Effects Of Carbon Chain Length And Hydroxyl Position On Chemical Properties Of RCCI Exhaust Particles

Particulate matter poses a severe threat to the atmospheric environment and human health,so it is imperative to study particulate matter’s formation mechanism and control technology.Scholars build solutions on fuel design and combustion patterns.Among many biomass fuels,alcohol fuels have made a significant contribution to energy saving and emission reduction to ensure good power performance.In addition,the change in the molecular structure of alcohol fuels,such as the increase of carbon chain length or the internal displacement of hydroxyl position,will significantly impact combustion.Reactivity Controlled Compression Ignition（RCCI）has attracted much attention as a combustion mode with controllable combustion,clean emission,high efficiency and stability,among many new combustion modes.The research shows that the combination of alcohol fuels and RCCI combustion mode has a bright future in practical application,which provides the possibility for further reducing particulate matters.Therefore,this study is based on a modified six-cylinder heavy diesel engine,which controls the total cycle energy and rotational speed at 4000J and 1500rpm,the injection timing（start of injection,SOI）of-10°CA ATDC,and the guaranteed premixing ratio（premix ratio,Rp）of30%,40%and 50%,respectively.Five kinds of alcohol fuels with molecular structure changes were selected:ethanol,n-propanol,iso-propanol,n-butanol and sec-butanol were injected at the port as low reactivity fuels,respectively,and diesel was injected directly into the cylinder as high reactivity fuel to realize RCCI combustion.The effects of carbon chain length and hydroxyl position on the chemical properties of RCCI exhaust particles were studied.The main contents and conclusions of this paper are as follows:（1）With the increase of two kinds of carbon chain length(CCL and CCL_OHP),the change rule of C element content is entirely opposite,and the O element content almost does not change as a whole;the change of C element content under different Rp conditions is slightly different with the internal displacement of OHP,and O element content shows three different change rules under three kinds of Rp,that is,increasing,unchanged and decreasing.With the increase of Rp,the contents of C and O in most alcohol fuels particles increased.In addition,under any three conditions,the changes of Si and other trace elements are complex and irregular.There are no trace elements in n-propanol RCCI particles under three kinds of Rp,but no trace elements are produced only in CCL and CCL_OHPunder Rp=40%.（2）X-ray photoelectron spectroscopy（XPS）is used to characterize and analyze RCCI exhaust particulates.According to XPS full-spectrum scanning,the surface elements of ethanol/diesel RCCI particles are mainly oxygen,carbon and silicon,and the molar ratio of oxygen to carbon（ηo/ηc）was 1.31.In addition,XPS full spectrum analysis showed that the percentages of sp hybrid carbon,sp³/sp² hybrid carbon ratio,C-OH functional group,and carbonyl functional group were 26.17%,87%,13.08%and 6.34%,respectively.The carbon-oxygen functional group（C-O in ether/alcohol）is dominant on the surface of particles,and the hydroxyl（C-OH）functional group and carbonyl（C=O）functional group contribute less to the carbon-oxygen functional group on the surface of particles.（3）The correlation and regression analysis of the chemical composition of RCCI particles showed that CCL_OHP was related to all elements and was more sensitive to C elements.Only the C element is related to OHP and CCL,and only the O element is associated with Rp.The real influence factors of different element components are obtained,and the sensitivity sequence is as follows:C element is CCL>CCL_OHP>OHP,O element is CCL_OHP>Rp,Si element is only CCL_OHP.