针对天然气高压喷射(high pressure direct injection,HPDI)模式双燃料船用低速机缸内的压力振荡现象,基于计算流体动力学软件CONVERGE耦合化学反应动力学机理,采用三维数值模拟方法,研究天然气及引燃柴油喷射时刻对缸内压力振荡和燃烧...针对天然气高压喷射(high pressure direct injection,HPDI)模式双燃料船用低速机缸内的压力振荡现象,基于计算流体动力学软件CONVERGE耦合化学反应动力学机理,采用三维数值模拟方法,研究天然气及引燃柴油喷射时刻对缸内压力振荡和燃烧粗暴的影响.结果表明:天然气喷射提前或引燃油喷射推迟均会增大天然气预混燃烧比例,燃烧剧烈程度增加,导致燃烧粗暴恶化,缸内压力峰值升高,压力升高率增大,但后者会推迟天然气被引燃的时刻,造成燃烧相位推迟.天然气喷射时刻提前至-4°CA ATDC时,缸内出现压力振荡.对于天然气燃烧粗暴且出现压力振荡的工况,提前喷射引燃油,两种燃料可能会同时发生燃烧粗暴,造成燃烧进一步恶化.天然气压燃有利于缓解引燃导致的燃烧初期较强的压力振荡,然而随着燃烧进程的发展,会造成更加剧烈的燃烧粗暴,但可通过引入引燃油缓解此现象.实际应用中,可以考虑在引燃天然气之前实现部分压燃以降低整体压力振荡强度.分析甲烷氧化反应路径中关键中间产物发现,HCO(醛基)可用于表征双燃料发动机燃烧粗暴及压力振荡的剧烈程度及持续期长短;CH_(3)(甲基)可作为燃烧粗暴及压力振荡的指示物质,其短时大量积累预示着燃烧粗暴的发生;同时,CH_(3)可以作为甲烷开始从低温反应过渡到高温反应的表征物质.展开更多
The aim of this paper was preliminary design of the process for low-temperature coal tar hydrocracking in supercritical gasoline based on Aspen Plus with the concept of energy self-sustainability.In order to ensure th...The aim of this paper was preliminary design of the process for low-temperature coal tar hydrocracking in supercritical gasoline based on Aspen Plus with the concept of energy self-sustainability.In order to ensure the correctness and accuracy of the simulation,we did the following tasks:selecting reasonable model compounds for low-temperature coal tar;describing the nature of products gasoline and diesel accurately;and confirming the proper property study method for each block by means of experience and trial.The purpose of energy self-sustainability could be possibly achieved,on one hand,by using hot stream to preheat cold stream and achieving temperature control of streams,and on the other hand,by utilizing gas(byproduct of the coal tar hydrocracking)combustion reaction to provide energy.Results showed that the whole process could provide a positive net power of about 609 kW·h for processing the lowtemperature coal tar with a flowrate of 2 268 kg/h.The total heat recovery amounted to 2 229 kW·h,among which 845kW·h was obtained from the gas combustion reaction,and 1 116 kW·h was provided by the reactor’s outlet stream,with the rest furnished by hot streams of the products gasoline,diesel and residue.In addition,the process flow sheet could achieve products separation well,and specifically the purity of product gasoline and diesel reached 97.2%and 100%,respectively.展开更多
基于高压直喷(high pressure direct injection,HPDI)天然气船用低速机,采用计算流体力学(CFD)软件Converge开展三维数值模拟研究,探究了天然气喷射规律对缸内着火及燃烧特性的影响.结果表明,随着天然气喷射速率的降低,缸压、放热率和...基于高压直喷(high pressure direct injection,HPDI)天然气船用低速机,采用计算流体力学(CFD)软件Converge开展三维数值模拟研究,探究了天然气喷射规律对缸内着火及燃烧特性的影响.结果表明,随着天然气喷射速率的降低,缸压、放热率和平均温度峰值显著降低.当喷射速率从1.30 kg/s降低到0.78 kg/s时,放热率峰值持续时间延长了约15°CA,缸压降低了约2MPa,导致燃烧相位延后,发动机做功能力降低.降低喷射速率使得缸内火焰发展速度变慢且火焰浮升长度更晚到达稳定值.进一步分析燃烧过程的高温反应和低温反应发现,天然气喷射速率降低使得燃烧初期的低温反应速率降低;2.5°CA前总体高温反应无明显变化,但随后高温反应随着天然气喷射速率的降低而减弱.天然气喷射速率越低,燃烧反应进行至约1.5°CA后富燃区低温产物CH_(2)O和H_(2)O_(2)浓度峰值越高,且峰值持续时间更久,其原因为富燃区低温产物消耗较慢且火焰对富燃区的影响相对滞后,使低温产物快速消耗的时刻推迟.展开更多
For saving energy and protecting the environment,natural gas has been widely used in internal combustion engines,which makes the study on the ignition characteristics of natural gas/diesel mixtures important.In this w...For saving energy and protecting the environment,natural gas has been widely used in internal combustion engines,which makes the study on the ignition characteristics of natural gas/diesel mixtures important.In this work,the effects of trace methane addition on the ignition delay of n-heptane/air mixtures are numerically studied using a detailed n-heptane mechanism under marine engine-like conditions.The simulations are carried out based on the software CHEMKIN-PRO 18.0 with a closed homogeneous reactor.Results show that the prolonged ignition delay times(IDs)of n-heptane/air mixtures are observed over the whole initial temperature range after methane is added,and the increment of IDs in the negative temperature coefficient(NTC)region is significantly higher than that in high temperature region.The sensitivity analysis indicates that both inhibition and promotion effects of important elementary reactions on n-heptane oxidation are weakened because of methane addition.However,the weakening influence on the promoting effect is more prominent.In addition,the inhibition effect of some elementary reactions that are related to the methane oxidation is enhanced.Thus,the IDs of n-heptane/air mixture are prolonged.The analyses of reaction rate of production(ROP)show that the both the production and consumption rates of key radicals decrease significantly in NTC region after methane is added,but it is negligible in the high temperature region.The study can extend the theoretical basis of ignition characteristics of methane/n-heptane blends under elevated temperatures and pressures.展开更多
