AE 412 THERMODYNAMIC CYCLE SIMULATION II Prof.Dr. Demir Bayka

MODES OF HEAT TRANSFER 1) CONDUCTION BETWEEN MATING ENGINE COMPONENTS

MODES OF HEAT TRANSFER 2) CONVECTION BETWEEN GAS & CYLINDER SURFACE

MODES OF HEAT TRANSFER 3) RADIATION BETWEEN SOOT & CYLINDER SURFACE IN CI ENGINES

Heat Transfer Rate Calculations Continuously changing gas temperature and air movement existing in any combustion engine effect the heat transfer rates at the interface of the working gas and walls. Owing to the complexity of the physical situation, it is impossible to formulate the affecting factors in any rigorous manner. During compression stroke heat transfer is, for all practical purposes entirely convective.

Convective Heat Transfer In the internal combustion engine heat transfer is predominantly by forced convection enhanced by the intense air movement in the combustion chamber. In a naturally aspirated four stroke engine, the creation of air movement is primarily by the motion of the piston which induces directional flow patterns in the form of swirl and squish in the combustion chamber.

Convective Heat Transfer As the flow conditions involved are well inside the turbulent region, secondary air movements in the form of small scale eddies are created as a result of viscous dissipation and these are superimposed onto the general flow pattern. During combustion period of the working cycle combustion induced turbulence would be additional to the air movement already existing. Also in the spark ignited engines expansion of hot burned gases creates local velocity changes.

Convective Heat Transfer In the view of the complexity of such a system, it is reasonable to expect quite large variations in the general magnitude of convective heat transfer from point to point at any time. Unless a precise description of local charge movement as well as local gas temperature is made, it would be impossible to approach the in any rigorous manner

The usual approach has been to characterize the flow pattern by the mean piston speed on the assumption that,in a given configuration flow velocities will be at least approximately proportional to that value. The bulk mean temperature has been used as the driving temperature during the compression period but for the combustion and expansion periods temperature distribution in the combustion chamber is considered. Convective Heat Transfer

HEAT TRANSFER FROM THE WORKING GAS TO THE CYLINDER WALLS

EMPIRICAL RELATIONSHIP WAS PROPOSED BY ANNAND

HEAT TRANSFER IS TO ; 1) CYLINDER HEAD 2) PISTON TOP 3) CYLINDER LINER EACH AREA HAS A DIFFERENT AND APPROXİMATELY CONSTANT SURFACE TEMPERATURE. THESE TEMPERATURES WILL VARY SLIGHTLY WITH RESPECT TO THE TYPE OF ENGINE THE SWING OF CYLINDER HEAD TEMPERATURE IS APPROXIMATELY 10 C

HEAT TRANSFER AREAS CYLINDER HEAD AND PİSTON TOP : LINER AREA

PROPERTIES