重型车用柴油机燃用乳化柴油的燃烧与排放特性试验研究

在不改变发动机任何参数的情况下,对高压共轨重型车用柴油机分别燃用柴油和乳化柴油的燃烧与排放特性进行了对比试验研究。试验结果表明:与纯柴油相比,乳化柴油在试验工况下着火滞燃期延长,瞬时放热率峰值提高,燃烧持续期变短;缸内最高压力在低负荷时较柴油高,但在高负荷时较柴油低;在全负荷下,相比于柴油,燃用乳化柴油有效功率平均降低了16.90%,但发动机有效热效率平均提高了2.42%;燃用乳化柴油在常用转速1 800 r/min的负荷范围内时,NOx和碳烟排放分别比柴油平均降低了12.77%和58.90%,改善了NOx和碳烟排放的权衡曲线关系;高负荷时,燃用乳化柴油的CO排放减少,但HC排放增加。     

Development and validation of a comprehensive two-zone model for combustion and emissions formation in a DI diesel engine

A two-zone model for the calculation of the closed cycle of a direct injection (DI) diesel engine is presented. The cylinder contents are taken to comprise a non-burning zone of air and another homogeneous zone in which fuel is continuously supplied from the injector holes during injection and burned with entrained air from the air zone. The growth of the fuel spray zone, consisting of a number of fuel–air conical jets equal to the injector nozzle holes, is carefully modelled by incorporating jet mixing to determine the amount of oxygen available for combustion. Application of the mass, energy and state equations in each one of the two zones yields local temperatures and cylinder pressure histories. For calculating the concentration of constituents in the exhaust gases, a chemical equilibrium scheme is adopted for the C–H–O system of the 11 species considered, together with chemical rate equations for the calculation of nitric oxide (NO). A model for the evaluation of soot formation and oxidation rates is incorporated. A comparison is made between the theoretical results from the computer program implementing the analysis, with experimental results from a vast experimental investigation conducted on a fully automated test bed, direct injection, standard ‘Hydra’, diesel engine located at the authors' laboratory, with very good results, following a multi-parametric study of the constants incorporated in the various sub-models. Pressure indicator diagrams and plots of temperature, NO, soot density and of other interesting quantities are presented as a function of crank angle, for various loads and injection timings, elucidating the physical mechanisms governing combustion and pollutants formation. Copyright © 2003 John Wiley & Sons, Ltd.     

Increasing the efficiency of a diesel engine running on biodiesel through butanol fumigation

A single-cylinder, direct-injection diesel engine was tested with regular diesel oil, neat Jatropha biodiesel, and biodiesel with butanol injection into the inlet manifold. An engine fueled with neat biodiesel showed 5% reduction of the fuel conversion efficiency and 17% increase in specific fuel consumption relative to diesel oil. With butanol injection at a rate of 25% of the total fuel consumption, the efficiency was equivalent to that of diesel oil and specific fuel consumption was less than that of neat biodiesel. Engine emissions with biofuel were improved except for carbon monoxide and unburned hydrocarbons. It was concluded that the diesel engine can operate on the neat biofuel (biodiesel plus alcohol) with the fuel conversion efficiency equivalent to that of the diesel oil.     

在直喷式柴油机上进行HCCI新概念燃烧的探索研究

从形成均匀预混合气及着火后具有良好化学反应动力学效应的角度出发,在单缸135直喷式柴油机上采用双收口型燃烧室、P型喷油泵、预喷射、伞喷油嘴、乳化柴油及乙醇柴油等方法,对实现均质充量压缩着火(homogeneous charge compression ignition,HCCI)燃烧的多种途径进行了对比试验。结果表明:应用伞喷油嘴有效促进了着火前缸内均质预混合气的形成,具有进一步在小排量增压中冷、高压电喷柴油机上推广的潜力;通过燃料设计可控制着火在上止点附近并提高燃烧速率,有利于实现高效、低排放的近似等压预混合燃烧方式。     