文摘针对天然气高压喷射(high pressure direct injection,HPDI)模式双燃料船用低速机缸内的压力振荡现象,基于计算流体动力学软件CONVERGE耦合化学反应动力学机理,采用三维数值模拟方法,研究天然气及引燃柴油喷射时刻对缸内压力振荡和燃烧粗暴的影响.结果表明:天然气喷射提前或引燃油喷射推迟均会增大天然气预混燃烧比例,燃烧剧烈程度增加,导致燃烧粗暴恶化,缸内压力峰值升高,压力升高率增大,但后者会推迟天然气被引燃的时刻,造成燃烧相位推迟.天然气喷射时刻提前至-4°CA ATDC时,缸内出现压力振荡.对于天然气燃烧粗暴且出现压力振荡的工况,提前喷射引燃油,两种燃料可能会同时发生燃烧粗暴,造成燃烧进一步恶化.天然气压燃有利于缓解引燃导致的燃烧初期较强的压力振荡,然而随着燃烧进程的发展,会造成更加剧烈的燃烧粗暴,但可通过引入引燃油缓解此现象.实际应用中,可以考虑在引燃天然气之前实现部分压燃以降低整体压力振荡强度.分析甲烷氧化反应路径中关键中间产物发现,HCO(醛基)可用于表征双燃料发动机燃烧粗暴及压力振荡的剧烈程度及持续期长短;CH_(3)(甲基)可作为燃烧粗暴及压力振荡的指示物质,其短时大量积累预示着燃烧粗暴的发生;同时,CH_(3)可以作为甲烷开始从低温反应过渡到高温反应的表征物质.
基金the financial support from the National Natural Science Foundation of China(No.2117619)the Shaanxi Province Major Project of Innovation of Science and Technology(No.2008zkc03205,No.2011KTZB03-03-01)
文摘The aim of this paper was preliminary design of the process for low-temperature coal tar hydrocracking in supercritical gasoline based on Aspen Plus with the concept of energy self-sustainability.In order to ensure the correctness and accuracy of the simulation,we did the following tasks:selecting reasonable model compounds for low-temperature coal tar;describing the nature of products gasoline and diesel accurately;and confirming the proper property study method for each block by means of experience and trial.The purpose of energy self-sustainability could be possibly achieved,on one hand,by using hot stream to preheat cold stream and achieving temperature control of streams,and on the other hand,by utilizing gas(byproduct of the coal tar hydrocracking)combustion reaction to provide energy.Results showed that the whole process could provide a positive net power of about 609 kW·h for processing the lowtemperature coal tar with a flowrate of 2 268 kg/h.The total heat recovery amounted to 2 229 kW·h,among which 845kW·h was obtained from the gas combustion reaction,and 1 116 kW·h was provided by the reactor’s outlet stream,with the rest furnished by hot streams of the products gasoline,diesel and residue.In addition,the process flow sheet could achieve products separation well,and specifically the purity of product gasoline and diesel reached 97.2%and 100%,respectively.
基金supported by the National Natural Science Foundation of China(Grant Nos.91741119,91641203,51606133)the Marine Low-Speed Engine Project(Phase I)。
文摘For saving energy and protecting the environment,natural gas has been widely used in internal combustion engines,which makes the study on the ignition characteristics of natural gas/diesel mixtures important.In this work,the effects of trace methane addition on the ignition delay of n-heptane/air mixtures are numerically studied using a detailed n-heptane mechanism under marine engine-like conditions.The simulations are carried out based on the software CHEMKIN-PRO 18.0 with a closed homogeneous reactor.Results show that the prolonged ignition delay times(IDs)of n-heptane/air mixtures are observed over the whole initial temperature range after methane is added,and the increment of IDs in the negative temperature coefficient(NTC)region is significantly higher than that in high temperature region.The sensitivity analysis indicates that both inhibition and promotion effects of important elementary reactions on n-heptane oxidation are weakened because of methane addition.However,the weakening influence on the promoting effect is more prominent.In addition,the inhibition effect of some elementary reactions that are related to the methane oxidation is enhanced.Thus,the IDs of n-heptane/air mixture are prolonged.The analyses of reaction rate of production(ROP)show that the both the production and consumption rates of key radicals decrease significantly in NTC region after methane is added,but it is negligible in the high temperature region.The study can extend the theoretical basis of ignition characteristics of methane/n-heptane blends under elevated temperatures and pressures.
