Effect of equivalence ratio on diesel direct injection spark ignition combustion

Aviation heavy-fuel spark ignition(SI)piston engines have been paid more and more attention in the area of small aviation.Aviation heavy-fuel refers to aviation kerosene or light diesel fuel,which is safer to use and store compared to gasoline fuel.And diesel fuel is more suitable for small aviation application on land.In this study,numerical simulation was performed to evaluate the possibility of switching from gasoline direct injection spark ignition(DISI)to diesel DISI combustion.Diesel was injected into the cylinder by original DI system and ignited by spark.In the simulation,computational models were calibrated by test data from a DI engine.Based on the calibrated models,furthermore,the behavior of diesel DISI combustion was investigated.The results indicate that diesel DISI combustion is slower compared to gasoline,and the knock tendency of diesel in SI combustion is higher.For a diesel/air mixture with an equivalence ratio of 0.6 to 1.4,higher combustion pressure and faster burning rate occur when the equivalence ratios are 1.2 and 1.0,but the latter has a higher possibility of knock.In summary,the SI combustion of diesel fuel with a rich mixture can achieve better combustion performance in the engine.

Numerical Study on the Effects of Contraction Ratio in a Two-Phase Flow Injection Nozzle

The Euler-Euler numerical method was used to investigate the effects of contraction ratio on twophase flow mixing with mass transfer in the flow injection nozzle. The geometric shape of the nozzle was modified to improve carbonation efficiency. A gas inlet hole was created to increase the flow mixing of CO2 with water. A nozzle throat was also introduced to increase the gas dissolution by increasing flow rates. Various contraction ratios of nozzle throat, inlet gas and liquid velocities, and gas bubble sizes were employed to determine their effects on gas hold-up, gas concentration, and mass transfer coefficient. Results revealed that the flow injection nozzle with high contraction ratios improved carbonation because of high gas hold-up. Gas concentration was directly related to contraction ratio and gas flow velocities. Carbonation reduced when high liquid velocities and large gas bubbles were employed because of inefficient flow mixing. This study indicated that flow injection nozzle with large contraction ratios were suitable for carbonation because of their ability to increase gas hold-up, gas concentration, and mass transfer coefficient.

A New Method for the Dynamic Reserves of Gas Condensate Reservoir Using Cyclic Gas Injection Based on the Effects of Reinjection Ratio and Water Influx

As we all know, cyclic gas injection is one of the most effective development methods to improve condensate oil recovery. When dealing with the calculation of the reserves, the injection-production differences and water influx create great influence on the accuracy. Based on the existing research, we proposed a new material balance equation which considered the differences of composition between produced and injected fluids and the effect of water influx, and a solution was provided in this paper. The results of the method are closer to the actual situation because they are built on the law of conservation of mass, and the using of curve fitting method can not only avoid the use of water influx coefficient but also obtain the water influx rate and reserves at the same time. The YH-23 gas condensate reservoir is taking as a typical subject to do the research, which has been exploited by cycle gas injection for 14 years. Three different methods are used to calculate the reserves, and the results show that the method proposed in this paper has minimum error of 2.96%.

A numerical investigation into the effect of altering compression ratio, injection timing, and injection duration on the performance of a diesel engine fuelled with diesel-biodiesel-butanol blend

