小缸径柴油机采用浅ω型燃烧系统的研究──燃烧率与NO_x排放

在两台采用浅ω型燃烧系统的高速柴油机上，对延迟供油的燃油消耗率、最高燃烧压力、NOx排放与排气烟度的影响进行了试验研究，并依据实测示功图采用现象学燃烧模型推求燃烧率与NOx生成，据此对试验结果作出理论解释。     

在稳定性指标制约下汽油机应用稀燃和EGR的局限性

本文应用微机检测发动机稳定性指标,在一台采用涡流室火花塞组成快速燃烧系统的汽油机中,对影响燃油消耗率、NO_x排放和稳定性指标的主要参数如空燃比、点火提前角和废气再循环率进行了试验研究。结果进一步表明:在稳定性指标制约条件下,稀燃能节油,但不能降低NO_x排放;EGR能降低NO_x排放,但不能节油。     

用启发式优化控制方法控制柴油机排放量

利用启发式智能优化控制方法建立了降低柴油机排放和油耗率的优化控制模型,并在一台卡车用高速直喷式柴油机上通过调节变截面涡轮开度和喷油定时实现了降低ＮＯＸ排放量和油耗率的控制策略。     

掺混比例和喷射定时对二甲醚-乙醇发动机燃烧和排放的影响

在一台电控共轨发动机上,试验研究了乙醇掺混比例和喷射定时对二甲醚-乙醇混合燃料燃烧及排放的影响。结果表明:随乙醇比例的增加,滞燃期延长,燃烧持续期缩短,最大压力升高率上升。随喷射推迟,滞燃期延长,燃烧相位延后,燃烧持续期在纯二甲醚时延长,而在掺混乙醇时则先延长后缩短,最大压力升高率先下降后上升。掺混乙醇和推迟喷射使预混燃烧比例增加。随喷射推迟,混合燃料的排气温度升高,喷射推迟到上止点后,排气温度随乙醇比例的增加而升高,排气温度高,则废气能量高,增压器增压比大,进气流量大,导致缸内压缩压力升高。在上止点前喷射时,掺混乙醇能使HC和CO排放保持在较低范围的同时,一定程度降低NO_x排放,掺混15%的乙醇较纯二甲醚最大降低约11%NO_x排放。随推迟喷射,NO_x排放降低,最大降幅达52%,在过分推迟燃料喷射时,因热效率低,循环喷射量增加,含15%乙醇混合燃料的NO_x排放会高于纯二甲醚。HC和CO排放随喷射推迟而升高,且升高幅度增大。     

负阀重叠早喷模式HCCI燃烧数学模型与计算分析

针对早喷模式中的排气上止点燃油喷射(ETCI)模式,综合广安博之模型、Bai模型的优点加以改进,并将空间均质燃烧与油膜蒸发燃烧相耦合,建立了一种新型的基于喷雾、燃油附壁、油膜蒸发、燃烧等一系列过程适用于缸内早喷模式的数学模型。利用该模型对135单缸柴油机ETCI燃烧模式进行校核计算,并通过试验验证进一步对燃烧过程中的工况参数及调节参数进行了研究。研究结果表明:在ETCI模式下,存在部分油膜附壁,油膜的蒸发主要与缸内的气体温度与壁温有关,且存在明显的两阶段加热过程。累积放热率与排气门关闭时刻和壁温基本呈线性关系,排气门关闭时刻提前10°CA,累积放热率上升约6%;壁温升高50K,累积放热率上升4%。增压压力升高,累积放热率降低,增压压力越大,累积放热率降低的幅度越小。     

