The aim of this work, consisting of 9 individual, self-contained booklets, is to describe commercial vehicle technology in a way that is clear, concise and illustrative. Compact and easy to understand, it provides an overview of the technology that goes into modern commercial vehicles. Starting from the customers fundamental requirements, the characteristics and systems that define the design of the vehicles are presented knowledgeably in a series of articles, each of which can be read and studied on their own.  This volume, The Diesel Engine, provides an initial overview of the vast topic that is the diesel engine. It offers basic information about the mechanical functioning of the engine. The integration of the engine in the vehicle and major systems such as the cooling system, the fuel system and the exhaust gas treatment system are explained so that readers in training and in a practical setting may gain an understanding of the diesel engine.