With diesel now regarded as the cleaner choice of fuel at the pumps, it's now 'petroleum' now often concocts the image of impure and polluting gasoline. In fact, petrol and diesel aren't too dissimilar; the latter is considered a distillation of its fuel oil counterpart. The only exception to this rule is biodiesel, which is of course derived through more diverse means.
Petrol & Diesel Differences
The main difference comes in the way diesel oil is treated in the engine, and the way it helps the motor run. Diesel is treated so that it serves as a lubricant, preparing the working parts of the engine to cause the combustion. This is why repairs can be so devastatingly expensive in misfuelling of a DERV (diesel engine road vehicle); as unleaded petrol is a solvent, it strips away the lubricated parts and can cause serious damage.
Low Emission Diesel Cars
Diesel is mostly constructed from a variety of hydrocarbon formations, though its previous curse of loud, smelly exhaust has been attributed to the high level of sulphur found in the mix. Over the next few years we can expect the 'clean-up' of diesel to come to a head with the phasing out of heavy quantities of sulphur to accommodate for an ultra-low formula to take its place at the pumps.