Internal combustion engines are still widely used for propulsion in modern vehicles. Upcoming emission legislation imposes stricter limits on exhaust emissions. One method to achieve emission compliance is by using a three-way catalyst (TWC), which offers excellent emission reduction if the mixture is stoichiometric. However, stoichiometric mixtures in spark-ignited engines have the drawback of increased knock propensity. Knock can be mitigated by using water injection, which serves as both a diluent and utilizes latent heat to reduce the temperature, thereby reducing the reactivity of the unburned mixture. Methanol as a fuel has received more attention thanks to its high research octane number (RON) and its potential to contribute to decarbonization when produced as e- or bio-methanol. In the current study, Direct Water Injection (DWI) was evaluated on a Heavy-Duty (HD) single-cylinder research engine fueled by methanol. This work aims to fill a research gap on methanol-fueled engines with water injection. A direct injection system of water was chosen as it offers the freedom to inject during the closed cycle. Furthermore, a chemical kinetic study on the oxidation of stoichiometric methanol–water mixtures was conducted based on findings in the literature suggesting that, under certain conditions, water mixed with alcohol (in this case, ethanol) can reduce the ignition delay. The experimental results demonstrate that DWI effectively suppresses knock and reduced Nitrogen Oxides (NOx), albeit with deteriorated combustion efficiency. The chemical kinetic study suggested that at lower to intermediate temperatures, water acts as an efficient third-body collider, which lowers the ignition delay. However, this effect is not significant for the typical timescales encountered in HD engines.

Methanol as a fuel is gaining popularity due to its favorable properties and potential for sustainable production as bio- or electro-methanol. By operating according to the Spark-Ignited (SI) principle with a Three-Way Catalyst (TWC), low emissions can be achieved. The main phenomena limiting the efficiency of the SI engine when operating with stoichiometric mixtures are knock and, occasionally, pre-ignition. One method to suppress both knock and pre-ignition is water injection. This study explores the possibility of suppressing knock in-cycle using direct water injection for cycles with an elevated risk of knocking. The prediction was based on the observation that, at knock-limited operation, only cycles with the most advanced combustion phasing knock. Furthermore, at knock-limited loads, combustion predominantly consisted of a single combustion mode: deflagration. The results demonstrated partial knock suppression and allowed for a combustion phasing advancement of 1.5°at loads of 10 and 15 bar gross indicated mean effective pressure. The earliest practical point during the combustion cycle to confidently determine if knock will occur was when about 10%–20% of the fuel had been consumed. However, theoretically, in a best-case scenario, this could be as early as when 5% of the fuel was consumed. An experiment simulating pre-ignition also demonstrated the ability to detect such cycles and partially suppress the ensuing knock. A major limitation of the method is that the window between detecting a cycle with a high likelihood of knock and knock onset was less than 7°at 1000 rpm.

Reaching the particle emissions regulatory limits for the combustion engine is a challenge for developers.Particle filters have been the standard solution to reduce particle emissions, but filters arelimited in storage capacity and need to be regenerated, a process emitting more carbon dioxide(CO2) as more fuel is consumed to regenerate the filter. In previous research, it was found that theengine can emit large spikes in particle numbers (PNs) under stationary operating conditions. Thesespikes were several orders of magnitude higher than for the base particle emissions level and occurredseemingly at random. The source of the spikes was believed to be the cylinder-piston-ring systemand as 50–99% of the particles stemmed from these spikes, the influence on the particle emissionsmade it an interesting investigation to find the root cause of it. The experiments were performedfor different piston ring loads, locked ring positions, and different oil compositions. The resultsindicate a possibility to control the PN emissions through the experiment alterations, with lockedpiston rings having the greatest influence at a higher load. There was no clear relation between ringrotation and flutter with the spikes observed. The locked piston ring configurations did indicate thering gap not to be the main contributor to the spiking as fully aligned gaps did not result in thehighest levels of particle emissions. Variations to the oil composition indicate that a high-volatilityoil will emit higher levels of small, sub-10 nm particles compared to the standard baseline oil. Ahigh-viscosity oil instead lowers the particle emissions, possibly due to the higher inner friction athigh temperatures reducing the oil ingress into the combustion chamber. The link between the PNspiking phenomenon and the oil pathway past the piston ring was not established through theexperiments reported in this publication.