Using renewable fuels for diesel engines can reduce both air pollution and dependence on fossil fuels.A computer simulation was constructed to predict the performance,combustion characteristics,and NOx emissions of a diesel engine fuelled with diesel-biodiesel-butanol blends.The simulation was validated by comparing the modelling results against experimental data and a good agreement between the results was found.The fuels used for the validation were diesel(B0),biodiesel(B100),diesel-biodiesel blend(B50),and two diesel-biodiesel-butanol blends with 45%diesel-45%biodiesel-10%butanol(Bu10)and 40%diesel-40%biodiesel-20%butanol(Bu20)by volume.Experimental results showed that the addition of butanol reduced NOx emissions but deteriorated the engine performance.The aim of the current work was the numerical optimization of the different parameters to enhance the engine performance while using butanol to decrease NOx emissions.The engine compression ratio(CR)varied from 14 to 24,in increments of 2.Fuel injection timing(IT)was reduced from 30°before top dead centre(bTDC)to 5°bTDC in increments of 5°.Also,the fuel injection duration(IDur)was extended from 20°to 50°in increments of 10°.Results showed that the increase in the CR improved engine performance for the two investigated fuels,Bu10 and Bu20.The maximum engine brake power(BP),thermal efficiency(BTE),and minimum brake-specific fuel consumption(BSFC)of 1.46 kW,32.3%,and 0.273 kg/kWh respectively,were obtained when the Bu10 fuel was injected under the optimum conditions of 24 CR,15°bTDC IT,and 40°IDur.Under these optimum conditions,the BP,BTE,and BSFC improved by 3%-3.5%for Bu10 and Bu20 fuel blends compared with the base engine conditions of a CR of 22,30°IDur,and 10°bTDC IT.The heat release rate during the premixed phase increased when the IT was advanced,while the mixing-controlled combustion phase was enhanced when the IT was reduced.NOx emissions increased with increasing CR,while both an increase in IDur at constant IT and the reduction of the IT decreased the engine NOx emissions.Under the optimum conditions,the NOx emissions for Bu10 and Bu20 were further decreased by 2.2%and 0.9%,respectively,compared with the experimental results under base engine conditions.Reducing the IT from 15°to 5°bTDC at a CR of 24 and IDur of 40°caused the NOx emissions for Bu10 and Bu20 to decrease by 16%.When the IDur was increased from 20°to 50°at a CR of 24 and an IT of 15°bTDC,the NOx emissions for Bu10 and Bu20 decreased by 12.3%and 11.8%,respectively.The addition of butanol to the diesel-biodiesel blend under optimum conditions showed results that were comparable to those of pure diesel,with a decrease in NOx emissions.

Research into polymer injection timing for Bohai heavy oil reservoirs

Polymer flooding has been proven to effectively improve oil recovery in the Bohai Oil Field. However, due to high oil viscosity and significant formation heterogeneity, it is necessary to further improve the displacement effectiveness of polymer flooding in heavy oil reservoirs in the service life of offshore platforms. In this paper, the effects of the water/oil mobility ratio in heavy oil reservoirs and the dimensionless oil productivity index on polymer flooding effectiveness were studied utilizing rel- ative permeability curves. The results showed that when the water saturation was less than the value, where the water/oil mobility ratio was equal to 1, polymer flooding could effectively control the increase of fractional water flow, which meant that the upper limit of water/oil ratio suitable for polymer flooding should be the value when the water/oil mobility ratio was equal to 1. Mean while, by injecting a certain volume of water to create water channels in the reservoir, the polymer flooding would be the most effective in improving sweep efficiency, and lower the fractional flow of water to the value corresponding to △Jmax. Considering the service life of the platform and the polymer mobility control capacity, the best polymer injection timing for heavy oil reservoirs was optimized. It has been tested for reservoirs with crude oil viscosity of 123 and 70 mPa s, the optimum polymer flooding effec- tiveness could be obtained when the polymer floods were initiated at the time when the fractional flow of water were 10 % and 25 %, respectively. The injection timing range for polymer flooding was also theoretically analyzed for the Bohai Oil Field utilizing which provided methods for effectiveness. relative permeability curves, improving polymer flooding

Adaptability research of hydrofoil surface water injection on cavitation suppression

To study the effectiveness of hydrofoil surface water injection on cavitation suppression,the unsteady cavitation flow field around the NACA0066 hydrofoil at attack angle of 6°was simulated by the modified RNG k-εturbulence model combined with the full-cavitation model.The structure of cavitation flow field and the hydrodynamic performance of hydrofoil were analyzed at the cavitation number of 0.85,0.70,0.55,respectively.The results show that barriered by the jet,the momentum of the reentrant jet was reduced;The development of cavitation and the strength of cavity shedding were weakened to some extent.Cavitation suppression effect was very obvious in the cavitation conditions with the cavitation number of 0.7 and above when the injection position was at 37% chord length from the hydrofoil leading edge and the jet-flow ratio kept 0.3.Time-averaged lift and drag coefficient were reduced,and the lift-drag ratio increased in water injection conditions.

Numerical Calculation of the Attenuation of Neutral Beam Injection on HL-2A

The arrangement of the neutral beam line in HL-2A tokamak is introduced. Attenuation of neutral beam injection is analyzed numerically under different plasma conditions： different plasma densities, beam energies, electron temperatures, and impurity concentrations. Both optimized plasma density and beam energy for plasma heating are obtained.

