Analysis of combustion phenomena and knock mitigation techniques for high efficient spark ignition engines through experimental and simulation investigations

Different technologies are being utilized nowadays aiming to boost the fuel efficiency of Spark-Ignition (SI) engines. Two promising technologies which are used to improve the part load efficiency of SI engines are the utilization of downsizing in combination with turbocharging and cylinder deactivation. Both technologies allow a shift of load points towards higher loads and therefore towards more efficient zones of the engine map, while performance is being preserved or even enhanced despite the smaller displacement thanks to high boost levels. However, utilization of both technologies will increase the risk of knock dramatically. Therefore, the abovementioned systems can be coupled with other technologies such as gasoline direct injection, Miller cycle and water injection to mitigate knock at higher load operating conditions. Therefore, the aim of the current work is to investigate, through experimental and numerical analysis, the potential benefits of different knock mitigation techniques and to develop reliable and predictive simulation models aiming to detect root cause of cyclic variations and knock phenomena in downsized turbocharged SI engines. After a brief introduction in Chapter 1, three different typical European downsized turbocharged SI engines have been introduced in Chapter 2, which were used for both experimental and simulation investigations, named as Engine A, which is downsized and turbocharged, Port Fuel Injection (PFI) with fixed valve lift and represents the baseline; Engine B, represents an upgraded version of Engine A, featuring Variable Valve Actuation (VVA), and Engine C which is a direct injection and further downsized engine. Engine B, equipped with MultiAir VVA system, was utilized to evaluate the possible benefits of cylinder deactivation in terms of fuel economy at part load condition, which is discussed in Chapter 3. Since the MultiAir VVA system does not allow exhaust valve deactivation, an innovative strategy was developed, exploiting internal Exhaust Gas Recirculation (iEGR) in the inactive cylinders in order to minimize their pumping losses. However, at higher load operating condition, risk of knock occurrence limits the performance of the engine. Therefore, the possible benefits of different knock mitigation techniques such as Miller Cycle and water injection in terms of fuel consumption were discussed in Chapter 4. Potential benefits of Miller cycle in terms of knock mitigation are evaluated experimentally using Engine B, as shown in Chapter 4.2. After a preliminary investigation, the superior knock mitigation effect of Late Intake Valve Closure (LIVC) with respect to Early Intake Valve Closure (EIVC) strategy was confirmed; therefore, the study was mainly focused on the latter system. It was found out that utilization of LIVC leads up to 20% improvement in the engine indicated fuel conversion efficiency. Afterwards, Engine C, a gasoline direct injection engine, has been utilized in order to understand the potential benefits of water injection for knock mitigation technology coupled with the Miller Cycle, which is discussed in Chapter 4.3. Thanks to water injection potential for knock mitigation, the compression ratio could be increased from 10 to 13, which leads to an impressive efficiency improvement of 4.5%. However, utilization of various advanced knock mitigation techniques in the development of SI engines make the system more complex, which invokes the necessity to develop reliable models to predict knock and to find the optimized configuration of modern high-performance, downsized and turbocharged SI engines. Considering that knock is strictly related to Cycle-to-Cycle Variations (CCV) of in-cylinder pressure, CCV prediction is an important step to predict the risk of abnormal combustion on a cycle by cycle basis. Consequently, in Chapter 5, a procedure has been introduced aiming to predict the mean in-cylinder pressure and to mimic CCV at different operating conditions. First, a 0D turbulent combustion model has been calibrated based on the experimental data including various technologies used for knock mitigation which can impact significantly on the combustion process, such as Long Route EGR and water injection. Afterwards, suitable perturbations are adapted to the mean cycle aiming to mimic CCV. Finally, the model has been coupled with a 0D knock model aiming to predict knock limited spark advance at different operating conditions. Finally, in order to provide a further contribution towards the prediction of CCV, 3D-CFD Large Eddy Simulation (LES) has been carried out in order to better understand the root cause of CCV, presented in Chapter 6. Such analysis could be used to extract the physical perturbation from the 3D-CFD and to use it as an input for the 0D combustion model to predict CCV. The operating condition studied in this work is at 2500 rpm, 16 bar brake mean effective pressure (bmep) and stoichiometric condition. Based on the analysis conducted using LES, it was found out that the variability in combustion can be mainly attributed to both the direction of the velocity flow-field and its magnitude in the region around the spark plug. Furthermore, the effect of velocity field and equivalence ratio on the combustion has been decoupled, confirming that the former has the dominant effect while the latter has minor impact on combustion variability. In conclusion, simulation models using 0D and 3D-CFD tools when calibrated properly based on experimental measurements can be used to support the design and the development of innovative downsized turbocharged SI engines considering the effects of CCV and knock on engine performance parameters

Examination of causes behind procrastination among Shahrekord University of Medical Sciences employees and proposing some strategies for their preventing: A study using the Van Wyk’s Model

Background: Competition among the organizations and enterprises plays a particularly important role in the gathering of the profits and acquisition of internal and external resources. Procrastination is one of the main barriers to efforts made towards increasing the productivity and efficiency in the organizations. Accordingly, the main goal of this research was to explore the reasons of procrastination among the employees based on Van Wyk’s model and present some strategies for preventing it. Methods: Descriptive-analytical in nature, this study was conducted on a sample of 200 employees selected from Shahrekord University of Medical Sciences using a self-designed checklist developed based on the informational components incorporated in the Van Wyk’s model. This model consists of 9 factors affecting the level of procrastination observed among the employees i.e. resistance, boredom, perfectionism, last-minute syndrome, lack of motivation for a task, fear of failure, skill deficit, rebelliousness and disorganization. The validity of the developed checklist was checked using its assessment by the expert professors and its reliability was measured with Cronbach's alpha. Both of them were confirmed (Cronbach's alpha of 90%). To analyze the data, T-test and variance analysis were used.Results: The results of the study showed that there was a statistically significant relationship between employee’s resistance, boredom, perfectionism and lack of motivation for task and procrastination (p=0.001); however, the association between fear of failure, rebelliousness and disorganization and procrastination was not statistically significant (p=0.871).Conclusions: The availability of high quality organizational capital will enhance the chance of organization’s success, survival and advancement. As a result, identifying the attributes of human resources and the factors influencing their efficiency so as to exploit the human capital more optimally and remove the reasons of procrastination is of high significance.