Ethanol, as the most produced renewable biofuel, is considered a promising low-carbon alternative to petroleum-based fuels in the transport sector due to its high energy density and auto-ignition resistance. The lean-burn combustion in spark-ignition (SI) engines has the potential to further improve thermal efficiency in regard to knock mitigation and the reduction of combustion temperature. However, the characteristics of lean-burn combustion in an ethanol-fueled engine in relation to the combustion losses and the gas-exchange process remain unclear, especially for high-load operation. This study contributes with a deeper understanding of the high-load performance of an ethanol-fueled heavy-duty SI engine using lean-burn combustion. Based on the experimental results from a single-cylinder engine test, a 6-cylinder engine model is built by integrating a validated predictive combustion model to characterize the lean-burn combustion process. The engine’s thermal efficiency and combustion phasing are evaluated for knock limited operation and then compared to the theoretical optimum which is regardless of knock. The energy and exergy balances are applied to evaluate the effect of dilution with excess air ratios up to 1.8. Losses through heat transfer, exhaust flow, and incomplete combustion are quantified. In addition, entropy generated through combustion is discussed to identify the relationship between exergy destruction and different operating conditions. In the context of lean-burn combustion, the thermal efficiency at high-load operation incrementally increases from 40.4% at stoichiometric condition to 47.3% at an excess air ratio of 1.8. At the same time, the exergy destruction through combustion increases by 3.3 percentage points across the selected dilution range. Furthermore, the challenging requirements to realize lean-burn combustion with lower exhaust gas temperatures and higher intake boost pressures is assessed through an exergy analysis of the turbocharging system.

Stoichiometric operation of a Port Fueled Injection (PFI) Spark-Ignited (SI) engine with a three-way catalytic converter offers excellent CO2 reduction when run on renewable fuel. The main drawbacks with stoichiometric operation are the increased knock propensity, high exhaust temperature and reduced efficiency. Knock is typically mitigated with a reactive knock controller, with retarded ignition timing whenever knock is detected and the timing then slowly advanced until knock is detected again. This will cause some cycles to operate with non-ideal ignition timing. The current work evaluates the possibility to predict knock using the measured and modelled temperatures at Inlet Valve Closing (IVC) and Top Dead Center (TDC). Feedback effects are studied beyond steady state operation by using induced ignition timing disturbances. The approach is based on a deterministic controller where the timing is advanced beyond steady state knock limited operation or vastly retarded to produce warmer residuals in the following cycle. The results indicate that for the current engine there is no feedback effect. Chemical kinetics explains the lack of feedback due to lack of reactivity at TDC conditions. The chemical kinetic study in conjunction with the established auto ignition models described by Livengood-Wu reveals that the charge mixture entered a region of reactivity around the 50% burned point. It was also found that knocking and non-knocking cycles can have overlapping thermodynamic trajectories but for knocking cycles there is less dispersion. The study uses a solver which corrects the IVC temperature to minimize the error between observed knock onset and the point where the Livengood-Wu expression reaches unity for a knocking cycle. The corrections were found to have a correlation to uncaptured evaporation effects. Combined experimental and modelling results were in line with previous findings, namely that cycle-to-cycle combustion variations are plausibly explained by early flame propagation.

Modern spark-ignited (SI) engines offer excellent emission reduction when operated with a stoichiometric mixture and a three-way catalytic converter. A challenge with stoichiometric compared to diluted operation is the knock propensity due to the high reactivity of the mixture. This limits the compression ratio, thus reducing engine efficiency and increasing exhaust temperature. The current work evaluated a model of conditions at inlet valve closing (IVC) and top dead center (TDC) for steady state operation. The IVC temperature model is achieved by a cycle-to-cycle resolved residual gas fraction estimator. Due to the potential charge cooling effect from methanol, a method was proposed to determine the fraction of fuel sourced from a wall film. Determining the level of charge cooling is important as it heavily impacts the IVC and TDC temperatures. This method is based on air flow measurement and comparing information from the compression event during a transient from fired to motored conditions, while keeping the intake density constant. Experiments were conducted on a high compression ratio (14:1) heavy duty (HD) single cylinder research engine (SCRE). The fuel was methanol, injected via port fuel injection (PFI). The results indicate that the latent heat of vaporization of the fuel is far from being fully utilized, due to inherent design limitations of the intake system. It was also found that charge cooling could be altered by utilizing features of the swirl optimized cylinder head, while the same features also hinted that some stratification was possible. Accurate estimation of the IVC state and the later thermodynamic evolution is important for any closed cycle analysis. The result from the IVC and TDC condition estimators indicate that it is possible to capture expected trends.

