Impact of Discharge Duration on Lean Combustion in Spark Ignition Engines

Fuel-lean combustion in spark ignition engines is a promising strategy to improve engine efficiency. However, a fuel lean cylinder charge tends to lower the burning velocity because of the lowered chemical reactivity of the mixture, unless the flame propagation is accelerated by introducing an intensified flow field in the combustion chamber. Nevertheless, the literature reveals that the lean burn strategy with intensified flow fields can impose severe challenges on the ignition and flame development processes both in present and upcoming production engines. To address these issues and to better secure the flame kernel at the initial stage of combustion, various ignition strategies have been proposed with the aim of developing higher discharge current and longer discharge duration in the ignition processes, compared to those encountered with conventional spark ignition techniques. Moreover, while both current amplitude and duration of the plasma channel are fundamental to the flame kernel formation and development, their roles have not been fully clarified, let alone adequately quantified, in respect to the extensive variations in pressure, temperature, flow status, and mixture strength. Consequently, in this study, the impacts of discharge current amplitude and duration on the flame kernel initiation were investigated empirically using a constant volume combustion chamber and a single-cylinder research engine platform. The constant volume combustion chamber system was constructed so that a gas mixture with independently controlled pressure, composition, and flow intensity could be supplied. High-speed imaging was used to enable spatial and temporal characterizations of the flame kernel initiation process. Turbulence was generated inside the combustion chamber by a jet flow setup. A field programmable gate array (FPGA) controller was used to synchronize the controls of the sparking events, jet flow, and high-speed imaging. To achieve independent control of the discharge current amplitude and duration, the discharge current profile was modulated to form a quasi-rectangular shape by using a variety of hardware configurations and event controls. Ignition studies with various discharge current amplitudes and durations were conducted under both quiescent and flow conditions. Combustion test results showed that both discharge current amplitude and discharge duration had minimal impact on the ignition process under quiescent condition. However, under flow conditions, a longer discharge duration contributed to tailing flame kernels near the spark gap, and a higher discharge current amplitude contributed to larger flame kernels. Based on the experimental results and analysis, a correlation between the discharge current profiles and the flame kernel development was established with ultra-lean mixtures under intensified flow conditions. Additionally, the operational principles of the single-coil repetitive discharge and dual-coil offset discharge strategies were explored and explained. The necessary control algorithms for the repetitive and offset discharge strategies were established by analyzing the empirically acquired electrical waveforms of the discharge events. Finally, a preliminary investigation of the impact of discharge duration on the ignition stability was conducted using a single-cylinder research engine fitted with precise coolant conditioning, flexible air and fuel management, and comprehensive measurement and data acquisition. The experimental results indicated that a longer discharge duration contributed to improved combustion stability. However, ignition delay and combustion duration were unaffected by the prolonged discharge duration

Modeling and Characterization of Power Distribution Networks with Installed Distributed Generation and Connected PHEVs

This thesis is focused on the modeling and characterization of power distribution networks with installed distributed generation and connected plug-in hybrid electric vehicles (PHEV). A PHEV charging/discharging (bidirectional) model has been developed in MATLAB®-Simulink. Installed photovoltaic systems with varying irradiance rates are modeled and characterized. Moreover, installed wind generators with varying wind speeds are modeled and characterized. Furthermore, the charging and discharging characteristics of connected PHEV are determined. The system characteristics are determined and investigated against the PHEV battery state of charge (SOC)

A chronological literature review of electric vehicle interactions with power distribution systems

In the last decade, the deployment of electric vehicles (EVs) has been largely promoted. This development has increased challenges in the power systems in the context of planning and operation due to the massive amount of recharge needed for EVs. Furthermore, EVs may also offer new opportunities and can be used to support the grid to provide auxiliary services. In this regard, and considering the research around EVs and power grids, this paper presents a chronological background review of EVs and their interactions with power systems, particularly electric distribution networks, considering publications from the IEEE Xplore database. The review is extended from 1973 to 2019 and is developed via systematic classification using key categories that describe the types of interactions between EVs and power grids. These interactions are in the framework of the power quality, study of scenarios, electricity markets, demand response, demand management, power system stability, Vehicle-to-Grid (V2G) concept, and optimal location of battery swap and charging stations.Introduction General Overview Chronological Review: Part I Chronological Review: Part II Brief Observations Conclusions and Future Works Final Reflections Author Contributions Funding Acknowledgments Conflicts of Interest Reference

Powertrain Systems for Net-Zero Transport

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government’s announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe. Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine’s role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed. Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries

Advanced Ignition Strategies for Future Internal Combustion Engines with Lean and Diluted Fuel-Air Mixtures

