A method and device for measuring friction and accessory loss of diesel engine

Abstract

The present invention discloses a method for measuring friction and accessory loss of a diesel engine, which belongs to the technical field of engine friction loss detection. It mainly solves the technical problem of poor accuracy of existing detection methods. The method is specifically as follows: controlling the intake pressure of the diesel engine and running the diesel engine in reverse to simulate normal operation of the diesel engine, and obtaining reverse power; measuring the cylinder pressure of the intake and exhaust processes of the diesel engine in real time; if the cylinder pressure is greater than a threshold, calculating the indicated power of the pure compression and pure expansion processes according to the thermodynamic polynomial equation; otherwise, obtaining the cylinder pressure curve of the intake and exhaust processes according to the cylinder pressure, and integrating the cylinder pressure curve to obtain the pumping air loss power; obtaining the friction and accessory loss power by reverse power-pumping air loss power+indicated power, and obtaining FMEP by converting the friction and accessory loss power. The present invention also discloses a device for measuring friction and accessory loss of a diesel engine. The present invention can improve measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of engine friction loss detection, and more specifically, to a diesel engine friction and accessory loss measurement method and device. Background Art

[0002] In the development of diesel engines, since the power torque of diesel engines is significantly affected by displacement, in order to study the performance of diesel engines under the same displacement, the effective output power is usually converted into the average pressure per unit displacement, namely BMEP (Brake mean effective pressure). The friction and accessory loss power of diesel engines concerned by this patent can also be converted into the average pressure per unit displacement, namely FMEP (Friction mean effective pressure).

[0003] The most primitive method to obtain FMEP is to reverse the power dynamometer. The operation process is simple, but the reverse power includes the loss of the engine pumping process, so the FMEP obtained is too large. Currently, this method is rarely used to solve FMEP. Studies have found that the FMEP of diesel engines is related to explosion pressure and speed. Figure 1 The curve showing the relationship between the FMEP of a diesel engine and the speed and explosion pressure: as the explosion pressure increases, the crankshaft force will increase, and the friction loss will increase; as the engine speed increases, the speed of the accessories (water pump, oil pump, etc.) will also increase, and the power consumption of the accessories will increase. At the same time, the friction loss of the engine shaft system will also increase with the increase in speed. In order to obtain the FMEP of a diesel engine, it is usually solved by measuring the pressure curve within a working cycle when the engine is in normal working condition. Figure 2 The cylinder pressure curve of a typical diesel engine working cycle is shown in Figure 2. The entire working cycle is divided into four stages: intake-compression-combustion and expansion work-exhaust. According to the thermodynamic formula, the value of the work done by the device can be obtained by integrating the pressure (Y axis) and volume (X axis). The cylinder pressure-volume (PV) curve under a working cycle ( Figure 2 The indicated power of the engine is obtained by integrating the indicated power of the engine, and the indicated mean pressure (IMEP) is obtained by conversion. The actual output power of the diesel engine is measured on the test bench and converted to the diesel engine mean effective pressure (BMEP). The indicated pressure (IMEP) in the cylinder minus the mean effective pressure (BMEP) is the FMEP under the working condition. This is the most commonly used method for measuring friction and accessory losses of diesel engines.

[0004] Since the working pressure of diesel engines varies widely, usually in the range of 0 to 200 bar, and half of the working time is in the low pressure area of ​​2 to 4 bar. At present, the diesel engine field usually uses Kistler's high-response high-pressure sensor to measure the cylinder pressure, with a measurement range of 0 to 300 bar. According to experience, it tends to measure high pressures above 50 bar, and the pressure measurement accuracy below 5 bar is poor. Therefore, the current device cannot accurately measure the cylinder pressure curve in the entire working area. Figure 2 It can also be seen that in the low-pressure stage, the cylinder pressure curve shows obvious fluctuations, which will affect the final integration result of the cylinder pressure curve, that is, affect the calculation of the final power.

[0005] In addition, diesel engine combustion is relatively rough, and combustion is a very complex chemical reaction process with strong randomness, which will cause the working cycle of the diesel engine to fluctuate greatly. Figure 3 The figure shows the fluctuation curve of the maximum cylinder pressure of a diesel engine under 250 consecutive working cycles, with an average value of 125 bar. However, in fact, due to the instability of combustion, the maximum explosion pressure fluctuates by about 3 bar. The fluctuation of the working cycle will bring great difficulties to the cylinder pressure collection. The usual practice is to average the cylinder pressure of these 250 cycles as the cylinder pressure curve under this working condition, but this inevitably brings errors. Summary of the invention

[0006] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art. One purpose of the present invention is to provide a method for measuring diesel engine friction and accessory losses that can improve measurement accuracy.

