Thesis (MScEng)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Realisation of the depletable nature of fossil fuel has increased the need for its optimal
use. Increasing global pressure to reduce the emission of greenhouse gases and other
harmful gases that affect the chemical cycles or destroy the greenhouse gases in the
tropospheric ozone, has attracted a increased worldwide concern. Waste heat recovery
devices have been around for more than 50 years and researches and scientists have
been very much involved in identifying the correct type of systems to meet the
requireme?ts of industries and mankind more efficiently. Waste heat can be identified
in the form of unburned but combustible fuel, sensible heat discharges in drain water,
and latent and sensible heat discharge in exhaust gases.
In this project the feasibility of a small scale waste heat recovery system has been
investigated. Sets of preliminary investigations were performed to evaluate the
amount of waste heat that can be extracted from the exhaust gases of typical diesel
powered truck engines. A waste heat recovery unit was designed, implemented and
evaluated through simulation and experimental investigations.
Preliminary calculations were performed usmg the readings presented by
Koorts (1998) for a typical 6-litre diesel engine. The calculations showed that it is
possible to extract about 77kW of waste heat from the exhaust gases from such an
engine. A simple Rankine cycle was then investigated to be operated on the waste
heat recovered. The optimal parameters for such a Rankine cycle was determined
using a spreadsheet program and was found to be an optimal pressure of 800kPa with
a temperature of 227.2°C and a water mass flow rate of 0.0015kgls as the working
fluid. For such a Rankine cycle, based on the efficiencies of commercially available
pumps, turbines and heat exchangers it was found that it is possible to extract 2782kW
of power per unit mass flow rate of water.
The next stage of the project was designing and implementing an exhaust gas pipe
network from the engine test cells at the Centre for Automotive Engineering (CAE)
located on the ground floor to the Energy Systems Laboratory (ESL) at the first floor.
This pipe network was equipped with a valve system that can be operated from the
ESL and allows the selection of the route of the exhaust gases and two bellows to compensate for thermal expansion. A continuous combustion unit was also linked to
the exhaust gas supply pipes as an alternative source of exhaust gases. The waste heat
exchanger designed and selected was purchased and linked into the exhaust gas
stream after calibration tests were carried out on the same in the wind tunnel. The
water supply and a steam separator were then connected to the waste heat exchanger.
In the final experimental stage of the project, two sets of tests were carried out. The
first set of tests was performed using exhaust gases from the continuous combustion
unit and the second using exhaust gases from the internal combustion engines in CAE.
Superheated steam was obtained in both cases indicating the possibility of operating a
turbine with the dry steam generated. With exhaust gases originating from the
continuous combustion unit, an air fuel ratio of9.14:1 was used and exhaust gases at a
temperature of 540°C were obtained with an air inflow of 1400kglh and a fuel
consumption rate of7.11 kg/h. The exhaust gases degraded to 360°C at the waste heat
recovery inlet due to losses through the bare pipes. 11.12kW of energy was extracted
from the exhaust gases to the water stream with an efficiency of 98%. With the
exhaust gases from the 10-litre diesel internal combustion engine, an exhaust gas flow
rate of O.22kgls was used and with a heat transfer efficiency of 89%, 18.5kW of
power was extracted at the waste heat recovery unit. This represents a 4.9% of the
thermal content of the fuel used. A rate of energy production balance on the internal
combustion engine showed that 34% is lost in exhaust gases and 29% in coolant and
other losses while only 37% is used produced as shaft power.
The results obtained therefore show that there is ample room for further investigation
for the use afwaste heat in exhaust gases of typical diesel engines.
It can therefore be concluded that the aims of the project that were to set up a testing
facility and an exhaust gas pipe network and evaluation of a small scale waste heat
recovery apparatus were achieved.
The tests performed can still be optimised with more waste heat removal from the
exhaust gases of typical diesel truck engines and hence better recovery of waste heat
and a reduction of fuel consumption. / AFRIKAANSE OPSOMMING: Met die besef van die kwynende beskikbaarheid van fosielbrandstof het die
behoefte vir die optimale benutting van die brandstof toegeneem. Toenemende
globale druk om die emissies van groenhuis gasse en ander gevaarlike gasse wat
chemiese siklusse beïnvloed in die troposfeer te verrniner, geniet wêreldwye
aandag. Oorskotenergie-toestelle is alreeds beskikbaar die afgelope 50 jaar en
navorsers en wetenskaplikes was tot op hede betrokke met die identifisering van
die korrekte tipe sisteme om meer effektief aan die industrie en samelewing se
behoeftes te voldoen. Oorskotenergie bestaan uit onder andere onverbrande
maar brandbare brandstof, voelbare warmte in dreinwater, en latente en voelbare
warmte in uitlaatgasse.
