Influence Of Ash And Lubricating Oil On DPF Regeneration By Non-thermal Plasma Technology

The ash deposited in the diesel particulate filter（DPF）will cause the capture efficiency and regeneration efficiency of DPF to decrease,and increase the additional fuel consumption of the diesel engine.When the situation is serious,it is necessary to replace the DPF to restore the performance of the diesel engine.Therefore,it is important to study the ash deposited inside the DPF.In this paper,non-thermal plasma（NTP）technology is used to treat the particulate matter（PM）produced by diesel engines and DPF deposited by PM.The oxidation properties of PM by NTP and the influence of ash on the performance of DPF were investigated,and a detailed study was made on the variable of lubricating oil.The main researches are as follows:（1）Taking the ash under different load conditions as the research object,test benches for DPF capture and regeneration were built.Taking the trapping differential pressure,trapping efficiency,regeneration time and regeneration temperature as the test indexes,the influence of ash under different load conditions on DPF capture and regeneration process was explored.The test revealed that the load of diesel engine will affect the morphology and characteristics of ash.As the load increases,ash changes from powder to strips.In addition,the differential pressure and efficiency in the capture process of DPF are significantly improved by the ash.The initial differential pressure of DPF is increased,and the trapping pressure gradually increases with the increase of trapping time.The trapping differential pressure of DPF₇₅ is the largest,reaching 15.59 k Pa.For the capture efficiency of DPF,the capture efficiency of DPF has increased significantly due to the presence of ash.The ash of 25%loading has a high capture efficiency for the small PM,while the ash of 50%loading has a higher capture efficiency for the large PM.Considering the regeneration temperature,it is found that the ash does not affect the law of the regeneration temperature.The ash of 25%loading resulted in the increase of the reaction rate of NTP and PM,and the regeneration time was shortened to 119.5 min in DPF₂₅.The regeneration time of DPF₅₀ and DPF₇₅ increases,indicating that the ash of 50%loading and 75%loading will reduce the oxidation efficiency inside the DPF.（2）The composition and oxidation characteristics of PM are affected by aged lubricating oil.Thermo-gravimetric analyzer（TGA）is used to analyze the changes in PM oxidation characteristics by NTP technology,and fourier transform infrared spectrometer（FTIR）and gas chromatograph-mass spectrometer（GC-MS）to analyze the type of functional groups and SOF composition by NTP technology.Studies have found that the aged lubricating oil leads to an increase in the proportion of volatile fraction（VF）in PM and a decrease of elemental carbon（EC）.In the experiment,the VF component preferentially undergoes oxidation reaction with NTP substances.The oxidation activity of EC component in PM decreases with the aged lubricating oil,but increases with NTP.However,for different index temperatures,the effects of lubricating oil and NTP are different.Regarding the ignition temperature and final combustion temperature,when aged lubricating oil and NTP technology are used at the same time,the ignition temperature and final combustion temperature of EC components show a rising trend,indicating that aged lubricating oil has a greater impact on the oxidation activity of EC components.For the temperature of maximum weight loss rate,the effect of NTP is more significant when the two factors work together,and the temperature of the EC component reduces.After NTP oxidation,the C=C in the PM sample is broken,the unsaturated hydrocarbon groups are reduced,and saturated hydrocarbon groups and C=O functional groups are obtained.Through GC-MS analysis,it is found that the carbon chain length of A-fresh is mostly less than C₂₁,the alkane is mainly derived from diesel,and the carbon chain number of A-age is larger,the proportion of C₂₇H₅₆ reaches 9.38%,and the oxidation products after NTP also follow this rule.（3）A test bench for regenerating DPF by NTP technology was built,and the influence of aged lubricant on DPF regeneration was studied.Characterization methods such as energy dispersive X-ray spectroscopy（EDX）,scanning electron microscope（SEM）,and transmission electron microscope（TEM）were used to analyze the properties and morphology of the ash.The study concluded that the internal oxidation reaction of DPF-age proceeded smoothly during regeneration,and the oxidation rate decreased slowly,which resulted in shortened T_unit and increased regeneration efficiency.The ash regenerated by the NTP technology presents a hollow column shape and is a loose powdery agglomerate.There are two types of walls of ash@L-fresh,which are smooth and chain type.The walls of ash@L-age are only smooth.Chain-type ash is produced due to the oxidized PM layer pulls the ash layer away from the wall of the DPF.Analysis of the TEM results found that single ash is irregular flakes,with oxide/metal fine particles attached to the outline.Due to its small size and aggregability,the ash flakes are easy to overlap each other to form agglomerates.The size of individual ash produced by lubricating oil aging is small,and the degree of overlap is low.Analysis shows that the sustained regeneration time of DPF-age and the large airflow resistance result in weaker adhesion between ash@L-age ash clusters than ash@L-fresh.