车用增压柴油机全工况燃烧放热规律分析

根据某车用增压柴油机实测示功图得到全工况实测放热规律,使用三韦伯函数对实测燃烧放热规律进行模拟,将性能综合参数与放热规律关键点结合作为优化目标和约束条件,对三韦伯参数进行了优化分析,获得了能够有效模拟全工况实测放热规律的一系列放热规律函数。对所获得的三韦伯放热规律参数进行分析,通过优化获得了三韦伯参数与无量纲转速、喷油量及燃烧过量空气系数之间的经验关系式。采用三韦伯函数及其参数的经验关系式能够有效的模拟全工况实测燃烧放热率,全工况油耗率平均偏差为0.6%,最高燃烧压力平均偏差为2%,涡轮前排气温度平均偏差为0.36%,表明所获得的三韦伯放热率模型可用于车用增压柴油机全工况性能模拟研究。     

柴油机放热规律在数值计算中的应用

柴油机缸内燃烧过程的模拟是柴油机工作过程模拟的基础,燃料燃烧放热规律决定了缸内压力变化和能量转换的过程,进而影响整个燃烧过程。笔者以TBD234V12增压中冷柴油机为母型机,根据热力学第一定律,利用MATLAB语言编制了柴油机实测示功图反算放热率的程序,计算出燃烧放热率,以此作为已知数据进行工作过程计算,为柴油机工作过程和燃烧过程的研究提供了更为真实准确的燃烧放热规律。同时,利用三韦伯曲线来模拟缸内的放热规律,在达到同样柴油机综合性能指标条件下,分析二者的共同点与不同点。     

预测涡流室柴油机放热规律的一种新方法

提出了由喷油规律预测涡流室柴油机总放热规律和主、副室放热规律的一种新方法。该方法将主室、副室作为一个统一的整体,通过对喷油规律依时间先后次序分段,各分量燃油按各自韦柏规律分别进行预混合燃烧或扩散燃烧,从而可求得总放热规律;考虑主室、副室燃烧差异和容积比变化,将总放热规律按一定的数理关系在主室、副室中进行分配,即或求得主室、副室各自的放热规律。     

柴油机放热率的修正计算方法

在相关由试验的缸压数据计算放热率的研究成果基础上,根据实际应用中遇到的问题提出了一种放热率的修正计算方法,并针对该修正方法进行了误差分析。研究结果表明:采用从原计算放热率中减去估算的系统误差放热率的方法,在不增加计算复杂程度的前提下有利于减小放热率实际计算中的误差;当需要对某一发动机各工况的放热率进行计算时,可以采用一组根据试验倒拖工况计算的多变指数进行修正计算。     

进行分层燃烧的四种燃烧室

本文介绍四种能进行分层燃烧的柴油机燃烧室,它们具有初始放热率低、中期放热率高等较理想的放热规律,并具有发动机工作柔和、平均有效压力高、燃油耗率低等诸多特点。     

神经网络在柴油机放热规律预测中的应用

引言 柴油机喷油规律与放热规律之间是一种非线性的因果关系。由于神经网络具有高度非线性映射功能,本文以２４０直喷式柴油机为样机建立了一个从喷油规律预测放热规律的ＢＰ神经网络模型。该模型采用误差反向传播算法即ＢＰ算法,以长期运行的试验数据为样本对网络训练,通过删除冗余权值和节点对网络结构进行了优化,选择了样本的确定原则、处理方法及输人方式,针对２４０柴油机放热规律具有双峰的特点,采取了分段预测的方法。该模型以喷油规律作为输入,可对放热规律进行预测,为柴油机放热规律的预测研究提供了一种新方法。１　放热…     

用等效热力系统法求解涡流室柴油机燃烧放热率的计算模型

就涡流室式柴油机燃烧放热率理论模型及其算法问题，提出了严谨的等效热力系统物理模型及其等效原则，以及完整的燃烧放热率计算模型，解决了主、副燃烧室间连接通道处流量系数瞬态值的计算问题。通过对Ｓ１９５涡流室式柴油机燃烧放热率的计算，揭示出瞬态流量系数随曲轴转角的变化规律及其回归关系，以及主、副燃烧室各自的燃烧形态和燃烧放热率。该种模型可进一步提高涡流室式柴油机燃烧放热率的计算精度。     

