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In this paper, the engine-in-the-loop (EIL) methodology was used to study real driving emissions of a heavy-duty vehicle on an engine test bed. The virtual vehicle was combined with the actual engine to establish an EIL test platform. The result of the vehicle speed followability shows that the difference between the EIL simulated vehicle speed and the actual vehicle speed is within ±2 km/h, indicating that the vehicle cycle can be well reproduced on the engine test bed by EIL method. The EIL method shows high coincidence of engine operating points. Compared with real driving, the CO2, NOx and PN of EIL is 3.6%, 72.3% and 40% lower for this vehicle, respectively. Analysis shows that equipment difference is the key influencing factor for PN test accuracy of EIL, while the control of exhaust temperature and intercooler temperature play important roles in NOx test accuracy of EIL.

A 6.2 L diesel engine that meets China VI emission standard was selected to run world harmonized transient cycle (WHTC) and California Low Load Cycle (LLC) to measure the pollutants. The brake specific emission under the two cycles were compared, and nitrogen oxides (NOx) emission were analyzed carefully. The results show that the NOx emission of the LLC of this engine is about 15 times than that of the hot WHTC, and 4.7 times than that of the limitation of current China VI emission standard. The low inlet temperature of selective catalytic reduction (SCR) is the predominant reason for the high NOx emission in the LLC. The SCR inlet temperature of lower than 200°C in LLC accounts for 52% of the total time with an average inlet temperature of only 190°C. While the inlet temperature of lower than 200°C of the hot WHTC only accounts for 7% with the average inlet temperature of 275°C. The average SCR catalytic efficiency calculated by NOx sensor amounted on the upstream and downstream of LLC is only 75%, while the efficiency is 98% for hot WHTC. It is necessary to focus on thermal management of the aftertreatment system and the SCR catalytic performance at low temperature.

Real driving emissions of a heavy-duty vehicle with a maximum total mass of 18000 kg were investigated by the engine-in-the-loop (EIL) methodology. Virtual vehicle model, driver model and real road model was established, then to combined with the actual engine and emission test equipment to fulfill the vehicle emission evaluation on engine test bed. The results indicate the road driving can be well reproduced on engine laboratory with good vehicle speed followability, engine speed and torque consistence. However, the emission results show a larger difference with a 3.6 gap for CO2, a 72.3% gap for NOx and a 40% gap for PN., respectively. Analysis shows that the intercooler temperature, the exhaust temperature and equipment difference has a combined effect on the emission accuracy.

Pollutants and carbon dioxide (CO2) under different vehicle loading were investigated on a dump truck with a maximum designed total mass of 18000 kg. An engine-in-the-loop (EIL) methodology was applied to achieve the test consistency because EIL can use the same road, driver and vehicle model. The results show that the total CO2 emission increases while the brake specific CO2 emission decrease as the vehicle loading increases. Both the total and specific emissions of PN increase when vehicle loading increases. The effect regularity of increasing vehicle loading on NOx, THC and CO is not significant. It is necessary to comprehensively consider the changes in the raw exhaust due to the engine operation points changes and in the SCR catalytic efficiency derived from the SCR inlet temperature variation. The DPF generation is also need to be concerned because the CO2, PN and NOx emissions will rapidly increase during this period.