Radial Non-uniformity Index Research on High-density,High-flux CFB Riser with Stratified Injection

A high-density, high-flux circulating fluidized bed （CFB） riser （100 mm in ID and 10.614 m in height） was ap- plied in a wide range of operating conditions （with solid fluxes up to 400 kg/m2s and superficial gas velocities up to 12 m/s） to examine its radial non-uniformity dynamics. The solids holdup was determined through the use of a fiber-optic probe at 11 axial levels. The results indicated that under all operating conditions, the high superficial gas velocity and low solid flux- es maintained a low radial non-uniformity index （RNI）. The high-density/flux CFB riser had several unique characteristics, so that the peak of the radial solids holdup profile occurred at a position with r/R=0.8. The RNI and solids holdup at the cross-sectional position had a good logarithmic relationship at the low-density condition （with a mean solids holdup of 〈0.2）, and the RNI decreased when the mean solids holdup exceeded 0.2. Investigation of the dynamics of stratified injec- tion revealed that the feed ratio had an important effect on G, and on solids holdup distribution. A novel ＂〈＂ shaped axial solids holdup profile was found. Gs decreased sharply when the up-flow feed ratio exceeded 0.5, and RNI was lowest when the up-flow feed ratio was 1.

Combustion and emission characteristics of a dual injection system applied to a DISI engine

Concerns about environmental pollution and energy shortages have increased worldwide. One approach to reduce CO2 emissions from gasoline engines is to achieve stratified charge combustion with various injection ratios using port fuel injection （PFI） and direct injection. The combustion and emission characteristics of a 4-valve direct injection spark ignition （DISI） engine equipped with a dual injection system were investigated while the injection ratio was varied. When the direct injection ratio increased, the lean limit A/F was extended. This suggests that the dual injection gasoline engine with both PFI and direct injection can meet severe vehicle emission and fuel economy requirements. The dual injection system had higher combustion pressure than that of either a conventional or direct injection systems. Therefore, the engine power of a dual injection DISI engine would be higher than that of a single injection DISI engine. However, NOx emissions increased compared with the emission levels in both PFI and DISI systems.

Silver removal from molten lead through zinc powder injection

A silver removal process was carried out on a Pb-Ag alloy through zinc powder injection of three different sizes （3.55, 44.4 and 734.8μm） with a top submerged lance using nitrogen as carrying gas. The higher silver removal was obtained for the zinc powder size of 44.4μm, while the lowest silver removal efficiency was attained for the smaller particle size. The AgZn phase was detected in the slag for the 44.4 and 734.8μm particle sizes by XRD, which was in agreement with SEM-EDS analysis. Experimental behavior was explained according to the melting and residence time of the injected particles.

A new method for evaluating the injection effect of chemical flooding

Hall plot analysis,as a widespread injection evaluation method,however,often fails to achieve the desired result because of the inconspicuous change of the curve shape.Based on the cumulative injection volume,injection rate,and the injection pressure,this paper establishes a new method using the ratio of the pressure to the injection rate（RPI） and the rate of change of the RPI to evaluate the injection efficiency of chemical flooding.The relationship between the RPI and the apparent resistance factor（apparent residual resistance factor） is obtained,similarly to the relationship between the rate of change of the RPI and the resistance factor.In order to estimate a thief zone in a reservoir,the influence of chemical crossflow on the rate of change of the RPI is analyzed.The new method has been applied successfully in the western part of the Gudong 7th reservoir.Compared with the Hall plot analysis,it is more accurate in real-time injection data interpretation and crossflow estimation.Specially,the rate of change of the RPI could be particularly suitably applied for new wells or converted wells lacking early water flooding history.