Creating a Virtual Test Bed Using a Dynamic Engine Model with Integrated Controls to Support in-the-Loop Hardware and Software Optimization and Calibration

In the current study, a 0D/1D engine model built in the commercial code GT-Suite was coupled with the Electronic Control Unit (ECU) model created in the Simulink environment, aiming to more accurately predict the interaction of the engine and aftertreatment system (ATS) operating parameters, both during steady-state and transient maneuvers. After a detailed validation based on extensive experimental data from a heavy-duty commercial diesel Internal Combustion Engine (ICE), the engine model was fine-tuned and the 0D predictive diesel combustion model, DIPulse, was calibrated to best predict the combustion process, including engine-out NOx emissions. For correct prediction of the engine’s behavior in transient operations, the complete control strategy of the air path, including boost, exhaust gas recirculation (EGR), main and pilot Start of Injection (SOI), injection pressure, and exhaust flap, was implemented in the Simulink environment. To demonstrate the predictive capability of the model, a hot World Harmonized Transient Cycle (WHTC) was simulated, obtaining good agreement with the experimental data both in terms of emissions and performance parameters, confirming the reliability of the proposed approach. Finally, a case study on possible fuel consumption improvement through thermal insulation of the exhaust manifold, exhaust ports, and turbocharger was carried out

Creating a Virtual Test Bed Using a Dynamic Engine Model with Integrated Controls to Support in-the-Loop Hardware and Software Optimization and Calibration

In the current study, a 0D/1D engine model built in the commercial code GT-Suite was coupled with the Electronic Control Unit (ECU) model created in the Simulink environment, aiming to more accurately predict the interaction of the engine and aftertreatment system (ATS) operating parameters, both during steady-state and transient maneuvers. After a detailed validation based on extensive experimental data from a heavy-duty commercial diesel Internal Combustion Engine (ICE), the engine model was fine-tuned and the 0D predictive diesel combustion model, DIPulse, was calibrated to best predict the combustion process, including engine-out NOx emissions. For correct prediction of the engine’s behavior in transient operations, the complete control strategy of the air path, including boost, exhaust gas recirculation (EGR), main and pilot Start of Injection (SOI), injection pressure, and exhaust flap, was implemented in the Simulink environment. To demonstrate the predictive capability of the model, a hot World Harmonized Transient Cycle (WHTC) was simulated, obtaining good agreement with the experimental data both in terms of emissions and performance parameters, confirming the reliability of the proposed approach. Finally, a case study on possible fuel consumption improvement through thermal insulation of the exhaust manifold, exhaust ports, and turbocharger was carried out

Assessment of the Predictive Capabilities of a Combustion Model for a Modern Downsized Turbocharged SI Engine

A 0D phenomenological turbulence model, based on the K-k and k- ɛ approaches, was coupled with a predictive turbulent combustion model using the commercial code GT-Suite, and its predictive capabilities were assessed for a downsized turbocharged SI engine.Differently from the 3D-CFD approach which is typically utilized to describe the evolution of the in-cylinder flow field, and which has very high computational requirements, the 0D phenomenological approach adopted in this work gives the opportunity to predict the evolution of the in-cylinder charge motion and the subsequent combustion process by means of a turbulent combustion model, with a significantly reduced computational effort, thus paving the way for the simulation of the whole engine operating map.Moreover, a procedure has been adopted to calibrate the turbulent combustion model parameters by means of a Design of Experiments (DoE) coupled with Genetic Algorithm (GA) approach, in order to predict the burn rate at various engine operating points.Finally, a detailed validation process, based on an extensive experimental data set, was carried out concerning the predicted burn rates and the in-cylinder pressure traces for several engine operating points, including load, speed and spark timing sweeps, achieving a satisfactory agreement and thus confirming the reliability of the proposed approach

Engine displacement modularity for enhancing automotive s.i. engines efficiency at part load

Cylinder deactivation is a well-known and effective technology to improve spark ignition engines’ efficiency at part load, thanks to its capability of significantly reducing pumping losses, by switching off a fraction of the cylinders at part load, while operating the active cylinders at higher loads and therefore with higher efficiencies. This technology can be utilized as an alternative to, or in combination with, other efficiency improving measures such as engine downsizing and Variable Valve Actuation (VVA). It is worth mentioning however that the implementation of a cylinder deactivation strategy generally requires intake and exhaust valve deactivation in deactivated cylinders, so to minimize pumping losses thanks to the “gas spring” behavior of the trapped charge. In this paper the effects and possible benefits of cylinder deactivation on a four cylinder turbocharged downsized gasoline engine equipped with MultiAir VVA system were experimentally investigated, aiming to obtain further reductions of pumping losses beyond those achievable through normally adopted Early Intake Valve Closure (EIVC) strategies. Moreover, since the MultiAir VVA system does not allow exhaust valve deactivation, an innovative strategy was developed, exploiting internal Exhaust Gas Recirculation (iEGR) in the inactive cylinders in order to minimize their pumping losses. This innovative cylinder deactivation technique was demonstrated to be effective in the low speed and low load operating region of the engine map, leading to an impressive 30% reduction of pumping losses compared to the EIVC unthrottled load control