Engine Cycle Simulation Research Articles

1-D ENGINE MODELING OF 4-CYLINDER TURBOCHARGED GASOLINE ENGINE

This project is conducted to explore one-dimensional (1D) simulation for a 4-cylinder gasoline engine. The simulation and computational development of modeling for the study are conducted by using the commercial Computational Fluid Dynamics (CFD) of AVL BOOST software. The engine model was developed corresponding to a Proton 1.6-litre CamPro 4-cylinder turbocharged gasoline engine including the real engine geometry and parameters. The engine model is based on 1D equation of the gas exchange process, progressive engine combustion process, isentropic compression and expansion, and accounting for the heat transfer as well as the frictional losses. The aim of the study is to predict the steady-state performance of the engine model at full and partload conditions from 1000 to 5000 rpm by using engine cycle simulation. In this study, three parameter tuning works have been performed, which are combustion model tuning, intake manifold temperature tuning and turbocharger’s scaling factor tuning. In addition, the comparison and validation were done for the output performance parameters based on the provided experimental data. Overall, the engine performance behavior have been observed to determine how accurate AVL BOOST software can evaluate engine performance compare to experiment conducted on the real engine. The most accurate validation of the engine performance parameters have been achieved by manifold absolute pressure (MAP) with 3.14% error. However, by comparing with experimental data, major discrepancy is noticeable on several engine performance parameters. From this study, the results showed that the engine model is able to simulate engine’s combustion process and produce reasonable prediction.

Multi-branch junction boundary model of an internal combustion engine intake and exhaust manifold system

Multi-branch junctions are commonly used in highly integrated supercharged internal combustion engines. Accurate prediction of flow performance is critical to engine cycle simulation. However, the few studies on this type of junction boundary model focus on incompressible fluid, which leads to insufficient accuracy in predicting compressible flow. In this study, based on a constant-pressure model commonly used to calculate multi-branch junctions, by considering fluid compressibility, we developed a momentum conservation model and a pressure loss coefficient model, respectively, that are tailored to multi-branch junctions. The momentum conservation model accounts for structural parameters such as branch angle and the influence of Mach number, and hence it improved the prediction accuracy. For a certain type of high-power-density internal combustion engine, the maximum simulation error is reduced from 7.58% to 2.47% in the engine performance prediction at the rated speed after using the momentum conservation model. The proposed pressure loss coefficient model was mainly used to compensate for the shortcomings of the momentum conservation model in the multi-branch calculation efficiency reduction, which is more dependent on the pressure loss coefficient database provided by the experiment. The influence of fluid compressibility was also considered. This investigation can provide tailored tools for multi-branch junction performance prediction in different functional simulation scenes.

Numerical Modelling of Emission Characteristic for a Single Cylinder Spark Ignition Engine

The main objective of this study is to elaborate an engine cycle simulation program using GT-Suite software to analyze the influence of equivalence ration and compression ratio on the main emissions of a four-stroke direct injection spark ignition engine. The experimental result is used to compare the cylinder pressure result obtained with the developed model. The present article is a study of the effect of compression ratio and equivalence ratio on the main emissions of the direct injection spark engine for a two-zone combustion analytical model and by using of the GT-Suite simulation software. The developed analytical model is validated by the use of experimental data. The analytical curve of the pressure in the combustion chamber is experimentally validated with a difference of the order of 6%.

A combined Combustion-Conjugate heat transfer analysis for Design of partially insulated pistons

Insulating engine combustion chamber surfaces with thermal barrier coatings (TBCs) provides engine thermal efficiency improvement by reducing the heat transfer to the coolant when done appropriately. However, reducing heat losses using traditional ceramic insulation increases combustion chamber wall temperatures during the whole engine cycle, including intake stroke resulting in a decreased engine volumetric efficiency due to excessive intake air heating. This paper presents the concept of partial insulation coverage on a selective area of combustion chamber wall by simulations to improve the engine's thermal efficiency. A combined combustion–conjugate heat transfer analysis methodology was developed to determine the partial-coverage insulation area by analyzing the heat flux and surface temperature distribution across the combustion chamber wall. Engine cycle simulations were run to compare the engine performance with various partial insulation designs, and an optimal insulation area was proposed. To validate the simulation results, the full-coverage coated piston technology with 0.5 mm thick Yttria Stabilized Zrconia (YSZ) coating has been experimentally evaluated on a prototype engine and compared to the non-insulated baseline aluminum piston. It was found that the partial coverage insulation showed a thermal efficiency improvement of 1.98% relative to a full-coverage insulated piston efficiency of 2.06%.

