Influence of molecular structure of various hydrocarbons on soot formation

Many types of combustion system emit particles into the atmosphere which are known to be a major hazard due to their toxicity to human health, particularly the respiratory and cardiovascular systems. The smaller particles (less than about 100nm in size) are believed to be the most hazardous, as they can penetrate deep into the human lung. The purpose of this proposal is to gather scientific information on how the structure of fuel molecules affects the production of soot and particulates. During the next 10 to 20 years one can anticipate increasing interest in synthetic fuels which use molecules specifically developed to burn more efficiently and cleanly. The development of such molecules will require knowledge of how different molecular structures affect the production of harmful particulates and other emissions. Such clean fuels may be derived from fossil sources such as coal or increasingly from biomass (starches, sugars, and cellulosic materials) using chemical or biological conversion methods. The proposed project aims to determine in detail which features of a molecule's structure are responsible for producing more soot than others. The project relies on a new methodology which has not been used by the combustion research community previously to any significant extent. The methodology involves the replacement within a hydrocarbon molecule of selected commonplace 12C atoms with 13C atoms carrying a stable isotope label (extra neutron) which survives combustion intact, without altering the chemical and transport properties of the molecule. This label , which can be detected in the soot particles, provides a unique ability to determine which atoms or group of atoms of a molecule become soot particles. Two extensive series of experiments will be conducted, the first on a laminar diffusion flame and the second on a diesel engine. Unlike a diesel engine, the laminar flame allows the principal influences on soot formation to be chemical ones, by eliminating spray formation and evaporation and the effects of turbulent mixing and intermittent combustion. A laminar flame also allows readily the sampling and analysis of the contents of its envelope and it permits the introduction of controlled amounts of oxygen and other diluents at its base so as to study how these diluents affect soot formation. The second series of experiments will be on a diesel engine which represents a commonplace practical combustion system. Although the fuel spray in a diesel engine is less accessible, a diesel engine it is a truly realistic environment in which the pollutant particulate is formed. A total of 15, 13C-labelled fuel molecules have been selected to study the effect of their structure on soot and particulate formation. These 15 molecules have a wide range of structural features that could potentially affect soot and particulate formation and the 13C labelling method will allow the influences of these features to be evaluated. By the completion of the project it is envisaged that the knowledge gained could guide the production of future synthetic fuels so that the molecules they contain result in less soot and toxic particulates when combusted.

The knowledge gained from this research will be at a fundamental level and it will help researchers worldwide to understanding soot formation better. It could also assist in testing computational models of soot formation. The results will thus form a seminal contribution to scientific knowledge in the field of soot formation and will enhance the UK's standing within the international scientific community through journal publications and presentations at important international meetings. We envisage that the knowledge gained from the project will also be useful to energy companies who could use it to develop synthesised molecules, including ones produced from sustainable sources, which result in less soot when combusted. For example, the results of the project could guide development of bio-chemical processes so that they are not just efficient in terms of productivity and resources but they also produce molecules which may burn more cleanly when combusted. In a similar manner, chemical post-processes may be optimised so that the post-processed molecules, originating from biomass or fossil fuels, produce lower levels of particulates. Likewise, biologists could be guided by the results of the project so as to develop micro-organisms (e.g. through genetic engineering) which in turn produce molecules from biomass (starches, sugars and cellulosic materials) which are more suitable for combustion and which produce lower levels of particulates. Particulate matter emitted from diesel and gasoline engines is a major toxic pollutant controlled by legislation internationally. The development of fuels producing lower soot levels would have a very substantial beneficial impact on human health. The project will result in a PhD graduate highly trained in a wide range of multidisciplinary skills, including engineering design and manufacture, rig and engine experimentation, analysis and interpretation of complex experimental results, complex analytical techniques such as 13C isotope analysis, communication of scientific results to researchers at international meetings, and time management. UCL's relationship with the sponsoring company (BP) will be strengthened and a new collaborative relationship between the applicants and Professor Tim Atkinson, Director of the UCL Bloomsbury Environmental Isotope Facility will be established.