|The addition of Al or Al2O3 nanoparticles increases the probability of ignition. Click to enlarge.|
Adding aluminum and aluminum oxide nanoparticles to diesel can improve the fuel’s ignition properties, according to a new study published online in the journal Nano Letters.
Arizona State University mechanical engineer Patrick E. Phelan and colleagues varied both particle size (15 and 50 nm) as well as the volume fraction (0%, 0.1%, and 0.5%) of aluminum (Al) and aluminum oxide (Al2O3) nanoparticles at several temperatures within the range 688 °C up to 768 °C. In a series of hot plate studies, they found that in all cases the ignition probability of the nanoparticles + diesel mixtures was much higher than that of pure diesel.
Although several studies have shown that the addition of nanoparticles to solid fuels and propellants can result in shortened ignition delay, increased energy density, and high burn rates, there has been little work has been reported in the past on the effect of adding nanoparticles to liquid fuels, according to the researchers.
...ignition delay and ignition temperature are critical parameters that characterize the performance of a diesel engine. Both efficiency as well as emission levels from a diesel engine can potentially be improved by optimizing the ignition delay and ignition temperature....It was observed that the hot plate ignition probability of the diesel fuel increases significantly by the addition of the nanoparticles. Moreover, the presence of some residue particles on the hot plate surface is also believed to contribute to an increase in the ignition probability of pure diesel.
They found that neither the change in nanoparticle material nor the nanoparticle size influenced the ignition probability of the nanoparticle + diesel mixtures. The researchers suggest that adding nanoparticles to the fuel caused significant improvements in its radiative and heat/mass transfer properties and hence the droplets ignited at a much lower temperature and also more often as compared to pure diesel.
Such an increase in heat and mass transfer properties of the fuel has the potential of reducing the evaporation (and ignition) time of droplets within a diesel engine and hence should favorably influence its ignition delay. Moreover, SEM analyses of the hot plate surface indicate that the presence of residue particles on the hot plate surface may have also participated in the enhancement of the ignition probability of pure diesel.
Himanshu Tyagi, Patrick E. Phelan, Ravi Prasher, Robert Peck, Taewoo Lee, Jose R. Pacheco, and Paul Arentzen (2008) Increased Hot-Plate Ignition Probability for Nanoparticle-Laden Diesel Fuel, Nano Lett, DOI: 10.1021/nl080277d