Abstract
Exhaust gas recirculation (EGR) can improve the fuel economy of gasoline direct-injection (GDI) engines, but at the same time it will have a significant impact on emissions. In this paper, the effects of low-pressure exhaust gas recirculation (LP-EGR) and its rate on the main gaseous and particulate emission characteristic of a GDI engine were investigated. The results showed that the particle size distribution of the GDI engine presented bimodal peaks in nucleation and accumulation mode, and the nucleation mode particles comprised the vast majority of the total particles. The effect of LP-EGR on emissions depended on the engine conditions. At low and medium speed, the particle emissions increased with the increase in the EGR rate, while at high speed, a reduction in the particle emission was observed. When the engine operated in full load condition, an increase in the EGR rate reduced the particle number (PN) concentration significantly, but increased the particle mass (PM) concentration. In terms of the gaseous emission, the EGR could reduce as much as 80% of the NOx emission; however, the total hydrocarbons (THC) emission presented an increased trend, and the maximum increase reached 23.5%. At low and medium loads, the EGR could reduce the CO emission, but at high load, the CO emission worsened with the EGR.
Highlights
Compared with traditional port fuel injection (PFI) gasoline engines, gasoline direct-injection (GDI) engines directly inject fuel into the combustion chamber of each cylinder to achieve higher fuel economy performance and a higher compression ratio; they can reduce the tendency to knock and improve the transient response [1]
The results show that, under a 1000 r/min full load condition, compared with the engine without Exhaust gas recirculation (EGR), the indicated mean effective pressure (IMEP) of the engine at 5% EGR rate increased by about 2%
The results show that EGR can effectively reduce the pressure rise rate and suppress knocking; it plays a role in improving fuel economy and NOx emissions
Summary
Compared with traditional port fuel injection (PFI) gasoline engines, GDI engines directly inject fuel into the combustion chamber of each cylinder to achieve higher fuel economy performance and a higher compression ratio; they can reduce the tendency to knock and improve the transient response [1]. In order to further improve GDI engine particle and gaseous matter emissions, in this study, we used a four-cylinder, 1.5 L GDI engine to assess the influence of LP-EGR rate on the particle size, number concentration, and mass concentration of nucleation/accumulation mode particles and gaseous emissions under different working conditions. At 4000 r/min, the peak concentration of accumulation mode particle decreases with the increase in EGR rate.
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