small engines as bottoming cycle steam expanders for

Research ArticleSmall Engines as Bottoming Cycle Steam Expanders forInternal Combustion Engines

RohithaWeerasinghe and Sandra Hounsham

Department of Engineering Design and Mathematics University of the West of England Coldharbour Lane Bristol BS16 1QY UK

Correspondence should be addressed to Rohitha Weerasinghe sujithrohithayahoocom

Received 16 January 2017 Revised 4 April 2017 Accepted 20 April 2017 Published 31 May 2017

Academic Editor Paul Hellier

Copyright copy 2017 Rohitha Weerasinghe and Sandra Hounsham This is an open access article distributed under the CreativeCommons Attribution License which permits unrestricted use distribution and reproduction in any medium provided theoriginal work is properly cited

Heat recovery bottoming cycles for internal combustion engines have opened new avenues for research into small steam expanders(Stobart andWeerasinghe 2006) Dependable data for small steam expanders will allow us to predict their suitability as bottomingcycle engines and the fuel economy achieved by using them as bottoming cycles Present paper is based on results of experimentscarried out on small scale Wankel and two-stroke reciprocating engines as air expanders and as steam expanders A test facilitydeveloped at Sussex used for measurements is comprised of a torque power and speed measurements electronic actuation ofvalves synchronized data acquisition of pressure and temperatures of steam and inside of the engines for steam and internalcombustion cycles Results are presented for four engine modes namely reciprocating engine in uniflow steam expansion modeand air expansionmode and rotaryWankel engine in steam expansionmode and air expansionmodeThe air tests will provide basedata for friction and motoring effects whereas steam tests will tell how effective the engines will be in this mode Results for powertorque and 119901-119881 diagrams are compared to determine the change in performance from air expansion mode to steam expansionmode

1 Introduction and Motivation

Finding a suitable bottoming cycle for recovery of low gradeheat recovered from an internal combustion engine is basedon the temperature range of operation and the expectedefficiency Thermoelectric heat recovery provides a relativelycleaner less complicated option but with very low efficiencySteam on the other hand has been proven to work in heatrecovery cycles with a decent efficiency range Thomas New-comenrsquos atmospheric engine today referred to as the New-comen engine was the first practical device that harnessedpower of steam to produce mechanical work James Wattdeveloped it further and steam reciprocating engines havebeen in use for the last 200 years [1]The use of steam engineshas diminished in the advent of the internal combustionengine and the electric motor However steam engines arestill being used in various engineering applications especiallyin the power generation industry Small steam expansionengines are in limited use [2] this is usually because a steamgenerating system is also required which makes them uneco-nomical There have been attempts to use steam expanders

as primary power plant of an automobile [3] however thepresent work is based on steam small engines as bottomingcycle expanders There has not been much research done inthis area Particularly there are no data available on perfor-mance of these engines The work is intended to provide aplatform for the development of small steam engines thatcan be used as bottoming cycle heat expanders There arevarious options as steam expanders for example vane rotorsand microturbines However reciprocating expanders andWankel engines are readily available as small engines that canbe converted into steam expanders The range of the enginesin the study has been limited by the size and power that canbe mounted on the test apparatus a table-top dynamometerEssentially the rage has been restricted to less than 20 cccylinder capacityThe primary parameters of the two enginesthat have been used in the study are listed in Table 1

11 The Rankine Cycle The steam engine generally operateson the Rankine thermodynamic cycle Rankine cycles [4]have been widely used in both prime movers and bottoming

HindawiJournal of CombustionVolume 2017 Article ID 1742138 8 pageshttpsdoiorg10115520171742138

2 Journal of Combustion

Table 1 Engine data

EngineFour strokereciprocating

engine

Wankel rotaryengine

Model OS 32 SX OS 49 PIBore (mm) 195 NAStroke (mm) 175 NACapacity (cc) 523 497Compression ratio 10 1 7 1 (approx)

p

BDCTDC Swept volume

1 2

3

45 4Condenser pressure

Clearance volume Exhaust port opens

Steam cuto

Steam chest pressure

Figure 1 Rankine cycle reciprocating expander 119875-119881 diagram

cycle expanders The reciprocating Rankine cycle has beenused in locomotives ships and stationary engines Rotaryexpanders primarily steam turbines are used in powergeneration The use of rotary engine has been restricted bythe optimum operating range it offers in comparison to thewide range offered by the reciprocating engine The use ofthe steam expander used in this study is mainly aimed asa directly coupled engine that can operate in sync with aninternal combustion engine A reciprocating engine offerssimilar torques power characteristics to an IC engine Theother main advantage is the availability of small engines thatcan be converted into steam expanders

111 Rankine Cycle with a Reciprocating Expander A recip-rocating Rankine cycle shown in Figure 1 is explained by thefollowing steps