Effect of peak firing pressure constraint on thermal efficiency of a Sabathe-Miller engine

How to Improve the thermal efficiency of internal combustion engine is an eternal topic since it is directly related to energy consumption and pollution emissions. Among lots of technologies applied on heavy duty diesel engine, Miller cycle which increases the effective expansion ratio in relation to the compression is proved to be a good choice to balance engine performance with fuel economy and CO2/NOx/smoke emissions. However, limitation of peak firing pressure (PFP) will restrict the intake pressure or compression ratio of miller engines which in turn influence the thermal efficiency, and their in-depth trade-off relationship is not clear yet. Using the engine cycle simulation, this paper explores the most reasonable cylinder pressure waveform limited by PFP and found there exists an optimized pressure ratio values which slightly affected by other operating conditions for Sabathe-Miller cycle engine. Thereafter, effects of PFP limit on the performance of a large single cylinder engine were investigated considering the effect of engine load, miller degree, equivalence ratio as well as engine speed. It is found that under full load condition, the maximum brake thermal efficiency occurs when pressure ratio (PR) is about 1.2, and PFP constraint plays a dominant role on brake efficiency and could contribute more than 4.0% efficiency by increasing PFP constraint from 250bar to 350bar. Compared with full load condition, the brake thermal efficiency increases 4.6% and 6.3% respectively under fuel-rich (extremely high CR) and lean-burn (low heat loss) half load conditions. Meanwhile, miller degree was optimized for Sabathe-Miller cycle, and it plays a key role on reducing combustion temperature instead of increasing thermal efficiency compared with effect of PFP constraint.

Influence of thermal piston insulation on the indicated efficiency of SI-engines

High efficiency gasoline combustion engines with up to 50 % indicated efficiency are the target of current research work. To reach this goal, it’s essential to reduce all the combustion engine losses as much as possible. One major loss, with about 30 % of the total fuel energy, is the wall heat transfer loss. To reduce this loss, one solution is a temperature swing insulation, which is characterized by a low thermal conductivity and at the same time a low volumetric heat capacity. In order to analyze the thermal efficiency potential of different insulation materials, a thermal insulation model for one-dimensional engine process simulations has been developed and is presented in this paper. The insulation is discretized by a thermal node model and is coupled to an engine process simulation using the simulation tool GT-Power. The heat transfer and temperature swing behavior of the thermal insulation model is validated against 3D-CFD engine cycle simulations. A predictive detailed chemistry combustion model is used in 3D-CFD simulations to evaluate the influence of thermal insulations on the knocking tendency. Two different thermal insulation materials are investigated using the developed simulation model. One is yttria stabilized zirconia (YSZ) as a common thermal sprayed coating. The second material is produced by an electrolytic oxidation of the piston surface (anodizing). With thermal piston insulation, there is only a small increase in thermal efficiency in the range of 0.2 % to 0.6 % possible with both materials, whereby the potential increases at low speeds and medium loads. The reason can be found in the relative heat losses, which increases with a constant center of combustion and increasing load. An efficiency loss analysis shows that the exhaust losses increase by about two third of the reduced heat losses. Due to its lower volumetric heat capacity and similar heat conductivity, the anodized piston surface shows a thermal efficiency advantage compared to YSZ. The simulation results are finally validated by measurements conducted with a single-cylinder research engine for an YSZ coated piston surface as well as a hard anodized piston surface.