氢发动机排气污染及NOx排放优化控制

研究了在汽油中加入氢气后混合燃料发动机的排放特性,给出了氢汽油混合燃料可以全面改善汽油机的废气排放,然后进行了高压喷射型氢发动机的两个主要运转参数(点火提前角和喷氢提前角)对NOx排放影响的研究。试验表明点火提前角、喷氢提前角对NOx排放量有很大影响。在建立以点火提前角、喷氢提前角、喷氢量为控制变量,以动力性或经济性为性能指标泛函,且排放不超标等为约束条件的氢发动机最优控制模型的基础上,提出了分别以径向基(RBF)网络、模糊神经网络(FNN)求解最优控制模型的新方法,进行了仿真计算和试验数据的对比研究。研究结果给出了两种网络均可以成功取代传统MAP而满足要求。其中以模糊神经网络所用时间较短。     

喷油提前角对非道路移动机械用柴油机性能的影响

以一台四缸非道路移动机械用柴油机为试验发动机,在喷油提前角为3℃A、1℃A和-1℃A条件下,对发动机的外特性、经济特性以及排放特性进行了研究。研究表明:喷油提前角的推迟,对发动机动力性影响不大;但对柴油机的经济性影响比较大,尤其是发动机运行在中高转速时;喷油提前角对排放也有较大影响,随着喷油提前角的推迟,CO和HC排放增加,NOx排放得到一定程度的改善;喷油提前角3℃A下的八工况点比排放得到大幅改善。因此,通过调整喷油提前角可使该非道路用柴油机达到拟国3排放法规的要求。     

2100型柴油机燃烧系统的改进和性能试验

介绍了紊流型燃烧系统利用进气道产生的涡流和燃烧室结构产生的强挤流和微紊流的混合效应，促进油气的充分混合，提高燃烧速度。在延迟喷油定时的条件下，可降低噪声和ＭＯｘ的排放，改善烟度，从而兼顾了小型车用柴油机的经济性、动力性和排放性能，通过在２１００型柴油机上的试验研究证实了其应用效果。     

时间控制式电控VE分配泵的开发

时间控制式电控VE分配泵是在对机械式VE分配泵进行改进和简化的基础上,引入了电控单元和高速电磁阀,实现了喷油量和喷油定时的数字化控制。匹配试验结果表明,时间控制式全电控VE分配泵达到了降低柴油机排放,提高柴油机燃油经济性的目的。     

Numerical investigation and Pareto optimization on performance,emission and in-cylinder reforming characteristics for two cylinder reciprocating engine with COx free fuel

The main objective of this study is to introduce the applicability of ammonia to the downsized compression ignition diesel engine for power generation or range extender. For this research objective, the two cylinder engine, which was the result of the previous study, fueled with diesel-ammonia blends was considered and the performance and NOx emission tendency were identified using the numerical method. Ammonia was mixed with diesel via injection at a specific fuel energy fraction (0%, 5%, 10%, or 15%) to evaluate the engine performance and emission characteristics. In addition, concept of “in-cylinder reforming” was introduced adopting negative valve overlap (NVO) by advancing the exhaust valve closing time to investigate the effect of adding ammonia as a hydrogen carrier. Subsequently, the primary variables affecting the brake-specific fuel consumption and NO_X are determined via multi-objective Pareto analysis. The optimal Pareto front confirms that exhaust valve timing exerts a greater effect on the performance and emissions than injection timing. Moreover, in-cylinder reformed hydrogen was increased under negative valve overlap strategy.     

An integrated model for negative valve overlap early injection HCCI combustion

Using exhaust top dead center injection (ETCI) mode to realize homogeneous charge compression ignition (HCCI) combustion would cause fuel wall wetting and combustion efficiency reduction, and there is no effective one-dimension simulation model to calculate and analyze the fuel wall wetting and evaporation process. In the research, a new type of integrated model is developed for the new application, HCCI combustion simulation based on ETCI mode. The model includes the following sub-models: fuel injection model, impingement model, film evaporation model, and combustion model. The improved Hiroyasu model and the Bai's model are coupled with homogenous combustion model and film evaporation model to calculate impingement fuel evaporation. The developed model is validated by experiment in a single cylinder diesel engine with ETCI combustion mode. The simulation and experimental results show that, film evaporation is mainly related to cylinder gas temperature and wall temperature, and there is an evident two stage heating process. The cumulate heat release rate is linear with exhaust valve closing (EVC) timing and wall temperature. The burned fuel fraction increases by 6 percent as the EVC timing advances by every 10 °CA, and increases by 4 percent as the wall temperature increases by every 50 K. The cumulate heat release rate decreases with the increase of boosting pressure, and the higher the boosting pressure, the smaller the decrease degree of cumulate heat release rate is.     

