the plant.

IV.

Results and analysis IV.1 Pressure curves

Fig. 3. shows a sample screen print obtaiend after processing the data using Premet v4.12 software which shows the variation of the pressure(bar) inside the cylinder with the crank angle (deg. rotation) of the cylinder. The dp/da curve was obtained by derivating the first curve by the software. The green curves are for night time and the blue curves are for day time. The Mean Indicated Pressure (MIP) value, peak pressure, and minimum pressure values are also obtainable from the plot with relavant crank position by positioing the curser at the required point in the curve. Table I below shows the variation of different parameters obtained from the pressure characteristic curves for day and night time operations of the engine for all 18 cylinders. According to the information extracted from the pressure curves, the Mean Indicated Pressure (MIP) was found to be higher in the night than that of the day time for all cylinders, the average value being 0.8bar.

International Review of Mechanical Engineering, Vol. 7, no.7


Diffusive burning point

Kinetic burning point

Pressure variation curve

curve Crank angle

Fig. 3 Pressure and rate of pressure derivative with respect to crank angle for day time and night time operation

. TABLE I CHANGE OF PARAMETERS OF THE PRESSURE – CRANK ANGLE CURVE DURING DAY AND NIGHT TIME OPERATIONS

MIP – Mean Effective Pressure, PP – Peak Pressure, KB – Kinetic Burning, DB – Diffusive Burning Cylinder number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Avg

Delay in relevant night time curves w.r.t. day time (deg )

MIP (bar) Night

Day

PP (bar)

Dp/da KB

Dp/da DB

28.1 26.8 27.2 27.1 28.3 29.0 27.2 28.1 26.9 27.6 26.6 27.2 26.1 26.1 26.0 26.7 26.6 26.0 27.1

25.6 26.3 26.0 26.0 27.2 27.9 26.7 26.9 26.4 26.9 26.3 26.1 25.6 25.6 25.5 26.1 26.4 25.4 26.3

3.00 0.75 2.00 1.25 1.50 1.00 0.75 1.25 2.00 1.50 1.00 1.00 0.75 0.75 1.25 1.75 1.50 2.00 1.40

2.00 0.75 0.75 1.00 1.50 1.25 0.75 1.50 0.75 1.25 1.00 0.75 0.50 0.50 2.00 1.00 1.25 1.50 1.10

1.00 0.50 0.50 0.75 1.00 0.50 1.00 0.75 0.75 0.50 1.00 0.50 1.00 1.00 0.75 0.50 0.50 1.00 0.70

The maximum pressure development was also found to be delayed in night time compared to day time value, the maximum and minimum values being 3 o and 0.75o after TDC. The kinetic burning and diffusive


burning points were also found to be delayed in the night time. The delay in kinetic burning (premixed burning) signifies that atomization occurs closer to the TDC and initiates the combustion at a higher pressure. The higher MIP during night time is an indication that total energy per cycle is high. Hence the power increases while maintaining the same speed. As the power is regulated at 17MW, the fuel consumption is automatically reduced by the controlled mechanism giving less fuel consumption during night time where the charge air temperature is low and the humidity is high. These are in agreement with the similar studies reported for small capacity automotive diesel engines [1 – 3, 8]. TABLE II AMBIENT AND CHARGE AIR PROPERTIES Ambient air Time Pressure (bar)

Charge air (After turbo)

Temp (oC)

RH%

Pressure (bar)

Before cooler Temp ( oC)

After cooler Temp (oC)

Day

1

33

45

4

176

65

Night

1

27

86

4

172

59

The increase in energy development per cycle can also be due to the increase of moisture in the charge air in the night time. The ambient air and charge air average properties are given in Table II. The night time moisture in the charge air is obtained from the psychrometric chart knowing the dry bulb temperature (ambient) and the relative humidity. The moisture content in night was therefore 19.5g/kg of dry International Review of Mechanical Engineering, Vol. 7, no.7


air in the night and 14g/kg of dry air in the day time. Previous studies reported in literature suggested that moisture present in the charge air contributed significantly to increase the power and decrease the SFC [7]. However, the degree of contribution to affect the performance of the engine from temperature change and the humidity change cannot be exactly determined; the effect can be explained as combine influence of both.

The fuel efficiency was found to increase by 0.8% for a drop of 6oC in charge air temperature. As a whole reduced charge air temperature is economically advantages even though for a small increase in fuel efficiency as large quantity of fuel is used in power generation applications of diesel engines which give a considerable monetary savings.

IV.2 Fuel Efficiency

Authors wish to acknowledge the Ceylon Electricity Board and staff of the Heladhanavi Thermal Power Plant for facilitating to conduct this study.

Table III shows the average experimental readings recorded for electrical energy exported and fuel consumption during the day time and night time operations. TABLE III ENERGY EXPORT AND FUEL CONSUMPTION

Time

Energy meter export MWh/hr

Energy export MJ/hr

Fuel consumption kg/hr

Day

16.85

60660

3573.33

Night

16.85

60661

3506.67

The fuel consumption recorded in the flow meters during the day time and night time operation coincident with the combustion analysis indicated that the day time average fuel consumption was 3573.33 kg/hr and for the night time it was 3506.67kg/hr. The improvement in the night time was 66.67kg/hr compared to the day time (1.9 % reduction). The fuel efficiency was calculated using the following equation with lower heating value of the fuel as 40.5MJ/kg.

The fuel efficiency for day time is 41.9% and for the night time is 42.7% with the exported amount of energy. This is an improvement of 0.8% for the night comparative to the day time for a decrement of 6oC charge air temperature.

V.

