How to test engine power

The effective output power of the engine is the power emitted by the engine output shaft, which is a comprehensive indicator of the engine. Through testing, you can understand the technical condition of the engine, determine whether the engine needs overhaul or identify the quality of engine repair. Engine power measurement can be divided into steady-state power measurement and dynamic power measurement. Steady-state power measurement refers to the method of testing power with a dynamometer on the engine test bench. By measuring the output torque and speed of the engine, the effective power of the engine can be calculated by the following formula: where: PE - engine power, kw; - engine speed, rpm; me - engine Output torque, n? m. Dynamic power measurement means that when the engine is running at a low speed, the engine is accelerated by suddenly opening the throttle fully or setting the throttle gear to the maximum, and the maximum power can be directly reflected by the acceleration performance. This method can be carried out on the experimental bench, can also be carried out on an unloaded vehicle, but the measurement accuracy is worse than the steady-state dynamometer. First, the engine bench dynamometer test on the test bench to measure the engine output power of the test equipment are tachometer, water temperature gauge, oil pressure gauge, oil temperature gauge, meteorological instruments (hygrometers, barometers, thermometers), timers, fuel gauges, dynamometers and so on. Dynamometer as an engine load, can adjust the measured working conditions, simulate the changes of the external load when the car is actually driving, and at the same time measure the output torque and speed of the engine, so as to calculate the power of the engine. Dynamometers are important equipment for engine performance testing. The main types are hydraulic, electric and eddy current. Hydraulic dynamometers use water as the working medium to regulate braking torque. Electric dynamometers utilize changing the excitation voltage of the stator magnetic field to generate braking torque. Eddy current dynamometers utilize electromagnetic induction to generate eddy currents to form a braking effect. Here only introduce the structure and working principle of eddy current dynamometer.1.Structure and working principle of eddy current dynamometer(1)Structure of eddy current dynamometerEddy current dynamometer can be divided into two kinds of disc type and inductor type due to different structure. At present, the widely used is the inductive eddy current dynamometer. Figure 2-1 shows the structure of an inductive eddy current dynamometer. The brake consists of a rotor and a stator and is made into a balanced structure. The rotor is a toothed disk made of iron. The stator is a complex structure consisting of excitation windings, eddy current rings, and an iron core. All the engine power absorbed by the eddy current dynamometer is converted into heat. Cooling water cools the dynamometer when it is operating. Figure 2-1:Eddy current dynamometer structure 1-rotor; 2-rotor shaft; 3-connecting disk; 4-cooling water pipe; 5-excitation winding; 6-case; 7-cooling water chamber; 8-speed sensors; 9-base; 10-bearing housing; 1-inlet pipe (2) Eddy current dyno working principle When the DC current flows through the excitation winding, a magnetic flux is produced in the closed magnetic circuit consisting of the inductance, the air gap, the eddy current ring and the iron core. Generate magnetic flux. When the rotor rotates, the air gap changes and so does the flux density. The flux density is high at the top of the rotor teeth, but low at the root of the teeth. According to the laws of electromagnetic induction, an induced potential is generated at this point to try to stop the change in magnetic flux, so eddy currents are induced in the eddy current ring, which causes a braking effect on the rotor. The eddy current ring absorbs the power of the engine, and the heat generated will be carried away by the cooling water.2. Test Procedure (1) Install the engine on the dynamometer stand so that the centerline of the engine crankshaft coincides with the centerline of the dynamometer spindle. (2) Install the instrument, connect the electrical wiring, and connect various piping. (3) Check and adjust the valve clearance, distributor circuit breaker contact gap, spark plug electrode gap and ignition advance angle, and tighten all the bolts and nuts. Diesel engine should check and adjust: injector injection advance angle, injection pressure, injection cone angle and spray condition. (4) Record the air pressure and temperature at that time. (5) Start the engine, operate the test instrument, observe the operation of the instrument, record the data, and calculate and plot the Pe, Me, ge curves according to the recorded data. II. When removing the engine from the car, it will be time-consuming and laborious, increasing the parking time of the car. In addition, the disassembly of fittings not only leads to changes in the original running surface, but also causes damage to seals and connections, as well as greatly shortening the working life of the mechanism. When the engine is used for no-load power measurement, the engine power can be quickly measured without disassembling the engine.1. Principle of the engine no-load dynamometerThe engine no-load dynamometer does not require an external loading device. Its principle of measurement is: for a certain structure of the engine, the rotational inertia of its moving parts can be regarded as a certain value, that is, the inertial load of the engine acceleration. Therefore, the power performance of the engine can be known by simply measuring the average acceleration of the engine within a specified speed range. Alternatively, the power of the engine can be determined by measuring the instantaneous acceleration at a given speed. The greater the instantaneous acceleration, the greater