滞燃期对柴油机性能影响的试验研究

利用试验手段研究了滞燃期对直喷式柴油机工作过程及性能的影响.分析结果表明：滞燃期的长短决定了速燃期内的放热速度和加速度的大小,从而决定了缸内压力的变化;适当调整滞燃期可以提高柴油机的动力性、经济性,降低排放.     

柴油机燃用柴油/二甲氧基甲烷混合燃料滞燃期研究

开展了柴油机燃用柴油/二甲氧基甲烷混合燃料滞燃期的研究,并基于发动机试验数据拟合了一个适合柴油/二甲氧基甲烷混合燃料滞燃期的预测关系式。研究结果表明,改进后的关系式比已有的滞燃期预测关系式更能准确地预测柴油/二甲氧基甲烷混合燃料着火滞燃期。研究发现混合燃料实际十六烷值随含氧量增加而降低,但降低幅度小于基于燃料质量比例推算出的数值,认为基于燃料质量比例对混合燃料十六烷值推算与实际存在较大差异。     

柴油机起动过程引入EGR对滞燃期影响的研究

试验研究表明,在柴油机首着火循环前引入EGR可以改善柴油机首着火循环的冷起动性能。在试验研究的基础上,进行了化学动力学计算,进一步研究了EGR对起动燃烧的影响。计算发现着火循环前排气成分中的完全燃烧产物少,而未燃燃油和中间氧化产物的含量大,因此改善了燃烧。通过对不同EGR率和不同燃空当量比下,混合气在定容状态下的滞燃期进行分析,得到了混合气着火性能随着EGR率的变化规律。     

在高温高压容弹中甲醇滞燃期的研究

本文研究了甲醇在高温高压条件下滞燃期的变化规律。为了能够较准确而直观地测出甲醇的滞燃期，本文采用阴影及自然光双像法，取得了较满意的结果。在取得了大量实测数据的基础上，建立了甲醇滞燃期的经验公式。     

在高温高压容弹中甲醇滞燃期的研究

本文研究了甲醇在高温高压条件下滞燃期的变化规律。为了能够较准确而直观地测出甲醇的滞燃期，本文采用阴影及自然光双像法，取得了较满意的结果。在取得了大量实测数据的基础上，建立了甲醇滞燃期的经验公式。     

柴油机预混合燃烧滞燃期的试验

滞燃期是柴油机预混合燃烧当中一个极为重要的参数.在电控共轨柴油机上进行了EGR率、喷油始点、喷油压力、负荷、转速和进气温度等单一参数对预混合燃烧滞燃期的试验研究.结果表明,名义过量空气系数能够帮助解释各试验参数对柴油机预混合燃烧滞燃期的影响.混合气的温度、压力和混合气中O2浓度影响柴油机预混合燃烧的滞燃期.提高进气温度...     

二甲基醚/天然气双燃料均质压燃化学动力学数值模拟

使用零维详细化学反应动力学模型，研究了二甲基醚和天然气双燃料均质压燃燃烧的化学反应动力学过程，缸内压力计算值和实测结果相当一致，计算结果表明，双燃料燃烧过程分为低温反应和高温反应两个阶段，低温反应主要是二甲基醚燃烧氧化，而高温反应主要是天然气的氧化，低温反应二甲基醚生成了大量自由基加速了天然气的燃烧反应．混合气初始温度升高，放热率增大，燃烧持续期缩短；二甲基醚浓度主要影响低温燃烧过程，天然气浓度则主要影响高温燃烧过程；惰性气体(CO2)使燃烧反应推迟，燃烧反应速率降低．通过控制二甲基醚、天然气和惰性气体浓度可以有效控制均质压燃燃烧过程，拓宽运行范围。     

舰用大功率柴油机瞬态工况滞燃期的研究

采用示功图的二阶导数d2p/dφ2来确定燃烧始点的新方法,对一台增压中冷柴油机定转速下加载时瞬态工况下的滞燃期进行了研究.结果表明瞬态工况下空燃比对滞燃期有较大的影响,由此对上海交大滞燃期公式进行了修正.     

