Performance and emission analysis of CI engine operated micro-trigeneration system for power, heating and space cooling

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Applied Thermal Engineering xxx (2014) 1e9

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Applied Thermal Engineering

journal homepage: www.elsevier .com/locate/apthermeng

Performance and emission analysis of CI engine operated micro-trigeneration system for power, heating and space cooling

Rahul Goyal*, Dilip Sharma, S.L. Soni, Pradeep Kumar Gupta, Dheeraj Johar, Deepesh SonarMechanical Engineering Department, MNIT Jaipur, Rajasthan, India

h i g h l i g h t s

� Complete experimental setup was developed for micro trigeneration system.� Micro trigeneration system was experimentally investigated.� Engine exhaust was used for space cooling using four units of VA system.� Exergy and energy analysis was done for complete trigeneration system.� CO2 emission was 54% & 58% lesser in CHP & CCHP compared to single generation.

a r t i c l e i n f o

Article history:Received 21 June 2014Accepted 6 October 2014Available online xxx

Keywords:TrigenerationMicro trigenerationWaste heatVapor absorption systemSpace coolingSpecific fuel consumptionEmissionExergy efficiency

* Corresponding author. Tel.: þ91 9460763566.E-mail address: [email protected] (R. G

http://dx.doi.org/10.1016/j.applthermaleng.2014.10.021359-4311/© 2014 Elsevier Ltd. All rights reserved.

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a b s t r a c t

To achieve an optimal solution for the current energy crisis, the world needs to focus more on (a)renewable sources of energy or (b) look for recycling/appropriate utilization of energy being wasted. Analarming amount of heat is wasted from exhaust systems of various engines e stationary or in auto-mobiles. Trigeneration systems use waste heat from prime movers to generate heating and cooling alongwith power. They are more efficient, less polluting & more economical than conventional systems. Thispaper describes the performance and emission characteristics of a micro trigeneration system based on asingle cylinder diesel engine. In this trigeneration system, in addition to the electricity generated fromthe genset, waste heat from hot exhaust gas of diesel engine was used to drive a combination of fourunits of Electrolux vapor absorption (VA) system for space cooling, and compact type heat exchanger wasused for hot water production. The capacity and heat input of each unit of VA system was 51 L and95 W respectively. A cabin (3' � 5' � 6') made of ply wood was fabricated as a space for cooling. The testresults show that a temperature drop of 6.5 �C was obtained in cabin at full engine load about 6 h aftersystem start up. The reduction of CO2 emission in kg per kWh of useful energy output was 53.83% incombined heating and power (CHP), 57.46% in combined cooling, heating and power (CCHP) and 8.02% incombined cooling and power (CCP) mode compared to that of single generation (power generation only)at full load. The decrease in specific fuel consumption was 53.24%, 51.29% and 6.89% in case of CHP, CCHPand CCP mode respectively compared to that in single generation at full load. From the exergetic point ofview, exergy efficiency of either of the integrated systems was marginally higher compared to thetraditional power generation system (single generation). Hence, the results show that micro trigenera-tion systems using single cylinder CI engine for power, heating and space cooling are very effective andthat they can be projected as strategic means to achieve energy security and efficiency, with positiveimpact on economy, simultaneously reducing environmental threats, leading to sustainabledevelopment.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Cogeneration and trigeneration have emerged as fast growingtechniques to solve energy related problems, such as increasing

oyal).

6

, et al., Performance and emihermal Engineering (2014), h

energy demand, increasing energy cost, energy supply security andenvironmental concerns. Cogeneration and trigeneration respec-tively mean the production of two and three useful forms of energyfrom the same energy source [1,2]. Low grade waste heat availableat the end of power generation process is utilized in heating andcooling/refrigeration. Cogeneration defines the simultaneous pro-duction of cooling/heating and power, while the trigeneration

