Quality Assurance for Combustion Chamber Thermal Boundary Conditions - A Combined Experimental and Analytical Approach

The increasing cost of prototype engine design and development has placed new emphasis on the importance of accurate analysis of combustion chamber components. A method to assess and improve the quality of thermal boundary conditions is described. The integration of analytical approaches and experimental techniques to validate and improve thermal boundary conditions is dependent on continuous improvement of theoretical models and correlation with measured results. To monitor and improve quality, it is important to operate a closed loop of prediction, measurement and feedback to the analysis system.

The development of advanced computational methods, particularly the Finite Element Method (FEM) has increased the opportunities to include detailed component thermal analysis in combustion chamber design studies. In using FEM, much emphasis is traditionally placed on “accurate” mesh generation in order to minimise element distortion and optimise element polynomial order. Whilst this is important experience has shown that often the most significant source of error in thermal analysis is associated with incorrectly specified boundary conditions.

The process of calculating and validating boundary conditions for gas side combustion chamber heat transfer, material thermal conductivity and coolant side heat transfer characteristics are discussed in detail. The important principles involved in predictive models including spatially resolved in-cylinder definitions are highlighted. The design of new instrumentation and test techniques are also described with emphasis placed on minimum intrusion and the importance of recordable calibration systems. Results from direct and indirect injection diesel engines together with data from modern tumbling multi-valve gasoline engines are presented and discussed.