某空调系统性能提升的仿真分析

文章通过模拟计算的方法,分析某空调系统部件更换后对空调系统性能提升的影响。标定某空调系统模型后,分别更换空调系统中压缩机、冷凝器、蒸发器,通过分析其对空调系统制冷量、压缩机排气压力、冷凝器出口过冷度、蒸发器出口过热度及COP等参数的影响,研究系统部件更换对空调系统性能提升的影响。     

电动汽车热泵空调制热模式启动性能的试验研究

利用电动汽车热泵空调试验系统,测试了热泵空调系统制热模式从启动至稳定过程中,不同环境温度及压缩机转速下系统高压侧压力、低压侧压力、压缩机出口温度、车外换热器进口温度、车室内温度随时间变化的关系,并分析了环境温度及压缩机转速对电动汽车热泵空调制热模式启动性能的影响。试验表明,环境温度越低,电动汽车热泵空调系统未启动时平衡压力越低,启动后达到稳定状态的时间越长,热泵空调系统制热量越低;压缩机转速越高,系统达到稳定状态的时间越短,热泵空调系统制热量越高。     

汽车空调系统性能仿真与参数分析

以压缩机、冷凝器、蒸发器、膨胀阀的结构参数和单体试验性能为基础,建立了汽车空调系统一维仿真模型,并通过系统台架试验,验证了模型的可靠性。基于试验设计(DOE)方法,研究了温度、湿度、风量及压缩机转速对空调性能的影响,明确了制冷量、制冷系数(COP)、排气压力等性能的关键影响因素,分析了压缩机转速、蒸发器风量和冷凝器风量3种可控因素对系统性能的影响规律。     

利用回热器提高HFC134a汽车空调系统性能的试验研究

利用汽车空调系统台架试验,研究了回热器在不同车速和模式下对HFC134a汽车空调系统性能的影响,并在环境模拟试验中测试了回热器对汽车整车性能的影响.台架试验结果表明,在恶劣工况下,回热器可使空调系统制冷量及COP分别提高14.7%和20%.环境模拟试验表明.整车运行约45 min后,回热器系统出风口平均温度比原系统降低约1.5℃.     

工质种类及充注量对电动汽车热泵空调影响的试验研究

针对电动汽车热泵空调,搭建了热泵空调试验台架,采取控制变量法,研究R134A充注量以及工质种类对系统制热性能的影响。结果表明,工质充注量较大时,压缩机出口温度及压力、蒸发器进口压力较大,系统功耗较大,同时制热量较大;工质充注量较小时,蒸发器内工质吸热过少,制热量不足。环境温度低至-10℃及-15℃时,R134A、R407C以及R410A3种工质中R407C制热性能综合效果最好。     

R1234yf新能源汽车热泵空调系统实验研究

R1234yf是R134a理想替代制冷剂之一,为研究R1234yf系统制冷和制热性能,搭建了新能源汽车热泵空调实验台架,通过实验对比研究了R1234yf系统与R134a系统的制冷和制热性能差异。实验结果表明：制冷工况下,R1234yf系统的制冷量和COP均低于R134a系统;制热工况下,R1234yf系统与R134a系统制热量相当,COP低于R134a系统,在低温下制热能力衰减均比较严重。R1234yf系统由于其较低的排气温度更有利于系统稳定运行。     

非均匀气流与温度分布对汽车空调性能的影响

受低温散热器、中冷器等散热元件布置位置的影响,流经散热元件的部分区域进风温度会升高、流速会降低,从而使冷凝器外侧风速和风温形成非均匀的分布状态。通过建立空调系统模型,从制冷量、排气压力、压缩机功耗等方面对比分析了这种非均匀气流与温度分布对空调系统性能的影响,研究了风速、风温、散热元件布置位置等因素对空调性能的影响程度。     

电动汽车热泵空调系统1D和3D耦合仿真分析

文章针对在开发的某款电动汽车搭建了其热泵空调系统仿真分析平台,利用1D和3D耦合分析的方法对乘员舱温度进行了预测,判断该热泵系统是否满足整车采暖的需求,并对不同环境温度下的空调系统性能进行了对比分析。结果表明,采用该热泵系统在-10℃环境温度下脚部平均温度达到16.2℃,未能满足-10℃的整车采暖要求,但能效比达到了2.9,辅助1KWPTC后能够满足整车采暖要求;随着环境温度的降低,系统的制热量和压缩机功耗降低,系统COP增加。     

不同控制策略下新能源汽车跨临界CO2热泵最优运行特性

对于跨临界CO₂汽车热泵系统,在不同控制策略下,研究了影响最优排气压力的主要因素。基于GT-Suite仿真平台建立仿真模型,并用制热性能实验数据对其进行校准。以恒定送风温度来约束制热量。数字模拟了在不同环境温度、不同送风温度和不同风量下的最优排气压力,与定转速控制方式进行对比。结果表明：在定转速控制模式下,没有最优排气压力;在定送风控制方式下,最优排气压力随室内风量增大、环境温度增加、出风温度增大而增大。送风温度影响最优排气压力变化13.09%;环境温度影响最优排气压力变化9.64%;风量影响最优排气压力变化5.95%。提出了基于仿真数据的最优排气压力关联式。     

