Entire Engine Research Articles

Coupled Dynamic Simulation of Two Stage Variable Compression Ratio (VCR) Connecting Rod Using Virtual Dynamics

<div class="section abstract"><div class="htmlview paragraph">The fuel consumption of combustion engines requires continuous reduction to meet future CO2 fleet targets. The progression of emission legislations shifted the focus on PN and NOX emissions in real world driving scenarios (RDE). Recently, the monitoring of CO emissions puts high load fuel enrichment for component protection into focus and a ban on enrichment is widely expected. Hence, gasoline engine technologies, which enable Lambda 1 operation in the entire engine map are specifically promoted. Variable Compression Ratio (VCR) attacks all these topics already at the combustion process. In addition to the well-known CO2 capability, VCR also enables enlargement of the lambda 1 operation in gasoline engines as well as reduced NOX emissions in diesel engines. The basic principle of developed VCR solution is to change the effective length of the connecting rod (and thereby the compression ratio) in two stages by several millimeters. Basically, the VCR connecting rod consists of a mechanical and hydraulic system which is fed with oil by the connecting rod bearing. All functional elements to realize the variability such as an eccentric, lever, support rods, check valves and shift valve are integrated into the connecting rod. The system works without “external” energy supply but uses mass- and gas forces - acting on the piston pin - to vary its length. In order to analyze and optimize the system dynamics, a highly sophisticated simulation approach based on coupled simulations of the mechanical and the hydraulic subsystem of the VCR connecting rod. The co-simulation is carried out in time domain using the commercial software Virtual Dynamics for the elastic multi body simulations and GT-Suite for 1D fluid simulations. In this article the coupled 3D-multi body simulation/1D-hydraulic co-simulation as used to optimize the VCR connecting rod performance are presented.</div></div>

An Efficiency Methodology for Unsteady Full-engine simulation

When carrying out numerical analysis for the entire gas turbine engine, it is necessary to numerically model the flow field, heat conduction, and combustion in the compressor, combustor, and exhaust turbine section, which are its components. The calculation cost tends to increase because it is necessary to consider the complexity of shape, non-stationaryness, and the time scale of each physical phenomenon being largely different. In this paper, we apply approximate solution method of unsteady calculation with using nonlinear harmonic method, and introduce the analysis result of the whole engine including combustion analysis with comparison with the steady calculation result.

Effect of Cylindrical Turbulators on the Mixing Process in Basic Venturi Gas Mixer Using OpenFOAM

This study was devoted to improving the mixing quality in a Venturi gas mixer. It is well known that the performance of industrial gas engines strongly depends on the quality of air and fuel mixture and therefore on its homogeneity. Incorrect mixture proportions may lead to unstable operation of the entire industrial gas engine and excessive emissions exceeding environmental standards of the European Union. The effectiveness of the mixing process in a Venturi gas mixer depends on many factors, i.e. correct proportions between Air inlet, Venturi Throat diameter, as well as gas inlet area. To improve the intensification of the whole mixing process, as well as to increase the mixing time between gas and air, it was decided to insert disturbing elements in form of cylindrical turbulators into the Venturi pipe. Therefore numerical calculations were performed for the most commonly consumed by industrial gas engines lean Air-Fuel mixture, with an air excess coefficient ratio of λ = 1.6. In numerical analysis, OpenFOAM software was used to investigate the impact of cylindrical turbulators on the whole mixing process in a basic Venturi gas mixer. Particular attention was focused on the Air-Fuel Ratio (AFR) changes, Turbulent Kinetic Energy (TKE) and Pressure loss [Pa], which is one of the most qualitative evaluation parameters of a gas mixer.

Estimation of fuel consumption based on data from opening fuel injector valve

Abstract In indirect injection, the basic task of the fuel injectors is to prepare the most homogeneous fuel-air mixture at the correct ratio. The electronic engine control regulates the entire engine and changes the amount of injected fuel in respect of the accelerator position and the engine operating state. The vehicle sensors provide a control unit the parameters needed to prepare the fuel mixture (amount of fuel injected). The parameters needed for the estimated fuel consumption were recorded using a performance dynamometer. The recorded parameters, there are the PRM, the time of the injector opening and the amount of fuel injected.

