An experimental study on spray and combustion characteristics of LPG for application in direct-injection

As an alternative fuel that can be used in SI engines, LPG is a clean fuel with larger H/C ratio compared to gasoline, low CO₂ emission, and small amount of pollutants such as sulfur compounds. In the Spark-ignition (SI) engine, Direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need for a throttle valve. DI allows engine operation with the stratified charge, which enables a relatively higher combustion efficiency. Stratified charge can be supplied to nearby spark plugs to allow for overall lean combustion, which improves thermal efficiency and can cope with problems regarding emission regulations. In this study, a visualization experiment system that consists of visualization combustion chamber, air supply control system, emission control system, LPG fuel supply system, electronic control system and image data acquisition system was designed and manufactured. For all cases for which ignition was successful, flame propagation image was digitally recorded using ICCD camera, and the recorded flame propagation characteristics were examined. This study, in its results, is expected to make a contribution in terms of important data for the design and optimization of a Spark-ignited direct injection (SIDI) LPG engine.

     

Supercharging performance of a gasoline engine with a supercharger

Supercharging of intake air can improve the engine power and combustion characteristics by boosting the intake pressure above atmospheric pressure. In this work, the supercharging performance of a supercharged gasoline engine was discussed on the basis of experimental investigation. The investigation results showed that the output and torque performance of a supercharged engine were improved in comparison with the naturally aspirated engine. In the engine system with a supercharger, owing to supercharging of intake air into the cylinder, the combustion pressure, the rate of heat release, and the burning rate of fuel-air mixture were found to be higher than those of the naturally aspirated engine. In this paper, the effect of the drive pulley ratio and the pressure ratio of supercharger, and the other factors on the supercharging performance were also investigated.     

柴油加氢装置循环氢压缩机气阀故障原因分析及解决方法

环氢压缩机气阀故障的原因,针对影响压缩机气阀安全运行的瓶颈,采取一系列行之有效的措施,降低了柴油加氢装置循环氢压缩机气阀检修频次,确保了装置安全平稳运行.     

公共汽车液化石油气／柴油混燃系统

为达到现行国家汽车的排放标准,对在用柴油公共汽车的燃料系统进行了双燃料混燃的改装。讨论了机械式和电子式两种LPG／柴油混燃装置的构造和特点,并在改造前后对YC6108Q发动机进行了台架试验,测量出LPG／D的掺烧比和工作关系图,在控制中尽量按照该测量结果进行控制,改造后使用效果良好。     

变压缩比活塞结构设计与仿真

为了改善大排量柴油发动机的冷起动性能,提高发动机中小负荷的动力性,避免发动机大载荷发生爆震,设计了一种变压缩比活塞。该变压缩比活塞由内体、外体两部分组成,外体直径为180 mm,内体与外体之间通过梯形槽产生相对的螺旋运动,在改变发动机压缩比的同时可以实现清除积炭的目的。通过对变压缩比活塞的内部结构设计,实现了液压控制的发动机压缩比随着发动机工况变化的自动调节。通过建立活塞外体的ANSYS有限元模型,分析了在最大压缩比情况下活塞外体的应力及应变分布规律。结果表明:在压缩比为21、材料弹性模量为0.7 MPa、泊松比为0.3、外体的瞬时温度为588 K、最大爆发压力为13.5 MPa情况下,变压缩比活塞外体的应力及应变分布与最大压缩比时外体相对于活塞销的转动位置有关,同时与距活塞顶面和裙部的位置有关。     

CVT ratio control for improvement of fuel economy by considering powertrain response lag

A high level CVT ratio control algorithm is proposed to improve the engine performance by considering the powertrain response lag. In this algorithm, the desired CVT speed ratio is modified from the vehicle velocity, which is estimated after the time delay due to the powertrain response lag. In addition, the acceleration map is constructed to estimate the vehicle acceleration from the throttle pedal position and the CVT ratio. Using the CVT ratio control algorithm and the acceleration map, vehicle performance simulations are performed to evaluate the engine performance and fuel economy. It is found that the fuel economy can be improved about 3.6% for FUDS by the ratio control algorithm for the target vehicle. In selecting the appropriate time delay, compromise between the fuel economy and the acceleration performance is required.     

