| Summary: | Increasing exhaust gas temperature (EGT) and providing hydrocarbon (HC) reactants by in-cylinder post injection are effective measures to assist diesel engine exhaust aftertreatment operation for efficient pollution control. The aim of this study is to explore calibration guidance of post injection for base engine performance and aftertreatment requirements. Therefore, the effect of start of post injection (SOPI) timing on engine performance and emissions, especially the relationship between the variations of the EGT and HC emissions caused by different post injection timings were experimentally studied with a 2.0 L high-pressure common-rail diesel engine at different loads. The results showed that the maximum torque contribution was produced by post injection at the earliest SOPI timing at all load levels. When the post injection timing was retarded, the engine brake torque decreased gradually, and more energy of the post injected fuel raised the EGT. The EGT decreased and the HC emissions increased significantly as the SOPI timing was further retarded. At the 20%, 50%, and 80% loads, the maximum EGTs were 357.7, 465.4, and 615.8 °C, increased by 11.6%, 8.6%, and 7%, respectively. The maximum HC emissions were 4932, 3929, and 2746 ppm, increased by 12.44, 1.8, and 5.18 times, respectively. Moreover, a tradeoff relationship between the EGT and the HC emissions was observed at different SOPI timings by a normalized analysis. However, no clear tradeoff relationship between the soot and the NOxemissions was found in the SOPI timing sweep. Consequently, the appropriate SOPI timing range should be determined based on the needs of the aftertreatment system, and multiple post injections may be required to simultaneously increase the EGT and provide the HC reactants for aftertreatment. The optimal SOPI timing also needs to be selected based on impacts on soot and NOxat different loads.
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