榆树林油田CCUS采油工程方案优化设计与实践

大庆榆树林油田扶杨油层属低孔、特低渗透储层,针对以往开发过程中存在注水困难、压裂有效期短、水驱开发难以有效动用的问题,开展CO_(2)驱油技术现场试验。从经济性、技术适应性、配套工艺成熟性等角度对采油工程方案进行综合评价,优选出单、双管分层注入工艺、高气液比举升工艺、注采两端个性化防腐工艺及物理化学组合解冻堵工艺等CCUS采油工程技术。结果表明:试验区投产初期及目前生产情况均达到了油藏预测指标;采出井平均泵效及检泵周期与外围油田平均水平相持平,注气井与采出井腐蚀速率小于行业指标;实现CO_(2)有效埋存108.9×10^(4) t,比水驱预测采出程度提高采收率4.39百分点,取得较好的驱油开发效果。研究成果为CCUS示范区的高效建设提供了技术支撑,开辟了大庆油田外围难采储量有效动用的新途径。

进气歧管喷水对发动机燃烧性能的试验研究

为研究进气歧管喷水技术对汽油发动机热效率的提升潜力,基于一台研究型单缸汽油发动机,采用试验的手段对比研究了不同的喷水比例、不同的负荷工况及不同的压缩比下进气歧管喷水对发动机燃烧性能的影响。结果表明,采用进气歧管喷水技术可有效降低发动机的爆震趋势,随着喷水比例的增加,CA50逐渐提前,燃料的滞燃期及燃烧持续期增加,同时伴随着传热损失逐渐增加。相比于无喷水(w/o PWI)的结果,喷水的引入虽然导致未燃损失增加,但有利于排气能量损失大幅降低,最终反应到经济性的表现为热效率随着喷水比例的增大呈先增加后降低的趋势,油耗率的表现同热效率的结果相反;此时最佳的净指示热效率(GITE)为43.1%,相比于w/o PWI的结果升高了2.5%;最佳的净指示油耗率(GISFC)为197.9 g/(kW·h),相比于w/o PWI的结果降低了11.8 g/(kW·h)。高负荷运用喷水技术将达到更显著的热效率改善及油耗改善效果;同时,喷水技术的引入使得发动机高压缩比的应用成为可能。

国内某高炉喷吹煤粉的性能评价

高炉喷吹煤粉的优点主要包括显著降低炼铁焦比及生产成本、有效调节高炉热制度、喷吹煤粉反应过程中提高煤气的穿透扩散能力和还原能力、缓解焦煤需求量、减少炼焦投资和环境污染等。为进一步优化高炉喷吹燃料结构和降低炼铁成本,文章对国内某高炉喷吹使用的煤粉的煤质特性进行了深入研究。结果表明:1#煤为烟煤,固定碳含量低、挥发分高,氢元素含量在所试验煤粉中最高,灰分中的CaO和MgO的含量之和最高,超过24%;其他煤种为无烟煤;4#煤的可磨性指数低于40;需要控制其在混煤中的配比。

延长油田H区块剩余油分布规律及开发技术研究

为了更好的明确延长油田H区域剩余油的分布特征、开发潜力,以及有效的开发策略,运用油藏工程、动态监测、数值模拟相结合的方法,认识剩余油分布规律及主控因素,进一步揭示剩余油分布特征,为下一步注水开发提供理论基础。依据油藏工程及数值模拟精细描述成果,提出了能够提高采收率的合理注采比及地层压力保持水平,优选出中高含水阶段密井网下合理的开发技术,为研究区高效注水开发提供可靠的技术支撑。

基于全扇区统一占空比函数的Ⅰ型NPC三电平SVPWM载波化算法

Ⅰ型中性点钳位(neutral point clamped, NPC)三电平变流器作为中大容量新能源发电系统的核心设备,其调制策略直接影响变流器的能量转换效率、谐波特性和运行控制特性等。鉴于Ⅰ型三电平变流器的传统空间矢量脉宽调制(space vector pulse width modulation, SVPWM)策略在实施过程中包含大量三角函数运算,基于三相静止坐标系进行调制算法的大小扇区判断和矢量作用时间计算等,并通过归纳整理,按照单调制波双载波的载波化思路,获得了适用于全扇区的三相统一的占空比函数。借助该占空比函数,变流器的数字控制器仅需通过简单的关系运算和数值计算,便可获得变流器功率管的控制信号,省去了大量三角函数计算,节约了硬件资源。此外,将SVPWM与正弦波脉宽调制(sinusoidal pulse width modulation, SPWM)+3次谐波注入调制算法进行对比,从调制波层面,揭示了这2种调制算法之间的内在差异。最后,通过仿真验证了该算法的有效性。

