New 0D/1D Physical Approach for Modelling the Gas Dynamics Behavior Inside the Intake System of an Engine

The competition among carmakers to introduce the most innovative solutions is growing day by day. Since few years, simulation is being used widely in automotive industries. Instead of building costly prototypes and expending fuel for doing tests on a real engine, simulation became a good solution before taking new decisions. Concerning the study of gas dynamics and pressure wave's propagation in the intake system of an internal combustion engine, a precise modelling is needed in order to obtain good results. Unfortunately, the computational time for these simulations is considered as high compared to the real time. The main objective of the new approach presented in this paper, is to reduce simulation time of models in the internal combustion engine simulation code, allowing them to accomplish many engine simulations faster than one-dimensional non-linear approach. A transfer function is defined to link directly the relative pressure and the air mass flow rate. In a second time, the model is included into an internal combustion engine simulation code. The results obtained with this code are compared to experimental ones which are measured on a one-cylinder engine test bench. A good agreement is obtained between the experimental results and the numerical one. The model was improved by adding a transfer function for temperature evolution. The convergence time is then reduced as well as the global simulation time of the model.     

Fluid dynamic modeling of junctions in internal combustion engine inlet and exhaust systems

The modeling of inlet and exhaust systems of internal combustion engine is very important in order to evaluate the engine performance. This paper presents new pressure losses models which can be included in a one dimensional engine simulation code. In a first part, a CFD analysis is made in order to show the importance of the den- sity in the modeling approach. Then, the CFD code is used, as a numerical test bench, for the pressure losses models development. These coefficients depend on the geometrical characteristics of the junction and an experi- mental validation is made with the use of a shock tube test bench. All the models are then included in the engine simulation code of the laboratory. The numerical calculation of unsteady compressible flow, in each pipe of the inlet and exhaust systems, is made and the calculated engine torque is compared with experimental measurements.     

CFD modeling and experimental study of combustion and nitric oxide emissions in hydrogen-fueled spark-ignition engine operating in a very wide range of EGR rates

In the current work, the variation of EGR rates is investigated in a hydrogen-fueled, spark-ignition engine. This technique is followed in order to control the engine load and decrease the exhaust nitrogen oxides emissions. The external EGR is varied in the very wide range of 12% up to 47% (by mass), where in each test case the in-cylinder mixture is stoichiometric, diluted with the appropriate EGR rate. The operation of this engine is explored using measured data with the aid of a validated CFD code. Moreover, a new residual gas term existing in the expression of the hydrogen laminar flame speed, which has been derived from a one-dimensional chemical kinetics code, is tested in a real application for appraising its capabilities. The investigation conducted provides insight on the performance and indicated efficiency of the engine, the combustion processes, and the emissions of nitrogen oxides. More precisely, an experimental study has been deployed with the aim to identify the characteristics of such a technique, using very high EGR rates, focusing on the combustion phenomena. At the same time, the CFD results are compared with the corresponding measured ones, in order to evaluate the CFD code under such non-conventional operating conditions and to test a recent expression for the residual gas term included in the hydrogen laminar flame speed expression. It is revealed that the combustion takes place in few degrees of crank angle, especially at high engine loads (low EGR rates), whereas the exhaust nitrogen oxides emissions are significantly decreased in comparison to the use of lean mixtures for controlling the engine load. Additionally, the recent expression of the residual gas term, which has been tested and incorporated in the CFD code, seems to be adequate for the calculation of combustion phenomena in highly diluted, with EGR, hydrogen-fueled spark-ignition engines, as for every EGR rate tested (even for the higher ones) the computational results are compared in good terms with the measured data.     

