Method for assessing the changes of the thermal state of cylinder head of engine with air-cooling when boosting

Abstract

The diesel engines with air-cooling have lower than engines with liquid cooling values of the average effective pressure. This happens because of lower stiffness of body parts of air-cooled diesel engines and the difficulty of maintaining within acceptable limits the temperature of the parts of the cylinder group when increasing power. Most heat-stressed elements of the design of the air-cooled diesel are cylinders heads. When boosting diesel with supercharge the question arises about possible limits of increasing boost pressure and the required depth of the charge of air cooling, where the cylinder head temperatures do not exceed the permissible limits. Predictive calculation at various levels of boosting the temperature fields in the cylinders heads by solving the heat equation through numerical methods faces the problem of determining with sufficient accuracy of the boundary conditions, primarily from the side of the cooling air. For air-cooled diesel engines ready or prepared for production is typically conducted the thermometering of cylinders heads defining, inter alia, the temperature value at the head surface at the bottom in most heat-stressed zones. A method for estimating changes in the thermal state of the head cylinder of engine with air-cooling when boosting, based on using data of testing and thermometering of diesel with initial level of boosting, is proposed. The method allows to set the limits of the possible boosting at various adjustments of diesel. The effectiveness of the method is confirmed by an example calculation for tractor diesel 8ChVN15/16. Comparison of the results of calculation of the maximum temperature value of cylinder head bottom with experimental data indicates that the values differ by no more than 1.8%. The proposed method correctly predicts the change of the thermal state of the cylinder head when boosting diesel with air-cooling by supercharge and can be used in engineering practice to assess the possible limits of boosting such diesels, choosing adjustments of fuel handling and parameters of coolant of charging air.