EGR对汽油机HCCI燃烧过程的影响机理

以甲苯掺比燃料作为汽油燃料替代混合物,利用零维单区化学动力学模型,在EGR率为20％时,分析和研究EGR中添加不同摩尔分数的CO、NO和CH2O对汽油机HCCI燃烧的化学作用,进而分析添加物对生成物中有害物质的影响.通过模拟分析可知,不同摩尔分数的添加物可以使气缸内的温度和压力有一定程度的提高,同时能够降低废气中的CO、NOx和UHC等有害物质的排放.     

Experimental investigations on a hydrogen diesel homogeneous charge compression ignition engine with exhaust gas recirculation

In this experimental study, hydrogen was inducted along with air and diesel was injected into the cylinder using a high pressure common rail system, in a single cylinder homogeneous charge compression ignition engine. An electronic controller was used to set the required injection timing of diesel for best thermal efficiency. The influences of hydrogen to diesel energy ratio, output of the engine and exhaust gas recirculation (EGR) on performance, emissions and combustion were studied in detail. An increase in the amount of hydrogen improved the thermal efficiency by retarding the combustion process. It also lowered the exhaust emissions. Large amounts of hydrogen and EGR were needed at high outputs for suppressing knock. The range of operation was brake mean effective pressures of 2–4 bar. The levels of HC and CO emitted were not significantly influenced by the amount of hydrogen that was used.     

A novel approach to reduce hydrocarbon emissions from the HCCI engine

A novel approach is proposed and investigated to reduce unburned hydrocarbon emissions from a homogeneous charge compression ignition (HCCI) engine by using in-cylinder catalysts. The combustion and emission characteristics of this HCCI engine are numerically simulated in three cases, i.e., the baseline engine with an uncoated piston crown, the engine with a platinum coating on the top and side surfaces of the piston crown (full coated case) and the engine with a platinum coating only on the side surface of the piston crown (partial coated case). A detailed reaction mechanism of methane oxidation on platinum catalyst is adopted. The results show that the unburned hydrocarbons of the HCCI engine arise primarily from sources near the combustion chamber wall, such as flame quenching at the entrance of crevice volumes and at the combustion chamber wall, and the adsorption and desorption of methane into and from the cylinder wall. The in-cylinder catalyst gives rise to a reduction of exhaust unburned hydrocarbon (UHC) emissions by approximately 15% with the full coating of platinum catalyst on the piston crown, however, with the partial coating, the in-cylinder catalyst can reduce the UHC emissions by approximately 20%.     

A study on the reduction of exhaust emissions through HCCI combustion by using a narrow spray angle and advanced injection timing in a DME engine

This paper describes the combustion and emission characteristics as well as engine performance according to the narrow spray angle and advanced injection timing for homogeneous charge compression ignition (HCCI) combustion in dimethyl ether (DME) fueled diesel engine. The bowl shape of the piston head was modified to apply the narrow spray angle and advanced injection timing. The spray, combustion and emission characteristics in a DME HCCI engine were calculated by using numerical method of the KIVA-3 V code coupled with the detailed chemical kinetic model of DME oxidation. Model validation was conducted by a comparison of experimental results for the accurate prediction. The injection timing ranging from BTDC 80° to BTDC 10° and two fuel masses were selected to evaluate the combustion, emission and engine performance. The calculated results were in good accordance with the experimental results of the combustion and emissions of the engine. Nitrogen oxide (NOx) emissions at injection timing before BTDC 30° remarkably decreased, while hydrocarbon (HC) and carbon monoxide (CO) emissions at an injection timing of BTDC 70° showed high levels. Also, the IMEP and ISFC have decreasing and increasing patterns respectively as the injection timing was advanced.     