Research on real-time simulation modelling of a diesel engine based on fuel inter-zone transfer and an array calculation method

This paper proposed a real-time simulation model of a diesel engine based on the fuel transfer in the combustion zone and an array calculation method. The proposed model conducts real-time optimized modelling of the diesel engine multi-zone model from two aspects: a modelling method and a model algorithm. From the modelling method perspective, the model proposed a combustion process model that transfers fuel mass and momentum between the combustion zones. Based on the diesel combustion characteristics, this modelling method divides the cylinder into three thermodynamic zones: an unburned area, a premixed combustion zone, and a diffusion combustion zone. This division addresses the assumption that fuel mass and momentum transfer are not performed between combustion zones in the traditional multi-zone model. While reducing the computation regions and improving the simulation calculation speed, the combustion process of the premixed combustion zone and the diffusion combustion zone were described using the method of Stefan flow and entrainment combustion. The physical depth and the predictivity of the model was enhanced, which rendered the description of the combustion process more consistent with the diesel combustion characteristics. The thermodynamic calculation process of the three regions was maintained throughout the entire cyclic operation in the entire diesel engine operating cycle. From the model calculation perspective, the model proposed a direct single-step calculation method for temperature and pressure to satisfy the demand of real-time model calculation. To optimize the multi-cylinder multi-zone plan in a real-time environment, the model utilizes an array method for calculation. The results of the model verification of a diesel engine in high and low loading conditions and using fixed combustion model parameters indicate that the difference between the calculation results and the experimental data is less than 5% and the results are consistent, which proves that the model has predictivity. The analysis of the model calculation results indicates that the model can accurately reflect the performance change pattern and regional change characteristics for different working conditions and provide a suitable foundation platform for controlling system combustion performance optimization. In addition, the array algorithm and multi-zone through-operation calculation method were validated in a real-time hardware system test environment. The methods can effectively reduce the multi cylinder multi-zone model simulation time to 30%. The application range of the real-time system model was expanded; thus, this method is very suitable for real-time system calculation.

Design and Application of a Multidisciplinary Predesign Process for Novel Engine Concepts

The purpose of this paper is to present a multidisciplinary predesign process and its application to three aero-engine models. First, a twin spool mixed flow turbofan engine model is created for validation purposes. The second and third engine models investigated comprise future engine concepts: a counter rotating open rotor (CROR) and an ultrahigh bypass turbofan. The turbofan used for validation is based on publicly available reference data from manufacturing and emission certification. At first, the identified interfaces and constraints of the entire predesign process are presented. An important factor of complexity in this highly iterative procedure is the intricate data flow, as well as the extensive amount of data transferred between all involved disciplines and among different fidelity levels applied within the design phases. To cope with the inherent complexity, data modeling techniques have been applied to explicitly determine required data structures of those complex systems. The resulting data model characterizing the components of a gas turbine and their relationships in the design process is presented in detail. Based on the data model, the entire engine predesign process is presented. Starting with the definition of a flight mission scenario and resulting top level engine requirements, thermodynamic engine performance models are developed. By means of these thermodynamic models, a detailed engine component predesign is conducted. The aerodynamic and structural design of the engine components are executed using a stepwise increase in level of detail and are continuously evaluated in context of the overall engine system.

Influence of Charge Motion and Compression Ratio on the Performance of a Combustion Concept Employing In-Cylinder Gasoline and Natural Gas Blending