Energy efficiency trade‐off with phasing of HCCI combustion

Homogeneous charge compression ignition (HCCI) combustion in diesel engines offers the potential of simultaneous low NOx and soot emissions. However, this is normally accompanied by high hydrocarbon (HC) levels in the exhaust and an early combustion phasing before the top‐dead‐center (TDC) that may drain out substantial amounts of fuel energy from the engine cycle. Exhaust gas recirculation is usually applied to delay the onset of combustion, thereby shifting the phasing of the heat release close to the TDC. Although the retarded phasing improves the engine energy efficiency, a significant increase in HC and carbon monoxide emissions will deteriorate the combustion efficiency. Therefore, an inherent trade‐off exists between the combustion phasing and the combustion efficiency that needs to be minimized for improved energy efficiency. In this work, both theoretical and experimental studies have been carried out to evaluate the combustion efficiency‐phasing (CEP) trade‐off. Engine tests have been conducted to analyze the losses in combustion (burning) and phasing efficiencies, and along with theoretical analyses, the CEP trade‐off has been evaluated in terms of a ‘coefficient of combustion inefficiency’ (CCI). The CCI quantitatively correlates the losses in combustion and phasing efficiencies and provides a reference for improving the combustion phasing of the HCCI operation vis‐à‐vis the combustibles in the exhaust. The focus of this research is to carry out a quantitative analysis of the energy efficiency of HCCI cycles. Copyright © 2011 John Wiley & Sons, Ltd.     

进气初始条件对柴油机低温燃烧及PAHs排放特性的影响

应用三维CFD模型耦合化学动力学模型的方法,研究了进气初始条件对柴油机低温燃烧及多环芳香烃(PAHs)排放特性的影响规律。结果表明:进气温度降低,滞燃期延长,同时由于进气密度增大,使柴油机的循环进气量增多,空燃比升高,燃油在缸内燃烧更充分,在较低的进气温度工况时缸内生成PAHs各组分相对较低;进气压力升高,PAHs各组分的生成时刻提前,并且PAHs各组分的含量依次减少。燃烧起始阶段,苯(C6H6)主要分布在燃烧室凹坑附近。在燃烧中期与后期,其主要分布在凹坑壁面附近。     

某型号柴油机低温起动性能优化

基于缸内燃烧理论对某型号柴油机低温起动困难问题进行分析,提出提高压缩比、采取不同进气加热方式、优化气门间隙3种措施提升缸内温度,并对改进后柴油机开展低温起动性能对比试验.结果 表明:采用高压缩比可明显提升缸内压缩温度,利于改善低温起动性能;分缸加热可明显提升进气温度,相同加热时间下,分缸加热比格栅加热进气温度提升约53...     

供油提前角对柴油/水煤浆混合燃料燃烧排放性能的影响

通过柴油机台架试验,分析了供油提前角变化对柴油/水煤浆混合燃料燃烧排放的影响.试验结果表明:当供油提前角调定为18 ℃A时,柴油/水煤浆混合燃料的有效燃油消耗率降低,热效率升高,燃烧持续期最短,增加或减少供油提前角都将延长燃烧持续期;供油提前角变化对柴油/水煤浆混合燃料的排放有较大影响,逐步增大供油提前角(由17到18 ℃A,再到19 ℃A),混合燃烧的烟度排放降低,Nox的排放先降低再升高,CO的排放先升高再降低,HC排放升高.     

Hybrid operation of triboelectric nanogenerator for electricity generation by a low‐temperature differential heat engine

There are many types of triboelectric nanogenerators (TENGs) which differ in their operational modes (contact mode, sliding mode, etc.), converting mechanical energy into electrical energy. This paper introduces electricity generation from a small low‐temperature differential heat engine capable of utilizing low‐grade thermal energy. The engine is similar to the Gamma‐type Stirling engine and could run on temperature differentials ranging from 90 down to a few degrees Celsius. The work presented here gives technical details of how a small low‐temperature differential heat engine could be integrated with a TENG for electricity generation. Two different schemes were tested for the operation of TENG: one in non‐contact sliding mode and the other in vertical contact‐separation mode. For the temperature difference of 74.4 °C, the former delivered a maximum output voltage of 70 V whereas the latter resulted in 35 V. A maximum combined output voltage of 105 V was obtained capable of charging a 4.7 μF capacitor and discharged through LED lighting. Copyright © 2017 John Wiley & Sons, Ltd.     

