基于DPF主动再生温度需求的柴油机进气节流控制策略

Intake throttling control strategy based on DPF active regeneration temperature for diesel

为得到DPF主动再生温度控制的全工况区域内进气节流控制策略,选取大、中、小负荷下的3种典型工况研究进气节流阀开度对柴油机泵气损失、排气热状态、缸内燃烧及排放特性的影响规律。台架稳态试验结果表明:随着节流阀开度的减小,节流作用增强,各工况下进气量逐渐降低,过量空气系数减小,最大燃烧压力下降,比油耗、CO、NO_X及烟度排放升高;但进气量的减少使得燃烧始点推迟,滞燃期延长,缸内燃烧温度及排气温度升高,抑制了HC的生成。当进气节流阀开度减小至20%时,低速小负荷工况进气流量减少率较大,排气温度提升更为显著,增幅可达62.7%,而高负荷工况排温略有升高,但泵气损失较大,增幅高达19.2%,严重恶化了发动机的经济性。因此该文综合3种代表工况下的排温提升潜力及主要性能变化规律,将A、B、C工况进气节流阀开度分别控制在35%~45%,50%~60%和70%~80%范围内,并依据排温分布特点得出发动机全工况范围内进气节流控制策略,即小负荷工况采用较小的节流阀开度,随负荷增大节流阀开度增大直至全开。

Diesel engines are widely applied in the field of transportation and manufacturing because of its better power and fuel economic performances.However,diesel engine emits huge quantities of particulate matter（PM） which pose a great threat to the human health and environment.As emission regulations are becoming gradually stricter,it is imperative to stringently control diesel PM emission with a feasible after-treatment technic.Diesel particulate filter（DPF） is considered as the most effective mean to reduce diesel PM emission.The core of DPF regeneration is the control of upstream temperature of DPF.DPF regeneration is mainly divided into active and passive regeneration,the regeneration temperature is mainly controlled by the air management and injection strategy for the active regeneration.Air management is mainly by changing the intake throttle valve to control the intake air flow,and then controlling the exhaust temperature,which is important to match and improve the low temperature performance of the after treatment system,but the change of intake air flow will inevitably affect performances of the engine.So the control strategy of air management needs to be studied in depth.In order to obtain the intake throttling control strategy based on DPF active regeneration temperature under the whole working area of diesel engine,three typical working conditions were designed,including low-speed light load（working condition A：1 250 r/min 25% load）,middle-speed medium load（working condition B：2 000 r/min 40% load） and high-speed heavy load（working condition C：3 000 r/min 70% load）,and the effects of intake throttle opening on pumping loss,exhaust thermal condition,in-cylinder combustion and emission characteristics of diesel engine were studied.The experimental results showed that the throttle effect was enhanced,the air intake flow gradually reduced under the different working conditions with the increasing of the throttle valve opening,which lead to the deterioration of combustion in cylinder,the decrease of the maximum combustion pressure,the increase of the BSFC,CO,NOX and smoke emissions.However,the decrease of the intake air flow delayed the start timing of combustion,prolonged the ignition delay period and increased the combustion temperature as well as the exhaust temperature,which inhibited the generation of HC effectively.When the intake throttle valve opening was reduced to 20%,the reduction rate of air intake flow was greater under the low-speed light load condition,the increase rate of exhaust temperature was more significant as much as 63%,while under the heavy load conditions,the exhaust temperature was slightly increased,but the pumping loss was increased by up to 19.2%,which seriously deteriorate the fuel economic performance.Based on the experimental results,the intake throttle valve opening was set respectively 35%-45%,50%-60% and 70%-80% range according to the increasing potential for the exhaust temperature and performance deterioration under working conditions A,B,C in this paper.Moreover,the intake throttling strategy was given within the scope of all working conditions based on exhaust temperature distribution of the engine that light loads adopted the larger intake throttle valve opening,with the increasing of load,the throttle valve opening was gradually increased to the full open state.