[0007] A second object of the present invention is to provide a diesel engine friction and accessory loss measuring device that can improve measurement accuracy.

[0008] In order to achieve the above-mentioned first objective, the present invention provides a method for measuring friction and accessory loss of a diesel engine, the method being specifically as follows:

[0009] Controlling the intake pressure of the diesel engine and running the diesel engine in reverse to simulate normal operation of the diesel engine, thereby obtaining reverse power;

[0010] Real-time measurement of the cylinder pressure during the intake and exhaust processes of the diesel engine when it is running;

[0011] If the cylinder pressure is greater than a threshold, the indicated power of pure compression and pure expansion processes is calculated according to the thermodynamic polynomial equation; otherwise, the cylinder pressure curves of the intake and exhaust processes are obtained according to the cylinder pressure, and the pumping loss power is obtained by integrating the cylinder pressure curves;

[0012] The friction and accessory loss power is obtained by reverse drag power-pump air loss power+indicated power, and FMEP is obtained by converting the friction and accessory loss power.

[0013] As a further improvement, the diesel engine is operated by reverse dragging with an electric dynamometer, and the cylinder pressure of the intake and exhaust processes of the diesel engine during operation is measured in real time with a transient pressure sensor.

[0014] Furthermore, the intake pressure ranges from 4.5 to 5 bar.

[0015] Furthermore, the threshold value is 4.5 bar.

[0016] Furthermore, the transient pressure sensor has a measurement range of 0 to 5 bar, and a measurement error of less than 0.02 bar.

[0017] Furthermore, the engine oil of the diesel engine is heated to the engine oil temperature under normal operation of the diesel engine.

[0018] In order to achieve the above-mentioned second objective, the present invention provides a diesel engine friction and accessory loss measuring device, comprising a test bench for installing a diesel engine, an electric dynamometer for towing the diesel engine, and a computer electrically connected to the test bench and the electric dynamometer, and also comprising a transient pressure sensor, an external supercharging device, and an oil heating device. The transient pressure sensor is installed on the cylinder block of the diesel engine, the signal end of the transient pressure sensor is electrically connected to the computer, the external supercharging device is connected to the intake pipe of the diesel engine, and the oil heating device is connected to the oil return pipe and the oil outlet pipe of the diesel engine; the computer calculates FMEP based on data from the test bench, the towing power fed back by the electric dynamometer, and the cylinder pressure fed back by the transient pressure sensor.

[0019] As a further improvement, the oil heating device includes an oil storage tank, a heating module is provided at the bottom of the oil storage tank, one side wall of the oil storage tank is provided with an oil return joint for connecting to the oil return pipe and an oil outlet joint for connecting to the oil outlet pipe, the other side wall of the oil storage tank is provided with a cooling fan and a mounting frame for installing the cooling fan, and the other side wall of the oil storage tank is also provided with cooling fins.

[0020] Furthermore, the external boosting device includes a turbo pump and a motor connected to the turbo pump.

[0021] Furthermore, a pressure regulating valve is provided at the output end of the external boosting device.

[0022] Beneficial Effects

[0023] Compared with the prior art, the present invention has the following advantages: the present invention increases the cylinder explosion pressure of the diesel engine by means of intake pressurization, and can effectively simulate the stress condition of the shaft system under the actual working condition of the diesel engine by reverse towing the diesel engine on an electric dynamometer, without a combustion process, eliminating the cyclic fluctuation caused by combustion instability; using a low-range pressure sensor at low pressure can effectively improve the measurement accuracy of the pressure curve of the pumping process, thereby improving the accuracy of the pumping loss power obtained by integrating the pressure curve; at high pressure, the indicated power of the pure compression and pure expansion processes is calculated by the thermodynamic polynomial equation, which can avoid the error caused by processing the fluctuation curve of the maximum cylinder pressure; finally, FMEP is obtained by converting the reverse towing power, pumping loss power and indicated power, which can effectively improve the measurement accuracy; by controlling different reverse towing speeds and intake pressures, the friction and accessory loss FMEP at different speeds and different diesel engine explosion pressures can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the curve diagram of FMEP of diesel engine changing with speed and explosion pressure;

[0025] Figure 2 Cylinder pressure-volume curve diagram for diesel engine operation;

[0026] Figure 3 This is the variation diagram of the maximum cylinder pressure during the diesel engine working cycle;

[0027] Figure 4 It is a structural schematic diagram of the present invention;

[0028] Figure 5 It is a structural schematic diagram of the oil heating device in the present invention.