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Nomenclature

E energym mass flow rate (kg/s)Cp specific heat (kJ/kg K)T temperature (K)h efficiency (%)C heat capacity (kW/K)U overall heat transfer coefficient (kW/m2 K)A area (m2)T0 ambient temperature (K)P pressureCHP combined heating and power (cogeneration)CCP combined cooling and power (cogeneration)CCHP combined cooling, heating and power (trigeneration)COP coefficient of performance

Subscripts used in equationsf fuelex. exhausteng. enginecw cold waterH.E. heat exchangerref refrigerationcab cabint totalgen generatorhi hot fluid inci cold fluid ine exergygen generatoreva evaporator

R. Goyal et al. / Applied Thermal Engineering xxx (2014) 1e92

systemdefines the simultaneous production of cooling, heating andpower from single energy source (i.e., the fuel only). A typical tri-generation system consists of a prime mover or the driving unit,electricity generator, thermally activated equipment and heat re-covery system. There are various options for prime mover, such as,internal combustion engine, gas turbine, steam turbine, Stirlingengine, fuel cells, etc. Prime mover drives a generator which pro-vides electric power [3]. Waste heat (as a by-product) from theprime mover is recovered and used to (a) drive thermally activatedcomponents such as vapor absorption system or adsorption chilleror desiccant dehumidifier [4e6] and (b) produce hot water, steam,warm air or other heated fluid with the use of a heat exchanger.Depending upon the size, the cogeneration and trigeneration sys-tems are classified as large, medium, small or micro cogeneration/trigeneration systems. Both cogeneration and trigeneration haveapplication in commercial sector (office buildings, etc.) as well as inindustrial sector [7e9]. A number of studies have been conductedto investigate the performance of a large scale cogeneration/tri-generation system [10e12]. However, very little work has beendone in real life cases at small residential or commercial levelespecially for space cooling. Applying cogeneration/trigenerationtechnology to small scale residential use is an attractive optionbecause of the large potential market. Khatri et al. [13] and Lin Linet al. [14] designed and analyzedmicro trigeneration systems basedon small diesel engines. The experimental results show that theidea of actualizing a household size trigeneration system is feasibleand the design of such trigeneration system is successful. G.Angrisani et al. [15] carried out an experimental study to investi-gate the performance of both micro cogeneration system andmicrotrigeneration system. The experimental data were analyzed fromenergy, economy and environmental point of view and the per-formance of the proposed system was compared with the con-ventional system. Andre Alexio [16] investigated an experimentalstudy of an ammonia water absorption refrigeration system usingthe exhaust of an internal combustion engine as energy source andresult show that the cooling capacity can be improved & carbonmonoxide emissions were reduced. Harish Tiwari et al. [17] havedescribed the experimental investigation of an adsorption refrig-eration system for cabin cooling of trucks using exhaust heat. J.Godefroy et al. [18] have described the design, testing and mathe-matical modeling of a small trigeneration system based on a gasengine with 5.5 kW electricity output and an ejector cooling cycle,analysis of which shows that an overall efficiency of around 50%could be achieved. Y. Huangfu et al. [19] had discussed the eco-nomic and exergetic analysis of novel micro scale combined

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cooling, heating and power system using small scale internalcombustion engine with rated electricity power 12 kW and anadsorption chiller with refrigerating capacity of 9 kW. Deepeshet al. [20] presented a brief review on micro trigeneration systemsand concluded that micro-trigeneration systems can be projectedas strategic means to achieve energy security and efficiency, withpositive impact on economy, simultaneously reducing environ-mental threats, leading to sustainable development. Aysegul Abu-soglu et al. [21] described the thermodynamic analysis of the dieselengine operated cogeneration system and found the thermal effi-ciency of the overall plant was 44.2% and exergetic efficiency was40.7%.

The objective of the current study was to investigate the feasi-bility, performance (energy & exergy analysis) and exhaust emis-sions of small capacity agricultural diesel engine (3.7 kW) operatedmicro trigeneration system for power, heating (hot water produc-tion) and space cooling. For space cooling, four units of Electroluxvapor absorption systems, each with a capacity of 51 L and heatinput of 95 W, were used. Exhaust gas from the engine was thesource of thermal energy for this VA system. Whereas, for pro-duction of hot water, compact type heat exchanger was used toraise the temperature of cooling water coming out of engine blockwith the help of exhaust gas coming from the engine/VA system.

