Y.K. Kim

Investigation of the Optimal Injection Conditions for a PCCI Diesel Engine

Premixed charge compression ignition (PCCI) engines have the potential with their attractive advanced combustion process to achieve a more homogeneous mixture and a lower peak combustion temperature resulting in both lower nitrogen oxides (NOx) and diesel particulate matter (PM) emissions. In this study, the spray characteristics for a PCCI engine according to various injection conditions were introduced and then the effects of injection strategies such as injection angles, injection timings and times on combustion and emissions were studied for a single cylinder PCCI engine using early multiple injections first. Add more, a method of early-main type split injection was used for a 4-cylinder PCCI engine and the effects of injection conditions on the combustion and emission characteristics were investigated. Finally flame visualization tests were performed to validate the result obtained from the engine test.The experimental results showed that the mixture formation, indicated mean effective pressure (IMEP), and emission characteristics were dominantly affected by the injection conditions and the multiple injection method resulted in higher IMEP and still low smoke level characteristics. It appeared that more homogeneous mixture could be formed with decreasing of spray penetration and increasing of fuel evaporation rate for the early multiple injections. In case of the split injection, both injection timing and injected fuel ratio of the early and main injection largely affected engine combustion and emission characteristics. From the results, as the early injection rate increased premixed combustion was activated, on the other hand, as the main injection rate increased conventional diesel combustion was activated, therefore suitable split injection conditions could be selected for the 4-cylinder PCCI engine.Copyright

Development of InSb cryogenic detector for ultra high-resolution energy spectroscopy

High-resolution X-ray spectroscopy is required in research and application areas such as neutrino mass measurement, X-ray astronomy, semiconductor device technology and material analysis. The conventional detectors such as Si or Ge do not have enough energy resolution to meet the requirements from the various fields. Compound semiconductor with small band gap can be possible candidate detector to get the ultra-high resolution. InSb Schottky diode is being developed as the radiation detector because of their low band gap energy. The dependency of detector performance on electrode size, etching method, and operating temperature was studied. The polished wafers were cut into with size of 10times10 mm2, and the wafer surfaces were cleaned and etched. Gold electrode was deposited on one side of the etched wafer and In was deposited on the opposite side of the wafer. The I-V curve of each diode was measured and the results were compared to optimize the fabrication process of InSb Schottky detector.

Thermal annealing of metal-semiconductor contact for CZT detectors

CZT can be used for high-resolution X-ray and gamma-ray spectroscopy at room temperature. Previously the thermal annealing process has been studied to decrease the leakage current of the detector and obtain a stable detector performance. Because of its low work function, indium can be used as the metal contact for a CZT Schottky detector. The low temperature annealing effect on the In/CZT contact was studied in our work. A CZT Schottky detector with indium/CZT/gold structure was fabricated. The leakage current and the energy resolution of each detector were measured. The detector was annealed for 10 hours in vacuum, and for 2, 4, 8 hours in air. The leakage current and the energy resolution of the detector were measured after the annealing process and they were compared with the data before the annealing. It was found that the detector performance of the CZT Schottky detector was enhanced with the low temperature annealing process in air.