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Green Corner


 

 

 

An A-Z of the environment & issues

by Peter Hatswell

 

 

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D is for diesel

 

If there were no diesel fuel and we used only petrol and coal, our atmosphere would contain more carbon dioxide than the dangerous levels that exist today. It is thanks to the efficiency of the Diesel cycle in engines (compared with the Otto cycle for petrol engines) that we can get many more miles per gallon and hence less CO2.

However, it is not all good news because diesel engines emit more carbon particles per mile. These are strongly linked to respiratory illness and filtering them all out would significantly compromise the advantage of efficiency.

 

The compression-ignition diesel engine was patented by Herbert Ackroyd-Stewart in 1890 but improved by Rudolf Diesel into the most successful and flexible power source since the steam engine.

Diesel oil is a fossil fuel which comes from the middle of the fractional distillation column of crude oil, just above lubricating oils and just below paraffin and petrol. It boils between 2600C and 3400C and when introduced to hot air in an engine cylinder, self-ignites and causes the expansion necessary to force the pistons to turn the crankshaft, giving us power. It is the relatively high pressure inside the cylinders that is responsible for the knocking noise that we often hear and the need for heavy and strong engines – more suited to commercial vehicles, power plants, boats etc.

 

Until the advent of “City diesel” fuel, all diesel engines suffered from the ‘bad egg’ sulphurous smell and the sulphur emitted combined with water vapour to form acids with devastating effects on life in inland lakes, in forests and the erosion of building materials - including those used to construct Dunstable Priory. To be fair, coal, lignite and heavy oil were the worst offenders in this respect but untreated diesel had a significant effect because of its widespread use.

 

Happily, the diesel cycle works fine with renewable carbon-neutral fuels such as bio-diesel (new and reclaimed vegetable oil) and without the sulphur problem. You may however notice the smell of frying when following a vegetable powered vehicle!

 

 

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