2. Experimental setup and research methodology

Fig. 1(a) and (b) shows the schematic layout of the experimentalsetup and photograph of trigeneration test rig in the laboratoryrespectively. The experimental setup for the study consisted ofsingle cylinder four stroke water cooled constant speed, Kirloskarmake 5 HP (3.7 kWModel AV1) diesel engine coupled with electricgenerator and Electrolux vapor absorption system (four units) forspace cooling.

Four identical VA units were arranged in rectangular patternwith two rows and two columns consisting of two VA units each.Henceforth, the four VA units will be addressed as top left, top right,bottom left and bottom right VA units according to their position inthe VA system while looking from the front of the VA system. Airflow rate in the engine was determined using air box method bymeasuring the pressure drop across a sharp edge orifice of air surgechamber with the help of a manometer. Burette method was usedto measure the volumetric flow rate of diesel. Governor was used tokeep engine rpm constant while varying the load on engine forcreation of various test results. The load was varied by switching onthe desired numbers of electric bulbs.

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Fig. 1. (a) Schematic layout of experimental setup for trigeneration system, (b) photograph of the trigeneration test rig in the laboratory.

R. Goyal et al. / Applied Thermal Engineering xxx (2014) 1e9 3

Digital tachometer was used to confirm that the engine speedremains constant under varying load conditions. AVL make DITEST(AVL DiGas 4000 light) 5 gas analyzer was used to analyze theexhaust emission from the engine. The exhaust emission includedNOx, CO, HC, CO2 and O2, out of which, CO, HC and CO2 weremeasured by an NDIR technique and NOx and O2 were measured byelectrochemical sensors. They give HC and NOx emissions in PPMand that of other gases in percentage. Smoke in exhaust wasmeasured with the help of AVL smoke meter. The drop in intensityof light (lux level) between a source of light and a receiver wasmeasured to calculate the opacity of exhaust gas. This calculation isbased on BeereLambert Law.

Combination of four units of Electrolux vapor absorption sys-tem, each with a capacity of 51 L and heat input of 95 W, was usedfor space cooling. This type of cooling system is also called threefluids absorption system. The three fluids used in the system wereammonia, hydrogen and water. Ammonia was used as refrigerantbecause it possesses most of the desirable properties for refrig-erant. Hydrogen being the lightest gas was used to increase the rateof absorption of liquid ammonia passing through the absorber.Water was used as a solvent because it has the ability to absorbammonia readily. Fig. 2 shows the schematic setup of vapor ab-sorption refrigerator system in the laboratory. The main parts of thesystemwere generator, condenser, absorber and evaporator. In thisVA system, pump was not used.

Fig. 2. Schematic setup of vapor absorption refrigerator system in the laboratory.

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A wooden cabin of 3 feet width, 5 feet length and 6 feet heightwas fabricated for test of space cooling. For proper insulation ofcabin, so as to minimize the loss of cooling effect, nitrile rubber wasused on the rear wall of cabin, over which glass wool layer was usedand further on the top of glass wool, aluminum foil was pasted,hence, giving the cabin rear a three layer firm insulation cover. Theside wall of the cabin which was adjacent to the engine was pro-videdwith thermal insulation by 3 layers of 1 inch thick thermocoalsheets making it a 3 inch insulating layer of thermocoal. The cabinroof was provided with one layer of 1 inch thermocoal sheet abovethe ply wood ceiling. The other twowalls did not need insulation asthosewere away from the engine. Two fans were used to reduce theexcessive heat from top left and top right condensers. Also, two fanswere used between VA system and cabin to suck the cold air fromevaporator coil and deliver it into the cabin. The power required torun the fans (i.e. 100 W for four fans) was supplied by the enginegenset. Exhaust gas coming out from VA systemwas used to furtherheat the cooling water coming out from the engine block. For this acompact type heat exchanger was used. The heat exchanger usedwas 340 mm high, 300 mm wide and 50 mm thick cross flow,multi-flattened tube and finned, made of brass tubes and copperfins.

