流动阻力损失对斯特林热机功率和效率影响的理论分析

目前对斯特林热机的理论热工分析主要集中在热阻、热漏和回热损失对效率和功率的影响。讨论了在加进流动阻力损失后,对斯特林热机功率和效率的影响,并对功率和效率曲线进行了理论模拟。     

船用柴油机转动惯量分布对自振频率的影响

本文研究了２００型柴油机转动惯量的分布对自振频率的影响，提出了集中质量订单节频率的影响比分布质量要大的结论。在保证原系统总惯量不变的前提下，当曲轴配置平衡重后，可以通过调整飞轮惯量，使系统的自报频率不但不下降，还略有提高。     

燃气机热泵变负荷特性的试验研究

燃气机热泵是一项高效节能技术，在试验条件下其一次能源利用率PER为1．13～1．79。为了解交负荷时燃气机热泵的性能，通过试验得到了燃气机热泵的发动机负荷特性、发动机余热回收和燃气机热泵的总体特性曲线。结果表明：随着发动机转速的增加，燃气机热泵的COP和PER是下降的，但下降的幅度较为平缓，且保持较高的数值。通过对IPL Vcop值的分析，发现燃气机热泵的IPL Vcop比热泵系统的大，这说明燃气机热泵的部分负荷性能好，可以很好地实现交负荷运行。     

轻便轴承对增压器机械效率及发动机加速性能的影响

为改善涡轮增压器机械效率及发动机加速性能,分析原轴承系统和轻便轴承系统的旋转部件质量及转动惯量,试验研究原轴承系统和轻便轴承系统的机械效率及发动机加速性能.结果 表明:与原轴承系统相比,增压器转速为60 000～80 000 r/min时,轻便轴承系统机械效率改善2.73％ ～ 8.08％;增压器转速为60 000～1...     

汽油机燃烧放热特征参数的量化研究及简化数模开发

基于多台汽油机性能对标试验数据的二次开发,总结出了此类发动机的燃烧效率、燃烧持续期、燃烧放热率曲线的形状参数随发动机转速、负荷、过量空气系数等运行参数的变化规律。结果表明:燃烧效率几乎只与过量空气系数相关,二者有明确的线性关系;燃烧品质参数m值主要与发动机的负荷相关,与发动机其他设计及运行参数的关系较弱,在很低负荷时m值随发动机负荷的增大而稍微增加,而当负荷高到一定值时m值稳定在2.0左右不变;燃烧放热率曲线形状呈对称形态;燃烧持续期在低负荷时随发动机负荷的增高而减小,但当平均有效压力(BMEP)大于0.8MPa后,燃烧持续期基本稳定不变。燃烧持续期随发动机运行参数的变化趋势,可用简单的线性关系来表述,并有较好的预测精度。     

甲醇缸内直喷热氛围燃烧的试验研究

在单缸直喷式柴油机上进行了二甲醚(dimethyl ether,DME)气道喷射和甲醇缸内直喷的甲醇热氛围燃烧试验研究．结果表明,该燃烧方式呈现分布式放热规律,燃烧过程可分为DME低温放热、高温放热和甲醇扩散燃烧 3个阶段．随负荷的增加,实现稳定燃烧的最小DME比例减小．随DME比例减小,DME高温放热和甲醇燃烧滞后．在稳定燃烧的情况下,随DME比例的增大,燃烧效率和热效率降低,HC和NOx排放呈上升趋势,而CO排放先升高后降低．综合考虑,采用最小比例DME有利于提高其热效率、降低排放．此时热效率、HC排放与原柴油机相当, NOx降低约50％,但CO排放相对原柴油机有较大幅度的增加．     

Experimental Study on Thermal Balance of Regulated Two-Stage Turbocharged Diesel Engine at Variable Altitudes

It is significant to study thermal balance of diesel engine under different variable geometry turbocharger(VGT) vane openings at variable altitudes, which is helpful to assess the heat distribution, control the heat load and improve the heat efficiency of the diesel engine. A thermal balance test system was built to study the influence of the VGT vane opening angles on a regulated two-stage turbocharged(RTST) diesel engine's thermal balance performance. The experiment was conducted under full load operating conditions at different altitudes(0 m, 3500 m and 5500 m). Results indicated that the heat load of engine increased and the thermal efficiency decreased with the increase of altitudes under all operating conditions. As the VGT vane openings increased, the exhaust and maximum combustion temperature increased, while the maximum cylinder combustion pressure decreased. In particular, the maximum combustion temperature was more than 2000 K when the VGT vane openings were greater than 70% at the altitude of 5500 m, and the maximum combustion pressure exceeded 17 MPa when the opening of VGT vane was 70% at 0 m. The thermal efficiency of the engine decreased with the increase of VGT vane openings at the altitudes of 0 m and 5500 m, but the thermal efficiency increased and then decreased at the altitude of 3500 m. It was finally obtained that the best openings of VGT vane was 80%, 60% and 50% under the engine speed of 2100 r/min at 0 m, 3500 m and 5500 m, respectively.     