(1-2) Admission of steam at steam chest pressure

(2-3) Expansion of steam until the exhaust port isopen

(3-41015840) Blow down of the steam to condenser pressure

(4-5) Exhaust of steamuntil the exhaust port is closed

(5-1) Compression of steam left in the cylinder

The work and heat for the cycle can be found done byobtaining the specific enthalpies ℎ

119899 where 119899 refers to steps in

Figure 1 The theoretical work by the cycle is given by ℎ2ndashℎ3

and the heat supplied is given by ℎ2minusℎ1The efficiency is given

by

120578 =(ℎ2minus ℎ3)

(ℎ2minus ℎ1) (1)

The pump work is neglected as it is small compared tothe heat in Reciprocating steam expanders were the mostcommon type of expanders known for their high torqueand simple operation These are mostly used as marine andold locomotive prime movers The speed achievable fromlarge steam engines is limited Uniflow and counter-flowarrangements are possible with reciprocating expanders [1]However the valve arrangements become more complexwith counter-flow arrangement [5] Reciprocating enginesare perceived to be easier to implement thanWankel engines[6]

112 Rotary Steam Engines Steam turbines are efficientdevices but the range of operation is limited hence not verysuitable for automotive applications The major attraction ofthe turbine cycle is the high overall efficiency in operationHowever the flexibility of operation outweighs the efficiencyfactor and makes the reciprocating Rankine cycle morepractical In addition the ability to cater to fluctuating torqueand velocity conditions of the reciprocating cyclemakes it thepreferred device for automotive applications Nevertheless ifthe energy developed in a turbine is converted into electricityand used to drive an electric motor it leads to a practicalsolution for hybrid vehicles [7]

An intermediate solution is the Wankel rotary expander[8] Wankel engine offers some advantages of both theturbine cycle and the flexibility of the reciprocating engine [910] Micro-Wankel engines can be fabricated with improvedfabrication technology [11] Attempts have been made tocorrectly emulate the operation of the Wankel engine [12]but the current application is using steam as the working fluidwithout internal combustion Figure 2 shows the theoreticalRankine cycle and the pressure volume diagram of a Rankinecycle

12 Waste Heat Recovery The major attraction of Rankinecycle [13] today is its applicability in the waste heat recoverysystems [12] In power generation Rankine turbines aredriven by steam generated through waste heat recovery Useof reciprocating engines in waste heat recovery systems isseldom On the other hand use of rotary steam engines insmall scale applications is not common Ability of Rankinecycle to operate on low grade heat sources such as steammakes it attractive to employ in a bottoming cycle [14] Twomain types of expanders have been applied in Rankine cycleapplications that are of two types first one is the velocity typesuch as axial turbines and radial-flow turbines the other ispositive displacement type such as scroll expanders screwexpanders piston expanders and rotary vane expanders [15]These expanders feed off a steam reservoir courtesy of heatrecovery in a bottoming cycle [16 17]

Journal of Combustion 3

T

WinQout

Qout

Wout

4

1

2

3

Actual cycleIdealcycle

S

Win

Qin

Qin

Wout

4

1 2

3

Expander

pump

Condenser

Steamaccumulator

1 2

34

Chest pressure

Exhaust pressure

p

Figure 2 A simple Rankine cycle and Wankel Rankine expander 119875-119881 diagram

2 Experimental Setup

The experimental setup consists of a dynamometer a dataacquisition system controlled by LabVIEW software asteamair supply and a condenser unit The sensor inputs arefed to the system through a multichannel data acquisitioncard Figure 3 shows the components of the system and howthey are linked

21 The Dynamometer Testing of small scale engines offerthe advantages of portability less instrumentation low spacecosts and flexibility However there are no readily availabledynamometer setups for testing small engines Hence asmall scale dynamometer facility pictured in Figure 4 hadto be developed to mount the small engines for testing Thedynamometer was derived from a model makersrsquo lathe andthe drive train was modified to absorb power and to motorwhen necessary The engine output shaft is mounted inlinewith the lathe shaft Torque transducer arrangement connectsthe engine output shaft and the lathe shaft A 400WDCmotor drives the main shaft that can also absorb power Theend of the drive shaft is fitted to a pulse encoder that generatesthree pulse streams namely (i) pulse per revolution (ppr)(ii) pulse per revolution minus90∘ (directional indicator) and (iii)pulse per crank angle degree (pcd)

The engines used were modified model hobby enginesmanufactured by OS (Japan)The following data are availableof the engines used

For the use as steam expanders the inlets and exhaustshad to be modified to induct and exhaust steam The engineheads weremodified to accommodate for steam connections

Figure 4 shows a schematic of how the steam inductionand exhaust connections and valves are configured Thepicture shows the configuration of the ports controls andsteam in and out The arrangement is the same for the rotaryengine except for the fact that the rotary engine has two inletvalves and two exhaust valvesThe opening and closing of therotary engine valves take place without electronic control

