Study On Effect Of PODE On Pm Properties Of Diesel Engine Exhaust And DPF Regeneration

Diesel particulate matter?PM?emission is an important pollution source of PM exhaust.The diesel particulate filter?DPF?is considered to be one of the most effective post-treatment technology for controlling PM emissions with a capture rate of no less than 90%.However,after a period of capture,the channels of the DPF are blocked by deposits,which leads to an increase in exhaust back pressure,a decrease in engine power,and an increase in fuel consumption.Therefore,the DPF needs to be regenerated to recover its particle capture ability.The regeneration efficiency of DPF is affected by the oxidation activity of the deposits in the channels of the DPF.The increase in the oxygen content of the fuel is beneficial to increase the oxidation activity of particles and the regeneration efficiency of DPF.Polymethoxy dimethyl ether?PODE?has high oxygen content,high cetane number,and no C-C bond in the molecule.Blending PODE in diesel can effectively reduce PM emissions of diesel engines and increase PM oxidation activity.Therefore,PODE is considered to be an ideal oxygen additive of diesel.Non-thermal plasma?NTP?technology is considered to be an effective means for DPF regeneration,because of its non-thermal,low energy consumption,high efficiency of regeneration and no secondary pollution.In this paper,a constant-volume combustion chamber test system and a modified cooperative fuel research?CFR?engine bench are established to analysis the ignition and heat release characteristics of PODE/diesel fuel blends.The influence of PODE on combustion process of fuel blends is analyzed by chemical reaction dynamics.An engine bench test system is employed to study the effect of PODE blending ratio on emission characteristics of the diesel engine.The effect of PODE blending ratios on DPF capture efficiency is studied,and the physicochemical properties and oxidation activity of the particle samples on the upstream end plane of DPFs are analyzed.The NTP generation system is established to study the effect of PODE on the improvement of diesel PM emissions by NTP technology.An DPF regeneration system is constructed to investigate the effect of the PODE blending ratio on DPF regeneration efficiency under the same NTP conditions.The main research contents of this paper are as follows:?1?PODE is blended with diesel at volume ratios of PODE 0%/diesel 100%,PODE10%/diesel 90%,PODE 20%/diesel 80%and PODE 30%/diesel 70%?denoted as P0,P10,P20,and P30?.The evaporation characteristics and oxidation activity of the blending fuels with the different PODE blending ratios are analyzed by thermogravimetric analyzer.The experimental studies are carried out on a constant-volume combustion chamber to analysis the ignition characteristics of the PODE/diesel blends at the different intake temperatures and the different environmental O₂ contents.The physical and chemical ignition delay of fuel are distinguished by CH₂O^*and OH^*spectral signals.A CFR engine is conducted to study the combustion characteristics and the heat release rate of the PODE/diesel blends.Moreover,a numerical study of the ignition process of the PODE/n-heptane blends is performed by using a detailed reaction mechanism of PODE and n-heptane.The results show that blending PODE in diesel is beneficial to improve the evaporation and oxidation characteristics.Compared to diesel,PODE/diesel blends is beneficial to shorten the physical and chemical ignition delay.Blending PODE in diesel leads to the heat release rate gets earlier,and the peak of heat release rate decreases.The ignition process of the PODE/diesel blends on the CFR engine is divided into two stages:low-temperature heat release?LTHR?and high-temperature heat release?HTHR?.As the compression ratio increases,phasing and peak value of the LTHR are approximately the same.The increasing of PODE blending ratio leads to a decrease of the critical compression ratio?CCR?.The LTHR is advanced and the peak value of the LTHR is larger as PODE blending ratio is increased.The marks of the two-stage ignition are the pool formation of CH₂O^*?OH^*radicals.Compared to n-heptane,the production rate of CH₂O^*?OH^*radicals is higher for PODE/n-heptane blends.?2?The emission tests are carried on a light-duty direct injection diesel engine.PM of the diesel engine is sampled and subjected to gas chromatography-mass spectrometry.?GC-MS?analysis.The results show that NO_x emissions rise first and then fall under the same engine operating conditions as the PODE blending ratio increases.The NO_x emissions are highest with PODE blending ratio of 10%.Increasing the PODE blending ratio is beneficial to reduce the PM emissions of the diesel engine,and the PM particle size distribution shifts toward the small particle size.Burning the fuel blends by employing 30%of PODE can effectively reduce the PM emissions by more than52.21%.Blending PODE in diesel is beneficial to increase the content of Oxygenated compounds in soluble organic fractions?SOF?and reduce the content of compounds with long carbon chains.?3?The DPF filtering tests is carried on by using PODE/diesel blends at a fixed engine condition.The differential pressure before and after the DPF are measured to achieve the same exhaust back pressure.The particle samples on the upstream end plane of DPFs are taken in order to analyze the particle particulates by Raman spectroscopy analyzer,Fourier transform infrared spectroscopy?FT-IR?analyzer,X-ray photoelectron spectroscopy?XPS?analyzer and thermogravimetric analyzer.The results show that as PODE blending ratio increases,the total capture rate of DPFs and the capture rate of all modes particles decreases.However,the total capture rate of DPFs is still over 94%with the increase of PODE blending ratio,which has a good capture effect.Comepared to diesel,longer time is needed to get a same bake pressure by blending PODE in diesel.Therefore,the service life of DPFs is prolonged.The chemical heterogeneity and disorder of particle samples are improved by burning PODE/diesel blends.The branching of aliphatic hydrocarbons and the relative content of hydrocarbons in aliphatics of particles are also increased.Meanwhile,blending PODE in diesel is beneficial to increase the O/C ratio and the relative content of carbonyl functional groups of particles,decrease the relative content of hydroxyl functional groups,and increase the oxidation activity of particles.Compared to other particle samples,the P20sample has a lower apparent activation energy,which indicating a higher oxidation activity.?4?The NTP generation system is established to generate the NTP reactive gas.The NTP reactive gas is passed into a NTP reaction chamber to react with the diesel exhaust.The particle size distributions of the diesel engine before and after the action of NTP are measured.The PM in the exhaust pipe is sampled by the filter papers and subjected to thermogravimetric analysis.The results show that blending PODE in diesel is beneficial to enhance the decomposition of PM by NTP.The improvement effect is sorted as:P20>P30>P10>P0.Blending PODE in diesel and NTP technology are beneficial to enhance the oxidative activity of PM.Compared to other PM samples,the P20 PM sample has a lower apparent activation energy and a higher oxidation activity.A higher oxidation activity makes the better decomposition of PM by NTP.?5?DPF regeneration system using NTP technology is established to regenerate the DPFs captured PM generated by burning PODE/diesel blends for 240 min at the same NTP conditions.The volume fraction of the PM decomposition products such as CO and CO₂ in the outlet pipe are measured.The temperature measuring points are placed in the DPF channels to observe the changes of the temperature versus time during the regeneration.The results show that under the same regeneration conditions,using PODE/diesel blends is beneficial to accelerate the reactions between the deposits in the DPF and NTP reactive substances.The decomposition amount of the deposits in the DPF is increased.The temperature of a measuring point in DPF channels climbs to the top and then decreases indicating the complete regeneration of deposits near this point.During the same regeneration time,DPF captured by burning four blend fuels have 4,6,8,and 6 measuring points show a complete regeneration trend respectively.The regeneration efficiency of DPF captured by burning P20 blend fuel is better under NTP technology.