The main objective of this research was to study the mechanisms of the spark ignition process of lean or diluted fuel-air mixtures under enhanced gas flow conditions for applications in future internal combustion engines. Various spark ignition strategies were deployed by controlling the spark discharge process via different spark ignition hardware configurations. Modulated spark discharge parameters, such as enhanced discharge power, prolonged discharge duration, and boosted discharge current were facilitated in the research. The impact of gas flow on the spark discharge process in air was investigated under varying air flow conditions with a range of flow velocities from 0 m/s to 60 m/s. The ignition performance of the spark strategies was investigated with lean or diluted fuel-air mixtures under controlled gas flow conditions in an optical constant volume combustion chamber test platform. The mixture flow velocity across the spark gap ranged from 0 m/s to 35 m/s during the combustion tests.Experiments were carried out with air as the background media. Short circuits and restrikes were observed under air flow conditions. The frequency of these occurrences increased with increased air flow velocity. The length of the spark plasma increased, due to the stretch of the plasma channel by the air flow. The plasma was stretched at a speed similar to the air flow velocity across the spark gap. The maximum length of the spark plasma was affected by the air flow velocity and the spark gap size. The spark discharge duration reduced with increased air flow velocity. To enhance the ignition of a lean or diluted fuel-air mixture under quiescent conditions, high spark discharge power or high spark discharge current were applied. With equivalent spark discharge energy, a larger flame kernel was achieved by the high-power spark whereas the impacts of spark discharge current level and discharge duration during the arc and glow phases were insignificant on the flame kernel growth. A transient high-current spark also generated a larger flame kernel, although with much higher spark energy as compared with that from a conventional spark. Under gas flow conditions, both the spark discharge current magnitude and discharge duration were critical for the flame kernel growth. It is postulated that this kernel growth was the result of a prolonged spark discharge duration effectively increasing the interaction volume between the plasma channel and the combustible gas engulfed by the mixture flow. Consequently, a longer spark discharge duration proved beneficial in establishing a larger flame kernel, probably because the spark discharge current was sufficient to support the flame kernel growth. Indeed, it was observed that boosted spark current was advantageous for the flame kernel growth, especially at higher flow velocities. However, the high-power spark and transient high-current spark proved to be less effective with higher flow velocities, probably because of the short discharge duration

EcoBlock: Grid Impacts, Scaling, and Resilience

Widespread deployment of EcoBlocks has the potential to transform today's electricity system into one that is more resilient, flexible, efficient and sustainable. In this vision, the system will consist of self- su cient, renewable-powered, block-scale entities that can deliberately adjust their net power exchange and can optimize performance, maintain stability, support each other, or disconnect entirely from the grid as needed. This report is intended as an independent analysis of the potential relationships, both constructive and adverse, between EcoBlocks and the grid

A novel power management and control design framework for resilient operation of microgrids

This thesis concerns the investigation of the integration of the microgrid, a form of future electric grids, with renewable energy sources, and electric vehicles. It presents an innovative modular tri-level hierarchical management and control design framework for the future grid as a radical departure from the ‘centralised’ paradigm in conventional systems, by capturing and exploiting the unique characteristics of a host of new actors in the energy arena - renewable energy sources, storage systems and electric vehicles. The formulation of the tri-level hierarchical management and control design framework involves a new perspective on the problem description of the power management of EVs within a microgrid, with the consideration of, among others, the bi-directional energy flow between storage and renewable sources. The chronological structure of the tri-level hierarchical management operation facilitates a modular power management and control framework from three levels: Microgrid Operator (MGO), Charging Station Operator (CSO), and Electric Vehicle Operator (EVO). At the top level is the MGO that handles long-term decisions of balancing the power flow between the Distributed Generators (DGs) and the electrical demand for a restructure realistic microgrid model. Optimal scheduling operation of the DGs and EVs is used within the MGO to minimise the total combined operating and emission costs of a hybrid microgrid including the unit commitment strategy. The results have convincingly revealed that discharging EVs could reduce the total cost of the microgrid operation. At the middle level is the CSO that manages medium-term decisions of centralising the operation of aggregated EVs connected to the bus-bar of the microgrid. An energy management concept of charging or discharging the power of EVs in different situations includes the impacts of frequency and voltage deviation on the system, which is developed upon the MGO model above. Comprehensive case studies show that the EVs can act as a regulator of the microgrid, and can control their participating role by discharging active or reactive power in mitigating frequency and/or voltage deviations. Finally, at the low level is the EVO that handles the short-term decisions of decentralising the functioning of an EV and essential power interfacing circuitry, as well as the generation of low-level switching functions. EVO level is a novel Power and Energy Management System (PEMS), which is further structured into three modular, hierarchical processes: Energy Management Shell (EMS), Power Management Shell (PMS), and Power Electronic Shell (PES). The shells operate chronologically with a different object and a different period term. Controlling the power electronics interfacing circuitry is an essential part of the integration of EVs into the microgrid within the EMS. A modified, multi-level, H-bridge cascade inverter without the use of a main (bulky) inductor is proposed to achieve good performance, high power density, and high efficiency. The proposed inverter can operate with multiple energy resources connected in series to create a synergized energy system. In addition, the integration of EVs into a simulated microgrid environment via a modified multi-level architecture with a novel method of Space Vector Modulation (SVM) by the PES is implemented and validated experimentally. The results from the SVM implementation demonstrate a viable alternative switching scheme for high-performance inverters in EV applications. The comprehensive simulation results from the MGO and CSO models, together with the experimental results at the EVO level, not only validate the distinctive functionality of each layer within a novel synergy to harness multiple energy resources, but also serve to provide compelling evidence for the potential of the proposed energy management and control framework in the design of future electric grids. The design framework provides an essential design to for grid modernisation