甲醇发动机排放特性的研究

以一台电控M85甲醇燃料发动机为研究对象,在发动机台架上,采用废气分析仪和气相色谱仪,分别研究了甲醇发动机的常规排放和非常规碳氢排放。研究表明:M85甲醇发动机可以实现很低的常规排放,在非常规碳氢排放方面,甲醛在总碳氢排放占有较大的比例,而甲醇的排放接近0。三效催化反应器对甲醛的净化率较低,并且存在随负荷增大,净化率降低的趋势。甲醇的净化率始终接近100％。     

高比例甲醇汽油的发动机台架试验研究

M100是一种具有代表性的高比例甲醇汽油。通过在发动机上分别燃用93#汽油和M100甲醇汽油两种燃料,对比两种燃料的动力性、经济性以及排放性能,并对其进行分析。试验表明,在发动机上使用灵活燃料控制器后,M100甲醇汽油具有良好的适应性。与燃用93#汽油相比,M100甲醇汽油的动力性和经济型提高。常规排放的尾气中CO,HC和NOx显著降低,而非常规排放物甲醛排放增加。     

甲醇裂解气发动机排放性能试验

以一台点火式电控发动机为研究对象,甲醇裂解装置安装在发动机排气管上回收废气余热,进行了甲醇裂解气在点燃式发动机上应用燃烧的排放性能试验研究.研究表明:通过甲醇裂解气在发动机上的稀燃,其动力性较之原机稍微有所下降,下降幅度仅为5%;甲醇裂解气发动机利用回收废气余热以及稀燃条件减少泵吸损失的优势,对比与原汽油机经济性有较大的提高.同时,稀燃可使NOx排放较原汽油机降低90%;与汽油机CO对比,降低了50%左右,而HC排放接近汽油;此外,甲醇裂解气发动机尾气中的非常规排放物甲醛的体积分数低于汽油机,经过尾气处理后,甲醛排放接近零排放,原机三效催化转化器对甲醛的消除有很好的效果.     

汽油机燃用甲醇汽油的芳香族碳氢排放试验研究

通过汽油机直接燃用甲醇汽油的发动机台架试验,并应用FTIR排放分析仪,对不同掺混比例甲醇汽油在不同工况下的芳香族碳氢排放进行了检测。试验结果表明:发动机使用甲醇汽油作为燃料,催化器前的排放中,芳香族碳氢的含量随着甲醇掺混比例的升高而减少;对于同一种甲醇汽油燃料,芳香族碳氢排放随发动机转速升高而下降;相同转速下,芳香族碳氢排放随负荷变化不超过20%;芳香族碳氢排放随发动机排气温度升高呈先减后增的趋势,拐点在630℃左右。催化器前后的芳香烃排放变化表明:三效催化器对芳香烃有较好的催化转化效果,大部分工况下芳香烃催化转化率在90%以上。     

铜基/钯基催化剂甲醇裂解气发动机性能

以一台点火式电控发动机为原型机,在其排气管上串接一甲醇裂解器,利用废气余热裂解甲醇制取裂解气,然后作为发动机燃料.在改造后的发动机上,分别进行了铜基和钯基催化剂作用下甲醇裂解为裂解气的应用性能研究.结果表明,铜基或钯基催化剂裂解气发动机动力性能够达到原机95％以上,裂解气发动机当量燃料消耗率较之汽油机下降了24％左右,在仅用前级催化转化器时发动机碳氢(HC)排放和一氧化碳(CO)排放仅为原机的10％左右,氮氧化物(NOx)排放为原机的20％左右.与铜基催化剂相比,钯基催化剂裂解气发动机性能更好,而且其催化裂解效率、可靠性、催化剂附着性等方面均优于前者.     

柴油/甲醇组合燃烧增压共轨发动机的燃烧特性和排放特性

在增压共轨发动机上采用柴油,甲醇组合燃烧(DMCC)方式进行燃烧特性分析和排放特性分析.对DMCC模式下放热率、缸内压力变化和p-V图的分析表明,DMCC模式具有吸热汽化、推迟着火时间、提高定容燃烧度、降低排气温度等优点,从而大幅度提高了燃料的燃烧效率.对M100(纯甲醇)和M90(含水10%的甲醇)的排放量进行检测,表明M90比M100更能降低甲醛、NOJ、HC和CO排放.     

稀燃对甲醇直喷点燃式发动机性能的影响北大核心CSCD

将一台增压直喷米勒循环汽油机改制成高压缩比(13.8)甲醇直喷点燃式发动机,在2 750 r/min、平均有效压力(brake mean effective pressure,BMEP)为1.1 MPa及1.5 MPa工况下研究了稀燃对甲醇直喷发动机燃烧、排放及热效率的影响。结果表明:随过量空气系数λ增大,甲醇直喷发动机滞燃期和燃烧持续期逐渐延长,高稀释率下燃烧滞燃期和持续期明显短于汽油原机。在1.1 MPa BMEP工况下,发动机的稳定燃烧极限从汽油原机的λ=1.5拓宽到甲醇直喷的1.7以上。气体排放方面,随λ增大,甲醇直喷发动机HC排放逐渐增加,而CO排放先降低后升高,在λ=1.1附近CO排放最低。与汽油原机相比,甲醇直喷发动机在各过量空气系数下均表现出更低的NOx、HC及CO排放。热效率方面,发动机在BMEP为1.1 MPa下,汽油原机和甲醇直喷的最大有效热效率分别为39.8%和44.1%,热效率绝对值分别较当量比燃烧提升2.5%和3.2%。BMEP提高到1.5 MPa后,甲醇直喷发动机在λ=1.4实现了44.5%的最大有效热效率。     

甲醇燃料在车用发动机上的应用研究

结合甲醇燃料的理化特性,分别在495Q和JT468Q汽油发动机进行了燃用高比例M85甲醇汽油燃料和全甲醇燃料的对比试验。试验结果表明：直接燃烧定比例甲醇燃料时,功率和扭矩都略有提高;提高压缩比后,功率和扭矩都大幅度提高,燃油消耗也大幅度降低、排放明显改善。     

车用甲醇裂解器设计及其对发动机排放性能影响的研究

甲醇是一种清洁可再生能源,利用发动机尾气余热提高燃料热值是一种新型的节能方式。基于醇氢动力系统,对三种不同结构的甲醇裂解器进行数值模拟,且通过试验选择研究了安装螺旋管式甲醇裂解器发动机的排放性能。研究结果表明,螺旋管式甲醇裂解器较直管式和U型管式换热效果更好,能够满足车载甲醇裂解器对热量的需求。相同负荷下,随着甲醇替代比的增加,CO排放浓度呈现先降低后升高的趋势,HC排放较原机下降了28.7%,NOx排放增加了16.9%。     

甲醇/汽油混合燃料发动机非常规排放成分测量方法研究

对使用气相色谱仪检测甲醇／汽油混合燃料发动机排气中醇醛类排放方法进行了研究，优化选择了采样方法、载气流速、柱温等参数，证明安装PEG色谱柱的GC2010完全可以对甲醇／汽油混合燃料发动机排气中的醇、醛进行精确的检测分析。发动机尾气测试结果表明，汽油机燃用M10混合燃料时，排气中的甲醛中低负荷高达0．2mg／L。此外，发动机燃用市售汽油和M10两种燃料时，排气中的甲醇、乙醇和乙醛量相差在10％左右，经三效催化转化器后，可以被控制到接近零排放的水平。     

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.     

Contents in Volume 23,2014

<正>~~     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

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.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.