Jing Wang

Thermal design and simulation of automotive headlamps using white LEDs

With an urgent need for energy conservation and pollution reduction, the trend of replacing traditional incandescent or fluorescent lamps with high-power LEDs is growing more and more popular. In this research, high power white LED chips are used in automotive headlamp low beam system design. Several different cooling devices are designed for headlamp cooling, the heat dissipation performances are simulated and analysed both by the finite volume method (FVM) in FloEFD and experimental measurements. The simulation and experimental results show that nature convection cooling is not an effective method for LED headlamp cooling. Heat sink combined with heat pipes technology can greatly improve the heat dissipation performance. When the liquid filled ratio is 10%, heat pipes with evaporator length 30mm, adiabatic section length 40mm and condenser length 50mm have the best cooling performance. Cooling device with heat pipes placed dispersedly makes the junction temperature lower than cooling device with heat pipes isometric placed in the same plane. The liquid filled ratio of heat pipes can influence the equivalent heat transfer coefficient significantly, and the optimal filling rate is 30% in our study.

Experimental Study of Non-thermal Plasma Injection System Converting NOx in Simulated Diesel Emissions

In order to study the removal effect of non-thermal plasma (NTP) after-treatment system on diesel engine harmful emissions, a dielectric barrier discharge (DBD) plasma reactor is designed, and the NOx removal effect is studied under the conditions of different NTP injected gas flow rates and simulated diesel engine exhaust gas temperatures using a NTP injection system which is located outside the diesel engine exhaust pipe. The results show that the injection system can play an effective role in dealing with the harmful emissions of diesel engines; in NTP environment, conversion of NO to NO2 is the main reaction; with increasing the peak-to-peak applied voltage, NO conversion rate first rises and then falls; correspondingly, when the flow rates of simulated diesel engine exhaust gas are different, the flow rates of NTP injected gas are various, there is an optimum value which lead to the maximum conversion rate of NO; high temperature goes against the NO conversion.

Thermal Model Design and Analysis of High-Power LED Headlamp Cooling Device Based on the Thermoelectric Effect

In view of the characteristics of high-power light-emitting diodes (LEDs), such as strict junction temperature (Ti) control, the enhanced cooling models based on the thermoelectric cooler (TEC) were presented to meet the thermal demand of high-power LED headlight. The cooling performance of different devices (air cooling and TEC, and liquid cooling and TEC) was evaluated and compared by measuring the LED case temperature. The details of the heat transfer performance, particularly, the startup performances of the TEC cooler as well as the influence of the fan rotate speed or liquid velocity on the system thermal performance, were obtained. It was found that the thermal performance had been elevated dramatically due to the reduction in hot-side temperature, and the TEC was more sensitive to the external fan speed or liquid velocity than purely air cooling or liquid cooling. In addition, the optimal current for air cooling and TEC was 3 and 5 A for liquid cooling + TEC. The investigations of the simulated ambient temperature on junction temperature, forward voltage, and output light were conducted. The results indicated that the case temperature changed linearly basically with the increase in heating power or the simulated ambient temperature. When the ambient temperature was within its severe level (60°C-65°C), the junction temperature could be calculated to 59.5°C, and the corresponding output light was 1607.3 lm.

Experimental study on optical-thermal associated characteristics of LED car lamps under the action of ionic wind

Abstract The working temperature of a LED chip has a great influence on its photoelectric properties. This paper is concerned with the application of ionic wind produced by corona discharge to cool a LED car headlamp. Both theoretical and experimental procedures are studied. A DC ‘needles-to-mesh’ ionic wind generator was designed for the experimental study. The mechanism of the association between optical and thermal properties was explored. The results indicated that the ionic wind could weaken the red shifting of the chromaticity coordinates and reduce the radiant power. It also showed a better working performance when the corona discharge power increased, but it only changed slightly as the corona power continued increasing. Ultimately, it would result in more symmetrical and uniform light distribution and the illumination gradient varied gently, which was more suitable for the driving beam lighting. The luminous flux was 1957.6 lm and the junction temperature was 29.8 °C after 6 min working of the ionic wind generator under a corona discharge power of 3 W. All the test values complied with the regulatory requirements.

