what the temperature of source and sink is in an otto cycle? Since the temperature of the surroundings continuously change during the isochoric parts, we cannot have a single source and sink temperature?
For the idealized Otto cycle the heat absorption and rejection processes are modeled as isochoric processes in which heat is absorbed from, and rejected to, a series of temperature reservoirs not single reservoirs.
This is an idealization. The “heat absorbed” is in reality a short-time conversion of chemical energy to thermal energy following compression resulting from spark ignition. The “heat rejected” is in reality the escape of hot exhaust gases when the exhaust valve opens.
Hope this helps.