Predicting the soot emission tendency of real fuels - A relative assessment based on an empirical formula

Significant progress is going on in the development of non-fossil based alternative fuels which are designed to be sustainable, have potential to substitute (fully or partially) the fossil-based fuels and importantly are targeted to reduce emissions. Though soot emission characteristics has not been focus of fuel certification process yet, due to growing environmental concerns it is important to consider this aspect in the fuel design and understand its emission patterns. It is known that soot formation in combustion is linked to the degree of branching, degree of unsaturation or the degree of cyclization of a fuel molecule. This information is used to extract soot emission properties of complex real fuel mixtures. To do so, we use the definition of hydrogen deficiency (HD) which gives information on the number of double bonds or cyclic structures present in a fuel. With the help of one measured emission property, the same property of different fuels is predicted using HD. This way, we obtain a relative assessment of fuels' sooting tendency compared to other known fuels. In this work, soot emission pattern of six jet fuels (reference fuels and synthetic fuels) is predicted based on HD and compared them with the recent ground-test measurements of V2527-A5 engine of an Airbus A320. In addition, two more test cases are provided: aviation fuels and diesel fuels, to predict sooting tendency using HD to support our concept. The prediction of the sooting propensity based on HD was found in excellent agreement with the measurements.