EGR率对柴油机低温燃烧滞燃期影响的试验研究

根据缸内压力求得缸内平均温度和放热规律,分析了进排气系统的O2体积分数、燃烧始点、喷油始点和终点的温度、压力对低温燃烧早喷射和晚喷射两种情况下滞燃期的影响,早喷射和晚喷射一样随着废气再循环(EGR)率的增大而延长了滞燃期。早喷射的滞燃期要短于晚喷射的滞燃期,因此为了能够让空气与燃油有更多的时间混合,早喷射比晚喷射需要更大的EGR率。但随着大量EGR的加入,过量空气系数不能反映混合气中O2体积分数,滞燃期与混合气温度、压力和O2体积分数有关,在影响低温燃烧滞燃期的因素当中,温度对滞燃期的影响最为明显。     

稀燃天然气发动机燃烧循环变动影响因素研究

通过对一台点燃式多点电喷稀燃天然气发动机进行试验,获得了不同工况下的平均指示压力循环变动系数,以此为基础研究了燃空当量比、节气门开度、转速及点火时刻对稀燃天然气发动机燃烧循环变动的影响趋势。结果表明:混合气燃空当量比越小,燃烧循环变动越明显,当燃空当量比降低到一定值时,平均指示压力循环变动系数的增长会突然加大;节气门开度越小燃烧循环变动越明显,节气门开度小于30%后,其对燃烧循环变动影响更加明显;燃烧循环变动量随转速上升有增加的趋势,在高转速工况下燃烧循环变动的加强尤其明显;在工况一定的条件下存在一个最优的点火时刻可使稀燃天然气发动机的燃烧循环变动最小。     

An approach of droplet ignition delay time

When a droplet is suddenly injected into a high‐temperature environment, the droplet self‐ignition phenomenon occurs. A simple model, based on the temperature history of target gas mixture of which the equivalent ratio is equal to 1, was proposed to predict the droplet ignition delay time in this paper. This approach clearly divides the droplet self‐ignition delay into two parts, the physical delay and the chemical delay. The predicted droplet ignition times agree well with the experimental data and numerical simulation results. In addition, the influence of droplet diameter on the droplet ignition delay was discussed in detail using this approach. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20240     

Numerical study on the spark ignition characteristics of a methane-air mixture using detailed chemical kinetics: Effect of equivalence ratio, electrode gap distance, and electrode radius on MIE, quenching distance, and ignition delay

The minimum ignition energy (MIE) is an important property for designing safety standards and understanding the ignition process of combustible mixtures. Even though the formation of flame kernels in quiescent methane-air mixtures has been simulated numerically, the ignition mechanism has never been satisfactorily explained. This study investigated the spark ignition of methane-air mixtures through a numerical analysis using detailed chemical kinetics consisting of 53 species and 325 elementary reactions while considering the heat loss to the electrode. The simulation was used to investigate the quenching distance and the effects on the MIE of the electrode size, electrode gap distance, ignition duration, and equivalence ratio. The effect of the equivalence ratio on the ignition delay time was also examined. The simulated results showed the same trend as previous experimental results.     

Effect of 2,5-dimethylfuran addition on ignition delay times of n-heptane at high temperatures

The shock tube autoignition of 2,5-dimethylfuran (DMF)/n-heptane blends (DMF0-100%, by mole fraction) with equivalence ratios of 0.5, 1.0, and 2.0 over the temperature range of 1200–1800 K and pressures of 2.0 atm and 10.0 atm were investigated. A detailed blend chemical kinetic model resulting from the merging of validated kinetic models for the components of the fuel blends was developed. The experimental observations indicate that the ignition delay times nonlinearly increase with an increase in the DMF addition level. Chemical kinetic analysis including radical pool analysis and flux analysis were conducted to explain the DMF addition effects. The kinetic analysis shows that at lower DMF blending levels, the two fuels have negligible impacts on the consumption pathways of each other. As the DMF addition increases to relatively higher levels, the consumption path of n-heptane is significantly changed due to the competition of small radicals, which primarily leads to the nonlinear increase in the ignition delay times of DMF/n-heptane blends.     