排气门正时对柴油机冷起动性能的影响

通过在一台单缸直喷柴油机上进行实验,分析了不同排气门正时条件对柴油机冷起动过程燃烧及排放性能的影响.结果表明,通过调节排气门关闭正时,适当增大缸内残余废气量,可显著改善起动过程初始着火循环的着火燃烧性能和提高起动过程缸内燃烧的稳定性.不同排气门关闭条件对起动过程的排放有着非常重要的影响.适当提前排气门关闭时刻,可以显著降低冷起动过程的烟度排放,特别是降低冷起动过程初始阶段的烟度排放.而对于NO2排放,由于残余废气具有很强的热效应,随着排气门关闭时刻提前,Nox排放呈上升趋势.     

A highly efficient six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery

A concept adding two strokes to the Otto or Diesel engine cycle to increase fuel efficiency is presented here. It can be thought of as a four-stroke Otto or Diesel cycle followed by a two-stroke heat recovery steam cycle. A partial exhaust event coupled with water injection adds an additional power stroke. Waste heat from two sources is effectively converted into usable work: engine coolant and exhaust gas. An ideal thermodynamics model of the exhaust gas compression, water injection and expansion was used to investigate this modification. By changing the exhaust valve closing timing during the exhaust stroke, the optimum amount of exhaust can be recompressed, maximizing the net mean effective pressure of the steam expansion stroke (MEP_steam). The valve closing timing for maximum MEP_steam is limited by either 1 bar or the dew point temperature of the expansion gas/moisture mixture when the exhaust valve opens. The range of MEP_steam calculated for the geometry of a conventional gasoline engine and is from 0.75 to 2.5 bars. Typical combustion mean effective pressures (MEP_combustion) of naturally aspirated gasoline engines are up to 10 bar, thus this concept has the potential to significantly increase the engine efficiency and fuel economy.     

Part-load characteristics of direct injection spark ignition engine using exhaust gas trap

Internal exhaust gas recirculation (EGR) is an effective strategy to reduce pumping loss and improve fuel economy using mixture dilution than traditional external EGR. In this paper, the internal EGR was obtained by exhaust gas trap (EGT) using the negative valve overlap (NVO) method. The effects of EGT on the part-load characteristics, including energy conversion, combustion and emission characteristics were studied in a direct injection spark ignition (DISI) engine. The experimental results showed that EGT can save fuel consumption by 5–16% due to reduced pumping loss and improved combustion efficiency, while it also can increase the engine cyclic variation and combustion duration. The engine cyclic variation increases with increasing of the EGT level; this can be overcome by advancing spark timing to stabilize the combustion. The flame propagation and compression combustion occurred simultaneously when high EGT level and high compression ratio were adopted; the combined combustion can reduce combustion duration but increase the engine cyclic variation. The stratified mixture using the two-stage injection strategy can reduce the engine cyclic variation and shorten the combustion duration so as to improve the thermal efficiency. Moreover, the second injection mass ratio and timing take an important effect on the combustion and emission characteristics in DISI engines using EGT strategy.     

