Enhancing the solubility of biodiesel impurities for improved performance of FAME Fuels during cold weather

Abstract: Low level polar manufacturing impurities in FAME fuels, such as residual glycerol (GLY) and saturated monoglycerides (SMGs), have low solubilities that induce the formation of problematic fuel-filter capturable heterophases (HPs) mainly during cold weather. Currently enforced international limits on residual glycerides are mainly intended to curb noxious exhaust emissions, while GLY residuals have less recognized additional constraints due to low solubilities in FAME, further exacerbated by blending with hydrocarbon diesel fuels. Unfortunately, such limits fail to thwart HP formation leading to inhibited fuel flows through low micron filters, thereby disrupting programmed fuel/air ratios, and at times blocking flows unexpectedly. Modifications of FAME/fuel formulations with low percentages of polar adjuvants, such as alcohols, can substantially increase solubilities to levels more conducive to cold weather operations. However, few prospective adjuvants meet requirements needed for cold weather operations, due to phase separation, low flash points, or poor oxidative stability. Presented are candidates evaluated favorably elsewhere for key engine and exhaust requirements, and here found to enhance the solubilities of key HP formers needed for operations in colder environments. At low percentages, n-butanol adjuvants meet key fuel criteria while improving the solubility of both GLY and SMG residuals, substantially reducing risks of using FAME fuels during winter months.