The modification of the fuel injection rate in heavy-duty diesel engines. Part 1: Effects on engine performance and emissions

An experimental study has been performed on the effects of injection rate shaping on the combustion process and exhaust emissions of a direct-injection diesel engine. Boot-type injections were generated by means of a modified pump-line-nozzle system, which is able to modulate the instantaneous fuel injection rate. The interest of the study reported here was the evaluation of the effective changes produced in the injection rate at different engine operating conditions, when the engine rotating speed and the total fuel injected were changed. In addition, the influence of these new injection rates was quantified on the global engine performance and pollutant emissions. In particular, the focus was placed on producing “boot-like” injection rate shapes, with the main objective of reducing NO_x emissions.Results show how this system is capable of achieving boot-type injections at different boot pressures and boot durations. Also, even though the general trend of the system is to reduce NO_x and to increase soot and fuel consumption, emissions and performance trade-offs can be improved for some specific boot shapes. On the contrary, the modulation of the injection rate showed to be ineffective at medium engine load, since the increase in soot was greater than the relative decrease in NO_x.The analysis of the modifications produced by these strategies on the combustion process, and on the rate of heat release are the base of a second paper.     

An optimization technique of robust load frequency stabilizer for superconducting magnetic energy storage

As an interconnected power system is subjected to rapid load disturbances with changing frequencies in the vicinity of the inter-area oscillation mode, a system frequency may be heavily disturbed and oscillate. Under the circumstances, the stabilizing effect of the conventional load frequency control (LFC), i.e. a governor, cannot be expected. To compensate for such load disturbances and stabilize frequency oscillations, the active power controlled by superconducting magnetic energy storage (SMES) can be applied. In this paper, a new optimization technique of a robust load frequency stabilizer equipped with SMES is presented. To enhance the robustness of the load frequency stabilizer against system uncertainties such as various load changes, system parameters variations etc., the multiplicative uncertainty is included in the system modeling. As a result, the robust stability of the stabilized system can be easily guaranteed in terms of the multiplicative stability margin (MSM). The configuration of the load frequency stabilizer is practically based on a second order lead/lag compensator with a single feedback input. The control parameters are automatically optimized by a tabu search algorithm, so that the desired damping ratio of the target inter-area mode and the best MSM are achieved. The simulation study exhibits the high robustness of the load frequency stabilizer against uncertainties. Moreover, a SMES unit requires small power capacity for frequency stabilization.     

Dynamic simulation of a beta-type Stirling engine with cam-drive mechanism via the combination of the thermodynamic and dynamic models

Dynamic simulation of a beta-type Stirling engine with cam-drive mechanism used in concentrating solar power system has been performed. A dynamic model of the mechanism is developed and then incorporated with the thermodynamic model so as to predict the transient behavior of the engine in the hot-start period. In this study, the engine is started from an initial rotational speed. The torques exerted by the flywheel of the engine at any time instant can be calculated by the dynamic model as long as the gas pressures in the chambers, the mass inertia, the friction force, and the external load have been evaluated. The instantaneous rotation speed of the engine is then determined by integration of the equation of rotational motion with respect to time, which in return affects the instantaneous variations in pressure and other thermodynamic properties of the gas inside the chambers. Therefore, the transient variations in gas properties inside the engine chambers and the dynamic behavior of the engine mechanism should be handled simultaneously via the coupling of the thermodynamic and dynamic models. An extensive parametric study of the effects of different operating and geometrical parameters has been performed, and results regarding the effects of mass moment of inertia of the flywheel, initial rotational speed, initial charged pressure, heat source temperature, phase angle, gap size, displacer length, and piston stroke on the engine transient behavior are investigated.     

