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4. Task4 Development of Power Generation Technology 4.1 Targets for Research and Development Considering the development of a hydrogen combustion diesel engine (600kW scale system) having about 45% thermal efficiency at terminal and 85% total thermal efficiency, the following targets shall be achieved in the second stage of this project. (1) Development of a single-cylinder hydrogen combustion diesel engine rated 100kW for co-generation system. This engine having about 45% efficiency at terminal and more than 85% total efficiency(higher heating value basis), if converted into 600kW scale system, shall be free of any emission of environmental pollution. (2) Development and continuous test operation shall be performed and problems shall be picked up to realize the engine as practical use. To achieve the above mentioned targets, the development of element technologies, basic tests, and the investigation of the single-cylinder experimental engine system, shall be conducted in fiscal 1999. 4.2 Result of Investigation and Development in Fiscal 1999 4.2.1 Development of Element Technologies 4.2.1.1 Development of Hydrogen Injection Facilities (1) Study of Hydrogen Injection Valve To develop the hydrogen injection facilities for a 100kW scale argon circulated type single-cylinder hydrogen diesel experimental engine, the gas velocity at fuel injection nozzle, hydrogen jet reaching distance in the combustion chamber, and air excess ratio in the injection stream were calculated and the specifications for hydrogen injection nozzle were investigated. As the result, it was found out that when the number of injection nozzles is the same as in the conventional diesel engine, using a three times larger diameter of the conventional diesel engine injection nozzle, nearly the same hydrogen reaching distance and excess oxygen ratio in hydrogen jets could be maintained. (2) Investigation of Hydrogen Injection Control Method As a pre-examination to develop hydrogen injection devices for the single-cylinder test machine, the improvement of small amount gas injection metering characteristics was investigated and experimentally evaluated. By decreasing the volume of the oil piping between the electric solenoid valve and the actuating piston chamber of the electronic control type hydraulic hydrogen injection device developed for the rapid compression/expansion equipment, it was confirmed that up to about 1/3 of the specified injection rate could be controlled. 4.2.1.2 Development of Exhaust Gas Condenser and Gas-Liquid Separator The basic design of argon oxygen exhaust gas condenser which will be used at the 100kW scale argon circulated type single-cylinder hydrogen diesel engine was carried out, and the gas-liquid separator was selected. Concerning the exhaust gas condenser, three types including a shell and tube type, a spiral plate type, and a plate type were compared and evaluated to obtain the most compact size. As the result, it was made clear that the required heat transfer area increases in the order of the plate type, the shell and tube type and the spiral plate type, and the pressure drop decreases in the same order. Concerning the outside dimension, there are no remarkable differences, but the dimensions of the plate type were relatively compact. The outside dimension of horizontal mist separator using corrugated plates was 450mm(W)~570mm(H)~700mm(D). 4.2.1.3 Development of Turbocharger and Expansion Turbine The specifications for the turbocharger and the expansion turbine which are expected to have high performance at a 600kW scale argon circulated type hydrogen diesel system were studied. As the result, it was confirmed that about 15.8kW electric power could be recovered at present, which suggests the possibility of realization target value of 19.9kW. Additionally, in order to realize a more efficient system, the prototypes of compressor impellers and diffusers, turbine rotating blades and nozzles, in which measures to improve efficiency are included, were planned and by flow pattern analyses, good results were obtained. 4.2.2 Element Test 4.2.2.1 Hydrogen Conbustion Test (1) Self Ignition Combustion Test <1>Procedure Using a 1/4 model (that covers the range of 90-degree angle viewing from the cylinder center) of the combustion chamber and fuel injection valve of a 100kW scale single-cylinder test machine, hydrogen burning tests using a rapid compression/expansion equipment were performed. By measuring the pressure in the cylinder and also piston stroke, the amount of the indicated work was calculated and the indicated thermal efficiency was evaluated. Furthermore, from the change of pressure and chamber volume, the approximate receiving rate of heat was calculated and evaluated. <2>Influence by intake air and combustion chamber temperature When the temperatures of intake air and a combustion chamber are 100℃, the indicated efficiency was higher than that at 45℃. However efficiency went down at 150℃. It is considered when the temperatures of intake air and the combustion chamber went up, heat loss went down including the influence of