控制进气门闭合时间对燃烧的影响及改进

进气门提前闭合时，影响燃烧的各种因素包括：ａ．气缸中气体温度与压力；ｂ．有效压缩比；ｃ．废气再循环；ｄ．残余废气；ｅ．其它因素。进气门提前闭合时气体运动减弱是引起燃烧时间延长的一个原因，通过电加热器和热进气空气可提高缸内气体温度和压力。另外，通过控制排气门的闭合时间来提高残余废气系数的方法，对提高气缸气体温度更为有效。     

二氧化碳汽车空调系统的动态仿真

文章建立了跨临界CO2汽车空调系统的动态仿真模型。利用移动边界法和平均空泡系数法对蒸发器建立了集总参数模型;利用移动边界法对气冷器和中间换热器分别建立了集总参数模型;由于压缩机和节流阀的热惯性较小,利用经验公式对其建立了稳态模型。计算结果同实验数据的比较表明,该动态模型比较准确地体现系统实际的动态性能。     

Performance characteristics of a supplementary stack-cooling system for fuel-cell vehicles using a carbon dioxide air-conditioning unit

In fuel-cell-powered vehicles, the fuel-cell system requires a thermal-management subsystem to dissipate heat released during the reaction of hydrogen with oxygen. When the stack generates power at a high rate, a large amount of heat is also generated. If cooling by the radiator is insufficient, a supplementary stack-cooling system is needed to maintain a safe operating temperature. In this study, the performance of a CO₂ air-conditioning unit for stack cooling was investigated under various conditions, and the relationship between cabin cooling and stack cooling was also studied. The coefficient of performance (COP) increased from 1.9 to 2.4, with an increase in cabin-air inlet flow rate from 0 to 8 m³/min. When the air-conditioning unit was turned off, the cooling capacity of the stack cooler was increased; correspondingly, as the cabin-cooling capacity was increased, that of the stack cooler decreased. With an increase in ambient-air inlet temperature from 38°C to 45°C, the COP decreased by 24%. Additionally, both the stack-cooling capacity and cabin-cooling capacity were decreased by about 12% and 16%, respectively, due to reduced heat transfer in the gas cooler as the ambient air inlet temperature was increased. It is expected that the experimental results can serve as a resource in designing a stack-cooling system using a CO₂ air-conditioning unit to enhance stack power generation and efficiency.     

Heat exchanger/catalytic system for reducing the exhaust emissions from diesel engines

A system has been researched over the past 3 years for reducing the exhaust pollutants from diesel engines for light commercial vehicles. The system researched achieves Euro 6 standards for reduction of polluting gases (CO, HC, PM, NO). It consists of 4 main sections: 1. A heater and heat exchanger (HE); 2. A CO/HC oxidising catalyst (D°C); 3. Pt catalyst on a diesel particulate filter (DPF); 4. A NO reducing reaction (SCR) within the DPF. The system operates as follows. The exhaust gas contains oxidising gases, namely both O₂ and NO₂. The levels of CO and HC are oxidised by O₂ to CO₂ for temperatures above 200°C. Carbon (PM) is oxidised to CO₂ by NO₂ but requires a temperature above 250°C. The operating exhaust temperature of 300°C is ideal for the removal of NO by using the Pt catalyst and the CO generated within the DPF. The heater is required to be able to raise the exhaust temperature at any time to 300°C in order to optimise the performance of the system, since diesel engine exhaust temperatures vary between 160°C (slow speeds) to 350°C (high speeds). Considerable heat is required (??3 kW) to maintain the exhaust gas for a 2l engine at 300°C for engine idle conditions. Therefore a heat exchanger is required to re-circulate the input heat and thereby reduce the maximum power consumption to a maximum of 500W over the engine full operating test cycle. This energy is supplied by the engine battery and alternator. Experimental results have been obtained for the exhaust from a Kubota diesel engine and the reductions in exhaust emissions of 83% (CO/ HC), 58% (NOx) and 99% (PM) were obtained. The PM was continuously cleaned so that there was no build up of back pressure.     

EGR增压柴油机的燃烧及排放特性研究

在1台增压中冷柴油机上,采用从涡轮前取气回流到压气机后的高压EGR系统,研究了恒定转速不同负荷下发动机的燃烧和排放特性。在同一工况下,随着EGR率增加,压缩终了混合气温度升高,着火延迟期缩短,燃气压力和温度下降,燃烧持续期延长。分析了柴油机燃烧过程及排放污染物的形成机理。研究发现,当发动机负荷由大变小时,随着EGR率增加,CO的形成因受温度控制增幅越来越大,HC受着火延迟期和供氧的影响增幅越来越小,NO_x的降幅几乎随EGR率呈线性变化,而排气烟度则呈二阶多项式趋势的恶化。     

Design of a compressor-power-based exhaust manifold pressure estimator for diesel engine air management

