Modeling the effects of fuel properties on end-use performance in light-duty road transport and aviation

The present Doctoral Dissertation belongs to the field of Energy Technology with a focus on System-Level modeling and end-use analysis of renewable fuels in the transport sector. The scope includes on-road transportation and aviation, where the impact of alternative fuel properties was investigated for the regular fleet of spark-ignition engines, flex-fuel engines, and aircraft jet engines. Based on literature data the matrices containing fuel properties as independent variables and fuel consumption as an output property were constructed for the modeling purpose. The Multiple Linear Regression with incorporated quantitative analysis was employed to develop state-of-the-art mathematical models representing the impact of fuel properties exclusively. The current work consists of 4 journal publications. The first publication is focused on the development of the Fuel Consumption (FC) model for Spark-Ignition Light-Duty Vehicles (SI-LDVs). Tested fuels were blends of ethanol and isomers of butanol with gasoline. The most important parameters for FC in regular SI-LDVs turned out to be Research Octane Number (RON), calorific content, density, and oxygen content. The model achieved high accuracy reflected by an R-Square of 0.989, and an average absolute error of 1.1% in external validation. The second publication extended the scope to Flex-Fuel Vehicles (FFV) engines, which are better optimized for non-drop-in fuels such as E85. In the case of FFVs, besides ethanol and butanol, blends containing methanol and ethyl tertbutyl ether were investigated, including their binary and tertiary combinations. The results show that for FFV engines, octane sensitivity, calorific content, density, and vapor pressure were the most significant fuel properties. The high accuracy of the model expressed by R-Square of 0.994 was confirmed in external validation by an average absolute error of 1.9%. While further findings indicated that FFV engines utilize alternative fuels more efficiently than regular SI engines. The third publication was focused on jet engines and Sustainable Aviation Fuels (SAF), where a model containing the effect of viscosity, density, and calorific content was developed for end-use analysis. The achieved high R-Square of 0.993 translated into 0.68% error in external validation. The fourth publication studied various challenges to the successful market uptake of renewable fuels highlighting that the current tank-to-wheel (TTW) approach in emissions estimation should be extended to more robust well-to-wheel or cradle-to-grave type of assessments. The present work showed that the collective impact of fuel properties could successfully be applied to model and simulate fuel consumption for various alternative fuels in end-use sectors. The results show that although some alternative fuels might increase volumetric fuel consumption, they tend to reduce TTW carbon dioxide emissions and energy consumption such as in the case of alcohols or specific SAF.