R&D on Environment-Friendly, Electronically Controlled Diesel Engine

20000 M4.2.2 R&D on Environment-Friendly, Electronically Controlled Diesel Engine (Electronically Controlled Diesel Engine Group) Nobuyasu Matsudaira, Koji Imoto, Hiroshi Morimoto, Akira Numata, Toshimitsu Koga, Shuji Shinkai, Takafumi Hakozaki, Takuya Kumagai, Yoshinori Nagae, Keizo Goto, Tadao Ohmura 1. Contents of Empirical Research With the increase in energy consumption, environmental pollution has become an international problem and now there are great demands for reductions in carbon dioxide, nitrogen oxides and other emissions from internal combustion engines. On resolving these problems, the objectives of this research are to increase the thermal efficiency of diesel engines with originally high thermal efficiency as a power system, to get lower emissions while simultaneously developing a new-model engine optimized for electric power stations. 1.1 Target of Empirical Research In this research, the diesel engines of 3000 kw class are developed for electric power station equipment, especially for cogeneration systems of high total efficiency with the targets shown in the table1.1-1. Table 1.1-1 Development target values Thermal efficiency (%) NOx (ppm: Excess O 2 13%) Particulate Matter (g/nm 3 ) Present status (on the market) 40 950 0.05 Intermediate target 45 or more 750 or less 0.05 Final target of this research 45 or more 220 or less 0.05 1.2 Problems and Resolution Methods In order to achieve low CO 2 (high thermal efficiency), low NOx and low particulate matter, all simultaneously, it is important not only to control the formation of fuel-air mixture and combustion but also to improve the total engine system. Consequently, we will resolve the problems by realizing the constant-pressure combustion cycle with high compression ratio, developing electronically controlled VG (Variable Geometry) turbocharger with high pressure ratio and electronically controlled fuel injection system and combining these methods with assistant means. The key technologies to achieve the targets are listed in the table 1.2-1. 1

Table 1.2-1 Key technologies for achieving the targets 1) High-compression-ratio, constant-pressure combustion cycle 2) Electronically-controlled, high-pressure-ratio VG turbocharger 3) Electronically-controlled fuel injection system 4) Structure for withstanding higher maximum combustion pressure High compression ratio, Optimum intake/exhaust valve timing, Long stroke, High Maximum combustion pressure/constant pressure combustion cycle Increased efficiency by improving compressor and turbine blade shape High-pressure injection, Control of injection duration/injection rate 5) Application of assistant means Water injection system High-strength crankshaft, High-rigidity cylinder head, other The major research themes are listed as follows. (1) Study by simulations and computations (2) Development of main components and testing (3) Single-cylinder engine testing (4) Multiple-cylinder engine production and testing 1.3 Contents of Empirical Research in 1999 The themes as follows were carried out in 1999 out of the items (1) to (4) mentioned in the section 1.2: studying by using engine performance simulator, fuel injection pump performance testing, single-cylinder engine testing, and multiple-cylinder prototype engine design and production. (1) Studying by using engine performance simulator In order to achieve the targets of high thermal efficiency and low NOx of diesel engines, an engine performance simulator was used to calculate the effect of each parameter (compression ratio, maximum combustion pressure, valve timing, charge air supply conditions, etc.) on the engine performance, and some studies were made about the quantitative condition of measures and effects their affects. (2) Fuel injection pump performance testing As a means of realizing high output and high thermal efficiency, a fuel injection system aimed to be operated at high pressure and high injection rate was designed and produced, and fuel injection pump single-unit performance tests were performed. (3) Single-cylinder engine testing Using an existing single cylinder engine, combustion performance tests were performed to evaluate the effect on engine performance of intake and exhaust setting conditions, compression ratio and fuel injection valve specifications (high pressure/high injection rate). 2

