多缸汽油HCCI发动机燃烧循环变动的研究

在均质混合气压燃(HCCI)发动机研发中多缸不均匀性是一个重要的问题.通过在缸内直喷汽油机(GDI)上采用两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,研究了汽油HCCI发动机在不同燃烧模式下的多缸燃烧循环波动特性.研究结果表明:在汽油机中低负荷典型工况下,HCCI燃烧pi的缸内循环波动率小于2%,缸间循环波动率小于3%;HCCI发动机缸间循环波动主要受进气量的影响,与SI燃烧模式相比,采用稀燃模式的汽油HCCI燃烧缸间循环波动较小,HCCI燃烧的压力升高率和最高燃烧压力的循环波动率较小.     

多缸汽油机倒拖示功图分析

简要介绍了作者开发的可对多缸汽油机各缸压力进行同时检测的测量系统;报导了利用该系统对４９２ Ｑ Ｃ汽油机各缸倒拖压力进行测量及比较分析的结果。在转速分别为ｎ＝ ９９９ ｒ／ｍ ｉｎ、１ ３９３ ｒ／ｍ ｉｎ、２ ３１８ ｒ／ｍ ｉｎ、３ ８０４ ｒ／ｍ ｉｎ 的条件下,测量了节气门开度变化时的各缸倒拖压力,比较分析了可近似反映各缸进气量大小的各缸倒拖压力最大值。结果表明,采用作者开发的多缸发动机各缸压力同时测量系统可有效地对多缸发动机倒拖时的缸间充气量差异进行评价。试验用发动机的第１ 缸倒拖最大压力的变动大于第２ 缸,第３ 缸的倒拖最大压力的变化大于第４ 缸;第４ 缸的进气量最大,第２ 缸的进气量最小;各缸的倒拖最大压力偏差率在－ ９％ ～６％ 的范围内变化     

船用微引燃双燃料发动机多缸平衡控制的试验

针对船用微引燃双燃料发动机多缸不平衡问题,开展了多缸平衡控制的仿真与试验,建立发动机仿真模型,用试验测量的进气歧管压力验证了模型精度,基于仿真模型定量分析了发动机各缸燃气量和过量空气系数的差异.采用燃气喷射量补偿的方法对各缸进行缸平衡控制的研究,分别以各缸爆发压力、平均指示有效压力(IMEP)和排气温度为控制变量修正各缸燃气喷射脉宽.研究表明:各缸燃气喷射量相对偏差最大可达2.76%;各平衡模式下其各缸对应的控制变量相对偏差均有效降低,其中爆发压力平衡时各缸爆压不均匀系数低于1.2%,IMEP平衡时IMEP不均匀系数低于0.8%,排气温度平衡时各缸排气温度差异控制在11℃之内;考虑发动机运行的稳定性和安全性因素,在中、低负荷时激活IMEP平衡模式以降低失火或弱燃的概率;在高负荷时激活爆压平衡模式以降低气缸压力异常升高的概率.     

读者问答

<正> 1 多缸柴油机大修后各缸压缩比为何不同? 答,不少拖拉机和汽车修理厂常出现多缸发动机大修后车速不稳、机身振动和敲缸等现象。经检查,曲柄连杆机构、配气机构、燃油系统、缸体和缸盖等运动件和密封件原都符合说明书上的技术要求。照理不该出现的故障却时有发生,这些大修发动机经气缸压力表测试后发现各缸压力不一致,若     

瞬变工况下多缸汽油机各缸进气均匀性

采用动态压力实测与数值计算相耦合的方法,在路试工况下对一台搭载在乘用车上的多缸汽油机各缸进排气参数进行连续检测,得到随循环数变化的各缸气体状态变化历程.通过对比分析各缸进、排气参数(如缸内新鲜充量、残余废气量等)差异性的变化范围及影响因素,揭示了各缸残余废气系数不均匀性的变化规律和诱因,以及对进气性能的影响.结果表明,在中低转速和负荷区域,各缸残余废气系数相对偏差在±10%,以内,此时主要受进气平均压力的影响;在高速高负荷区域,各缸残余废气系数相对偏差在±20%,以内,此时主要受排气压力波的影响.优化发动机排气系统结构和布置方式,是改变各缸进气均匀性的重要途径.     

电控汽油机起动及暖机工况燃烧状况的分析统计

根据在电控汽油机上实测的气缸压力、瞬时转速等参数 ,对汽油机起动及怠速暖机过程中正常燃烧、不完全燃烧及失火时相应的示功图及瞬时转速波形的特点进行了分析。结果表明 :汽油机冷起动后 ,缸内处于不稳定的燃烧状态 ,出现不完全燃烧或失火 ,并且各缸间的燃烧稳定性相差很大。     

小缸径多缸柴油机行业现状研讨

1前言通常小缸径多缸柴油机(以下简称多缸小柴)系指气缸直径75～98、气缸数≥2缸的系列机型。多缸小柴在全国内燃机系列型谱中分属高速柴油机第3系列(D=75～82)、第4系列(D=85～90)和第5系列(D=93～98)。至今,机电部先后公布两批高速柴油机列入国家内燃机系列产品。多缸小柴已被确认为国家内燃机系列产品见表。     

根据飞轮瞬时转速诊断发动机各缸燃烧差异的探讨

对于在用的汽车、拖拉机与工程机械用发动机来说，是无法采用示功器同时测录各缸示功图并据以评判各缸的燃烧过程的。本文介绍了一种根据飞轮瞬时转速诊断发动机各缸燃烧差异的方法，并以Ｒ４１０２及Ｒ６１０２工程机械用柴油机为例，研究探讨了根据多缸机飞轮瞬时转速推求各缸间燃烧压力差异的原理。文中对推求偏差进行了分析讨论，得出在压缩上止点后１０℃Ａ～８０℃Ａ期间，各缸间燃烧压力差值的推求偏差在±０．１ＭＰａ。     

汽油机点火提前调整特性模拟分析

论文利用AVL Boost建立了四缸四冲程汽油机的热力学仿真模型,并从气缸压力的变化及缸内气流运动的角度出发,分析了点火提前角对最高燃烧压力的影响,从而确定各转速下的点火提前角变化范围.在此基础上进一步分析了点火提前角对汽油机动力性及经济性的影响,以期确定较为合理的点火提前特性匹配方案.分析结果显示:随着转速的增加,增大点火提前角,有利于提高发动机的动力性和燃油经济性;合理的匹配不同转速下的点火提前角,可扩大汽油机的理想工作范围.     

