The fuel consumption and emissions of diesel engines is strongly influenced by the injection rate pattern, which influences the in-cylinder mixing and combustion process. Knowing the exact injection rate is mandatory for an optimal diesel combustion development. The short injection time of no more than some milliseconds prevents a direct flow rate measurement. However, the injection rate is deduced from the pressure change caused by injecting into a fuel reservoir or pipe. In an ideal case, the pressure increase in a fuel pipe correlates with the flow rate. Unfortunately, real measurement devices show measurement inaccuracies and errors, caused by non-ideal geometrical shapes as well as variable fuel temperature and fuel properties along the measurement pipe. To analyze the thermal effect onto the measurement results, an available rate measurement device is extended with a flexible heating system as well as multiple pressure and temperature sensors. With the help of a one-dimensional simulation, the temperature and geometrical effects are further analyzed and available measurement results are confirmed. Afterwards, a correction algorithm is developed which optimizes an assumed injection rate in the simulation model until measured and simulated pressure signals match. A high specialization of the developed algorithm to the optimization task and multiple CPU cores allows a calculation time reduction from multiple hours to minutes in combination with a high flow-rate resolution.