N2O is known to have a significantly high global warming potential. We measured N2O emissions in engine-bench tests by changing the NO/NH3 ratio and exhaust gas temperature at the oxidation catalyst inlet in a heavy-duty diesel engine equipped with a urea SCR (selective catalytic reduction) system. The results showed that the peak N 2O production ratio occurred at an exhaust gas temperature of around 200°C and the maximum value was 84%. Moreover, the N2O production ratio increased with increasing NO/NH3. Thus, we concluded that N2O is produced via the NO branching reaction. Based on our results, two methods were proposed to decrease N2O formation. At low temperatures ∼200°C, NO should be reduced by controlling diesel combustion to lower the contribution of NO to N2O production. This is essential because the SCR system cannot reduce NOx at low temperatures. At temperatures higher than 200°C, it is necessary to reduce NH3 slip because N2O is produced via reactions involving NO generated by NH3 oxidation and NH3 slip. To investigate methods to reduce NH3 slip from the SCR catalyst, we conducted chemical kinetics simulations using Boost v5.1 by AVL. The main parameters governing NH 3 slip were the urea equivalence ratio (UER) and SCR catalyst volume. It is recommended that NH3 emitted from the tailpipe should be lower than 10 ppm. We identified the optimal UER and volume ratio (defined as SCR catalyst volume to engine displacement ratio) at different temperatures to ensure that catalyst outlet NH3 emissions were less than 10 ppm. At 200°C, the results showed that decreasing the UER was sufficient to reduce NH3 slip. At 400°C, we also considered a 90% NOx reduction efficiency. We demonstrated that an increase in the volume ratio was required to sufficiently reduce NH3 slip at high temperatures.
|ホスト出版物のタイトル||SAE Technical Papers|
|出版ステータス||Published - 2012|
|イベント||SAE 2012 International Powertrains, Fuels and Lubricants Meeting, FFL 2012 - Malmo|
継続期間: 2012 9月 18 → 2012 9月 20
|Other||SAE 2012 International Powertrains, Fuels and Lubricants Meeting, FFL 2012|
|Period||12/9/18 → 12/9/20|
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