Many studies have demonstrated that an efficient control of the combustion process is crucial in order to comply with increasingly emerging Diesel emission standards and demanding for reduced fuel consumption.Methodologies based on real-time techniques are imperative and even if newly sensors will be available in the near future for on-board installation inside the cylinder, non intrusive measurements are still considered very attractive.This paper presents an experimental activity devoted to analyze the noise emission from a small displacement two-cylinder Diesel engine equipped by HPCR (high pressure common rail) fuel injection system. The signals acquired during stationary operation of the engine are analyzed and processed in order to highlight the different sources contributing to the overall emission. Particular attention is devoted to the specific samples of the signal that are mainly caused by the combustion process in order to extract the combustion contribution. The relationship between such a noise contribution and the in-cylinder pressure development during the combustion process is analyzed with the final aim of developing an algorithm in which the engine acoustic emission is used to compute key parameters able to fully characterize the pattern of the pressure development during the combustion process.In the paper, the methodology is presented and the experimental set-up is described. Results related to tests in the complete engine operative field are presented and discussed.