Analysis of BJ493 diesel engine lubrication system properties

The BJ493ZLQ4A diesel engine design is based on the primary model of BJ493ZLQ3, of which exhaust level is upgraded to the National GB5 standard due to the improved design of combustion and injection systems. Given the above changes in the diesel lubrication system, its improved properties are analyzed in this paper. According to the structures, technical parameters and indices of the lubrication system, the lubrication system model of BJ493ZLQ4A diesel engine was constructed using the Flowmaster flow simulation software. The properties of the diesel engine lubrication system, such as the oil flow rate and pressure at different rotational speeds were analyzed for the schemes involving large- and small-scale oil filters. The calculated values of the main oil channel pressure are in good agreement with the experimental results, which verifies the proposed model feasibility. The calculation results show that the main oil channel pressure and maximum oil flow rate values for the large-scale oil filter scheme satisfy the design requirements, while the small-scale scheme yields too low main oil channel’s pressure and too high. Therefore, application of small-scale oil filters is hazardous, and the large-scale scheme is recommended.


Diesel lubrication system and arrangement
As shown in figure 1, the BJ493ZLQ4A diesel lubrication system includes oil pump, oil filter, oil cooler, main shaft, connecting rod shaft, cam shaft bearing, turbo lubrication, piston cooling jet (PCJ), air compressor lubrication, timing gear shaft lubrication, and oil pump lubrication. Among these, the lubrication of the main shaft, connecting rod shaft, cam shaft bearing, gears, cylinder head, and PCJ: these parts are provided through the main and cylinder body inner oil channels [3]; while the turbo and air compressor are lubricated through the external oil pipes of the cylinder body.   Figure 2 depicts the conditions of the 3# main bearing and main oil channel connections. The main oil channel in the cylinder body of the diesel BJ493ZLQ4A is located at the right bottom part of the cylinder body (viewed from the back of the engine), while the main shaft neck is lubricated by a changeable oil channel (of 8.4 mm or 7 mm in diameter) with the inclination angle of 15º to the horizontal plane, and another downward oil channel (of 10 mm in diameter) with the inclination angle of 45º to the horizontal plane. The intrinsic feature of 3# main bearing oil channel arrangement is that 3 1234567890 6th Global Conference on Materials Science and Engineering IOP Publishing IOP Conf. Series: Materials Science and Engineering 283 (2017) 012005 doi:10.1088/1757-899X/283/1/012005 the main oil channel supplies oil to 3# main bearing and 2# cam bearing through the inner cylinder body oil channel, while providing oil directly to the PCJ and diesel oil pump. Figures 3-6 depict the oil-connecting conditions for 1#, 2#, 4#, 5# main bearings and main oil channels.

2.2.Cam shaft lubrication
As seen from figure 7, the diesel engine cam shaft is arranged at the right side of its middle line (viewed from the diesel's back), and provides oil for the main oil channel via the inner oil channel of cylinder body at 5#, 3#, 1# main shaft bearings, then returns to the oil bottom shell by the natural oil re-circulation method. The diameter of oil channel connected to the bearing bush is 6 mm, and its length is 15.5 mm.

2.3.PCJ bearing lubrication
As seen from figure 8, oil flows into the connecting pipe of piston cooling jet (PCJ) bearing, which protrudes from the cylinder body [4]. The area of injection outlet nozzle is 1.77 mm 2 , and the diameter of PCJ pipe is 3 mm.

2.4.Gear lubrication
As seen from figure 9, gears lubrication mainly relies on the oil provided via the main oil channel, while air compressor, oil pump and idler gear of the air compressor are supplied by oil via the external oil pipe, which is connected with the main oil channel. Idler gear A is connected with the main bearing bush oil nozzle. The diameter of the external oil pipe of the oil pump is 6 mm, the diameter of the idler gear near air compressor is 4 mm, while the diameter of spatter oil supplying pipe is 1 mm. Figure 9. Gear lubrication.

2.5.Turbo
As shown in figure 10, the external inlet oil pipe of the turbo is connected with the main oil channel directly [5]. The pipe inner diameter is 6 mm, the length is about 510 mm.

2.6.Oil pump
The diameter of oil pump external connection oil pipe is 6 mm, as is shown in figure 11.

2.7.Shaft main bearing bush
Shaft main bearing has 5 channels, its diameter is 70 mm and width is 21.9 mm, while the width of oil tank is 180°×3 mm, the depth is 0.85 mm; standard gap is 0.033-0.079 mm, under the limited size conditions, the relative gap of bearing is 0.113%.

2.8.Shaft connecting rod neck bearing bush
Connecting rod neck bearing has 4 channels, its diameter is 53 mm and width is 24.7 mm; there is no oil tank; standard gap is 0.029-0.075 mm, under the limited size conditions, the relative gap of bearing is 0.140%; the axial gap between connecting rod and shaft is 0.175-0.29 mm.