Thermal Analysis and Optimization of High Power LED Automotive Headlamp Cooling Device

High power LED headlamp cannot operate normally and efficiently in case the maximum junction temperature exceeds 120°C. Therefore, it is essential to install external cooling device with excellent thermal management. A model based on plate-fin heat sink is presented, the heat transfer plates (HTPS) are added to bridge aluminum substrate and heat sink. And its thermal performance is evaluated compared with the one only installing heat sink. Results reveal the HTPS coupled with heat sink has a good cooling performance. In addition, the correlation between the junction temperature and the HTPS length is investigated. The optimum length is 47 mm. Furthermore, considerable simulation and experiment are conducted on the junction temperature variation subject to input power, ambient temperature, as well as the installation angle respectively. Finally, a fan is added based on the original device to enhance cooling. It indicates that the junction temperature decreases gradually with the presence of velocity air flow.

Simulation and Optimization of Urea-SCR System in Diesel Engine

A three-dimensional Urea-SCR catalytic converter model was simulated with the method of CFD coupled with chemical reaction dynamic in this paper. With the modeling of urea solution injection and spray, the urea spray angle was optimized to reduce the urea wallfilm on the pipe wall. The flow fields and component distributions of a full scale Urea-SCR catalyst system were obtained to analyze the flow and chemical reaction characteristic of SCR system. Finally, an SCR system with a simple blade SCR mixer was simulated, the results indicated that the mixer can accelerate the evaporation and thermolysis of urea solution, and improve reductant uniformity and NOx conversion efficiency of Urea-SCR system.

Laboratory Study on the Liquefaction Properties of the Saturation Structural Loess

The structural property is an important influence factor in loess liquefaction, which contains the interaction between the soil granules. According to study by Gao, the loess could be divided into three types as weak cemented loess, half cemented loess and cemented loess based on the grain composition, the consolidation and the weather conditions of the loess when it formed. In this paper, based on microstructure test and dynamic triaxial test of the loess from the Loess Plateau region, liquefaction properties of structural loess was analyzed. The results show that: (1) the structural strength of loess of weak cementing type, half cementing type and cementing type increases in order, and so does the liquefaction strength, (2) the change mechanism of different structural loess’s dynamic strain during liquefying is different, (3) the change of saturation loess’s pore water pressure during liquefying is related to the type of pore and the structural strength.

Thermal Design of Automotive Headlamp with High Power LED

With an urgent need for energy conservation and pollution reduction, the trend of replacing traditional incandescent or fluorescent lamps with high-power LEDs is growing more and more popular. However, heat dissipation of high-power LED is the main bottleneck for its application. In this research, a kind of automotive headlamp low beam system model is designed with high power LED chips. Several different cooling devices are designed for headlamp cooling, the heat dissipation performances are simulated and analyzed both by the finite volume method (FVM) in FloEFD and experimental measurements. The obtained results indicate that loop heat pipe combined with fined heat sink is the most effective way for heat dissipation in the designed automotive low beam system, even in 80¡æ environmental temperature can ensure the LED headlamp system working stability. The research lays a theoretical basis for the follow-up study.

Experimental Study of Urea-SCR System Under Open-Loop Control Strategy

Open-loop control strategy of SCR urea injection system for MD/HD vehicle diesel engine is established firstly in this paper. Then the emission test is performed for a domestic diesel engine in test bench. Test results show that NOX emissions of ESC and ETC are much lower than the limit values of National-IV emission regulation under a simple injection strategy. The results also show that the urea solution consumption accounts for only 5.8% of the fuel consumption. What’s more, the tests have been accumulated for achieving accurate matching between urea injection and diesel engine.

A Simulated Study on the Combustion and Emission Performances of Diesel Engines

Based on the KIVA-3V source program and coupling the multidimensional model of in-cylinder combustion, this thesis designs a simulation platform of the combustion and emission performances of diesel engines. Results of the test on the in-cylinder pressure change and emission of the experimental subject proves the accuracy of the platform, showing that the platform is able to objectively reflect the real working process of the subject, and that it can be used to research the combustion and emission performances of the experimental engines for a further improvement of the working performances.