Numerical investigation on ignition intensification of n-butane with tert-butyl hydroperoxide (TBHP) addition

Aimed to intensify the ignition and combustion process of n-butane fuel in micro internal combustion (IC) engines, ignition delay characteristics of n-butane/air mixtures with tert-butyl hydroperoxide (TBHP) addition ratios below 10% were investigated numerically by CHEMKIN-PRO software. Results show that ignition delay times of n-butane can be shortened nonlinearly with TBHP addition at initial temperatures of 650 K to 1000 K, namely, the reduction rate of ignition delay times rises slowly as the TBHP addition ratio increases. In addition, the negative temperature coefficient (NTC) behavior can be weakened significantly with TBHP addition at 650 K to 1000 K. Especially, the ignition delay time of n-butane can be reduced about 32 times with 10% TBHP addition at 750 K. However, the ignition intensification effect of TBHP addition is slight when the initial temperature is above 1000 K. The acting mechanism of TBHP addition was investigated in detail by the rate of production and consumption (ROP), sensitivity, and reaction pathway analysis. The ROP analysis shows that the released and quickly consumed OH radicals with TBHP addition play an important role in promoting n-butane ignition at the lower initial temperature. However, the relatively slow consumption rate of OH radicals at higher temperature weakens the intensification effect. Furthermore, the sensitivity analysis and reaction pathway analysis indicate that the dominated elemental reactions and reaction pathway vary significantly with TBHP addition at lower initial temperature.     

Effects of hydrogen peroxide addition on two-stage ignition characteristics of n-heptane/air mixtures

Rising fuel cost and environmental concerns of greenhouse emissions have driven the development of advanced engine technology with optimal fuel strategy that can simultaneously yield high thermal efficiency and low emissions. Due to its strong reactivity and extra oxygen atom serving as an oxidizer, hydrogen peroxide (H₂O₂) has been used along with other hydrocarbons to promote overall combustion process. To explore the potential benefits of H₂O₂ in clean combustion technology, a numerical study with detailed chemistry is conducted to investigate the effects of H₂O₂ addition on the two-stage ignition characteristics of n-heptane/air mixtures at low-to-intermediate temperatures (below 1000 K), with due emphasis on how the negative temperature coefficient (NTC) behavior is affected. The results show that H₂O₂ addition shortens both the first-stage and total ignition delay times of n-heptane/air mixtures and suppresses the NTC behavior by reducing the upper turnover temperature. With increasing H₂O₂ addition, the lower turnover temperature, corresponding to the first-stage ignition delay minimum, is found to increase first and then decrease. Chemical kinetic analyses show that the addition of H₂O₂ promotes both first- and second-stage ignition reactivity by enhancing OH production through H₂O₂ decomposition. Furthermore, low-temperature chemistry controls the first-stage ignition, while H₂O₂ chemistry dominates the second-stage ignition.     

NH3/DME混合物着火特性试验与数值模拟研究

为了探究NH₃/DME混合物的着火特性,利用激波管测量了初始温度T=1 250～1 800 K、当量比Φ=0.5～2.0、DME掺混比X_DME=0～1.0、压力p=1 MPa条件下NH₃/DME混合物的着火延迟时间。基于测量的试验数据,更新了Issayev等人构建的NH₃/DME燃烧反应动力学模型的部分基元反应,更新后的模型表现出对NH₃/DME着火延迟时间的良好预测。在此基础上,进一步开展了NH₃/DME着火特性值模拟研究。结果表明：NH₃/DME高温着火延迟时间随二甲醚(DME)掺混比的增加呈指数降低;NH₃/DME的着火延迟时间随当量比的增加先降低后升高,且不同温度下达到最低着火延迟时间的当量比不同;中低温下NH₃/DME的着火延迟时间随初始温度的变化规律与高温下不同,呈现出明显的负温度系数(NTC)现象。     

