1. Could you explain the significance of your article to the non-specialist?

The development of computational models for autoignition phenomena is important for the identification of explosion hazards, as can occur if fuel + air mixtures encounter hot surfaces in industrial processing. The models have to include chemistry containing significant numbers of individual reactions. The predictive capability depends on the quality of the data to describe these reactions. The mathematical methods discussed here enable us to highlight the components within the mechanism to which autoignition is most sensitive. The potential improvements to the model that follow have implications for process hazard mitigation, as is the objective in this EU supported project. 

2. What has motivated you to conduct this work?

There is a need for, and considerable interest in, reliable models which describe autoignition for a range of hydrocarbon fuels, which have applications in clean and efficient engine research and development as well as chemical process safety. The increasing understanding of the chemical kinetic mechanisms involved and the mathematical developments in automatic mechanism generation yield highly sophisticated models as the basis for the prediction of fuels performance. This is a substantial achievement, but to put it on a sound quantitative footing the consequences of the inherent uncertainties within the model predictions should be understood, just as errors would be reported for equivalent experimental data. Often, such uncertainties are caused by a small portion of the input data to which the model is highly sensitive. Our motivation was to identify these sensitive aspects of the mechanisms, as exemplified here with respect to the prediction of autoignition for alkanes. 

3. Where do you this work developing in the feature? 

The work highlights that the simulation of experiments in microgravity can provide a more rigorous test of complex chemical mechanisms than those conducted under terrestrial conditions. Low gravitational forces enable heat and mass transport to be driven by pure diffusion, rather than the complex mixture of diffusion and convection that occurs in terrestrial experiments, so the representation of the physics of the problem is more rigorous. The evaluation of combustion mechanisms by relating the predictions of models to the experiments performed under microgravity conditions provides a rich area for future research. The significant outcome of the work is the identification of a few especially important parameters within the mechanism that lead to model uncertainties, which should, therefore, be the subject of further study by chemical kineticists in order to improve the parameterisations. 

4. Are their any particular challenges facing future research in this area?

A major mathematical challenge is to be able to extend the methods applied here to larger kinetic mechanisms, since there is a dramatic increase in the computational burden of the mathematical techniques. Work in parallel is aimed at developing more computationally efficient methods for assessing global uncertainties and these will need to be employed in order to cover the extensive range of fuel types of practical interest. On the experimental front there is already a long history of microgravity experiments in "free fall" drop towers, and an impetus has been gained in NASA's Skylab, as well as in NASA and ESA parabolic flight programmes, but studies of autoignition are limited. We have focused here on alkane combustion, for which data are available from Professor Pearlman's unique programme, but practical applications suggest the need for similar studies for a range of hydrocarbon fuels including alkenes and aromatic compounds.