醇醚双燃料发动机均质压缩燃烧试验研究

以ZS195型直喷式柴油机为原型机,开展了进气道喷射醇醚混合燃料HCCI试验研究。试验研究结果表明,甲醇的添加能够抑制二甲醚(DME)低温反应,降低缸内最大爆发压力和燃烧温度,推后主燃烧反应时刻,解决二甲醚的过快和过早燃烧,可以有效调节HCCI着火时刻和扩展其运行工况。双燃料HCCI发动机的指示热效率最高可以达到49%左右,超过原柴油机10%。通过调节甲醇喷油量,可实现HCCI燃烧着火点可控以及扩展HCCI发动机运行负荷范围。     

Double-Wiebe function: An approach for single-zone HCCI engine modeling

Single-zone Wiebe-function HCCI combustion models tend to over-predict the peak cylinder pressure. The over-prediction arises because it is not possible for the standard Wiebe function to fully match both the slower combustion (i.e. the large spread of autoignition times) that occurs in the cooler boundary regions adjacent to the walls and the faster combustion (small spread of autoignition times) in the hot core. The slower combustion by the wall is commonly modeled with a multi-zone approach. The aim of this work was to improve the ability of a single-zone model to predict cylinder pressure without introducing a separate wall zone. This was accomplished by using, within a single zone, a double-Wiebe function combustion model in which most of the fuel burns as usual but a minor fraction (typically 10–20%) burns at a reduced rate. In the present article, cylinder pressure traces predicted by using both standard and double-Wiebe functions are compared to experimental pressure traces obtained from a Ricardo Hydra HCCI engine. The best agreement with the experiments was obtained by using double-Wiebe function approach.     

车用汽油机的节油潜力及高效汽油机的可行性

本文通过对未来30年的主要交通能源和乘用车动力主流产品的分析,指出研发汽油机节油技术的重要性。车用汽油机还有很大节油潜力,尤其是均质压燃汽油机克服了点燃燃烧对发动机空燃比和压缩比的限制,能够提高汽车平均燃油效率达25%以上。均质压燃的燃烧时间能在各种情况下得到可靠控制,因而能够在车辆上应用。目前国内车用发动机技术研发现状不容乐观。要避免在10年内陷入困境,应建立车用发动机创新研究的体制。     

耦合动力学的微发动机燃烧过程研究

基于丙烷燃烧化学动力学机理并考虑传热、漏气过程对微型自由活塞发动机均质充量压缩燃烧(HC-CI)过程进行数值模拟研究,结合Star-CD/Kinetics软件实现了自由活塞运动与燃烧过程耦合的计算方法,在此基础上,详细研究了不同参数下微型发动机燃烧过程压力、温度的变化规律,探讨了微发动机循环过程中传热损失和混合气泄漏对微尺度燃烧过程的影响,研究结果表明:当量比、压缩比和自由活塞频率显著影响微发动机燃烧过程,传热损失对微HCCI自由活塞发动机燃烧过程的影响不大,而混合气泄漏损失的影响比较明显.     

Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

HCCI combustion has been drawing the considerable attention due to high efficiency and lower nitrogen oxide (NO_x) and particulate matter (PM) emissions. However, there are still tough challenges in the successful operation of HCCI engines, such as controlling the combustion phasing, extending the operating range, and high unburned hydrocarbon and CO emissions. Massive research throughout the world has led to great progress in the control of HCCI combustion. The first thing paid attention to is that a great deal of fundamental theoretical research has been carried out. First, numerical simulation has become a good observation and a powerful tool to investigate HCCI and to develop control strategies for HCCI because of its greater flexibility and lower cost compared with engine experiments. Five types of models applied to HCCI engine modelling are discussed in the present paper. Second, HCCI can be applied to a variety of fuel types. Combustion phasing and operation range can be controlled by the modification of fuel characteristics. Third, it has been realized that advanced control strategies of fuel/air mixture are more important than simple homogeneous charge in the process of the controlling of HCCI combustion processes. The stratification strategy has the potential to extend the HCCI operation range to higher loads, and low temperature combustion (LTC) diluted by exhaust gas recirculation (EGR) has the potential to extend the operation range to high loads; even to full loads, for diesel engines. Fourth, optical diagnostics has been applied widely to reveal in-cylinder combustion processes. In addition, the key to diesel-fuelled HCCI combustion control is mixture preparation, while EGR is the main path to achieve gasoline-fuelled HCCI combustion. Specific strategies for diesel-fuelled, gasoline-fuelled and other alternative fuelled HCCI combustion are also discussed in the present paper.     

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.