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Internal diesel injector deposits (IDID) are now a well understood phenomenon and a standard test procedure has been developed and partially approved by the Coordinating European Council (CEC). The engine test procedure has been approved for simulation of sodium soap deposits by dosing the test fuel with a sodium salt and dodecenyl succinic acid (DDSA), whilst amide lacquer deposits simulation by dosing the test fuel with a low molecular weight (MWt) polyisobutylene succinimide (PIBSI) is still under development. The solubility of these contaminants in the base fuel should be reasonably constant to achieve consistent results. With the introduction of diesel from varying sources, this study focused on the effect of near-zero aromatics EN 15940 compliant gas-to-liquids GTL diesel, very similar to hydrotreated vegetable oil (HVO), on IDID severity across two different engine platforms, and the response of a modern deposit control additive.

Gas to Liquids (GTL) diesel has been produced commercially for several years. GTL diesel is known for its excellent properties, including zero aromatics, near zero sulphur and a high cetane number. Most of the GTL diesel produced by commercial plants is utilised as a blend component, especially in blends up to 20%. In these applications, the cold flow properties are potentially less critical, as the cold flow properties of the blend will mostly be determined by the petroleum-derived component. In certain markets, however, it is possible that GTL diesel can be used as a neat diesel, therefore requiring good cold flow properties. An advantage of GTL technology is that the cold flow properties of GTL diesel can be tailored to meet the climatic requirements of a specific geographical area. In the current study, GTL diesel samples with cold flow properties ranging from ‘summer type’ to ‘winter type’ and varying intermediate cold flow qualities were evaluated.

The success of modern diesel passenger cars is, to some extent, attributable to the advent of common rail diesel injection technology. Today almost all new diesel engines use this technology which is characterised by high fuel injection pressure and very small diameter nozzle holes. The industry rapidly developed a new test procedure to assess a fuel's propensity to cause injector fouling and also to assess the ability of additives to clean and to keep such injectors clean. The CEC F-98-08 DW10 test procedure was approved in March 2008 by the CEC and is now considered an industry standard test method. The test method requires 1ppm zinc to be dosed into all test fuels in order to accelerate injector fouling. This paper presents DW10 test results for gas-to-liquids (GTL) diesel. A similar test method, using a different engine, was developed in-house and showed good correlation with the DW10 test.

There is a worldwide drive to reduce the dependence on fossil fuels, mainly driven by volatility in the crude oil price, political instability in oil-producing countries and environmental concerns. In several European countries, diesel passenger cars outsell gasoline-powered cars by a significant margin. Common rail diesel injection technology has played a significant role in making diesel engines more acceptable in light-duty applications, given the significantly improved emissions (due to better atomization) and engine noise offered by this technology. These developments have contributed to a renewed interest in alternative diesels like biodiesel and Gas to Liquid (GTL) diesel. Recently, CEN TS 15940:2012 was approved for publication. This specification will enable paraffinic diesel (including GTL diesel) to be sold commercially as a neat fuel or as a blend, containing up to 7% fatty acid methyl ester biodiesel (FAME).

Iso-stoichiometric ternary blends - in which three-component blends of gasoline, ethanol and methanol are configured to the same stoichiometric air-fuel ratio as an equivalent binary ethanol-gasoline blend - can function as invisible "drop-in" fuels suitable for the existing E85/gasoline flex-fuel vehicle fleet. This has been demonstrated for the two principal means of detecting alcohol content in such vehicles, which are considered to be a virtual, or software-based, sensor, and a physical sensor in the fuel line. Furthermore when using such fuels the tailpipe CO₂ emissions are essentially identical to those found when the vehicle is operated on E85. Because of the fact that methanol can be made from a wider range of feed stocks than ethanol and at a cheaper price, these blends then provide opportunities to improve energy security, to reduce greenhouse gas emissions and to produce a fuel blend which could potentially be cheaper on a cost-per-unit-energy basis than gasoline or diesel.

The combination of high crude oil prices, energy security concerns and environmental drivers have resulted in an increased focus on alternative fuels. Gas to liquids (GTL) diesel is considered to be a promising alternative diesel fuel, given that it can be used directly as a diesel fuel or be blended with petroleum-derived diesel or biodiesel. GTL diesel fuels are predominantly paraffinic and possess several excellent inherent properties including virtually zero sulfur, very low aromatics (≺1%) and very high cetane values (typically ≻75). Currently GTL diesel is mostly sold into the European market as a blend stock for the extending and upgrading of petroleum-derived diesel fuels. Given GTL diesel's inherent paraffinic nature, the density of this product is below the European minimum 820 kg/m₃ EN590 specification (at 15°C).

Direct Injection Spark Ignition (DISI) engine technology is becoming increasingly common in the South African and global vehicle parcs. South Africa is in a unique position because a significant portion of all liquid fuels consumed are synthetically produced from coal and gas. These fuels are mainly supplied into the inland regions, particularly the Gauteng province, the economic heartland of South Africa and the most densely populated area in the country. It is important to understand the performance of synthetic fuels in the latest generation engines, in order to ensure that these fuels are fit for use in these new applications. The latest generation DISI gasoline engines (also known as Gasoline Direct Injection™ and Fuel Stratified Injection™) differ significantly in operation to older Port-Fuel-Injected (PFI) engines.