The effects of hydrogen addition on soot formation in counterflow diffusion n-heptane flames

The effects of H₂ addition on soot formation are investigated in counterflow diffusion n-heptane flames. Three effects including chemical, thermal, and dilution are fully isolated and characterized by additions of H₂, He, and Ar. Soot volume fractions are measured using LE-calibrated LII technique, and flame temperatures are measured using OH-TLAF method along with a thermocouple. Numerical simulations are conducted with a detailed mechanism with soot model. The simulated soot volume fractions and flame temperatures are in good agreement with experimental data. The experimental results show that H₂ addition can greatly reduce the soot formation. It is also found that the chemical and dilution effects suppress soot formation, while the thermal effect with increasing flame temperature promotes soot formation. Kinetic analysis suggests that HACA growth rate could be the dominant factor that controls the final soot formation through the three effects due to H₂ addition.     

Effect of hydrogen and helium addition to fuel on soot formation in an axisymmetric coflow laminar methane/air diffusion flame

A detailed numerical study was conducted to investigate the effects of hydrogen and helium addition to fuel on soot formation in atmospheric axisymmetric coflow laminar methane/air diffusion flame. Detailed gas-phase chemistry and thermal and transport properties were employed in the numerical calculations. Soot was modeled using a PAH based inception model and the HACA mechanism for surface growth and oxidation. Numerical results were compared with available experimental data. Both experimental and numerical results show that helium addition is more effective than hydrogen addition in reducing soot loading in the methane/air diffusion flame. These results are different from the previous investigations in ethylene/air diffusion flames. Hydrogen chemically enhances soot formation when added to methane. The different chemical effects of hydrogen addition to ethylene and methane on soot formation are explained in terms of the different effects of hydrogen addition on propargyl, benzene, and pyrene formation low in the flames.     

Effects of hydrogen addition on soot formation and oxidation in laminar premixed C2H2/air flames

In an effort to elucidate the influence of hydrogen addition on soot formation and oxidation, a series of numerical investigations was performed for fuel rich laminar C₂H₂/air premixed flat flames using a modified CHEMKIN-II PREMIX code with a detailed soot chemistry mechanism. To clarify the influence of hydrogen addition, the hydrogen content (in volume %) in the fuel mixture was gradually increased from 10 to 50%. The hydrogen addition was found to slow the oxidation of C₂H₂ near the burner surface. The lowered rate of C₂H₂ oxidation coupled with lower C₂H₂ concentration near the burner surface impedes the formation of benzene. However, the formation of benzene was enhanced with the hydrogen addition as the height above burner (HAB) was increased. This was due to the increased reverse rate of the H abstraction reaction that prevents the radical formation process. Through the identical mechanism, the hydrogen addition slows further growth of benzene to larger polycyclic aromatic hydrocarbons (PAHs), eventually lowering the rate of particle inception. Numerical results also indicated that reductions in the soot emissions were mainly attributed to a significant reduction in the mass growth of soot particles. The abundance of hydrogen in the flames deactivated the surface site of soot particles covered with C-H bonds, lowering the surface growth rate (which leads to reductions in the mass growth of soot particles).     

自由活塞式发动机NO_x排放的数值计算研究

以燃烧反应化学动力学程序 SENKIN为基础 ,建立了预测发动机排放的计算模型 ,并针对自由活塞式发动机的特点进行了修正 ,并对修正后的模型进行了实验验证。利用该模型对自由活塞式发动机的排放进行了数值计算。计算结果揭示了该种发动机排放物的生成特点以及发动机转速、混合气燃空比对排放产物的影响规律     

Modeling study of soot formation and oxidation in DI diesel engine using an improved soot model