基于缸压的船用柴油机燃烧闭环控制策略研究

针对柴油机全寿命过程中动力性下降及各缸工作不均匀的问题,以MAN 6L16/24型船用柴油机为研究对象,模拟因各缸喷油器老化而引起柴油机动力性下降和各缸工作不均匀,对比分析开环、转速闭环和燃烧闭环等不同控制策略改善柴油机动力性、工作均匀性的效果及动态控制性能,针对燃烧闭环控制转速滞后较大的问题,提出转速-燃烧闭环协同控制策略,分析了该控制策略对轨压波动和进气流道阻塞干扰因素的鲁棒性。仿真结果表明,协同控制策略可有效改善柴油机各缸工作不均匀现象,提升转速响应速度。     

The effect of mixed nanoadditive‐blended diesel–water emulsion on the performance,combustion, and emission characteristics of a DI diesel engine

The present paper examines the impact of mixed nanoadditive (Al₂O₃ and ZnO) incorporated diesel–water emulsion on the combustion, performance, and emission of a single‐cylinder diesel engine under varying load conditions. The test fuels consist of constant fuel ratio of 88% diesel, 10% water, and 2% surfactant. Also, different concentrations of mixed nanoadditives—50 ppm, 100 ppm, and 150 ppm—are added to the test fuel. The ultrasonicator bath is employed for agitation or stirring of test fuels. The test results indicate that the mixed nanoadditives in diesel–water emulsion improve combustion characteristics, brake thermal efficiency, and brake‐specific fuel consumption, whereas the maximum improvement is achieved at full load. It is also determined from the test results that the nanoadditive‐blended test fuel showed a noticeable decrement in CO, NO_x, and hydrocarbon emissions as compared with neat diesel. The optimum results are obtained for D88S2W10ZA150 blend. Owing to the higher surface‐to‐volume ratio, enhanced atomization rate, high catalytic behavior, and shortened ignition delay are possible reasons to improve diesel engine working characteristics.     

Investigation of flow characteristics in supersonic combustion ramjet combustor toward improvement of combustion efficiency

Supersonic combustion ramjet (scramjet) is a variant of ramjet in which the combustion takes place at supersonic velocity. The flow physics inside the scramjet combustor is quite complex due to the fact that the mixing and completion of the combustion take place in a short time, which is of the order of milliseconds. This study focuses on flow characteristics within the combustion chamber of the scramjet engine that is designed to improve energy efficiency by enhancing combustion efficiency. The effect on combustion performance and thereby the energy efficiency on using strut‐based flame stabilizer is evaluated at different positions. Reynolds averaged Navier‐Stokes equations are solved with the Shear Stress Transport k‐ω turbulence model. Single strut configuration is used to validate with the experimental data. Single strut is then compared with three‐strut configuration. In the three‐strut configuration, the location of the primary strut is kept constant, and the secondary struts are relocated in x and y directions. Combustion performance was evaluated for the cases of flow from primary strut only and through three struts. It was found that the placement of secondary strut in a three‐strut configuration plays a vital role in improving energy efficiency. A maximum of 33.86% improvement in combustion efficiency was observed in comparison to the single strut combustor. A reduction in unburned fuel was observed, making the system more energy efficient. If the struts are not placed optimally, the combustion performance of the combustor was observed to be lower than that of a single‐strut configuration. The shock reflection and expansion fans within the primary combustion zone and the secondary strut region enhance the combustion efficiency. The wall static pressure was observed to increase with the addition of secondary struts. For certain strut configurations, flow separation was seen on the combustor walls. If the secondary strut was placed close to the primary strut, combustion efficiency was found to enhance. It was seen that combustion efficiency was also enhanced for the cases of reacting flow from primary strut only. It could also help to increase fuel efficiency, as additional fuel is not supplied to the secondary strut, making the overall system energy efficient. As the secondary strut is introduced, total pressure loss also increases. It could also be noted that if the combustor length was increased, there could be further increased in combustion efficiency.     

