As Improvement on Performance in Marine Diesel Engines by Use of Electronic Control Systems

Transcription

1 39 As Improvement on Performance in Marine Diesel Engines by Use of Electronic Control Systems Shinji Baba**, Tadataka Asada**,Satoshi Suzuki* *, Tadashi Kawasaki* *,Toshiaki Hada * * *, Kenji Sawada * * * In recent years, electronic control systems have been widely used for the engine. The authors developed a new system using hydraulic-actuated mechanisms, and applied to the fuel injection control and the drive control of he suction valve/exhaust valve of the medium-speed four-stroke test engine. Then, it was applied to the fuel injection control system and the exhaust valve drive system of the largebore, two-stroke test engine, and it was confirmed that it is possible to achieve the same or higher engine performance as compared to the case with conventional cam system. Moreover, combining "Electronically Controlled Exhaust Valve system'' and Scavenging Controlled Valve system" as a mechanism of a new concept, the authors were able to control freely the scavenging air and exhaust timing of engine. As a result, the effective work of the engine was increased, and the specific fuel oil consumption was improved by 8g/kwh. 1. Introduction Electronic control systems have demonstrated their effectiveness in controlling exhaust gas emissions and improving the performance and efficiency of automotive engines, but their development for use in marine engines lags behind that of automotive applications. Marine engines demand particularly high levels of reliability, and electronic systems, up to now, have not been judged equal to the task, and have thus met with only limited acceptance in this area. Nevertheless, recent advances in electronic techno1ogies have led to greater system reliability, and reflecting the trend to-ward reduced labor and manning on marine vessels, electronic control systems are steadily being introduced for marine engine applications. In this paper, we report the results of our research on applying electronic control technologies to marine engines and evaluate their performance. *Translated from Journal of the MESJ Vo1. 3 I, No. 1 (Manuscript received Sep. 28, 1995) Lectured Ju1. 18, 1995 **Hitachi Zosen Corporation (Taisho-ku, Osaka City) ***Hitachi Zosen Corporation (Konohana-ku, Osaka City) 2. Development of Electronic Control Technology 2.1 Target of Development and its Effects The main mechanism part and the control contents of the diesel engine to be studied are shown in Table 1.The conventional mechanism in the table means the parts to be driven or controlled by the mechanical cam mechanism (hereinafter, referred to as "cam type"), and comprises the governor system and the fuel injection system, the exhaust valve driving system, the starting-air supply, system, the cylinder liner lubricating, oil supply system, etc. By replacing these devices with the electro-hydraulic control system, the present cam drive mechanism can be omitted, the engine mechanism can be simplified, the cost can be reduced, and further, the optimum operation control can be realized. In addition, this new mechanism exploits the advantages of electro-hydraulic control techno1ogy and provides a control system unattainable in conventional engines that can arbitrarily modify timing, displacement (magnitude),and patterns. Electronic control systems can be expected to dramatically improve the performance of diesel engines. 2.2 Key Elements of Electro-Hydraulic Control Technology Fig. 1 shows the application of the electronic control technology to a large-bore diesel engine. This February 1997 (39)

2 40 Shinji Baba, Tadataka Asada, Satoshi Suzuki, Tadashi Kawasaki, Toshiaki Hada. Kenji Sawada control system comprises three components, i.e., an electronic control unit section consisting of the electronic circuit, a hydraulic driving unit section to drive the mechanical devices to be controlled, and the control program to operate the control unit. First, precise angular data obtained from an angular detector (en-coder) mounted on the crankshaft and data obtained from various sensors mounted on the engine are fed to subsystems within the electronic control unit, which in turn, calculates and outputs control and command values, such as valve timing in the engine for each cycle Next, these command signals are sent to the hydraulic drive unit to activate high-speed electromagnetic valves to supply hydraulic pressure generated by a hydraulic pump unit to drive actuators, etc., or by releasing hydraulic pressure, to drive operating mechanisms such as exhaust valves, etc. And finally, the control software monitors engine operating conditions [revolutional speed (rpm), displacement, etc.] by getting feedback data from various sensors. It also corrects for overal1 response characteristics of the subject equipment (response lag and irregularity), resulting in optimum en-g1ne operation. First, to develop three element technologies of an electronic control unit, a hydraulic drive unit and the control program, the electronic control of the fuel injection system, the intake/exhaust valve operating system, and the starting valve control system is challenged using the 4-stroke diesel engine indicated in Table 2. Through this initial development effort, we were able to study the characteristics of each system device independently and by using installed tests to verify operating characteristics, attain an optimum combination of these key technologies. Then, based on these results, application is made to the 2-stroke diesel engine indicated in the table to complete the new control system and realize installed tests. 3. Application to Small-Bore 4-stroke Diesel Engine 3.1 Electro-hydraulic Control system Electronic Control Unit In the test engine to which the electronic control system is applied, four valves (starting valve, fuel valve, intake valve, and exhaust valve) to be contro1led are provided. If the injection valve opening timing and the injection valve closing timing are controlled with the resolution of 0.5o in crank angle for each of these three cylinders, a series of processing (the input of the crank angle, the checking of the correctness of the angular information, the input of the rotational speed, the corrective calculation of the opening/c1osing timing of the valve according to the rotational speed, comparison of the corrective value with the crank angle, the output of the control signal in the case of matching, etc.) must be achieved within a very short time interval (a few LL sec), and the operational load becomes too large for a single control computer. However, given the processing speed of modem computers, the thinking is that this timing would not present a problem, but the authors differ in this view-point, and we propose to distribute processing using the (40) Bulletin of the M.E.S.J., Vol. 25, No.1