Heating and Evaporation of Droplets of Multicomponent and Blended Fuels: A Review of Recent Modeling Approaches

In this review, recent models for the heating/evaporation of multicomponent and blended fuel droplets and their implementation into numerical codes, used for the analysis of the processes in internal combustion engines, are reviewed. In these models, the diffusion of species, recirculation, and temperature gradient inside droplets are considered. The focus of the review is on the group of models based on the implementation of the analytical solutions to the heat transfer and species diffusion equations inside droplets into numerical codes. Four key aspects are summarized: (1) application of the Discrete Component (DC) model and the Multi-Dimensional Quasi-Discrete Model (MDQDM) to a broad range of fuels, including petrol, diesel, ethanol, and biodiesel fuels and their blends, (2) formulation of fuel surrogates, with a focus on the recently introduced Complex Fuel Surrogate Model (CFSM), (3) overview of the recently introduced transient algorithm, Transient Multi-Dimensional Quasi-Discrete Model (TMDQDM), for an autogeneration of quasi-components, and (4) implementation of the latter into a computational fluid dynamics (CFD) code for a realistic engineering application to full cycle simulation in internal combustion engines. The original and modified versions of the DC model and MDQDM are evaluated for the heating and evaporation of droplets of bio/fossil-fuel (e.g., ethanol/petrol/biodiesel/diesel) blends. These were implemented into commercial CFD software and validated. The feasibility of formulating complex fuel surrogates for fuel blends, their implementation into CFD codes, and their application in the full engine cycle simulation before and after the onset of combustion (autoignition) are described.

Real-time engine model development based on time complexity analysis

Real-time simulation models play an important role in the development of engine control systems. The mean value model (MVM) meets real-time requirements but has limited accuracy. By contrast, a crank-angle resolved model, such as the filling -and-empty model, can be used to simulate engine performance with high accuracy but cannot meet real-time requirements. Time complexity analysis is used to develop a real-time crank-angle resolved model with high accuracy in this study. A method used in computer science, program static analysis, is used to theoretically determine the computational time for a multicylinder engine filling-and-empty (crank-angle resolved) model. Then, a prediction formula for the engine cycle simulation time is obtained and verified by a program run test. The influence of the time step, program structure, algorithm and hardware on the cycle simulation time are analyzed systematically. The multicylinder phase shift method and a fast calculation method for the turbocharger characteristics are used to improve the crank-angle resolved filling-and-empty model to meet real-time requirements. The improved model meets the real-time requirement, and the real-time factor is improved by 3.04 times. A performance simulation for a high-power medium-speed diesel engine shows that the improved model has a max error of 5.76% and a real-time factor of 3.93, which meets the requirement for a hardware-in-the-loop (HIL) simulation during control system development.

Improvement in accuracy of engine cycle simulations by using a turbocharger prediction model instead of measured efficiency map

In the downsizing concept, the turbocharger (T/C) is one of the key devices for improving thermal efficiency and exhaust emissions of internal combustion engines for automobiles. In order to maximize the supercharged engine performance, the size of the T/C applied for the given engine system has been optimized by using a 1-D engine cycle simulation. For this reason, T/C performance prediction model for engine cycle simulation is required to be accurate over a wide operating range. In the conventional T/C performance prediction model, the turbine performance was predicted by extrapolating from the efficiency map measured under steady flow. However, the accuracy of the extrapolation method is uncertain, and it has been pointed out that the prediction accuracy is low in the low load operations. In this study, a 1-D T/C model developed based on hydrodynamics and thermodynamics was used. Using the 1-D T/C model, a grid efficiency map over the entire operating range was calculated and the grid map was applied to 1-D engine cycle simulation. The accuracy of the T/C model was verified by comparing the experimentally measured efficiency under steady flow.

Acausal Modeling Method and Its Verification of Engine Cycle Simulation for Emissions Prediction

Acausal Modeling Method and Its Verification of Engine Cycle Simulation for Emissions Prediction

Numerical Investigation and Multi-Objective Optimization of Internal EGR and Post-Injection Strategies on the Combustion, Emission and Performance of a Single Cylinder, Heavy-Duty Diesel Engine

