重型车低负荷运行特征及NOx排放特性

利用远程监控数据分析了北京国六重型柴油城市用车在低负荷运行特征和排放特征,并选取了一台满足国六排放标准的6L柴油机,结合发动机在环方法在发动机台架上开展了国六法规循环(WHTC)和加州低负荷循环(LLC)的排放试验,对比分析了低负荷循环下的氮氧化物(NO_x)排放特性。结果表明:国六城市柴油车的低负荷运行时间长,并且低负荷运行阶段NO_x排放占比高。加州构建的LLC循环能够能反映长时间运行在低负荷以及长时间怠速造成排温降低导致NO_x转化效率降低的实际情况。LLC循环下的NO_x排放很高,主要原因是由于排温较低所致。中国也应该根据商用车实际行驶特征,开发低负荷工况来控制低负荷条件下的NO_x排放。但由于车辆载荷对NO_x转化效率和NO_x排放有较大影响,因此开发低负荷工况时,需要考虑载荷设置。

Low load running characteristics and NOx emission under low load for heavy-duty diesel vehicles

The operation and emission performances of a heavy-duty diesel urban vehicle which meets the China VI emission standard have been investigated based on remote monitoring data. Furthermore, a 6L diesel engine which also meets the China VI emission standard has been adopted to carry out the World Harmonized Transient-State Cycle (WHTC) and California Low Load Cycle (LLC) emission tests on an engine test bench using the engine-in-the-loop methodology. The NO_x emission characteristics under the low-load conditions have been studied. Results suggest that the heavy-duty diesel urban vehicle tends to run under the low-load conditions, accompanied with a large portion of NO_x emitted. The LLC test reveals the fact that the engine spends more time running under the low-load condition, which leads to a low emission temperature as well as low NO_x conversion efficiency. The high NO_x emission under the LLC test is mainly caused by the low exhaust temperature. China is suggested to develop low-load cycle to control the NO_x emissions under such conditions according to the actual driving characteristics of commercial vehicles. The loading setting should be taken into consideration when developing the low-load cycle given the fact that the NO_x conversion and emission are significantly affected by the vehicle loading.