不同点火时刻下天然气掺氢缸内直喷发动机燃烧与排放特性

在缸内直喷火花点火发动机上开展了天然气掺混0％-18％氢气的混合燃料不同点火时刻下的试验研究。结果表明：对于给定的喷射时刻和喷射持续期，点火时刻对发动机性能、燃烧和排放有较大影响，喷射结束时刻与点火时刻的间隔对直喷天然气发动机极为重要，喷射结束时刻与点火时刻的间隔缩短时，混合气分层程度高，燃烧速率快，热效率高。最大放热率等燃烧特征参数随点火时刻的提前而增加。HC排放随点火时刻的提前而下降，CO2和NOx排放随点火时刻的提前而增加，NOx排放的增加在大点火提前角下更明显。掺氢可降低HC排放，对CO和CO2排放影响不大。掺氢量大于10％时可提高天然气发动机热效率。     

气门二次开启策略对柴油机性能及能量损失的影响

基于一台两级增压高压共轨柴油机,建立了整机一维热力学仿真模型,研究不同气门二次开启策略对柴油机燃烧特性、NOx排放及能量分布的影响.研究结果表明:在相同气门升程时,随进气门、排气门二次开启时刻提前及进排气门同时二次开启时刻间隔增大,缸内压力和瞬时放热率峰值升高,燃烧重心前移,有效热效率升高,燃烧温度升高,NOx排放升高...     

气道喷水和废气再循环对重型柴油机性能和排放影响的优化匹配试验研究

在一台高压共轨重型柴油机上开展了气道喷水结合高压废气再循环(EGR)的试验研究。基于世界统一稳态测试循环(WHSC)各工况点探索引入高压EGR和气道喷水技术对柴油机排放和燃油经济性的影响;在此基础上对各工况的燃烧相位进行优化,得到WHSC各工况点下基于喷水和EGR的优化策略。结果表明:综合考虑排放和燃油经济性,低负荷工况宜单独引入高压EGR,并通过提前喷油时刻(start injection timing,SOI)优化燃烧相位;中高负荷工况宜少量喷水并引入适当EGR,满负荷则应单独采取气道喷水策略。WHSC加权结果表明,在保持较低的HC、CO和碳烟排放前提下,优化后的加权NOx比排放降低7.71g/(kW·h),降幅约45.2%,有效燃油消耗率降低约1.20g/(kW·h)。     

二冲程汽油机电控燃油喷射系统的试验研究

开发了一种适用于二冲程汽油机的电控喷射系统，对不同喷射方案进行了系统的试验研究，提出了适合于电子控制低压汽油喷射的喷油器位置，喷油开始时间等参数。台架试验结果表明，电控喷射式二冲程汽油机与化油器式二冲程汽油机相比，在燃油经济性和排放指标两方面都有明显的改善。     

缸内直喷汽油机HCCI燃烧对压缩比和辛烷值的适应性研究

在缸内直喷汽油机（GDI）上采用多次燃油喷射和可变配气技术来控制缸内混合气形成和燃烧,实现了SI/HCCI复合燃烧方式。研究了不同压缩比和辛烷值对均质混合气压燃（HCCI）燃烧排放特性的影响。结果表明,汽油HCCI燃烧呈现单阶段燃烧燃料特性,HCCI着火发生在上止点附近时油耗低。低压缩比下,HCCI燃烧可以在较浓空燃比下工作,NOx排放较高。高辛烷值燃料HCCI燃烧可运行的负荷范围窄。汽油HCCI发动机在偏高压缩比条件下燃用偏低辛烷值汽油可以获得较好的经济性和排放性能。     

低压EGR对GDI增压汽油机外特性下性能和排放影响

通过一款涡轮增压汽油直喷(gasoline direct injection,GDI)发动机低压废气再循环(exhaust gas recirculation,EGR)的试验,研究了EGR率和点火提前角的综合作用对增压GDI发动机的燃烧、缸压、排放和油耗等方面的影响。结果表明,在GDI增压发动机中加入EGR后,由于废气的稀释和热容作用,使缸内燃烧持续期增大,排气温度下降,燃烧相位也发生了改变。这对发动机外特性的有利影响是油耗减少,CO和NO_x排放也明显减少;不利影响是EGR的加入提高了增压发动机的排气压力,导致泵气损失增加。此外,总碳氢(total hydro carbons,THC)排放也有所增加。在GDI增压汽油机中使用EGR系统并配合点火角的调节能够有效提高热效率,降低NO_x排放。