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In response to the global concerns towards oil scarcity and climate change, the automotive industry is currently focusing on improving fuel economy and reducing exhaust emissions. Modern downsized gasoline engines that come with a package that includes a boosting system, variable valve train and direct fuel injection system is effective for fuel economy improvement and emission reduction. However, the knocking issue becomes severe at high load operations as a result of the high intake boosting pressure. In regard to the part load conditions, the gas exchange process requires extra work to draw in air into the cylinder due to a lower amount of pressure in the intake manifold caused by the restriction of the throttle plate. The Miller cycle is regarded as a potential strategy of knock control for downsized gasoline engines. Extensive works have sought to examine the performance improvement via the Miller cycle, yet only limited research has been conducted on the manner in which it can influence knock suppression. The focus of this thesis is to investigate early and late intake valve closing timings in terms of how they affect the compression process, the ability to suppress engine knock and meet the power output required at high loads for spark-ignited gasoline engines. Apart from that, this research also demonstrates the Miller cycle potential by utilising fully variable valve timing in controlling the load at the part load condition without using a throttle. The early intake valve closing with different valve lifts was tested in order to investigate the impact during the gas exchange process, particularly the pumping losses and the potential to improve fuel economy. This study includes both experimental and simulation studies. A Lotus single-cylinder research engine referred to as SCORE was mainly used for the experimental component of the study. The simulation work was conducted using a one-dimensional spark ignition engine model built in the Ricardo WAVE software for naturally-aspirated and downsized engines. The engine model values are validated against the experimental values from the Lotus SCORE and Lotus SABRE engines. The combustion model with a reduced kinetics mechanism was validated using a Rover K-series engine. A broad matrix of the engine operations has been investigated combining a variety of engine speeds and engine loads. The Miller cycle effects on knock suppression in a downsized engine environment have been investigated in three parts, namely the Miller cycle at different speed-load, knock suppression with extreme Miller cycle, and knock analysis with combustion kinetics. Through the works, the Miller cycle has demonstrated its capability to suppress engine knocking in a more efficient manner as opposed to the standard engine operation. This is contributed by the fact that early and late intake valve closings could affect the end gas condition at the end of the compression stroke, thus making it possible to suppress the engine knocking. The experimental study for controlling load without using throttle under the naturally-aspirated condition found that the Miller cycle with an early intake calve closing strategy able to improve fuel consumption by reducing pumping losses. The downsized engine condition, which has been evaluated via modelling work, also showed an improved performance trend using the unthrottled Miller cycle strategy. The open cycle and close cycle efficiencies have improved through the Miller cycle implementation. The contribution of this work is made in order to establish the comparison of the Miller cycle strategy in suppressing knocking between the early intake valve closing and late intake valve closing under a boosted environment. For the part load condition of the downsized engine, the research contributes to the existing body of knowledge by comparing the throttle-less Miller cycle and the standard throttled operation as a load control strategy.