This work presents a numerical study that investigates the optimum post-injection strategy and internal exhaust gas recirculation (iEGR) application with intake valve re-opening (2IVO) aiming to optimize the brake specific nitric oxide (bsNO) and brake specific soot (bsSoot) trade-off with reasonable brake specific fuel consumption (BSFC) via 1D engine cycle simulation. For model validation, single and post-injection test results obtained from a heavy-duty single cylinder diesel research engine were used. Then, the model was modified for 2IVO application. Following the simulations performed based on Latin hypercube DoE; BSFC, bsNO and bsSoot response surfaces trained by feedforward neural network were generated as a function of the injection (start of main injection, post-injection quantity, post-injection dwell time) and iEGR (2IVO dwell) parameters. After examining the effect of each parameter on pollutant emission and engine performance, multi-objective pareto optimization was performed to obtain pareto optimum solutions in the BSFC-bsNO-bsSoot space for 8.47 bar brake mean effective pressure (BMEP) load and 1500 rpm speed condition. The results show that iEGR and post-injection can significantly reduce NO and soot emissions, respectively. The soot oxidation capability of post-injection comes out only if it is not too close to the main injection and its efficiency and effective timing are substantially affected by iEGR rate and main injection timing. It could also be inferred that by the combination of iEGR and post-injection, NO and soot could be reduced simultaneously with a reasonable increase in BSFC if start of main injection is phased properly.

Predictive simulation of single cylinder n-butanol HCCI engine

Homogeneous Charge Compression Ignition (HCCI) is a commonly research new combustion mode due to its advantages over conventional combustion in internal combustion engine such as higher thermal efficiency as well as lower particulate matter (PM) and nitrogen oxides (NOx) emission. However, combustion phasing control difficulty is the main challenge in order to achieve this HCCI combustion due to the absence of direct auto-ignition control. The aim of this study is to investigate the effects of engine load conditions, intake charge temperature and exhaust gas recirculation (EGR) rate numerically on the combustion characteristics of HCCI engine in a single-cylinder and four-stroke engine fuelled with n-butanol. Predictive one-dimensional engine cycle simulation with single-zone model is employed in this study. A chemical kinetic mechanism of n-butanol is used to in this model to capture the chemical reaction process during the combustion. It was found that these parameters play important roles towards the combustion phasing of the HCCI engine as well as the in-cylinder pressure. This HCCI model is able to predict the trend of the combustion characteristics comprehensively with the variation of these critical parameters resulting in a good agreement with previous HCCI studies.

Computationally efficient evaluation of optimum homogeneous charge compression ignition operating range with accelerated multizone engine cycle simulation

The very intensive calculations necessary to define a performance map requiring evaluation of over a hundred individual operating points can be efficiently conducted with accelerated multizone for engine cycle simulation, leading to a definition of regions of acceptable and optimum homogeneous charge compression ignition operation. Accelerated multizone for engine cycle simulation has the virtue of enabling accurate evaluation of many operating conditions based on thermal stratification data from a single fluid mechanics run at motored conditions. This is possible because thermal stratification is more sensitive to engine geometry than to operating conditions. In this article, accuracy of accelerated multizone for engine cycle simulation is demonstrated by comparison with experimental data for iso-octane homogeneous charge compression ignition operation over a broad range of lean equivalence ratios (0.14–0.28). The validated accelerated multizone for engine cycle simulation model is then applied to generating a performance map for an engine controlled by appropriately adjusting equivalence ratio and internal exhaust gas recirculation. Regions of acceptable and optimum combustion are identified. It is finally demonstrated that while indicated mean effective pressure remains low for optimum homogeneous charge compression ignition operation (1–4 bar), this is sufficient for a large fraction of typical driving in light-duty vehicles. Much driving including idle can therefore be done in homogeneous charge compression ignition mode at high efficiency and low (essentially zero) NO x and particulate matter emissions.

High Efficiency by Miller Valve Timing and Stoichiometric Combustion for a Naturally Aspirated Single Cylinder Gas Engine

