Characterisation of synergestic and antagonistic petrol component chemical class effects on octane blending behaviour

Thesis (MEng)--Stellenbosch University, 2020.ENGLISH ABSTRACT: Knock free operation has influenced the development of internal combustion (IC) engine technology and spark ignition (SI) fuels. Knock is the noise associated with the harmful and abnormal combustion phenomenon known as autoignition. For a given engine configuration, the propensity of knock in IC engines depends primarily on the anti-knock quality of the fuel. Research octane number (RON) and motor octane number (MON) are measured fuel properties indicating a fuel s resistance to autoignition. Fuel producers ultimately seek to produce fuels with RON and MON values suitable for modern IC engines, however, the highly complex non-linear blending interactions between the constituents of the fuel recipe make this challenging. The present research was undertaken to characterise the non-linear synergistic and antagonistic octane blending behaviours between important common chemical class components, carefully selected to represent the SI fuel recipe on a fundamental level. The RON and MON values for all binary combinations of these components at various blend ratios were measured using Stellenbosch University’s uniquely modified Cooperative Fuels Research engine. All octane experiments were performed in accordance with the American Society for Testing and Materials D2699 and D2700 standards. The measured RON and MON data showed results consistent with the literature and highlighted a shortage of research data for some binary blends. The project hypothesis was supported, showing that non-linearities do exist in octane blending between binary combinations and that more than one non-linearity can exist in a binary blend. Using this and the measured data, conclusions were drawn on the links between the various chemical classes, blending ratios and the non-linearities in octane number. It was demonstrated that octane sensitivity is a function of blend ratio and provides insight into improving fuel recipes for modern SI engines. The octane boosting capabilities of a non-metallic octane booster, was shown to significantly boost the octane of some of the selected components and had no significant effect on others. It was found to influence the RON value more than the MON value of a blend. The suitability of two well established empirical octane prediction models were investigated for use in predicting octane. The predicted data was compared to the measured data and deficiency in the better performing model was identified and then optimised to improve the octane predictions for the binary blends.AFRIKAANSE OPSOMMING: Die ontwikkeling van binnebrand motor-tegnologie en vonkontsteking (VO) brandstowwe word beïnvloed deur die vereiste vir klopvrye werking van die enjin. Klop is die geraas verwant aan die skadelike en abnormale verbrandingsverskynsel wat bekend staan as outo-ontsteking. Die neiging tot klop vir ‘n gegewe binnebrand motor konfigurasie, is hoofsaaklik afhanklik van die anti-klop kwaliteit van die brandstof. Die navorsingsoktaansyfer (NOS) en mo- toroktaansyfer (MOS) is meetbare brandstof eienskappe wat ‘n aanduiding gee van die brandstof se weerstand teen outo-ontsteking. Brandstof vervaardigers poog om brandstowwe, met gepaste NOS en MOS waardes, vir moderne binne- brand motors te vervaardig, hoewel die hoogs gekompliseerde meng interaksies tussen die samestellende komponente van die brandstofresep ‘n uitdaging is. Die huidige navorsing is onderneem om die nie-lineere saamwerkende en teenstrydige oktaan meng gedragte tussen belangrike alledaagse chemise-klas komponente te karakteriseer. Die voorafgaande is sorgvuldig gekies om die VO brandstofresep op ‘n fundamentele vlak te verteenwoordig. Die NOS en MOS waardes vir alle binere kombinasies van hierdie komponente is gemeet by verskeie mengselverhoudings met behulp van die Universiteit van Stellenbosch se uniek gewysigde Samewerkende Brandstof Navorsings (SBN) motor. Alle oktaan eksperimente is uitgevoer in ooreenstemming met die Amerikaanse Vereniging vir Toetsing en Materiale se D2699 en D2700 standaarde. Die afgemete NOS en MOS data het resultate gelewer wat konsekwent is met die literatuur en het die tekort aan navorsingsdata vir binere mengsels beklemtoon. Die projek se hipotese is ondersteun deur te toon dat nie-lineere gedrag wel bestaan in oktaan menging tussen binere kombinasies van die komponente en dat meer as een nie-lineere verwantskap (saamwerkend en teen- strydig) kan bestaan in so ‘n mengsel kombinasie. Deur gebruik te maak van hierdie resultaat en die afgemete data, is daar gevolgtrekkings gemaak met betrekking tot die verwantskap tussen verskeie chemiese klasse, mengsel verhoudings en die nie-lineeriteite in die oktaan syfer. Daar is gedemonstreer dat oktaan sensitiwiteit ‘n funksie van meng-verhoudings is wat bydra tot die verbetering van brandstofresepte vir moderne VO motors. Die oktaan aanjagingsvermoe van ‘n nie-metaal oktaan aanjaer (NMOA) het n beduidende verhewing in die oktaan van sekere van die geselekteerde komponente gehad, terwyl dit geen beduidende efek op ander gehad het nie. Daar is gevind dat dit ‘n groter invloed op die NOS waarde van ‘n mengsel het as wat dit op die MOS waarde van ‘n mengsel het. Die gepastheid van twee goed gevestigde empiriese oktaan voorspellingsmodelle is ondersoek. Die voorspelde data is vergelyk met die afgemete data en tekortkominge in die model wat die beste gepresteer het, is geïdentifiseer en is vervolgens geoptimeer om by te dra tot die verbetering van oktaan voorspellings vir binere mengsels.Master