Abstract: A spark-plug assembly comprises a fitting mounted on the piston cylinder of an internal-combustion engine and formed with a generally closed firing chamber, at least one firing port extending between the firing chamber and the piston cylinder for fluid communication therebetween, and a storage compartment opening only into the firing chamber. The fitting being provided with a flame-blocking element or formation preventing the entrance of a flame front from the firing chamber into the storage compartment. This firing chamber is open substantially only to the storage compartment and to the piston cylinder. A spark plug has electrodes in the firing chamber. The electrodes form a spark gap lying in the firing chamber between the storage compartment and the port and the storage compartment opens only into the firing chamber.