In the last 15 years, diesel engines in passenger cars have evolved rapidly. The combination of performance, fuel consumption, emissions and refinement offered by a modern diesel engine makes it the preferred engine choice in many sectors of the market. The enormous progress made has resulted from technological improvements such as low swirl 4-valve per cylinder, direct injection combustion systems complemented by high pressure common rail fuel systems and high levels of turbocharger boost pressure.
The durability and output potential of such engines is strongly linked to the operating temperature of certain key components. Accurate temperature predictions are an essential pre-requisite to the continuing evolution, thus placing emphasis on the need for high quality predictive tools. Despite this, existing methods for predicting heat flux and component operating temperatures in diesel engines rest mainly with methodology developed over 50 years ago, often updated in the light of more recent experimental data. It is questionable how well those methods represent modern diesel engines.
In order to look at this issue, the authors have undertaken a wide-ranging experimental and analytical study using a highly instrumented modern diesel engine. The engine had 109 thermocouples implanted into the walls of the cylinders and cylinder head to reveal the spatial variation of temperature and heat flux over a wide range of operating conditions. In this paper some of the results of the study are discussed, together with comparisons of experimental data and the existing predictive models. Areas of agreement and discrepancy are highlighted in the context of the operating conditions and engine characteristics, and proposals for improved methodology are discussed.