[0029] Among them: 1-diesel engine, 2-electric dynamometer, 3-transient pressure sensor, 4-computer, 5-external boost device, 6-oil heating device, 7-cylinder block, 8-intake pipe, 9-oil return pipe, 10-oil outlet pipe, 11-oil storage tank, 12-heating module, 13-cooling fan, 14-mounting frame, 15-cooling fins. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the specific embodiments in the accompanying drawings.

[0031] See also Figure 4 , 5 , a diesel engine friction and accessory loss measurement method, the method is as follows:

[0032] The intake pressure of the diesel engine 1 is controlled and the diesel engine 1 is operated in reverse to simulate the normal operation of the diesel engine 1 to obtain the reverse power. The intake pressure ranges from 4.5 to 5 bar.

[0033] Real-time measurement of the cylinder pressure during the intake and exhaust processes of the diesel engine 1 when it is running;

[0034] If the cylinder pressure is greater than the threshold, the indicated power of pure compression and pure expansion processes is calculated according to the thermodynamic polynomial equation; otherwise, the cylinder pressure curve of the intake and exhaust processes is obtained according to the cylinder pressure, and the cylinder pressure curve is integrated to obtain the pump air loss power; the threshold is 4.5 bar;

[0035] The friction and accessory loss power is obtained by reverse drag power-pump air loss power+indicated power, and FMEP is obtained by converting the friction and accessory loss power. According to the above method, by controlling different reverse drag speeds and intake pressures, the friction and accessory loss FMEP at different speeds and different diesel engine explosion pressures can be obtained.

[0036] In this embodiment, the diesel engine 1 is operated by reverse towing the diesel engine 1 on the test bench through the electric dynamometer 2, and the cylinder pressure of the diesel engine 1 during the intake and exhaust process is measured in real time through the transient pressure sensor 3. The measurement range of the transient pressure sensor 3 is 0 to 5 bar, and the measurement error is less than 0.02 bar. A small-range pressure sensor of model 4049B05 can be selected, with a measurement range of 0 to 5 bar and a measurement error of -0.015 bar to 0.015 bar. In the low-pressure section, the measurement accuracy of the pressure curve of the pumping process can be effectively improved, thereby improving the accuracy of the pumping power loss obtained by integrating the pressure curve.

[0037] According to the polynomial equation of thermodynamic closed system, P2 / P1 = (V1 / V2)^n, for the pure compression process of diesel engine, n = 1.34. The initial pressure P1 and volume V1 can be measured by low-pressure transient sensor 3. Since the change of diesel engine cylinder volume with crankshaft angle is regular, it can be calculated, that is, the volume V2 can be obtained according to the crankshaft angle. According to the polynomial equation, the pressure P2 can be solved. Then the indicated power of pure compression and pure expansion process is calculated by thermodynamic equation.

[0038] The engine oil of the diesel engine 1 is heated to the engine oil temperature under normal operation of the diesel engine 1. The engine oil temperature is maintained at 90-110°C to ensure that the internal moving parts of the diesel engine 1 move under normal lubrication conditions, which is more in line with reality, thereby ensuring measurement accuracy.

[0039] A diesel engine friction and accessory loss measuring device can implement the above-mentioned measurement method, including a test bench for installing a diesel engine 1, an electric dynamometer 2 for reverse towing the diesel engine 1, and a computer 4 electrically connected to the test bench and the electric dynamometer 2, and also including a transient pressure sensor 3, an external supercharging device 5, and an oil heating device 6. The transient pressure sensor 3 is installed on a cylinder block 7 of the diesel engine 1, and the signal end of the transient pressure sensor 3 is electrically connected to the computer 4. The external supercharging device 5 is connected to an intake pipe 8 of the diesel engine 1, and the oil heating device 6 is connected to an oil return pipe 9 and an oil outlet pipe 10 of the diesel engine 1; the computer 4 calculates FMEP based on data from the test bench, the reverse towing power fed back by the electric dynamometer 2, and the cylinder pressure fed back by the transient pressure sensor.