Numerical study on the spark ignition characteristics of hydrogen-air mixture using detailed chemical kinetics

Hydrogen is a promising fuel and is expected to replace hydrocarbon fuels for its significant potentials to reduce the pollutants and greenhouse gases. It is very important to investigate Minimum ignition energy (MIE) on safety standards and ignition process of hydrogen-air mixtures. Even though the formation of flame kernels in quiescent hydrogen-air mixtures has been researched numerically and experimentally, the details of ignition mechanism have never been satisfactorily explained. In this study, the spark ignition of hydrogen-air mixture is investigated by using detailed chemical kinetics and considering the heat loss to the electrode. The purpose of this study is emphasized in the effects of the energy supply procedure, the radius of the spark channel, electrode size and electrode gap distance on the MIE. In addition, the effects of mixture temperature, electrode gap distance and electrode size on relationship between the equivalence ratio and the MIE are examined.     

The effect of ignition delay time on the explosion behavior in non-uniform hydrogen-air mixtures

The purpose of this study is to examine the explosion characteristics of non-uniform hydrogen-air mixtures with turbulent mixing. In the experiment, hydrogen is first filled into a 20 L spherical chamber to a desired initial pressure, then air is introduced into the same chamber through a fast response solenoid valve, by adjusting the ignition delay time (t_d), i.e., the time period between the end of air injection and the action of ignition, the turbulent mixing strengthen (or called uniformity of hydrogen-air mixture) is then changed. The experimental results show that the explosions are overall enhanced as t_d decreases, which indicates that turbulence plays a leading role in enhancing the explosion behaviors. In addition, it is found that the effect of turbulence on p_max is more prominent in end-wall ignition than that in center ignition. This is because the heat loss per unit time is higher in end-wall ignition due to the flame front continuously contacts with inner wall of the chamber throughout the explosion process, although the explosion duration time t_e for both ignition cases is reduced when turbulence is introduced, heat loss reduction for end-wall ignition is generally larger than that in center ignition. Lately, a systematical analysis of the turbulent effect associated with various equivalence ratios on the explosion characteristics is conducted in end-wall ignition. Those experimental results illustrate that the turbulence-enhancing influence is more noticeable when hydrogen-air mixtures move toward the lower explosion limit. However, no significant influence of turbulence on explosion process can be found as combustible mixtures tend to the fuel-rich side. This is mainly because that when hydrogen-air mixtures tend to fuel-rich side, τ_e reduction caused by the presence of turbulence is relatively weak as compared with that under quiescent condition, resulting in heat loss during explosion process changes slightly, hence there is no significant impact on explosion parameters.     

Experimental and kinetic study on ignition delay times of lean n-butane/hydrogen/argon mixtures at elevated pressures

Measurements on ignition delay times of n-butane/hydrogen/oxygen mixtures diluted by argon were conducted using the shock tube at pressures of 2, 10 and 20 atm, temperatures from 1000 to 1600 K and hydrogen fractions (${\mathrm{X}}_{{\mathrm{H}}_2}$) from 0 to 98%. It is found that hydrogen addition has a non-linear promoting effect on ignition delay of n-butane. Results also show that for ${\mathrm{X}}_{{\mathrm{H}}_2}$ less than 95%, ignition delay time shows an Arrhenius type dependence and the increase of pressure and temperature lead to shorter ignition delay times. However, for ${\mathrm{X}}_{{\mathrm{H}}_2}$ = 98% and 100% mixtures, non-monotonic pressure dependence of ignition delay time were observed. The performances of the Aramco2.0 model, San Diego 2016 model and USC2.0 model were evaluated against the experimental data. Only the Aramco2.0 model gives a reasonable agreement with all the measurements, which was conducted in this study to interpret the effect of pressure and hydrogen addition on the ignition chemistry of n-butane.