Carbonaceous engine deposits tend to accumulate on most of the inner surfaces of the car engine. The presence of these deposits leads to a deteriorated efficiency of the engine and a number of adverse effects, such as higher propensity of the engine to knock. It has been proposed that selective adsorption of some of the fuel components in the porous deposits (and changing composition of the pre-combustion fuel) could be a contributing mechanism of the diminished efficiency of the engine. This, as well as other mechanisms of the deposits action, crucially depend on the porous structure of the material. Therefore, the aim of this investigation is to develop a method, which is able to accurately characterize the internal porous structure of the engine deposits and predict their adsorption properties at different conditions. This should allow us to assess whether the selective adsorption of fuel components is indeed a plausible contributing mechanism to the diminished performance of the engine. Accurate characterization of the engine deposits faces several difficulties due to their complex porous structure and chemical composition. A widely adopted approach in the characterization of activated carbons, which combines molecular simulation, specifically grand canonical Monte Carlo (GCMC) in slit pores, and experimental adsorption isotherms, is the starting point for the method suggested in this work. In this thesis, we will demonstrate that, by systematic modification of the solid-fluid interaction in the molecular simulation, we are able to correctly account for the chemical structural heterogeneity of the samples used. The new parameters of solid-fluid interaction allow us to extract representative pore size distributions and investigate the adsorption properties under different conditions of temperature and pressure, based on the obtained pore size distribution. Specifically, using the experimental data from a single ethane isotherm at 278K we accurately predict ethane adsorption at other temperatures and in different samples. Additionally, the proposed method is able to predict the adsorption of more complex hydrocarbons, i.e. n-butane and isobutane. The performance of the method is assessed by comparing the simulations results with the experimental adsorption measurements data on the engine deposits samples. Another important capability of the method is that it enables us to generate adsorption predictions of two key components commonly used to represent the combustion properties of the fuel, n-heptane and isooctane. We explore the equilibrium adsorption properties of these components based on the determined pore size distributions of the deposit samples. The results presented in the thesis highlight the importance of the adsorption in the internal porous structure of the engine deposits. The present study reinforces the value of molecular simulation combined with a limited number of experimental measurements, to accurately characterize heterogeneous carbonaceous materials and to make predictions at different conditions with sufficient precision.

Increasing the efficiency of the spark-ignition engine can help to reduce the environmental impact of the transportation sector. Engine knock obstructs the increased efficiency that could be gained by increasing the compression ratio in a spark-ignition (SI) engine. A fuel’s propensity to knock is measured by the research octane number (RON) and the motor octane number (MON) in a co-operative fuel research (CFR) engine. A fuel’s octane sensitivity (OS) is the difference between the RON and MON. Modern downsized and turbocharged engines operate at what is considered to be beyond-RON conditions. Studies have shown that having a fuel with higher OS improves knock resistance at beyond-RON conditions. This study aims to gain a better understanding of the role of intermediate-temperature heat release (ITHR) in defining OS and its subsequent impact on SI operation through the experimental framework. The ITHR of toluene primary reference fuels (TPRFs) fuels with matching RON and varying OS was studied at RON-like and MON-like homogeneous charge compression ignition (HCCI) conditions for two different matching criteria. The first criterion was to control the combustion phasing by matching half of the heat release (CA50) to 3 crank angle degrees after top dead center. The second criterion was to match the compression ratios. Results showed that at RON-like HCCI conditions, TPRF fuels display decreasing ITHR with increasing OS. Furthermore, it was shown that TPRF fuels with low sensitivity displayed a greater increase in ITHR from MON-like conditions to RON-like conditions. Thus, the sensitivity of ITHR to changes in operating conditions was found to be a contributing factor to OS. In the beyond-RON conditions (relevant to current modern engines), there is a potential for improved engine efficiency by using fuels with high OS to allow for higher compression ratios. The experimental results of this work show that OS is negatively correlated with ITHR. Thus, high-sensitivity fuels can be designed by choosing components and additives that reduce the amount of ITHR.

