Abstract
Exhaust thermal management is essential to allow engines to meet the Euro VI emissions standards and reducing nitrogen oxide emissions is one of the most important targets being pursued nowadays. Along these lines, in the present study, engine’s thermal performances have been evaluated on the basis of a WHTC test, namely a transient engine dynamometer schedule defined by the global technical regulation (GTR) developed by the UN ECE GRPE group (the GTR is covering a world-wide harmonized heavy-duty certification (WHDC) procedure for engine exhaust emissions). The influence of thermal management on fuel consumption, intake, and tailpipe NOx have been quantitatively analyzed for the overrun state. The results have shown that there can be a strong influence on the after-treatment temperatures and tailpipe NOx. In particular, the average temperature upstream of the diesel oxidation catalyst (DOC) has been found to increase from 245°C to 254°C, the average temperature of the selective catalytic reduction (SCR) to increase from 248°C to 253°C, the SCR’s minimum temperature to increase from 196°C to 204°C, and the peak value of the NOx emissions in the low-temperature region to decrease from 73 to 51 mg/s. However, the influence of the overrun state’s thermal management strategy on the fuel consumption, the air intake, the ammonia storage, the NO2/NOx ratio, and the urea consumption has been observed to be relatively limited.
Highlights
Strict nitrogen oxide (NOx) emissions from heavy-duty diesel engines require clean combustion in the cylinder and an efficient after-treatment system [1]
The diesel oxidation catalyst (DOC)’s average temperature increased from 245°C to 254°C, the selective catalytic reduction (SCR)’s average temperature increased from 248°C to 253°C, and the nitrogen oxide emissions were reduced by 24% when thermal management strategies were adopted
The total amount of air intake decreased by 3.2%
Summary
Strict nitrogen oxide (NOx) emissions from heavy-duty diesel engines require clean combustion in the cylinder and an efficient after-treatment system [1]. The world harmonized transient cycle (WHTC) is a transient test cycle with 1,800 operating points It includes a cold-start WHTC and a hot-start WHTC, and a test cycle runs for a total of 1,800 s. Euro VI emissions regulations require the WHTC tail exhaust NOx, including the after-treatment aging coefficient (with a value of 1.15), to be less than 0.46 g/kW ⋅ h. Engineering margin coefficients, such as the product consistency, are generally set to 1.1; the NOx emissions should not exceed 0.36 g/kW ⋅ h. The hotstart WHTC attempts to control the NOx emissions so they are as low as possible
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