<div class="section abstract"><div class="htmlview paragraph">Small-scale cogeneration units (P<sub>el</sub> < 50 kW) frequently use lean mixture and late ignition timing to comply with current NO<sub>x</sub> emission limits. Future tightened NO<sub>x</sub> limits might still be met by means of increased dilution, though both indicated and brake efficiency drop due to further retarded combustion phasing and reduced brake power. As an alternative, when changing the combustion process from lean burn to stoichiometric, a three-way-catalyst allows for a significant reduction of NO<sub>x</sub> emissions. Combustion timing can be advanced, resulting in enhanced heat release and thus increased engine efficiency.</div><div class="htmlview paragraph">Based on this approach, this work presents the development of a stoichiometric combustion process for a small naturally aspirated single cylinder gas engine (P<sub>el</sub> = 5.5 kW) originally operated with lean mixture. To ensure low NO<sub>x</sub> emissions, a three-way-catalyst is used. In order to achieve high engine efficiency, measures implemented include Miller valve timing, optimized intake system, reduced engine speed and increased compression ratio. In the first step, a detailed 1D engine cycle simulation model was used to investigate the efficiency benefit of Miller valve timing and increased compression ratio. Within the numerical study, inlet valve closing timing and intake pipe length were varied, yet a closed-loop control was implemented to maintain a constant effective compression ratio of 14.66 by adjusting geometrical compression ratio for each configuration. Subsequently, the most expedient valve timing was designed using multi-body simulation of the inlet valve train, while increased compression ratio was achieved by modifying the series piston bowl geometry.</div><div class="htmlview paragraph">Engine trials agree with simulation results and show highest efficiency for a Miller valve timing closing +15 °CA later to the series valve timing and geometrical compression ratio of 15.36. Compared to the series lean burn engine, indicated and brake efficiency increase by 3.2 %-points to 39.0 % and by 3.9 %-points to 34.4 %, respectively, while maintaining original brake power of P<sub>e</sub> = 6.1 kW. Finally, an experimental study accompanied by 3D-CFD simulations was conducted to investigate the potential of optimized piston geometry to further increase efficiency. However, results reveal only minor effect of piston geometry on efficiency, what is likely stemming from interrelation of combustion efficiency, wall heat losses and heat release rate.</div></div>

Prediction of Marine Diesel Engine Combustion Characteristic in Transient Condition By Using Seiliger Process Cycle

Modern diesel engine cycle can be predicted by applying variety of simulation methods. These models are used for optimization of engine parameters, investigation of control strategies or evaluation phenomena that are difficult to measure. In practice, using engine cycle simulation methods, the number of expensive experiments studies could be reduced and very useful result could be obtained for prediction of engine design parameters in a short period of time. Furthermore, these models are also used to test different solutions (technologies) or control strategies which can help to reduce fuel consumption, increase power output, reduce emissions to meet emission requirement. In diesel engine modeling process, in cylinder pressure measurement is the fundamental method to investigate the combustion process and an effective way to get insight into the combustion phenomena. The main objective of the paper is focusing on the transient modeling of marine two stroke diesel engine and calculating (prediction) the parameter of the cylinder process model by using the Seiliger cycle process. The research approach is carried out using data from a MAN-10L90MC diesel engine and mathematical model of the test engine is calculated by using Microsoft Visual 6.0 VC++ programming.

Analytical and Experimental Study of a Naturally Aspirated Indirect Injection 4-Stroke Spark Ignition Engine

One of the objectives of this study is to elaborate an engine cycle simulation program in FORTRAN language to analyze the influence of operating parameters on the performance (theeffective power, torque and specific fuel consumption) of a four-stroke gasoline engine (Ford ZSG 416 gasoline engine) for different engine operating parameters. The GT-Powerengine simulation software was used to compare the results obtained with the developed computer program and to improve it. In this program, a single-zone thermodynamicmodel was considered, which describes each phase of the engine cycle. In order to validate the developed program, a comparison of the experimental results with those obtainedusing GT-Power software was carried out. The other objective of this paper is to investigate the influence of a number of significant engine parameters such as compression ratio, cylinder wall temperature, cylinder diameter, stroke-bore ratio and ignition angle on the performance of the chosen engine. Examining the experimental results and those obtained with the developed program, it was observed that the power difference was in the order of ± 3%, the torque difference was ± 6%, while the BSFC difference was about ± 10%. It has been noted that the most significant parameters in improving the performance of the gasoline engine are the compression ratio, the fuel/air ratio, the engine geometry and the ignition begin. The variation of these parameters was not arbitrary, the knock criteria, in other words, the achievement of normal combustion were taken into account.

