Experiments were performed to clarify the ignition characteristics of dimethyl ether (DME) injected by a D.I. diesel injector into a high-pressure, high-temperature vessel. Ambient air pressure, temperature, oxygen concentration and nozzle valve opening pressure were changed as experimental parameters. The results clarify the differences between the DME and a conventional diesel fuel in the ignition characteristics such as flame luminosity characteristics and ignition delay. A non-luminous flame is observed in the ignition process of the DME spray. In the case of ordinary air (oxygen concentration 21%), the ignition delay for the DME spray is almost the same as the diesel fuel spray under a high ambient pressure, whereas under a low ambient pressure, the ignition delay for the DME spray is shorter than the diesel fuel spray. In the case of low oxygen concentration, the ignition delay for the DME spray is shorter than the diesel fuel spray under high ambient pressure as well as low ambient pressure. The effect of the nozzle valve opening pressure on the ignition delay is very small for the DME spray, whereas the ignition delay for the diesel fuel spray is increased with decrease in the valve opening pressure.
In order to study nitrogen release from different nitrogen functionality, two types of model coals with different nitrogen structures have been prepared using cellulose and phenolic nitrogen compounds, 2-hydroxycarbazole and 6-hydroxyquinoline. Carbon and nitrogen structures in the model coals have been analyzed by solid-state 13CNMR, pyrolysis GC-NPD and GC-MS. The 13C-NMR spectra of the model coals very closely resemble those of natural coals with similar carbon content, and the pyrolysis GCNPD analyses show that the model coals have the same nitrogen-containing skeleton as the original nitrogen compounds. Addition of Ca and Fe catalysts on the model coals has also been carried out to make clear the effects of the Ca and Fe on nitrogen release from the model coals. Nitrogen release during pyrolysis of the model coals without and with catalyst has been studied in a fixed-bed reactor at 50°C/min up to 1, 000°C. The pyrolysis results show that thermal decomposition behavior of pyrrolic and pyridinic nitrogen in the model coals is similar, and both calcium and iron catalysts are effective on nitrogen removal from the model coals prepared at 200°C. However, the efficiency of nitrogen removal by the catalysts depends on the preparation temperature of the model coals.