22 Steam Expanders Steam expanders are available in theform of reciprocating expanders and rotary expanders In the

Control soware(LabVIEW)

Computer

Motorcontroller

Data acquisitioncard (NI)

Temperatureand pressuresensors

Opticalencoder

Torquetransducer

Steam

Engine

Reheater

Motor

Condenser

Scale

Figure 3 The experimental setup

present context uniflow reciprocating expander and a rotaryWankel engine are tested

221 Reciprocating Steam Engine A two-stroke internalcombustion engine has been modified to accommodatesteam admission through an electrically operated overheadvalve An automotive fuel injection valve has been modifiedfor the purpose The steam enters through an electrically


Inlet valve Exhaust valve

Pressure transducer

Temperature sensor

Steam quality measurement


Steam generation

Control Control

Figure 4 Schematic of the cylinder arrangement

operated inlet valve and exhausts through a port at the BDCThe timing of steam admission is critical for propulsion Thevalve timing was set to 3∘ BTDC and kept for 100∘ for the inletvalve Exhaust takes place through a 6mm long 25mm wideport before BDC

222 Valve Arrangement for the Two-Stroke ReciprocatingEngine Two pulse streams are utilized from the opticalencoder by the data acquisition card the pulse per revolution(ppr) and the pulse per crank angle degree (pcd) The pprpulse is aligned with the top dead centre of the pistonLabVIEW software that controls the actuation of the valveand samples the data for storage uses the pcd pulse as a sourceof clock ticks and ppr pulse as a trigger for an output pulseThe timing of the valve actuation is synchronized with pcdpulse and is variable

223 Wankel Steam Engine A modified small scale internalcombustion Wankel engine is used as a steam expander Theflow through the Wankel engine is uniflow and continuousgeneration of torque is available with three expansions percycle of the rotor The 119875-V diagram for a Wankel Rankinecycle is not available in the literature However Figure 9shows a pressure plot drawn against the crank angle as that ismore appropriate than a 119875-V diagram A 5 cm3modelWankelengine has beenmodified to run as aWankel steam expanderThere are two inlet ports and two exhaust ports They werechanged to obtain optimum performance The inlet port isat 20∘ to the original line of the engine and the exhaustvalves have been changed to a side exhaust arrangement asin Figure 5

23 Instrumentation and Measurements The engine is sup-plied with air or steam as appropriate and the fluid flow rate iscontrolled electronicallyMeasurements were taken at two setpressures of 7 bars and 15 bars for air and steam respectivelyPressure temperature torque speed and pulse signals are fedthrough the National Instruments (NI) data acquisition cardto the computer Communication with the scales takes placevia an RS232 connection All the data acquisition and controlare performed using LabVIEW software The sampling wastriggered by the pulse per crank angle degree (pcd) pulse fromthe optical encoder

Steam in

Torque meter

Injector

To main sha

Steam

Engine

TP

Figure 5 The dynamometer with the reciprocating enginemounted 119875 = pressure sensor 119879 = thermocouple

231 Pressure Pressure measurements were acquired for theengine inlet engine outlet inside of the cylinder reheaterinlet and reheater outlet via piezoelectric pressure sensors

232 Temperature The temperatures at engine inlet engineoutlet inside of the engine reheater inlet and reheater outletwere acquired using119870 type thermocouples

233 Torque and Speed Torque and speed are obtained viathe inline torque transducer from these readings power isgiven by

119875 = 2120587119873119879 (2)

234 Mass Flow Rate The condensate from the engine iscollected in a vessel on the electronic scales The incrementalweight against time gives the mass flow rate

235 Steam Quality The analysis of the steam quality ofthe exhausted steam required a new device setup The steamcoming out of the engine is wet and hence the pressure andtemperature alone would not give the steam condition Areheater section is fitted to the exhaust pipes which bringsthe steam to a superheated condition at which the pressureand temperature alone would be able to give the state of thesteam Figure 6 shows the temperature and pressure tappingpoint and Figure 7 shows the steam quality analyzer

Pressure and temperature sensors are placed at the inputto the SQA (ri) and the exit point from the SQA (re) Thereadings are used to obtain the specific enthalpy ℎre at re fromsteam tables Then ℎri is given by

ℎre minus ℎri =119881119868119905

119872 (3)

where 119872 is the mass of water collected in time t VI is therecorded voltage and current used by the reheater sectionThe most important measurements of the system are thepressures and temperatures of the inlet outlet and inside of


Steam in

Enginecasing

T

P T

Coupling tomain sha

Steam out

Figure 6TheWankel engine 119875 = pressure sensor 119879 = thermocou-ple

Δe = VIt

prepri

TreTri

ri

re

T

s

Figure 7 Steam quality analyzer (SQA)

the engineThesemeasurements can be used to determine theinlet and outlet conditions of the steam and hence to developan energy balance

