An integrated transient analysis simulation model applied in thermal loading calculations of an air-cooled diesel engine under variable speed and load conditions

摘要

A comprehensive transient analysis simulation model is used for the calculation of diesel engine performance under variable speed and load conditions. The analysis includes a detailed description of engine subsystems under transient conditions, thus accounting for the continuously changing character of transient operation, simulating among others the fuel injection, transient mechanical friction, heat losses to the walls, and governor operation. The results of engine performance, at every time step during the transient event, are used as inputs for the formulation of thermal boundary conditions, which are needed for the calculation in a parallel way of the thermal transients propagating inside the engine structure. Two- and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner, cylinder head), in a way that the temperate and heat flux variations are calculated at every point of engine structure during any transient event. An extensive set of experimental measurements was conducted on a Lister LV1, four-stroke, air-cooled, direct-injection, single-cylinder diesel engine in order to test the model's validity. The most important engine variables were continuously recorded, with the aid of two on-line computers through analog-to-digital converter and submultiplexer cards. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements under all conditions tested. Presentation of temperature distributions for the cylinder head, in the form of iso-thermal areas (thermographs), provides insight into the mechanism of heat propagation inside it. The utilization of the model also reveals the most sensitive points concerning the generation of sharp temperature excursions during the engine operating transient, which lead to higher thermal loading.