基于合理地层压力的X油田吸水能力评价

地层压力是影响注水井的注入压力和吸水能力的重要因素,保持合理地层压力是实现油田稳产的基础。针对X油田A、B两个区块地层压力差异导致的油井产液降低的问题,采用生产指示曲线法结合油水井生产动态对X油田的地层压力进行了评价,确定了X油田的合理地层压力,构建了不同注水量下吸水指数与地层压力的关系图版,给出了地层压力恢复方案。研究结果表明,目前A区块处于合理地层压力范围内,B区块地层压力偏低,应补充注入井注水量;同时两区块实际注水量均偏低,应进一步提高注水强度。基于合理地层压力的油田吸水能力评价方法对油田水驱开发具有重要指导作用。

带压环境下泥浆-泡沫组合改良级配不良砂剪切特性研究

盾构穿越富水砂性地层时易出现排渣不畅或喷涌等风险,仅采用泡沫改良往往无法有效改善级配不良渣土的流动性与抗渗性,归因于泡沫易消散和流失,故须引入膨润土泥浆进行组合改良。正确认识土舱压力环境泥浆-泡沫组合改良级配不良砂土的剪切大变形行为有助于优化满足盾构安全掘进的渣土组合改良方案。因此,开展了泥浆-泡沫组合改良级配不良砂土的加压十字板剪切试验,研究结果表明:在土舱压力环境下,组合改良砂土的初始孔隙比和饱和度随泥浆注入比(bentonite injection ratio,简称BIR)增加而增大,有效应力降低,进而导致峰值强度和残余强度降低;然而剪切强度的剪切率相关性和有效内摩擦角对BIR的敏感性较弱;BIR增加还使大变形后改良砂土的屈服应力有所降低。此外,对比常压下流动性相似的3类不同改良砂土带压剪切大变形行为,表明带压环境下提高BIR或泡沫注入比(foam injection ratio,简称FIR)均可提高孔隙比且减小有效应力,但相较于纯泡沫改良砂土,组合改良砂土具有更低的有效应力和剪切强度。该类级配不良砂土的合适组合改良参数为FIR=20%、BIR=10%~15%。最后,细观成像结果揭示了膨润土对改良砂土剪切强度的双重削弱作用:(1)吸附砂土颗粒表面,降低颗粒间摩擦力;(2)延缓泡沫衰变,使得小粒径气泡较均匀分布于孔隙中,进而有效削弱土骨架强度。

预喷比例对正丁醇、PODE掺混柴油燃料燃烧和排放的影响

以柴油(B0)为基础燃料,分别配制掺混体积比为20%的正丁醇(B20)及掺混体积比为20%的正丁醇+20%聚甲氧基二甲醚(PODE)的混合燃料(B20P20).通过一台轻型柴油机研究了预喷比例对B0、B20和B20P20燃烧和排放的影响,在转速为1600r/min、负荷为35%且预喷比例为总油量20%~50%下进行试验.结果表明:相较于单次喷油,预喷射能显著提高热效率,降低NO_(x)排放.随预喷比例增加,有效热效率先升高后降低,NO_(x)排放减少,HC排放显著增加.在柴油中加入正丁醇后,燃烧效率和有效热效率降低,NO_(x)排放和颗粒物质量减少,但HC、CO排放和颗粒物数量显著增加,颗粒物粒径分布向核模态颗粒物转移.在B20中加入PODE后,热效率明显改善.综合排放指标和热效率指标,B20P20最佳的预喷比例为40%,且PODE的加入可以降低排放对预喷比例的敏感性.

鄂尔多斯盆地延长油田双河西区块长6油藏开发参数

鄂尔多斯盆地延长油田双河西区块长6油藏为低渗透油藏,常规开发指标计算方法并不利于油田进行油藏地质研究、开发政策制定与成本控制。对延长油田双河西区块长6油藏产量递减规律、水驱储量动用程度、注采比、含水率、注水利用状况及采收率进行分析。结果表明:双河西区块长6油藏产量递减规律为双曲递减模式;区块注水开发潜力较大,目前该区块水驱储量控制程度为74.54%,水驱储量动用程度为36.94%,注采连通率为27.27%;合理注采比约为2.5,随着采出程度增加,含水率上升速度先增大,后有所减小;根据存水率、耗水指数及水驱指数可知,开发后期,区块注水开发效果逐渐变好,最终采收率增加,研究区在开发过程中含水上升率应尽量小于6.1%,地层合理压力应大于9.1 MPa,在该开发条件下,研究区最终采收率约为23%。