基于试验拟合的低速二冲程柴油机放热率经验模型研究

针对某Tier Ⅲ船用低速二冲程柴油机,开展了负荷、EGR率及喷油参数对放热率及其特征参数的影响研究。研究表明:负荷和轨压是影响燃烧始点的主要因素,负荷、轨压升高使燃烧始点提前;轨压升高及喷油正时提前使CA50提前,指示热效率升高;小EGR率对燃烧过程影响不大,EGR率高于26%后会显著推迟CA50,增大燃烧持续期,降低指示热效率。基于实测放热率对三韦伯函数参数进行了研究,获得了多因素对经验放热模型的作用规律,得到了适用于低速机的经验放热率模型。     

增压直喷柴油机瞬态工况燃烧参数的变化规律

为了研究车用增压柴油机瞬态工况下燃烧参数的变化规律,利用燃烧分析仪在试验台上研究了恒转速变转矩瞬态工况下,油门开度变化率对燃烧参数的影响规律。试验研究了该柴油机在1 000 r/min转速下,油门开度分别在5 s、10 s和15 s内由10%匀速增加到90%时柴油机的响应特性和燃烧参数的变化规律。试验结果表明:发动机存在转矩的增加相对于供油滞后的现象,且随着转矩变化率的增加,这种滞后更加明显;在同一转速增转矩工况中,随着负荷的增加,着火滞燃期缩短,最大放热率降低且前移,放热率重心前移;在油门开度相同的情况下,随着转矩变化率的增加,最高燃烧压力下降、最高燃烧压力点前移、着火滞燃期延长、燃烧持续期缩短、最大放热率降低且后移、放热率重心前移、最高燃烧温度下降。     

生物柴油掺烧率对非道路用柴油机燃烧循环变动特性的影响

针对非道路用186FA柴油机掺烧生物柴油燃烧循环变动情况,进行了燃用不同生物柴油掺烧率的试验.根据实测示功图对主要燃烧参数进行了循环变动分析.结果表明:随着生物柴油的掺烧,燃烧始点提前,放热率峰值减小;平均指示压力(pmi)、缸内压力峰值(pmax)、放热率峰值循环变动系数(COV)呈减小的趋势,而其对应相位波动比纯柴油大;最大压力升高率在中低负荷时循环变动显著;平均指示压力与缸内压力峰值和放热率峰值都有很好的对应关系.     

Heat release rate markers for premixed combustion

The validity of the commonly used flame marker for heat release rate (HRR) visualization, namely the rate of the reaction OH + CH₂O ⇔ HCO + H₂O is re-examined. This is done both for methane–air and multi-component fuel–air mixtures for lean and stoichiometric conditions. Two different methods are used to identify HRR correlations, and it is found that HRR correlations vary strongly with stoichiometry. For the methane mixture there exist alternative HRR markers, while for the multi-component fuel flame the above correlation is found to be inadequate. Alternative markers for the HRR visualization are thus proposed and their performance under turbulent conditions is evaluated using DNS data.     

旋流预混燃烧室火焰动力学奇异谱分析研究

为了从预混燃烧室大涡模拟产生的非稳态、短时及含噪声的热释放率时序数据中有效提取火焰动力学特性以指导设计。首先采用激励响应法获得该序列,使用奇异谱分析重构并降解,并用传递路径函数识别火焰动态响应,同时与动力学模态降解模态对比。结果表明,采用传统火焰传递函数方法,火焰响应特性易被噪声掩盖。采用奇异谱分析重构的热释放率序列可吻合原始序列。获得的奇异谱模态可解析出更多的内在火焰响应频率。该频率与动力学模态降解法获得的频率一致。从动力学模态降解法获得的模态形状可以看出火焰内外层有剪切运动,回流区有混合作用。     

Reconstruction model for heat release rate based on artificial neural network

Optimizing the distribution of heat release rate (HRR) is the key to improve the performance of various combustors. However, limited by current diagnostic techniques, the spatial measurement of HRR in many realistic combustion devices is often difficult or even impossible. HRR prediction is theoretically possible through establishing correlations between HRR and other quantities (e.g., chemiluminescence intensity) that can be experimentally determined; however, up to now, few universal correlations have been established. A novel artificial neural network (ANN) approach was adopted to build the mapping relationship between the combustion heat release rate and the measurable chemiluminescent species. Proper orthogonal decomposition (POD) technology is used to extract the combustion physics and reduce the data of the spatial-temporally high-resolution combustion field. The correlation between the reduced-order HRR and chemiluminescent species is built using an ANN model. A unique segmentation approach was proposed to improve the training efficiency and accuracy. Validation in a supersonic hydrogen-oxygen nonpremixed flame proves the accuracy and efficiency of the proposed HRR reconstruction model based on the reduced-order POD method and data-driven ANN model.     