The present paper represents a small piece of an extensive experimental effort investigating the dual-fuel operation of a light-duty spark ignited engine. Natural gas (NG) was directly injected into the cylinder and gasoline was injected into the intake-port. Direct injection (DI) of NG was used in order to overcome the power density loss usually experienced with NG port-fuel injection (PFI) as it allows an injection after intake valve closing. Having two separate fuel systems allows for a continuum of in-cylinder blend levels from pure gasoline to pure NG operation. The huge benefit of gasoline is its availability and energy density, whereas NG allows efficient operation at high load due to improved combustion phasing enabled by its higher knock resistance. Furthermore, using NG allowed a reduction of carbon dioxide emissions across the entire engine map due to the higher hydrogen-to-carbon ratio. Exhaust gas recirculation (EGR) was used to (a) increase efficiency at low and part-load operation and (b) reduce the propensity of knock at higher compression ratios (CRs) thereby enabling blend levels with greater amount of gasoline across a wider operating range. Two integral engine parameters, CR and in-cylinder turbulence levels, were varied in order to study their influence on efficiency, emissions, and performance over a specific speed and load range. Increasing the CR from 10.5 to 14.5 allowed an absolute increase in indicated thermal efficiency of more than 3% for 75% NG (25% gasoline) operation at 8 bar net indicated mean effective pressure (IMEP) and 2500 rpm. However, as anticipated, the achievable peak load at CR 14.5 with 100% gasoline was greatly reduced due to its lower knock resistance. The in-cylinder turbulence level was varied by means of tumble plates (TPs) as well as an insert for the NG injector that guides the injection “spray” to augment the tumble motion. The usage of TPs showed a significant increase in EGR dilution tolerance for pure gasoline operation, however, no such impact was found for blended operation of gasoline and NG.

Study of advanced engine operating strategies on a turbocharged diesel engine by using coupled numerical approaches

As a consequence of the negative influence of the transport sector on the environment, the European Union imposed a series of regulations that aim at reducing its harmful effect. Therefore, in the last decade, the increase in engine combustion and thermal efficiency, and a decrease in exhaust gas emissions are the primary goals of diesel engine research. The efficiency increase of the entire engine cycle is achieved by introducing different advanced operating strategies, such as optimisation of injection process and employment of various exhaust gas recirculation and engine boosting systems. This research presents a numerical study on the efficiency improvement of a turbocharged diesel engine using advanced engine operating strategies. A single operating point of a production type diesel engine was modelled by using the computational fluid dynamics tool AVL FIRE™. The results of released heat were transferred to a cycle engine simulation created in AVL BOOST™ that covers the entire engine system, including the intake and exhaust flow path, low and high pressure exhaust gas residual loops, exhaust gas residual and intake charge cooling, and turbomachinery. The cycle simulation was used to assess the entire engine system performance and cycle efficiency for different engine operating strategies. With the analysis performed in this work, it was concluded that the highest engine brake thermal efficiency of 31.86% could be achieved if a high pressure exhaust gas recirculation loop without electric compounding turbocharger is used.

Optimization design of piston structure for abnormal noise control in a single-cylinder gasoline engine

The noise characteristic of an entire single-cylinder gasoline engine was tested through acoustic spectral and intensity analyses to solve its abnormal noise problem in idling condition. Then, the ...

The evaluation of a direct injection diesel engine operating with waste cooking oil biodiesel in point of the environmental and enviroeconomic aspects

ABSTRACTIn this study, the environmental and enviroeconomic analyzes were implemented to the single-cylinder, four-stroke, direct-injection diesel engine operating with diesel fuel, waste cooking oil biodiesel and their blends (B5, B10, B20, and B30) under different fuel injection pressures (170–220 bars) and engine speeds (1000–3200 rpm) and at full load conditions. The environmental and enviroeconomic analyzes results showed that B20 was the worst fuel at the other fuel injection pressures, while diesel fuel was the worst fuel at the original fuel injection pressure. It was determined that B100 gave the best results among the other fuels the entire engine operating conditions.