Particulate emission is one of the most deleterious pollutants generated by Diesel fuel combustion. The ability to predict soot formation is one of the key elements needed to optimize the engine performance and minimize soot emissions. This paper reports work on developing, a phenomenological soot model to better model the physical and chemical processes of soot formation in Diesel fuel combustion. This hybrid model features that the effect of turbulence on the chemical reaction rate was considered in soot oxidation. Soot formation and oxidation processes were modeled with the application of a hybrid method involving particle turbulent transport controlled rate and soot oxidation rate. Compared with the original soot model, the in-cylinder pressures, heat release rate and soot emissions predicted by this hybrid model agreed better with the experimental results. The verified hybrid model was used to investigate the effect of injection timing on engine performance. The results show that the new soot model predicted reasonable soot spatial profiles within the combustion chamber. The high temperature gas zone in cylinder for hybrid model case is distributed broadly soot and NOx emission dependence on the start-of-injection (SOI) timing. Retarded SOI timing increased the portion of diffusion combustion and the soot concentration increased significantly with retarding of the fuel injection timing. The predicted distributions of soot concentration and particle mass provide some new insights on the soot formation and oxidation processes in direct injection (DI) engines. The hybrid phenomenological soot model shows greater potential for enhancing understanding of combustion and soot formation processes in DI diesel engines.     

Effects of water vapor addition to the air stream on soot formation and flame properties in a laminar coflow ethylene/air diffusion flame

The effects of adding water vapor to the air stream on flame properties and soot volume fraction were investigated numerically in a laminar coflow ethylene/air diffusion flame at atmospheric pressure by solving the fully elliptic conservation equations and using a detailed C₂ reaction mechanism including PAH up to pyrene and detailed thermal and transport properties. Thermal radiation was calculated using the discrete-ordinates method and a statistical narrow-band correlated-k based wide band model for the absorption coefficients of CO₂ and H₂O. Soot formation was modeled using a PAH based inception model and the HACA mechanism for surface growth and oxidation. Addition of water vapor significantly reduces radiation heat loss from the flame primarily through reduced soot loading and flame temperature. The added water vapor affects soot formation and flame properties through not only dilution and thermal effects, but also through chemical effect. The chemical effect is as significant as the dilution and thermal effects. The primary pathway for the chemical effect of water vapor is the reverse reaction of OH + H₂ ↔ H + H₂O. Our numerical results confirm that the reduced H radical concentration leads to lower PAH concentrations and consequently lower soot inception rates. In contrast, the radiation effect due to the added water vapor was found to have a minor influence on both flame structure and soot formation in the laminar diffusion flame investigated.     

用光导纤维多色法对柴油机燃烧室内火焰温度与碳粒生成的研究

本文介绍了作者研制的分叉光导纤维４色法测量装置和采用它对直喷式４１３５型柴油机燃烧室内火焰温度和碳烟浓度测量的结果。以双色法为基础的４色法，通过数学方法可优化试验结果，减小测量误差。测量结果表明：在燃烧过程中，碳粒生成时间落后于温度上升时间，持续高温产生碳粒高浓度，后燃烧使碳粒浓度增加。随着负荷的增加，燃烧火焰温度及碳粒浓度增加，它们持续的时间也延长。燃烧终了破粒浓度和排气烟度增大。在喷注区会产生很高的碳粒质量浓度值，稀混合气区火焰温度上升较早。过后燃烧或供油提前角减小，使燃烧终了碳粒浓度增大。     

The effects of hydrogen addition on NO formation in atmospheric-pressure, fuel-rich-premixed, burner-stabilized methane, ethane and propane flames