3 42 Shinji Baba, Tadataka Asada, Satoshi Suzuki, Tadashi Kawasaki, Toshiaki Hada, Kenji Sawada Under actual conditions, there is a response delay between the time the electronic control unit issues a command to open or c1ose the valve and the time the valve is actually opened or closed. This is because of the 1ength of the hydraulic lines linking the components and the action of the solenoid valve, etc. Consequently, we conducted stand-alone tests to derive the overall response characteristics of the system prior to installing it on an engine. The plot of these characteristics is shown in Fig. 3. 2) Intake/Exhaust Valve Drive System Fig. 4 illustrates the hydraulic system which was fabricated based on a low-speed engine in which the exhaust valves were hydraulically controlled. A hydraulically operated directional transfer valve opens the valve and an existing spring closes the valve. Hydraulic pressure was supplied by a hydraulic pump unit and stored in an accumulator. In addition, for the hydraulic transfer valve, we converted a commercially available servo valve into a high-speed directional transfer valve. Response characteristics were confirmed by per-forming stand-alone tests in a similar manner to the fuel injection system. Further, these response characteristics were combined with those of the fuel injection system, and emp1oyed as the correction map within the control software to be de-scribed later. Assembler language, and a parameter gable that passes values such as control variables back and forth between the two. The main program sets engine operation conditions or control parameters, including engine rpm, fuel injection beginning, intake/exhaust opening/c1osing timing, etc. It also issues commands to display engine operating conditions. Meanwhile the high-speed governor pro-gram acts in a way corresponding to the governor in a conventional mechanical system. It monitors the operating conditions of the engine and shuts it down when anomalous behavior is detected, and applies a correction to the valve opening/closing timing based on the aforementioned response characteristics. 3.2 Installed Tests In the installed test, we modified the three-cylinder four-stroke diesel engine for electronic operation ("EFI" system). Because an "EFI" system has a fuel accumulator, it can offer an outstanding feature as the fuel injection pressure can be set freely (changing the injection period in response to pressure). Fig. 6 shows the engine characteristics when the "EH" system was Control Software Fig. 5 shows the flow chart for the software used for electronic operation based on an electronic control unit and a hydraulic drive unit. The software consists of a main program written in BASIC, a high-speed governor program written in (42) Bu1letin of the M.E.S.J., Vo1. 25, No.1

4 An Improvement on Performance in Marine Diesel Engines by Use of Electronic Control Systems 43 used. The engine was run first with the fuel injection pressure set at a level equivalent to the injection pres-sure in a mechanical system, and then under conditions in which it was set at a higher level of 9.8 Mpa. With the injected volume set equivalent to the operating conditions of a mechanical system, the engine was run modifying the fuel injection period in response to various 1oads. This had almost no effect on general engine performance, as the maximum combustion pres-sure was equivalent to that of the mechanical system. In addition, under partial 1oads, fuel consumption showed a tendency to drop slightly. It should also be noted that, in the installed test for the electro-hydraulically con-trolled intake/exhaust valves, the timing could be completely changed at will by commands issued from the electronic controller. Using the aforementioned four-stroke diesel engine, we were able to define characteristics of the electronic control unit, hydraulic drive unit (transfer valve), including response delays, etc., and were able to verify basic control functions. 4. Application to Large-Bore Two-Stroke Diesel Engine 4.1 Hydraulic Drive Unit We were able to adapt the electronic control unit and the control software developed using the four-stroke engine with almost no modifications. It proved difficult, however, to similarly design the hydraulic drive unit in the case of a four-stroke engine. The volume of fuel injected is greater in the larger engine, and the greater driving force is required for exhaust valves, etc. Consequently, a study was made of a new control mechanism. 1) Fuel Injection System Fig. 7 shows an electronic control system [EFI] February 1997 (43)