(4) Multiple-cylinder prototype engine design and production Studies were made of the design concept of a multiple cylinder test engine with the potential to achieve the target performance and computations were made of the strength of each key component. The results of these studies were reflected in the design and production of such an engine. 2. Results of Empirical Research and Analysis 2.1 Results of study using engine performance simulator The engine performance simulator used in this research made it possible to predict unsteady phenomena quantitatively that could occur in the cylinders or intake/exhaust pipes of the internal combustion engine, and to investigate the effect of each parameter on engine performance. And this simulator also would be a very effective tool for understanding the characteristics of the difficult problems such as specific fuel consumption vs. NOx trade-off and for studying measures on them. First of all, the conditions of computations in this study are mentioned as follows. (1) The calculation model consisted of some elements shown in the figure 2.1-1. (2) The orifice area of intake and exhaust valve changed during the opening duration and an orifice of fixed area was assumed for turbocharger. (3) The calculation type of the phenomena in the exhaust pipes was the volumetric type and pulsation was not considered. (4) In calculations, fuel injection quantities were adjusted to reach target output (output focused calculation). (5) Ignition timing was adjusted to reach target maximum combustion pressure. (6) NOx concentrations were estimated by using the relations between cycle maximum temperature and measurement data. Since the input data were including some estimation based on the measurement data on other similar engines, measurement data on the single-cylinder test engine and multiple-cylinder engine would be reflected on the input data to improve accuracy of the calculations. Here, the calculation results were used as indexes of the effect of changes in each parameter. The calculation results of the effect of each parameter by this simulator and investigations of them are mentioned as follows. 3

Cylinder cycle calculation Charge air cooler Cubic capacity of unlimited volume Pressure and Temperature constant (Quantities of state unchanged) Exhaust pipe Cubic capacity fixed volume Pressure/ Temperature change After exhaust turbine Cubic capacity of unlimited volume Pressure/ Temperature constant (Quantities of state unchanged) Figure 2.1-1 The model of simulation Charge air orifice Intake valve opened area Exhaust orifice Exhaust valve opened area Exhaust turbine orifice Fixed area (1) Effect of compression ratio and maximum combustion pressure The examples of parametric calculation results with the engine performance simulator are shown in the figure 2.1-2. In this figure, the vertical axis represents the specific fuel consumption and the horizontal axis represents NOx concentration. The effects of maximum combustion pressure and compression ratio, the basic parameters, on engine performance are shown. Through this kind of study, measures or approaches to achieve the targets of the engine performance could be obtained. The figure indicates that an increase in compression ratio is effective for reducing NOx concentration and that a rise in maximum combustion pressure is effective for improving the specific fuel consumption. Specific fuel consumption be (g/kw-h) NOx concentration (ppm 13% O 2 ) Figure 2.1-2 Relation between Engine performance and both compression ratio and maximum combustion pressure 4

(2) Effect of each parameter The results of other parametric studies are listed here and investigation their results will be discussed briefly. The effect of exhaust valve opening timing on engine performance is shown in the figure 2.1-3. The specific fuel consumption got worse drastically advancing the exhaust valve opening timing from the current timing. Conversely, the specific fuel consumption was improved although slightly retarding the exhaust valve opening timing by 132 degrees ATDC (After Top Dead Center). From the fact that no improvement in specific fuel consumption could be expected retarding the exhaust valve opening timing even more, retarding the valve exhaust valve opening timing excessively was found to obstruct the exhaust gas flow and to result in an increasing of the specific fuel consumption. There is almost no effect from exhaust valve opening timing on NOx concentration. The effect of intake valve closed timing on engine performance is shown in the figure 2.1-4. This figure indicates that advancing the intake valve closed timing 30 degrees from the current timing of 606 degrees ATDC to 576 degrees ATDC, an increase in the charged air mass resulted in an increasing of the specific fuel consumption and reducing in NOx concentration. This increasing of specific fuel consumption was due to retarding the ignition timing to keep the maximum combustion pressure constant together with an increasing in charged air. The effect of valve overlap on engine performance is shown in the figure 2.1-5. This figure indicates that the specific fuel consumption decreased gradually together with a shortening of valve overlap. And more, this figure indicates that valve overlap has almost no effect on NOx concentration. Specific fuel consumption be (g/kw-h) Current timing at 112 deg ATDC NOx concentration (ppm 13% O 2 ) Figure 2.1-3 Exhaust valve opening timing EVO (deg ATDC) Effect of exhaust valve opening timing on engine performance 5

