HCCI燃烧技术在直喷式柴油机上应用的试验研究

在1135型四冲程直喷式柴油机上,通过采用双收口燃烧室、P型喷油泵高压喷射、伞喷油嘴和多孔油嘴预喷射、乳化柴油及乙醇柴油等技术措施,形成最佳的预混合气,达到产生良好化学反应及动力学效应。通过调整试验,控制上止点后着火,实现近似等压预混合燃烧。     

醇类燃料HCCI发动机燃烧特性的实验研究

在Ricardo Hydra单缸四冲程发动机上利用内部废气再循环策略实现了4种醇类燃料(纯甲醇燃料、纯乙醇燃料、体积分数为50％的甲醇与汽油混合燃料和体积分数为50％的乙醇与汽油混合燃料)的HCCI燃烧．通过调整HCCI发动机的空燃比、转速和气门相位角,研究了醇类燃料HCCI发动机的燃烧特性．结果表明,醇类燃料的 HCCI燃烧不同于普通汽油,燃烧可以在较稀的混合气浓度范围区域内实现,使发动机的运行范围向小负荷和高转速方向拓展,其中纯乙醇可以向高低负荷两个方向拓展运行范围．醇类的着火时刻受化学反应特性和加热的共同影响,其中甲醇燃料的着火在所比较的范围内都是最早的,而且甲醇燃料的着火持续期短于乙醇燃料．除了纯甲醇以外,其他醇类燃料的平均指示压力都高于汽油．     

直喷式柴油机高强化燃烧新技术的研究

本文介绍了在4气门1135型直喷式试验机上采取提高混合气形成质量、组织稀薄均质预混合燃烧方式，控制在上止点着火等措施获得理想放热规律，取得了经济性和排放性全面改善的效果。同时还介绍了模拟增压试验，不同增压比、气门重叠角、喷测定时及喷孔尺寸等实验研究。结果表明：适当提高增压比和加大气门重叠角，是柴油机强化燃烧的重要措施。     

HCCI甲醇发动机的燃烧与排放特性

在Ricardo Hydra单缸四冲程发动机上利用内部废气再循环策略实现了甲醇燃料的HCCI燃烧.通过调整HCCI发动机的过量空气系数和转速,研究了HCCI甲醇发动机的燃烧和排放特性.结果表明,甲醇燃料的HCCI燃烧不同于普通汽油,其着火更早、燃烧更快,但在低转速时,平均指示压力相对较低.甲醇燃料可以在更稀的混合气条件下实现HCCI燃烧.在相同的转速和过量空气系数下,甲醇燃料的NOx和HC排放低于汽油.     

直喷式柴油机强化燃烧的研究

本文阐述对直喷式柴油机强化燃烧的研究,重点通过所建立的优化直喷式柴油机工作过程的数学模型模拟计算,研究和分析了直喷式柴油机的工作过程和燃烧性能。计算与试验研究均表明,提高喷油压力、缩短喷油期、提高增压压力和采用预喷射快速燃烧、均质预混合燃烧等技术,均可强化柴油机燃烧过程以满足动力性、经济性和排放的要求。     

改善高速直喷式柴油机燃烧特性的研究

本文主要研究燃烧室设计、缸内气体流动与蓄压式高压喷油系统三者之间的最佳匹配,以改善高速直喷式柴油机的燃烧特性、降低油耗和烟度。     

小型高速直喷式柴油机燃烧过程的研究

本文论述了组织小型高速直喷式柴油机燃烧过程的困难原因,给出了在175F直喷式柴油机上的试验研究结果,并与175F涡流预燃室柴油机的性能作了比较,其中油耗率下降了(6.2～9.8)%。本研究结果为我国研制(75～95)mm缸径的高速直喷式柴油机提供了相当的依据。     

直喷式柴油机燃烧低十六烷值柴油的研究

通过实测直喷式柴油机燃烧不同十六烷值柴油时的缸内压力示功图,以此计算出相应的燃烧放热规律。通过分析影响放热规律的有关参数,确定了对几项因子通过试验匹配来进行直喷式柴油机燃用低十六烷值柴油机的初步研究。以试验研究为基础,利用神经网络的非线性映射性能得出了燃用低十六烷值柴油机时几个参数的调整方案。     

直喷柴油机喷油系统对燃烧和排放影响的三维模拟研究

直喷柴油机的喷油过程影响燃烧过程、影响发动机性能和污染物排放。为了研究喷油特性(如不同的喷油压力、喷油定时和喷孔直径等)对燃烧性能的影响,利用三维数值模拟软件K IVA-3代码,对喷油过程、燃烧过程和发动机性能进行了数值模拟。计算结果显示了不同喷油特性下的NO和碳烟排放的变化趋势。     

Effects of EGR on combustion process of DI diesel engine during cold start

Experiments on the effects of external and internal exhaust gas recirculation (EGR) on combustion and emission performance during a cold start process were investigated in a 135 single-cylinder DI diesel engine. Combustion was improved during the initial ignition cycles by introducing internal or external EGR. The addition of an appropriate amount of internal or external EGR can promote the combustion stability significantly. However, excessive amounts of external EGR could lead to extremely unstable combustion or even misfiring. An appropriate amount of internal or external EGR decreased smoke opacity effectively during a cold start. External EGR reduced NO _x emissions effectively while internal EGR led to an increase in NO _x emissions due to thermal effects. __________ Translated from Transactions of CSICE, 2007, 25(3): 193–201 [译自:内燃机学报]     