5 43 Shinji Baba, Tadataka Asada, Satoshi Suzuki, Tadashi Kawasaki, Toshiaki Hada, Kenji Sawada based on a pressure booster system devised for use in the fuel injection system. The advantages of the accumulator system utilized in the four-stroke engine described above are that the operational mechanisms and control are, by nature, simple merely adjusting the opening and closing timing of the transfer valve. However, this approach also has its shortcomings, including the fact that the units are bulkier because the hydraulic paths in entire system must be capable of handling high pressures, and also that larger surges are prone to occur. In contrast, a pressure booster system supplies fuel to the fuel injection valve by using a pressure booster cylinder. At the point when fuel needs to be injected, hydraulic pressure is applied to a large-bore cylinder which, in turn, intensifies the pressure on the fuel oil contained in a smal1-bore cylinder. The mechanisms and control in such a system are, by nature, complex, but offer superior combustion control because they make it possible to control injection patterns, injection pressure, etc. Also, the problems of high-pressure specifications and surging evident in accumulator systems are reso1ved, and the equipment also can be made smaller and more compact. In addition, existing fuel injection valves can be used. In the pressure booster system, the piston within the large-bore side of the booster cylinder has two surfaces to apply pressure. During operation, a large volume of hydraulic fluid must flow extremely rapidly into the cylinder to apply pressure to one surface of the piston while flowing out from the other side of the piston. Because a standard solenoid valve is incapable of handling this flow and pressure, we developed a hydraulic control unit that combines a small solenoid servo valve with a pair of large piloted check-valves as shown in Fig. 7 (b). The control procedure for the pressure-boosted fuel injection system is to first activate the high-speed transfer valve (solenoid-operated) in the hydraulic path by a "start injection" command from the electronic control unit, open the pilots of the check valves by hydraulic pressure, which will cause a large volume of hydraulic fluid to rapidly flow into upper "surface A" on the large-bore side of the piston while causing the hydraulic fluid on the lower "surface B" to flow out rapidly, thus driving the pressure boosting piston and injecting the fuel. Fuel injection ends when the by-pass port of the small-bore cylinder opens. Also, the amount of fuel injected on each cycle is determined by the initial compression position of the smal1-bore piston. Before the next injection, the metering servo valve allows hydraulic fluid to flow out from upper "surface A" and flow into 1ower"surface B", causing the piston to move back to a set position. A plunger position detector mounted on the back of the pressure booster provides stroke value data on the position of the piston to allow its movement to be con-trolled. 2) Exhaust Valve Drive System For the exhaust valve drive system, a prototype exhaust valve drive unit was built using the electro-hydraulic control system [EEV] shown in Fig. 8.In conventional cam-driven systems, the timing of the opening and closing of the exhaust valves, operating speed, and lift are totally determined by the profile of the cams. In contrast, the exhaust valves in an "EEV" system are activated by hydraulic fluid from a hydraulic pump unit flowing into and out of a cylinder through a transfer valve. The timing of the opening and c1osing of the exhaust valve can be deter-mined by using command signals output from an electronic controller to control the transfer valve. In addition, the operating speed can be controlled by the hydraulic fluid pressure and volume. Consequently,,(44) Bulletin of the M.E.S.J., Vo1. 25, No.1