the engine power.2. Engine No-Load Dynamometer Method For no-load power measurement, the engine is first separated from the transmission system, and the temperature and speed of the engine reach the specified values. Then, the sensor is installed in the clutch housing in the special hole, quickly open the throttle (gasoline engine) to accelerate the engine. At this point the power meter shows the power of the engine being measured. In order to obtain a more accurate measurement, the test can be repeated several times and the average value taken. There are two ways to accelerate the test, one is to accelerate the gasoline engine by opening the throttle quickly; the other is to cut off the ignition circuit while the engine is running, and then turn on the ignition circuit to accelerate the engine after the engine speed drops. The latter method of acceleration eliminates the additional fuel supply from the carburetor accelerator pump, so the quality of carburetor regulation can be checked. The no-load dynamometer can measure the full power of the engine or the power of a cylinder (when the ignition of a cylinder is turned off or the high-pressure fuel circuit is turned off, the difference between the measured power and the full power is the single-cylinder power of the cylinder). By comparing the power of each cylinder, you can determine the technical condition of each cylinder (mainly wear and tear).3. The use of no-load dynamometer no-load dynamometer can be made into a single function of the portable dynamometer, can also be combined with other test instruments to become a desktop engine integrated tester. The use of no-load dynamometer is as follows: (1) instrument self-calibration and warm-up according to the instruction manual, the instrument is warmed up 0.5h, and then self-calibration (its panel diagram shown in Figure 2-2). Turn the counting check knob 1 to "check" position, the left side of the time (t) meter pointer 1s swing once. Turn knob 1 to "test" position, knob 3 to "self-calibration" position, and then slowly rotate the "analog speed" knob 2. Note that the speed (n), the meter pointer slowly to the right Note the RPM (n) and the meter needle slowly deflects to the right (simulating an increase in RPM). When the pointer is deflected to the initial speed n1=1000r rpm, the gate control indicator lights up. When the analog speed is continuously increased to n2 = 2800r rpm, the "T" meter indicates the acceleration time to indicate the analog speed. Press the "zero" button, the instrument pointer to zero, the gate control indicator light is off, indicating that the instrument regulation is normal. Otherwise, fine-tune the n1 and n2 potentiometers. Figure 2-2; Portable no-load dynamometer panel (2) Warm up the engine and install the speed sensor. Preheat the engine to normal operating temperature (85~95) and allow the engine to idle normally. Put the transmission in neutral, and then connect the two connection cards of the instrument speed sensor to the low-voltage terminal of the distributor and the iron connection wire respectively. (3) Measure the acceleration time operator in the cab quickly to the gas pedal to the end, the engine speed suddenly rise. When the "T" meter pointer shows the acceleration time (or power), you should immediately release the gas pedal, prohibit a long period of high-speed starting the engine. Write down the reading and the instrument will return to zero. Repeat the operation three times and calculate the average value of the readings. The pocket-sized no-load dynamometer with telescopic antenna receives ignition pulse signals while the engine is running, without any wired connection to the engine. To use, hold the dynamometer in your hand. Many no-load dynamometers are equipped with sensors to detect the diesel engine, thus detecting the power of the diesel engine.4. Test results analysis According to the measurement results, to determine the technical condition of the engine. The engine power of the vehicle in use shall not be less than 75% of the original rated power, and the engine power after overhaul shall not be less than 90% of the original rated power. (1) If the engine power is low, the fuel supply system is in poor condition and the ignition system is in poor technical condition, the oil and circuit should be adjusted. If power remains low after adjustment, check cylinder pressure and intake manifold vacuum to determine if mechanical parts are defective. (2) When there is doubt about the technical condition of individual cylinders, the power can be measured after the power is cut off, and the working condition of the cylinders can be diagnosed from the power drop. You can also use a single cylinder misfire measured engine speed drop to evaluate the working condition of each cylinder. When a normal engine is idling steadily at a certain speed, the indicated power and friction power of the engine are balanced. At this point, if the operation of any cylinder is canceled, the engine speed will have the same reduction value. It is required that the difference between the maximum and minimum reduction does not exceed 30% of the average reduction value. If the speed drop value is lower than some specified value, it means that the disconnected cylinder is not working properly. The smaller the speed drop value, the lower the power of a single cylinder. When the drop value is equal to zero, the single-cylinder power is also equal to zero, that is, the cylinder does not work. Engine single-cylinder power is generally low due to the cylinder high-pressure ignition wire or spark plug poor technical condition, poor cylinder sealing performance, cylinder oiling (oil) and other reasons, should be adjusted or overhauled. (3) engine power and altitude are closely related. The result measured by the no-load dynamometer is the engine power at actual atmospheric pressure. If you want to correct to standard atmospheric pressure, multiply by the correction factor.