Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: To reduce exhaust gas emissions in diesel engines and for engine upgrade purposes the
major parameters and equipment that should be looked at are boost pressure, intake
charge temperature, combustion chamber design and fuel injection equipment. Boost
pressure is governed by the turbo-charger; with high-efficiency variable geometry turbochargers,
effective control is possible to increase airflow rate at all operating conditions
of the engine. Efficient air-to-air inter-cooling results in the engine being filled with a
cooler air charge that will influence engine durability and heat rejection to the cooling
system. The main objective of the investigation is to look at the influence of boost
pressure and intake charge temperature on diesel combustion to better understand the
processes where boost pressure is increased and intake charge temperature reduced to
increase the brake mean effective pressure of the engine and reduce emissions generation.
By running an engine at different intake boost pressures and intake charge temperatures a
25-point matrix was formed at three different operating conditions. On completion of the
engine testing, data processing and data evaluation, a number of important conclusions
were made about the behaviour of the engine running under different conditions. This
enabled the researcher to understand how boost pressure and intake charge temperature
influence engine power output, fuel consumption, engine durability and exhaust gas
emissions. The opinion is proved when, in most cases, the 75 test points were used to
build multiple linear regression models to determine which engine parameters (dependent
variables) have a significant effect on emissions generation and durability parameters.
From the data it is evident that boost pressure has a positive influence on most engine
parameters, as an increase in boost pressure results in an increase in air mass flow
through the engine. An increase in air mass flow reduces combustion chamber gas
temperature as the result of an increase in excess air ratio during combustion.
A further result of the increase in excess air ratio is that less soot is formed during the
first part of combustion and more soot and partly decomposed Hydrocarbon (HC)
compounds are oxidised during the late combustion phase. Therefore, with an increase in
boost pressure, Bosch smoke emissions reduce, but with a change in intake air
temperature no difference in smoke concentration is seen except at the very low boost
pressure and very high boost temperature test points where low air/fuel ratios exist and
the slight increase in air-flow rate as a result of lower air inlet temperature has a big
influence.
Nitric Oxide (NO) emissions, on the other hand, are more dependent on intake air
temperature than on boost pressure, which was proved in the multiple regressions
modelling performed on the test data. The flame zone and the post-flame zone
temperature play the dominant role in NO formation. As explained in the results
discussion on NO formation, intake air temperature influences the ignition mixture
temperature and the subsequent flame zone temperature. A lower intake air condition
results in longer ignition delay and increases the initial rate of combustion. / AFRIKAANSE OPSOMMING: Die hoofparameters en toerusting wat in ag geneem moet word om uitlaatgasemissies in
dieselenjins te verminder en om enjinkraguitset te verhoog, is inlaatdruk, inlaat
lugtemperatuur, verbrandingskamerontwerp en brandstofinspuittoerusting. Inlaatdruk
word beheer deur die turb-aanjaer. Met hoë effektiwiteit, veranderlike geometrie turboaanjaging,
is effektiewe beheer moontlik om lugvloei-tempo deur die enjin te verhoog
onder alle enjinwerkstoestande. Effektiewe lug-tot-lug tussenverkoeling laat die enjin
met koeler inlaatlug vul, wat 'n uitwerking het op enjinlewensduur en hitte-verlies na die
verkoelingsstelsel. Die hoofdoel van die navorsing is om die invloed van inlaatdruk en
inlaat lugtemperatuur op dieselverbranding te ondersoek. Sodoende kry die navorser 'n
beter begrip omtrent die prosesse waar inlaatdruk verhoog en inlaat lugtemperatuur
verlaag word, om rem-gemiddelde effektiewe druk van die enjin te verhoog en uitlaatgas
emissies te verlaag.
'n 25-punt matriks is opgestel deur die enjin by verskillende inlaatdrukke en inlaat
lugtemperture te opereer, en by drie verskillende wringkragwerkstoestande. 'n Aantal
belangrike gevolgtrekkings is gemaak omtrent enjinwerking onder verskillende
werkstoestande na voltooiing van die enjintoetse, dataverwerking en data-evaluering.
Sodoende het die navorser bepaal hoe inlaatdruk en inlaat lugtemperatuur kraglewering,
brandstofverbruik, enjinlewensduur en uitlaatgasemissies beïnvloed. Om bogenoemde
begrippe verder te ondersteun is 'n meervoudige, lineëre regressiemodel opgestel om te
bepaal watter enjinparameters (afhanklike veranderlikes) 'n wesenlike effek op emissiegenerasie
en lewensduur het.
Van die data word afgelei dat inlaatdruk 'n positiewe effek op die meeste enjinparameters
het, omdat hoër inlaatdruk die lugvloeitempo deur die enjin verhoog. Hoër lugmassavloei
verminder verbrandingsgastemperatuur as gevolg van 'n hoër oortollige lugverhouding
tydens verbranding.
'n Verdere gevolg van 'n hoër oortollige lugverhouding is dat minder roet gevorm word
gedurende die eerste verbrandingsfase en meer roet en gedeeltelik verbrande
koolwaterstofverbindings oksideer gedurende die finale verbrandingsfase. Dus, met 'n
hoër inlaatdruk word Bosch rookemmissies verlaag. Geen wesenlike verandering in
rookkonsentrasies word egter gesien met 'n verandering in inlaatlugtemperatuur nie,
behalwe by baie lae inlaatdruk- en hoë inlaat lugtemperatuur-toetskondisies waar lae
lug/brandstofverhoudings bestaan en 'n klein toename in lugmassavloei as gevolg van
laer inlaat lugtempertuur'n groot invloed het.
Stikstofmonoksied (NO) emissies is meer afhanklik van inlaat lugtemperatuur as
inlaatdruk. Dit is bewys in die meervoudige regressiemodel. Die vlamsone- en die navlamsone-
temperatuur speel 'n groot rol in NO vorming. Inlaat lugtemperatuur beïnvloed
die temperatuur van die onstekingsmengsel en die daaropvolgende vlamsonetemperatuur.
'n Laer inlaat lugtemperatuur veroorsaak 'n langer onstekingsvertraging en
verhoog die aanvanklike verbrandingstempo.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52520 |
| Date | 12 1900 |
| Creators | Emslie, Lovell Donald |
| Contributors | 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 | English |
| Type | Thesis |
| Format | 181, [6] p. : ill. |
| Rights | Stellenbosch University |
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