Underground » Health and Safety
This project has used an engine dynamometer to undertake emissions testing of a range of 'alternative' diesel fuels in two different engine configurations. Various blends of different biodiesels, mixed with low sulphur 'pump' fuel, reduced the mass of diesel particulate matter(DPM) by as much as 92%, compared with low sulphur 'pump' diesel as now used by mines. The exact reduction varied with the fuel, engine type, load and speed, with the minimum result being a 13% reduction.
A reduction in DPM mass is consistent with other researchers' findings, but the best result found is more than others have shown. However the origin of the bio fuel, and the model of the test engine, are both known to influence the results, and this information is generally not detailed in other researchers' work.
Tests with an imported synthetic diesel blend fuel also showed some significant DPM mass reductions; however the huge cost of this fuel in Australia at this time makes it unlikely to be a credible option for widespread mine use in the short term. There is evidence to suggest the test engine was not optimally designed or tuned for this fuel, but that may not change the ultimate outcome.
By testing the same fuels with common rail injection and direct injection, it was shown that in all but one full speed/full load test, the common rail injection format produced lower DPM mass than the direct injection. At other load points, the variation between injection systems was 50% to 90%. In isolation, this suggests newer technology engines will probably reduce DPM mass.
Mass emissions varied by as much as 30 times, between full speed/full load, and half speed/half load. The observed variability between load, speed and injection technologies might suggest an individual operator could use this information to reduce DPM emissions, but a thorough understanding of their intended duty cycle would be needed to make a realistic assessment based solely on this data. The usefulness of the current AS3584 test points may need examination in light of this finding, as it is clear that duty cycle plays a huge role in DPM emissions.
In an attempt to assess the overall change in occupational risk from the alternative fuels, this project also examined the DPM particle number and particle size distribution. There is now clear evidence from other researchers that particle number and size are just as important, and perhaps more important, than mass, which is what the industry has focussed on so far. This alone is a critical finding which might influence any future work.
The tests conducted showed a large variation in particle number from the different bio diesels, with considerable reductions in some cases but considerable increases in others. This indicates a potential increase in risk associated with some of the fuels, despite the reduction in DPM mass. From the variation observed between the fuels, it is also evident that selecting one bio diesel in favour of another can have a huge impact on the nature of the DPM emissions.
It has been suggested that the median DPM particle size may be an indication of lung deposition risk. In most of the tests size reductions were found, and again the variation between the various fuels was considerable. Only the synthetic blend fuel in the direct injection engine produced a size increase. Based solely on this aspect, the bio blend fuels might offer increased problems in terms of lung deposition, but the real level of risk change (if any) is indeterminate. It is clear that a greater understanding of the mechanisms of DPM toxicity, and a wider scope of study including lung depositional modelling, would be needed to achieve a reliable estimate of the net risk change from the alternative fuels.
The various fuels were also tested for the presence of toxic chemicals adsorbed onto the DPM, but the results are insufficient to report conclusively on the relative risk associated with the fuels.
Experiences in handling and using the fuels suggest there are no negative issues with any of the fuels tested. In general terms, engine operators would not be able to differentiate between the fuels based on engine performance or handling characteristics.