Combustion chamber heat rejection modelling

Abstract

The overall goal of this Master thesis is to understand the process of heat rejection from the combustion chamber of diesel engine to the cooling oil and the influence of thermal barrier coating to the reduction of heat losses through a piston wall. Two types of TBC are analysed in this project ceramics and air layer. In order to do that 1D conduction model is developed in MATLAB. The model is based on one dimensional conduction equation with boundary conditions considering convection on the left side and constant temperature of the cooling oil on the right side.

Partial differential equation is discretized using finite difference method.

Boundary conditions model in this thesis is a separate function which provide gas temperature and convective heat transfer coefficient to the main model. Woschni correlation is used to obtain heat transfer coefficient since it seems to be accurate enough and demonstrates good results during the model validation.

Different simulations are performed using the model where the influence of thickness and thermo-mechanical properties of thermal barrier coating to the heat flux rejected from the combustion chamber is investigated. The most important properties of ceramics influencing heat flux are heat conductivity, specific heat capacity and density. Among other engine parameters varied in this project are engine speed and burn duration.

As the conclusion to the project economical justification is presented showing the potential of thermal barrier coating for the improvement not only thermal efficiency but also the cost reduction of the engine operation.