Moiré interferometry measurements of neartip deformation in inhomogeneous elasticplastic fracture specimens

Moiré interferometry was used for direct measurements of the crack tip behavior in the homogeneous compact tension (CT) specimens of A533B and HT80 steels, and in electron-beam welded inhomogeneous CT specimens of the two materials. These two materials have considerably different yield stresses, although their elastic properties are the same. Five types of homogeneous and inhomogeneous specimens were used in the experiment. Moiré fringe patterns of the five specimen types were directly compared for elastic, elastic-plastic and unloaded stages. Although the global deformations in terms of the load versus COD relations exhibit little inhomogeneity effects, large inhomogeneity effects were observed in the moiré fringe patterns in the elastic-plastic and unloaded stages. The near-tip deformations were also compared with the corresponding HRR singular fields. In a horizontal weld specimen, due to strong hardening in the weld region, the slope of the displacement field does not shift the characteristic HRR field for the A533B or the HT80 steel for increasing load.     

Effect of a heat release rate on reproducibility of fire test for hydrogen storage cylinders

The paper addresses the reproducibility of the fire test in the United Nations “Global technical regulation on hydrogen and fuel cell vehicles” (GTR#13) and similar fire test protocols in other regulations, codes and standards (RCS). Currently, GTR#13 requires controlling the flame temperature beneath the tank. An original Ulster conjugate heat transfer numerical model was applied to carry out a study demonstrating the dependence of a fire resistance rating (FRR) of a composite hydrogen tank on a fire heat release rate (HRR). No thermally activated pressure relief device was used. The validation experiments conducted afterwards at Karlsruhe Institute of Technology (KIT) plus a former USA fire test have confirmed the Ulster's conclusion to control not only temperatures, yet the fire HRR. This will improve the GTR#13 fire test reproducibility in different laboratories worldwide. The numerically observed variations of FRR were confirmed by the unique experimental data of the authors' collaborators: FRR = 16–22 min for HRR = 79 kW, 7–8 min (HRR = 165 kW) – both tests were carried out at KIT with identical 36 L volume and 700 bar pressure tanks; and 6–7 min (HRR = 370 kW), though this test in USA was performed with a larger volume tank of 72.4 L and 350 bar. The data on pool fire test with significantly higher HRR, i.e. 4100 kW, and tank volume of 100 L and 700 bar pressure confirmed the “saturation” effect in the dependence of FRR on HRR at HRR above 350 kW. The results of the study underpin the suggested amendment to GTR#13 to improve the reproducibility of the fire test and perform tests with onboard storage tanks at HRR>350 kW.     

Heat release rate and thermal fume behavior estimation of fuel cell vehicles in tunnel fires

This study proposes a heat release rate (HRR) estimation method for a carrier loaded with fuel cell vehicles (FCVs) trapped in a tunnel fire. The carrier is divided into several parts, and the HRR is estimated by adding the HRRs of all system parts (carrier and FCVs). The HRR of one FCV was compared with that of a gasoline vehicle. The thermal fume behavior in longitudinally inclined tunnel fires was also investigated. Even a modest inclination hastened the thermal fume propagation of the FCV fires. Of relevance to the prevention of tunnel fire disasters, the thermal fume behavior differed between FCV and gasoline fires. For safety assessment of tunnel fires, the thermal fume behaviors of an FCV fire and gasoline vehicle fire in a tunnel were investigated by the proposed method. In the case of no longitudinal inclination, the thermal fume of the FCV fire arrived earlier than that of the gasoline vehicle fire (by 1 min at x = 200 m and over 4 min at x = 250 m) because of the emitted hydrogen gas. At 2% longitudinal inclination, the thermal fume of the FCV fire propagated to the downstream side 4 min before that of the gasoline vehicle fire. At 4% longitudinal inclination, the thermal fume propagated 50 m downstream of the initial fire after 10 min. Therefore, after the hydrogen emission, the thermal fume of the FCV fire traveled faster than that of the gasoline vehicle fire. The proposed HRR estimation method can contribute to the risk analysis of various types of tunnel fires.     

