LNG-柴油双燃料增压船用发动机气门重叠期LNG燃料的泄漏分析

针对液化天然气(LNG)-柴油双燃料增压发动机采用AVL-Boost发动机性能仿真计算,分析气门重叠期间LNG燃料通过排气门的泄漏及其影响因素。研究结果表明:气门重叠角是排气门LNG燃料泄漏最重要影响因素,LNG泄漏随着气门重叠角的增大而急剧增加,进气提前角和排气延迟角对LNG泄漏的影响基本相同;LNG泄漏量随着增压比的增加而增加,较高增压比时继续提高增压比会导致LNG泄漏量继续增加,但是LNG百分比泄漏量基本不变;对于增压比为1.8~3.0的LNG-柴油双燃料增压发动机(标定转速为1000r/min,进气提前角为50°CA),排气门LNG燃料泄漏量可以达到全部LNG燃料的1%~5%;适当减小排气门直径是减少LNG泄漏的有效措施。     

天然气发动机在不同喷射和点火时刻下的性能优化研究

为解决改装的天然气发动机动力性比原柴油机低,燃料消耗率比原柴油机高的问题,对影响燃烧时刻的喷射提前角与点火提前角这两个重要参数进行模拟实验,研究其对发动机的缸内压力与功率、燃气消耗率的影响,并根据研究结果进行优化设计。结果表明,对于缸内直喷天然气发动机,适当增大喷气提前角和选择恰当的点火提前角能在较经济的情况下提高发动机的动力性;发动机转速增加,点火提前角和喷射提前角也应提前,保证燃料的充分混合和最大化做功能力;在所有转速下,天然气发动机的功率都能恢复到原柴油机的水平。     

VVT对发动机性能影响的试验研究

研究了VVT对发动机充量系数、燃烧、动力性和排放的影响。试验结果表明:充量系数随着气门重叠角的增大而增大,缸内气流运动影响最佳燃烧对应的气门重叠角,进气VVT主要影响发动机的动力性,合适的进气VVT能够使扭矩提高11.6%,而排气VVT则影响发动机的排放,随着排气VVT的提前,NOx下降36%。     

天然气发动机燃烧制动性能仿真研究

利用GT-Power仿真软件建立某一型号发动机模型,研究点火时刻、转速和减压气门运行参数对发动机燃烧制动性能的影响。研究结果表明:随着点火时刻的提前,发动机制动功率呈线性增加;点火时刻一定时,发动机转速越高制动功率越大,减压气门升程越高制动功率也越大。当转速一定时,每个减压气门升程都对应一个最佳气门提前角使得制动功率的峰值最大,且最佳气门提前角随着气门升程的增大而减小;当升程一定时,每个转速都对应一个最佳气门提前角使得制动功率的峰值最大,且最佳气门提前角随着转速增大而增大。当气门升程为4mm、转速为2 400r/min时,最大制动功率可达137kW,可达发动机标定功率的1.7倍。     

预燃室点火控制对大功率稀燃天然气发动机性能影响的试验研究

介绍了大功率天然气发动机采用的稀薄燃烧的技术特点,以及为实现稀薄燃烧所采用的预燃室点火控制的主要结构和特点。为研究预燃室点火控制对于发动机性能的影响,设计了三种不同类型的试验方案,分别对预燃室进气喷射提前角、预燃室进气喷射压力、预燃室进气喷射持续期进行试验研究,为大功率稀燃天然气发动机性能优化提供了技术依据。     

基于可变气门定时策略的HCCI汽油机试验研究

在电控气口喷射四冲程单缸试验机上,利用特殊设计的小包角配气凸轮,通过负气门重叠角实现了由内部残余废气控制的汽油HCCI燃烧,详细研究了气门定时参数对HCCI燃烧的影响.结果表明,就进排气门定时比较而言,排气门关闭时刻对内部EGR率和负荷的影响更大,而进气门开启时刻对HCCI燃烧的影响相对较小.在进排气门相位对称条件下,随着气门重叠负角的减小,最大压力升高率增加,着火时刻提前,负荷也增大.随着转速的增加,内部EGR率增加,排气温度升高,着火时刻也提前.通过调整气门定时,在不需要进气加热的条件下,可在转速880～4 000 r/min,负荷0.25～0.75 MPa（pIMEP）的范围实现HCCI燃烧.     