Investigating the effect of crevice flow on internal combustion engines using a new simple crevice model implemented in a CFD code

A theoretical investigation is conducted to examine the way the crevice regions affect the mean cylinder pressure, the in-cylinder temperature, and the velocity field of internal combustion engines running at motoring conditions. For the calculation of the wall heat flux, a wall heat transfer formulation developed by the authors is used, while for the simulation of the crevices and the blow-by a newly developed simplified simulation model is presented herein. These sub-models are incorporated into an in-house Computational Fluid Dynamics (CFD) code. The main advantage of the new crevice model is that it can be applied in cases where no detailed information of the ring-pack configuration is available, which is important as this information is rarely known or may have been altered during the engine’s life. Thus, an adequate estimation of the blow-by effect on the cylinder pressure can be drawn. To validate the new model, the measured in-cylinder pressure traces of a diesel engine, located at the authors’ laboratory, running under motoring conditions at four engine speeds were used as reference, together with measured velocity profiles and turbulence data of a motored spark-ignition engine. Comparing the predicted and measured cylinder pressure traces of the diesel engine for all cases examined, it is observed that by incorporating the new crevice sub-model into the in-house CFD code, significant improvements on the predictive accuracy of the model is obtained. The calculated cylinder pressure traces almost coincide with the measured ones, thus avoiding the use of any calibration constants as would have been the case with the crevice effect omitted. Concerning the radial and swirl velocity profiles and the turbulent kinetic energy measured in the spark-ignition engine, the validation process revealed that the developed crevice model has a minor influence on the aforementioned parameters. The theoretical study has been extended by investigating in the same spark-ignition engine, during the induction and compression strokes, the way crevice flow affects the thermodynamic properties of the air trapped in the cylinder.     

双燃料发动机燃烧放热规律分析及燃烧特性研究

从热力学和内燃机燃烧的基本理论入手 ,推导了计算分析双燃料发动机缸内工质成分和热力学参数的计算关系式以及求解双燃料发动机燃烧放热规律的微分方程式 ,基于面向对象技术开发了双燃料发动机燃烧放热规律计算软件。研究结果表明 :用传统柴油机分析方法计算双燃料发动机的放热率峰值偏小 ,所计算的缸内工质平均温度偏高 ,新模型计算的结果与实际情况更为吻合。该分析软件可以适用于多种燃料发动机 ,是内燃机燃烧放热规律的通用计算软件。双燃料发动机燃烧特性研究表明 :双燃料发动机初始放热率比纯柴油大 ,若着火始点在上止点后 ,双燃料缸内最大爆发压力比纯柴油低 ,否则比纯柴油高 ;控制双燃料发动机着火始点是控制缸内最大爆发压力和 NOx 排放的关键 ,双燃料发动机着火始点应在上止点后 ,可以使发动机爆发压力和 NOx 排放比纯柴油低。     

A thermodynamics model for the compression and expansion process during the engine’s motoring and a new method for the determination of TDC with simulation technique

In this paper, a thermodynamics model describes the pressure change during the motoring process of the internal combustion engine was given based on the mass conservation, energy conservation law and the state equation of perfect gas. The factors that affect the maximal pressure point position relative to the minimal volume point (top dead center) were analysed with the thermodynamics model. The one to one correspondence between the geometrical characteristics of the pressure diagram and the maximum pressure point position relative to the top dead center (TDC) was proven. Based on the model described, a new method for the determination of the TDC of the internal combustion engine was given. The simulation and experimental results indicate that the new method could determine the top dead center with an error smaller than 0.05 crank angle.     

Experimental evaluation of local instantaneous heat transfer characteristics in the combustion chamber of air-cooled direct injection diesel engine