Performance Optimization of a Diesel Engine with a Two-Stage Turbocharging System and Dual-Loop EGR Using Multi-Objective Pareto Optimization Based on Diesel Cycle Simulation

The effects of an electric supercharger (eS) and a dual-loop exhaust gas recirculation (EGR) system on a passenger car’s diesel engine’s emissions and fuel efficiency under various worldwide harmonized light-duty vehicles test procedure (WLTP) reference operation points were investigated using a one-dimensional engine cycle simulation, called GT-Power. After heavy EGR application, the in-cylinder pressure and temperature declined due to a dilution effect. As eS power and rpm increased, the brake-specific fuel consumption (BSFC) decreased because the effects of the air flow rate increased. However, it was unavoidable that nitrogen oxide (NOx) emissions also increased due to the higher in-cylinder pressure and temperature. To induce more EGR to the intake system, a dual-loop EGR system was applied with eS at different low-pressure EGR (LP-EGR) fractions (0, 0.25, 0.5, 0.75, and 1.0). Under these conditions, a design of experiment (DoE) procedure was carried out and response surface plots of the BSFC and brake-specific NOx (BSNOx) were prepared. A multi-objective Pareto optimization method was used to improve the trade-off in results between the BSFC and BSNOx. Through optimization, optimal Pareto fronts were obtained, which suggested design parameters for eS power and rpm to control the engine under various LP fraction conditions.

Combustion System Design of a Genset Diesel Engine by Using DFSS Methodology

In this study, an optimum design for the combustion system of a genset diesel engine was conducted by using Design for Six Sigma (DFSS) methodology. As a result of this study, the best combination of design parameters to minimize the fuel consumption of the genset diesel engine was selected while meeting the requirements of NOx emission and peak firing pressure (PFP) limit. Compared to the initial design, the final design proposal has achieved 2.5 % and 1.6 % improvement in brake specific fuel consumption (BSFC) at switchable operating conditions, i.e., both 1500 and 1800 rpm. On the basis of this DFSS work, the design robustness was also enhanced. Hence, it is expected that the final design proposal would reduce the variability in fuel economy that could be caused by harsh environment and system aging. In this study, engine cycle simulation technique was employed to assess the effects of various design parameters on the performances of the genset diesel engine. The current optimum design work has considered four control factors such as turbocharger size, air temperature at charge air cooler (CAC) outlet, compression ratio, and fuel injection duration. Here, an L9 orthogonal array was used to efficiently choose the best design proposal among 81 design combinations (i.e., four independent control factors which individually have three different levels).

Analysis and simulation of combustion and emission on small engine

Liquefied Petroleum Gas (LPG) has become an interesting topic in the automotive industry to develop the engines with clean emission characteristics. The usage of gasoline as a fuel to power up the vehicle will contribute to the heavy environmental problem. A single cylinder four-stroke spark ignition (SI) engine that fueled by LPG and gasoline are used to predict and analyze the combustion process in the cylinder. A zero dimensional models are most suitable analytical models for engine cycle simulation. The simulation program has been developed using MATLAB software by implementing a single-zone thermodynamic model. The first law of thermodynamics is applying into this model and Annand’s model was used to compute the convection and radiation of heat transfer within the cylinder. The engine performance parameters computed including the in-cylinder pressure, gas temperature, net heat release, mass fraction burn, brake power, torque, indicated specific fuel consumption. Then, exhaust emission in the cylinder was predicted by the formation of emission model. The results of engine performance are compared between gasoline and LPG as a fuel. Results show LPG engine has contributed to the lower HC and NOx emissions compared to gasoline. It proved that the development of simulation program is useful to calculate the engine performance at different operating points.

Optimum design for intake and exhaust system of a heavy-duty diesel engine by using DFSS methodology

In this study, an optimum design for intake and exhaust system of a heavy-duty diesel engine was conducted by using the well-known design for six sigma (DFSS) methodology. As a result of this work, the NOx emission regulation has been successfully satisfied while minimizing the fuel consumption. On the basis of this DFSS work, the design robustness of the engine system was also enhanced. Hence, it is expected that the final design proposal would reduce the variability in brake thermal efficiency (BTE) that could be caused by the harsh environment and the system aging. Especially, this work has successfully raised the amount of exhaust gas recirculation (EGR) up to the target level by adopting the venturi tubes in the intake and exhaust lines. In this study, engine cycle simulation technique was employed to assess the effect of the various design parameters and the final design proposal was verified through a real engine test. The current optimum design work has considered four control factors such as the size of turbocharger, the diameter of intake and exhaust venturi pipes, and the efficiency of EGR cooler. Here, an L9 orthogonal array was employed to efficiently choose the best design proposal among 81 design combinations (i.e., four independent control factors which individually have three different levels).