2.1. Methodology

The experimental investigation of the performance of the tri-generation system was divided in various steps to suit the condi-tions of single generation, CCP, CHP and CCHP modes. Theschematic line diagram is shown in Fig. 1(a). For single generation,valves A and E are kept open and valves B, D and F are closed. ForCCP system, valves B, C and E are opened and valves A, D, F and Gare closed. For CHP system, valves D and F are opened and valves A,B and E are closed. And for CCHP system, valves B, F and G are keptopen while valves A, C, D and E are closed.

In the first step, a series of tests were carried out to evaluate theengine generator performance when it was to be run on a singlegeneration system. In the second step, a series of tests were con-ducted to evaluate the performance of CCP system mode. In thethird step, a series of tests were conducted to evaluate the perfor-mance of CHPmode. In the final or fourth step, a series of tests wereconducted to evaluate the performance of CCHP mode. In all foursteps, engine load was varied from zero to full load condition andrelevant data were recorded viz. Brake Specific Fuel Consumption(BSFC), Brake Thermal Efficiency (BTE) and emissions. Test sets



were prepared for 0 W, 1000 W, 2000 W, 3000 W and 3700 W (fullload) load conditions. The load was varied by switching on thedesired numbers of electric bulbs. To measure BSFC and BTE at eachload condition, time taken for 10 ml of fuel consumed was notedusing a stopwatch. For each load condition the percentage/PPM ofvarious gases in exhaust was noted using AVL 5 gas analyzer andAVL smoke meter. Different graphs were plotted for various con-ditions for BSFC, BTE and emissions and results were analyzed.

Since the temperature of cabin at different heights was different,hence, tomeasure space cooling effect, 3 thermocouples were placedin the cabin at a height of 0 mm, 900 mm and 1750 mm from theground and the average of these three temperatures was consideredas Tcab. Cooling effect was calculated using Equation (4) given below.

3. Thermodynamic energy & exergy analysis

This section explains the energy & exergy analysis of the dieselengine operated micro trigeneration system. The principles of massor energy conservation and the Second Law of thermodynamicshave been applied. The exergy analysis is carried out for the steadyflow steady state condition. For the exergy analysis the atmosphericpressure and temperature is taken as 1 atm & 40 �C (313 K)respectively as the reference state.

3.1. First law analysis (energy method)

The following equations are used to determine the performanceparameter of the diesel engine operatedmicro trigeneration systembased on energy principle.

Thermal energy content in fuel input:

Ef ¼ _mf LCV kW (1)

Thermal energy carried by the exhaust gas:

Eex ¼ _mexCpex

�Teng: ex: gas � Tambient

�kW (2)

Thermal energy recovered for engine cooling and exhaust:

Ecw ¼ _mwCpwfTH:E: ex: water � TH:E: in waterg

þ _mwCpw

�Teng: ex: water � Teng: in water

�kW (3)

eex ¼ _mexCpex


�� T0�Seng: ex gas � Sambient

��kW

Or

eex ¼ _mex

�Cpex


�� T0

�Cpex

ZdTT

� RlnPoutPin

�kW

(15)

Thermal energy recovered by VA system.

Eref ¼ UAfTambient � Tcabg kW (4)

Total useful energy for combined heating & power:

EtCHP ¼ Electric outputþ Ecw kW (5)

Total useful energy for combined cooling & power:

EtCCP ¼ Electric outputþ Eref kW (6)

Total useful energy for combined cooling, heating & power:


EtCCHP ¼ Electric outputþ Ecw þ Eref kW (7)

Thermal energy efficiency for the diesel engine (only power):

hp ¼ Electric outputEf

(8)

Thermal energy efficiency for combined heating & power:

hCHP ¼ EtCHPEf

(9)

Thermal energy efficiency for combined cooling & power:

hCCP ¼ EtCCPEf

(10)

Thermal energy efficiency for combined cooling, heating &power:

hCCHP ¼ EtCCHPEf

(11)

Total energy supplied to the generators of VA system:

Egen ¼ Cmin Thi� Tci

� �kW (12)

Coefficient of performance (COP):

COPVA ¼ ErefEgen

(13)

3.2. Second law analysis (exergy method)

Kotas [22] examined the ratio of input exergy to input energyðef=Ef Þ for hydrocarbons and found it to be constant and that theproportionality constant between fuel exergy and fuel energy is1.04.

