This is the 4262nd most frequent Russian word.
автомобильного
"Автомобильного" means "automobile" or "automotive" (relating to cars or vehicles).
Here, 'автомобильного' is an adjective derived from 'автомобиль' meaning 'car', and it modifies 'двигателя' (genitive singular form of 'двигатель', meaning 'engine'). It translates to 'car' or 'automotive' depending on the context.
Я изучаю работу автомобильного двигателя.
I study the operation of a car engine.
In this instance, 'автомобильного' modifies 'завода' (genitive singular form of 'завод', meaning 'factory') to describe the factory being automotive-related, such as for manufacturing cars.
На выставке представили макет нового автомобильного завода.
A model of a new automotive factory was presented at the exhibition.
Here, 'автомобильного' describes 'рынка' (genitive singular form of 'рынок', meaning 'market'), indicating that the market is related to cars or the automotive industry.