【作者】 夏孝朗；

【导师】 刘敬平；

【作者基本信息】 湖南大学 ， 车辆工程， 2013， 博士

【摘要】 对置活塞对置气缸二冲程发动机（opposed piston and opposed cylinder two stroke engine，简称OPOC发动机）是一种结构新颖的新型发动机，因其功率密度大、油耗低、相对传统二冲程发动机的排放有很大的改善，引起了国内外内燃机领域的密切关注。论文介绍了OPOC发动机独特的结构特点及性能优势，重点对OPOC发动机性能研发的关键技术进行了研究：系统地推导了活塞运动规律及其与气口定时的内在联系；以台架试验与仿真相结合的手段，着重对OPOC发动机的一维性能、扫气性能、缸内喷雾与燃烧进行了研究。活塞运动规律是其它相关研究的前提与基础。首次提出了OPOC发动机普遍适用的活塞运动规律公式，得出结论：①上止点与下止点的相位相差并不一定是180o曲轴转角，而是在该值附近；③进排气口高度越大，气口开启的最大面积越大、气口开启时刻越早、关闭时刻越晚、有效压缩比与有效膨胀比也越小。对OPOC发动机的一维性能的增压匹配、气口高度两个主要内容进行了研究。增压的独特之处为：①进气口压力一定要大于排气口压力，以便形成正的扫气压差进行扫气，保证发动机的正常运行；②引进ECT（电力辅助增压装置）对压气机进行助力，以保证一定的正值扫气压差。基于发动机动力性能目标，提出了一级涡轮增压、两级涡轮增压的预匹配数学模型，依据模型建立了发动机与增压器预匹配软件V2.0，并应用该软件对无外部EGR时一级涡轮增压方式与大量外部EGR时两级涡轮增压方式的增压器进行预选，然后对预选出的增压器再通过台架进行试验验证，试验表明：所提出的一级与两级涡轮增压预匹配模型具有可靠性与实用性，即增压器预匹配软件V2.0具有较高的工程应用价值。分别对进排气口高度进行了仿真优化，结果表明：当进气口高度一定时，排气口越长，发动机的高速性能越好，而低速性能则越差；当排气口高度一定时，进气口越长，发动机低速性能越好，而高速性能则越差。基于发动机台架试验数据，首先对外特性上及2000r·min-1负荷特性上的扫气性能进行了仿真分析，得出结论：①在发动机结构确定后，扫气效率取决于扫气压差与扫气绝对时间。扫气压差大，扫气效果好；扫气绝对时间长，则扫气效率高。其次，在3500r·min-1全负荷工况时对切向进气口倾角进行了仿真分析，得出结论：①随着进气口倾角的增大，扫气效率先增加后减小；缸内新鲜充量随进气口倾角变化的趋势与扫气效率随进气口倾角变化的趋势一致，而残余废气系数随进气口倾角变化的趋势却与此相反；给气比随着倾角的增加不断减小；捕获率随倾角加大而提高。②对扫气效率与新鲜充量而言，切向扫气口倾角最值佳角度为30o。说明了OPOC发动机独特的喷油嘴布置方式与燃烧室形状；对当量有效膨胀比（E.E.R）模型进行了修正与试验验证，运用该模型计算E.E.R值对后续研究的喷雾与燃烧进行分析评价；研究了喷孔数、喷油提前角、喷油规律、油束夹角等因素对缸内喷雾和燃烧的影响，得到如下结论：①喷孔总有效面积不变时，喷孔越数多，则喷孔直径越小，雾化效果越好，索特直径越小，雾化质量越好（在油束不发生相互干涉的情况下），扩散燃烧阶段的放热速率越快，缸内平均压力越大，温度越高，NOx排放越多， Soot最终生成量越少，燃油经济性越好。②喷油提前角越大，燃油雾化越快、滞燃期内的可燃预混气越多，缸内压升率、最高爆发压力等越高，缸内温度也越高，NOX排放量越多，Soot最终生成量越少；喷油提前角在某一合理角度时，燃油经济性最好。③预喷-主喷两阶段喷油规律对喷雾与燃烧的影响：在其它参数不变的情况下，随着预喷量的增加， NOX生成量先减少至最小值，然后不断增加；同时，随着预喷量的增加，由于压缩冲程内消耗的功太多，E.E.R值越来越小，燃油经济性越来越差。④比较不同油束夹角50o、60o、70o、80o和90o对喷雾与燃烧的影响，结果表明：油束夹角越大，喷油中期油束喷至活塞顶面的时间越早，积聚在活塞顶面的油量也越多，雾化越慢；喷油中期扩散燃烧较慢，维持缸内压力、温度降低的趋势，则NOX生成量越小，经济性能越差，这种现象与传统发动机完全不同。更多还原