基于热力学模型的液化石油气发动机 燃烧放热及排放分析

通过燃用汽油及液化石油气的对比试验得出了两种燃料的对比燃烧特性,从而在燃烧机理上分析了其燃烧及排放特性。结论表明以汽油机改装的LPG(液化石油气)发动机自身带有一些缺陷,但通过改装及调试是可以获得较理想的动力性并改善排放指标的。     

Green technology and performance consequences of an eco-friendly substance on a 4-stroke diesel engine at standard injection timing and compression ratio

Journal of Mechanical Science and Technology - This study experimentally focuses on finding the optimum blend ratio for Direct injection (D.I) diesel engine fuelled with mahua oildiesel and...     

Analysis of combustion and flame propagation characteristics of LPG and Gasoline fuels by laser deflection method

This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber. The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a great effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.     

LPG发动机系统及其应用

概述LPG燃料的特性及使用LPG作燃料的发动机的优点，重点介绍了1—3t叉车上采用的尼桑H系列汽油机与美国IMPCO LPG转换装置配套的汽油／LPG双燃料系统。     

Measurement of in-cylinder equivalence ratio during starting using a fast FID

In spite of the importance of the mixture preparation process during starting in affecting HC emissions, it has been poorly understood because the process is highly complicated by the multi component fuel, transient thermal environment, and two-phase mass transfer. For better understanding of the process, measurement of the equivalence ratio in the cylinder was attempted using a fast FID (Flame lonization Detector). Although extensive research has been made on the measurement using the fast FID, the method is not yet straightforward and needs careful operation. In this paper, the current status of the method is described. And within the limitations of the method the in-cylinder sampling test was conducted under the engine operating condition of 900 rpm, 0,527 bar intake pressure with gasoline injceted. The test results show that 15 to 20% of the injected fuel evaporates in the first cycle regardless of the amount of fuel injected. The lean limit of the equivalence ratio for engine firing was about 0.6. For secure firing in the first cycle, 5 to 6 times the stoichiometric fuel amount had to be injected. The contribution of the left-over fuel in the previous cycles to the mixture formation in the present cycle was found to be substantial.     

A study on in-cylinder flow field of a 125cc motorcycle engine at low engine speeds

The in-cylinder flow characteristics of a four-stroke, four-valve, pent-roof small engine of motorcycle at engine speeds from 2000 rpm to 4000 rpm were studied using computational fluid dynamics (CFD). The aim of this study was to investigate the in-cylinder flow characteristics of small engines, including tumble, swirl, turbulent kinetic energy (TKE), angular momentum, in-cylinder air mass, turbulent velocity, turbulent length scale, and air flow pattern (in both intake and compression strokes) under motoring conditions. The engine geometry was created using SolidWorks, then was exported and analyzed using CONVERGE, a commercial CFD method. Grid independence analysis was carried out for this small engine and the turbulence model was observed using the renormalized group (RNG) k-ɛ model. The pressure boundary conditions were used to define the fluid pressure at the intake and exhaust of the port. The results showed that the increase in the engine speed caused the swirl flow in the small engine to be irregularly shaped. The swirl flow had a tendency to be stable and almost constant in the beginning of the compression stroke and increased at the end of compression stroke. However, the increase of in engine speed had no significant effect on the increase in tumble ratio, especially during the intake stroke. There was an increase in tumble ratio due to the increase in engine speed at the end of compression stroke, but only a marginal increase. The increase in engine speed had no significant effect on the increase in angular momentum, TKE, or turbulent velocity from the early intake stroke until the middle of the intake stroke. However, the angular momentum increased due to the increase in engine speed from the middle of the intake stroke to the end of compression stroke, and the angular momentum achieved the biggest increase when the engine speed rose from 3000 to 4000 rpm by 10 % at the end of the intake stroke. The increase in engine speed caused an increase of TKE and turbulent velocity from the middle of intake stroke until the end of compression stroke. Moreover, the biggest increase of TKE and turbulent velocity occurred when the engine speed rose from 3000 to 4000 rpm at the middle of intake stroke around 50 % and 25 %, respectively. Turbulent length scales appeared to be insensitive to increasing engine speed, especially in the intake stroke until 490 °CA. From that point, the value of the turbulent length scale increased as engine speed increased. The biggest increase in the turbulent length scales occurred when the intake valve was almost closed (around 20 %) and the engine speed was within two specific ranges (2000 to 3000 rpm and 3000 to 4000 rpm). Regarding the effect of engine speed, there were no significant effects upon the accumulated air mass in the small engine. The increase in engine speed caused an increase of turbulence in the combustion chamber during the late stages of the compression stroke. The increase in turbulence enhanced the mixing of air and fuel and made the mixture more homogeneous. Moreover, the increase in turbulence directly increased the flame propagation speed. Further research is recommended using a new design with several types of intake ports as well as combinations of different intake ports and some type of piston face, so that changes in air flow characteristics in small engines can be analyzed. Finally, this study is expected to help decrease the number of experiments necessary to obtain optimized systems in small engines.