236 Engine Efficiency Efficiency of the engine can becalculatedwith the heat input values and the power developedby the engine

3 Engine Test Results

Figures 10 and 13 show the power curves for differentinlet pressures of the engine The optimum supply pressurelies around 30 bars that has been confirmed by previousPrasad [7] Pressures above this range will have a negativeeffect which is explained by a close analysis of the Molierdiagram for water Saturated steam at pressures above 30bars stores less enthalpy than steam at 30 bars Peak to peakmeasurements of pressures have been taken and the data arereferred against supply pressure of zero The readings are

Crank angle versus pressure per speed step

3

4

5

6

7

8

9

10

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle

100 rpm

100 rpm

2300 rpm

2300 rpm

Wankel engine 7-bar air tests

Figure 8Wankel engine 7-bar air tests crank angle versus pressure

P-v diagram per speed step

2300 rpm

100 rpm

3

4

5

6

7

8

9

10

Pres

sure

(bar

)

2 3 4 51

Volume (meters cubed)times10minus6


Figure 9 Wankel engine 7-bar air tests 119901-119881 diagram

plotted after taking the offset into account and reflect theabsolute value

31 Air Tests on Wankel Engine Air test data was acquiredfor rpm values 100 200 300 500 700 900 1100 1300 15001700 2000 and 2300 The pressure volume diagram for airtests for the Wankel engine is given in Figure 9 for 7-bar airThe pressure-crank angle relationship is shown in Figure 8When the supply pressure is low substantial motoring takesplace and is illustrated by the negative pressures in the 119875-Vdiagram

Air test data was acquired for rpm values 200 300 500900 1300 and 1700

32 Steam Tests on Wankel Engine Steam tests were doneat 10-bar supply pressure and 15-bar supply pressure 15-barresults are shown here as 15 bars was the highest pressure


Speed versus power and torque

PowerTorque

Speed (rpm)25002000150010005000

0

10

20

30

40

Pow

er (W

)

0

02

04

06

08

Torq

ue (N

m)

Wankel engine 7-bar air test

Figure 10 Wankel engine power and torque for 7-bar air


200 rpm

200 rpm

1700 rpm

1700 rpm

6

8

10

12

14

16

18

20

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle

Wankel engine 15-bar steam tests

Figure 11 Wankel engine 15-bar steam tests crank angle versuspressure

at which data were logged as in Figures 11 and 12 Testswere done with a pressure regulated steam supply off anindustrial boiler The major observation expected of thepressure characteristics of the steam tests is the effect ofexpansion

33 Air and Steam Tests on Reciprocating Engine Measure-ments were taken on the expansion of steam at 10 bars in thereciprocating engine Data was obtained only at 200 rpm to800 rpmThis is deemed appropriate as the engine is expectedto run at a lower speed than the IC engine The shape of the119875-V diagram is significantly consistent with the theoretical


1 15 2 25 3 35 4 545

Volume (meters cubed) times10minus6

4

5

6

7

8

9

10

11

12

13

14

Pres

sure

(bar

)

200 rpm

200 rpm


Figure 12 Wankel engine 15-bar steam tests 119901-119881 diagram

times104

3

35

4

45

5

55

6

Spec

ic p

ower

(wat

ts)

0

2

4

6

8

10

12

Torq

ue (N

m)

400 600 800 1000 1200 1400 1600 1800 2000 2200200Speed (rpm)

Power at 10Power at 15 bars

Torq at 10 barsTorq at 15 bars

bars

Figure 13 The Wankel engine power and torque for 10-bar and 15-bar steam

diagram as shown in Figure 14 Specific power and torquecharacteristics are shown in Figure 15 at 10 bar

The power torque diagram is also pretty impressive andis of expected shape except for the readings at 400 rpmHowever the general behavior is as expected

Table 2 summarizes the results obtained for the air andsteam tests Air test diagrams are not shown in here as theywere done only for validation purposes

34 Analysis of Results The 119875-119881 diagrams for air and steamexpansion in rotary and uniflow reciprocating engines arepresented The 119901-119881 characteristics of the Wankel expander


times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)

Figure 14 119875-V diagram reciprocating engine 10-bar steam withsolenoid inlet valve

0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)

Power at 10 barsTorq at 10 bars

Figure 15 Specific power and torque reciprocating engine 10-barsteam

are shown in Figures 9 and 12 The pressure against crankangle diagram for theWankel engine shows a clear expansionof steam at low speeds The expansion effect diminishes withhigher speedsThis is better explained by the torque curve forthe same The torque developed is high at lower speeds Theclear reason for this behavior is the time taken by steam toexpand [18]The expansion of steam ismuch higher than thatof air and the energy release is clearly visible The maximumpower curve for air gives a maximum at around 1000 rpm