Conclusions

The results of experimental investigation of parameters related to SFC during day time and night time operation of the intercooled direct injection diesel engine showed that MIP increase on average of 3% night time in which charge air temperature is lower than that of day time, resulting in lower SFC. Higher humidity of 41% more in the night compared to day time also contributed to the lower SFC. Further studies need to be carried out to determine the individual effect from humidity and temperature on the engine performance and hence the SFC.


Acknowledgements

References [1] R. Mamat, N. R. Abdullah, H. Xu, M. L. Wyszynski and A. Tsolakis, Effect of boost temperature on the performance and emissions of a common rail diesel engine operating with rapeseed methyl ester (RME), Proc. World Congress on Engineering, June 30 – July 2, 2010, London, UK. [2] H. A. Saber, R. R. Ibraheem Al-Barwari and Z. J. Talabany, Effect of ambient air temperature on specific fuel consumption of naturally aspirated diesel engine, Journal of Science and Engineering, Vol. 1 (1), pp. 1 -7, 2013. [3] S. Swami Nathan, J. M. Mallikarjuna and A. Ramesh, Effects of charge air temperature and exhaust gas re-circulation on combustion and emission characteristics of an acetylene fuelled HCCI engine, Fuel, Vol. 89, 2010, pp. 515 – 521. [4] C. Jayakumar, Z. Zheng, U. M. Joshi, W. Bryzik, N. A. Henein and E. Scattler, Effect of inlet air temperature on auto-ignition of fuels with different Cetane number and volatility, Proc. ASME International Combustion Engineering Division Fall Technical Conference (ICEF 2010), October 2 -5, 2011, Morgan Town, West Virginia, USA. [5] R. G. Papagiannakis, T. C. Zannis, E. A. Yfantis and D. T. Hountalas, Comparative evaluation of the effect of intake charge temperature, pilot fuel quantity and injection advance on dual fuel compression ignition engine performance characteristics and emitted pollutants, Proc. ASME 2009 International Mechanical Engineering Congress and Exposition, Vol. 3: Combustion Science and Engineering, Nov. 13 – 19, 2009, Florida, USA. [6] Abdulaziz H. El-Sinwai, K. Takrouri, O. Ostar and N. Haimour, The effect of high water content of fuel on diesel engine emission, Global Journal of Researches in Engineering (C), Vol. XII, Issue III, Version 1.0, 2012. [7] C. Y. Lin and Y.L Jeng, Influences of charge air humidity and temperature on the performance and emission characteristics of diesel engines, Journal Ship Research, Vol. 40, No. 2, pp. 172177, June 1996. [8] R. K. Maurya and A. K. Agarwal, Experimental investigation of the effect of the intake air temperature and mixture quality on the combustion of a methanol – and gasoline – fuelled homogeneous charge compression ignition engine, Proc. The Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, Vol. 223, No. 11, pp. 1445 – 1458, November 1, 2009. [9] A. Maiboom, X. Tauzia and J. Francosis Hetet, Experimental study of various effects of exhaust gas recirculation (EGR) on combustion and emissions of an automotive direct injection diesel engine, Energy, Vol.33, Issue 1, pp. 22 – 34, January 2008.



[10]

B. D. Hsu, Practical Diesel Engine Combustion Analysis, Society of Automotive Engineers, Inc., Warrendale, PA, USA, 2002.

VI.

Authors’ information

1

Mechanical Engineer, LTL Transformers (Pvt) Ltd., Sri Lanka. email: [email protected], Telephone: +94 773472787 2

Corresponding Author, Senior Lecturer, Department of Mechanical Engineering, Faculty of Engineering Technology, The Open University of Sri Lanka, Nugegoda, Sri Lanka, email: [email protected], Telephone: +94 11 2881314. Fax: +94 11 2822737 3

Senior Lecturer, Department of Mechanical Engineering, Faculty of Engineering Technology, The Open University of Sri Lanka, Nugegoda, Sri Lanka, email: [email protected], Telephone: +94 11 2881044. Fax:+94 11 2822737 G. A. Kahandagamage is graduated in Mechanical Engineering in ====== from the University Moratuawa, Sri Lanka. He at present is a student of M. Sc in Sustainable Energy Engineering Program offered worldwide by the Royal Institute of Technology in Sweden. He has a wide experience with working as an Operations Engineer and Maintenance Engineer at the Heladhanavi Power Plant Sri Lanka, the largest thermal power plant of operating in the country. At present he works a Mechanical Engineer at the LTL Transformers (pvt) Ltd in Sri Lanka. His current research interests are energy saving and sustainable power generation. N. S. Senanayake graduated in Mechanical Engineering in 1985. He joined the Open University of Sri Lanka (OUSL) in 1986 as an Assistant Lecturer in Mechanical Engineering. In 1996, he obtained his PhD from the University of Cranfield, United Kingdom in the area of Food Processing Machine Development. At present N. S. Senanayake works as a Senior LecturerGrade I in Mechanical Engineering at the OUSL. He is the Program Facilitator for the Sri Lankan students following the Worldwide M.Sc. program in Sustainable Energy Engineering conducted by the Royal Institute of Technology (KTH) in Sweden. His current research includes development of Open and Distance learning methods for engineering degree programmes and sustainable use of energy in the manufacturing industries. T.S.S. Jatunarachchi graduated in Chemical Engineering from the University of Moratuwa, Sri Lanka in1992. She joined the Open University of Sri Lanka in 1993 and obtained MPhil degree in the area of renewable energy sources and biomethanation process. Presently she is serving as a of Senior lecturer attached to the Department of Mechanical Engineering and as an academic she is engaged in teaching and other academic activities in the areas of Thermodynamics, Renewable Energy Technologies, Energy Management etc. She is involved in research projects related to biomass and gasification technologies.