内燃机名词、术语(五)

36.气缸直径(cylinder bore) 气缸的内径,简称缸径。用D表示,单位为mm(见图1中D)。内燃机的缸径应符合系列型谱的规定,特殊情况如果不符合系列型谱的规定,缸径的个位数出是0或5,最好不要小数。汽油机,由于燃烧过程的特点,气缸直径一般不大于120mm;柴油机,也由于燃烧     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

The Solar Office in context

The goal of sustainability in buildings can only hope to be realised if buildings are designed to both conserve and generate energy. The Solar Office at Doxford International is designed to minimise the use of energy while its external fabric is designed to replace such energy that is used. The recently completed building is now subject of a comprehensive monitoring programme. The programme covers both the performance of the 73 kW_p photovoltaic installation and the environmental conditions within the building as a whole. Hour by hour findings are posted on a dedicated web site. Photovoltaics could have the same impact on building form and layout as the invention of the passenger lift at the end of the last century.     

Hydrogen recovery from the photovoltaic electroflocculation-flotation process for harvesting Chlorella pyrenoidosa microalgae

In this paper, an integrated process using photovoltaic power to harvest microalgae by electro-flocculation (EF) and hydrogen recovery is presented. It is mainly favorable in regions with high solar radiation. The electro-flocculation efficiency (EFE) of Chlorella pyrenoidosa microalgae was investigated using various types of electrodes (aluminum, iron, zinc, copper and a non-sacrificial electrode of carbon). The best results regarding the EFE, and biomass contamination were achieved with aluminum and carbon electrodes where the electrical energy demand of the process for harvesting 1 kg of algae biomass was 0.28 and 0.34 kWh, respectively, while the energy yield of harvested hydrogen was 0.052 and 0.005 kWh kg^?1, respectively. The highest harvesting efficiency of 95.83 ± 0.87% was obtained with the aluminum electrode.The experimental hydrogen yields obtained were comparable with those calculated from theory. With a low net energy demand, microalgae EF may be a useful and low-cost technology.     

Electrochemical behavior of Mg–Li,Mg–Li–Al and Mg–Li–Al–Ce in sodium chloride solution

Mg–Li, Mg–Li–Al and Mg–Li–Al–Ce alloys were prepared and their electrochemical behavior in 0.7 M NaCl solutions was investigated by means of potentiodynamic polarization, potentiostatic current–time and electrochemical impedance spectroscopy measurements as well as by scanning electron microscopy examination. The effect of gallium oxide as an electrolyte additive on the potentiostatic discharge performance of these magnesium alloys was studied. The discharge activities and utilization efficiencies of these alloys increase in the order: Mg–Li < Mg–Li–Al < Mg–Li–Al–Ce, both in the absence and presence of Ga₂O₃. These alloys are more active than commercial magnesium alloy AZ31. The addition of Ga₂O₃ into NaCl electrolyte solution improved the discharging currents of the alloys by more than 4%, and enhanced the utilization efficiencies of the alloys by more than 6%. It also shortened the transition time for the discharge current to reach to a steady value. Electrochemical impedance spectroscopy measurements showed that the polarization resistance of the alloys decreases in the following order: Mg–Li > Mg–Li–Al > Mg–Li–Al–Ce. Mg–Li–Al–Ce exhibited the best performance in term of activity, utilization efficiency and activation time.     

Temperature dependence of the enthalpy of formation of metal hydrides characterized by an excess volume

A universal framework to calculate the temperature dependence of the excess enthalpy present in regions characterized by an excess volume is calculated for metals and metal hydrides. At high temperatures, the different contributions from the pressure–volume, heat capacity, entropy and work associated with the thermal expansion are studied separately and their magnitudes and signs are compared. It is found that the pressure–volume contribution opposes and dominates the other three contributions at both high temperature and excess volume, and it is thus found that this contribution becomes the leading temperature dependent contribution to the enthalpy of a material. The conditions under which a temperature change will reduce the enthalpy of formation of metal hydrides are also given and the Mg/MgH₂ system is studied as an example. Excluding the heat capacity contribution, an increase in temperature tends to offset the effect of the excess volume on the enthalpy of formation. It is also demonstrated that the impact of temperature will be more favorable to a reduction of the enthalpy of formation if a large fraction of the metal hydride is in a state of small excess volume compared to a small fraction of the hydride in a state of high excess volume.     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Tailored solar optics for maximal optical tolerance and concentration

Recently identified fundamental classes of dual-mirror double-tailored nonimaging optics have the potential to satisfy the pragmatic exigencies of concentrator photovoltaics. Via a comprehensive survey of their parameter space, including raytrace verification, we identify champion high-concentration high-efficiency designs that offer unprecedented optical tolerance (i.e., sensitivity to off-axis orientation) - a pivotal figure-of-merit with a basic bound that depends on concentration, exit angle, and effective solar angular radius. For comparison, results for the best corresponding dual-mirror aplanatic concentrators are also presented.