An experimental analysis is conducted investigating the differences between the variations of overall and local instantaneous heat transfer coefficients, during the engine cycle, in the combustion chamber walls of a direct injection (DI), air-cooled diesel engine located at the authors’ laboratory. For this purpose, a novel experimental installation is developed, which separates the engine transient temperature signals into two parts, namely the long- and the short-term response ones, processed in two independent data acquisition systems. Moreover, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an object-oriented control code for fast data acquisition have been designed and applied. Experimentally obtained cylinder pressure diagrams are used as a basis for the calculation of the overall heat transfer coefficients, whereas one-dimensional heat conduction theory with Fourier analysis techniques, combined with an iterative procedure between calculated and measured temperature data, are implemented in order to calculate the instantaneous local heat transfer coefficients in the engine cylinder. Analysis of the experimental results reveals interesting aspects of transient engine heat transfer. Significant differences are disclosed between the overall and local heat transfer coefficient variations, with the importance of the latter one on engine design being emphasized. The local heat transfer coefficient on the cylinder head is quantified based on the experimental data. The effect of engine speed and load as well as of the air swirling motion on the heat transfer variations are presented. From the analysis results it is concluded that the instantaneous heat transfer variation is non-uniform, unlike its values calculated from standard correlations that assume spatial uniformity, noting that such information, especially for air-cooled diesel engines, seems to be very scarce in the open literature.     

Air mass flow and pressure optimisation of a PEM fuel cell range extender system

In order to eliminate the local CO₂ emissions from vehicles and to combat the associated climate change, the classic internal combustion engine can be replaced by an electric motor. The two most advantageous variants for the necessary electrical energy storage in the vehicle are currently the purely electrochemical storage in batteries and the chemical storage in hydrogen with subsequent conversion into electrical energy by means of a fuel cell stack. The two variants can also be combined in a battery electric vehicle with a fuel cell range extender, so that the vehicle can be refuelled either purely electrically or using hydrogen. The air compressor, a key component of a PEM fuel cell system, can be operated at different air excess and pressure ratios, which influence the stack as well as the system efficiency. To asses the steady state behaviour of a PEM fuel cell range extender system, a system test bench utilising a commercially available 30 kW stack (96 cells, 409 cm² cell area) was developed. The influences of the operating parameters (air excess ratio 1.3 to 1.7, stack temperature 20 °C–60 °C, air compressor pressure ratio up to 1.67, load point 122 mA/cm² to 978 mA/cm²) on the fuel cell stack voltage level (constant ambient relative humidity of 45%) and the corresponding system efficiency were measured by utilising current, voltage, mass flow, temperature and pressure sensors. A fuel cell stack model was presented, which correlates closely with the experimental data (0.861% relative error). The air supply components were modelled utilising a surface fit. Subsequently, the system efficiency of the validated model was optimised by varying the air mass flow and air pressure. It is shown that higher air pressures and lower air excess ratios increase the system efficiency at high loads. The maximum achieved system efficiency is 55.21% at the lowest continuous load point and 43.74% at the highest continuous load point. Future work can utilise the test bench or the validated model for component design studies to further improve the system efficiency.     

Research on diagnosis of pre-ignition of hydrogen engine based on SOM-MAS

Abnormal combustion is an important factor in the development process of hydrogen engine and it mainly includes pre-ignition, backfire and knocking, among which pre-ignition has the most serious impact on hydrogen engine. In this paper, it is divided into four types: normal combustion, slight pre-ignition, moderate pre-ignition and severe pre-ignition according to different crankshaft rotation angles. In order to identify different combustion types, this paper proposes a fault diagnosis model based on the fusion of SOM neural network and Multi-Agent System (SOM-MAS). Firstly, different combustion types are identified by SOM. Secondly, the abnormal combustion is tracked and located mainly through the Multi-Agent System, and the location of the abnormality is identified. Finally, based on 44 sets of pressure data samples collected from the in-cylinder combustion of a hydrogen engine on the experimental bench, different combustion types were diagnosed and identified, and the location of abnormal combustion faults was tracked, which verifies the effectiveness of the proposed method shows that the method has certain feasibility and superiority for the diagnosis of hydrogen engine pre-ignition.     