     

LPG摩托车燃料系统预加热装置的研究与设计

对摩托车发动机缸头盖进行改进设计,在其内部设置U型铜管,利用发动机做功时产生的热量对液相LPG进行预加热,有效解决了减压调节器在工作过程的冷冻结霜现象.试验与计算结果表明,LPG摩托车燃料系统预加热装置结构简单、稳定可靠,综合性能好.     

滑阀式压缩空气发动机实验研究

为优化气动发动机设计,提高气动发动机的工作性能,在一台由四冲程汽油机改装的二冲程气动发动机上进行了详细的台架试验。提出一个评价气动发动机性能的新指标——气动发动机平均有效压力和缸内平均压力的比值。采用钢、铝和尼龙三种材料制作相同尺寸的配气滑块进行试验,结果表明配气滑块的质量,对气动发动机动力性有影响。对进气持续角为128 °、143 °和156 °的尼龙材料配气滑块进行试验,试验结果表明增大进气持续角可以提高压缩空气的膨胀效率。在三种不同压缩比的状况下进行了气动发动机试验。试验证明在传统内燃机的基础上改装气动发动机时,增大发动机压缩比,会降低压缩空气的膨胀效率。     

双燃料发动机天然气电子控制喷射系统的研究

受环境保护和能源短缺的牵掣,双燃料发动机改造技术在我国得到大力的发展,双燃料发动机电控喷射系统的研究是目前的一个热点。本文从硬件和软件两个方面详细论述了天灰气电控喷射系统的构成及基本原理,并进行了双燃料发动机台架实验,实验结果表明发动机的排放特性得到了改善,其可为工程实践提供参考。     

基于BP神经网络控制天然气发动机点火提前角

点火提前角控制是天然气发动机控制的最重要内容之一,精确控制点火提前角涉及到发动机运行的动力性和经济性。对此,开发采用BP神经网络控制的方法来实现天然气发动机的点火提前角控制问题,并基于发动机平均值模型进行了神经网络的MATLAB在线仿真。结果表明:点火提前角最大绝对误差0.4°CA,最大相对误差1.5%,该优化控制模型能准确地获取天然气发动机最佳点火提前角。     

双活塞液压自由活塞发动机原理样机的研制及其压缩比

液压自由活塞发动机是将内燃机和液压泵集成为一体,以液体为工作介质,利用油液的压力能实现动力非刚性传输的一种特种发动机。提出一种特殊结构的液压自由活塞发动机设计方案,并据此研制了双活塞液压自由活塞发动机原理样机。由于压缩比对自由活塞发动机的性能具有重要影响,所以从结构设计、安装方式与行程控制等不同层面,对双活塞液压自由活塞发动机原理样机压缩比进行了详细而系统的研究。研究结果为液压自由活塞发动机的结构设计、控制及安装方式的选择皆有指导意义。     

