Investigation of the effects of EGR rate, injection strategy and nozzle specification on engine performances and emissions of a single cylinder heavy duty diesel engine using the two color method

초록

This study focused on the effects of EGR rate, injection pressure, injection timing, and nozzle hole diameter on the nitrogen oxidize and particulate matter in a diesel engine. The optical engine equipped with the endoscope system were used and two color method theory were applied to calculate the flame temperature and PM density from the combustion images. Parametric experiments were performed by changing the EGR rate, injection pressure, and injection timing using a reference nozzle. According to the combustion images analysis, the flame temperature was greatly reduced by increasing EGR rate. Moreover, the EGR rate significantly affects the PM oxidation rate. As a result, the higher EGR rate, the higher PM density were observed. The NOx and PM emissions showed same trend with the results of flame temperature and PM density respectively. Unlike the EGR rate, the injection pressure affected the fuel atomization. Decreasing injection pressure diminished the PM oxidation. The high PM emissions and low NOx emissions were observed with low injection pressure. Retarding injection timing decreased both the flame temperature and PM density because of long ignition delay and low cylinder pressure. As the lack of time for the PM oxidation, retarding injection timing increased the PM emissions which showed trade-off relationship with the NOx emissions. Nozzle hole diameters were compared for various experimental conditions. Regardless of experimental conditions, the smaller nozzle hole diameter that had superior fuel atomization showed the high flame temperature and low PM density. The NOx and PM emissions showed same trend with the optical results.

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