Diesel-injection equipment parts deterioration after prolonged use of biodiesel

The application of biodiesel blends is known to significantly affect operation of diesel-injection equipment, especially the injectors and fuel pump. This paper summarizes experience on this subject from burning fuel blends with high-percentages of biodiesel (up to 70%) on a common-rail, high-pressure-injection diesel engine and a conventional DI engine. Both engines were unable to start after running for 100 h each and staying shut off for more than two months. In order to understand the wear characteristics of the injector nozzle, pump pistons, and elastomer parts (in the case of the high-pressure pump of the common-rail engine), due to the prolonged operation with high-percentage biodiesel blends, their injectors and pumps parts were examined and compared by performing normal photography and low magnification microscopy. Additionally, the various elastomer parts of the high-pressure fuel pump of the common-rail engine were examined for wear and deterioration. The results are compared with existing literature results from other researchers. The observed deterioration of diesel-injection equipment is caused by use of high-percentage biodiesel blends and subsequent engine shut down. © 2019 by the authors

Experimental investigation of the effect of biodiesel blends on a DI diesel engine's injection and combustion

Differences in the evolution of combustion in a single cylinder, DI (direct injection) diesel engine fuelled by B20 were observed upon processing of the respective indicator diagrams. Aiming to further investigate the effects of biodiesel on the engine injection and combustion process, the injection characteristics of B0, B20, B40, B60, B80 and B100 were measured at low injection pressure and visualized at low and standard injection pressures. The fuel atomization characteristics were investigated in terms of mean droplet velocity, Sauter mean diameter, droplet velocity and diameter distributions by using a spray visualization system and Laser Doppler Velocimetry. The jet break-up characteristics are mainly influenced by the Weber number, which is lower for biodiesel, mainly due to its higher surface tension. Thus, Sauter mean diameter (SMD) of sprays with biodiesel blended-fuel is higher. Volume mean diameter (VMD) and arithmetic mean diameter (AMD) values also increase with blending ratio. Kinematic viscosity and surface tension become higher as the biodiesel blending ratio increases. The SMD, VMD and AMD of diesel and biodiesel blended fuels decreased with an increase in the axial distance from spray tip. Comparison of estimated fuel burning rates for 60,000 droplets' samples points to a decrease in mean fuel burning rate for B20 and higher blends. © 2017 by the authors

Thermodynamic modeling and comparative analysis of supercritical carbon dioxide Brayton cycle

Supercritical CO2 cycles is a promising technology for the next generation power conversion cycles. Supercritical CO2 Brayton cycles offer equivalent or higher cycle efficiency when compared with steam cycles at similar temperatures. This paper presents an investigation of the sCO2 recompression cycle, where recompressing a fraction of the flow without heat rejection, results in an increase in thermal efficiency. A thermodynamic analysis of a 600 MWth power cycle has been carried out, in order to study the effect of the most significant design parameters on the components performance and cycle efficiency, using two different simulation tools to model the recompression system. An iterative model using basic thermodynamic equations describing the system's components was employed in this direction. The system was also modeled by means of commercial process modeling software for comparison. Hence, useful results regarding the operating pressures and temperatures of the cycle and how they affect the recuperators, the compressor and the turbine performance have been derived. Finally, a comparative analysis of the results of the two simulation tools and those of a reference cycle from the bibliography is carried out, showing deviations in the range of 2.8 to 4%. Copyright © 2017 ASME

Recuperators investigation for high temperature supercritical carbon dioxide power generation cycles

Supercritical carbon dioxide (s-CO2) Brayton cycles are a promising technology for the next generation power conversion cycles, attaining equivalent or higher cycle efficiency compared to conventional power cycles at similar temperatures (550–750 °C). The recompression cycle attracts the main research interest among the s-CO2 layouts. Recompressing a fraction of the flow without heat rejection, results to an increase in thermal efficiency, while the majority of heat transfer occurs in recuperators. In this study, a thermodynamic analysis of a 600 MWth power cycle has been carried out using two different simulation tools to model the recompression system. The analysis focuses on the parameters that have the most significant impact on the components and cycle efficiency. A segmental analysis of the recuperators took place to assess the effect of flow characteristics on the heat transfer. Finally, a comparative analysis of the results of the two simulation tools versus the results of a reference cycle from literature is carried out, showing that the prediction of the overall heat transfer coefficient and recuperator effectiveness between the developed code and reference model has a maximum deviation of 4%, whereas the prediction deviation between the commercial software and reference model is about 2.8%. © 2017 Elsevier Lt