[0040] In this embodiment, the oil heating device 6 includes an oil storage tank 11, a heating module 12 is provided at the bottom of the oil storage tank 11, and one side wall of the oil storage tank 11 is respectively provided with an oil return joint for connecting the oil return pipe 9 and an oil outlet joint for connecting the oil outlet pipe 10. The heating module 12 includes a heating wire, a temperature sensor and a temperature controller connected to the heating wire and the temperature sensor. The other side wall of the oil storage tank 11 is provided with a cooling fan 13 and a mounting bracket 14 for mounting the cooling fan 13. When the oil temperature is too high, the cooling fan 13 can quickly cool the oil, and cooperate with the heating module 12 to effectively control the oil heating temperature range. The other side wall of the oil storage tank 11 is also provided with a cooling fin 15, which can further accelerate the cooling speed and also improve the strength of the oil storage tank 11.

[0041] In this embodiment, the external supercharging device 5 includes a turbo pump and a motor connected to the turbo pump, and the motor drives the turbo pump to supercharge the intake air. A pressure regulating valve is provided at the output end of the external supercharging device 5 to facilitate adjusting the outlet pressure.

[0042] The present invention increases the cylinder explosion pressure of the diesel engine by means of intake pressurization, and can effectively simulate the stress condition of the shaft system under the actual working condition of the diesel engine by reverse towing the diesel engine on an electric dynamometer. There is no combustion process, and the cyclic fluctuation caused by combustion instability is eliminated. At low pressure, the use of a low-range pressure sensor can effectively improve the measurement accuracy of the pressure curve of the pumping process, thereby improving the accuracy of the pumping loss power obtained by integrating the pressure curve. At high pressure, the indicated power of the pure compression and pure expansion processes is calculated by the thermodynamic polynomial equation, which can avoid the error caused by processing the fluctuation curve of the maximum cylinder pressure. Finally, FMEP is obtained by converting the reverse towing power, pumping loss power and indicated power, which can effectively improve the measurement accuracy. The friction and accessory loss FMEP under different speeds and different diesel engine explosion pressures can be obtained by controlling different reverse towing speeds and intake pressures.

[0043] The above are only preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the structure of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A method for measuring friction and accessory losses of a diesel engine, characterized in that: A device for implementing the measurement method comprises a test bench for mounting a diesel engine (1), an electric dynamometer (2) for towing the diesel engine (1) in reverse, and a computer (4) electrically connected to the test bench and the electric dynamometer (2), and also comprises a transient pressure sensor (3), an external supercharging device (5), and an oil heating device (6), wherein the transient pressure sensor (3) is mounted on a cylinder block (7) of the diesel engine (1), a signal end of the transient pressure sensor (3) is electrically connected to the computer (4), the external supercharging device (5) is connected to an intake pipe (8) of the diesel engine (1), and the oil heating device (6) is connected to an oil return pipe (9) and an oil outlet pipe (10) of the diesel engine (1); The oil heating device (6) comprises an oil storage tank (11), a heating module (12) is provided at the bottom of the oil storage tank (11), a side wall of the oil storage tank (11) is provided with an oil return joint for connecting to the oil return pipe (9) and an oil outlet joint for connecting to the oil outlet pipe (10), the other side wall of the oil storage tank (11) is provided with a cooling fan (13) and a mounting frame (14) for mounting the cooling fan (13), and the other side wall of the oil storage tank (11) is also provided with cooling fins (15); The diesel engine (1) is operated by reverse dragging using an electric dynamometer (2), and the cylinder pressure of the diesel engine (1) during the intake and exhaust processes during operation is measured in real time using a transient pressure sensor (3); The transient pressure sensor (3) has a measurement range of 0 to 5 bar and a measurement error of less than 0.02 bar; The external boost device (5) comprises a turbo pump and a motor connected to the turbo pump; The output end of the external pressure boosting device (5) is provided with a pressure regulating valve; The method is as follows: Controlling the intake pressure of the diesel engine (1) and running the diesel engine (1) in reverse to simulate normal operation of the diesel engine (1) to obtain reverse power; Real-time measurement of the cylinder pressure during the intake and exhaust processes of the diesel engine (1) when it is running; If the cylinder pressure is greater than a threshold, the indicated power of pure compression and pure expansion processes is calculated according to the thermodynamic polynomial equation; otherwise, the cylinder pressure curves of the intake and exhaust processes are obtained according to the cylinder pressure, and the pumping loss power is obtained by integrating the cylinder pressure curves; The friction and accessory loss power is obtained by reverse drag power-pump air loss power+indicated power, and the FMEP is obtained by converting the friction and accessory loss power. The inlet pressure ranges from 4.5 to 5 bar; The threshold value is 4.5 bar; During the measurement process, the engine oil of the diesel engine (1) is heated to the engine oil temperature under normal operation of the diesel engine (1).

Images