Improving combustion characteristics of diesel and biodiesel droplets by graphite oxide addition for diesel engine applications

Graphite oxide (GO) is an important member of the graphene family of carbon nanomaterials with remarkable physical, chemical, and thermal properties. We conducted an experimental investigation on the combustion characteristics of diesel and biodiesel droplets dosed with 0.1% GO. The fuels were tested by a single droplet combustion experiment in which the temporal variation in the burning behavior of a suspended droplet was captured using a high‐speed camera. Numerical analysis of the combustion data suggests that the addition of GO in both fuels resulted in shortened ignition delay (by up to 38.2%), increased burn‐rate constant (by up to 29.4%), lowered peak temperature (by up to 7.8%), and shortened burning period (by up to 11.6%). To illustrate, the burn‐rate constant increased from 0.68 to 0.88 mm²/second, and the burning period reduced from 2.7 to 2.2 seconds when GO was dosed in diesel. By contrast, the ignition delay and peak temperature both decreased from 1.6 to 1.4 seconds and 659 to 611 K, respectively, when GO was added in biodiesel. Our results suggest that the fuel additive–induced benefits could effectively reduce emissions and improve fuel consumption for diesel engine applications.     

Impacts of low temperature combustion and diesel post injection on the in-cylinder production of hydrogen in a lean-burn compression ignition engine

Strategies were investigated for increased in-cylinder formation of hydrogen. The use of low intake oxygen with a post injection was proposed. An intake oxygen sweep was conducted on a lean-burn compression ignition engine by adjusting of the exhaust gas recirculation rate. The results revealed that the yield of hydrogen increased exponentially when the intake oxygen was reduced to achieve low temperature combustion. Further tests showed that low temperature combustion operation consistently produced more hydrogen than high temperature combustion for similar air-to-fuel ratios.To increase the hydrogen yield further, a post injection timing sweep was carried out with low temperature combustion operation. Increased yields of hydrogen were obtained, up to 0.76% by volume, when then the post injection timing was advanced from 70 to 20° crank angle after top dead centre. At the same time, the indicated NO_X emissions reduced to 0.013 g/kW·hr and the smoke emissions were 0.14 FSN. Thus, the tests established that the combination of low temperature combustion, low intake oxygen, and an early post injection produced a high yield of hydrogen with simultaneously ultra-low NO_X and smoke emissions. The main drawback of this strategy was the increased formation of methane, up to 3015 ppm by volume. However, further analysis showed that the hydrogen to methane ratio actually increased under low temperature combustion operation.     

Numerical simulation of biodiesel fuel combustion and emission characteristics in a direct injection diesel engine

The effect of the physical and chemical properties of biodiesel fuels on the combustion process and pollutants formation in Direct Injection (DI) engine are investigated numerically by using multi-dimensional Computational Fluid Dynamics (CFD) simulation. In the current study, methyl butanoate (MB) and n-heptane are used as the surrogates for the biodiesel fuel and the conventional diesel fuel. Detailed kinetic chemical mechanisms for MB and n-heptane are implemented to simulate the combustion process. It is shown that the differences in the chemical properties between the biodiesel fuel and the diesel fuel affect the whole combustion process more significantly than the differences in the physical properties. While the variations of both the chemical and the physical properties between the biodiesel and diesel fuel influence the soot formation at the equivalent level, the variations in the chemical properties play a crucial role in the NO_x emissions formation.     

Characteristics and energy distribution of modulated multi-pulse injection modes based diesel HCCI combustion and their effects on engine thermal efficiency and emissions

Cycle fuel energy distribution and combustion characteristics of early in-cylinder diesel homogenous charge compression ignition (HCCI) combustion organized by modulated multi-pulse injection modes are studied by the engine test. It is found that heat loss due to unburned fuel droplets and CO emission can be decreased effectively by injection mode regulation, and thermal efficiency can be potentially increased by 4%–12%. From the analyses of combustion process, it is also found that diesel HCCI combustion is a process with a finite reaction rate and is very sensitive to injection timing and injection mode. At injection timing of −90°CA ATDC, extra low NO_x emissions can be obtained along with high thermal efficiency. __________ Translated from Transactions of CSICE, 2006, 24(6): 385–393 [译自: 内燃机学报]     