prevention of the steam condensation. On the other hand, it is also considered that by the increase of viscosity of the working gas, the mixing rate of fuel slowed down and the degree of constant volume went down. <3>Influence by the proportion of argon in working gas When the proportion of argon in working gas increased to higher than 79%, the indicated thermal efficiency went down. It is considered that when the proportion increased due to the increase of the ratio of specific heat, the compression pressure went up, while due to the much more increase of the heat loss, the indicated thermal efficiency went down. <4>Influence by diameter of fuel injection nozzle and injection timing Indicated efficiency became higher when the diameter of injection nozzle is 0.5mm (injection timing about 45℃) than that when the diameter is 0.75mm (injection timing is about 20 ℃). Under the specified diameter of injection nozzle, at earlier injection timing, the indicated thermal efficiency had a tendency to go down. It is inferred that in case of the larger injection diameter and earlier injection timing, a large ratio of the heat generated during the early stage of combustion, when the piston did not move, became heat loss. <5>Estimate of net thermal efficiency As a result of basic combustion tests using a rapid compression/expansion equipment at the rated injection volume, the indicated thermal efficiency was about 52% (lower heating value basis). Based on the above result and hydrogen diesel simulation, net thermal efficiency was estimated at about 44%. By the trial calculation of a hydrogen diesel co-generation system, which was performed in fiscal 1997, the engine net efficiency was about 50%, then the above result of estimation was about 6 percent point low. Since compared to the combustion chamber of 100kW scale engine, the rate of surface area to volume of the rapid compression/expansion equipment combustion chamber was larger and its temperature was lower, so the above low efficiency is considered on a reasonable level. (2)Combustion Control Test by Laser Ignition A possibility of realizing the combustion mode in which laser is irradiated during the ignition delay period and the amount of premixed combustion is reduced, and also the condition of secure ignition when using air as working gas, were investigated. The shape of the combustion chamber is the same as that in the self ignition tests, and a laser target was equipped on the piston in one of the direction of two injection nozzles. However, in the laser ignited combustion tests, it was made clear that in case of the high combustion chamber temperature and high compression ratio near to the actual machine, the delay of ignition is shortened, and there is no effect by laser irradiation. It was confirmed that when air was used as working gas, the fuel was not self-ignited at all the tested conditions, but by the laser irradiation, the fuel surely ignited. 4.2.2.2 Lubrication Test of Piston Ring and Cylinder Liner To evaluate the suitability of lubrication oil as the oil for the hydrogen diesel engine, analysis and investigation on the available lubrication oil on the market were performed. Furthermore, reciprocating slide tests were applied on the typical lubrication oil (gas engine oil and marine engine oil) and seizing characteristics under high temperature were investigated. However since the every oil was new, there were no seizing phenomenon and it was confirmed that there is the possibility for the oils on the market can be utilized as far as the oil is new. 4.2.2.3 Simulation of the Cylinder Inside Phenomena of the Hydrogen Diesel Engine (1) (1) Numerical Analysis Model of the combustion chamber for rapid compression/expansion equipment was built up, and simulation tests were carried out in the 20MPa hydrogen injection pressure under non-combustion conditions. Conclusion of this simulation test was recognized to be almost equal to the laboratory test, when the hydrogen combustion analysis was carried out in the element reaction model under non-combustion condition. As the results, following knowledge were obtained: - Compared the result of inside cylinder pressure analysis with the result of the laboratory test, these data were quantitatively not conformed, but qualitatively the phenomena such as two pressure peak, rapid pressure rise after ignition, slow pressure increase after rapid pressure increase etc. those appears often in the hydrogen combustion test, are observed. - From the results of model analysis, it was confirmed that immediately after hydrogen injection, outside the hydrogen stream, OH radicals were generated and due to the sudden generation of OH, combustion were started, and that self ignition occurred at the upper stream of the hydrogen flow. (2) Element Test It was known that there are self radiation before the increase of pressure in cylinder , using the shadow graph photographing of hydrogen jet stream (non burning and burning state) and measuring of OH radical concentration as the data during the burning progress in the rapid compression/expansion equipment. These test result data were used for the above numerical analysis, and comparing the result of analysis with the actual test results, validity of the gas stream analysis model and combustion analysis model were examined. 