正庚烷HCCI燃烧过程的数值模拟及试验研究

结合详细化学动力学机理,运用最新的CHEMKIN—Ⅳ化学动力学软件包中的IC enginc模块模拟了正庚烷的HCCI燃烧过程。并在一台高速四缸柴油机上进行了单缸正庚烷HCCI燃烧试验。分别从理论和试验上研究了正庚烷的HCCI燃烧过程以及各种参数变化对燃烧过程的影响,研究表明：正庚炕燃烧过程由低温反应和高温反应两阶段组成,NC7KET裂解生成OH是低温阶段最重要的反应,高温阶段着火是由H2O2裂解所触发的,低温阶段着火对高温阶段着火起着关键作用;各种参数的变化会导致燃烧过程的显著变化。     

废气再循环与燃料辛烷值对均质压燃发动机性能和排放影响的试验研究

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）发动机性能和排放特性的影响。结果表明，混合气较稀，EGR对指示热效率影响较小，其影响和燃料辛烷值有关；混合气变浓，EGR对指示热效率的影响增大。不同辛烷值燃料最高指示热效率出现在高EGR率、混合气较浓的区域，并且靠近爆震燃烧边界，辛烷值为60的燃料最高指示热效率最高，并且覆盖的工况区域最宽。高EGR率区域，EGR对HC排放的影响十分明显，EGR率升高，HC排放急剧增大，而且随着燃料辛烷值增大，这种趋势越明显；CO排放与缸内燃烧温度有较大的相关性，EGR率升高，CO排放升高。NOx排放出现急剧升高的“拐点”是判断HCCI爆震燃烧的一个重要判据，EGR率增大，“拐点”出现的混合气浓度增大，在正常工作范围内，NOx排放极低，EGR对NOx排放几乎没有影响。     

调制多脉冲喷油模式放热特征和能量分布及其对热效率和排放的影响

从发动机实验结果详细分析了调制多脉冲喷油模式的循环油量能量分布及燃烧放热特征,发现喷油模式的调制能够有效降低未燃油滴损失和CO排放,热效率能增加4％-12％。同时,从燃烧放热特征分析可看出,由调制多脉冲喷油模式组织的柴油HCCI燃烧过程对喷油模式和喷油定时极为敏感,是一个有限反应速率的过程。在-90℃A ATDC喷油定时下,仔细调制的喷油模式能获得好的NOx排放和热效率折中。     

边界条件对正庚烷均质压燃燃烧过程的影响

应用零维详细化学反应动力学模型,对不同边界条件下正庚烷（n—heptane）均质压燃燃烧反应的化学反应动力学过程进行了数值模拟研究,得出了以初始温度和燃料当量空燃比这两类边界条件为函数,压缩比为17,转速为1400r／min的HCCI全工况解。结果表明：HCCI燃烧分为完全燃烧区域、低温反应和蓝焰反应区域、仅发生低温反应区域和失火区域;不发生热焰反应的关键是反应H＋O2=O＋OH进行程度浅,不能生成足够的OH自由基使CO氧化成CO2;蓝焰反应也不发生而仅发生低温反应的关键是H2O2分解反应的进行程度浅,H2O2只有在缸内温度达到1000K时才能快速分解,这就不能生成足够的OH自由基使甲醛转化成CO2低温反应和蓝焰反应区域是高CO排放区,仅发生低温反应的区域是高甲醛排放区。     

柴油燃料HCCI燃烧的稳定性研究

实现宽广负荷范围内的稳定燃烧是目前HCCI燃烧研究的热点之一．而HCCI燃烧在高、低负荷时的工作不稳定性是影响HCCI燃烧实用性的重要问题之一。在前期研究实现单缸柴油机HCCI燃烧的基础上,主要分析了发动机负荷和气门重叠期的变化对HCCI燃烧稳定性的影响,探讨了造成不稳定燃烧的原因。结果表明：HCCI燃烧在中间负荷燃烧稳定性最好,但在低负荷时容易产生失火,高负荷时容易产生燃烧压力振荡,造成不稳定燃烧;负气门重叠期增大有利于小负荷的燃烧稳定性,负气门重叠期减小有利于大负荷的燃烧稳定性。     

