In the design process of large marine diesel engines information on the maximum heat load on the piston surface experienced during the engine cycle is an important parameter. The peak heat load occurs during combustion when hot combustion products impinge on the piston surface. Although the maximum heat load is only present for a short time of the total engine cycle, it is a severe thermal load on the piston surface. At the same time, cooling of the piston crown is generally more complicated than cooling of the other components of the combustion chamber. This can occasionally cause problems with burning off piston surface material. In this work the peak heat load on the piston surface of large marine diesel engines during combustion was investigated. Measurements of the instantaneous surface temperature and surface heat flux on pistons in large marine engines are difficult due to expensive instrumentation and high engine running costs compared to automotive engines. Therefore the investigation in this work was carried out numerically with the use of a computational fluid dynamics (CFD) code. At the same time, numerical work on detailed in-cylinder wall heat transfer in engines has been quite limited. The numerical investigation focused on the simulation of a hot turbulent gas jet impinging on a wall under very high pressure, thus approximating the process of the actual impingement of hot combustion gasses on the piston surface during combustion. The surface heat flux at the wall was calculated under different conditions in the numerical setup in order to obtain information of the actual peak heat flux experienced at the piston in large marine diesel engines during combustion. The variation of physical parameters influencing the heat transfer during combustion included a variation of pressure, temperatures, jet velocity and jet turbulence intensity. The variation in heat flux predictions resulting from application of different turbulence models was also investigated by performing calculations with three different models: the V2F model, a k-ε RNG model and a low-Re k-ε model. The obtained results indicate peak heat fluxes in the order of 5-10 MW/m2 on the piston surface during the combustion phase of the engine cycle.
|Title of host publication||CIMAC World Congress 2010|
|Publication status||Published - 2010|
|Event||CIMAC World Congress 2010 - Bergen, Norway|
Duration: 1 Jan 2010 → …
|Conference||CIMAC World Congress 2010|
|Period||01/01/2010 → …|