In accordance with the development of hardware configurations in diesel engines, research on model-based control for these systems has been conducted for years. To control the air management system of a diesel engine, the exhaust manifold pressure should be selected as one of the control targets due to its internal dynamic stability and its physical importance in model-based control. However, it is difficult to measure exhaust pressure using sensors due to gas flow oscillation in the exhaust manifold in a reciprocated diesel engine. Moreover, the sensor is too costly to be equipped on production engines. Hence, the estimation strategies for exhaust manifold pressure have been regarded as a primary issue in diesel engine air management control. This paper proposes a new estimation method for determining the exhaust manifold pressure based on compressor power dynamics. With its simple and robust structure, this estimation leads to improved control performance compared with that of general observers. To compensate for the compressor efficiency error that varies with turbine speed, some correction maps are adopted in the compressor power equation. To verify the control system performance with the new estimator, a HiLS (hardware in the loop simulation) of the NRTC mode is performed. Experimental verification is also conducted using a test bench for the C1-08 mode.     

Experimental studies on the heating performance of the PTC heater and heat pump combined system in fuel cells and electric vehicles

In this study, a combined system consisting of a heat pump and a PTC heater was developed as a heating unit in electric vehicles. The system consists of a compressor, a condenser, an evaporator, an expansion device and a PTC heater. Experiments were conducted to examine the steady-state performance and dynamic characteristics of this system. The compressor speed, outdoor air inlet temperature, and indoor air inlet temperature were varied, and the performance of the system was experimentally investigated. The heating capacity, compressor power consumption and COP were obtained. Warm-up experiments were performed to investigate the dynamic characteristics of the system with a heat load of 1.5 kW in the indoor chamber. For the heat pump system, the PTC heater and the combined system, the heating performance and efficiency were investigated to determine an optimal control method. The results of this study agree well with the experimental results available in literature. This study provides experimental data of good quality for heating system design and the development of electric vehicles.     

Investigation on the flow and heat transfer characteristics of diesel engine EGR coolers

An important goal in diesel engine research is the development of a means to reduce the emissions of nitrogen oxides (NOx). The use of a cooled exhaust gas recirculation (EGR) system is one of the most effective techniques currently available for reducing nitrogen oxides. Since PM (Particulate Matter) fouling reduces the efficiency of an EGR cooler, a tradeoff exists between the amount of NOx and PM emissions, especially at high engine loads. In the present study, we performed engine dynamometer experiments and numerical analyses to investigate how the internal shape of an EGR cooler affects the heat exchanger efficiency. Heat exchanger efficiencies were examined for plain and spiral EGR coolers. The temperature and pressure distributions inside these EGR coolers were obtained in three dimensions using the numerical package program FLUENT.     

Pressure drop and heat transfer of catalyzed diesel particulate filters due to changes in soot loading and flow rate

When soot particles are loaded in a diesel particulate filter, it causes increase in back pressure of the exhaust system. To minimize this pressure drop due to DPF, the filter needs to be regenerated after a certain amount of soot has been accumulated. It is crucial to estimate the correct amount of soot that has been accumulated by measuring the differential pressure. It is also important to understand changes in pressure drop due to flow rate variations of the exhaust gas, since the pressure drop would be influenced by the exhaust flow rate as well as the amount of soot. Furthermore, the heat transfer characteristics of the catalyzed diesel particulate filter (CDPF) are another major issue, as the filter is occasionally exposed to high temperature gas. This study presents the characteristics of pressure drop according to the variation of soot loading and the mass flow rate in CDPF. In addition, heat transfer characteristics in the filter was investigated when a high temperature gas flows into the CDPF. Tests were performed in several CDPF samples having varying amounts of catalyst coating. Experimental results indicate that rig-based experiments are useful in understanding the characteristics of pressure drop in the CDPF. In the cake filtration region, a pressure drop has a proportional relationship according to soot loading and mass flow rate. It was found that an increased catalyst coating may lead to enhanced convective heat transfer.     

基于无机复合材料的排气管路保温性能研究

重型商用车后处理系统排气管路的保温性能对整车排放性性能有着重要的影响,减小排气管路沿程热损失,提高后处理器内部反应温度和污染物转化效率,是整车实现排放性能升级的重要途径.应用新型无机复合材料包覆排气管路,降低排气管路的热损失,提高后处理器内部化学反应温度,能够有效提升后处理器内部载体的转化能力.在不同的环境温度条件下,...     

Electromagnetic valve train for gasoline engine exhaust system

Electromagnetic valve train (EMVT) in camless engine offers large potential for both part load fuel economy and high load engine torque. However, it is more difficult to be applied on exhaust system than intake system. Because the gas pressure brings high demands for driving force, especially at high engine speed and full load. Based on the working characters of actuator, a method by increasing the transient currents in windings during valve’s opening motion is suggested to overcome the gas pressure. But this will cause more energy losses and heat. In order to make the EMVT used on exhaust system better, quantitative analysis is carried out against the additional power consumption caused by gas pressure under different conditions. Furthermore, an approach is introduced to define the optimal exhaust valve opening motion at full load conditions. It aims at making a better compromise between the engine power output and exhaust valves’ power consumption, thus both the efficiency of EMVT and engine performance are enhanced.