Heat pump enhanced gas turbine cogeneration

A significant fraction of the gaseous fuel supplied to industry will be used in medium- and small-size cogeneration plants. In this paper, a gas turbine and a gas engine of about 800 kW power output are compared at full and part load operation. When low-temperature heat (e.g., for space heating) is produced, the higher exhaust losses of the gas turbine yield a lower system efficiency, particularly at part load. A scheme is proposed to recover the exhaust gas energy by cooling to a temperature near ambient. The system features a heat pump to raise the recovered heat temperature to a usable level and an organic Rankine cycle (ORC) engine to drive the heat pump. The ORC engine uses the high-temperature fraction of the heat recovered from the exhaust. The data for the ORC engine are derived from an actual experimental engine. The performance is calculated for the system at full load.     

太阳能光伏光热建筑一体化系统的研究

太阳能光伏光热一体化不仅能够有效降低光伏组件的温度,提高光伏发电效率,而且能够产生热能,从而大大提高了太阳能的转换效率。对光伏光热建筑一体化(BIPV/T)系统的两种主要模式:水冷却型和空气冷却型系统的工作原理和系统模型进行了理论介绍,详细说明了两种系统中热产品在家庭中的应用。并对目前研究情况下两个系统中存在的问题提出了改进方案。与常规建筑相比,光伏光热建筑减少了墙体得热,改善了室内空调负荷状况,提高了建筑节能效果。     

某大功率柴油机推进动力模块动态特性研究

以某型16缸大功率增压柴油机动力模块为研究对象,采用AMESim软件建立了柴油机动力模块的仿真模型,并通过试验数据对仿真模型进行了标定.基于该模型对柴油机推进动力模块加速过程中模块转速与设定值的偏差,以及瞬态调速过程中模块带大惯量运行的规律以及喷油控制优化进行了仿真研究.研究结果表明:减小涡轮增压器惯量可以优化柴油机加...     

Heat release and engine performance effects of soybean oil ethyl ester blending into diesel fuel

The engine performance impact of soybean oil ethyl ester blending into diesel fuel was analyzed employing heat release analysis, in-cylinder exergy balances and dynamometric tests. Blends with concentrations of up to 30% of soybean oil ethyl ester in volume were used in steady-state experiments conducted in a high speed turbocharged direct injection engine. Modifications in fuel heat value, fuel-air equivalence ratio and combustion temperature were found to govern the impact resulting from the addition of biodiesel on engine performance. For the analyzed fuels, the 20% biodiesel blend presented the best results of brake thermal efficiency, while the 10% biodiesel blend presented the best results of brake power and sfc (specific fuel consumption). In relation to mineral diesel and in full load conditions, an average increase of 4.16% was observed in brake thermal efficiency with B20 blend. In the same conditions, an average gain of 1.15% in brake power and a reduction of 1.73% in sfc was observed with B10 blend.     

Optimization Potentials for the Waste Heat Recovery of a Gas-Steam Combined Cycle Power Plant Based on Absorption Heat Pump

A new waste heat recovery system is presented to recover exhausted steam waste heat from the steam turbine by absorption heat pump(AHP) in a gas-steam combined cycle(GSCC) power plant. The system can decrease energy consumption and further improve the energy utilization. The performance evaluation criteria are calculated, and exergy analysis for key components are implemented in terms of the energy and exergy analysis theory. Besides, the change of these criteria is also revealed before and after modification. The net power output approximately increases by 21738 kW, and equivalent coal consumption decreases by 5.58 g/kWh. A 1.81% and 1.92% increase in the thermal and exergy efficiency is respectively obtained in the new integrated system as the heating load is 401095 kJ at 100% condition. Meanwhile, the appropriate extraction parameters for heating have been also analyzed in the two systems. The proposed scheme can not only save energy consumption but also reduce emission and gain great economic benefit, which is proven to be a huge potential for practical application.     

Performance comparison of looped thermoacoustic electric generators with various thermoacoustic stages

Thermoacoustic engine is a kind of novel heat engine based on thermoacoustic effect, with the merits of environmental benignity, simplicity, and reliability. In this work, looped travelling-wave thermoacoustic electric generators (LTTEGs) with one to four thermoacoustic stages have been developed and experimentally studied. It is observed that adding thermoacoustic stages can improve the thermal-electric efficiency of LTTEGs, while whether the extra stages lead to efficiency gain depends on the number of existing stages and other operating parameters (hot temperature, for instance). One main reason is that the Gedeon streaming, which might cause severe heat loss, can be enhanced by adding thermoacoustic stages and increasing hot temperature. The results suggest that the suppression of streaming in the looped thermoacoustic engine with multiple stages is even more urgent than in the traditional travelling-wave engine with only one stage.     

