未着火循环废气改善柴油机冷起动的燃烧

采用柴油的替代研究燃料正庚烷和压燃式燃烧模型,计算研究了起动阶段引入未着火循环的燃烧产物对下一循环燃烧的影响.未着火循环的燃烧产物与完全燃烧循环有明显不同,其中含有许多未燃燃油和中间活性物质,将其以EGR的方式重新引入气缸中能有效改善下一循环的燃烧,计算结果表明,中间活性物质起到了关键作用.进行了EGR影响柴油机起动性能的试验研究,结果表明,起动初期的循环中,引入EGR可以改善燃烧,试验结果验证了计算分析的合理性,为改善柴油机冷起动性能提供了一种新思路.根据正庚烷燃烧的化学动力学理论,结合计算过程中各物质浓度的变化,研究了EGR改善燃烧的机理.     

喷射方式对2.0L直喷柴油机起动首循环燃烧过程的影响

基于2.0TC型高压共轨直喷增压柴油机,定义燃烧效率作为起动工况燃烧过程的评价指标,试验研究了不同喷射方式对起动首循环燃烧过程及起动过程瞬态燃烧过程的影响。研究结果表明:采用三次喷射方式时,起动首循环燃烧效率明显优于单次喷射或两次喷射方式,且三次喷射方式中两次预喷量的不同分配,对起动首循环的燃烧效率影响很大;混合气的着火特性好未必有利于改善首循环燃烧效率,滞燃期是控制首循环燃烧效率的关键;对于三次喷射方式,首循环燃烧效率的好坏不能决定起动过渡工况的平均燃烧效率,所以对起动首循环和起动过程的喷射方式有必要分别进行控制。     

EGR对直喷式柴油机冷起动过程着火燃烧的影响分析

通过在一台135单缸直喷柴油机上分别进行内部EGR（IEGR）、外部EGR（EEGR）条件下的冷起动试验,分析了内、外部EGR对柴油机冷起动过程着火燃烧性能及排放的影响。加入内、外部EGR后,由于EGR中含有大量的燃油蒸气、部分氧化产物等活性成分,初始着火循环的着火燃烧性能得到显著改善。在冷起动过程中,加入一定量的内部或外部EGR,有利于提高燃烧过程的稳定性。但过大的外部EGR量,将导致发动机燃烧极度不稳定甚至失火。由试验结果还可以看到,加入适当的内、外部EGR,均能有效地改善冷起动过程的烟度排放。对于NOx排放,当采用外部EGR方式时,有明显的改善作用;但当采用内部EGR方式时,由于残余废气的热效应,NOx排放随内部EGR量的增大而增大。     

废气再循环与燃料辛烷值对均质压燃燃烧特性影响的试验研究

在一台单缸直喷式柴油机上研究了废气再循环（EGR）对不同辛烷值燃料均质压燃（HCCI）燃烧特性及排放特性的影响.结果表明,EGR使HCCI着火燃烧推迟、燃烧反应速度降低、缸内压力和平均温度降低,HCCI工况范围向大负荷工况扩展;混合气浓度增大或燃料辛烷值增大,EGR对燃烧效率的影响增大,EGR率升高,燃烧效率降低;不同辛烷值燃料最高燃烧效率出现在高比例EGR率、混合气较浓、靠近爆震燃烧边界的区域.试验结果也表明,辛烷值为60的燃料采用EGR后HCCI覆盖的工况范围最宽.     

冷却液温度对柴油机起动首循环燃烧的影响

冷却液温度是柴油机起动过程中影响失火与燃烧不稳定性的重要因素。喷油首循环的燃烧对后续工作循环着火有较大影响。为了分析冷却液温度对柴油机起动首循环燃烧和排放的影响规律,利用基于循环控制的柴油机起动过程燃烧、排放测控系统,在一台单缸直喷式柴油机上进行了试验研究。试验结果表明冷却液温度对柴油机起动首循环燃烧的稳定性有较大影响。提高冷却液温度对于消除起动过程首循环燃烧状态的不稳定性具有较明显的作用。冷却液温度较低时,使着火滞后期增长,很容易导致失火或不完全燃烧现象,生成较高HC排放。试验也验证了所建立的测控系统为研究柴油机起动过程提供了一种有效的测试手段。     

