Investigations on the effect of measurement errors on estimated combustion and performance parameters in HCCI combustion engine

Several parameters derived from heat release analysis are used for combustion diagnostics and control in internal combustion engines. It is important to tune the input parameters used in heat release calculations, in order to get correct estimation of heat release rate. In this study, tuning of input parameters is carried out by using cumulative heat release calculations of cylinder pressure during motoring. This tuning procedure uses offline iterative processing of motoring in-cylinder pressure data. The tuned parameters obtained from this method can also be utilized for online analysis of combustion parameters. Input parameters used in these investigations are intake air temperature, intake air pressure, phasing between the acquired pressure and crank angle position, compression ratio and scaling factor of heat transfer coefficient. Effect of error in these input parameters on estimated combustion and performance parameters like IMEP, combustion phasing, combustion duration, heat release rate, and maximum mean gas temperature are evaluated. The relative importance of measurement error in input parameters and its maximum expected error in the final results is analyzed in a HCCI combustion engine. Results shows that measurement errors in phasing between pressure and crank angle position, compression ratio and inlet air pressure affect estimated combustion and performance parameters significantly.     

Effect of piston bowl shape on the in-cylinder flow characteristics of IC engines

Numerical simulation of the in-cylinder flow for internal combustion (IC) engine with different bowl shapes has been performed. The LES models are applied to a piston-cylinder assembly with a stationary valve and a harmonically moving piston. Gas motion inside the engine cylinder determines the thermal efficiency of an IC engine, and combustion chamber geometry affects the performance of the IC engine. Comparison of the flow characteristics inside the engine cylinder equipped with different piston geometries shows that the squish flow affects the turbulence generation process near the top dead center during compression stroke. The A-type combustion chamber with reentrant shape is shown to have higher radial velocity and turbulence intensity in the piston bowl compared with other types. Results of these simulations aid in the improved understanding of the effect of intake and compression process of piston geometry on the in-cylinder flow. The detailed flow characteristics inside the in-cylinder for different piston bowl shapes can offer basic guidelines to improve the combustion process.     

Source location of acoustic emission in diesel engines

This paper is the third in a series developing methods of mapping acoustic emission (AE) signals and wave propagation in engines and focuses on source location techniques for the multi-source signals on relatively complex structures typical of machinery applications. Two source location techniques, a traditional wave velocity-based and an AE energy-based technique, using triangular sensor arrays, are used to locate source positions on the cylinder head of a 74 kW diesel engine using simulated sources (pencil lead break) and real sources (e.g. injectors (INJs) and exhaust valves during engine running).Source location using both techniques is demonstrated on the cylinder head of a 74 kW four-stroke diesel engine. The velocity-based technique uses AE wave speeds and time-of-flight (wave arrival time) to locate source position and is found to be most effective for single source signals with a sharp rising edge and good signal to noise ratios. The energy-based technique is based on a simple absorption attenuation model and was found to be useful for multiple source signals such as INJ signals, although structure-specific attenuation coefficients need to be measured for accurate source location.     

Adaptation of a zero-dimensional cylinder pressure model for diesel engines using the crankshaft rotational speed

Tighter emission regulations are driving the development of advanced engine control strategies relying on feedback information from the combustion chamber. In this context, it is especially seeked for alternatives to expensive in-cylinder pressure sensors. The present study addresses these issues by pursuing a simulation-based approach. It focuses on the extension of an empirical, zero-dimensional cylinder pressure model using the engine speed signal in order to detect cylinder-wise variations in combustion. As a special feature, only information available from the standard sensor configuration are utilized. Within the study, different methods for the model-based reconstruction of the combustion pressure including nonlinear Kalman filtering are compared. As a result, the accuracy of the cylinder pressure model can be enhanced. At the same time, the inevitable limitations of the proposed methods are outlined.     

