Fig. 9 Effectiveness of Gas-Extraction Valve in Restraining The Hunting of The Working Plant
It can be seen that the gas-extraction valve began to open wider almost simultaneously with the decline in engine output, followed by orderly, corresponding decline in turbocharger speed commensurate with the change in engine output, and that the hunting in the scavenging and exhaust circuits so far observed following the end of decline in engine output was completely restrained.
Thus, the effectiveness of the gas-extraction method in restraining the hunting in the scavenging and exhaust circuits of the diesel generating plant in the process of reducing the engine output was successfully confirmed both theoretically by numerical simulation and experimentally by full-scale trial use in the working plant. It was also confirmed in the latter process that the SCR system could remove more than 95% of NOx emission per hour to an extremely low level of about 70 ppm, comparative to the emission from the gas-turbine plant.
The gas-extraction method devised by the authors has since been refined into a diesel generating plant transient dynamics control system complete with the gas-extraction valve and associated exhaust-gas ducting as well as with the control software and hardware. For the diesel generating plant with the SCR system large in heat capacity between the engine exhaust outlet and turbocharger gas inlet and thus susceptible to the hunting in the scavenging and exhaust circuits due to disruption in plant heat cycle especially when reducing the engine output, the newly devised transient dynamics control system ensures highly stabilized plant operation essentially by regulating the flow of exhaust-gas energy into the turbocharger alone and helps reduce the plant NOx emissions.
3. Conclusions
(1) The mechanism triggering the hunting to the detriment of dynamic characteristics of the two-stroke-cycle dynamo engine generating plant equipped with SCR system to reduce NOx emissions was explored by measurement as well as by numerical simulation.
(2) Using a numerical plant dynamics simulator devised, a method of controlling the flow of exhaust-gas energy into the engine turbocharger with a gas-extraction valve was worked out to restrain the hunting in the scavenging and exhaust circuits for stabilized plant operation unaffected by load change.
(3) The gas-extraction method devised in the working plant, in which a feedback control system was incorporated together with the gas-extraction valve installed before the turbocharger to detect the turbocharger speed and control the gas-extraction valve open/close operations accordingly. The test in the working plant showed that the hunting in the scavenging and exhaust circuits in the process of reducing the engine output could completely be restrained for stabilized plant operation even under the load change.
(4) Also, the plant NOx emissions were controlled to an extremely low level of about 70 ppm, witnessing to the high level of practical usefulness of gas-extraction system of plant transient dynamics control.
References
1) H. Ishida, Y. Tosa “Development of Engine Cycle Analysis for Various Kid of Fuel and Working Gas” JSME #69 Conference 1992
2) H. Ishida, Y. Tosa “A Performance Study on a Multi-cylinder Engine by a Pulsating Flow Simulator” JSME #73 Conference 1995