Table 2 Performance comparison of the engines

Wankel engine Reciprocating engineMaximum power (air) 1400Wkg 2800WkgMaximum torque (air) 080Nm 038NmMaximum power (steam) 5550Wkg 2600WkgMaximum torque (steam) 1165Nm 045Nm

whereas this for steam is at around 400 rpm This shows thehigher expansion rate of air The steam coming out of theengines being wet means that there is a phase change in theexpansion process The phase change process is slower thanthe direct expansion of air However when these are usedas bottoming cycles it is necessary to have a reduction ratioof around 10 1 to run parallel with an internal combustionengine This is due to the fact that optimum operating rpmrage of steam expanders lies within 100 to 250 whereas ICengines run optimum around 2000 rpm

The slow operation of steam does not make it a lessfavored candidate as a bottoming cycle expansionmedium Itallows the steam to build up and consumes at a slower rate aswell Once properly geared this should supply enough boosttorque through the drive train

In addition to the results obtained from testing certainissues were highlighted during testing The quality of thesteam is critical to the prolonged operation of the engine [19]A closed cycle system is hence preferred to an open cycleThe steam admission valve design is critical in the injectionof steam into the cylinder A mechanical device may be morerobust at least for the parts that are in contact with steamThe small engines may suffer from them being small so thatthe endurance of the engines is low It is anticipated to obtainbetter endurance from those engines

Proper scaling can be done when all the simulation andtest data are available for the engines

4 Conclusion and Future Work

Performance measurements have been carried out to predictthe suitability of small engines as steam expanders Theengines have been modified to suit steam expansion Theoperating speed range of steam is much lower than that ofinternal combustion engine This prevents us making directcomparisons The air tests provide a much comparable set ofdata for the expanders Comparing the maximum power andtorque data of the two engines it is evident that the Wankelengine provides a much better device as an expander

The major aim of this work is to measure the suitabilityof Rankine steam cycle as a heat recovery bottoming cycleand compare the performance of two engine types thereciprocating engine and the Wankel engine The powerand torque characteristics shown for small engines makethem very suitable for the purpose The work involves thedevelopment of complete Rankine bottoming cycle includingcontrols This includes the heat recovery system and thermalcontrol of the IC engine and the steam cycle Endurance testsneed to be done to steam engines developed to check the


longevity [3 20] Separate work is being done to develop thecontrol strategies and techniques

The scaled down dynamometer developed tomeasure theperformance of the engine provides a very useful tool forscaled model testing The torque and power curves obtainedcould be scaled up for a full size engine

The valve timing for the two-stroke engine is a sensitivefactor in the engine performance Small engines do not allowa great deal of flexibility for us to change this Only the timingcan be changed with electronic triggering In a full scaleengine much larger valves can be employed and there willbe room for finer adjustment

The tests revealed a number of areas for improvementThe reliability of the engines could be a major issue Use ofsteam oil that improves reliability is possible with a closedcycle In an open cycle this becomes an emission issue as itwill be released to the atmosphere

Using small engines to determine engine characteristicssupplies a basis for designing medium scale steam enginesThe finding can be backed up by simulations once a completeset of data are available The authors intend to do furthertesting on a larger engine with a heat recovery systemattached to an internal combustion engine

41 Engine Simulations The results can be compared withresults obtained from 1D engine simulation results Valuescan be obtained for air expansion and an optimum operatingpoint can be obtained No simulation results are presentedat this moment Initial comparisons which are not presentedhere however suggest that the measurements can be backedby simulationsThese results show that steam expanders evenat small scale are suitable devices for heat recovery bottomingcycles A full set of simulations as described above can beused for scaling up of the findings for commercial engineapplications The motoring effect and friction are expectedlyhigh in small engines as a percentage However they provideconcept proving valid statistics

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The authors would like to extend their gratitude to theEPSRC for funding the work [Grant no GRT1981001]Professor R K Stobart the principal investigator Ian Wallisand Barry Jackson of University of Sussex for their supportin conducting the research and Spirax Sarco Ltd UK forproviding steam facility and support

References

[1] P W B Semmens and A J Goldfinch How Steam LocomotivesReally Work Oxford University Press 2000

[2] G Ferrara G Manfrida and A Pescioni ldquoModel of a smallsteam engine for renewable domestic CHP (combined heat andpower) systemrdquo Energy vol 58 pp 78ndash85 2013

[3] S Jakuba and J A McGeehan ldquoComponent development ofautomotive reciprocating steam expandersrdquo SAE Prepr SAETechnical Paper 1975

[4] S Zhu K Deng and S Qu ldquoEnergy and exergy analyses ofa bottoming rankine cycle for engine exhaust heat recoveryrdquoEnergy vol 58 pp 448ndash457 2013

[5] M Badami and M Mura ldquoPreliminary design and controllingstrategies of a small-scale wood waste Rankine Cycle (RC) witha reciprocating steam engine (SE)rdquo Energy vol 34 no 9 pp1315ndash1324 2009

