The goal of reducing the impact of road transportation on the environment can be reached by different approaches. The use of non-fossil synthetic fuels from renewable energy sources in the entire fleet of internal combustion engine vehicles is only one promising pathway to minimize the vehicle’s carbon footprint during the use phase. The steadily tightening emissions legislation confront the developers of future combustion engines with major challenges: Historically, the chemical and physical improvement of the combustion process, tail pipe emissions reduction and the development of optimized after-treatment systems were linked to improvements in fuel quality. In order to further decrease exhaust gas emissions, the optimization of the chemical composition of renewable fuels are a basic requirement.
Due to the fact that the majority of the cycle emissions are generated during the cold start and the warm up phase, the operation before the light-off of the three-way catalyst plays a decisive role. One way to reduce the emissions before light-off is inducing a post-oxidation of the pollutants by secondary air introduction. The exothermic reaction oxidizes the pollutants and thereby increases the enthalpy of the exhaust gas. Besides the design influences, the engine operation and raw emissions determine the quality of the oxidation.
The influence of different fuel composition was investigated under cold start conditions on a research single cylinder engine and a flat six Porsche engine. Two flat six engines with different combustion designs and secondary air configurations were used to further evaluate the fuel composition influence on post oxidation. To indicate the dependencies of fuel parameters, variations of the influencing factors were undertaken.
Significant improvements of cold start emissions were obtained with different fuel compositions compared to existing types of market fuels. Beside the increase in post oxidation rates, a reduction of raw emissions was achieved.