In hierdie projek word die lewensvatbaarheid van 'n kleinskaal oorskotenergie
herwinningsisteem ondersoek. Voorlopige ondersoeke was gedoen om die
hoeveelheid oorskotenergie te bepaal wat herwin kan word uit die uitlaatgasse
van 'n tipiese 6 liter vragmotor dieselenjin. 'n oorskotenergie
herwinningseenheid was ontwerp, geïmplimenteer en ge-evalueer deur similasies
en eksperimentele ondersoeke.
Voorlopige berekeninge was uitgevoer op data wat deur Koorts (1998)
saamgestel is vir 'n tipiese vragmotor dieselenjin. Die berekeninge toon dat dit
moontlik is om ongeveer 77kW oorskotenergie van die uitlaatgasse van so enjin
te onttrek. Die moontlikheid was toe ondersoek om die herwinne energie te
gebruik om 'n eenvoudige Rankine siklus aan te dryf. Die optimale parameters
vir die Rankine siklus was bereken deur van 'n sigblad program gebruik te maak
en dit was gevind dat die optimale druk is 800kPa, die optimale temperatuur is
227.2°C teen 'n water massa vloeitempo van 0.0015kg/s. Vir so 'n Rankine
siklus, gebaseer op die effektiwiteit van kommersiële beskikbare pompe, turbines
en warmteruilers, was dit gevind dat dit moontlik is om 2782kW drywing per
eenheidsmassa vloeitempo van water, te onttrek. Die volgende stadium van die projek was die ontwerp en implimentering van 'n
uitlaatgas pypnetwerk vanaf die toetsselle van die Centre for Automotive
Engineering (CAE) op die grondvloer na die Energy Systems Laboratory (ESL)
op die eerste vloer. Die pypnetwerk was toegerus gewees met 'n kleptstelsel wat
vanaf ESL bedryf kan word en wat dit moontlik maak om die roete van die
uitlaatgasse te beheer. Twee samedrukbare koppelstukke was ook ingesluit in
die lang reguit pypseksie om vir termiese uitsetting te kompenseer. 'n
Aaneenlopende verbrandingseenheid was ook gekoppel met die uitlaatgasse
toevoerpype as 'n alternatiewe bron van uitlaatgasse. Die oorskotenergie
warmteruiier wat ontwerp en geselekteer was, was aangekoop en opgekoppel
met die uitlaatgas-stroom nadat kalibrasie toetse op die warmteruiier gedoen was
in 'n windtonnel. Die watertoevoer en 'n stoomskeier was gekoppel aan die
oorskotenergie warmteruiler.
Twee toetse was uitgevoer in die finale eksperimentele stadium van die projek.
Die eerste stel toetse was uitgevoer deur gebruik te maak van die uitlaatgasse van
die aaneenlopende verbrandingseenheid en met die tweede toets is van die
uitlaatgasse van die interne verbrandingsenjins van CAE gebruik gemaak.
Oorverhitte stoom was verkry in beide gevalle en wys dus dat daar 'n
moontlikheid is om 'n turbine met droë stoom aan te dryf. 'n Lug tot brandstof
verhouding van 9.14 : 1 was gebruik gewees in die aaneenlopende
verbrandingseenheid om uitlaatgasse te verskaf teen 540°C. Die
massavloeitempo van die lug was 1400kg/h en die brandstof 7.11kg/h. Die
uitlaatgasse se temperatuur het afgeneem tot 360°C tot voor die oorskotenergie
herwinningseenheid as gevolg van hitteverliese vanaf die ongeïsoleerde
pypnetwerk. 11.12kW energy was onttrek vanaf die uitlaatgasse en oorgedra aan
die waterstroom met 'n effektiwiteit van 98%. Die 10 liter diesel interne
verbrandingsenjin het uitlaatgas gelewer met 'n massa vloeitempo van O.22kg/s.
18.5kW energie was herwin gewees met 'n effektiwiteit van 89%. Dit
verteenwoording 4.9% van die termiese inhoud van die brandstof gebruik. 'n
Energie balans op die interne verbrandingsenjin het getoon dat 34% energie gaan verlore in die uitlaatgasse, 29% word aan die verkoelingsmiddeloorgedra en
37% is bruikbare meganiese drywing.
Die resultate wat verkry is, wys daarop dat daar nog groot ruimte is vir verdere
ondersoeke in die gebruik van oorskotenergie in uitlaatgasse van tipiese
vragmotor dieselenjins.
Die gevolgtrekking kan dus gemaak word dat die doelwitte van die projek
naamlik die opstel van 'n toetsfasiliteit, installering van 'n uitlaatgasse
pypnetwerk en die toets van a kleinskaalse oorskotenergie herwinningseenheid,
bereik was.
Die toetse wat uitgevoer was kan nog ge-optimeer word om meer energie te
herwin vanaf die uitlaatgasse van 'n tipiese vragmotor dieselenjin om sodoende
beter brandstofverbruik te bewerkstellig.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52179 |
| Date | 12 1900 |
| Creators | Lotun, Devprakash |
| Contributors | Harms, T. M., Taylor, A. B., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 1 v. (various foliations) : ill. |
| Rights | Stellenbosch University |
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