Numerical approach for assessing combustion noise in compression-ignited Diesel engines

Diesel combustion noise has become a crucial aspect for the engine manufacturers due to its impact on human health and influence on the customer purchasing decision. The interaction of the pressure waves after mixture self-ignition induces cavity resonances inside the combustion chamber. This complex phenomenon produces high-frequency pressure oscillations, hence traditional in-cylinder measurements do not provide enough information to characterise the in-cylinder acoustic field. In this paper, a numerical methodology is proposed for assessing the Diesel combustion as a noise source and to overcome measurement limitations. An optimisation procedure is also presented in order to determine the numerical calculation parameters, boundary conditions definition and initialization. Results show that local flow conditions at the start of combustion have a strong influence on the acoustic response of the in-cylinder noise source. These particular conditions are only achievable by the proposed methodology which considers entire engine cycle simulations with the complete cylinder domain. Therefore, traditional Computational Fluid Dynamic (CFD) approaches, such those used for predicting combustion stability or pollutant emissions, are not suitable for reproducing the physical mechanisms of noise generation and they cannot be used for acoustic purposes. The reliability of the proposed methodology to simulate the acoustic field accurately inside the combustion chamber has been validated by comparison with experiments.

Studies on biogas-fuelled compression ignition engine under dual fuel mode.

Experimental investigation has been carried out to utilize biogas as an alternative source of energy in compression ignition (CI) engine under dual fuel operational mode. Biogas was inducted into the inlet manifold at different flow rates along with fresh air through inlet manifold and diesel was injected as a pilot fuel to initiate combustion under dual fuel mode. The engine performance and emission characteristics of dual fuel operational mode were analyzed at different biogas flow rates and compared with baseline conventional diesel fuel. Based upon the improved performance and lower emission characteristics under the dual fuel operation, the optimum flow rate of biogas was observed to be 2.2kg/h. The lower brake thermal efficiency (BTE) and higher brake-specific energy consumption (BSEC) were noticed with biogas-diesel fuel under dual fuel mode when compared with neat diesel operation. Test results showed reduced NO x emissions and smoke opacity level in the exhaust tailpipe emissions. However, higher hydrocarbon (HC) and carbon monoxide (CO) emissions were noticed under dual fuel mode at entire engine loads when compared with baseline fossil petro-diesel. Hence, the use of low-cost gaseous fuel such as biogas would be an economically viable proposition to address the current and future problems of energy scarcity and associated environmental concerns.

Numerical investigation of a premixed combustion large marine two-stroke dual fuel engine for optimising engine settings via parametric runs

As the environmental regulations have become more stringent, the shipping industry has been focusing on more efficient and environmentally friendly means of propulsion and electric power generation. In this respect, dual fuel engines, which operate either in diesel mode or dual fuel (DF) mode by burning diesel fuel or natural gas and pilot diesel fuel to initiate ignition respectively, has become one of the most promising solutions as their dual fuel operation leads to reduced nitrogen oxide (NOx), carbon dioxide (CO2), as well as almost elimination of particulate matter (PM) and sulphur oxide (SOx) emissions. The present study focuses on the comprehensive investigation of a large marine two-stroke dual fuel engine of the low gas pressure concept by using the GT-Power software. Appropriate combustion, scavenging, heat transfer and friction models were used to fully represent the engine performance and emissions characteristics, whereas a knocking model was employed to characterise the engine abnormal combustion. The simulation results were initially validated against the manufacturer data and subsequently, the entire engine envelope in both operating modes was simulated. The derived results were used for analysing and discussing the engine operation, performance and emissions as well as for comparing the two operating modes in terms of the turbocharger matching. In addition, a parametric investigation was performed in the dual fuel mode and the results were used for identifying the settings that can further optimise the engine operation in terms of CO2 and NOx emissions trade-off. The results indicate that the CO2 and NOx emissions can be simultaneously reduced; however, the engine optimisation in the high load region is challenging due to the permissible cylinder pressure constraint.

Eksploatacja elektrycznych układów napędowych pojazdów hybrydowych w zróżnicowanych warunkach ruchu

Hybrid vehicles allow an increase in the powertrain efficiency thanks to their design. One such factor is the use of increased voltage supplying electric motors to the voltage supplying the high voltage battery. The battery voltage is increased several times in the inverter (boost) system to increase the final electric power supplied to the electric motor. The article presents the possibilities of using such a voltage boost in urban and non-urban driving conditions. The tests were performed on the latest generations of parallel hybrid drive systems in Lexus NX 300h and Toyota RAV4 hybrid vehicles. It has been shown that the boost system is used in about 30–40% of the urban drive distance (up to 20% of the driving time). The power supply voltage boost of the electric motors of both vehicles is used throughout the entire engine speed range of these machines at high torque values. Research has shown that the maximum voltage gain – approximately three times (up to 650 V) – is within the maximum torque range of the electric motors and allows for doubling the torque generated by the drive.