6 An lmprovement on Performance in Marine Diesel Engines by Use of Electronic Control Systems 45 these parameters can be modified at will, even while the engine is in operation. In addition, for the hydraulic cylinder, a flow control system devised by the authors was used, as shown in Fig. 8 (b). In this approach, the transfer valve is responsible only for control of the initial timing of valve opening and closing. Control of the completion of the valve opening and closing cycle is performed by the cylinder itself. This reso1ves the problem of response, and makes it possible to simplify both control and the mechanism. Further, it ensures both the prevention of piston overshoot at the point of maximum lift of the exhaust valve and loose seating at the time of valve closing. 4.2 Installed Tests 1) Electronic Fue1 Injection Unit Fig. 9 illustrates the results of a stand-alone installation of the pressure-booster electronic fuel injection system [EFI] in the test engine indicated in the previous paragraph. In a comparison of engine performance at equivalent maximum pressure in the cylinder, the specific fuel oil consumption [FOC] was lower at all load levels compared to the cam system, which is the conventional mechanism used to control fuel injection. In particular, "FOC" at reduced loads improved by 7-8 g/kwh. The reason for this is that, in the case of the fuel pump in a cam-driven system, the plunger speed drops at a low engine rpm, resulting in a drop in fuel injection pressure which, in turn, causes the conditions necessary for good fuel atomization to deteriorate. In contrast, in the case of the "EFI" system, fuel injection pressure can be set independently of the engine rpm and can be set at a high level even at low engine rpm. Thus, satisfactory fuel atomization can always be achieved and the increase in "FOC" can be kept in check. This is illustrated in Fig. 10. Here, in comparing the rate of heat release at a 257o load, the maximum rate of heat release is 607o higher for the "EFI" system in which the injection pressure can be set at a higher value than for the cam system. In other words, it is clear that combustion is completed quickly under excellent combustion conditions, resulting in an improved combustion diagram factor hgc, and improved thermal efficiency (FOC). 2) Electronically Controlled Exhaust Valve Drive Unit When we examined characteristics of the exhaust valve lift with the electronically controlled exhaust valve [EEV] mounted independently, we February (45)

7 46 Shinji Baba, Tadataka Asada, Satoshi Suzuki, Tadashi Kawasaki, Toshiaki Hada, Kenji Sawada combustion gas in the exhaust process. Consequently, FOC can be reduced by 0.68 g/kwh (as shown by a one-point-chain line in Fig. 11) by delaying the valve-opening timing by about 25 degrees at partial loads of less than 507o, under which the "EEV" system opens the exhaust valve faster than the cam-controlled system. Within the range of 507o or more loads, however, there is no difference in performance found between both systems since they are almost equal in the valve-opening speed and the angle for delaying the valve-opening timing is small. found that the valve-opening speed was 2 m/s, almost equal to that obtainable in a cam-contro1led system with the engine-rated (1O07o) 1oad, and that the speed was increased to approximately 3 m/ s, about 2.3 times as high as that obtainable in a cam-controlled system with a partial load (257o),by fixing the hydraulic pressure regardless of the operating conditions for the engine. Next, we compared the engine performance with the engine mounted between the "EEV" and cam-controlled systems. With the opening/c1osing timing of the exhaust valve set equal to that in the cam-controlled system, it was confirmed that both the compression pressure and the maximum combustion pressure were decreased at al1 1oads due to the higher valve-closing speed. Then we kept the valve-opening timing untouched and increased the valve-c1osing timing so that the compression pressure and the maximum combustion pressure can equal those in the cam-controlled system. The engine performance is shown in Fig. 11. The "EEV" system (indicated by a full line) consumes more fuel than the cam-controlled system (indicated by a broken line) in all load ranges since the former opens its exhaust valve faster than the latter to quicken the drop in the pressure in the cylinder during the exhaust process and increase the exhaust energy (exhaust temperature), thereby reducing the effective work of the piston. The comparison of the pressure in the cylinder in the exhaust process, between the "EEV" system and the cam-controlled system, is shown in Fig.12. The area indicated by slant lines in the figure shows the above-mentioned improved effects, which confirms that the effective work has been increased. At partial 1oads of 25% and 50% especially, the effective work is more improved (larger effective area) since the "EEV" system can open the exhaust valve faster than the cam-con-tro1led system. On the contrary, there is no remarkable improvement in effective work found at the engine-rated (100%) 1oad since both systems are almost equal in the exhaust valve-opening speed. From all the above findings, it is confirmed that the "EFI" system and the "EEV" system rival or outperform the cam-controlled system in operational properties and engine performance. In addition, the timing can be set unconditionally under any operating conditions, which allows a wider range of control for optimal operation. We test-operated the engine so that the effective work in the expansion process can be enhanced and the exhaust energy can be reduced by delaying the exhaust valve-opening timing since its high-speed valve opening can quicken the exhaust of (46) Bulletin of the M.E.S.J., Vo1. 25, No.1

