Today, the diesel engine is the most common engine on our roads. This is mostly due to its low fuel consumption, but ever stricter emission regulations call for more detailed knowledge about the combustion process. The division's diesel research mainly uses laser-based measurement techniques in optical engines. We study a range of processes in the cylinder but our focus during recent years has been to understand what determines the engines' emissions of soot. Large quantities of soot are formed early during the combustion process, but most of it is combusted before the exhaust valve opens. Our results suggest that this final combustion phase controls the soot emissions.