Assessing the Impact of FAME and Diesel Fuel Composition on Stability and Vehicle Filter Blocking

Abstract

In recent years, there has been an impetus in the automotive industry to develop newer diesel injection systems with a view to reducing fuel consumption and emissions. This development has led to hardware capable of higher pressures, typically up to 2500 bar. An increase in pressure will result in a corresponding increase in fuel temperature after compression with studies showing changes in fuel temperatures of up to 150 °C in 1000-2500 bar injection systems.Until recently, the addition of Fatty Acid Methyl Esters, FAME, to diesel had been blamed for a number of fuel system durability issues such as injector deposits and fuel filter blocking. Despite a growing acceptance within the automotive and petrochemical industries that FAME is not solely to blame for diesel instability, there is a lack of published literature in the area, with many studies still focusing on FAME oxidation to explain deposit formation and hardware durability.The majority of studies into diesel degradation are conducted under non-representative laboratory conditions, or are extrapolated from the deposits found in filters from vehicles with failed injectors. In this study, the cause of this degradation was investigated by using a novel High Pressure Common Rail (HPCR) non-firing rig designed to mimic a diesel common rail system, simulating realistic, albeit accelerated, operating conditions. The degree of deposition on the system fuel filter was monitored, for both petroleum diesel (B0), RF79 (B0), Bx (where x is percentage volume/volume of FAME) and surrogate diesel fuel components.A systematic study of synthetic surrogates demonstrated that, as well as FAME, any base fuel component, under sufficiently high pressures and temperatures experienced in the HPCR are prone to degradation irrespective of the concentration of the component in the original fuel. The most unstable component acts as the instigator, thus promoting fuel oxidation. The other components in the fuel such as FAME, aromatic and cycloalkane portions will also oxidise and eventually polymerise to form solids blocking the filter. This also demonstrates that while a large body of work on the oxidative instability of biodiesel in the chemical laboratory is indicative of instability this does not mimic what is seen under more realistic vehicle conditions and the focus on FAME instability is misleading.

Comparative analysis of filterability behavior of B30 and B40 biodiesel blends on various porosity and dimension of fuel filter

“…It was found that the presence of biodiesel had no effect on the clogging characteristics compared to conventional diesel, and the presence of aromatics and derivatives of nitrogen has a much more detrimental effect on oxidative stability. This is in accordance with a recent study, which focused on identifying the factors responsible for filter clogging by using a filter rig on a High-Pressure Common Rail (HPCR) system (Gopalan et al 2019). Furthermore, filter blockage can occur due to the accumulation of other impurities within the diesel engine filtration system.…”

Investigations of Diesel Injector Deposits Characterization and Testing

“…Injector deposits have been found in a number of locations in the injector, on the nozzle tip and in the spray holes external injector deposits (EDID) and since around 2008 internally on the push rod, the upper and lower springs and the needle. Though investigated for some time, these internal injector deposits (IDID) continue to be studied by groups worldwide because of their importance to the industry and a need to understand fully their nature [25][26][27][28][29][30][31][32][33]. Initial analysis by a number of groups contributed to identifying the deposits formed, leading to their classification in six distinct groups:…”

Diesel-Injection Equipment Parts Deterioration after Prolonged Use of Biodiesel

“…The use of high-percentage biodiesel blends is known to be associated with fuel injector deposits [11] and other types of injection system effects [12,13]. On the other hand, US and European market fuel surveys indicate that many retail biodiesel samples are out of specification, which means that poor quality biodiesel is not scarce [14,15].…”

“…The most demanding issue with the use of biodiesel is its oxidation stability, which affects performance, emissions, and engine durability ( Figure 1). The more general term biodiesel degradation is referred to the modification of its original composition and properties due to aging, oxidation, and metal corrosion during the storage process [12,16]. The compatibility of seal and hose materials commonly encountered in automotive fuel systems using conventional hydrocarbon fuels has long been established and elastomer manufacturers are able to make recommendations for their use.…”