【Abstract】 Opposed piston and opposed cylinder two stroke engine (OPOC engine) is a new type of engine. The idea was not new but many innovative ideas were derived in the last decade and now it becomes a hot spot of interest both overseas and domestic because its large power density, low fuel consumption and great potential for improvement to the traditional two stroke engine.In this thesis paper the special structural features and performance advantage s of the OPOC engine is introduced, then it is focused on the study of the key technologies of the OPOC engine: the inner relationship between the piston motion profile and the port opening area/timing is derived; The engine performance，scavenging process, fuel spray and the in-cylinder combustion process, are systematically studied via both numerical computation and bench testing.The piston movement profile is the premise and foundation of other study. The study demonstrates that:①TDC is not located at the maximum position of either the inner or the outer piston, because the inner and outer piston do not reach the extreme position of their displacement at the same time.②Phase difference between the TDC and BDC is not, although close to, necessarily180crankshaft angle.③The larger the intake and exhaust port heights are, the greater the maximum opening area is，the earlier the ports are opened, the later they are closed, and the smaller the effective compression ratio and the effective expansion ratio are. The OPOC engine performance is closely related to the boost level, port heights and other parameters. The turbocharged OPOC engine has its own uniquecharacteristics:①The inlet pressure at the intake ports must be greater than the that at the exhaust ports to form a pressure difference for positive scavenging, to ensure the normal operation of the engine;②Introducing ECT (Electrically Controlled Turbocharger) provides assistance for the compressor to guarantee a pressure difference for positive scavenging. For the matching between the OPOC engine with the turbocharger, this research revealed the inner-relationship between the engine performance goals with the required boost pressure level, derived the mathematical models for pre-matching of turbochargers of both one and two-stage turbocharging systems, and developed a engine/turbocharger pre-matching software V2.0. One-stage turbocharger without external EGR and two-stage turbochargers with large scale external EGR (up to40%by mass) are preselected and identified by application of the software, and verified by engine dyno tests. It is proven that the proposed pre-matching models with both one and two-stage turbochargers are reliable and the turbocharger pre-matching software V2.0has a high value in engineering. In addition, analysis results of the intake/exhaust port heights indicate that: with fixed intake port heights, the longer the exhaust ports are, the better the engine performance is at high speeds, but the worse at low speeds; Other the other hands, with fixed exhaust port heights, the longer the intake port is, the better the engine performance is at low speeds while the performance at high speeds get worse. Scavenging performance directly affects engine power, fuel economy andemissions performance of the engine. The article details the main evaluation indicators of scavenging performance: scavenging efficiency, delivery ratio, capture rate. Based on the engine bench test data, firstly focusing on the simulation calculation and analysis of the scavenging performance of the external characteristics, It comes to a conclusion that:①When the engine structure is determined, the scavenging efficiency depends on the different pressure and absolute time of scavenging.When pressure difference is large, the scavenging effect is better; When scavenging absolute time is long, the scavenging efficiency is higher.②The scavenging efficiency and delivery ratio are good, but the trapping ratio is low at low speed;the delivery ratio is moderate and the scavenging effect is good, but trapping ratio is low in middle speed;the delivery ratio is too small (less than1) and scavenging efficiency is poor, but the trapping ratio is high in high speed. Secondly, in full-load conditions at3500r·min-1,analyzing and simulated calculating the tangential angle of intake port, concluding that:①With the tangential angle is increasing, scavenging efficiency increases first and then decreases; the trends of fresh air changing with tangential angle increasing in cylinder is the same with scavenging efficiency when the intake port angle changes, but residual burned mass fraction shows just the opposite; delivering ratio decreases as the inclination angle increases (due to increasing angle, the intake port resistance increases and the flow coefficient will decrease, resulting in reduction of the intake port air mass flow in a equal time); Trapping ratio continues to increase with increasing inclination.②For the scavenging efficiency and fresh charge, the best value of the opening angle of the tangential scavenging is30o. The power, economy, emissions performance of the OPOC are directlydetermined by spray and combustion in cylinder. This paper introduces a relatively new parameters of evaluating thermal-power conversion process: equivalent effective expansion ratio (E.E.R), and it is revised and test validated, then appling to the analysis and evaluating combustion in cylinder; and making unique nozzle arrangement and the shape of the chamber about the OPOC engine, and studying the influence of the main parameters of the fuel injection system such as the number of nozzles, fuel injection timing, injection characteristics on the processes of spray and combustion, the following conclusions can be drawn:①The larger the number of nozzle holes is utilized, the smaller the nozzle hole diameter becomes, the smaller the spray Sauter diameter is, the better is the atomization quality (also the interferences between the fuel sprays can be avoided); the larger the number of nozzle holes is, the faster the burning rate is, the higher the cylinder pressure and temperature are; the larger the number of nozzle holes is, the higher the raw NOx emission is; as for the soot formation, because the speed of the post-oxidation is much faster with larger number of nozzle holes, the emission would become better; Lastly, the larger the number of nozzle holes is, the better the fuel economy is. The reason behind is that the atomizing effect and the combustion process are both improved with larger number of nozzles holes, producing a faster and more complete combustion and heat release process.②The larger the injection advance angle is, the sooner the fuel atomization happens, and the more combustible premixed gas is generated during the ignition delay period, the higher the cylinder pressure rise rate is, so is the higher peak cylinder pressure, the higher cylinder temperature, with much more raw NOX emissions and much lower Soot emissions. If the injection timing is reasonable, the combustion heat release curve would be ideal, the best E.E.R value can be achieved, with the best fuel economy.③The effects of pre-injection and main injection period: with increased pre-injection quantity, NOX formation decreases at the beginning but then increases in the end; since more compression power is consumed in the compression stroke, the economy is getting worse with too much pre-injection quantity.④Comparing between the different fuel spray angles, i.e.50,60,70,80and90degrees, indicates that when the beam angle is at60o, the mount of Soot will be the minimum, mainly because of the lower rate of Soot generates and the higher rate of oxidation. This phenomenon is different from conventional engines, mainly due to higher fuel beam angle, the amount of fuel which hits the piston top is reduced, this changed the law that the fuel spray speed increases with the spray beam angle in a conventional engine.更多还原