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]     

HCCI柴油机燃烧过程数值模拟研究

均质压燃(HCCI:homgeneous charge compression ignition)燃烧方式已成为发动机领域的硬件研究热点。针对CA4D32-09型柴油机,对HCCI燃烧过程进行了计算模拟,并利用统计的方法对影响HCCI燃烧特性的因素进行分析,通过计算得出HCCI发动机燃烧过程的影响因素及发动机主要参数对混合气均质特性的作用。     

The effect of hydrogen addition on combustion and emission characteristics of an n-heptane fuelled HCCI engine

The mechanisms of the influence of hydrogen enrichment on the combustion and emission characteristics of an n-heptane fuelled homogeneous charge compression ignition (HCCI) engine was numerically investigated using a multi-zone model. The model calculation successfully captured the most available experimental data. The results show that hydrogen addition retards combustion phasing of an n-heptane fuelled HCCI engine due to the dilution and chemical effects, with the dilution effect being more significant. It is because of the chemical effect that combustion duration is reduced at a constant compression ratio if an appropriate amount of hydrogen is added. As a result of retarded combustion phasing and reduced combustion duration, hydrogen addition increases indicated thermal efficiency at a constant combustion phasing. Hydrogen addition reduces indicated specific unburned hydrocarbon emissions, but slightly increases normalized unburned hydrocarbon emissions that are defined as the emissions per unit burned n-heptane mass. The increase in normalized unburned hydrocarbon emissions is caused by the presence of more remaining hydrocarbons that compete with hydrogen for some key radicals during high temperature combustion stage. At a given hydrogen addition level, N₂O emissions increases with overly retarding combustion phasing, but hydrogen addition moderates this increase in N₂O emissions.     

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.     

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。     

Investigating various effects of reformer gas enrichment on a natural gas-fueled HCCI combustion engine

Homogenous charge compression ignition (HCCI) combustion has the potential to work with high thermal efficiency, low fuel consumption, and extremely low NO_x-PM emissions. In this study, zero-dimensional single-zone and quasi-dimensional multi-zone detailed chemical kinetics models were developed to predict and control an HCCI combustion engine fueled with a natural gas and reformer gas (RG) blend. The model was validated through experiments performed with a modified single-cylinder CFR engine. Both models were able to acceptably predict combustion initiation. The result shows that the chemical and thermodynamic effects of RG blending advance the start of combustion (SOC), whereas dilution retards SOC. In addition, the chemical effect was stronger than the dilution effect, which was in turn stronger than the thermal effect. Furthermore, it was found that the strength of the chemical effect was mainly dependent on H₂ content in RG. Moreover, the amount of RG and concentration of species (CO–H₂) were varied across a wide range of values to investigate their effects on the combustion behavior in an HCCI engine. It was found that the H₂ concentration in RG has a more significant effect on SOC at lower RG percentages in comparison with the CO concentration. However, in higher RG percentages, the CO mass concentration becomes more effective than H₂ in altering SOC.     

限流沿燃烧室中实现柴油喷雾稀扩散燃烧的混合气形成过程

提出了一种在于激光诱导荧光法的实验方案，采用增压式共轨喷油器，在定容燃烧实验装置内进行柴油喷雾形成、发展、撞壁和混合过程的实验。实验发现，燃油喷雾在燃料室壁面的沉积可通过在壁面设置一个“限流沿”（BUMP），使之从壁面剥离，剥离后的壁面射流形成一个迅速扩散的二次空间射流，进而形成较均匀、较稀薄的混合气，它有利于减少碳烟和NOx排放。     

Numerical study of EGR effects on reducing the pressure rise rate of HCCI engine combustion

The effects of the inert components of exhaust gas recirculation (EGR) gas on reducing the pressure rise rate of homogeneous charge compression ignition engine combustion were investigated numerically by utilizing the CHEMKIN II package and its SENKIN code, as well as Curran’s dimethyl ether reaction scheme. Calculations were conducted under constant volume combustion and engine combustion (one compression and one expansion only, respectively) conditions. Results show that with constant fuel amount and initial temperature and pressure, as EGR ratio increases, combustion timings are retarded and the duration of thermal ignition preparation extends non-linearly; peak values of pressure, pressure rising rate (PRR), and temperature decrease; and peak values of heat release rate in both low temperature heat release (LTHR) and high temperature heat release decrease. Moreover, maximum PRR decreases as CA50 is retarded. With constant fuel amount, mixtures with different EGR ratios can obtain the same CA50 by adjusting the initial temperature. Under the same CA50, as EGR ratio increases, the LTHR timing is advanced and the duration of thermal ignition preparation is extended. Maximum PRR is almost constant with the fixed CA50 despite the change in EGR ratio, indicating that the influence of EGR dilution on chemical reaction rate is offset by other factors. Further investigation on the mechanism of this phenomenon is needed.