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DAILY TELEGRAPH (UK) MOTORING: Diesel's a gas: Meanwhile in Europe, Shell is working on its cleanest ever diesel, says Andrew English  ( 22 Jan 05


(Filed: 22/01/2005)


"This is real racing fuel," said Shell's Jack Jacometti of his company's new "designer diesel", which is made from natural gas. "It produces no more carbon dioxide than conventional diesel, has virtually no sulphur or aromatics and about 60 per cent higher cetane value, which improves combustability."


Being the vice-president of the development of Shell's GTL synthetic fuel, you might expect Jacometti to make big claims for the gas-to-liquid (GTL) process that produces the fuel, but Shell has backed his claims. Its first GTL plant in Bintulu, Malaysia, has been operating for 10 years and supplied diesel fuel for some of the runners at the 2004 Michelin Bibendum Challenge (Motoring, October 30).


Last summer it signed a contract to build the world's largest GTL plant at Ras Laffan, Qatar. When operational in 2011, the $56 billion Pearl GTL plant will produce 140,000 barrels of GTL fuel a day, primarily for aircraft at less than $20 a barrel.


The Shell process is a derivation of the catalyst and steam-reforming Fischer-Tropsch method, patented by German scientists, Franz Fischer and Hans Tropsch in the early 1900s, and allows the conversion of low-density fuels like coal and natural gas into high-quality, cleaner-burning liquids. Although more expensive to produce than traditionally distilled crude oil, Fischer-Tropsch fuels are cleaner than conventional hydrocarbon fuels and, with low sulphur levels, produce low levels of particulates, hydrocarbons and carbon monoxides. Their high cetane value also allows improved combustion at lower temperatures and can reduce the production of oxides of nitrogen.


Shell has been testing its GTL fuel in London buses, a fleet of VW Golf cars in Germany and trucks in the US and Japan. The latest trial is in a fleet of Toyota Avensis cars equipped with the company's D-CAT diesel engine, which uses exhaust-gas recirculation and an oxidation catalyst.


The 20-litre, 114bhp unit needs to run on low-sulphur diesel and in the UK this means less than 10 parts per million (ppm) levels of sulphur, a standard that is also available in Germany.


However, diesel in some parts of Europe can have up to 350ppm of sulphur and in those circumstances drivers need to disengage the oxidation cat, via a dashboard button, or it could become blocked after prolonged running.


Current diesel engine requirements in Europe (Euro 4) require new engines to emit less than 025g/km of oxides of nitrogen (NOx) and 0025g/km of particulate matter (PM). Toyota is coy about what the D-CAT engine will produce in this respect, but says it would be more than happy if Europe lowered the limits for its Euro 5 standard to 0125g/km for NOx and 0005g/km for PM.


It's perhaps interesting to note that the proposed 2007 US Tier II Bin 5 standards are for 001g/km for both NOx and PM - small wonder car makers are complaining that the US is legislating the diesel out of existence.

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