엔진 파워팩 냉각계의 열평형 해석 및 최적화 연구

Abstract

Cooling system of engine power pack is designed to remove heat from the engine and various power pack components efficiently and to offer an optimum operating temperature for the power pack. Cooling system is a thermal flow network that connects engine, turbocharger intercooler, radiator, and oil coolers and these are linked in a serial or parallel circuits. The coolant temperature at each component device in this closed circuit cooling system is determined according to the ambient temperature and engine RPM. Because the thermal state of one component provides the boundary condition of the next component in the circuit, the heat and flow balance analysis of the cooling circuit is necessary to optimize the cooling system performance for various operating conditions and running conditions of the vehicle. In this study, heat and flow balance analysis of 1500 hp diesel engine cooling system has been conducted utilizing Flowmaster2 code. The cooling system in this study is characterized by two parallel circuits of high temperature and low temperature coolant.

The major component models such as engine, three-flow-path radiator and turbocharger intercooler as well as thermostat were constructed from the basic component models provided by the Flowmaster2 code. The completed cooling system model was first tested and adjusted against the design specifications of each component of the cooling system until the amounts of deviations of the calculated flow and heat balance lie within the accepted design margins of the power pack components. Then the model was used to simulate thermal behavior of the cooling system under various ambient temperatures in the range of 44oC to -32oC, which are the upper and the lower design temperatures of the power pack. In cool ambient temperature condition in which the thermostat is likely to operate, a converged steady-state solution was successfully obtained by a transient calculation of such multi-component, multi-circuit cooling system. The calculated coolant pump suction pressure in each case was examined to discuss the occurrence of cavitation in the pump.