Are Cold Filter Plugging Point and Cloud Point reliable enough to prevent cold-start operability problems in vehicles using biodiesel blends?

Abstract

Despite being subjected to tight sustainability restrictions in the last decade (Directives 2009-28-CE, 2015-1513-CE, and EU-2018-2001), the use of biodiesel in compression ignition engines is still increasing in the European Union. As known, one of the main drawbacks of biodiesel is cold flow behavior, along with oxidation stability problems. According to European standards, the Cold Filter Plugging Point and Cloud Point methods are the ones used to ensure diesel vehicle operability in temperate and arctic climates, respectively, within the EU. Despite the existing standards, several issues related to startability have occurred in the northern European countries due to filter clogging. In this frame, this study checks the reliability of the conventional Cold Filter Plugging Point and Cloud Point tests by comparing their results with those coming from an experimental rig that simulates the low-pressure fuel circuit of a diesel vehicle. Baseline diesel was blended with two biodiesel fuels (7% and 10% by volume) produced from palm oil. Regardless of the fuel used and the blend (B7 or B10), Cold Filter Plugging Point and Cloud Point methods underestimate the temperature at which the filter clogging occurs compared to real conditions, these differences being as significant as 4°C when compared to Cold Filter Plugging Point and Cloud Point, respectively. Results obtained encourage either searching for more reliable standards to quantify the cold flow behavior of biodiesel fuels or limiting the maximum content of the main compounds causing cold-start problems.