DOC/SCR对聚甲氧基二甲醚/甲醇双燃料发动机NOx排放的影响

为了控制双燃料发动机的NO_x排放，采用电控共轨柴油机在缸内直喷聚甲氧基二甲醚(PODE)引燃甲醇预混气，实现双燃料燃烧模式。采用傅里叶变换红外光谱多组分测量技术，研究了柴油机氧化催化转化器(DOC)和选择性催化还原(SCR)催化转化器对PODE/甲醇双燃料发动机燃烧NO_x排放的影响规律。结果表明：随着甲醇比例的增加，低负荷时的缸内最高温度降低，高负荷时的缸内高温持续时间缩短，并且甲醇的加入使得发动机排气温度降低，最终导致双燃料燃烧生成的NO_x量降低，而m(NO₂)/m(NO_x)却显著提高。经过DOC催化后，PODE/甲醇双燃料和纯PODE压燃2种模式下的NO_x排放量均有所增加，PODE/甲醇双燃料模式的NO₂与NO_x的质量比(m(NO₂)/m(NO_x))明显降低，而纯PODE压燃模式的m(NO₂)/m(NO_x)升高。PODE/甲醇双燃料和纯PODE压燃2种模式下，当NH₃与NO_x的摩尔比(n(NH₃)/n(NO_x))为1.2时，SCR催化转化器对NO_x的转化效率达到最高(57.3%)，进一步增加尿素喷射量会导致NH₃排放量明显提高。

Effects of DOC/SCR on NOx Emission of Polyoxymethylene Dimethyl Ethers/Methanol Dual-Fuel Engine

To control the NO_x emission from the dual-fuel engine, polyoxymethylene dimethyl ethers (PODE)/methanol dual fuel combustion was conducted on an electronic control common-rail engine, where the premixed methanol was ignited by PODE that injected directly into the cylinder. The effects of diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) catalystic converter on the NO_x emission from PODE/methanol combustion were studied by using the Fourier transform infrared (FTIR) spectroscopy multi-component measurement technology. Results show that, with the increase of methanol ratio, the in cylinder maximum temperature under low load decreases, the in cylinder high temperature duration under high load shortens, and the addition of methanol reduces the exhaust temperature, eventually leads to the decrease of NO_x generated by dual-fuel combustion, and the increase of the m(NO₂)/m(NO_x). After the purification of DOC, the NO_x emission of dual-fuel and pure PODE increases, m(NO₂)/m(NO_x) of dual-fuel decreases, while the NO_x emission of pure PODE shows an opposite trend. When the n(NH₃)/n(NO_x) is 1.2, the conversion efficiency of the SCR to NO_x is the highest, and the catalytic efficiency of NO_x reaches 57.3%. However, further increasing the amount of urea injection will lead to a significant increase in NH₃ emission.