This paper presents an experimental methodology to obtain information about the in-cylinder pressure development during the combustion process of a small displacement diesel engine by using the acoustic emission. The research activity arises from two considerations. On one end, an efficient control of the combustion process has demonstrated to be crucial to ensure complying with increasingly emerging diesel emission standards and to reduce fuel consumption. On the other end, even if nowadays the employment of in-cylinder pressure sensors in combustion control techniques appears to be a very promising technology, solutions based on non-intrusive methodologies offer the indubitable advantages of guaranteeing the absence of any interaction with the engine operation. Furthermore, these solutions allow the sensor to be installed in any kind of production engine without the need of modification. In the present paper, the engine noise emissions have been analyzed with the aim to extract the combustion related contribution. Particular attention has been devoted to the definition of indicators able to characterize both the noise and the in-cylinder pressure development. The relationship between these indices in the entire engine operative field allowed to evaluate the combustion properties by using only the sound radiation signal as input. (C) 2014 Elsevier Ltd. All rights reserved.