The input exergy to the diesel engine:

ef ¼ 1:04Ef kW (14)

Exergy lost in exhaust gas without cooling & heating:

Exergy recovered for engine cooling and exhaust:

ecw¼ _mwCpw

�fTH:E:ex:water �TH:E: inwaterg�T0 ln

�TH:E:ex:water

TH:E: inwater

�

þ _mwCpw

"�Teng:ex:water�Teng: inwater

�

�T0 ln

Teng:ex:water

Teng: inwater

!#

(16)

Exergy recovered by VA system.


Table 2Exergy analysis at engine full load.

S. No. Parameters Singlegeneration

CCP CHP CCHP

1 Exergy content in fuel input (kW) 12.639 12.88 12.88 13.3452 Exergy recovered from engine

cooling and engine exhaust (kW)0.111 0.0853

3 Exergy loss in exhaust gaswithout cooling and heating (kW)

1.34

4 Exergy recovered by VAsystem (kW)

0.37 0.528

5 Total useful exergy (kW) 3.75 4.12 3.861 4.3636 Exergy efficiency % 29.69 31.98 29.96 32.697 (COP)rev 2.18 2.188 Exergetic efficiency for VA system 0.096 0.096


eref ¼ _mexCpex

��Teng: ex: gas�Tex: VA

��T0 ln�Teng: ex: gasTex: VA

�kW

(17)

Total useful exergy for combined heating & power:

etCHP ¼ Electric outputþ ecw (18)

Total useful exergy for combined cooling & power:

etCCP ¼ Electric outputþ eref (19)

Total useful exergy for combined cooling, heating & power:

etCCHP ¼ Electric outputþ ecw þ eref (20)

Exergy efficiency of diesel engine (only power):

hp ¼ Electric outputef

(21)

Exergy efficiency for combined heating & power:

hCHP ¼ etCHPef

(22)

Exergy efficiency for combined cooling & power:

hCCP ¼ etCCPef

(23)

Exergy efficiency for combined cooling, heating & power:

hCCHP ¼ etCCHPef

(24)

Maximum possible coefficient of performance:

COPE ¼�1� T0

Tgen

��Teva

T0 � Teva

�(25)

Exegetic efficiency for VA system:

Table 1Energy analysis at engine full load.

S. no. Parameters Singlegeneration

CCP CHP CCHP

1 Fuel input (kg/h) 1.02 1.04 1.04 1.0772 LCV (kJ/kg) 42,893 42,893 42,893 42,8933 Thermal energy content

in fuel input (kW)12.15 12.39 12.39 12.83

4 Electrical output (kW) 3.75 3.75 3.75 3.755 Engine exhaust temperature (�C) 360 360 360 3606 Exhaust gas mass flow (kg/h) 24.295 25.15 25.15 25.387 Thermal efficiency (%) 30.85 30.26 30.26 29.228 Energy loss in exhaust gas without

cooling and heating (kW)2.17

9 Thermal energy recoveredfrom engine cooling and engineexhaust (kW)

4.38 4.145

10 Thermal energy recoveredby VA system (kW)

0.24 0.24

11 Total useful energy output(electricity þ heat þ power) (kW)

3.75 3.99 8.13 8.135

12 Overall thermal efficiencyof integrated system (%)

30.85 32.2 65.61 63.4

13 COP 0.211 0.211


hex ¼ COPCOPE

(26)

