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.

This work focuses on the cooling of diesel engines. Facing heavy constraints such<p>as emissions control or fossil energy management, political leaders are forcing car<p>manufacturers to drastically reduce the fuel consumption of passenger vehicles. For<p>instance, in Europe, this fuel consumption has to reach 120 g CO2 km by 2012, namely 25 % reduction from today's level.<p>Such objectives can only be reached with an optimization of all engines components<p>from injection strategies to power steering. A classical energy balance of an internal<p>combustion engine shows four main losses: enthalpy losses at the exhaust, heat<p>transfer to the cylinder walls, friction losses and external devices driving. An<p>optimized cooling will improve three of them: the heat transfer losses by increasing<p>the cylinder walls temperature, the friction losses by reducing the oil viscosity and<p>the coolant pump power consumption.<p>A model is first built to simulate the engine thermal behavior from the combustion<p>itself to the temperatures of the different engine components. It is composed by two<p>models with different time scales. First, a thermodynamic model computes the in cylinder<p>pressure and temperature as well as the heat flows for each crank angle.<p>These heat flows are the main input parameters for the second model: the nodal<p>one. This last model computes all the engine components temperatures according<p>to the nodal model theory. The cylinder walls temperature is then given back to<p>the thermodynamic model to compute the heat flows.<p>The models are then validated through test bench measurements giving excellent<p>results for both Mean Effective Pressure and fluids (coolant and oil) temperatures.<p>The used engine is a 1.9l displacement turbocharged piston engine equipped with<p>an in-cylinder pressure sensor for the thermodynamic model validation and thermocouples<p>for the nodal model validation.<p>The model is then used to optimize the coolant mass flow rate as a function of<p>the engine temperature level. Simulations have been done for both stationary<p>conditions with effciency improvement up to 7% for specific points (low load, high<p>engine speed) and transient ones with a heating time improvement of about 2000s.<p>This gains are then validated on the test bench showing again good agreement. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished