S195柴油机燃用纯甲醇、采用多火花助燃的研究

本文介绍了在S 195柴油机上燃用纯甲醇、采用多火花助燃的研究结果。选取合适的火花塞电极间隙、电极间隙与喷注空间匹配和正确的喷油、点火定时是保证非均相可燃混合气可靠着火燃烧的关键。当优化了上述参数后,发动机能在广阔的转速、负荷范围内稳定运行。燃用纯甲醇的柴油机与燃用柴油时热效率接近,并能实现无烟燃烧。试验表明,这种高压缩比、强涡流的柴油机对多火花点火系统有更好的适应性。     

Experimental investigations on combustion, performance and emissions characteristics of neat karanji biodiesel and its methanol blend in a diesel engine

The increased focus on alternative fuels research in the recent years are mainly driven by escalating crude oil prices, stringent emission norms and the concern on clean environment. The processed form of vegetable oil (biodiesel) has emerged as a potential substitute for diesel fuel on account of its renewable source and lesser emissions. The experimental work reported here has been carried out on a turbocharged, direct injection, multi-cylinder truck diesel engine fitted with mechanical distributor type fuel injection pump using biodiesel-methanol blend and neat karanji oil derived biodiesel under constant speed and varying load conditions without altering injection timings. The results of the experimental investigation indicate that the ignition delay for biodiesel-methanol blend is slightly higher as compared to neat biodiesel and the maximum increase is limited to 1 deg. CA. The maximum rate of pressure rise follow a trend of the ignition delay variations at these operating conditions. However, the peak cylinder pressure and peak energy release rate decreases for biodiesel-methanol blend. In general, a delayed start of combustion and lower combustion duration are observed for biodiesel-methanol blend compared to neat biodiesel fuel. A maximum thermal efficiency increase of 4.2% due to 10% methanol addition in the biodiesel is seen at 80% load and 16.67 s⁻¹ engine speed. The unburnt hydrocarbon and carbon monoxide emissions are slightly higher for the methanol blend compared to neat biodiesel at low load conditions whereas at higher load conditions unburnt hydrocarbon emissions are comparable for the two fuels and carbon monoxide emissions decrease significantly for the methanol blend. A significant reduction in nitric oxide and smoke emissions are observed with the biodiesel-methanol blend investigated.     

Effect of pressure and equivalence ratio on the ignition characteristics of dimethyl ether-hydrogen mixtures

Experimental and numerical study on the effect of pressure and equivalence ratio on the ignition delay times of the DME/H₂/O₂ mixtures diluted in argon were conducted using a shock tube and CHEMKIN II package at equivalence ratios of 0.5–2.0, pressures of 1.2–10 atm and hydrogen fractions of 0–100%. It was found that the measured ignition delay times of the DME/H₂ mixtures demonstrate three ignition regimes. For the DME/H₂ mixture at XH₂$X_{{\text{H}}_2}$ ≤80%, the ignition is controlled by the DME chemistry and ignition delay times present a typical Arrhenius pressure dependence and weak equivalence ratio dependence. For the DME/H₂ mixture at 80% < XH₂$X_{{\text{H}}_2}$ < 98%, the ignition is controlled by the combined chemistries of DME and hydrogen, and the ignition delay times give higher ignition activation energy at higher pressures and a typical Arrhenius equivalence ratio dependence. However, for the DME/H₂ mixture at XH₂$X_{{\text{H}}_2}$≥98%, the ignition is controlled by the hydrogen chemistry and ignition delay time shows complex pressure dependence and weak equivalence ratio dependence. Comparison of the measurements of neat DME and neat hydrogen with the calculations using three generally accepted mechanisms, NUIG Aramco Mech 1.3 [1], LLNL DME Mech 2, 3 and 4 and Princeton-Zhao Mech [5], shows that NUIG Aramco Mech 1.3 gives the best predictions and can well capture the pressure and equivalence ratio dependence at various hydrogen fractions. The sensitivity and normalized H-radicals consumption analysis were performed using NUIG Aramco Mech 1.3 and the key reactions that control the ignition characteristics of DME/H₂ mixtures were revealed. Further chemical kinetic analysis was made to interpret the ignition delay time dependence on pressure and equivalence ratio at varied hydrogen fractions.     