基于飞轮加速度的缸间差异和循环差异研究

针对发动机缸间差异和循环差异缺少定量计算的研究现状,利用Matlab软件对发动机怠速时的飞轮原始数据进行处理,定量计算内燃机飞轮的最大角速度缸间差异参数、循环差异参数和抖振参数（lowest normalized value,简称LNV）,分析其与相应气缸压力参数之间的相关性及随内燃机转速和载荷的变化规律。分析结果表明,内燃机最大角速度缸间差异、循环差异和LNV值分别与相应的气缸压力参数高度线性正相关;随着怠速升高,缸间差异减小,循环差异基本保持不变;起初随着怠速升高,内燃机的抖振变小,当怠速升高到一定程度,抖振基本保持不变。随着内燃机载荷的增加,缸间差异、循环差异和抖振都减小,但循环差异比缸间差异受载荷影响更大。     

Misfire and compression fault detection through the energy model

This article proposes a simple algorithm for misfire detection in reciprocating engines. The algorithm, based on an energy model of the engine, requires the measurement of the instantaneous angular speed. By processing the engine dynamics in the angular domain, variations in the working parameters of the engine, such as external load and mean angular speed, are compensated. A dimensionless feature has been abstracted for evaluation of the combustion as well as compression process of each cylinder. The proposed technique is expected to be easy to implement and to provide useful information for on-line monitoring of the in-cylinder processes in an internal combustion engine.     

Analysis and modeling of exhaust gas temperature in an ethanol fuelled HCCI engine

Low exhaust temperature in homogeneous charge compression ignition (HCCI) significantly limits efficiency of an exhaust aftertreatment system to mitigate high HC and CO emissions in HCCI engines. This article aims to understand the effect of varying input parameters on HCCI exhaust gas temperature (T_exh) for an ethanol fuelled engine. A single cylinder engine is used to collect experimental data at 100 different HCCI conditions. The results indicate that variation in combustion parameters such as start of combustion (SOC), burn duration (BD) and maximum in-cylinder pressure (P_max) are not effectively correlated with variations of Texh, but the indicated mean effective pressure (IMEP) and constant-volume adiabatic flame temperature (T_ad) are strongly related to T_exh. These experimental findings were then used to design an artificial neural network (ANN) model to predict T_exh. The model was validated with the experimental data, indicating an average error less than 4.5°C between predicted and measured T_exh.     

基于数值模拟优化分析的某型汽油机发动机燃烧系统正向开发

文中主要基于喷雾标定的结果进行发动机缸内燃烧系统的正向开发和优化.在喷雾试验数据的基础上建立了喷雾模型,并利用喷雾模型和发动机相关数据进行了缸内燃烧计算,分析了缸内流场和油气混合情况.分析表明:缸内流场方面,在压缩冲程中不同工况下均形成了非常明显的滚流流场,同时滚流比大小的变化存在明显的"双峰"现象,不同工况下均有燃油...     

缸内直喷汽油机冷启动燃烧与排放光学试验研究

结合光学单缸机和激光诱导荧光测量技术对直喷汽油机冷怠速工况缸内油气混合与燃烧过程进行了可视化试验研究。试验采用了屋脊形透明缸套和双侧激光,利用统计图像评估方法得到了缸内混合气浓度和燃烧火焰分布图像,通过缸压传感器和燃烧分析仪对燃烧稳定性进行了分析,采用废气分析仪和光学传感器分别对碳氢和碳烟排放进行了分析评估。研究表明：燃烧稳定时燃油与缸套碰壁是碳氢排放产生的主要原因,碳烟排放则主要由活塞顶部燃油碰壁造成;适当推迟第二次喷油时刻有利于点火时刻火花塞附近稳定浓混合气的形成,继而提高燃烧稳定性,同时减少碳氢排放,过迟喷射会导致碳烟明显增加,过早喷射会造成缸内失火,碳氢排放增加。     

Phenomenological combustion modeling of a direct injection diesel engine with in-cylinder flow effects

