Nonwoven Coalescing Fuel-Water Filter Media for Diesel Engines

Fuel-water filters are a promising solution for the removal of water from diesel fuel and frequently rely on a depth coalescing nonwoven medium and a barrier mesh. Water is a fuel contaminant that can cause severe damage to engine injectors by promoting corrosion and microbial growth. Coalescing water out of diesel fuel has become challenging because of the increasing amount of bio-diesel and performance enhancing additives that are present to meet emission control regulations. High water content and the reduction in interfacial tension (IFT) between the water and diesel are associated with formation of more stable emulsions and the generation of smaller water droplets that are harder to remove. This research systematically investigates the characteristics of bio-diesel and surfactant (monoolein) blends with standard diesel fuel, and explores the factors affecting the efficient removal of water from fuel by means of depth coalescing media composed of poly(butylene terephthalate) (PBT) meltblown fabrics. It was established that bio-diesel and monoolein do not influence the IFT of water in fuel in a comparable manner and the resulting water droplet size distributions (DSD) are substantially different, which has implications in terms of the interpretation of results from commonly used ISO and SAE standard test methods. Fuels blended with bio-diesel exhibited higher viscosity and water content than fuel freshly blended with monoolein. Online measurement of water droplet sizes revealed substantially smaller water droplets in bio-diesel blends compared to monoolien blends at the same IFT measured using offline tensiometry. The surface wetting characteristics of PBT meltblown media were modified by alkaline hydrolysis independently of fabric geometric configuration and treated fabrics exhibited greater coalescence efficiencies (up to a 150% increase) but a lower quality factor than untreated samples due to a higher pressure drop attributed to increased water retention. The optimal wetting behaviour of fibres for achieving maximal coalescence efficiency was not the same for reference diesel and fuel containing surfactant, i.e. monoolein. A universal filter medium with a high coalescence performance cannot therefore be readily achieved if based solely on tuning fibre wetting properties. It was found that the fundamental trade-off between coalescence efficiency and pressure drop could be addressed by dynamic modification of fabric porosity (from 93% to 98%). By enabling fabric dimensions and geometric configuration to be modified in forced flow conditions, improvements in both coalescence efficiency (up to a 150% increase) and quality factor (up to 99 times greater) compared to the control flat sheet filter samples were achieved for both bio-diesel and monoolein-blended fuels.