Effect of using plastic nanofuel as a fuel in a light‐duty diesel engine

A novel nanofuel is formulated using aluminum oxide (alumina) nanoparticles (AONs) in neat plastic oil (PO). A light‐duty compression‐ignition engine is used in the present investigation to analyze the effect of a 100% plastic nanofuel under different concentrations of nanoparticle on performance, combustion, and emission characteristics. The modified fuels used for conducting the experiment were formulated by mixing PO with 100, 150, and 200 mg/L of AON. The results of the physical and chemical properties of neat PO were significantly improved, in addition to AON. The nanofuels exhibited lower in‐cylinder pressure, delay period, and combustion duration than that of neat PO operation. The performance analysis revealed a 10.3% increase in thermal efficiency for PAN200 nanofuel compared with PO and it was almost the same as that of conventional diesel fuel. The emission levels of HC, CO, and smoke for PO‐based nanofuels were reduced significantly at all brake mean effective pressure values, whereas the reduction in the NO_X emission was only marginal. At full load, the emission of smoke, HC and CO of the PAN200 nanofuel were lower than the diesel operation. Overall, the engine fueled with nanofuel exhibited superior characteristics compared to that of neat PO operation.     

Development of low‐temperature properties on biodiesel fuel: a review

The use of biodiesel as a diesel fuel alternative is rapidly increasing. An important aspect of applying this alternative is the transportation and application in cold weather. In this article, different kinds of methods and technologies were briefly reviewed to improve the low‐temperature properties of biodiesel. The compositions of fatty acids would be effectively changed by choosing available material with high content of unsaturated fatty acids or by reducing saturated fatty acids via winterization process. Branched alcohols can be used to change biodiesel structures that improve the low‐temperature properties. As a technically feasible method, there is still a constant demand to search cost‐effective raw materials for economic branched alcohols production. In order to enhance the impact of crystal morphology and decrease freezing point, the blending chemical additives and petroleum fuels would be a promising method that have been widely used. Besides, other treatments such as epoxidation, hydroisomerization, and ozonization were also discussed. However, each method applied for improving low‐temperature properties of biodiesel should be effective and economical so that the biodiesel would continue to compete with fossil and other renewable fuels for market share. Copyright © 2015 John Wiley & Sons, Ltd.     

An experimental investigation on manifold‐injected hydrogen as a dual fuel for diesel engine system with different injection duration

Stringent emission norms and rapid depletion of petroleum resources have resulted in a continuous effort to search for alternative fuels. Hydrogen is one of the best alternatives for conventional fuels. Hydrogen has both the benefits and limitation to be used as a fuel in an automotive engine system. In the present investigation, hydrogen was injected into the intake manifold by using a hydrogen gas injector and diesel was introduced in the conventional, mode which also acts as an ignition source for hydrogen combustion. The flow rate of hydrogen was set at 5.5 l min^?1 at all the load conditions. The injection timing was kept constant at top dead center (TDC) and injection duration was adjusted to find the optimized injection condition. Experiments were conducted on a single cylinder, four stroke, water‐cooled, direct injection diesel engine coupled to an electrical generator. At 75% load the maximum brake thermal efficiency for hydrogen operation at injection timing of TDC and with injection duration of 30°CA is 25.66% compared with 21.59% for diesel. The oxides of nitrogen (NO_X) emission are 21.7 g kWh^?1 for hydrogen compared with diesel of 17.9 g k Wh^?1. Smoke emissions reduced to 1 Bosch smoke number (BSN) in hydrogen compared with diesel of 2.2 BSN. Hydrogen operation in the dual fuel mode with diesel exhibits a better performance and reduction in emissions compared with diesel in the entire load spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

进气中氮气的体积分数对柴油机着火与燃烧影响的研究

在一台可以拍摄缸内混合气形成和燃烧过程的发动机上，用高速摄像机研究了在进气加入不同体积分数的N2后柴油机的油束发展，混合气形成，着火以及燃烧过程，同时还采用了三基色法对高速摄像机拍摄出的燃烧火焰的照片进行了温度场分布的计算分析，拍摄的图像和计算结果表明，加入N2后，对燃油束的喷雾及混合气体形成过程没有影响，对着火滞燃期的影响也不大，但对火焰的燃烧最高温度和燃烧室的平均温度影响很大，N2的加入量越大，燃烧温度下降越多，燃烧过程的结束也就越早。