I detta projekt presenteras ett arbete där en serieproducerad 5 cylindrig motor med gasdrift modifieras till drift på enbart en cylinder. En konceptstudie genomförs där för och nackdelar vägs mot varandra där sedan ett koncept implementeras. Tidigare lösningar har använts där avaktivering av cylindrar uppnåtts genom att ta bort komponenter till gasväxlingssystemet och med hål borrade i kolvarna. Motorn är tänkt att vid ett senare skede installeras i en test-cell på avdelningen för förbränningsmotorteknik på Kungliga Tekniska Högskolan.Oönskat kompressionsarbete i avaktiverade cylindrar minimeras genom att låta dessa ventilera mot atmosfären. Detta sker genom att plocka bort insugsventilerna och igentäppning av ventilstyrningar. Ventilation mot atmosfären sker med hjälp av ett modifierat insug. Ett system för att ta hand om olja som annars skulle ha förbränts i de avaktiverade cylindrarna konstrueras. Med denna lösning behöver inte den roterande massan modifieras vilket annars hade påverkat motorns balansering.Ett kapacitivt tändsystem där gnistenergi kan ändras under drift implementeras. Tändsystemet är uppbyggt av två stycken tändenheter och tändspolar som är kopplade till samma tändstift. Denna lösning tillåter bättre kontroll när multipla gnistor under en cykel är önskvärt. Motorn är tänkt att använda en experimentell styrning av tändning vilket kräver att tiden från när en gnista önskas till gnistinitiering minimeras.För kontroll av bränsle och tändning i ett initialt skede installeras ett eftermarknads motorstyrsystem. Detta styrsystem ansluts till motorns standard sensorer. Styrsystemet kan ändra relevanta driftparametrar under drift genom ett grafiskt gränssnitt, systemet inkluderar återkoppling för luft-bränsleblandning samt skyddsfunktioner för okontrollerad självantändning. Standardsystemet för avgasåterledning modifieras för att kunna styras av tidigare nämnt styrsystem.Hjälpaggregat och andra komponenter ej nödvändiga för drift i testcell demonteras. Motorn förbereds även så att en högtryckspump för direktinsprutning kan monteras i framtiden.

In this project, a 5-cylinder SI port-injected engine is converted to single cylinder operation by deactivating four of the cylinders. A concept generation process resulted in four different concepts where one of them was chosen to be implemented. Previous setups have been used before where cylinders have been deactivated by drilling holes in the piston.Unwanted compression work for the deactivated cylinders is minimized by allowing ventilation to the atmosphere. The inlet valves are removed and the inlet guides plugged. A modified intake connects the deactivated cylinders to the atmosphere. To manage the oil in the deactivated cylinders which otherwise would be combusted is routed to a manifold and finally a catch tank. With this setup, the rotating assembly is untouched thereby retaining the stock engine balance.A capacitive ignition system where the spark energy can be altered during operation is implemented. The ignition system is comprised of two separate ignition units and coils which is connected to the same spark plug. This setup allows full control of when the second spark is released when operated in a multi-spark mode. The system has been designed to minimize the time from spark demand to spark initiation. This is to prepare for future use where an experimental control algorithm will be used which doesn’t use traditional look-up tables.In an initial stage, the fuel and spark will be controlled by an aftermarket engine control unit. The system is installed using the standard sensors on the engine. The control unit can alter relevant parameters during operation using a graphical user interface. The system incorporates closed-looped lambda and knock control for safe operation. The stock exhaust gas recirculation system is incorporated with the engine control unit.Auxiliary units and other components not necessary for single operate are removed. The engine is also prepared to accommodate a high-pressure pump for future direct injection.