The effects of hydrogen addition on NO formation in fuel-rich, burner-stabilized methane, ethane and propane flames are reported. Profiles of temperature and NO mole fraction were obtained using spontaneous Raman scattering and laser-induced fluorescence (LIF), respectively. Experiments were performed at equivalent ratio of 1.3, with 0 and 0.2 mole fraction of hydrogen in the fuel; and the mass flux through the burner was varied for each mixture. The addition of hydrogen only modestly affects the flame temperature and NO mole fraction. For the vast majority of the flames studied, the temperature and NO decrease by less than 40 K and 20% (relative), respectively, upon hydrogen addition. The decrease in NO fraction is more distinct in methane and propane flames, and more modest for ethane. The comparison of the experimental data obtained for a given fuel in near-adiabatic C_nH_2n+2/H₂/O₂/N₂ and burner-stabilized C_nH_2n+2/Air flames shows that the NO mole fraction at a given mass flux is practically independent of the composition of the oxidizer. Comparison of the experimental profiles with the predictions of one-dimensional flame calculations with detailed chemical mechanisms indicates that the decrease in the Fenimore NO formation with hydrogen addition arises from the concomitant decrease in CH fraction. Analysis of the computational results suggests that the reaction NCN + H → CH + N₂ returns a considerable fraction of NCN back to N₂.     

高原地区不同配比生物柴油的排放特性

本文在高原环境（81kpa）下,对4100QBZL柴油机燃用不同配比生物柴油混合燃料后NOx与碳烟的排放进行了试验研究。试验结果表明：与柴油相比,纯生物柴油的NOx排放上升了0%~0.22%,而掺混比为30%以内的混合燃料的NOx排放则下降了2.9%~4.5%;碳烟的排放明显降低,且随掺混比的增加而降低,纯生物柴油的碳烟排放下降了33%~53%,掺混比为30%以内的混合燃料的碳烟排放下降了10%~31%。综合考虑,燃用掺混比为30%以内的生物柴油混合燃料,能同时有效地降低NOx与碳烟的排放。     

Motion characteristic of a free piston linear engine

A mathematical model of a free piston linear engine is established. The motion characteristics as well as the natural frequency map of the free piston are established. Then, its motion characteristics are successfully explained from the oscillation point. The full simulation model is built up in Matlab/Simulink for a better understanding of its motion features. The results show that the free piston system is a forced vibration system with variable damping coefficient and stiffness. Its steady-state response of periodical excitation is convergent which means that the system is stable under the periodical combustion. Furthermore, it has some unique features which are different from those of traditional Internal Combustion (IC) engines.     

Effect of hydrogen addition on the combustion and emission of a diesel free-piston engine

The free-piston engine (FPE) is a new crankless engine, which operates with variable compression ratio, flexible fuel applicability and low pollution potential. A numerical model which couples with dynamic, combustion and gas exchange was established and verified by experiment to simulate the effects of different hydrogen addition on the combustion and emission of a diesel FPE. Results indicate that a small amount of hydrogen addition has a little effect on the combustion process of the FPE. However, when the ratio of hydrogen addition (R_H2) is more than 0.1, the R_H2 gives a positive effect on the peak in-cylinder gas pressure, temperature, and nitric oxide emission of the FPE, while soot emission decreases with the increase of hydrogen addition. Moreover, the larger R_H2 induces a longer ignition delay, shorter rapid combustion period, weaker post-combustion effect, greater heat release rate, and earlier peak heat release rate for the FPE. Nevertheless, the released heat in rapid combustion period is significantly enhanced by the increase of R_H2.     

高负荷柴油机锻钢活塞的研究开发

为满足新型发动机高负荷的要求,开发了摩擦焊接成型的锻钢活塞。试验表明,摩擦焊接锻钢活塞较铝合金活塞有效的降低了发动机的漏气量、机油耗,提高了发动机的可靠性,可成功的应用于中重型柴油发动机。与整体锻钢活塞相比,摩擦焊接锻钢活塞在降低漏气量等方面也有着显著的效果。     

二冲程液压自由活塞发动机半直接喷射的仿真研究

利用CONVERGE软件建立了半直喷式液压自由活塞发动机的三维计算流体力学(computational fluid dynamics,CFD)仿真模型,研究了喷射角度、喷油定时、缸头倾角、进气压力对燃料捕集和混合气生成的影响.结果表明:随喷射时刻的推迟,燃料捕获率增加,蒸发时间变长;喷射角度越大,燃料捕获率越高,蒸发时...