[6] G Bidini A Manuali and S Saetta ldquoReciprocating steamengine power plants fed by woodwasterdquo International Journalof Energy Research vol 22 no 3 pp 237ndash248 1998

[7] S B Prasad ldquoSteam engine characteristics and theoreticalperformancerdquo Energy Conversion and Management vol 34 no12 pp 1323ndash1333 1993

[8] G A Brown and D A Bowlus ldquoRotary piston expanderenginerdquo in Proceedings of the 11th ICECEC pp 1187ndash1191 1976

[9] O Badr S Naik P W OrsquoCallaghan and S D Probert ldquoExpan-sion machine for a low powerndashoutput steam Rankine-cycleenginerdquo Applied Energy vol 39 no 2 pp 93ndash116 1991

[10] J D Wade R M Tompkins G A Brown and G J SilvestrildquoRotary expander engine testing and analysisrdquo in Proceeding of18th IECEC pp 636ndash641 1983

[11] C H Lee K C Jiang P Jin and P D Prewett ldquoDesign andfabrication of a microWankel engine usingMEMS technologyrdquoMicroelectronic Engineering vol 73-74 pp 529ndash534 2004

[12] L Tartakovsky V BaibikovMGutmanMVeinblat and J ReifldquoSimulation of Wankel engine performance using commercialsoftware for piston enginesrdquo SAE Technical Papers vol 4 2012

[13] B Fu Y Lee and J Hsieh ldquoExperimental investigation of a 250-kW turbine organic rankine cycle system for low-grade wasteheat recoveryrdquo International Journal of Green Energy vol 13 no14 pp 1442ndash1450 2016

[14] R Stobart and R Weerasinghe ldquoHeat recovery and bottomingcycles for SI and CI enginesndashA perspectiverdquo SAE TechnicalPapers no 0662 2006

[15] GQiuH Liu and S Riffat ldquoExpanders formicro-CHP systemswith organic Rankine cyclerdquo Applied Thermal Engineering vol31 no 16 pp 3301ndash3307 2011

[16] F J Bayley ldquoThe saturated liquid reservoir for energy storagein hybrid vehiclesrdquo in Proceedings of the IMechE AutomobileDivision SoUthern Centre Conference on Total Vehicle Technol-ogy Challenging Current Thinking September 2001

[17] R Stobart S Hounsham and R Weerasinghe ldquoControllabilityof vapour based thermal recovery systems in vehiclesrdquo SAEInternational World Congress no 0270 2007

[18] W M S R Weerasinghe R K Stobart and S M HounshamldquoThermal efficiency improvement in high output diesel enginesa comparison of a Rankine cycle with turbo-compoundingrdquoApplied Thermal Engineering vol 30 no 14-15 pp 2253ndash22562010

[19] V Dolz R Novella A Garcıa and J Sanchez ldquoHD Dieselengine equippedwith a bottoming Rankine cycle as a waste heatrecovery system Part 1 study and analysis of the waste heatenergyrdquoAppliedThermal Engineering vol 36 no 1 pp 269ndash2782012

[20] A Nuvolari B Verspagen and N von Tunzelmann ldquoTheearly diffusion of the steam engine in Britain 1700ndash1800 areappraisalrdquo Cliometrica vol 5 no 3 pp 291ndash321 2011

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Table 1 Engine data

EngineFour strokereciprocating

engine

Wankel rotaryengine

Model OS 32 SX OS 49 PIBore (mm) 195 NAStroke (mm) 175 NACapacity (cc) 523 497Compression ratio 10 1 7 1 (approx)

p

BDCTDC Swept volume

1 2

3

45 4Condenser pressure

Clearance volume Exhaust port opens

Steam cuto

Steam chest pressure

Figure 1 Rankine cycle reciprocating expander 119875-119881 diagram

cycle expanders The reciprocating Rankine cycle has beenused in locomotives ships and stationary engines Rotaryexpanders primarily steam turbines are used in powergeneration The use of rotary engine has been restricted bythe optimum operating range it offers in comparison to thewide range offered by the reciprocating engine The use ofthe steam expander used in this study is mainly aimed asa directly coupled engine that can operate in sync with aninternal combustion engine A reciprocating engine offerssimilar torques power characteristics to an IC engine Theother main advantage is the availability of small engines thatcan be converted into steam expanders

111 Rankine Cycle with a Reciprocating Expander A recip-rocating Rankine cycle shown in Figure 1 is explained by thefollowing steps

(1-2) Admission of steam at steam chest pressure

(2-3) Expansion of steam until the exhaust port isopen

(3-41015840) Blow down of the steam to condenser pressure

(4-5) Exhaust of steamuntil the exhaust port is closed

(5-1) Compression of steam left in the cylinder

The work and heat for the cycle can be found done byobtaining the specific enthalpies ℎ

