The single valve system consists of the main valve made of heat-resistant Nimonic, which is located at the cylinder center, and the sub valve made of stainless steel, which is placed coaxially against the main valve. The sub valve turns the channels, air intake or exhaust, which are arranged in the cylinder cover made of cast steel.
Both air and exhaust gas passages are optimized through 3-D CFD analysis and the aerodynamic testing using a wooden model. The swirl intensity is adjustable by replacing the swirler to optimize the engine performance depending on the engine specification.
Both main and sub valves are opened by hydraulic oil pressure, which is fed through the high pressure pipes from the hydraulic pumps driven by the cams, and closed by common spring air pressure. The system oil is used as the hydraulic oil. The hydraulic system is well-designed through the unsteady oil flow calculation coupled with the reduction in weight of moving parts as keeping the strength. Fig. 7 shows the valve lifts and the hydraulic oil pressure measured on the prototype. This system ensures the stable and quiet operation. In addition, a reduced number of parts makes the maintenance job easy in combination with the unnecessity of regular oiling. The overhaul inspection of 6ADD60V for the 3.1MW power plant made after 8,000 operating hours showed that every component had been working in good order. It should be noted that both valve seats are kept clean owing to the cleaning effect of intaken air.
Fig. 7 Measured Valve Lift and Hydraulic Oil Pressure of Main and Sub Valves
3.6 Fuel Injection System
The side injection system, in which two fuel valves are placed on the cylinder periphery, is applied to the single valve gas exchanging system instead of the conventional center injection system.
The fuel injection pressure is raised up to 200MPa in order to achieve the good combustion under the high B.M.E.P, by improving the air-fuel mixture. All the high pressure passages are extrude-honed so that they withstand the high pressure by rounding sharp edges and corners. Each fuel injection pump of Bosch type is provided with the compact damper of an air spring type to allow for the stable injection. The plunger, the speed of which is increased up to 4m/s to minimize the size, is coated with TiN for seizure-proof.
The durability of the high-pressure fuel injection system is well-proven through the endurance test on the motor-driven test stand as well as the prototype under the max. pressure of 200MPa.
The high injection pressure does not always yield the high thermal efficiency since the increased power for pressurizing compensates the gain in combustion. Consequently, the practical injection pressure is reduced to 160MPa by reducing the plunger speed to 3.4m/s.
4. Test Results
Since there was no precedent for the single valve gas exchanging system coupled with the side injection system, many kinds of fundamental analyses and experiments were made in order to evaluate the effects of various parameters on thermal efficiency and exhaust emission. Thereafter, the performance tests were carried out with the prototype 6ADD30V as well as the single cylinder engine by changing the geometry of combustion chamber, the geometry of atomizer holes, the swirl intensity etc..