柴油在甲醇/空气高温热氛围中的着火和燃烧特性

在定容燃烧弹上进行了柴油分别在空气和在甲醇/空气预混均质混合气中着火燃烧的实验研究.结果表明,与空气热氛围相比,甲醇混合气热氛围延长了柴油的滞燃期和加长了火焰浮起高度.采用正庚烷-甲醇的详细化学反应机理,利用数值模拟的方法计算了零维模型中正庚烷及正庚烷加甲醇的燃烧反应过程和中间产物历程.其结果表明,甲醇的加入使得正庚烷的高低温放热反应开始时刻后移,滞燃期延长,低温放热反应峰值明显下降,且无明显的负温度系数区,高温反应放热峰值高于其在空气氛围中,归其原因在于甲醇大量消耗着火的OH自由基,并将其转化为低温氧化中不活跃的H2O2,使得系统着火前反应活性减弱.实验和计算结果均表现出甲醇具有抑制柴油及其参比燃料着火的作用.     

甲醇发动机的点火正时和喷射正时优选的试验研究

缸内喷射、火花助燃甲醇发动机是在缸内形成一种层状分布的不均匀混合气，为获得优良的燃烧和排放性能，存在一个最佳的点火和喷射正时。此时着火延迟期最短，缸内混合气浓、稀分布最合理，平均火焰传播速度最快，热效率最高，效率和排放折衷最好。本文详细介绍了点火正时和喷射正时的优选过程及对缸内混合气浓度分布及燃烧过程的影响。     

用汽油和甲醇燃油分层拓展HCCI燃烧高负荷的试验研究

在一台单缸HCCI发动机上研究了进气道喷射汽油缸内喷射甲醇形成汽油甲醇燃油分层的HCCI燃烧排放特性,探索了其拓展HCCI燃烧高负荷的潜力。试验结果表明:在汽油HCCI燃烧中喷射甲醇能够有效降低缸内混合气的温度,推迟着火时刻,延长燃烧持续期,从而降低压力升高率和缸内最高燃烧压力,有利于拓展HCCI燃烧高负荷。一定的HCCI负荷工况存在最佳的汽油甲醇比例,且汽油甲醇最佳比例随着负荷的增加不断减小。在最大压力升高率0.5MPa/°CA和较高的指示效率的限制下,自然吸气条件下采用汽油和甲醇燃油分层的HCCI燃烧最高负荷比汽油HCCI燃烧提高了近50%,达到0.62MPa。     

涡流室式柴油机燃用纯甲醇的研究

本文介绍了涡流室式柴油机采用电热塞点火方式燃用纯甲醇的研究.通过设计以电热塞为热源的热面点火系统,采用部分稳定氧化锆(PSE)涂层的涡流室,以及改变涡流室通道的形状,使发动机燃用甲醇时的性能得到改善,在各工况下均降低了电热塞的功率和燃料消耗率(按热值计).发动机燃用甲醇时的NO_x排放量比燃用柴油时显著降低,但HC和CO排放量却有一定程度的上升.     

HCCI发动机着火时刻控制参数的研究

以二甲醚、甲烷/丙烷混和物、异辛烷/正庚烷混合物作为燃料，模拟研究了燃料成分、压缩比、燃空当量比、进气温度、进气压力对均质充量压燃（HCCI）发动机着火时刻的影响。计算结果表明：随燃料十六烷值的增加，着火延迟期减小；随燃料辛烷值的增加，着火延迟期增加。而压缩比，燃空当量比，进气温度对三种燃料着火时刻有显著影响。进气压力的变化对高十六烷值的燃料着火延迟期影响较小，但对辛烷值高的气体燃料着火延迟期影响比较明显。     

Feasibility of compression ignition for hydrogen fueled engine with neat hydrogen-air pre-mixture by using high compression

Compression ignition of hydrogen engines with a homogeneous pre-mixture is a promising method to enhance the thermal efficiency as well as to reduce unique NO_x exhausted from the engine due to spatial reaction of the mixture. However, hydrogen gas has a relatively high self-ignition temperature. Therefore, compression ignition for a neat hydrogen-air pre-mixture is considered impossible to achieve without additives. Research on this has not yet been attempted for this reason.