Experimental study of hydrogen enriched compressed natural gas (HCNG) engine and application of support vector machine (SVM) on prediction of engine performance at specific condition

The effect of excess air ratio (λ) and ignition advance angle (θ_ig) on the combustion and emission characteristics of hydrogen enriched compressed natural gas (HCNG) on a 6-cylinder compressed natural gas (CNG) engine has been experimental studied in an engine test bench, aiming at enriching the sophisticated calibration of HCNG fueled engine and increasing the prediction accuracy of the SVM method on automobile engines. Three different fuel blends were selected for the experiment: 0%, 20% and 40% volumetric hydrogen blend ratios. It is noted that combustion intensity varies with the excess air ratio and the ignition advance angle, so are the emissions. The optimal value of λ or θ_ig has been explored in the specific engine condition. Results show that blending hydrogen can enhance and advance the combustion and stability of CNG engine, and it also has some benefic influence on the emissions such as reducing the CO and CH₄. Meanwhile, a simulation research on forecasting the engine performance by using the support vector machine (SVM) method was conducted in detail. The torque, brake specific fuel consumption and NO_x emission have been selected to characterize the power, economic and emissions of the engine with various HCNG fuels, respectively. It can be seen that the optimal model built by the SVM method can highly describe the relationship of the engine properties and condition parameters, since the value of the complex correlation coefficient is larger than 0.97. Secondly, the prediction performance of the optimal model for torque or BSFC is much better than the case of NO_x. Besides, the optimal model built by the PSO optimization method has the best prediction accuracy, and the accuracy of the model obtained based on the training group with 20% hydrogen blend ratio is the best compared with those of others. The upshots in this article provide experimental support and theoretical basis for the adoption of HCNG fuel on internal combustion engines as well as the application of intelligent algorithmic in the engine calibration technology field.     

层流小火焰模型在柴油机湍流燃烧中的应用

将湍流燃烧的层流小火焰模型应用于典型的柴油机扩散燃烧过程.以混合分数为自变量,以标量耗散率为参数,建立相空间中的层流小火焰数据库.应用KIVA-3程序模拟内燃机缸内多维湍流流场,并补充求解混合分数的时均值和脉动均方值的湍流输运方程.将两部分结果通过Beta概率密度函数进行耦合积分,便可得到组分质量分数和温度等参数在柴油机工作过程中的时间、空间分布.对一台直喷式柴油机的湍流燃烧过程进行了模拟计算,所得结果符合实际.     

天然气直喷发动机当量比与稀薄燃烧对比研究

针对一台自然吸气四缸天然气缸内直喷发动机,建立了发动机仿真模型,通过台架试验数据对模型进行了验证。开展了均质当量比燃烧和稀薄燃烧两种方案的整机动力性、热负荷和经济性对比研究。结果表明：稀薄燃烧时动力性下降明显,当量比燃烧时热负荷较高,空燃比稍大于当量比时经济性最好。     

电喷汽油机进气管空气动态模型的仿真与试验研究

由理想气体状态方程、质量守恒方程、能量守恒方程和速度密度方程建立了电控燃油喷射汽油机进气歧管空气动态的均值模型.为满足基于模型进行空燃比实时控制的要求,基于以下两个假设对模型进行了简化：（1）假设进气流量与模型所建立的关于节气门开度和进气压力的表达式的乘积成线性关系;（2）充量系数和进气压力的乘积与进气压力成线性关系.在MATLAB/Simulink仿真环境中对模型进行了仿真分析,得到了模型的主要参数.最后分别在稳态和瞬态工况下将仿真结果与台架试验结果进行了对比,结果表明：模型中所作的假设成立,稳态和瞬态工况下模型的误差分别在2%和3%以内,说明模型具有较高的精度,且结构简单,能够满足控制过程实时性的要求.     

