Experimental And Simulation Of Partially Premixed Combustion Of Diesel And N-butanol/diesel Blends

The particulate matter in the engine exhaust is harmful to the environment and human health,so the new emission regulations have strict requirements on the total number and mass of particulate matter emissions.Partially premixed combustion(PPC)mode has lower particulate matter and NOx emissions than the conventional combustion mode,and PPC mode has better combustion controllability than HCCI combustion mode because of charge stratification.As a renewable energy,butanol has the characteristics of low cetane number,high volatility and high oxygen content,and is effective alternative fuel for partially premixed combustion of diesel engines.However,the current understanding of the particle-size distribution,morphology,oxidation activity and nanostructure of soot particles in the PPC mode,the effect of blending high proportion of butanol on combustion and particulate matter emission characteristics in the PPC mode,and the synergistic effect of oxygenated fuel and late injection strategy on emission characteristics of soot particles in the PPC mode is still unclear.Focusing on these issues,based on a turbocharged,high-pressure common rail diesel engine the effects of injection strategy and fuel physicochemical parameters on particulate matter emission characteristic,nano-morphology and micro-structure of particulate matter in the PPC mode were studied in this paper.1.The effects of injection strategy on the in-cylinder combustion process and particulate matter emission characteristics,morphological characteristics and nanostructure of PPC mode were studied,and the results show that the total number and mass concentration of particulate matter are very high in the conventional combustion mode.Most of the particulates are accumulation mode particulates.In the early-injection PPC mode,the mass concentration of particulate matter decreases greatly.Increasing injection pressure can reduce the concentration of accumulation mode particulates and increase the concentration of nucleation mode particulates.In the split-injection strategy,the accumulation mode particulates are dominant.Reasonable adjustment of pilot-injection timing and fuel ratio can reduce the total number and mass concentration of particulate matter at the same time.The nanostructure of particles generated in the early-injection PPC mode is complex,the boundary between amorphous carbon core and layered shell of particulate matter is not clear,and the mean primary particle diameter,fractal dimension and fringe length of particles are significantly reduced.In the split-injection PPC strategy,more Long chain-like particles appear,and the number of small aggregates decreases compared with the single-injection strategy.The mean primary particle diameter and fringe length decreased at the early pilot injection timing.2.The emission characteristics and morphological structure of particulate matter in engine exhaust in the PPC mode with high proportion butanol were studied,and the results show that in the single-injection strategy,with the increase of butanol blending ratio,the peak value of accumulation mode particulates decreased,and the peak value of nucleation mode particulates increased sharply,which indicates that blending butanol makes the engine exhaust particulate matter smaller.In the split-injection strategy,with the increase of butanol blending ratio,the total number and total mass concentration of particulate matter decrease significantly.Particulate microcrystalline fringes are more distorted and structural defects are more obvious,and the mean primary particle diameter,fractal dimension and fringe length are all decreased with the increase of butanol blending ratio,which indicates that the addition of butanol changes the carbonization process of the particles,making them more reactive.3.The synergistic effects of high proportion butanol-diesel blends on engine combustion and particulate matter emissions in the post-injection strategy were studied,and the results show that when pure diesel is used,the total number concentration of particulate matter decreases with the post-injection timing,and the total number is lower than the baseline when the post-injection timing is later than 15°CA ATDC.When B50 blends are used,compared with the baseline,the post-injection strategy can reduce the number concentration of particulate matter to a small extent.When three types of fuel are used,with the increase of post-injection fuel,the mean primary particle diameter and fractal dimension decrease with the increase of post-injection fuel,and the fringe length does not change significantly.Compared with the post-injection strategy,the physical and chemical characteristics of fuel have a greater impact on the micro-nanostructure of particulate matter.4.Based on the KIVA-3V source code coupled with CHEMKIN,evolution process in cylinder under the early-injection and late-injection partially premixed combustion are simulated using a detailed chemical reaction mechanism,and the whole simulation process is calibrated by engine experimental data.The results show that the changing process of the core components in PPC is much different from those in conventional combustion mode.Ketohydroperoxide plays a major role in the first stage ignition of PPC,and NOx is largely observed in the downstream of the spray where OH was formed while soot is formed in the fuel-rich mixture near the combustion chamber wall.