Underground » Health and Safety
A used, mine specification Caterpillar 3304 PCNA engine coupled to a dynamometer, was used to test and contrast the emissions from 8 disparate diesel fuels, one of which included a proprietary, after-market additive.
No "optimum" fuel specification could be found as all of the fuels tested gave acceptable performance with regard to emission characteristics and none would have failed the statutory emission tests in the test engine. The immediate conclusion from this is that the cheapest should be used, however there are complications discussed below.
Fuel density is the most significant fuel property affecting emission and performance behaviour, directly linked to carbon monoxide, NOx and particulates, under most operating conditions. However, the desirable benefits associated with reduced fuel density can produce some undesirable effects in other emission characteristics. Also, there is a power performance penalty (max 13%) associated with the lower density fuels, which might have a significant impact on the functional operation of diesel equipment.
A number of the emission products showed significant variations from fuel to fuel and which could not be statistically related to fuel properties. In particular, aldehyde emissions could not be correlated against any of the fuel properties examined in this project.
Although none of the fuels produced emission levels that exceeded the statutory limits for raw exhaust, there were some considerable variations, especially Carbon Monoxide and particulates. Some fuels provide a greater margin between statutory limits and raw exhaust carbon monoxide levels, suggesting that an engine that was marginal with respect to statutory limits with one fuel, might well be entirely acceptable with another fuel. This suggests type approval and in-service testing must consider fuel specification. The current practice of specifying a diesel fuel that meets AS3570 is clearly inadequate as many different fuels meet this.
Testing of a proprietary additive gave 15 to 20% reductions in carbon monoxide emissions under most operating conditions. Other reductions were noted for some emission characteristics under some circumstances and the use of an additive would have to be assessed in this light.
The variability in emissions between fuels and engine duty indicates that mines have to take extreme care in trying to solve emission-based problems by altering fuel specification. No single specification is a universal panacea for all emission based problems, and each individual problem must be addressed individually and holistically.