جستجوی مقالات مرتبط با کلیدواژه « ارزیابی چرخه حیات » در نشریات گروه « مکانیک »

The investigation of alternative fuels, such as biodiesel, have been prompted by the detrimental emissions resulting from the combustion of fossil fuels. Undoubtedly, the primary concern in fuel selection lies in the examination of emissions. Hence, the present study aims to examine the performance and environmental life cycle assessment methodologies of a dual fuel diesel engine. Furthermore, a fuel blend is made by combining biodiesel sourced from sunflower oil with varying concentrations of bioethanol (3%, 5%, and 7%) and pure biogas, with a percentage ranging from 50% to 80%. This fuel blend is intended for use in the combustion process. In this study, a total of eight fuel samples were meticulously produced and subsequently examined, alongside diesel fuel which served as the control fuel. The entire life cycle evaluation encompasses several stages, starting with the manufacturing of inputs to the combustion of fuel samples. This includes the extraction of oil from sunflower seeds, the production of biodiesel and bioethanol, as well as the generation of natural gas produced from pure biogas. These processes are regarded as captivating and pioneering topics within the field. The provided samples underwent combustion within a dual fuel engine. The findings indicate that the B5 fuel sample, when combined with a 3% bioethanol additive, demonstrates superior engine performance and reduced exhaust emissions. Furthermore, enhanced conditions were achieved in terms of engine performance and exhaust emissions when operating at the lowest rate of natural gas fractionation, which was 50%. The findings of a thorough life cycle evaluation, which examines the entire process from farm to combustion, indicate that the blend B5E7, consisting of 50% natural gas portion at maximum engine load, demonstrates both environmental friendliness and appropriate performance characteristics.

Greenhouse gas emissions, specifically carbon dioxide emissions, cause global warming and climate change. There are methods to reduce the amount of carbon dioxide in the atmosphere by capturing and utilizing the carbon dioxide. One method is the direct capture of carbon to produce fuels such as transportation fuels. However, to determine if the system is environmentally friendly, it is required to perform a life cycle assessment. This paper presents a life cycle assessment of an integrated system for transportation fuel production using direct air capture. This system absorbs carbon dioxide at first and then converts it into syngas using water electrolysis and reverse water-gas shift reaction. Subsequently, Fischer-Tropsch Synthesis takes place to produce fuel from the syngas. Environmental impacts are evaluated under three scenarios: using Iran’s electricity grid, future electricity grids, and clean (100% renewable) electricity. Using Iran’s electricity grid, the impacts of the system are 4.6 gCO2 eq./gCO2 captured; the most polluting part of the integrated system is the electricity for hydrogen production used in the Fischer-Tropsch and RWGS. Therefore, the electricity emission factor is identified as the most important factor in determining the integrated system with low environmental effects. In the second scenario, the system has an impact of 0.8 gCO2 eq./gCO2 captured. The environmental impacts of clean electricity are reduced to 0.72 gCO2 eq./gCO2 captured. The results show that the emission factor of the electricity has a significant impact. Therefore, this system can be used only where electricity is generated partly from renewable resources.

Increased demand for fossil fuels has led to climate change, global warming, and declining energy reserves. The use of renewable energy, such as solar energy, is a suitable approach to generating electricity and heat. One of the common systems in using solar energy is parabolic collectors, which enable this clean energy by converting the incoming radiation into thermal energy. In the present paper, to assess the potential of climates to make optimal use of solar parabolic collectors, a numerical model was developed in MATLAB software. Then, while validating the model with existing experimental results, the effect of climate change has been studied in four areas: energy, exergy, economy, and environment. For this purpose, five cities: Rasht, Shiraz, Tehran, Abadan, and Sanandaj, have been selected as representatives of Iran's climate and energy efficiency and exergy, the unit cost of energy, and the amount of carbon dioxide produced during the life cycle of the system has been obtained. The results show that Shiraz, with a  Semi-Arid Cool climate and thermal efficiency of 72% and a unit cost of  0. 035 $/ kWh, is the optimal climate in the fields of energy and economy, and Sanandaj with a Humid Continental climate and exergy efficiency of 17. 7% is the optimal climate in the field of exergy. In the environment, Rasht, with a Humid Subtropical Climate, was introduced as the optimal climate.

Concerns about increasing environmental pollution and increasing greenhouse gas emissions from fossil fuels have led researchers to use renewable energy. In this research, the environmental impacts of bioethanol production from potato waste were investigated from the agricultural stage to the production stage of bioethanol (crushing and malt production, enzymatic hydrolysis, fermentation and dehydration). Investigation of environmental impact of the data collection was done using a life cycle assessment method in the form of 15 impact groups and 4 final indicators, and its functional unit was considered to produce 1 kg of bioethanol. The results obtained from the impact groups in two stages of agriculture and bioethanol production showed that the agricultural stage in all the affected groups except the carcinogenicity group had higher values than the stages of bioethanol production (malt production, hydrolysis, fermentation and dewatering). Also the results showed that the highest contribution to creating different impact groups is related to energy consumption of electricity, steel, agricultural machinery, nitrogen, phosphate and direct emission of pollutants from the field and manufactory. The comparison between different environmental endpoints indicator shows that the human health index is 9.90 times higher than ecosystem quality, 1.28 times higher than climate change and 1.48 times higher than that of resources with destructive effects on bioethanol fuel production.