A cycle simulation program is developed and its predictions are compared with the test bed measurements of a direct injection (DI) diesel engine. It is based on the mass and energy conservation equations with phenomenological models for diesel combustion. Two modeling approaches for combustion have been tested; a multi-zone model by Hiroyasu et al (1976) and the other one coupled with an in-cylinder flow model. The results of the two combustion models are compared with the measured imep, pressure trace and NOx and soot emissions over a range of the engine loads and speeds. A parametric study is performed for the fuel injection timing and pressure, the swirl ratio, and the squish area. The calculation results agree with the measured data, and with intuitive understanding of the general operating characteristics of a DI diesel engine.     

Investigation of in-cylinder flow patterns in 4 valve S. I. Engine by using single-frame particle tracking velocimetry

The in-cylinder flow field of gasoline engine comprises unsteady compressible turbulent flows caused by the intake port, combustion chamber geometry. Thus, the quantitative analysis of the in-cylinder flow characteristics plays an important role in the improvement of engine performances and the reduction of exhaust emission. In order to obtain the quantitative analysis of the in-cylinder gas flows for a gasoline engine, the single-frame particle tracking velocimetry was developed, which is designed to measure 2-dimensional gas flow field. In this paper, influences of the swirl and tumble intensifying valves on the in-cylinder flow characteristics under the various intake flow conditions were investigated by using this PTV method. Based on the results of experiment, the generation process of swirl and tumble flow in a cylinder during intake stroke was clarified. Its effect on the tumble ratio at the end of compression stroke was also investigated.     

Simulation of combustion in a porous-medium diesel engine

The future internal-combustion (IC) engines should have minimum emissions level under lowest feasible fuel consumption. This aim can be achievable with a homogeneous combustion process in diesel engines. We used a porous medium (PM) to homogenize the combustion process. This research studies simulation of a direct-injection diesel engine, equipped with a chemically inert hemispherical PM. Methane is injected into a hot PM, assuming mounted up the cylinder in head. Combustion with lean mixture occurs inside PM. A numerical model of PM engine was carried out using a modified version of the KIVA-3V code. PM results were evaluated with experimental data of unsteady combustion-wave of methane in a porous tube. The results show the mass fraction of methane, CO, NO and temperature in solid and gas phases of the PM and in-cylinder fluid. Also presented are the effects of injection timing and compression ratio on combustion.

     

车用柴油机燃烧和热流分析的数值研究

利用商用软件STAR—CD及ES—ICE对某D6114柴油机在的缸内燃烧过程进行了数值模拟计算,分析和比较了不同喷油提前角对缸内燃烧过程和燃烧室表面热流的影响。研究结果表明：喷油提前角提前,柴油机缸内的燃烧效果优于喷油提前角推迟,燃烧过程中缸内的压力和温度比推迟喷油提前角时要大,同时缸内的最高燃烧压力和最高温度也高;喷油提前角对缸盖和活塞顶壁面平均热流的影响与其对缸内平均温度的影响相似,对缸套壁面的影响是喷油提前角提前越早,传给缸套的热流越小。数值计算结果为高功率、高强化和低热损的柴油机设计提供理论依据。．     

Experimental investigation and mechanism of material removal in nano finishing of MMCs using abrasive flow finishing (AFF) process

Aluminum alloy and its composites appear to have a good future as a candidate material for engineering and structural components. Finishing of these materials is a big challenge as they are heterogeneous in nature having abrasive particles randomly distributed and oriented in the matrix material. Metal matrix composite (MMC-aluminum alloy and its reinforcement with SiC) workpieces were initially ground to a surface roughness value in the range of 0.6 ± 0.1 μm, and later were finished to the R_a value of 0.25 ± 0.05 μm by using Abrasive Flow Finishing (AFF) process. The effects of different process parameters, such as extrusion pressure, number of cycles and viscosity of the medium were studied on a change in average surface roughness (ΔR_a) and material removal. The relationship between extrusion pressure and ΔR_a shows an optimum at about 6 MPa. In the same way, the relationship between weight percentage of processing oil (plasticizer) and ΔR_a also shows an optimum at 10 wt%. Further, an increase in workpiece hardness requires more number of cycles to achieve the same level of improvement in ΔR_a. Material removal also increases with an increase in extrusion pressure and number of cycles while it decreases with an increase in processing oil content in the medium. It is also concluded that the mechanism of finishing and material removal in case of alloys is different from that in case of MMC.     