高压氢气环境下橡胶O形圈静密封结构有限元分析

利用ABAQUS软件建立了高压氢气环境下橡胶O形圈静密封结构的有限元分析模型,研究了高压氢气作用下由于橡胶材料的吸氢膨胀对O形圈变形及应力的影响,探讨了不同初始压缩率、氢气压力、沟槽间隙、有无挡圈等工况下O形圈最大Von Mises应力、最大剪切应力和最大接触应力的变化规律。结果表明:高压氢气环境下,吸氢膨胀会导致橡胶O形圈的截面高度和面积的增加,但对O形圈的应力基本无影响。增加O形圈压缩率会提高初始安装工况下的接触应力,有利于初始密封的形成,但当介质压力较大时,过高的压缩率会显著增加剪切应力,导致O形圈发生剪切破坏。相较于低压工况,高压下密封沟槽间隙对O形圈的Mises应力和剪切的影响非常显著,较大的沟槽间隙会使O形圈发生挤出和剪切破坏,而安装密封挡圈可明显改善O形圈的变形和应力情况,有效防止O形圈被挤入沟槽间隙,同时提高密封性能。     

Simulation research on the effect of cooled EGR, supercharging and compression ratio on downsized SI engine knock

Knock in spark-ignition(SI) engines severely limits engine performance and thermal efficiency. The researches on knock of downsized SI engine have mainly focused on structural design, performance optimization and advanced combustion modes, however there is little for simulation study on the effect of cooled exhaust gas recirculation(EGR) combined with downsizing technologies on SI engine performance. On the basis of mean pressure and oscillating pressure during combustion process, the effect of different levels of cooled EGR ratio, supercharging and compression ratio on engine dynamic and knock characteristic is researched with three- dimensional KIVA-3V program coupled with pressure wave equation. The cylinder pressure, combustion temperature, ignition delay timing, combustion duration, maximum mean pressure, and maximum oscillating pressure at different initial conditions are discussed and analyzed to investigate potential approaches to inhibiting engine knock while improving power output. The calculation results of the effect of just cooled EGR on knock characteristic show that appropriate levels of cooled EGR ratio can effectively suppress cylinder high-frequency pressure oscillations without obvious decrease in mean pressure. Analysis of the synergistic effect of cooled EGR, supercharging and compression ratio on knock characteristic indicates that under the condition of high supercharging and compression ratio, several times more cooled EGR ratio than that under the original condition is necessarily utilized to suppress knock occurrence effectively. The proposed method of synergistic effect of cooled EGR and downsizing technologies on knock characteristic, analyzed from the aspects of mean pressure and oscillating pressure, is an effective way to study downsized SI engine knock and provides knock inhibition approaches in practical engineering.     

Cycle resolved no emissions and its relation with combustion chamber pressure in an s.i. engine with fast response no analyzer

A fast response NO analyzer was applied to investigate the relation between cycle-by-cycle NO emissions and combustion chamber pressure. NO emissions were sampled at an isolated exhaust manifold of 4-stroke spark ignition engine to avoid the interference of exhaust gas from other cylinders. The linear correlation analysis was performed with collected data of NO emissions and combustion chamber pressure with respect to the various air-fuel mixture ratios and engine loads. The sampled data sets were obtained during 200 cycles at each operating condition. The results showed that there was a typical pattern in NO emissions from an exhaust port through a cycle. It was possible to set a block of crank angle in which the linear correlation coefficient between NO emissions and combustion chamber pressure was high. As the engine load increased, NO emissions were more dependent on combustion chamber pressure after TDC. It was also analyzed that the correlation between two parameters with respect to air-fuel mixture ratio tended to increase as mixture went leaner. Furthermore, this correlation coefficient for the mixture near the lean limit seemed to be kept high even though combustion was unstable.