抄録
The chemical gas-phase reduction process used to reduce nitric oxide (NO) in diesel engine exhaust is applied to a high-speed, light-duty diesel engine. The chemical gas-phase reduction process involves adding a methylamine (CH_3NH_2) in water solution to the exhaust gas as a NO reduction agent. In our previous experiments, the NO reduction process was examined by passing a fraction of the diesel exhaust through a heated quartz flow reactor. The results revealed that the sufficient mixing of methylamine with diesel exhaust effectively breaks down NO into nitrogen and water. It was also found that particulate matter such as soot was found to inhibit the NO reduction. When the particulate matter was filtered from the exhaust, 80% NOx removal was achieved at a reactor temperature of 420 ℃ and a residence time of about 0.14 seconds with a molar ratio CH_3NH_2/NO (φM) of 1. In this study, an experimental selective non-catalytic NO reduction system designed to be used with a diesel engine is used to evaluate this technique for practical use. Experiments were conducted using a single-cylinder, four-cycle, water-cooled, direct-injection, 857 cm^3 of stroke volume, naturally- aspirated diesel engine at an engine speed of 1800 rpm and a brake mean effective pressure of 0.63 MPa. The NO concentration at the inlet of the mixing chamber was 1250 ppm. The same molar amount of methylamine as NO in the exhaust was added to a mixing chamber. Two different mixing chambers with different volumes and residence times (0.1 s and 0.17 s) were tested. The temperature at the inlet of the mixing chamber (T_<inlet>) was approximately 420 ℃. Figure 2 shows the NOx reduction ratio (R_<NOx>) of methylamine processes with and without the installation of a particulate filter. In this figure, the results of the flow reactor experiment from the previous study are shown for comparison. Longer residence times were required to achieve a given level of NOx reduction in unfiltered exhaust, suggesting that the presence of particulate matter inhibits NO reduction. For the standard residence times, the process achieved 64% NO reduction in unfiltered diesel exhaust, increasing to 80% NO reduction when a particle filter is fitted to the system.
