Application of PIV measurements and snapshot POD analysis in a cylinder head of diesel engine

The characteristic of coolant flow field in the water jacket of a cylinder head plays an important role in heat exchange, which could even influence the diesel engine's performance and service life. Measurements and analysis methods to coolant flow field are limited by the complex internal geometrical structure of the cylinder head. In this paper, flow fields in a small and complicated spatial structure are measured by particle image velocimetry (PIV) system and the data are analyzed using proper orthogonal decomposition (POD) method. Time varying coolant flow structures located among two valve seats, a fuel injector seat and a side wall in a real cylinder head are measured by a two dimensional PIV system. PIV results of three measuring planes are displayed in different ways to show flow structures in the water jacket. Distinctive areas can be recognized easily in distributions of different flow parameters. A snapshot POD method is employed to analyze PIV data. Flow structures, which contain different amount of energy, are decomposed into different modes by POD method. POD Mode 1 and ensemble mean flow field are compared together and the relevance index shows a relatively high similarity between these two flow fields. The results also indicate a significant convergence of energy distribution. Energy contained in Mode 1 varies from 22% to 61% of the total energy in different measuring planes. 90% of the total energy is captured in top 10% of the total modes which belong to low-order modes. Energy in high-order modes, which occupy more than 60% of the total modes, contains less than 1% of the total energy. In summary, this paper presents the application of PIV measurements to coolant flow field in a real cylinder head and data processing using a snapshot POD method to analyze PIV results. A set of comprehensive properties showing the spatial and temporal characteristics of coolant flow structure is discussed and concluded detailedly. The data obtained can be used to build an experimental database to optimize coolant flow field structures and verify CFD numerical simulations in order to promote coolant flow passage design and simulation credibility of the diesel engine cooling system.