This book gathers two research articles that are easy mathematical modellings for internal combustion engines ICE and for mechanical injection systems.Based on the results of the modellings, this book proposes also new methods for the maintenance and even the manufacturing of internal combustion systems and their injection systems. The results of this research can also be used for all kinds of energetic studies that are related to the work of ICE heat engines.This book is consequently dedicated to the beginners and even to the experts of engineering who are interested in automotive or industrial heat engines and their components.