Specific fuel consumption be (g/kw-h) Current timing at 606 deg ATDC NOx concentration (ppm 13% O 2 ) Intake valve closed timing IVC (deg ATDC) Figure 2.1-4 Effect of intake valve closed timing on engine performance Specific fuel consumption be (g/kw-h) Current duration at 131 deg NOx concentration (ppm 13% O 2 ) Valve overlap (deg) Figure 2.1-5 Effect of valve overlap on engine performance 6

The effect of the charge air pressure on the engine performance is shown in the figure 2.1-6. This figure indicates that the specific fuel consumption is the best when the charge air pressure is 0.33 MPa, current value. No advantage of specific fuel consumption with increasing the charge air pressure to increase the charge air mass was due to retarding the ignition timing to keep the maximum combustion pressure constant. The NOx concentration decreased drastically with an increase in charge air pressure. This fact resulted in a decrease in the combustion temperature due to the increase in charge air mass together with an increase in charge air pressure. The effect of charge air temperature on engine performance is shown in the figure 2.1-7. The lower the charge air temperature is than the current temperature, the larger the improvements that are obtained in both specific fuel consumption and NOx concentration. These improvements resulted from an increase in intake air mass due to a drop in charge air temperature and from a drop in combustion temperature due to the increase in charge air mass. These results indicate that a drop in charge air temperature is extremely effective to improve engine performance. Specific fuel consumption be (g/kw-h) Current pressure at 0.33 MPa NOx concentration (ppm 13% O 2 ) Charge air pressure Ps (MPa) Figure 2.1-6 Effect of charge air pressure on engine performance 7

Specific fuel consumption be (g/kw-h) Current temperature at 320.5 K NOx concentration (ppm 13% O 2 ) Figure 2.1-7 Charge air temperature Ts (K) Effect of charge air temperature on engine performance (3) The summary of the engine performance simulator The effect on engine performance of each parameter in this study is shown in the table 2.1-1. This table indicates that engine performance varies by each parameter, and it is possible to improve the engine performance overall by combining these various parameters. The results of this study are to be reflected in single-cylinder engine tests and in the design of multiple-cylinder engines. 8

Table 2.1-1 Effects of each parameter on engine performance Effect Parameter Specific fuel consumption NOx Increased maximum combustion pressure ++ -- Increased compression ratio ++ + Optimization of exhaust valve opening timing ++ 0 Optimization of intake valve closed timing + - Shortening valve overlap duration ++ 0 Increased charge air pressure + + Reduced charge air temperature ++ + Increased total efficiency of turbocharger + 0 Shortening of combustion duration ++ - ++: Large effect +: Effect present 0: No effect -: Slight worsening --: Major worsening 2.2 Results of fuel injection pump performance test On adopting a fuel injection system with the aim of high pressure and high injection rate as one approach of realizing high output and high thermal efficiency, its injection pump performance tests were performed with a fuel injection pump unit tester shown in the figure 2.2-1. The major specifications of the fuel injection system are shown in the table 2.2-1. This table could indicate that the fuel oil feed rate (plunger diameter plunger speed) is 2.6 times as large as the average specification of this class. The tests of this injection system were performed on the conditions shown in the table 2.2-2. Nozzle hole specifications were varied at the target injection quantity of 2.3 cc/stroke for the rated output. Injection quantity, pressure at pump outlet and nozzle inlet and needle valve lift was measured in this test. The summaries of test results are shown in the figure 2.2-2. This figure indicates that the targets, maximum injection pressure of 180 MPa and injection duration of 26.5 degrees can be achieved for the injection nozzle with 10 holes of 0.42 mm diameter each. The needle valve lift and injection pressures at this time are shown in the figure 2.2-3. No cavitations or other abnormal injection could be seen as high pressure and high injection rate were realized. In comparison to current conditions, injection pressure increased by 67 MPa and injection duration was shortened by 5 degrees, so that remarkably high pressure and high injection rate are achieved. 9

