Down-to-earth diesel

Some weeks ago Pippo Psaila got so involved with "highlighting the inaccurate and misleading assertions in the learned professors' letter" that he did not seem to realise that he did a good demolition job on his own. His "really magic diesel" that did not emit greenhouse gases has suddenly found itself chained by percentages of this and that.

Magic apart, it needs to be made clear that any discussion of these matters requires clarity on fuel types, mixtures, engines and driving conditions. For instance "diesel ex-Enemalta" now has a sulphur content 10 times smaller (0.05 per cent) than stated by Mr Psaila, even if this is still higher than that of biodiesel.

Mr Psaila's initial set of figures come from a US source; they refer to tailpipe emissions from heavy duty engines (static or mobile?) except for CO2, where lifecycle values are given. Lifecycle emissions of any pollutant include those emissions produced in preparing the fuel, as well as tailpipe emissions which result from fuel use. We have used two sources: one from Harwell, UK (H) and the other coming from the Australian Greenhouse Office (AGO). The latter source is the more complete; both sources give emissions of some pollutants from rapeseed diesel (known in the trade as rapeseed methyl ester or RME) and (in the case of AGO) also from waste oil biodiesel (WOD) compared to low sulphur diesel (LSD). Mr Psaila's US figures do not specify biodiesel type.

For CO2 lifecycle emissions both our sources give around 50 per cent for rapeseed (RME), higher than Mr Psaila, and one source measures 10 per cent for waste oil biodiesel (WOD), which must be closer to the edible oil product. For CO, Harwell gives no reduction, in strong disagreement with Mr Psaila. For nitrogen oxides (NOx), our sources and Mr Psaila's agree: biodiesel produces more NOx than LSD, even if the uncertainties in the results are quite large. On the other hand, hydrocarbon emissions - essentially unburnt fuel - for RME are about the same as LSD in our sources. Mr Psaila's figures agree with ours for WOD.

Of course, the main bone of contention lies in the level of particulate emissions. Our AGO source has RME and WOD emitting around 50 per cent of the LSD particulates, with large uncertainties on the results. This figure is close to Mr Psaila's value. The Harwell source has RME with twice the particulate emissions of LSD, without any indication of the uncertainties on that result. But numbers of particles apart, the absence of benzene-like compounds in biodiesel (even if these are produced whenever a carbon-containing substance is burnt) makes its particles less dangerous than those of mineral diesel, less dangerous in a carcinogenic sense. So even the Harwell result, if it is to be believed, could indicate less harmful particle emission.

Both our sources mention the possibility of chemical attack from biodiesel on certain types of elastomer and natural rubber compounds.

Now to get down to practicalities. There is no doubt - as we have said before - that there is a good case for biodiesel without any "magic" having to be invoked. As an examination of results shows, there is a problem with conflicting and uneven quality results. However, Mr Psaila has a way out of that maze. He can undertake testing of his brand of biodiesel in use in the Edible Oil and EPD vehicles. That way he (and the public) can have some idea of the qualities of the product under local conditions, without any need to invoke any magic.