热EGR对氢内燃机性能及排放影响的试验研究

氢内燃机燃烧产物与传统内燃机不同,因此其EGR的作用机制与传统内燃机有很大差别.为了研究EGR对氢内燃机的动力性和排放特性的影响规律,以一台4缸2.0 L的氢内燃机为研究对象进行了试验研究,并探讨了缸内燃烧的发展过程和特点.试验表明:在循环喷氢量不变时,可以通过调节EGR率改变混合气的当量燃空比.在当量燃空比小于1时,EGR率的变化对输出转矩影响不大,在当量燃空比超过1后,输出转矩随EGR率的增加线性下降;在小负荷时使用热EGR将导致缸内温度的升高、增大NO相似文献   

柴油机预混合燃烧滞燃期的试验

滞燃期是柴油机预混合燃烧当中一个极为重要的参数.在电控共轨柴油机上进行了EGR率、喷油始点、喷油压力、负荷、转速和进气温度等单一参数对预混合燃烧滞燃期的试验研究.结果表明,名义过量空气系数能够帮助解释各试验参数对柴油机预混合燃烧滞燃期的影响.混合气的温度、压力和混合气中O2浓度影响柴油机预混合燃烧的滞燃期.提高进气温度...     

喷油提前角对柴油机燃烧特性的影响

为了研究柴油机在不同喷油提前角下的燃烧特性,采用三维流体数值分析软件AVLFIRE建立了某型柴油机燃烧计算模型.在不同喷油提前角下,对燃烧滞燃期、油气混合程度、温度、燃空当量比、放热率和压力进行分析,得出:随着喷油提前角的增大,滞燃期延长,着火时刻形成的可燃混合气增多,缸内最高燃烧压力和最高温度也随之升高同时放热规律相...     

进气温度对直喷式柴油机冷起动初始期燃烧和排放的影响

为了研究进气温度对柴油机起动过程燃烧不稳定性和排放的影响规律,利用柴油机起动过程燃烧、排放测控系统,在一台直喷式单缸柴油机上进行了试验。试验结果表明：进气温度对柴油机冷机起动过程初始期燃烧有较大影响,随进气温度的升高,冷机起动着火滞后期明显减小,扩散燃烧增加。提高进气温度能够明显改善着火条件,降低起动过程供油量,减少失火循环,从而明显改善起动过程中的HC排放。     

-43℃下多次喷射对柴油机冷起动特性的影响

为了改善极寒条件下柴油机的起动性能和怠速稳定性,基于起动/发电一体式电机拖动柴油机进行-43℃下的冷起动试验,研究了单次、两次（预喷1+主喷）和三次喷射（预喷2+预喷1+主喷）3种喷射方式对柴油机冷起动过程及燃烧特性的影响,分析了不同喷射组合对极寒条件下柴油机冷起动过程的影响规律。研究表明：在-43℃环境温度下,柴油机采用三次喷射时,冷起动性能明显优于单次和两次喷射。随着喷射次数的增加,起动燃烧首循环的缸内压力峰值升高,峰值相位提前,压力升高率和瞬时放热率峰值显著降低,滞燃期缩短;在冷起动过程中,相比单次喷射,两次和三次喷射时倒拖阶段和升速阶段所需时间分别减少9个循环和22个循环,最高燃烧压力升高,循环变动率分别降低37.7%和46.8%,使得起动时间分别缩短0.88 s和2.58 s,起动累积油量分别减少511 mg和1 290 mg;在起动后的怠速过程,怠速转速波动率分别降低54.2%和82.2%,随着喷射次数的增加,怠速稳定性显著提高。研究结果可为柴油机极寒条件下冷起动过程的控制和参数标定提供理论依据。     