4.2.3 Development of Single-cylinder Test Machine 4.2.3.1 Basic plan of the test facilities (1) Basic Plan of Fuel and Working Gas Supply Facilities. Basic specifications of each equipment used in the closed-cycle test system forcusing the argon circulating single-cylinder hydrogen diesel test engine and the laboratory arrangement where the equipments will be installed, are investigated. As the result, it was made clear that the fuel and working gas supply equipment can be some sets of cylindrical vessels which are always installed and replaced 1 or 2 times a week. (2) (2) Basic Plan of Gas Circulating Line It was decided in fiscal 2000 that a hydrogen compressor was to be selected from an electric motor driven type or a booster method type driven by compressed air. The Gas circulation line shall be closed system, and argon and oxygen shall be completely recovered and reused considering their high costs. Since the work needed for the compression of fuel gas is comparatively large, compression of fuel gas shall be performed mostly by utilizing an exhaust turbocharger. (3) Layout Plan of Building for Laboratory and Equipments Since high pressure gas production facilities being installed, in the view of safety, a basic plan of the laboratory was investigated. As the result, it was made clear that a hydrogen diesel single-cylinder system comprising main and auxiliary equipments can be located and installed in the room having about 150m2 area. 4.2.3.2 Design and Investigation of Single-cylinder Test Engine The combustion chamber temperatures of an argon circulation hydrogen diesel engine were estimated by the calculation of the gas temperatures in the cylinders of conventional and argon circulation hydrogen diesel engines and the measurement of the conventional engine combustion chamber. As the result, the temperature at the cylinder head of the argon circulation hydrogen diesel engine is about 34℃ higher than that of the conventional diesel engine. 4.3 Schedule in Future and Problems 4.3.1 Development of Element Technology (1) Development of Hydrogen Injection Equipment As for the hydrogen injection device for 100kW class argon circulated type single- cylinder hydrogen diesel experimental engine, an electronic type hydraulic control system of injection device of the same type developed for the rapid compression/expansion equipment, and other types of control system shall be investigated comparatively. The facility will be designed and manufactured in fiscal 2000, and test operation will be performed after fiscal 2001. (2) Development of Exhaust Gas Condenser and Gas-liquid Separator. As the exhaust gas condenser for 100kW class argon circulated type single-cylinder hydrogen diesel test engine, 3 types of condensers were investigated this year. From among the 3 types, one type shall be selected, and the model of that type shall be designed and manufactured considering the cost in fiscal 2000. The gas-liquid separator of the result of the investigation this year shall be purchased in fiscal 2000 or later. (3) Development of Turbocharger and Expansion Turbine Based on the specifications which were investigated this year, the turbocharger for a 600kW scale system shall be mechanically designed in fiscal 2000. Regarding the expansion turbine, the specifications of an electric generator shall be made clear, and a prototype machine shall be planned and analyzed in fiscal 2000. 4.3.2 Fundamental Test (1) Self Ignition Combustion Test As the result of the basic combustion tests using a rapid compression/expansion equipment, it was suggested that heat loss had a great influence on the indicated thermal efficiency. Heat loss shall be directly measured by using the rapid compression/expansion equipment in fiscal 2000. (2) Combustion Control Test Using Laser Igniter In the single-cylinder engine, in case of using argon/oxygen as working gas, practice of the self-ignition shall be confirmed. And in order to decrease the cost of the laser equipment, possibility of reducing ignition energy shall be researched. (3) Lubrication Test of Piston Ring and Cylinder Liner At the commercial machine, since short supply of lubricating oil and/or supply of degraded oil is anticipated, evaluation under more severe conditions shall be performed. (4) Analysis of Phenomenon in the Cylinder of Hydrogen Diesel Engine. By the improvement of the burning model etc., an accurate burning analysis which contributes the analysis of hydrogen engine performance shall be carried out. 4.3.3 Development of Single-cylinder Test Machine System (1) Test Facilities Based on the basic plan, the detailed design for the argon circulated type single-cylinder hydrogen combustion diesel engine shall be performed in fiscal 2000. (2) Single-cylinder Test Engine Including the countermeasure of melted zirconium powder spraying etc. detailed design of the combustion chamber shall be performed in fiscal 2000.
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