نشریه سوخت و احتراق
سال هجدهم شماره 1 (پیاپی 50، بهار 1404)

The present study investigates the combustion of an ammonia/methane mixture in a porous medium and the impact of various parameters on the stability and intensity of this process. The use of ammonia as a carbon-free fuel presents challenges such as reduced flame temperature and speed, which may hinder effective heat transfer in combustion systems. Additionally, the nitrogen present in ammonia can lead to increased production of nitrogen oxides (NOx), which are major air pollutants. To address these issues, the use of a porous medium in the combustion chamber can help improve combustion conditions and reduce pollutant emissions. In this study, the effects of various parameters, such as the porosity of the porous medium (ranging from 0.5 to 1.0), the ammonia fuel fraction in the ammonia/methane mixture (ranging from 0.1 to 0.9), and the fuel-to-air equivalence ratio (ranging from 0.5 to 1.5), were numerically investigated and compared with experimental data. The results show that variations in porosity and fuel ratio have significant effects on combustion temperature, pollutant emissions, and flame stability. An increase in porosity enhances heat and mass transfer, thereby improving flame stability and combustion temperature. Furthermore, increasing the methane fraction in the fuel mixture raises the combustion temperature, while increasing the ammonia share can result in lower temperature and higher NOx production. These findings highlight the importance of optimizing the porosity, fuel ratio, and equivalence ratio simultaneously in combustion systems to reduce pollutants and enhance the efficiency of combustion processes.
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In this study, the performance of an annular combustion chamber of a microturbine was simulated using syngas derived from coal and biomass. The primary objective is to investigate the combustion chamber’s performance and pollutant emissions under premixed combustion conditions. The simulations are conducted using a partially premixed combustion model and the k-epsilon Realizable turbulence model. The partially premixed combustion model, by integrating the advantages of both premixed and non-premixed combustion, enabled an accurate analysis of the combustion process and provided precise predictions of complex turbulent flow behaviors and chemical reactions. The fuel and air were assumed to be premixed, which improved temperature uniformity and contributed to a reduction in NOx emissions when using syngas. An analysis of the OH mass fraction revealed that coal-derived syngas, due to its high hydrogen content and faster combustion rate, produces the shortest flame. The NOx and CO emissions for this fuel were 3.23 ppm and 227.3 ppm, respectively. On the other hand, biomass-derived syngas generates a temperature field similar to that of pure methane combustion due to its methane content. However, the high concentrations of methane and carbon monoxide resulted in a significant CO emission of 2914 ppm. This fuel also exhibited the highest NOx emission, reaching 29.9 ppm. The findings indicate that utilizing coal-derived syngas in premixed combustion conditions reduces NOx emissions and thermal hotspots.

Reduction of chemical mechanisms is of particular importance to decrease the computational time of combustion simulations. The main goal of this research is to reduce the chemical mechanism of JP-10. To achieve this, an innovative approach was applied, which combined various mechanism reduction methods, including sensitivity analysis, directed relation graphs (DRG), and directed relation graphs with error propagation (DRGEP). Using this approach, the detailed JP-10 mechanism, consisting of 7,740 reactions and 320 species, was reduced to 257 reactions and 48 species. In this regard, ANSYS CHEMKIN was employed for mechanism reduction and combustion simulation. The combustion simulation results for JP-10 in a homogeneous reactor model were then compared using both the detailed and reduced mechanisms. The results exhibited a high level of agreement, with simulation errors below 10%. Furthermore, the results demonstrated that DRG and DRGEP methods are both fast and accurate in identifying less significant species in the mechanism, whereas the sensitivity analysis method is comparatively slower. Validation of the results with experimental data from other researchers confirmed that the model used in this study is highly accurate, making the proposed mechanism reliable for use in combustion simulations.

This study examines the conceptual design and optimization of an air gas turbine combustion chamber. The combustion chamber under investigation is based on the CFM56-3 engine, with initial data sourced from Gasturb software and similar studies. The method for calculating the reference area and diameter is explored, and a systematic approach for selecting the optimal diameter is presented. Key aspects of combustion chamber design, including air distribution, diffuser, flame stabilizer, flame temperature, the number and size of holes in various sections, combustion efficiency, and pollutant emissions, are analyzed using chemical and semi-empirical methods. Next, the designs were coupled using the multi-objective optimization algorithm NSGA-II and MATLAB software. Optimizations in this study were performed for four simultaneous and conflicting goals: increasing combustion efficiency, reducing the length of the combustion chamber, and reducing carbon monoxide and NOx emissions. The results of this study showed that if multi-objective algorithms are used and performance constraints are appropriately applied to the combustion chamber of gas turbines, thermal performance can be improved by 1.5%, combustion chamber length by 7.8%, and average emissions by 64% compared to the original design.
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The present study investigates the effect of oxygenated fuel additives on diesel engine performance. Publications aim to evaluate these additives not only from the point of view of performance but also by considering environmental factors through the lens of the extra-environmental method. This research evaluates diesel engine performance using conventional and oxygenated fuel blends, focusing on biodiesel, dimethyl carbonate (DMC), and diethylene glycol (DEG), including comparing fuel efficiency, emissions, and engine behavior with these additives. This study uses the exergoenvironmental method to understand environmental implications, integrating exergy analysis with environmental considerations. The results show that using these oxygen additives affects engine performance and greenhouse gas emissions. Adding biodiesel reduces greenhouse gas emissions, such as particulate matter and nitrogen oxides. At the same time, DMC and DEG also help reduce emissions but have different effects on engine efficiency. Environmental externality analysis provides a comprehensive perspective on these fuel additives' environmental costs and benefits. Overall, this study provides insights into how oxygenated fuel additives can affect diesel engine performance and emissions, emphasizing the importance of balancing performance with environmental impact. These findings contribute to the continued exploration of cleaner fuel alternatives in diesel engines, focusing on optimizing engine performance and environmental sustainability.