2.9.Cam shaft bearing
Cam shaft bearing of 50 mm in diameter has 3 channels of width equal to 26, 234, and 23 mm for the first, second, and third channels, respectively. There is no oil tank; the standard gap between cam bearing bushing nozzle and cam shaft bearing neck is 0.015-0.085 mm, the limit of gap abrasion is 0.12 mm, and under the limited size conditions, the relative gap of bearing is 0.17%.

Elaboration of models for software simulation
According to the structural features and the arrangement conditions of lubricated parts of BJ493ZLQ4A diesel, the simulation models [6] were elaborated, as shown in figures 12 and 13. The structures and principles of the lubrication models correspond to the actual engine set-up, such as the main shaft bearing, cam shaft bearing, connecting bearing, the main oil channel, and the engine's components' lubrication: turbo, air compressor, cylinders, oil pump, PCJ, positive crankcase ventilation valve (PCV), etc. The data on their sizes and properties, especially for lubrication materials and systems, can be input into the model, and they fully correspond to the actual engine operating conditions. Insofar as the simulation results are also close to the actual engine test data, the elaborated model feasibility is confirmed.    Properties of 5W40 oil The 5W40 oil viscosity-temperature curve is shown in figure 14. The curve and its relevant data refer to the actual conditions obtained from the suppliers [7] and were exported from the Flowmaster database, of which data exhibit a good fit with the experimental results. Positive Crankcase Ventilation Valve (PCV) PCV feature's curve is plotted in figure 15.
 Features of Oil Pump Oil pump's curves are plotted using the available experimental data. Figures 16(a) and 16(b) depict the volume efficiency-pressure and flow rate-pressure curves, respectively, of the oil pump at different rotation speeds.

 Properties of Oil Filter and Oil Cooler
Large-and small-scale oil filter schemes [8,9] have been adopted in the oil filter design. For both schemes, the simulation of the diesel's lubrication system operation was performed separately. According to the data provided by suppliers, the effective area of small-scale oil filter is 0.22 m 2 , standard flow rate is 33 L/min, the recommended flow rate is below 30 L/min; while the effective area of large-scale oil filter is 0.38 m 2 , standard flow rate is 45 L/min, the recommended flow rate is below 40 L/min.  Piston Cooling Jet (PCJ) features of the injection nozzle. The pressure difference-flow rate curve of PCJ is shown in figure 17.

Selection of benchmarks for calculation
For analyzing the effects of two oil filter and oil cooler parts on the diesel's lubrication system, separate calculations were performed for the oil cooler with the large-and small-scale oil filters [10].
The boundary conditions for the both schemes are basically the same, except for the oil filter and oil cooler curves. Seven benchmark rotation speeds were selected, namely 800, 1200, 1500, 2000, 2800, 3200, 3600 rpm, whereas 800 rpm corresponds to the idle speed point, 1200, 1500, 2800 rpm are transition speed points, 2000 rpm is a predicted PCJ full point; 3200rpm is the rated point; 3600 rpm is the primary optimization point. For these benchmarks, which characterize diesel's properties and features, the calculations of the lubrication system's total oil flow rate, branch flow rate of the parts and each point's pressure values were conducted.

Calculation results and discussion
6.1.Calculation results of small-scale oil filter scheme 6.1.1. Pressure distribution. As shown in figure 18, with an increase in the diesel engine rotation speed, the parts' oil pressure increased constantly. When the engine speed was below 2800 rpm, the pressure of the parts increased rapidly. When it exceeded 2800 rpm, the oil re-circulation flow rate of PCV increased (between 3.2-6.3 L/min) with speed, the pressure increase of parts slowed down. For rotation speed between 3200-3600 rpm, the pressure of the inner main oil channel remained unchanged at about 0.376 MPa, while the oil pressure of parts exhibited a steady state [11,12].  Table 2 lists the main parts' oil pressure design requirements and simulated contrasting conditions. The simulated results indicate that under small-scale oil filter conditions, the pressure of the main oil channel cannot satisfy the design requirements for the diesel optimized condition and requires the experimental verification. Figure 19 depicts the oil flow rate distribution conditions of the lubrication system parts for the small-scale oil filter scheme. With an increase in the engine rotation speed, the total oil flow rate is increased from 7.18 L/min to 38.8 L/min. While the engine speed is between 2800 and 3600 rpm, the main shaft bearing oil flow rate is in the range of 12.5 to 14.95 L/min; connection rod large head shaft bearing oil flow rate is from 5.7 to 6.5 L/min; the PCJ effective flow rate is between 8.2 and 8.52 L/min, which exceeds the requirement of 8 L/min for the The maximum values of oil flow rate are: 1.16 L/min for turbo (at 3200 rpm) and 0.15 L/min for air compressor (at 3600 rpm), while the maximum value of the oil pump quantity rate is 0.35 L/min (at 3600 rpm). Under the increased rotation speed condition of 3600 rpm, the oil flow rate of oil filter is 32.5 L/min, which exceeds the maximal value of 30 L/min recommended by the producer, but this value is slightly less than the small-scale oil filter's standard flow rate of 33 L/min. Therefore, application of the small-scale oil filter scheme under increased rotation speed conditions may be hazardous due to inadequate oil supply. Conclusions and proposals Pressure of main oil channel exceeds 1.5 bar at 125º C 1.64 Approved Pressure of main oil channel exceeds 3.85 bar at 125º C for the engine speed of 3200 rpm