8 An lmprovement on Performance in Marine Diesel Engines by Use of Electronic Control Systems 47 "Scavenging Control Valve" [SCV] which worked to open and close the scavenging ports combining the newly developed valve "SCV" with the above-mentioned "EEV" to control the scavenging and exhaust timings independently. 5.2 Scavenging Control Valve 5. Application of Electronic Control for Attaining Higher-Efficiency 5.1 Possibility for Higher Efficiency As shown in Fig. 13, the authors have presumed by use of numerical simulations that improving the exhaust diagram factor would be very effective in gaining higher thermal efficiency in a two-stroke diesel engine [1]. However, such great improvements in efficiency as expected through simulations can not be attained in existing engines since the opening and closing timings of the scavenging ports can not be contro1led independently; therefore, the setup for mutual relations between the opening/closing timings of the exhaust valve and that of the scavenging ports is limited. In order to attain further improvement in efficiency, we made the most of such electronic control features so that settings of timings, operating speeds and patterns can be selected as desired and devised. A The system configuration of the scavenging con-tro1 valve "SCV" and the detailed sectional views of the drive cylinder and the contro1 valve are shown in Fig.14. Since the opening and closing timings of the scavenging ports in existing engines are determined unconditionally by geometric relations between the piston and the scavenging ports provided in the lower part of the cylinder, the exhaust valve-opening timing can not be delayed at random because the delayed opening timing of the exhaust valve coincides with the opening timing of the scavenging ports, thereby causing blowbacks. As shown in the figure, a new slide valve is provided in this system. The valve is provided on the outer circumference at the lower part of the cylinder liner, moving upward and downward to open and close the scavenging ports. Driving this valve by electro-hydraulic control allows unconditional setting of the scavenging timing. In principle, this device allows expansion until the piston comes to the bottom dead center and the "SCV" opens in order to exchange gases, thereby enhancing effective work. As shown in the figure, the barrel-shaped scavenging contro1 valve encircling the cylinder liner is actuated by three drive cylinders. Just like the above-mentioned electronic control systems for "EFI" and "EEV", the electronic controller sends the timing command for the opening and the c1osing of the control valve based on the numerical values of the crank angle to the valve control unit, thus actuating the control valve by feeding the working fluid to the drive cylinder or removing it. Since the open time of the scavenging ports is restricted and rather short, the scavenging ports about 70% higher and an opening area larger than the standard is used so that the resistance in the gas flow can be minimized in the scavenging and exhaust processes. 5.3 Mount Test Next, we mounted the "SCV" on a test engine and tested the valve for its performance when combined with the "EEV". Fig. 15 shows a pressure diagram in the exhaust process when the timings of the scavenging-ports opening and the exhaust-valve opening are delayed by 33 degrees and 40 degrees respectively. Compared with the cam-controlled system under the same operating conditions, it is confirmed that effective work has been apparently increased (indicated by the slant lines in the February 1997 (47)

9 48 Shinji Baba, Tadataka Asada, Satoshi Suzuki, Tadashi Kawasaki, Toshiaki Hada, Kenji Sawada figure) and in fact far more than that in the system equipped with the EEV" alone. At this time, the exhaust diagram factor (η gex) amounts to 96Vo to 997o.According to the comparison in engine performance shown in Fig. 16, optimizing the scavenging and exhaust timings and the engine-operating conditions enhances effective work, thus reducing "FOC" by about 8 g/kwh at the maximum. However, the specific air consumption is reduced, thereby slightly increasing thermal 1oads inside the combustion chamber which is demonstrated by rises in the temperature on the surfaces of the cylinder cover and liner. In this way, the introduction of the SCV'' allows the engine performance to be improved greatly through full utilization of the features of the electronic control system. These findings correspond to the results of our previous simulations, which confirms that the numerical simulators are correct. 6. Conclusion Applying electronic control technology to four-stroke engines has al1owed fundamental control techniques to be consolidated, and through our research on applications to large-bore two-stroke marine engines, the following has been clarified: 1) The electronic control system ensures optima1 operation of engines through unconditional control of operating conditions. 2) The electronic control system ensures satisfactory engine performance as well as conventional mechanical controllers. 3) Adding new mechanisms that can reinforce the features of the electronic control system al1ows setting of operating conditions that have not been available with conventional mechanical controllers, thus ensuring a drastic improvement in engine (48) Bulletin of the M.E.S.J., Vo1. 25, No.1

10 An Improvement on Performance in Marine DieseI Engines by Use of Electronic Control Systems 49 efficiency and enabling optimal operation control. There are sti1l many hurdles to overcome concerning the improvement of durability (reliability) and the reduction of costs. References 1) Suzuki, S., Nagai, M., "Examination on Thermal Efficiency Improvement of Marine Diesel Engine", ISME Tokyo 183, Tech. Paper, 1983, P. 87 February ( 49)