The practical application value of n-butanol in a heavy-duty engine: Energy-exergy-emission-environmental cost (4E) and sustainability analysis

Environmental analysis methods, such as environmental cost accounting, are widely used in the aeroengine field, playing a crucial role in enhancing energy utilization. Therefore, to extend these benefits to heavy-duty engines and investigate the sustainability and environmental cost of n-butanol/diesel blends with different alcohol energy fractions, this study was carried out on a heavy-duty engine. The following fuels were tested: pure diesel (AEF0), 85 % diesel + 15 % n-butanol (by volume) (AEF12), and 70 % diesel + 30 % n-butanol (by volume) (AEF25). The results showed that the higher the alcohol energy fraction, the poorer the fuel economy. However, both energy efficiency and exergy efficiency can be improved with the addition of n-butanol. Energy efficiency was consistently higher than exergy efficiency across all operating conditions, reaching maximum values of 43.27 % and 40.04 %, respectively, under identical conditions. Furthermore, the Sustainability index (SI) and Improvement potential (IP) both exhibited a change in trend at 14 bar, with a sharp increase in SI and a decrease in IP. With increasing alcohol energy fraction, these inflection points shifted to lower loads. Soot emissions decreased significantly with increasing alcohol energy fraction, with the highest decrease of 65.2 %. However, NOx emissions of the blend fuels increased significantly at medium and high loads, exceeding 800 ppm under certain conditions. Additionally, the environmental effects of n-butanol were significantly increased under medium and high loads, resulting in an increase in environmental cost from 7.1 % to 34.4 × 10-3 €/kWh at loads around 18 bar. This study provides a reference for evaluating the practical application value of alcohol additives.