稀燃和EGR对汽油发动机性能影响研究

基于一台带有低压废气再循环系统的1.5 L涡轮增压直喷汽油发动机进行了稀燃和废气再循环(EGR)影响发动机燃烧性能的试验研究。结果表明,随着稀释率的上升,EGR和稀燃均导致发动机滞燃期、燃烧持续期延长,燃烧重心提前,有效燃油消耗率下降,排气温度下降,平均绝热指数上升。相同稀释率下,相比稀燃,EGR的滞燃期长,燃烧重心提前,两者燃烧持续期基本相等,稀释极限低,绝热指数小,排气温度低。在稀释率分别为20%、35.9%时,最大可减小有效燃油消耗率4.7%、7.2%。热容对燃油经济性的影响占主导地位,相同稀释率下,循环变动系数小于3%时,相比稀燃,EGR具有更好的燃油经济性。     

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。     

Study of low emission homogeneous charge compression ignition (HCCI) engine using combined internal and external exhaust gas recirculation (EGR)

This paper focuses on the effects of internal and cooled external exhaust gas recirculation (EGR) on the combustion and emission performance of diesel fuel homogeneous charge compression ignition (HCCI). The use of fuel injection before the top center (TC) of an exhaust stroke and the negative valve overlap (NVO) to form the homogeneous mixture achieves low NO_x and smoke emissions HCCI. Internal and external EGR are combined to control the combustion. Internal exhaust gas recirculation (IEGR) benefits to form a homogeneous mixture and reduces smoke emission further, but lower the high load limits of HCCI. Cooled external EGR can delay the start of combustion (SOC) effectively, which is very useful for high cetane fuel (diesel) HCCI because these fuels can easily self-ignited, making the SOC earlier. External EGR can avoid the knock combustion of HCCI at high load, which means it can expand the high load limit. HCCI maintains low smoke emission at various EGR rates and various loads compared with a conventional diesel engine because there are no fuel-rich volumes in the cylinder.     

The effect of EGR and hydrogen addition to natural gas on performance and exhaust emissions in a diesel engine by AVL fire multi-domain simulation,GPR model,and multi-objective genetic algorithm

In this study, the effect of adding hydrogen to natural gas and EGR ratio was conducted on a diesel engine to investigate the engine performance and exhaust gases by AVL Fire multi-domain simulation software.For this investigation, a mixture of hydrogen fuel and natural gas replaced diesel fuel. The percentage of hydrogen in blend fuel changed from 0% to 40%. The compression ratio converted from 17:1 to 15:1. The EGR ratios were in three steps of 5%, 10%, and 15%, with different engine speeds from 1000 to 1800 RPM. The Gaussian process regression (GPR) was developed to model engine performance and exhaust emissions. The optimal values of EGR and the percentage of hydrogen in the blend of HCNG were extracted using a multi-objective genetic algorithm (MOGA).The results showed that by increasing EGR, thermal efficiency, the engine power, and specific fuel consumption decreased due to prolongation of combustion length while cumulative heat release increased but, its effect on cylinder pressure is insignificant. Adding hydrogen to natural gas increased the combustion temperature and, consequently NOx. While the amount of CO and HC decreased. The results of GPR and MOGA illustrated that at different engine speeds, the optimum values of EGR and HCNG were 6.35% and 31%, respectively.     

稀燃及废气再循环提高增压汽油机热效率的对比研究

在一台直列4缸增压直喷汽油机上针对万有特性最低油耗工况点,进行了稀薄燃烧与废气再循环(exhaust gas recirculation,EGR)提高发动机热效率的对比试验研究。试验结果表明:稀薄燃烧及EGR均能有效降低发动机燃油消耗率,稀释率分别为33%和19%时,采用稀燃和EGR时的最高有效热效率绝对值分别增加2.8%和1.7%,其中稀燃的有效热效率达到了39.9%,稀燃实现更高热效率主要归因于较低的传热损失和未燃损失。从燃烧角度来看,稀燃及EGR稀释都延长了燃烧滞燃期及持续期,但同样稀释率下稀燃的滞燃期更短,稀燃更高的稀释极限实现了更低的传热损失;但EGR抑制爆震,提前燃烧相位,使采用EGR时的排气能量损失低于稀燃。从排放角度来看,稀燃及EGR在高稀释率下均显著降低NO_x排放,而受益于高氧气浓度,相同稀释率下稀燃的HC及CO排放均低于采用EGR时,从而使稀燃的未燃损失更低。     

Energy efficiency improvement strategies for a diesel engine in low‐temperature combustion

