Analysis of a New Cleaning Technology Based on Supercritical Carbon Dioxide Pre-treatment for Diesel Engine Remanufacturing
Remanufacturing is the rebuilding of a used product to at least its original performance with a warranty that is equivalent or better than that of the newly manufactured product. It is a vital means in improving manufacturing sustainability, through saving raw materials, reducing carbon emissions and conserving product commercial values. As the one of the demanding steps in remanufacturing process, cleaning is also one polluting stage because of the use of environmental detrimental cleaning agents and the large amount of energy consumptions. The specific aim of the work demonstrated in this thesis is to find an alternative cleaning agent that could achieve the effective cleaning of decommissioned engine parts, in an environmentally greener way. More generally, the study in this thesis uses supercritical carbon dioxide (SC-CO₂) as the green agent to reduce the possible environment loads induced by conventional cleaning technologies and further investigate the feasibility of this method in removing other contaminants as an application extension. Organic contaminants, containing greases, lubricating substances and carbon depositions are the most commonly observed contaminants in a decommissioned engine, and they are analysed by a series of analytical methods to validate the feasibility of SC-CO₂ cleaning in this study. Experiments on grease, lubricating oil and paint coatings cleaning are carried out on the supercritical fluid (SCF) facility with the addition of liquid blasting to remove residues after SC-CO₂ treatment. A new cleaning method combining SC-CO₂ pre-treatment and liquid blasting post-treatment processes is proposed and a comparison is conducted between this method and conventional method (thermal decomposition and shot blasting cleaning). Operation parameters for liquid blasting process are determined through single particle blasting test and the comparison demonstrates the new method has a minimal impact on the surface properties of substrate materials, while the conventional cleaning method has a significant negative impact. Ultimately, the comparative life cycle assessment between two methods demonstrates the new cleaning technology can attain a higher cleanliness with better environmental performances. It is concluded that the SC-CO₂ cleaning could provide a “cleaner production” method for remanufacturing.