Wittmann, J. and Menger, L., "Novel Index for Evaluation of Particle Formation Tendencies of Fuels with Different Chemical Compositions," SAE Int. J. Fuels Lubr. 10(3):2017.
Current regulatory developments aim for stricter emission limits, increased environmental protection and purification of air on a local and global scale. In order to find solutions for a cleaner combustion process, it is necessary to identify the critical components and parameters responsible for the formation of emissions. This work provides an evaluation process for particle formation during combustion of a modern direct injection engine, which can help to create new aftertreatment techniques, such as a gasoline particle filter (GPF) system, that are fit for purpose. With the advent of “real driving emission” (RDE) regulations, which include market fuels for the particulate number testing procedure, the chemical composition and overall quality of the fuel cannot be neglected in order to yield a comparable emission test within the EU and worldwide. Even within the legislative boundaries such as the DIN EN 228 in Europe, critical gasoline parameters can vary greatly and influence the measured particle number. This work provides a straightforward approach to evaluate any gasoline worldwide considering particle emission tendencies via comprehensible chemical analyses and transparent interpretation. The Menger/Wittmann model (MW index) presented in this work consists of fourteen fundamental physico-chemical parameters (density, vapor pressure, distillation range, volumetric fraction of aromatics, olefins, etc.), measured with standardized and reproducible techniques. These macroscopic quantities incorporate the complex interactions of the chemical single components and directly represent the matrix effects responsible for the magnitude of particle formation during the combustion cycle. An exponential dependence of the PN emissions on the index model and its chemical foundation was found, supporting the notion of cumulative matrix effects of critical parameters applied in this model. In order to validate the correlation and to understand the fundamental parameters, which are necessary to evaluate fuels worldwide, the PN emissions of several reference, market and customized fuels were measured on an engine test bed under laboratory conditions with a customer-related RDE cycle. Thus a versatile method to comparatively evaluate fuels considering their potential particle forming tendency was developed.