EFFECTS OF COOLED EXTERNAL EXHAUST GAS RECIRCULATION ON DIESEL HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

The effects of cooled external exhaust gas recirculation (EGR) on the combustion and emission performance of diesel fuel homogeneous charge compression ignition (HCCI) are studied. Homogeneous mixture is formed by injecting fuel in-cylinder in the negative valve overlap (NVO) period. So, the HCCI combustion which has low NOx and smoke emission is achieved. Cooled external EGR can delay the start of combustion effectively, which is very useful for high cetane fuel (diesel) HCCI, because these fuels can easily self-ignition, which makes the start of combustion more early. External EGR can avoid the knock combustion of HCCI at high load which means that the EGR can expand the high load limit. HCCI maintains low smoke emission at various EGR rate and various load compared with conventional diesel engine because there is no fuel-rich area in cylinder..     

Numerical analysis of the combustion process in a four-stroke compressed natural gas engine with direct injection system

In this paper, a numerical study to simulate and analyze the combustion process occurred in a compressed natural gas direct injection (CNG-DI) engine by using a multi-dimensional computational fluid dynamics (CFD) code was presented. The investigation was performed on a single cylinder of the 1.6-liter engine running at wide open throttle at a fixed speed of 2000 rpm. The mesh generation was established via an embedded algorithm for moving meshes and boundaries for providing a more accurate transient condition of the operating engine. The combustion process was characterized with the eddy-break-up model of Magnussen for unpremixed or diffusion reaction. The modeling of gaseous fuel injection was described to define the start and end of injection timing. The utilized ignition strategy into the computational mesh was also explained to obtain the real spark ignition timing. The natural gas employed is considered to be 100% methane (CH₄) with three global step reaction scheme. The CFD simulation was started from the intake valves opening until the time before exhaust valves opening. The results of CFD simulation were then compared with the data obtained from the single-cylinder engine experiment and showed a close agreement. For verification purpose, comparison between numerical and experimental work are in the form of average in-cylinder pressure, engine power as well as emission level of CO and NO. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

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.     

基于虚拟技术的天然气发动机缸内压力信号采集系统

介绍了运用虚拟仪器技术开发的天然气发动机缸内压力信号采集和分析系统,系统以通用PC为平台并利用软件代替了大部分硬件功能,能够进行连续多循环采集、录制示功图并实现缸内的燃烧分析.着重探讨了缸内压力数据的采集方式、存储方式、滤波处理及它们的软件实现方法.     

喷射装置导管对大缸径气体燃料发动机缸内混合效果的影响

在喷射装置出口加装导管,将燃气分别导向大缸径多点电喷气体燃料发动机的螺旋进气道和切向进气道,建立了联合喷射装置内部流动区域的发动机瞬态CFD计算模型,分析了导管位置对缸内掺混过程的影响。研究结果表明：对于该切向气道、螺旋气道的组合进气道,进气冲程在缸内靠近缸盖截面上产生了干涉涡流,对于螺旋气道喷射方案,燃气向气缸中心靠近,压缩末了时刻燃气集中在缸盖附近;而对于切向气道喷射方案,燃气冲向活塞顶,压缩末了时刻燃气集中在活塞顶附近。点火时刻的混合效果从优到劣依次为螺旋气道喷射方案、无导管喷射方案、切向气道喷射方案。