A fuel independent heat transfer correlation for premixed spark ignition engines

Simulation models for internal combustion engines are an indispensable development tool, since engines have become increasingly complex, with many control variables and conflicting optimization targets. The heat transfer model, which computes the heat losses to the cylinder walls inside the engine is one of the most important sub-models, because it has an influence on the main three optimization targets (efficiency, emissions and power output). Although it is an important sub-model, little progress was reported in recent years due to the lack of accurate heat loss measurements inside an engine. Consequently, heat transfer models have not followed the evolution in engine technology and fuels and there is a need to improve them. This doctoral research investigated the heat losses in spark-ignition engines and focused on the effect of different alternative fuels. First, an accurate heat flux sensor was implemented in a test engine in the lab to measure the heat losses to the walls. This was not a straightforward step, since it is not a mature technology due to the required response and robustness. Second, the sensor was used to build a database of heat flux measurements in the engine which focuses on the effect of the fuel. Special care was devoted to the experimental design, resulting in a unique database which shows that the fuel can significantly affect the amount of heat losses. The obtained database allowed to better understand the heat transfer mechanism inside an internal combustion engine. Finally, these insights resulted in a new heat transfer model which is shown to be a significant improvement compared to the existing ones.