Design Analysis of a Silicon Nitride Firedeck in a Low-Heat-Rejection Diesel Engine 890294
The objectives of this project were to develop an analytical capability to analyze the thermomechanical behavior and probability of survival for a ceramic firedeck in a low-heat-rejection diesel engine and to gain a quantitative understanding of how to apply ceramics as structural engine components.
Since silicon nitride provides better thermal shock resistance than zirconia, it was selected as the firedeck material in this analysis. Air-gaps between the firedeck and cylinder head were introduced to provide the needed insulation for the LHR engine.
The MSC/NASTRAN finite element code was used to calculate the firedeck and cylinder head operating temperatures and the corresponding thermal expansion. FORTRAN programs were also developed to analyze the contact problems between the ceramic firedeck and the cast iron cylinder head. The contact forces, together with the thermal and the pressure load from the combustion gases, were input into the MSC/NASTRAN code to calculate the firedeck operating stresses. The stresses, operating temperatures, and volume for each element of the firedeck were used in the Structural Ceramics Analysis and Reliability Evaluation (SCARE) program for calculating the probability of survival of the firedeck. The combustion pressure was shown to induce high tensile stress in the valve bridge area. This high tensile stress may cause fracturing of the ceramic firedeck if the deck is not designed with adequate load carrying capacity.