Star formation has gained increasing attention during the last decades, as technical capabilities improved to perform more detailed analyses of the processes. As a multi-scale problem, it ranges from large molecular clouds through pre-stellar cores down to the creation of dust grains in protoplanetary disks. Many physical processes like turbulence, magnetic fields, radiation, accretion and outflows play an important role on these scales for low and high mass stars. One phenomenon in star formation is episodic accretion, which became a hot topic in the second half of the last century and especially with Spitzer starting its observations, allowing the investigation of the luminosity problem. This thesis focusses on observations of young eruptive stars and their modelling with an upgraded thermo-chemical code, with the goal to understand better the gas emission in young stars undergoing episodic accretion.