Recently, there has been automotive-industry-wide impetus to reduce the overall diesel vehicle emissions and the fuel consumption by increasing the fuel injection pressure within common-rail systems. Many production fuel injection systems are now capable of delivering rail pressures of 1800–2000 bar, with those able to achieve 3000 bar under development. In addition, there has been a gradual increase in the permitted fatty acid methyl ester content in EN 590 diesel from 5% to 7% with further increases to 10% proposed. With these changes, there has been mounting speculation that increasing the injection pressure, particularly with an elevated biodiesel content, can contribute to fuel degradation, deposit formation, fuel filter blocking and corresponding vehicle reliability issues. In this investigation, a bespoke high-pressure fuel injection rig was designed and commissioned to mimic conditions representative of those experienced within a modern vehicle engine. The impacts of the rail pressure, the biodiesel content and the accelerated testing conditions on the stability of the diesel fuel and deposit formation leading to filter blocking were assessed. Despite the abundance of literature on laboratory-based biodiesel degradation, in these more realistic operating conditions it was found that biodiesel did not increase the likelihood of deposit formation within the high-pressure fuel system, with the same level of filter blocking observed for both the baseline diesel B0 (i.e. no biodiesel) and the B10 blend (which contains 10% biodiesel). This implies that the filter-blocking problem caused by onboard fuel degradation has the potential to occur broadly in a wide range of different fuel compositions. B10 fuel tested with a rail pressure of 2000 bar resulted in a pressure drop across the fuel filter of 0.5 bar within 12,000 min (approximately 8.3 days), whereas the corresponding experiment at a rail pressure of 1000 bar showed no increase in the filter pressure. When using model (B10) fuel, filter blocking was observed at rail pressures of both 2000 bar and 1000 bar, but with a lower pressure at a much reduced rate, leading to the belief that the increases in the rail pressure towards 2000 bar has a significant effect on the propensity of vehicle diesel filters to block. Measures taken to increase the severity of the test, such as recirculating injected fuel to simulate shear effects, were found to increase the rate of degradation but did not change the chemical composition of the solids formed, thus implying that they were valid methods of reducing the test duration without introducing new degradation mechanisms. The rig presented here is therefore a suitable accelerated testing system for assessing the behaviour of fuels at higher pressures that will be common throughout the global diesel fleet in the near future.

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.

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In this investigation a range of ketone biofuels produced from the alkylation of isoamyl alcohol and isobutanol were examined as potential blending agents with Jet A-1 aviation kerosene. The fuels were synthesised under solvent-free conditions using a Pd/C catalyst with K3PO4, previously reported for the alkylation of acetone, butanol, ethanol (ABE) fermentation mixtures. Reasonable yields and selectivity were achieved for branched alkylation products with up to 61 % produced from isoamyl alcohol and 64 % from isobutanol. The key aviation fuel properties of the mixtures were tested unblended and in 50% and 20% blends with Jet A-1 aviation kerosene. The freezing point of the fuels were all found to be below the required-47 °C irrespective of blend or the temperature of the reaction. The energy density of the unblended fuels ranged between 30.4-41.36 MJ/kg depending on the temperature of the reaction and whether remaining alcohols were removed. While this is below the HHV of the Jet A-1 used (45.69 MJ/kg) the energy density of the 50% and 20% blends were more suitable with the isoamyl alcohol derived fuels having a maximum HHV of 44.31 MJ/kg at 50% blending and 44.99 MJ/kg at 20% blend with Jet A-1. The fuels derived from isoamyl alcohol produced above 140 °C were found to satisfy the flash point criterion (>38 °C) of the Jet A-1 specification, though the isobutanol derived fuels did not, producing fuels with flash points between 33 °C and 35 °C. The kinematic viscosity of the fuels were also tested at-20 °C. Unblended only a few of the fuels analysed met the maximum viscosity requirement at-20 °C of 8 mm 2 s-1 , though this fuel property was improved substantially on blending with jet fuel. This work demonstrates that ketones produced from isoamyl alcohol through a simple alkylation have the potential to be used as blending agents with Jet A-1.