Figure 2.2-1 Appearance of fuel injection pump unit tester Table 2.2-1 Major specifications of fuel injection system Item Unit New system Current system Comparison (with current system) Pump plunger diameter mm 26 20 1.7 area Stroke mm 28 20 1.4 Maximum cam velocity m/s at 500 rpm cam 2.84 1.87 1.5 Table 2.2-2 Test conditions of fuel injection system Item Unit Value Cam revolution speed rpm 500 Target injection quantity cc/stroke 2.3 Nozzle hole specifications Number of hole hole diameter 10 (0.42, 0.45, 0.48, 0.51) 12 0.38 10

Pressure at Nozzle Inlet (MPa) Current condition Figure 2.2-2 Injection Duration (degcrank) Test results of fuel injection system Needle valve lift (-) Injection pressure at the pump (MPa) Injection pressure at the nozzle (MPa) Crank angle (degree) Figure 2.2-3 Injection pressures and needle valve lift 11

2.3 Test result of single-cylinder engine The figure 2.3-1 shows a system diagram of the single-cylinder engine used in the R&D. The single-cylinder test engine does not have a turbocharger. So charge air compressed by the compressor driven by electric motor is stored in a surge tank and the pressure is controlled at the target charge air. Exhaust gas flows into the surge tank and its pressure and temperature are adjusted by varying the exhaust orifice area so that the ratio of charge air energy to exhaust gas energy would be an intended value. By using these equipment, an engine with exhaust turbocharger would be simulated. The figure 2.3-2 shows total efficiency of turbocharger calculated from the simulated results of engine performance test on the condition of varying the exhaust orifice area. As the total efficiency of turbocharger of the multiple-cylinder engine would be approximately between 0.64 and 0.70, it was found that an actual engine could be simulated well when the exhaust orifice area is 45 cm 2. For the single-cylinder engine, the effects of high pressure and high injection rate in the fuel injection system described above will be confirmed, and performance tests are scheduled to be performed in order to confirm the simulation results of an engine performance simulator. These engine test results will undergo reverse analysis by simulator; the orientation for low fuel consumption will be determined and advances will be made in design for efficiency. Meanwhile, engine main components, strength and reliability are scheduled to be confirmed. Concurrently with performance tests, for example, liner temperature measurements, and cylinder head firing surface temperature will be measured. Figure 2.3-1 System diagram of single-cylinder engine 12

Exhaust gas pressure (MPa) Total efficiency of turbocharger = adiabatic compression work of compressor theoretical work of turbine Exhaust gas temperature at cylinder head outlet (K) Total efficiency of turbocharger (-) Charge air pressure (MPa) Charge air pressure (MPa) Figure 2.3-2 Test results of single-cylinder engine 2.4 Design and production of prototype multiple-cylinder engine In 1999, in parallel with the empirical research mentioned above, a multiple-cylinder engine was designed and produced as a base of proceeding with this research. After the design concept of the multiple-cylinder engine shown in the figure 2.4-1 was studied and the specifications for each key component were clarified, these measures to achieve the intended performance were reflected in the design. Especially in order to endure high output and maximum combustion pressure, calculation the strength of engine main components was made by FEM (refer to the figure 2.4-2). VG turbocharger Cylinder liner with anti-polish ring Special coating piston ring Large diameter camshaft High rigidity cylinder head Composite piston (steel + ductile) High-pressure fuel injector - Fuel and water stratified injection - Injection rate control High unit pressure resistant bearing Large diameter crankshaft Figure 2.4-1 Design concept of multiple-cylinder engine 13