4. Results and discussion

The various parameters defined in the above section for theenergy and exergy analysis are evaluated and the values are givenin Tables 1 and 2 at full engine load condition. The diesel enginegenerator system performed satisfactorily on the single generationsystem, cogeneration system (combined cooling and power/com-bined heating and power) and the trigeneration systems. Thereadings were found to be quite consistent on repetition of tests.Three sets of readings were taken. The following sections show thetest results of average values of three tests for each parameter:

4.1. Engine generator performance for single generation,cogeneration and trigeneration systems

Fig. 3(a) and (b) shows the test results for BSFC and BTE of en-gine generator on single generation, cogeneration and trigenera-tion system respectively. The results show that BSFC and BTE ofsingle generation, cogeneration and trigeneration systems arenearly the same. It can be seen by results that the performance ofengine generator is not influenced adversely by addition of VAsystem and/or heat exchanger to the engine generator.

4.2. Engine emissions

Fig. 4 shows the emission of CO, HC, NOx, CO2, O2 and smokefrom single generation, cogeneration and trigeneration systems atvarious loads. The results show that the emissions from the engineon single generation, cogeneration and trigeneration systems arenearly the same at the same load.

In cogeneration/trigeneration system the pressure drop duringthe exhaust is taking place gradually because of longer length ofpipe, which results in improved scavenging during exhaust. Thisresults in improved combustion. Hence, CO, HC and CO2 gotreduced in cogeneration/trigeneration system compared to singlegeneration (only power) condition.

4.3. Performance of vapor absorption system driven by thermalenergy of engine exhaust

Different parameters of vapor absorption systemwere recordedand the performance of vapor absorption system was evaluatedduring the working of cogeneration/trigeneration system ondifferent engine loads. Four valves were provided for regulating theflow of exhaust coming out from the engine. Heat was to be pro-vided to generators of the four vapor absorption units for each unit


05101520253035

0 1 2 3 4

BT

E%

Load (kW)

OnlyPowerCCP

CHP

CCHP00.10.20.30.40.50.60.7

0 1 2 3 4

BSF

C (k

g/kW

h)

Load (kW)

(a) (b)

Fig. 3. Variation of (a) BSFC and (b) BTE with engine load for comparison of different operation modes.


to provide cooling effect. Hence, as the engine load was increased,the exhaust flowwas directed towards the four VA units one by oneby opening and closing the valves (as required) of the individual VAunits. The target was to reach a steady state condition i.e., to bringthe generator temperature of each VA unit to approx. 110 �C (as perthe specifications of the Electrolux VA System, the generator tem-perature should lie between 105 and 130 �C). To achieve this steadystate condition, different permutations and combinations of valveswas to be operated upon depending on the temperature conditionof each VA unit's generator. At full engine load and when all the VA

0

0.01

0.02

0.03

0.04

0.05

0.06

0 1 2 3 4

CO

%

Load (kW)

OPC

C

C

Fig. 4. Variation of CO, HC, NOx, CO2, O2 and smoke with en


units' generator temperatures were at 110 �C, all four valves wereopened. In the experimental set-up, it took approx. 4 h to reach thissteady state condition. And it took another 2 h to bring in anaverage temperature drop of 6.5 �C in the cabin compared to theambient temperature. The desired cooling effect could not beproduced until all four valves were opened and kept open forapprox. 6 h from engine start up. Hence, at full engine load andwhen all four valves were opened, remarkable temperature dif-ference between ambient and the cabin was obtained i.e. 6.5 �C,however, further drop in temperature was not achieved in the

0

2

4

6

8

10

12

0 1 2 3 4

CO

2 %

Load (kW)

nlyowerCP

HP

CHP

gine load for comparison of different operation modes.



cabin, thus balancing the cooling effect from VA system with theheat gain from the atmosphere and equipment. In this case, theheat input to the VA system, Egen, was 1134.35 W on an average forthe three tests; the cooling effect, Eref., was 240.90 W (includingconduction and convection losses) and COP of the VA system wasfound to be 0.2115. It is observed from literature review that COP ofVA system may vary in the range from 0.05 to 0.23 [12,13]. Hence,there is little more scope for improvement of the design of VAsystem to recover heat somewhat more effectively.

