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.
Optimization of the piston geometry of a diesel engine using a two-spray-angle nozzle
The objective of this research was to optimize a light-duty diesel engine in order to minimize the soot, nitrogen oxide (NO x ), carbon monoxide (CO), and unburned hydrocarbon emissions, and the peak pressure rise rate while minimizing the gross indicated specific fuel consumption (GISFC) in a low-oxygen low-temperature environment. The variables considered were the injection timings, the fractional amount of fuel per injection, the swirl, and the piston geometry. The KIVA-CHEMKIN code (a multi-dimensional computational fluid dynamics program with detailed chemistry) was used and was coupled to a multi-objective genetic algorithm, together with an automated grid generator. A unique two-spray-angle nozzle (2SAN) was explored. This nozzle allows both the lower and the upper portions of the bowl to be targeted simultaneously. With the 2SAN, stepped-bowl piston, and split-injection strategy, the NO x and soot emissions and the GISFC were further reduced in comparison with well-performing cases that used a single-hole nozzle (SHN) with two injections. The soot and NO x emissions were reduced by 67 per cent and 63 per cent respectively while the fuel consumption was improved by nearly 4 per cent. The second-injection timing was also varied with the selected case and compared with the well-performing SHN cases. This showed that the GISFC did not depend on the second-SOI timing as much as in the SHN cases. This leads to greater flexibility as to when the second SOI can occur. The 2SAN case performed particularly well with a highly diluted intake charge with an early second injection. Soot was further reduced while maintaining the GISFC. The last part of the study explored the benefits of the 2SAN at midload conditions (10.5 bar) at both 2000 r/min and 4000 r/min. The 2SAN reduced CO emissions by 20 per cent and 50 per cent for the low-speed and high-speed cases respectively. This research shows the importance of the bowl geometry, spray targeting, injection timing, split fuel amounts, and swirl on the emissions and fuel efficiency in direct-injection diesel engines.