119899 where 119899 refers to steps in

Figure 1 The theoretical work by the cycle is given by ℎ2ndashℎ3

and the heat supplied is given by ℎ2minusℎ1The efficiency is given

by

120578 =(ℎ2minus ℎ3)

(ℎ2minus ℎ1) (1)

The pump work is neglected as it is small compared tothe heat in Reciprocating steam expanders were the mostcommon type of expanders known for their high torqueand simple operation These are mostly used as marine andold locomotive prime movers The speed achievable fromlarge steam engines is limited Uniflow and counter-flowarrangements are possible with reciprocating expanders [1]However the valve arrangements become more complexwith counter-flow arrangement [5] Reciprocating enginesare perceived to be easier to implement thanWankel engines[6]

112 Rotary Steam Engines Steam turbines are efficientdevices but the range of operation is limited hence not verysuitable for automotive applications The major attraction ofthe turbine cycle is the high overall efficiency in operationHowever the flexibility of operation outweighs the efficiencyfactor and makes the reciprocating Rankine cycle morepractical In addition the ability to cater to fluctuating torqueand velocity conditions of the reciprocating cyclemakes it thepreferred device for automotive applications Nevertheless ifthe energy developed in a turbine is converted into electricityand used to drive an electric motor it leads to a practicalsolution for hybrid vehicles [7]

An intermediate solution is the Wankel rotary expander[8] Wankel engine offers some advantages of both theturbine cycle and the flexibility of the reciprocating engine [910] Micro-Wankel engines can be fabricated with improvedfabrication technology [11] Attempts have been made tocorrectly emulate the operation of the Wankel engine [12]but the current application is using steam as the working fluidwithout internal combustion Figure 2 shows the theoreticalRankine cycle and the pressure volume diagram of a Rankinecycle

12 Waste Heat Recovery The major attraction of Rankinecycle [13] today is its applicability in the waste heat recoverysystems [12] In power generation Rankine turbines aredriven by steam generated through waste heat recovery Useof reciprocating engines in waste heat recovery systems isseldom On the other hand use of rotary steam engines insmall scale applications is not common Ability of Rankinecycle to operate on low grade heat sources such as steammakes it attractive to employ in a bottoming cycle [14] Twomain types of expanders have been applied in Rankine cycleapplications that are of two types first one is the velocity typesuch as axial turbines and radial-flow turbines the other ispositive displacement type such as scroll expanders screwexpanders piston expanders and rotary vane expanders [15]These expanders feed off a steam reservoir courtesy of heatrecovery in a bottoming cycle [16 17]


T

WinQout

Qout

Wout

4

1

2

3


S

Win

Qin

Qin

Wout

4

1 2

3

Expander

pump

Condenser

Steamaccumulator

1 2

34

Chest pressure

Exhaust pressure

p










Computer

Motorcontroller



Opticalencoder

Torquetransducer

Steam

Engine

Reheater

Motor

Condenser

Scale






Pressure transducer

Temperature sensor



Steam generation

Control Control






Steam in

Torque meter

Injector

To main sha

Steam

Engine

TP





119875 = 2120587119873119879 (2)




ℎre minus ℎri =119881119868119905

119872 (3)



Steam in

Enginecasing

T

P T

Coupling tomain sha

Steam out


Δe = VIt

prepri

TreTri

ri

re

T

s







3

4

5

6

7

8

9

10

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle

100 rpm

100 rpm

2300 rpm

2300 rpm




2300 rpm

100 rpm

3

4

5

6

7

8

9

10

Pres

sure

(bar

)

2 3 4 51










PowerTorque

Speed (rpm)25002000150010005000

0

10

20

30

40

Pow

er (W

)

0

02

04

06

08

Torq

ue (N

m)




200 rpm

200 rpm

1700 rpm

1700 rpm

6

8

10

12

14

16

18

20

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle






1 15 2 25 3 35 4 545


4

5

6

7

8

9

10

11

12

13

14

Pres

sure

(bar

)

200 rpm

200 rpm



times104

3

35

4

45

5

55

6

Spec

ic p

ower

(wat

ts)

0

2

4

6

8

10

12

Torq

ue (N

m)

400 600 800 1000 1200 1400 1600 1800 2000 2200200Speed (rpm)



bars







times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)


0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)






















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










T

WinQout

Qout

Wout

4

1

2

3


S

Win

Qin

Qin

Wout

4

1 2

3

Expander

pump

Condenser

Steamaccumulator

1 2

34

Chest pressure

Exhaust pressure

p










Computer

Motorcontroller



Opticalencoder

Torquetransducer

Steam

Engine

Reheater

Motor

Condenser

Scale






Pressure transducer

Temperature sensor



Steam generation

Control Control






Steam in

Torque meter

Injector

To main sha

Steam

Engine

TP





119875 = 2120587119873119879 (2)