Nox conversion efficiency optimization based on NSGA-II and state-feedback nonlinear model predictive control of selective catalytic reduction system in diesel engine

The selective catalytic reduction (SCR) technology is a promising diesel after-treatment technology due to its high NOx reduction potential. A nonlinear model predictive control (NMPC) approach was proposed based on the three-state SCR model here for control and optimization of SCR system to maximize NOx reduction while minimizing NH3 slip and urea consumption; moreover, the ammonia coverage ratio was designed to asa control target, whose desired range was obtained by means of the singular perturbation method, that is to say, the upper limit of ammonia coverage ratio was derived by 10ppm NH3 slip while the lower limit was calculated by maximum NOx conversion efficiency, which was obtained through a novel model based non-dominated sorting genetic algorithm (NSGA-II) according to an optimum tradeoff between NOx conversion and NH3 slip at each engine operating point. The state-feedback NMPC algorithm was applied to ensure the estimated ammonia coverage ratio falling in the desired range so that the SCR performance can be optimized over entire engine operating. The standard European steady-state cycle (ESC) was performed for data generation from a diesel engine equipped with a commercial SCR and to verify the effectiveness of the designed control strategy. Simulation results over the entire ESC indicated that the NOx conversion efficiency may be optimal in various engine operating modes and the NMPC controller ensures the most part of the cycle may conform to the NOx emissions requirements; moreover, the downstream NH3 concentration was less than the limit; especially, the whole mean NH3 slip was 9.7ppm which is basically close to the given limit (10ppm); furthermore, the ammonia storage capacity falls rapidly along with growth of the temperature but the NMPC still worked well for prevention of any unacceptably high NH3 slip. The experimental verification was carried out and the results showed that the designed strategy was effective and acceptable compared with the simulated results.

Cycle-by-Cycle Optimization of the Combustion during Transient Engine Operation

In order to balance emissions accurately during highly transient engine operation, novel approaches of diesel engine control must achieve an appropriate interplay of the cycle-by-cycle fuel injection, i.e. the start position and mass of each fuel injection pulse, and the air system control scheme. Accordingly, this paper proposes a control concept that adjusts the fuel injection parameters as manipulated variables in dependence of the transient air system dynamics. The approach is based on a cylinder model that predicts the emissions and torque by means of physical and Gaussian Process Regression models. Fuel injection adjustments are determined by numerical optimization to minimize emissions while providing the desired engine torque. The optimization also considers the uncertainty of the emission predictions. This controller is tested by a high fidelity reference engine model which is also briefly introduced. It combines the cylinder description with a 1-dimensional air system model built up in the simulation environment GT-suite. The entire engine model is parametrized and validated using test-bench measurements.

Performance and emission characteristics of a DI diesel engine operated with diesel/DEE blended fuel

Diethyl ether (DEE) has long been known as a promising renewable fuel to be used in diesel engines due to its exceptional cetane number, reasonable energy density, high oxygen content, low auto-ignition temperature and high volatility. In this study, an experimental investigation was carried out to evaluate the effects of blending DEE with diesel on the performance, gas and particle emissions and combustion characteristics of a diesel engine. The blending percentages of DEE in the DEE/diesel blended fuel were set to 10, 25 and 50% by mass.Experimental results showed that highly stable engine operation was possible for blended fuels, and the fuel conversion efficiency was comparable to that of pure diesel. The combustion of DEE blended fuels produced less hydrocarbon (HC) and carbon monoxide (CO) emissions than diesel combustion over the entire engine load range. Particulate matter (PM) also decreased for blended fuels due to the high oxygen content of DEE. However, nitrogen oxides (NOx) from the blended fuels were higher than that of diesel over the entire engine load range of indicated mean effective pressures (IMEP) 0.2–0.8MPa due to the shorter ignition delay and high oxygen content.

