Experimental study on the particulate matter emission characteristics for a direct-injection gasoline engine

Abstract

In this work, a detailed study on the number of exhaust particles, the particle size distribution and the geometric mean diameter from a 1.5 l gasoline direct-injection engine running with different engine operating parameters was conducted. The air-to-fuel ratio, the spark timing, the injection timing and the exhaust gas recirculation rate were varied at the same engine speed and the same engine load in order to understand how the mixture condition before ignition and the oxygen concentration affect the particulate matter emissions in terms of the total number and the size distribution. The experimental results showed that a lean mixture can significantly reduce the total number of particles by up to 90% compared with the rich mixture condition. When a lean mixture was used, most of the particulate matter was in the nucleation mode. The higher air-to-fuel ratio may have enhanced the oxidation of particles in the combustion process. Delaying the spark timing can also reduce the particulate matter emissions, especially for nucleation-mode particles which decreased by up to 65.41% compared with those for the early-spark-timing condition. The lower in-cylinder temperature may have resulted in the formation of a reduced number of nucleation-mode particles. The injection timing affected both the mixing process and the heat release process and could be optimized to reduce the particulate matter emissions. For a brake mean effective pressure of 3 bar, advanced injection timing reduced the numbers of particles in both the nucleation mode and the accumulation mode. The longer mixing duration improved the mixture homogeneity and led to lower formation rates of particles. Increasing the exhaust gas recirculation rate was effective in reducing the accumulation-mode particle emissions, while increasing the nucleation-mode particle emissions.

Assessment of air management strategies on particulate number and size distributions from a 2-stroke compression-ignition engine operating with gasoline Partially Premixed Combustion concept

“…This trend may be linked to a considerable favoring of surface growth and coagulation rate provided by the significant increase in particle precursors (nuclei particles), which are formed when the partially premixed flame propagates through these locally fuel-rich zones. Additionally, in the A2000 and B2000 operation modes, it is clearly observed how the increase of the accumulation-mode particles decreases the nucleation-mode particles concentration, confirming that the soot particles increase their size through the absorption of volatile condensates, similar results were obtained in the works of Pei et al 63 and Singh et al 64 As in some operation points of the ΔP variation, in the operating points 66.4 CA and 67.4 CA in A2000 and B2000 operation mode, respectively there were high nucleation-mode particles concentrations and additionally was observed high HC emissions values (3.52 g/kWi for 66.4 CA in the A2000 operation mode and 2.87 g/kWi for 63.4 CA in the B2000 operation mode). This trend confirms the hypothesis that the particles formation is closely related to unburned hydrocarbons.…”

Part-load particulate matter from a GDI engine and the connection with combustion characteristics

“…The experimental results suggest that, as the engine speed is increased at 529 light-to-mid load, the influence of worsened mixing, which would normally lead to greater average 530 size [41], is mitigated by that of higher oxidation, as a result of higher exhaust gas temperature. In 531 agreement with Pei et al [33], advanced ignition timing and greater combustion temperature bear 532 no visible influence on the average size of the engine-out soot in this region. The net result of such 533 multi-faceted phenomena is that in region 3 the GMD remains approximately constant.…”

“…Remarkably, a strong resemblance is found between the distribution of GMD and that 507 of unburned gas temperature, (Tu) max (see figure 8). As suggested by Pei et al [33], greater 508 combustion temperature (of which (Tu) max gives an indication) would favour the formation of 509 particles in the accumulation mode. The inherent stratification of fuel at low speed and mid-to-high 510 load leads to greater particle inception, while simultaneously the high combustion temperature 511 enhances coagulation and/or agglomeration [41].…”

“…Pei et al [33], in their recent GDI engine investigation, emphasise the reliance of PM emissions on 177 engine operating parameters, at part-load conditions. Owing to the inherent incomplete gas-phase 178 mixing, the measured soot number density increases with decreasing Air Fuel Ratio (AFR), 179…”

A literature research about particle emissions from engines with direct gasoline injection and the potential to reduce these emissions

“…Therefore, gaining insight from each engine type is particularly relevant for reducing particles in DI gasoline engines. According to Hedge et al [76] and Pei et al [77], exhaust gas recirculation (EGR) leads to a reduction in particles, although according to Hedge et al [76], more volatile particles are produced in EGR, but these can be reduced by a three-way catalytic converter.…”