第八章内燃机台架性能实验

第八章 内燃机台架性能实验8-1 测量与计算参数v一 测量参数v1 转速n 转速传感器v2 油耗 油耗仪v3 测功器读数 测功器 v4 各种温度、压力v5 测量环境的温度、湿度、压力v二 计算参数v1实测有效扭矩 v v2 实测有效功率 （kW）v式中：n转速（r/min）v Me实测有效扭矩（nm）9550eeM nN v3小时耗油量GTv4耗油率vge=GT/Ne8-2 测试系统概述v一、扭矩测试仪器v台架上都采用吸收式测功器，常用的有水力测功器、电力测功器、电涡流测功器。v1）水力测功器v水力测功器是一种典型的吸收型测功器，它将发动机的输出功率转变为热量消耗掉，同时在此过程中完成转矩测量。v水力测功器主要有转子和定子（外壳）两部分组成。它的基本工作原理是利用转子在充满水的定子中旋转所产生的磨擦阻力来吸收发动机功率，同时通过与可摆动的外壳相连的测力机构测出转矩。由于转子的结构不同，水力测功器大体上分为柱销式、盘式和涡流式3种型式。内燃机带动测功机内燃机带动测功机转子旋转转子旋转,将水搅向外围将水搅向外围,水与搅棒的摩擦力带动定子转动。水与搅棒的摩擦力带动定子转动。水环越厚水环越厚,摩擦阻力越大摩擦阻力越大,相当于外界阻力矩越大。相当于外界阻力矩越大。v优点：优点：结构简单、价廉、工作可靠、应用范结构简单、价廉、工作可靠、应用范围广、功率储备大、使用方便；围广、功率储备大、使用方便；v缺点：测量精度低、排水温度不能太高、精缺点：测量精度低、排水温度不能太高、精度依赖供水压力稳定性。度依赖供水压力稳定性。v2平衡式电力测功器v其工作原理和普通发动机或电动机基本相同，可以将发动机的机械功利用发电机变为电能，也可用电动机把电能转变为拖动发动机的机械能。电机的转子和定子以磁通作为媒介，转子和定子之间的作用力和发作用力大小相等，方向相反。所以只要将其定子做成能自由摆动的浮动方式，便可应用与水力测功器一样的测力机构或拉压传感器测出发动机转矩。v分直流电力测功器、交流电力测功器v优点：负荷和转速调节范围广、工作稳定、使用方便、运行经济性好、吸收的能力可以利用，可以反拖发动机。v缺点：设备费用昂贵、占地面积大。v3电涡流测功器v利用涡电流产生制动力矩而起制动作用。由电涡流测功器结构图可知，感应子主要由旋转部分和摆动部分（电枢和励磁线圈）组成。转子轴上的感应子形状犹如齿轮，与转子同轴装有一个直流励磁线圈。当励磁线圈组通以直流电流时，其周围便有磁场存在，那么围绕励磁组就产生一闭合磁通。很明显，位于绕组左侧的感应子具有一个极性，右侧具有相反的极性。旋转时，由于磁密值的周期性变化而产生涡流，此涡流产生的磁场同产生它的磁场相互作用，从而产生与被试机反向的制动力矩，使电枢摆动，通过电枢上的力臂，将制动力传给测量装置。vDW系列电涡流测功器特性曲线表示测功器在不同转速下所能吸收的功率范围，它由OABCD组成。vAB最大扭矩线，当最大扭矩为常数时所能吸收的最大功率，随着转速的增加而上升，在A点达到扭矩强度所能允许的最大功率。vBC最大功率线。测功器达到最大扭矩点（A）后，随着转速的变化测功器所能允许吸收的最大功率。vCD最高转转速线。测功器在工作时允许的最大转速。v 上述三段限线所包围的区域为测功器的工作范围。凡动力机或机械设备的特性在OABCD所包围的范围内者均能用该型测功器进行特性试验。用主户在选用测功器时须留有余地。v二、耗油量测试仪器v可以分为容积式、质量式和重力式：以小野公司的油耗仪为例！vVolumetric Flow DetectorsvFour pistons are arranged radially in the flow detection unit,and move back and forth repeatedly according to the flow of fluid from the inlet to the outlet.The pistons are rotated by the crankshaft,and their movement is transmitted to the magnetic-coupled rotation detection unit.The rotary encoder mounted on the rotation detection unit generates pulse signals in accordance with the amount of piston movement.vWide measurement range thanks to a flow rate ratio of 1:400 or more vCapable of compensating for errors caused by pulsating or backflow by means of a function for detecting the direction of rotationvHigh reproducibility and high-speed response result in superb reliabilityvCapable of simultaneous measurement of temperature and pressure during flow rate measurement(FP-2240HA/2250A)vGravity Flow DetectorsvIf the fluid level falls below L3,the pressure signal generated by the detector causes the solenoid valve V1 to open and more fluid to flow in.When the fluid level reaches L2,valve V1 closes.Measurement of the flow rate starts after the specified time for the surface of the fluid to reach the fixed level has elapsed.As the fluid level falls from L2 as it is being consumed,the output from the differential pressure transducer changes in accordance with the gravity of the consumed fluid,and the gravity flow rate is obtained from this changed amount.Alarms are generated if the fluid reaches the L1 overflow level or falls to the L4 insufficient fluid level.vHigh-accuracy flow rate measurement over a wide range vBuilt-in air extractor function to counteract the mixing in of air bubblesvAlarm function to warn of overflows and low fluid levels vDensity corrections due to changes in the temperature are no longer required.vIncreased pressure and pressure feed are available as options.vMass Flow DetectorsvThe fluid that entered from the inlet passes through the tube and goes out through the outlet.With this flow meter,the application of its inherent vibration to the tube causes a movement equivalent to the angular velocity,thereby generating a Coriolis force.As shown in the figures above,since the tube for which the Coriolis force is being generated generates a twist proportional to the mass flow rate,the mass flow rate is calculated from the amount of this twist.vContinuous measurement without being affected by temperature,pressure,or densityvHigh measurement accuracy(up to a ratio of 40:1 within 0.1%of the reading accuracy)vDensity measurement enabledvThe case provided with each detector is capable of purging internal air.v其他：v三、转速测量五、测量方法五、测量方法v一 速度特性v 节气门或油门开度固定不动，内燃机运转，油温、水温达正常值。设定测定为速度特性测定，然后调整测功器负荷,使转速达到预定值,测量计算GT、ge、Ne和Me，在特性曲线图上标出该点。再调节测功器负荷，使转速达到第二个预定值,再测量计算GT、ge、Ne和Me，并在特性曲线图上标出该点 将所有点用一条光滑曲线连接。v二 负荷特性v内燃机运转，油温、水温达正常值。节气门或油门开度固定到第一个预定值，调整测功器负荷,使转速达到预定值。设定测定为速度特性测定，测量计算GT、ge 和Ne，在特性曲线图上标出该点。再调节节气门或油门开度到第二个预定值。再测量计算GT、ge 和Ne，并在特性曲线图上标出该点 将所有点用一条光滑曲线连接。