柴油、天然气双燃料发动机的燃烧特性分析

研究了柴油,天然气双燃料发动机的燃烧特性,并着重分析了引燃柴油供给系统参数对双燃料发支持性的影响。以试验为基础,首先简要比较了柴油,天然气双燃料发动机与柴油机的燃烧特性,并对比了负荷对双燃料发动机燃烧特性的影响。然后分析了最小循环喷油量,引燃柴油量,引燃油喷射压力,喷嘴参数及供油提前角等引燃柴油供给系统参数对最高爆发压力,燃烧放热率,着火开始时间、累积燃烧放热率等柴油,天然气双燃料发动机燃烧特性的     

小升程凸轮轴发动机HCCI燃烧特性的研究

为了在发动机的低速低负荷区实现均质充量压缩着火（HCCI）燃烧，设计了气门升程小和气门开启持续期短的进、排气门凸轮轴，并将其安装在Ricardo Hydra单缸汽油机上。试验研究了发动机使用理论空燃比混合气时的燃烧情况，结果表明，使用负气门重叠角可以在低速低负荷区实现HCCI燃烧。在HCCI燃烧方式下运行时的平均指示压力（PIMEP）依赖于气门定时和发动机转速。排气门关闭越早，缸内的残余废气量增加，每循环进气量减少，燃烧持续期变长，PIMEP减小，然而泵气损失减小；进气相位对PIMEP的影响小于排气相位的影响；高的发动机转速对燃烧过程的影响类似于排气门早关．     

CNG/柴油双燃料发动机供气技术发展与趋势

详细介绍并分析了CNG/柴油双燃料发动机的天然气预混合供气、进气喷射、缸内直接喷气技术,指出了CNG/柴油双燃料发动机技术的发展趋势是:将天然气电控多点顺序气口喷射和柴油共轨喷射技术相互结合。     

双VVT开度对GDI增压发动机性能的影响

通过对配置双VVT的GDI增压发动机进行试验,研究了双VVT开度变化对GDI增压发动机外特性和部分负荷性能的影响.试验结果表明,中等转速高负载采用较大的气门重叠角,可提高体积效率;低转速高负载采用较小的气门重叠角,可提高充量系数.部分负荷方面,较小气门重叠角对改善发动机稳定性有益.     

LNG柴油双燃料发动机多点顺序喷射试验研究

为将纯柴油发动机改造为LNG/柴油双燃料多点顺序喷射发动机,在不改变原型机结构前提下设计了一套天然气供给系统。为验证该供气系满足否满足原型机在额定工况下的需求,设计了进气道喷射模拟试验台。试验验证表明:该天然气供给系统能够满足发动机在额定工况下燃气供应量及喷射控制的需求,且整套系统能够根据发动机不同工况调整天然气的喷射量。试验结果可为发动机在双燃料模式下运行提供前期数据支撑。     

Pressure–time characteristics in diesel engine fueled with natural gas

Combustion pressure data are measured and presented for a dual fuel engine running on dual fuel of diesel and compressed natural gas, and compared to the diesel engine case. The maximum pressure rise rate during combustion is presented as a measure of combustion noise. Experimental investigation on diesel and dual fuel engines revealed the noise generated from combustion in both cases. A Ricardo E6 diesel version engine is converted to run on dual fuel of diesel and compressed natural gas and is used throughout the work. The engine is fully computerized and the cylinder pressure data, crank angle data are stored in a PC for off-line analysis. The effect of engine speeds, loads, pilot injection angle, and pilot fuel quantity on combustion noise is examined for both diesel and dual engine. Maximum pressure rise rate and some samples of ensemble averaged pressure–crank angle data are presented in the present work. The combustion noise, generally, is found to increase for the dual fuel engine case as compared to the diesel engine case.     

不同喷射方法柴油机进气甲醇预混过程的模拟

采用欧拉气相方程和拉格朗日液滴方程,考虑液滴破裂、蒸发、碰撞、聚合以及液滴的附壁、液膜剥离壁面和气门关闭挤出液膜等现象,建立了柴油机螺旋进气道-气门-气缸的进气喷射甲醇仿真模型.对柴油机进气喷射甲醇的醇气混合进行数值模拟,用于指导双燃料发动机的改造.双燃料发动机的台架试验表明,模型计算的缸内压力与试验值吻合较好.甲醇喷射时刻直接影响本次循环进入气缸的甲醇量,闭阀喷射有利于甲醇在进气过程的雾化混合.在选择甲醇喷射方向时,要以减小甲醇在低温壁面的附壁为原则.甲醇蒸气在气缸里的轴向质量分数分层比径向质量分数分层明显.     

