Design of the control circuit used in variable speed diesel generator set
The advanced circuit design of boost and inverter has created much interest in generator of variable speed diesel generating sets. The boost circuit and the topological structure of the three-phase half-bridge inverter were analyzed. The control strategy of Sinusoidal PWM (SPWM) was implemented. To reduce the noise in the control feedback, a low pass filter was in used. At the end of this paper, the authors performed a series of experiments to confirm the stability of the generator set. The experiment results verified that the boost circuit and the inverter designed in this paper are reasonable and can satisfy all the requirements of the diesel generator set.
Effects of piston bowl geometry on combustion and emission characteristics of biodiesel fueled diesel engines
This paper presents the numerical study of the effects of piston bowl geometry on combustion and emission characteristics of a diesel engine fueled with biodiesel under medium load condition. Three different bowl geometries namely: Hemispherical Combustion Chamber (HCC), Shallow depth Combustion Chamber (SCC), and the baseline Omega Combustion Chamber (OCC) were created with the same compression ratio of 18.5. To simulate the combustion process, computational fluid dynamics (CFD) modeling based on KIVA-4 code was performed. Moreover, CHEMKIN II code was integrated into the KIVA-4 code as the chemistry solver to incorporate detailed chemical kinetics mechanisms consisting of 69 species and 204 reactions for the biodiesel combustion, thereby improving the accuracy of the simulation. It is found that the narrow entrance of combustion chamber could generate a strong squish, especially at high engine speed, hence enhancing the mixing of air and fuel. Also, the simulation results indicate that in terms of performance SCC is favorable at low engine speed; whereas at high engine speed, OCC is preferred. As a consequence, SCC will generate relatively higher NO compared to other two piston bowl designs at low engine speed condition. Similarly, the high performance of OCC bowl geometry could result in a high NO emission at high engine speed condition.
Development of a Small-Scale Generator Set Model for Local Network Voltage and Frequency Stability Analysis
The integration of numerous small-scale generators into existing local networks (e.g., a microgrid) is anticipated to impact their operation, control, and protection. In particular, maintaining voltage and frequency stability within the defined limits is more onerous and requires investigation. The effect of protective limiters and characteristics such as the genuine inertia of the generation set must be taken into consideration in stability studies in order to accurately represent the overall dynamic characteristics of local distributed generators. This paper focuses on three fundamental aspects: 1) the development of a reciprocating engine/generator set model; 2) the laboratory testing of an experimental test rig; and 3) the influence of a volts-per-hertz ratio (volts-per-hertz ratio) limiter on the generator dynamic response. The experimental procedures used to determine the genuine inertia of the test rig are described and the system responses under different scenarios are used to validate the developed model. This emphasizes the significance of excitation protective limiters such as volts-per-hertz ratio, during the stability analysis.