Emission characteristics and heat release rate surrogates for ammonia premixed laminar flames

Ammonia is a carbon-free fuel that has the potential to meet increasing energy demand and to reduce CO₂ emissions. In the present work, the characteristics of pollutant emissions in ammonia premixed laminar flames are investigated using one-dimensional simulations, and heat release rate (HRR) surrogates for ammonia combustion are proposed. Both atmospheric and high-pressure conditions were considered, and four representative mechanisms for ammonia combustion were employed. It is shown that the total emission of NO and NH₃ achieves a minimum around an equivalence ratio (?) of 1.1 under atmospheric conditions, and there is no noticeable emission of NO and NH₃ for ? = 1.1 ~ 1.5 under high-pressure conditions. Three HRR surrogates, [NH₃][OH], [NH₂][O], and [NH₂][H], were proposed based on the analysis of HRR and elementary reaction profiles. The performance of HRR surrogates was found to vary with equivalence ratios. For example, with the Miller mechanism, [NH₃][OH], [NH₂][O], and [NH₂][H] have the best performance under atmospheric conditions at ? = 1.15, 0.95 and 1.05, respectively, and under high-pressure conditions at ? = 1.11, 0.87 and 0.96, respectively. Similar conclusions can also be drawn with other mechanisms. These findings provide valuable insights into emission control and flame identification of ammonia combustion.     

Direct numerical simulation of ignition of syngas (H2/CO) mixtures with temperature and composition stratifications relevant to HCCI conditions

In this paper, ignition characteristics of syngas (H₂/CO) under homogeneous charge compression ignition environment have been studied using direct numerical simulation (DNS) and detailed reaction mechanism with temperature stratification. 2D DNS are performed by varying several parameters such as fuel composition, temperature fluctuation $\left(T^{\prime }\right)$ and with different temperature and composition correlations. Results show that high H₂ content syngas mixture exhibits increase in peak mean heat release rate (HRR) and decrease in spreading of mean HRR. Also, for large $T^{\prime }$, deflagration mode of ignition becomes dominant source of HRR and reduces the effects of fuel composition on peak mean HRR. On the contrary, spontaneous mode of ignition becomes dominant source of HRR and occurs more homogenously for small $T^{\prime }$, and this phenomenon becomes significant for low H₂ content syngas mixture. The effect of different correlations between temperature and composition on ignition in syngas illustrate that HRR occurs from mixed mode of deflagration and spontaneous ignition for uncorrelated cases, whereas spontaneous mode of ignition occurring homogeneously is the major source of HRR for negatively correlated cases.     

Influence of hydrogen equivalence ratios on supersonic combustion based on large eddy simulations

Scramjet engines are propulsion systems with high specific impulse performances, which are widely implemented for the realization of hypersonic flight. In this study, the influence of global hydrogen equivalence ratios on supersonic combustion under hypersonic flow was evaluated by conducting a large eddy simulation. First, numerical simulation results revealed a good agreement between the experimentally determined wall pressure and shockwave signal, which verified the accuracy of the numerical method. Moreover, the influence of the equivalence ratio on the characteristics of supersonic combustion was investigated. The results revealed that the complexity of the waveform increased with an increase in the equivalence ratio, owing to the higher combustor pressure and significant interactions between the flames and boundary layer. In particular, the combustion expanded to the center of the flow field, and the average Mach number of the flow field decreased. In addition, the size of the auto-ignition region decreased; however, it was under supersonic flow. The influence of the equivalence ratio on the heat release rate (HRR) under different combustion modes was investigated. The results revealed that the total HRR increased with an increase in the equivalence ratio. Moreover, the majority HRR was in the auto-ignition region, and supersonic combustion was pre-dominant. This study was based on the scramjet model engine without flameholders under hypersonic conditions; therefore, the findings cannot be applied to scramjet combustors under other conditions.     

Numerical study of experimental feasible heat release rate markers for NH3–H2-air premixed flames

Ammonia (NH₃) and hydrogen (H₂) as carbon-free fuels have attracted much attention for combustion applications in recent years. Co-firing ammonia with hydrogen provides a solution to overcome the extremes in the reactivities of both pure ammonia and hydrogen fuels. Heat release rate (HRR) is one of the most important quantities in the study of turbulent combustion, but direct measurement of local HRR is not experimentally feasible. In this study, we explored several quantities, [NH], [O], and the gradient of [OH] (Grad [OH]) as potential experimentally feasible HRR markers for NH₃–H₂-air premixed flames using numerical simulations. The performance of these quantities over a wide range of equivalence ratios and H₂ blending ratios have been examined, and some key reactions have been identified to explain the corresponding variations of the correlation for [NH] and [O]. It is concluded that the [NH] and Grad [OH] can be used in general as a suitable HRR marker for NH₃–H₂-air premixed flames, and the use of [NH] is especially recommended for lean flame conditions. A strategy that slightly shifts the [NH] and Grad [OH] profiles to overlap the corresponding HRR shows a further improvement on the performance of [NH] and Grad [OH]. The use of [O] can be considered for rich flame conditions while cautions are needed for conditions with high H₂ blending ratios.