CFD analysis of hydrogen injection pressure and valve profile law effects on backfire and pre-ignition phenomena in hydrogen-diesel dual fuel engine

This paper focuses on optimizing the hydrogen TMI (timed manifold injection) system through valve lift law and hydrogen injection parameters (pressure, injection inclination and timing) in order to prevent backfire phenomena and improve the volumetric efficiency and mixture formation quality of a dual fuel diesel engine operating at high load and high hydrogen energy share. This was achieved through a numerical simulation using CFD code ANSYS Fluent, developed for a single cylinder hydrogen-diesel dual fuel engine, at constant engine speed of 1500 rpm, 90% of load and 42.5% hydrogen energy share. The developed tool was validated using experimental data. As a results, the operating conditions of maximum valve lift = 10.60 mm and inlet valve closing = 30 °CA ABDC (MVL10 IVC30) prevent the engine from backfire and pre-ignition, and ensure a high volumetric efficiency. Moreover, a hydrogen start of injection of 60 °CA ATDC (HSOI60) is appropriate to provide a pre-cooling effect and thus, reduce the pre-ignition sources and helps to quench any hot residual combustion products. While, the hydrogen injection pressure of 2.7 bar and an inclination of 60°, stimulate a better quality of hydrogen-air mixture. Afterwards, a comparison between combustion characteristics of the optimized hydrogen-diesel dual fuel mode and the baseline (diesel mode) was conducted. The result was, under dual fuel mode there is an increase in combustion characteristics and NOx emissions as well as a decrease in CO2 emissions. For further improvement of dual fuel mode, retarding diesel start of injection (DSOI) strategy was used.     

Effect of air injection on the characteristics of transient response in a turbocharged diesel engine

An experimental study was performed to investigate the improvement of transient characteristics of a turbocharged diesel engine under the conditions of low speed and fast acceleration with the load. In this study, the experiment for improving the low speed torque and acceleration performance is performed by means of injecting air into the intake manifold during the period of low speed and application of a fast acceleration. The effects of air injection into the intake manifold on the response performance are investigated at various thermodynamic parameters such as air injection pressure, air injection period, accelerating rate, accelerating time, engine speed and load. The experimental results show that air injection into the intake manifold at compressor exit is closely related to the improvement of low speed and acceleration performance of a turbocharged diesel engine. During the rapid acceleration period, the air injection into the intake manifold of turbocharged diesel engine indicates the improvement of the combustion characteristics and gas pressure in the cylinder. At low speed range of the engine, the effect of air injection shows the improvement of the pressure distribution of turbocharger and combustion pressure during the period of gas exchange pressure.     

液化天然气(LNG)-柴油双燃料汽车的开发

阐述了液化天然气(LNG)—柴油车的总体设计方案，主要是在保留原机的所有结构和柴油燃烧工作方式不变的前提下，增加了一套LNG供气系统和柴油—天然气双燃料电控喷射系统。系统既可以在柴油—LNG双燃料状态下工作，也可以在全柴油状态下工作，双燃料的工作状态由电子转换开关控制。试验表明天然气替代率高迭84％，经济效益和环保性能突出。     

新型可调进气管的试验研究

本文提出一种可调进气管,即在六缸柴油机进气总管内加一可调整节气门.同时,在6102柴油机上广泛测取了不同管径和管长新进气管充气效率、压力波和整机性能参数.试验表明新进气管进气动力效应利用得到改善,充气效率、最大扭矩获得提高,燃油消耗率、排气烟度得到降低.     

Reducing the idle speed of an SI CNG engine fueled by HCNG with high hydrogen ratio

This paper presents an experimental study aimed at idle characteristics of a CNG engine fueled by HCNG with 55% hydrogen blend. The idle speed was reduced from original 800 r/min to 750 r/min and 700 r/min, and the characteristics of combustion & emissions at reduced idle speed were investigated. It is found that, for the HCNG engine, only reducing idle speed cannot reduce fuel consumption at conditions of fixed λ. In order to reduce fuel consumption and keep the COV at rather low levels, the excess air ratio must be increased properly while reducing the engine idle speed. Due to the large valve overlap (30°) of this inlet inject HCNG engine, CH₄ emissions are mainly caused by scavenging, which account for the vast majority of THC emissions. The emissions of CO, THC and NOx are reduced with the decrease of ignition advance angle at a fixed λ.     

Performance and emission study in manifold hydrogen injection with diesel as an ignition source for different start of injection

Over the past two decades there has been a considerable effort to develop and introduce alternative transportation fuels to replace conventional fuels, gasoline and diesel. Environmental issues are the principal driving forces behind this effort. To date the bulk of research has focused on the carbon-based fuels such as reformulated gasoline, methanol and natural gas. One alternative fuel to carbon-based fuels is hydrogen which is considered to be low polluting fuel. In the present experimental investigation hydrogen was injected into the intake manifold by using an injector. Using an electronic control unit (ECU) the injection timing and the duration were controlled. From the results it is observed that the optimum injection timing is at gas exchange top dead center (GTDC). The efficiency improved by about 15% with an increase in NO_X emission by 3% compared to diesel. The smoke emission decreased by almost 100%. A net reduction in carbon emissions was also noticed due to the use of hydrogen. By adopting manifold injection technique the hydrogen–diesel dual fuel engine operates smoothly with a significant improvement in performance and reduction in emissions.