Thermodynamic analysis of a gas turbine engine with a rotating detonation combustor

A rotating detonation combustor is a form of “pressure gain combustion” where one or more detonations continuously travel around an annular channel. Pressure gain combustion is a prospective technology being explored to advance gas turbine power plants. These thermodynamic cycles could potentially deliver a performance increase of 20% beyond the current state of the art. However, the combustor operates at extremely unsteady harsh conditions, and the integration of the combustor with the turbomachinery represent unprecedented aero-thermo-structural challenges. At a given instant each stream line experiences a different compression process through the combustor. In contrast to conventional combustors, where a steady approach is valid, in rotating detonation engines the flow particles entering the compressor will be exposed to different processes depending on the relative position of the rotor shaft to the detonation front. Hence, the overall performance assessment requires the development of ad-hoc tools suitable for this new class of combustors, and the modeling of the turbine exposed to supersonic pulsating flows. This paper presents a numerical tool to evaluate precisely the thermodynamic and non-isentropic processes across the entire engine. The NASA’s Toolbox for the Modeling and Analysis of Thermodynamic Systems was used to implement new libraries to help us quantify the benefits of a rotating detonation engine versus the conventional technology equipped with constant pressure combustion. The new developed libraries, based on sets of physics-based principles, replicate the engine components performance. This model should allow the optimization of components with respect to energy availability to enable optimal engine sizing and operation. Finally, the paper presents the pressure ratios for which the rotating detonation based engine outperforms the conventional power plants based on the Brayton cycle.

Influence of swirl ratio on fuel distribution and cyclic variation under flash boiling conditions in a spark ignition direct injection gasoline engine

One effective way of suppressing the cycle-to-cycle variation in engine is to design a combustion system that is robust to the root causes of engine variation over the entire engine working process. Flash boiling has been demonstrated as an ideal technique to produce stable fuel spray. But the generation of stable intake flow and fuel mixture remains challenging. In this study, to evaluate the capability of enhanced swirl flow to produce repeatable fuel mixture formation, the fuel distribution inside a single cylinder optical engine under two swirl ratios were measured using laser induced fluorescence technique. The swirl ratio was regulated by a swirl control valve installed in one of the intake ports. A 266nm wavelength laser sheet from a frequency-quadrupled laser was directed into the optical engine through the quartz liner 15mm below the tip of the spark plug. The fluorescence signal from the polycyclic aromatic hydrocarbon in gasoline was collected by applying a 320–420nm band pass filter mounted in front of an intensified charge coupled device camera. Test results show that the in-cylinder fuel distribution is strongly influenced by the swirl ratio. Specifically, under high swirl condition, the fuel is mainly concentrated on the left side of the combustion chamber. While under the low swirl flow, fuel is distributed more randomly over the observing plane. This agrees well with the measurements of the stable flame location. Additionally, the cycle-to-cycle variation of the fuel distribution were analyzed. Results show that well organized fuel mixture with lower cycle-to-cycle variation is achieved by enhanced swirl flow.

Cylinder-to-cylinder and cycle-to-cycle variation in combustion process in radial aircraft engine

Cycle-to-cycle variation in combustion in a single cylinder of a radial engine has an impact on that in others and the entire engine. Steady- and transient-state engine operation was investigated, and the transient states were generated by cyclic changes in the timing of fuel injection to a given cylinder, having others operated on the same mixture composition. The measurement of pressure in the combustion chamber allowed for specifying indicated mean effective pressure (IMEP) in all cycles. The time series of IMEP were studied with mathematical techniques of non-linear dynamics, i.e. a wavelet transform and a multifractal analysis. Controlled disturbances in mixture composition in a single cylinder can have an impact on certain cylinders only. Cylinders 3, 5, 7 and 9 are most responsive to such disturbances, which proves their least cycle-to-cycle variation in combustion.