氮氧化物-大分子烷烃相互作用的化学动力学模型

为准确模拟氮氧化物与C7、C8等大分子烷烃燃料之间的氧化过程,在前人工作的基础上,提出了一个NO—NC7H16相互作用的化学动力学模型．该模型以Marinov的研究成果为基础,并对其进行了部分修改．在此基础上,采用Glaude等人的方法,增加了大分子碳氢燃料与NO之间的基元反应,并日．采用了Anderlohr等人最新的...     

火花点火激发均质压燃(SICI)组合燃烧的试验研究

均质混合气压燃(HCCI)燃烧高负荷拓展是内燃机燃烧领域的一个难题.在缸内直喷汽油机(GDI)上采用EGR、火花点火和可变配气技术来控制缸内混合气形成和燃烧,实现了3种燃烧方式:HCCI、火花点火激发均质压燃(SICI)组合燃烧方式、火花点火(SI)燃烧方式,研究了不同EGR率和点火提前角对SICI燃烧排放特性的影响.结果表明,汽油SICI组合燃烧方式呈现明显的两阶段燃烧特性,调整点燃放热比例可以实现HCCI燃烧向高负荷拓展(最大平均有效压力为0.82 MPa),同时能获得较低的NOx排放和高的热效率.     

Experimental study of the performances of a modified diesel engine operating in homogeneous charge compression ignition (HCCI) combustion mode versus the original diesel combustion mode

Homogeneous charge compression ignition (HCCI) combustion mode provides very low NO_x and soot emissions; however, it has some challenges associated with hydrocarbon (HC) emissions, fuel consumption, difficult control of start of ignition and bad behaviour to high loads. Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production in diesel and HCCI combustion mode. However EGR has different effects on combustion and emissions, which are difficult to distinguish. This work is intended to characterize an engine that has been modified from the base diesel engine (FL1 906 DEUTZ-DITER) to work in HCCI combustion mode. It shows the experimental results for the modified diesel engine in HCCI combustion mode fueled with commercial diesel fuel compared to the diesel engine mode. An experimental installation, in conjunction with systematic tests to determine the optimum crank angle of fuel injection, has been used to measure the evolution of the cylinder pressure and to get an estimate of the heat release rate from a single-zone numerical model. From these the angle of start of combustion has been obtained. The performances and emissions of HC, CO and the huge reduction of NO_x and smoke emissions of the engine are presented. These results have allowed a deeper analysis of the effects of external EGR on the HCCI operation mode, on some engine design parameters and also on NO_x emission reduction.     

Demonstrating direct use of wet ethanol in a homogeneous charge compression ignition (HCCI) engine

Homogeneous charge compression ignition (HCCI) engines are amenable to a large variety of fuels as long as the fuel can be fully vaporized, mixed with air, and receive sufficient heat during the compression stroke to reach the autoignition conditions. This study investigates an HCCI engine fueled with ethanol-in-water mixtures, or “wet ethanol”. The motivation for using wet ethanol fuel is that significant energy is required for distillation and dehydration of fermented ethanol (from biosources, not from petroleum), thus direct use of wet ethanol could improve the associated energy balance. Recent modeling studies have predicted that an HCCI engine can operate using fuel containing as little as 35% ethanol-in-water with surprisingly good performance and emissions. With the previous modeling study suggesting feasibility of wet ethanol use in HCCI engines, this paper focuses on experimental operation of a 4-cylinder 1.9-L engine running in HCCI mode fueled with wet ethanol. This paper investigates the effect of the ethanol-water fraction on the engine's operating limits, intake temperatures, heat release rates, and exhaust emissions for the engine operating with 100%, 90%, 80%, 60%, and 40% ethanol-in-water mixtures.     

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。