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This study has been performed at Powertrain Engineering Sweden AB (PES), a fully owned subsidiary of Volvo Cars Group, which is constantly working to develop and improve internal combustion engines. As part of this work, durability tests are performed to analyse the impact of wear on the engines. At present, there is a strong focus on visual inspections after the engines have undergone durability tests. PES wants to develop a method where collected data from these tests can be used to explain how the phenomenon of knocking and the control of lambda changes over time. The study analyses one specific durability test and investigates the methodology of data analysis by using the open-source software platform Sympathy for Data, with an add-on developed by Volvo Cars Group, for data management, visualisation and analysis. To execute the analysis, engine parameters that affect these systems as well as parameters suitable to use as response variables are identified through literature studies of internal combustion engine fundamentalsas well as internal material, and knowledge acquired at the company. The result is presented in the form of an analysis generated by the node for partial least squares regression (PLSR) which is pre-programmed in Sympathy for Data as well as the images and graphs obtained as output. For knock, the signal for the final ignition angle was found to be suitable to use as the response variable in the PLSR. A suitable response variable for lambda was more difficult to identify, this is why both signals for the measured lambda and lambda adaptation are analysed. Studies of the internal material and knowledge highlighted the fact that several engine subsystems are highly dependent on each other and that even deeper research would be necessary to fully understand the process and identify the primary cause for the variations observed in the generated models. However, partial least squares regression was performed using parameters derived from literature reviews as input (predictors) in order produce regression models to explain the variance in sought response. Well-fitting models could be created with a varying number of latent variables needed for the different responses. The output obtained from the PLSR enables further studies of the specific cases as well as the methodology itself, hence, increase the use of data analysis with the help of the software used in the department for durability testing at PES. / Denna studie är utförd hos Powertrain Engineering Sweden AB (PES), vilka är ett helägt dotterbolag till Volvo Cars Group, som arbetar med att ta fram och förbättra förbränningsmotorer. En del i detta arbete är att genomföra långtidstest för att analysera hur motorernas egenskaper ändras vid förslitning över tid. I nuläget ligger stort fokus på visuella inspektioner efter att motorerna genomgått långtidstester. PES önskar utveckla en metod där redan insamlad data som registrerats i dessa tester kan förklara hur fenomenet knack och regleringen för lambda förändras över tid. Studien är genomförd i form av en fallstudie av ett specifikt långtidstest där den öppna programvaran Sympathy for Data, tillsammans med det av Volvo Cars Group utvecklade tillägget, används för datahantering, visualisering och analys. Studien undersöker också metodiken för dataanalys med nämnd programvara. För att genomföra detta identifieras motorparametrar som påverkar de undersökta systemen samt parametrar som lämpar sig att användas som responsvariabler i en regressionsmodell. Dessa parametrar togs fram genom litteraturstudier om de fundamentala delarna i en förbränningsmotor samt från företaget förvärvad intern kunskap kring systemen. Resultatet presenteras i form av en analys genomförd med den, i Sympathy for Data, förprogrammerade noden för partial least squares regression(PLSR) samt de bilder och grafer som erhålls. För knack visade det sig att den slutliga tändningsvinkeln var lämplig att använda som respons i PLSR-modellen. En lämplig responsvariabel för lambda var mer svåridentifierad, detta förklarar varför signalerna för uppmätt lambda och lambda adaption analyseras. Inläsning av internt material och grundläggande information om förbränningsmotorer visade att delsystem i ottomotorn är beroende och påverkas av varandra vilket innebär att mer ingående studier i dessa delsystem är nödvändigt för att förstå hela processen och hitta grundorsakerna till variationerna som påvisas för responssignalerna. Vidare utfördes PLSR med de parametrar som härletts från litteraturstudier som indatasignaler (prediktorer) för att skapa en regressionsmodell som förklarar variansen i sökta responssignaler. Beroende av responssignal krävdes varierande antal latenta variabler för att uppnå en tillräckligt precis modell. Resultatet från PLSR möjliggör vidare forskning inom området och metoden som använts och har på så sätt möjliggjort för fortsatt utveckling. Detta i sin tur kan öka användandet av dataanalys med hjälp av den programvara som används vid avdelningen för långtidstest hos PES.

Táto diplomová práca je zameraná na preukazovanie vplyvov rôznych architektúr spätnej recirkulácie spalín na preplňované benzínové motory. Simulácie boli vytvorené v termodynamickom simulačnom programme GT-Power. Práca začína porovnávaním vplyvov spätnej recirkulácie na ustálené stavy motora, najmä z hľadiska spotreby, ktoré sú následne implementované do tranzientných modelov, simulujúc emisné testovacie cykly. Na konci práce sa venujem vplyvom spätnej recirkulácie na funkciu oxidačno-redukčného katalyzátora a na funkciu turbodúchadla.

Naturally aspirated petrol engine, pressure losses, EGR, low-pressure EGR, water injection, power increasing, BSFC, GT-Power, thermodynamic model, engine knock