Metals and fuel system polymers on exposure to Dimethyl Ether: A material compatibility study

Abstract

Material incompatibility between an alternative fuel and fuel system is a major issue that needs to be addressed for adoption of more sustainable alternatives to fossil fuel resources. Dimethyl ether (DME) has a high cetane number, low auto ignition temperature, low toxicity and is non– corrosive. It has low nitrogen oxides (NOx) and sulphur oxides (SOx) emissions and is thus environmental friendly. Hence it serves as an alternative to gasoline and diesel. The aim of this study is to evaluate the physical and chemical changes taking place in metals (mild steel [MS], stainless steel [SS], aluminum [Al] and brass) and nonmetals (High density polyethylene [HDPE], Polytetrafluoroethylene [PTFE], Polyurethane [PU] and Nitrile butadiene rubber [NBR]) typically used in auto parts and fuelling infrastructure, post exposure to DME maintained at 5 bar pressure at room temperature. The effects of the exposure were examined by comparing changes in gain/loss of mass, hardness and tensile strength. Hardness studies were done in accordance with the ASTM D2240-15 and tensile strength measurements as per ASTM D412. The surface morphology of coupons was characterized by scanning electron microscopy and elemental analysis of the test specimens were investigated by Energy Dispersive X-Ray Spectroscopy. The results show that there were no significant changes observed in metals post exposure to DME. This was also substantiated by FTIR studies. Polymeric materials were found to have gained mass in the order PTFE<HDPE<NBR<PU. This increase in mass is attributed to the absorption of polar groups present in the fuel by the elastomeric materials. Reduction in hardness and tensile strength values were observed for all materials when exposed to DME compared to unexposed surfaces. This has also been proven by SEM images.