双燃料内燃机引燃油混合气形成与燃烧过程模型研究

对于双燃料发动机，引燃油蒸发、混合与燃烧是在天然气与空气混合物为介质的情况下，通过采用离散液滴模型，模拟了引燃油的蒸发与混合过程；采用经过修正的Shell模型，对引燃油的着火过程进行了数值模拟；以阿伦纽斯公式为基础，综合湍流对化学动力学的影响，提出了一个新的燃烧模型．经过模拟计算与实验对比，验证了该数值模型的模拟效果．     

二甲醚发动机燃烧特性的试验与数值模拟研究

在一台直喷式压燃发动机上开展了二甲醚燃烧与排放特性的试验与数值模拟研究。测量了二甲醚在高压燃油泵内的泄漏量及其与发动机转速之间的定量关系,并就发动机分别燃用二甲醚和柴油的运转性能进行了对比试验研究,结果表明,发动机燃用二甲醚要比燃用柴油具有更好的性能与排放水平;另从二甲醚低温着火的化学反应机理人手,开展了其自燃着火过程的数值模拟研究,进而建立了计及温度、压力和燃空当量比因素的DME滞燃期数据库;通过将该数据库与发动机循环模拟程序相耦合,对DME发动机的运转性能进行了变参数预测分析,预测结果与试验结果吻合较好。     

Combustion characteristics and performance of natural gas in high speed indirect injection diesel engine

In recent years, efforts have been directed towards environmentally freindly sources of alternative fuels for internal combustion engines. This paper investigates combustion characteristics and performance of natural gas in an unmodified compression ignition engine using diesel fuel pilot injection. The factors influencing knock limits in dual fuel gas engines have been identified. This report is confined to experimental work in a naturally aspirated dual gas engine and the results obtained were compared with the diesel fueled test engine. Cylinder pressure diagrams recorded indicate longer ignition delay and burning rates with an increased pressure variation.     

Evaluation of a new computational fluid dynamics model for internal combustion engines using hydrogen under motoring conditions

The present work conducts a preliminary evaluation of a new CFD (computational fluid dynamics) model, which is under development at the authors' laboratory. Using this model, it is feasible to understand how the intake manifold and in-cylinder geometry affect the in-cylinder flow field and the mixing processes taking place in an Otto (spark-ignition) engine. The model is applied on a high-swirl, two-valve, four-stroke, transparent combustion chamber engine running under motoring conditions. To investigate the fuel–air mixing process, hydrogen is injected in the intake manifold. To evaluate the model three case studies are examined. First, the model is applied to simulate the external mixing in the intake manifold with a tee-mixer injection system. Secondly, the transient gas flow field in the intake manifold and engine cylinder is examined over the complete engine cycle. Finally, the transient mixing process in the intake manifold and the spatial and temporal distribution of species concentrations inside the cylinder are numerically computed using the developed model. To validate the model, the results obtained through the test cases examined are compared either with available experimental data or with simulated results, which are obtained using a commercially available CFD code applied under the same conditions.     

Development of an Oil Gallery Cooling Model for Internal Combustion Engines Considering the Cocktail Shaker Effect

An internal combustion engine oil gallery cooling model was developed, which can predict average heat transfer coefficients by considering the cocktail shaker effect due to the reciprocal motion of the engine piston. The model prediction showed good agreement with available experimental data. Using the gallery cooling model and a computational fluid dynamics code which was developed to predict the combustion process, the influence of various oil cooling methods was studied numerically. Comparing the peak temperature of air cooling and oil jet-with-gallery cooling cases, the difference of the piston surface temperature was predicted to be as much as 300 K.     

自然吸气式CNG发动机主充模型的研究

为了准确预测自然吸气式压缩天然气(Compressed Natural Gas,CNG)发动机的空气流量,基于汽油机进气系统平均值模型,构建了CNG发动机的主充模型。根据CNG发动机进气系统的实际工作环境,引入了温度修正系数、体积修正系数、燃气量修正系数等参数,计算了不同工况下CNG发动机的空气流量。通过CNG发动机台架试验,测量了不同转速、不同进气歧管压力下的空气流量;对比分析了空气流量的计算值和试验值的方法,评估了模型的预测性能。结果表明,所建立的主充模型能较好的预测不同转速下空气流量随CNG发动机进气歧管压力的变化规律,空气流量的预测值与实验值的最大误差小于3%,模型具有较高的预测精度。