Fuel consumption, and the physical behaviours behind it, have never been of greater interest to the automotive engineering community. The enormous design, development and infrastructure investment involved with a new engine family which will be in production for many years demands significant review of the base engine fundamental architecture.Future CO2 challenges are pushing car manufacturers to consider alternative engine configurations. As a result, a wide range of diesel engine architectures are available in production, particularly in the 1.4 to 1.6 L passenger car market, including variations in cylinder size, number of valves per cylinder, and bore:stroke (B/S) ratio. In addition, the 3 cylinder engine has entered the market in growing numbers, despite its historic NVH concerns.Ricardo has performed a generic architecture study for a midsize displacement engine in order to assess the pros and cons of each engine configuration. A range of concept engine designs were prepared, drawing heavily on design guidelines and benchmarking information. Friction analysis was used to predict friction levels for each design. 1-D gas dynamics simulation was used for performance and fuel consumption prediction, which incorporates pumping losses and in cylinder heat transfer. Heat release curves were derived using in-cylinder 3-D CFD. Vehicle modelling was then used to assess vehicle drive cycle fuel consumption across several cycles.Modelling detailed, small architectural changes challenges the simulation tools and techniques due to the balance of behaviours present, including friction, pumping and thermodynamic effects. Throughout the analysis activities, sensitivity studies on the modelling approach were carried out to ensure the approach was appropriate.The study has enabled the definition of what is considered an optimum fuel consumption architecture in terms of cylinder number, number of valves per cylinder and cylinder proportions, with a rigorous understanding of the behaviours contributing to the fuel consumption across the cycles, and the subtle interactions between them.