Controlling of Combustion Process in Energy and Power Systems

1. Introduction

As the demand for cleaner energy sources and more efficient power generation technologies continues to grow, the need for advanced combustion control strategies becomes increasingly critical for the zero-carbon emissions target [1,2]. Despite decarbonization efforts, fossil fuels, including coal, natural gas, and petroleum, continue to dominate global energy production and consumption and continue to play an important role in large-scale power generation and transportation [3]. So, the efficient utilization and combustion control of these fuels have become crucial for reducing emissions and improving energy efficiency [4]. Energy and power systems, such as coal-fired boilers, gas turbines, engines, and other power devices, are central to modern industrial and transportation infrastructures. These systems rely heavily on combustion processes to convert chemical energy into mechanical or electrical energy. However, traditional combustion methods often suffer from significant challenges to environmental sustainability and energy security. This research theme, “Controlling of Combustion Process in Energy and Power Systems”, is dedicated to exploring innovative methods and technologies, which optimize combustion efficiency, reduce pollutant emissions, and enhance system performance across a wide range of applications, from traditional power plants to emerging micro energy systems.

Combustion processes are often associated with significant challenges, such as incomplete combustion, high pollutant emissions, and suboptimal energy conversion efficiencies [5]. Addressing these challenges requires a deep understanding of the underlying combustion mechanisms and the development of sophisticated control strategies that can adapt to varying operating conditions and fuel properties. For instance, coal-fired boilers remain a cornerstone of large-scale power generation, particularly in regions with abundant coal reserves [6]. However, their operation is associated with significant emissions of CO₂, SO₂, NO_x, and particulate matter (PM). To mitigate these environmental impacts, advanced combustion control strategies such as staged combustion and flue gas recirculation have been developed [7]. By optimizing the combustion process, these strategies not only extend the operational lifespan of existing coal-fired power plants but also minimize their environmental footprint. Similarly, gas turbines, which are widely used in power generation and aviation due to their high efficiency and relatively lower emissions compared to coal-fired systems, also benefit from advanced combustion control [8]. Techniques such as lean premixed combustion and catalytic combustion are explored to achieve ultra-low emissions while maintaining high efficiency and reliability.

In the transportation sector, internal combustion engines continue to dominate despite the rise of electric vehicles. Optimizing combustion in engines through techniques like direct injection, turbocharging, and exhaust gas recirculation (EGR) can significantly improve fuel economy and reduce emissions [9,10]. Researches in this area focus on developing advanced combustion modes, such as homogeneous charge compression ignition (HCCI) and reactivity controlled compression ignition (RCCI), which offer the potential for high efficiency and low pollutant emissions [11,12]. Meanwhile, the development of micro power devices, such as micro gas turbines and micro combustors, is driven by the increasing demand for portable and distributed power generation [13]. These devices often operate on micro combustion processes, which face unique challenges due to the small combustion space, high surface-to-volume ratio, and significant heat loss. Optimizing combustion in micro power devices through innovative burner designs, catalytic combustion, and the use of high-energy-density fuels is essential for achieving the development of more compact, efficient, and reliable power sources [14,15].

To meet the growing global energy demand while minimizing environmental impact, the control of combustion processes in energy and power systems is of paramount importance. Optimizing combustion in coal-fired boilers, gas turbines, internal combustion engines, and micro power devices can lead to significant improvements in energy efficiency and reductions in pollutant emissions. This research theme, “Controlling of Combustion Process in Energy and Power Systems”, aims to explore advanced combustion control strategies and technologies that can address these challenges and contribute to a more sustainable and efficient energy future.

2. New Progress in Combustion Control

The reserves of low-rank coal are abundant, and a substantial amount of semi-coke is annually generated during its pyrolysis process [6]. As a byproduct of coal pyrolysis, semi-coke presents numerous challenges in achieving stable ignition and efficient combustion due to its low volatile content [16]. This issue is particularly prevalent in the combustion of low-volatile fuels, which constitute a significant proportion of coal reserves [17]. The co-firing methods traditionally involving coal or biomass necessitate complex fuel-feeding systems, invariably leading to increased costs and operational complexities. So, it becomes imperative to explore effective utilization pathways for semi-coke and develop novel technologies. Preheating prior to combustion, such as preheating air or fuel, has been widely acknowledged as an efficacious means to attain stable ignition and high-efficiency combustion. Zhang et al. [18] has proposed a novel preheating approach using a circulating fluidized bed (CFB) for pulverized fuels. As the preheating temperature increased, the CO/CO₂ ratio in the coal gas significantly increased, while the CH₄/CO₂ ratio remained almost unchanged. Over 50% of carbon was converted into coal gas, with the conversion order being C > H > N > S. Thermogravimetric analysis revealed that the ignition and burnout temperatures of the preheated char were lower than those of the semi-coke, and the reaction rate constant for the preheated char increased by 20 times. Three models were used to predict the variations in the conversion ratio with time, with the modified volumetric reaction model showing good agreement with the experiment. It provides valuable insights and support for the future development of preheating combustion technology, offering a potential solution to the combustion challenges associated with low-volatile fuels.

