저온 환경에서 LP EGR 사용 시 인터쿨러의 응축수 예측

Abstract

When using a diesel engine, many aftertreatment units are used to reduce NOx, and exhasut gas recirculation (EGR) is one of the aftertreatment system. There are high pressure loop (HP) EGR and low pressure loop (LP) EGR for EGR devices, and various researches have been conducted to use LP EGR to compensate for the decrease in HP EGR efficiency in the high load. Because LP EGR gas contains a lot of moisturethat cause water condesate, problems such as efficiency reduction and engine corrosion occur. In a low-temperature environment, it also leads freezing and even physical damage. In this study, through CFD analysis, the amount of condensate due to LP EGR usein the intercooler of a diesel engine is predicted under a low temperarute evviromnment. The gas temperature and LP EGR ratio were selected as test variables because the gas temperature reflects the effect of the EGR cooler and the LP EGR ratio affects NOx reduction. The most effective parameters on the condensate were identified. One pin model of the intercooler was simulated for reducing calculation time and flows and condensate were analyzed using Ansys Fluent and FENSAP Droplet, repectively. At first, CFD results for the full model was comapred with the actual vehicle test. Thereafter, CFD results for one pin model were verified based on numerical results from the full model. The actual vehicle experiment and the 3D full model were compared in the operation point of 1500 rpm-7 bar. Prediction accuracy could be obtained with 3% under –20℃ and 8% under –10℃. The error ranges wear to continuous experiments under chassis test condition, and the 3D full model has sufficient reliability. The 3D full model and one fin model are compared under 1500 rpm-10 bar. The result of the 3D full model divided by the number of fins is 5.3 g/h, and the one fin result is 4.6 g/h. Through the design of experiments factor analysis, it was confirmed that the most influential variable was gas temperature. A higher gas temperaure leads the lower amount of condensate due to the higher dew point temperature. When the gas temperature was low, the generation of condensate decreased with the decrease of the LP EGR ratio. In contrast, when the gas temperature was high, the amount of condensate decreased as the LP EGR ratio was increased. In conclusiopn, if LP EGR is used inunder a low-temperature environment, it is suggested that increasing the LP EGR ratio without using an EGR cooler is an ideal usage condition. However, if the LP EGR ratio is excessive, the air required for combustion decreases, so the combustion efficiency decreases, and it is expected that it is necessary to find the optimum LP EGR usage condition.