Figure 2.4-2 Examples of result of strength calculation by FEM 3. Results of Empirical Research (1) Studying using engine performance simulator Calculation and was performed to investigate the effect of compression ratio, maximum combustion pressure, valve timing, charge air conditions and other parameters on engine performance by using engine performance simulator. It was found to be clear that it was effective for reducing specific fuel consumption to increase maximum combustion pressure, to increase compression ratio, to retard exhaust valve opening timing, to shorten valve overlap, to reduce charge air temperature, to shorten combustion duration and to retard intake valve closing timing, to increase charge air pressure and to increase total efficiency of turbocharger. And it was found to be clear that it was effective for reducing NOx concentration to increase compression ratio, to increase charge air pressure and to reduce charge air. Furthermore, it was found to be clear that it was effective for improving the trade-off between specific fuel consumption and NOx to increase compression ratio, to reduce charge air temperature and to increase charge air pressure. All these investigations contributed to definite the quantitative setting value of measure and the level of effect of them, and could be reflected in decision the condition of single-cylinder engine test and reflected in design of the multiple-cylinder engine. (2) Fuel injection pump performance test A fuel injection system aimed at high pressure and high injection rate was designed and produced, and fuel injection pump single-unit performance tests were performed. As a result, it was found that the target maximum injection pressure of 180 MPa and injection duration of 26.5 degrees could be achieved and high pressure and high injection rate could be realized with 10 holes of 0.42 mm diameter each under the condition of increasing oil feed rate (larger plunger diameter, increased plunger speed). Maximum injection pressure was increased by 67 MPa and injection duration was shortened by 5 degrees for the current fuel injection system and the problem of cavitations and other trouble that can often occur at high pressure and high injection rate could be resolved at the same time. 14

(3) Single-cylinder engine test Using an existing single cylinder engine, combustion performance tests were performed to evaluate the effect on engine performance of intake and exhaust conditions, compression ratio and fuel injection nozzle specifications (high pressure and high injection rate). As a result, setting up the conditions of charge air (gas pressure and temperature) and exhaust (gas pressure and temperature: adjusting total efficiency of turbocharger by selecting exhaust orifice area) were performed in order to simulate the engine with exhaust turbocharger selected (multiple-cylinder engine) using single-cylinder engine and resulted in good simulation of an actual engine. (4) Design and production of multiple-cylinder prototype engine A multiple-cylinder test engine was designed and produced as a base to proceed with this research. First of all, the design concept of the multiple-cylinder prototype engine was studied and defined. The specifications required for each key component to endure the high output and high maximum combustion pressure were defined through studies of strength calculations by FEM (finite element method). The results obtained could be reflected in the design of a multiple-cylinder prototype engine and be produced. 4. Summaries 4.1 Empirical Research in 1999 In order to achieve the targets of high thermal efficiency and low NOx emission in the diesel engines of 3000 kw class for electric power station, calculations and investigations by using an engine performance simulator, fuel injection pump performance test, and single-cylinder engine tests were performed. And a multiple-cylinder prototype engine was designed and produced. The conclusions were listed as follows. (1) As a result of calculations and investigations with an engine performance simulator, the guide for high thermal efficiency and low NOx were obtained by such measures as increase of compression ratio, optimization of charge air/exhaust valve opening/closing timings, reduction of charge air temperature and increase of charge air pressure. (2) As a result of design, production, and unit performance tests of fuel injection system aimed at high pressure and high injection rate, the target maximum injection pressure of 180 MPa and injection duration of 26.5 degrees could be achieved and high pressure and high injection rate could be realized. (3) For an existing single-cylinder engine, intake and exhaust conditions were set up and an actual engine with exhaust turbocharger (multiple-cylinder engine) could be simulated well, which contributes for efficient testing of combustion performance after this. (4) Giving definition to designing concept of the multiple-cylinder test engine, calculation and studying of the strength of each key component and the results obtained in (1) above were reflected in the design of a multiple-cylinder engine, which was a base for this R&D. 15

4.2 Future Issues It is important to confirm the effects on performance by using single-cylinder engine of measures for high thermal efficiency and low NOx obtained through engine performance calculations and to improve the accuracy of the calculation by adopting the test results into input data of engine performance calculation. In this study, input data contained some estimation from measurement data on engines currently available, but after this, it will be possible to make more accurate input data based on measurement by single-cylinder test engine. The fuel injection system of high pressure and high injection rate, obtained in the present study, will be assembled on a single-cylinder engine and its effects will be examined. In addition, tests of multiple-cylinder engine will be prepared and performed. Copyright 2000 Petroleum Energy Center all rights reserved. 16