Abstract
Mobile source emissions have already accounted for a large proportion of environmental pollution, which seriously affect the symmetric characteristics of atmosphere, and automobile emissions have extremely serious deterioration of emissions under transient operation, especially particulate emissions. These factors exacerbate the asymmetry of the environment. So, the paper reports an experiment about the improvement of post injection strategy on combustion, regulated emissions (HC, CO, and NOx), and particle number emissions especially the emissions of different size particles in the transient process of an EGR diesel engine, meanwhile, the effects of post injection on the combustion of mixture are further analyzed by numerical simulation method. The test speed was 1600 r/min, and the torque increased from 5% of the maximum torque to 100%. The results indicated that the shorter the instantaneous loading time, the more severe the deterioration of particulate emissions, HC and CO emissions, but loading time has little effect on NOx emissions. The particles with the size range of 50–100 nm, 23–50 nm, and >100 nm are greatly affected by the loading process and post injection. In comparison, it has little effect on ultrafine particles with particle size of 15–23 nm and <15 nm. With the amount of post injection increased, the in-cylinder disturbance increased, and the oxygen-rich area in cylinder increased, the particle number concentration first decreased and then slightly increased. When the amount of post injection fuel is 2 mg and the main-post injection interval is 2000 us, the effects of suppressing particulate emissions are the best, for the 50–100 nm and >100 nm particles, the peak number concentration can be reduced by 25% and 50%, respectively. Due to the turbo charging lag, the peak of NOx emissions during the unloading process were slightly larger than the loading process.
Highlights
IntroductionWith the rapid development of the automotive industry, the energy consumption, symmetric characteristics and harmful emissions issues have become the focus of the world’s attention [1].Vehicle driving usually run under transient operating conditions of diesel engines, and with the mandatory requirements of emissions regulations for engine transient test cycles, the combustion and emissions problems of diesel engine transient process have become the research hotspot and focus of internal combustion engine scholars [2,3,4,5].Symmetry 2020, 12, 2002; doi:10.3390/sym12122002 www.mdpi.com/journal/symmetryIn steady-state conditions, a diesel engine’s air–fuel equivalent ratio, fuel injection pressure, exhaust temperature, thermal state in cylinder, coolant temperature, and exhaust pressure are all operated within the ideal calibration value range, and the engine performance can be better guaranteed.in a transient operating condition, since the oil supply of the engine and gas parameters are changing at any time, the parameters such as the air–fuel equivalent ratio and thermal state in the cylinder do not reached a steady state, so the combustion and emissions performances are quite different compared to steady-state operating conditions [6,7]
We verify the cylinder pressure measured value obtained from the test with the calculated value of the model, the results were shown in Figure 3, and the results showed that the model we established can accurately predict the combustion of the engine
Whether it is the total number concentration, the concentration of particles in the nucleation mode (5–35 nm) or accumulation mode (35–100 nm), there is a sharp increase trend during the loading process, the particles mostly exist in the form of accumulation mode
Summary
With the rapid development of the automotive industry, the energy consumption, symmetric characteristics and harmful emissions issues have become the focus of the world’s attention [1].Vehicle driving usually run under transient operating conditions of diesel engines, and with the mandatory requirements of emissions regulations for engine transient test cycles, the combustion and emissions problems of diesel engine transient process have become the research hotspot and focus of internal combustion engine scholars [2,3,4,5].Symmetry 2020, 12, 2002; doi:10.3390/sym12122002 www.mdpi.com/journal/symmetryIn steady-state conditions, a diesel engine’s air–fuel equivalent ratio, fuel injection pressure, exhaust temperature, thermal state in cylinder, coolant temperature, and exhaust pressure are all operated within the ideal calibration value range, and the engine performance can be better guaranteed.in a transient operating condition, since the oil supply of the engine and gas parameters are changing at any time, the parameters such as the air–fuel equivalent ratio and thermal state in the cylinder do not reached a steady state, so the combustion and emissions performances are quite different compared to steady-state operating conditions [6,7]. In steady-state conditions, a diesel engine’s air–fuel equivalent ratio, fuel injection pressure, exhaust temperature, thermal state in cylinder, coolant temperature, and exhaust pressure are all operated within the ideal calibration value range, and the engine performance can be better guaranteed. The main reason for this “difference” is that in the transient process, the response speed of the parameters such as fuel supply, air supply, and thermal atmosphere in the cylinder are inconsistent, which leads to the imbalance of the combustion boundary conditions of the transient operating conditions, resulting in the deterioration of combustion and emissions performance [8,9,10]. To solve the problem of diesel engine performance deterioration during transient process, the literatures [11,12,13,14] found that it can increase the response speed of intake air supply in transient process and improve the transient performance by reasonably matching the supercharger, two-stage supercharging, variable-geometry turbocharger and electric supercharging air supplement system
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