LPG/柴油双燃料发动机压缩比优化研究

采用燃料复合供给方式 ,在单缸直喷式柴油机上进行了LPG/柴油双燃料发动机压缩比的优化试验研究 ,对比分析了使用纯柴油和LPG/柴油双燃料的燃烧特性 ,着重研究分析了双燃料发动机在不同压缩比下的最高燃烧压力、最大压力升高率、压力循环波动及燃烧放热率 ,并以此为依据优选了双燃料发动机的压缩比。试验结果表明 :降低压缩比后 ,双燃料发动机的最高燃烧压力及最大压力升高率均有较大降低 ,同时压力循环波动变小 ,但滞燃期、燃烧持续期都会有所增加。经过优化 ,压缩比确定为 14.5时 ,ZH110 5W柴油机改燃LPG/柴油双燃料后在高负荷工况下无严重爆震现象 ,压力循环波动较小 ,且经济性较好 ,热效率损失不大     

Application of heat flux as a control variable in small-scale packed-bed steam reforming

In steam reformation, high thermal resistance and poor heat transfer of the packed catalyst bed can create time-lag between the moment when the heat is applied and the corresponding rise in temperature. Thus, problems arise from the dynamic requirements of the system, which can create a time-lag in the reactor's performance and also induce temperature oscillations resulting in a degrading catalyst. Lag compensation is necessary if one uses temperature feedback control to maintain the reactor temperature. A better solution is to recognize that heat flux is more suitable as a control variable, since available heat is what sustains the chemical reaction inside the reactor. Thus, controlling heat flux can directly influence the reaction and the resultant temperature inside the reactor. A heat flux controller is implemented for two small-scale, packed-bed, steam reformers. A standard temperature feedback controller is also implemented. The two systems are compared in their transient response. Temperature and reformate gas concentrations are measured to evaluate the performance of the two controller topologies. The heat flux based controller significantly outperforms the temperature feedback controller in both geometries tested.     

冷、热EGR对柴油机性能、燃烧及排放特性的影响

为在保持柴油机动力性和经济性能的同时有效改善其排放性能,在一台4缸柴油机上针对6、12、24mg循环喷油量的负荷工况(记作低、中、高负荷)对比研究了冷、热废气再循环(EGR)对性能、燃烧及排放特性的影响。结果表明:EGR的引入减少了新鲜进气量,整体上延长了滞燃期,减缓了燃烧放热速率,降低了压力升高率;热EGR提高了进气温度,使低负荷时的碳氢化合物(HC)排放显著降低,热效率提高,而高负荷高EGR率时由于过量空气系数偏低引起了热效率的明显降低,对最大压力升高率的降低作用也弱于冷EGR;随着EGR率的提高,三种负荷下的氮氧化物(NO_x)排放均大幅度降低,碳烟排放在低、中负荷时较低,而在高负荷时则明显升高,NO_x与碳烟排放之间出现此消彼长的矛盾趋势。冷的高EGR率下的碳烟排放升高幅度减小,有效地缓解了这种矛盾。综合分析低、中、高负荷下的热效率及排放,低负荷时为提高热效率宜采用热EGR,高负荷时为降低过高的压力升高率并兼顾热效率则更适合采用冷EGR。     

耦合太阳能的燃气轮机动态性能与控制特性研究

为深入研究耦合太阳能对燃机动态特性的影响,建立耦合太阳能的燃气轮机以及相应控制系统的动态模型。分析槽式集热器不同耦合方式对系统稳态性能的影响以及受到外界负荷及太阳直射辐射（DNI）扰动时各参数的动态响应,研究槽式集热器金属热容对系统动态特性的影响,针对比例积分（PI）控制,研究相应参数对系统调节效果的影响。结果表明,采用集热器布置在回热器前时,系统的排气温度相对较高,但系统效率会相对较低,受到外界负荷扰动时,系统响应更加迅速,采用集热器布置在回热器后时则可得到更高的燃料节省量;DNI变化时2种方式的系统响应速度相同;当集热器金属热容较小时,系统的响应时间主要受控制系统及回热器惯性影响,随着热容增加,调节集热器惯性参数为改变系统动态响应时间的最有效方式;比例系数K_p与积分系数K_i应合理选取,过大或过小均会使系统失调的危险性提高。