4.4. Performance of overall system

Various performance curves such as overall useful energyoutput, total thermal efficiency, specific fuel consumption and CO2emission in kg/kWh for various modes of operation are shown inFig. 5. Fig. 5 shows comparison of overall useful energy output, totalthermal efficiency, specific fuel consumption and CO2 emission inkg/kWh between CCHP, CHP, CCP, and single generation systems.

(1) Useful energy output: The useful energy output for CHPvaries from 2.7 kWat 1000W load to 8.13 kWat 3700W (Fullload) compared to 1000 We3700 W (Full Engine Load) forsingle generation system. However, in CHP (0.975 kW) andCCHP (0.731 kW) systems, energy is available in the form ofexhaust heat even when the engine is in idling (no load)condition. The increase in useful energy output is from 170%at 1000W to 119.72% at 3700W. The useful energy output forCCHP system varies from 2.46 kW at 1000 W to 8.135 kW at3700 W. Hence, the increase in useful energy output is from146% at 1000 W to 119.86% at 3700 W. In CCP system,refrigeration effect was obtained only at 3700 W i.e. fullengine load. So, in CCP mode, useful energy output variesfrom 1000 W to 3990 W compared to 1000 We3700 W forsingle generation system. The increase in useful energyoutput is from 0% at 1000 W to 7.83% at 3700 W.

0123456789

0 1 2 3 3.7Use

ful E

nerg

y O

utpu

t (k

W)

Load (kW)

onlypower

CCP

CHP

CCHP

00.10.20.30.40.50.60.7

1 2 3 3.7

SFC

(kg

/kW

h)

Load (kW)

OnlyPowerCCP

CHP

CCHP

Fig. 5. Comparison of useful energy output, overall efficiency, SFC and CO


(2) Total thermal efficiency: The total thermal efficiency for CHPvaries from 40.61% at 1000 W load to 65.61% at 3700 W (Fullengine load) compared to 14.47% and 30.85% respectively forsingle generation system. Hence, the increase in total ther-mal efficiency is from 180.64% at 1000 W to 112.67% at3700 W in the case of CHP. The total thermal efficiency forCCHP system varies from 36.28% at 1000 W to 63.4% at3700 W. Hence, for CCHP, the increase in total thermal effi-ciency is 150.72% at 1000 W and 105.51% at 3700 W. In CCPsystem, total thermal efficiency varies from 15.31% at1000 W to 32.2% at 3700 W. So, in CCP, increase in totalthermal efficiency is 5.80% at 1000Wand 4.37% at full engineload. Since, the COP of VA system is less than 1, it takes moreenergy in the form of heat as input than the output in theform of cooling, and so, the increase in efficiency in case ofCCP is extremely less as compared to that of CHP or CCHP.

(3) Specific fuel consumption: The SFC for CHP varies from0.206 kg/kWh at 1000 W load to 0.127 kg/kWh at3700 W (Full load) compared to 0.58 kg/kWh and 0.2716 kg/kWh respectively for single generation system. Hence, thereduction in SFC is 64.48% at 1000 W and 53.24% at 3700 W.The SFC for CCHP system varies from 0.231 kg/kWh at1000 W to 0.1323 kg/kWh at 3700 W. Thus, the reduction inSFC for CCHP is 60.17% at 1000 W and 51.29% at 3700 W. InCCP system, SFC varies from 0.54 kg/kWh at 1000 W to0.2616 kg/kWh at 3700 W. So, reduction in SFC for CCP sys-tem is 6.89% at 1000 W and 3.68% at full load.