The lowered combustion temperature in diesel engines is capable of reducing nitrogen oxides and soot simultaneously, which can be implemented by the heavy use of exhaust gas recirculation (EGR) or the homogeneous charge compression ignition (HCCI) type of combustion. However, the fuel efficiency of the low‐temperature combustion (LTC) cycles is commonly compromised by the high levels of hydrocarbon and carbon monoxide emissions. More seriously, the scheduling of fuel delivery in HCCI engines has lesser leverage on the exact timing of auto‐ignition that may even occur before the compression stroke is completed, which may cause excessive efficiency reduction and combustion roughness. New LTC control strategies have been explored experimentally to achieve ultralow emissions under independently controlled EGR, intake boost, exhaust backpressure, and multi‐event fuel‐injection events. Empirical comparisons have been made between the fuel efficiencies of LTC and conventional diesel cycles. Preliminary adaptive control strategies based on cylinder pressure characteristics have been implemented to enable and stabilize the LTC when heavy EGR is applied. The impact of heat‐release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with engine cycle simulations. This research intends to identify the major parameters that affect diesel LTC engine thermal efficiency. Copyright © 2008 John Wiley & Sons, Ltd.     

Numerical study of EGR effects on reducing the pressure rise rate of HCCI engine combustion

The effects of the inert components of exhaust gas recirculation (EGR) gas on reducing the pressure rise rate of homogeneous charge compression ignition engine combustion were investigated numerically by utilizing the CHEMKIN II package and its SENKIN code, as well as Curran’s dimethyl ether reaction scheme. Calculations were conducted under constant volume combustion and engine combustion (one compression and one expansion only, respectively) conditions. Results show that with constant fuel amount and initial temperature and pressure, as EGR ratio increases, combustion timings are retarded and the duration of thermal ignition preparation extends non-linearly; peak values of pressure, pressure rising rate (PRR), and temperature decrease; and peak values of heat release rate in both low temperature heat release (LTHR) and high temperature heat release decrease. Moreover, maximum PRR decreases as CA50 is retarded. With constant fuel amount, mixtures with different EGR ratios can obtain the same CA50 by adjusting the initial temperature. Under the same CA50, as EGR ratio increases, the LTHR timing is advanced and the duration of thermal ignition preparation is extended. Maximum PRR is almost constant with the fixed CA50 despite the change in EGR ratio, indicating that the influence of EGR dilution on chemical reaction rate is offset by other factors. Further investigation on the mechanism of this phenomenon is needed.     

Numerical study of EGR effects on reducing the pressure rise rate of HCCI engine combustion

The effects of the inert components of exhaust gas recirculation (EGR) gas on reducing the pressure rise rate of homogeneous charge compression ignition engine combustion were investigated numerically by utilizing the CHEMKIN II package and its SENKIN code, as well as Curran’s dimethyl ether reaction scheme. Calculations were conducted under constant volume combustion and engine combustion (one compression and one expansion only, respectively) conditions. Results show that with constant fuel amount and initial temperature and pressure, as EGR ratio increases, combustion timings are retarded and the duration of thermal ignition preparation extends non-linearly; peak values of pressure, pressure rising rate (PRR), and temperature decrease; and peak values of heat release rate in both low temperature heat release (LTHR) and high temperature heat release decrease. Moreover, maximum PRR decreases as CA50 is retarded. With constant fuel amount, mixtures with different EGR ratios can obtain the same CA50 by adjusting the initial temperature. Under the same CA50, as EGR ratio increases, the LTHR timing is advanced and the duration of thermal ignition preparation is extended. Maximum PRR is almost constant with the fixed CA50 despite the change in EGR ratio, indicating that the influence of EGR dilution on chemical reaction rate is offset by other factors. Further investigation on the mechanism of this phenomenon is needed.     

废气再循环率及点火时刻对天然气发动机燃烧和排温的影响

基于一台当量比燃烧的天然气发动机,采用三维燃烧分析与发动机一维热力学计算相结合的方式开展了废气再循环(exhaust gas recirculation,EGR)率及点火时刻对缸内燃烧过程和发动机排温的影响研究.研究结果表明:随着EG R率的增加,燃烧相位后移,燃烧持续期延长,放热率峰值减小,最大压升率、缸内最高燃烧压...