ℎre minus ℎri =119881119868119905

119872 (3)



Steam in

Enginecasing

T

P T

Coupling tomain sha

Steam out


Δe = VIt

prepri

TreTri

ri

re

T

s







3

4

5

6

7

8

9

10

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle

100 rpm

100 rpm

2300 rpm

2300 rpm




2300 rpm

100 rpm

3

4

5

6

7

8

9

10

Pres

sure

(bar

)

2 3 4 51










PowerTorque

Speed (rpm)25002000150010005000

0

10

20

30

40

Pow

er (W

)

0

02

04

06

08

Torq

ue (N

m)




200 rpm

200 rpm

1700 rpm

1700 rpm

6

8

10

12

14

16

18

20

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle






1 15 2 25 3 35 4 545


4

5

6

7

8

9

10

11

12

13

14

Pres

sure

(bar

)

200 rpm

200 rpm



times104

3

35

4

45

5

55

6

Spec

ic p

ower

(wat

ts)

0

2

4

6

8

10

12

Torq

ue (N

m)

400 600 800 1000 1200 1400 1600 1800 2000 2200200Speed (rpm)



bars







times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)


0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)






















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











Pressure transducer

Temperature sensor



Steam generation

Control Control






Steam in

Torque meter

Injector

To main sha

Steam

Engine

TP





119875 = 2120587119873119879 (2)




ℎre minus ℎri =119881119868119905

119872 (3)



Steam in

Enginecasing

T

P T

Coupling tomain sha

Steam out


Δe = VIt

prepri

TreTri

ri

re

T

s







3

4

5

6

7

8

9

10

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle

100 rpm

100 rpm

2300 rpm

2300 rpm




2300 rpm

100 rpm

3

4

5

6

7

8

9

10

Pres

sure

(bar

)

2 3 4 51










PowerTorque

Speed (rpm)25002000150010005000

0

10

20

30

40

Pow

er (W

)

0

02

04

06

08

Torq

ue (N

m)




200 rpm

200 rpm

1700 rpm

1700 rpm

6

8

10

12

14

16

18

20

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle






1 15 2 25 3 35 4 545


4

5

6

7

8

9

10

11

12

13

14

Pres

sure

(bar

)

200 rpm

200 rpm



times104

3

35

4

45

5

55

6

Spec

ic p

ower

(wat

ts)

0

2

4

6

8

10

12

Torq

ue (N

m)

400 600 800 1000 1200 1400 1600 1800 2000 2200200Speed (rpm)



bars







times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)


0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)






















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Steam in

Enginecasing

T

P T

Coupling tomain sha

Steam out


Δe = VIt

prepri

TreTri

ri

re

T

s







3

4

5

6

7

8

9

10

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle

100 rpm

100 rpm

2300 rpm

2300 rpm




2300 rpm

100 rpm

3

4

5

6

7

8

9

10

Pres

sure

(bar

)

2 3 4 51










PowerTorque

Speed (rpm)25002000150010005000

0

10

20

30

40

Pow

er (W

)

0

02

04

06

08

Torq

ue (N

m)




200 rpm

200 rpm

1700 rpm

1700 rpm

6

8

10

12

14

16

18

20

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle






1 15 2 25 3 35 4 545


4

5

6

7

8

9

10

11

12

13

14

Pres

sure

(bar

)

200 rpm

200 rpm



times104

3

35

4

45

5

55

6

Spec

ic p

ower

(wat

ts)

0

2

4

6

8

10

12

Torq

ue (N

m)

400 600 800 1000 1200 1400 1600 1800 2000 2200200Speed (rpm)



bars







times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)


0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)






















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











PowerTorque

Speed (rpm)25002000150010005000

0

10

20

30

40

Pow

er (W

)

0

02

04

06

08

Torq

ue (N

m)




200 rpm

200 rpm

1700 rpm

1700 rpm

6

8

10

12

14

16

18

20

Pres

sure

(bar

)

50 100 150 200 250 300 3500Crank angle






1 15 2 25 3 35 4 545


4

5

6

7

8

9

10

11

12

13

14

Pres

sure

(bar

)

200 rpm

200 rpm



times104

3

35

4

45

5

55

6

Spec

ic p

ower

(wat

ts)

0

2

4

6

8

10

12

Torq

ue (N

m)

400 600 800 1000 1200 1400 1600 1800 2000 2200200Speed (rpm)



bars







times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)


0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)






















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










times 41 2 3 40

0

4

8

12

200 p3 r m00 p

5 r00

Volume (m3)


0

01

02

03

04

05

Torq

ue (N

m)

0

500

1000

1500

2000

2500

Spec

ic p

ower

(wat

ts)

250 300 350 400 450 500 550 600200Speed (rpm)






















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation


















Acknowledgments


References





















RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









small engines as bottoming cycle steam expanders for

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