3.76
Experimental verification is proposed Turbo: the oil pressure is larger than 1.5 bar at 125º C for the engine speed above 1000 rpm

Approved
Air compressor: the oil pressure is larger than 3.0 bar at 125º C for the engine speed of 3600 rpm

Approved
Pressure from main shaft bearing to connecting rod shaft neck exceeds 2.2-2.8 bar at 125º C for the engine speed of 3200 rpm 3.7 Approved Figure 19. Oil flow rate distribution of various parts of the lubrication system (small-scale oil filter).
Flow rate design requirements and calculation results for the small-scale oil filter scheme are listed in table 3. Table 3. Flow rate design requirements and calculation results for mall-scale oil filter scheme.

Requirements
Calculated value Conclusions and proposals Oil pump: effective exhaust rate 37.12 L/min at 3200rpm for the oil pressure of 6 bar velocity is below 5-6 m/s, to ensure that the pressure loss is minimal. About 3 m/s. Under condition of increased rotation speed at 3600 rpm, the oil filter flow rate is less than 30 L/min 32.5 L/min Hazardous, requires test verification 6.2.Calculated results for the large-scale filter scheme 6.2.1. Pressure distribution conditions. As seen from figure 20, in case of the large-scale oil filter and oil cooler scheme application, the oil pressure in lubrication system parts increased constantly with the diesel engine speed. Thus, at rotation speed below 2800 rpm, pressure in all parts increased rapidly, and the main oil channel inner pressure rose from 0.164 MPa to 0.259 MPa; at the speed above 2800 rpm, pressure rise slowed down due to the increased PCV leak rate; while at the speed in the range of 3200-3600 rpm, the main oil channel inner pressure remained in the range of 0.38-0.39 MPa, and steady pressure values in all parts were observed.  As seen from figure 21, prior to reaching the oil cooler, oil flows into through a pipe of 10 mm in diameter and makes a turn at the right angle, which results in the pressure drop of about 0.045 MPa (at 3600 rpm), according to the calculations, In addition, a pressure drop in the oil pump transfer pipe is estimated as 0.05 MPa (at 3600 rpm), which is due to the fact that the oil transfer pipe diameter of 10 mm is too small, and the oil flow velocity is too high. Since the combination of these two geometric features leads to the total pressure drop of 0.095 MPa (at 3600 rpm), it is proposed to increase the oil channel diameter in these two points under the condition that the cylinder body structural integrity is not violated.  6.2.2. Flow rate distribution conditions. As shown in figure 22, the flow rate in lubrication system parts increased in the range from 7.19 to 39.2 L/min with the diesel engine speed: at 2800 rpm, the oil pump outlet pressure is 0.547 MPa, which exceeds the value of 0.54 MPa, which triggers the PCV opening, so the PCV begins to release at 2800 rpm, and the oil flow rate of PCV is 0.855 L/min, the main oil channel inner pressure being 0.37 MPa after releasing.
While the engine speed is below 2800 rpm, the main bearing oil flow rate is 4.07-8.75 L/min, connecting rod big head bearing oil flow rate is 1.89-4.02 L/min, cam shaft bearing flow rate is below 0.31 L/min, PCJ effective flow rate is 2.78-4.92 L/min, turbo compressor (TC) oil rate is below 0.8 L/min, oil pump flow rate is below 0.21 L/min, and air compressor flow rate is less than 0.084 L/min.
After the engine speed reached 2800 rpm, the PCV recirculation oil flow rate increases to the maximum of 6.17 L/min (at 3600 rpm), the total flow rate of the main oil channel inlet is 12.3-14.8 L/min, the oil flow rate of connecting rod big head bearing is 5.63-6.65 L/min, the oil flow rate of cam shaft is about 0.5 L/min, the maximum value of PCJ effective flow rate is 8.75 L/min (at 3200 rpm), the maximum oil flow rate of the turbo is 1.22 L/min (at 3200 rpm), the maximum oil flow rate of the pump is 0.355 L/min (at 3600 rpm), and the maximum oil flow rate of the air compressor is 0.15 L/min (at 3600 rpm).
The large-scale oil filter's design requirements and calculation results are listed in table 5. Table 5. Design requirements and calculation results for the large-scale oil filter scheme.

Requirements Calculated value
Conclusions and proposals Oil pump: effective exhaust rate of 37.12 L/min at 3200 rpm for the oil pressure of 6 bar Needs to be approved PCJ open pressure position: 2+/-0.25 bar; engine speed of 2800 rpm; recommended flow rate of 8.0 L/min or 2.0 L/min for each PCJ 8.5-8.75 L/min Needs to be approved Main oil channel's inner diameter is 15 mm, the inner diameter from oil pump to main oil channel needs to ensure that the oil flow velocity is below 6 m/s, to make sure that the pressure loss is minimal.