(4) CO2 emission in total useful output: The CO2 emission in kg/kWh for CHP varies from 0.456 kg/kWh at 1000 W load to0.2876 kg/kWh at 3700 W (Full load) compared to 1.22 kg/kWh and 0.623 kg/kWh respectively for single generationsystem. Hence, the reduction in CO2 emission in kg/kWh isfrom 62.62% at 1000W to 53.83% at 3700W for CHP. The CO2emission in kg/kWh for CCHP system varies from 0.421 kg/kWh at 1000 W to 0.265 kg/kWh at 3700 W. So, the reduc-tion in CO2 emission in kg/kWh for CCHP system is 65.49% at

010203040506070

0 1 2 3 3.7Ove

rall

eff

icie

ncu

%

Load (kW)

00.20.40.60.811.21.4

0 1 2 3 3.7

Co 2

kg/

kW h

Load (kW)

2 emissions for various modes of operation at various engine loads.


010203040506070

OnlyPower

CCP CHP CCHP

Eff

ienc

y %

Mode of operatiom

Energyeffiency

Exergyefficiency

Fig. 6. Comparison of overall efficiency for energy and exergy for various modes ofoperation.


1000 W and 57.46% at 3700 W. In CCP system, CO2 emissionin kg/kWh varies from 1.19 kg/kWh at 1000 W to 0.573 kg/kWh at 3700 W. So, the percentage change of CO2 emissionin kg/kWh for CCP system is 2.45% at 1000 W and 8.02% atfull load.

4.5. Comparison of energy & exergy efficiency

Fig. 6 shows the energy and exergy efficiency for single gener-ation, CCP, CHP and CCHP systems at full engine load. For singlegeneration, the energy efficiency was 30.85% at full load while theexergy efficiency was 29.69% at full load. The exergy efficiency ofsingle generation is slightly lower than energy efficiency becausechemical availability of fuel which is considered as the input inexergy analysis is slightly higher than the calorific value of fuelwhich is considered as the input in energy analysis [23]. It was seenfrom the graph that the exergy efficiency of CCP, CHP, and CCHPsystem was lower than its energy efficiency. The exergy efficiencyin the CCP, CHP and in CCHP modes are marginally higher than thatin single generation. It means the energy is more effectively utilizedin CCP, CHP and CCHP system than in traditional only power gen-eration system [19].

COP and exergetic efficiency of VA system was found to be 0.60and 32.01% respectively from the modeling done by J. Aman et al.[24]. However, this modeling was done for a solar heated 10 kWair-cooled ammonia water absorption chiller. In contrast to that, in ourexperimental analysis for the above mentioned system, COP andexergetic efficiency of VA system was found to be 0.211 and 9.6%respectively.

5. Conclusions

From the above results and discussions, conclusions can bedrawn as follows for an experimental study of CI engine operatedmicro trigeneration system:

i. BSFC and BTE for single generation, CCP, CHP and CCHPsystems are nearly the same. This proves that integration ofvapor absorption system and/or heat exchanger does notadversely effect the performance of engine generator.

ii. CO2 emission per kWh of useful energy output at full engineload was decreased in CHP, CCHP and CCP by 53.83%, 57.46%and 8.02% respectively compared to that of single generationsystemwhich is a substantial reduction. The impact in case ofCCP is less because the COP of VA system is less than 1, so ittakes more energy in the form of heat as input than theoutput in the form of cooling.

iii.The decrease in specific fuel consumption for CHP, CCHP andCCP systems over single generation system was 53.24%, 51.29%and 3.68% respectively at full engine load.


iv. The useful energy output of the engine with single genera-tion is only the brake power but in case of CHP, CCHP and CCPsystem, useful energy output is the sum of brake power alongwith the heating and cooling effects as the case may be. Theuseful energy output at full engine load for CHP, CCHP andCCP was found to be 219.72%, 219.86% and 107.83% respec-tively compared to that of single generation.

v. The total thermal efficiency at full engine load for CHP, CCHPand CCP was found to be 212.67%, 205.31% and 104.37%respectively compared to that of single generation.

vi. Exergy efficiency of the CHP, CCHP and CCP mode wasslightly higher than the exergy efficiency of single generationsystem. It means energy is more effectively utilized in theintegrated system compared to that in single generationsystem.

vii. No adverse impacts on any parameter were found whileoperating on cogeneration or trigeneration system ascompared to single generation system.

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