Electricity is essential for industrial production. Currently, thermal power generation remains crucial as renewable energy power has technological limitations. For instance, coal is the dominant energy source for power generation in China [6]. Boilers in power plants are key components, and optimizing their efficiency is of great significance for energy conservation and emission reduction. To achieve higher energy efficiency, it is essential to consider the concept of energy grade and analyze irreversible losses in the operation process, known as exergy analysis. Yin et al. [19] employed the second law of thermodynamics with boiler structure optimization to maximize the efficiency of a 350 MW power plant boiler. They reduced the heat exchange area of the economizer and increased that of the air preheater to minimize exergy loss during combustion. The exergy efficiency of the boiler decreases with the decrease of load, and the heat transfer exergy losses of the water wall and low-temperature reheater are relatively large. Furthermore, an improved scheme is proposed, which effectively increases the exergy efficiency from 47.29% to 48.35% by adjusting the heat exchange areas of the economizer and air preheater and improving the steam parameters. It provides a theoretical basis for optimizing boiler design and operation, offering practical insights for the energy efficiency improvement of power plant boilers.

In Europe, wood pellets are a significant biomass fuel for residential heating. With the improvement of building energy efficiency, there is a growing demand for low-power (<10 kW) heating system. However, operating such stoves at low power faces challenges low combustion chamber temperature, fuel supply fluctuations, and air leakage, which cause difficulties in low-pollution operation [20]. Moreover, existing tools are insufficient for simulating their transient behavior and testing control strategies, and optimizing control strategies is costly. Lustenberger et al. [21] developed a 0-D transient simulation tool in MATLAB-Simulink R2021b, consisting of five modules that simulate a generic pellet stove with staged combustion. The combustion models of pellets act as a superposition of individual pellet combustion cycles, assuming no interactions between pellets. A test setup was developed to determine the ignition and burning cycle of individual pellets, and the CO emissions behavior was based on an empirically grounded relation. Experiments on a 4 kW pellet stove test rig were conducted to validate the tool. Results showed the impacts of pellet supply and secondary air on combustion. A control strategy was developed and compared with constant flap position operation, demonstrating improved efficiency and similar CO emissions. The model reproduced temperature and other parameters well, although it had limitations in simulating long intervals between pellet supplies. The model’s effectiveness and simplicity make it a valuable tool for developing control strategies for other staged, pellet combustion systems, offering a theoretical basis for improving the performance of pellet stoves.

With the increasing stringency of environmental regulations, reducing pollutant emissions from diesel engines has become crucial. Biodiesel-diesel blended fuels show certain advantages, but further optimization of their combustion and emission performance is still needed [22]. EGR is a commonly used method, and understanding its impact on different fuel blends is of great significance for improving engine efficiency and reducing emissions. Huang et al. [9] systematically analyzed the impact of varying EGR rates on key performance and emission parameters, including cylinder pressure, temperature, brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), NO_x, HC, CO, and soot emissions. The results indicated that an increase in EGR rate led to a reduction in NO_x emissions, while it also caused an increase in HC, CO, and soot emissions. An EGR rate of 10% was optimal, balancing the reduction of NO_x emissions with the maintenance of engine power and economy. It is crucial for the development of advanced engine control strategies, making them a more viable option for sustainable transportation.

There is a growing need for micro energy power systems due to the development of micro-machining technology and the increasing demand for portable devices. Micro combustion, as the core of such systems, offers the advantages of high energy density and long operation time. However, due to the small combustion chamber size, it faces challenges like short residence time, high heat loss ratio, and weak flame stability. Kang et al. [23] reviews the application of micro power generation and the characteristics of micro combustion. Four main methods to enhance micro combustion stability are discussed in detail, including fuel selection and blended combustion, catalytic combustion, burner optimization, and porous media employment [24]. Key findings include the benefits of hydrogen addition to hydrocarbon fuels for enhanced stability and efficiency, the effectiveness of catalytic combustion in reducing ignition temperatures and NO_x emissions, and the role of porous media in improving heat transfer and flame stability. Future research should focus on adopting low-carbon or liquid fuels, applying new combustion technologies, optimizing combustors, and combining multiple power generation technologies to promote the development and application of micro power systems.

3. Conclusions

The research theme “Controlling of Combustion Process in Energy and Power Systems” has been extensively explored through various studies focusing on optimizing combustion technologies to enhance efficiency, reduce pollutant emissions, and improve system performance. The main findings include significant improvements in combustion efficiency and reductions in NO_x, CO, HC, and particulate matter emissions through advanced techniques such as preheating, EGR, catalytic combustion, and innovative burner designs. These optimizations are achieved by integrating interdisciplinary approaches, combining chemical kinetics, fluid dynamics, thermodynamics, and materials science. The studies highlight the importance of combustion control in enhancing overall system performance and suggest future directions, including the development of novel materials and combustion modes, to further improve efficiency and sustainability in both traditional and emerging energy systems.