bluuebunny/crossref_metadata_2025 huggingface dataset:
Concurrent Effects of Hot Streak and Gas Species Concentration on Aerothermal Characteristics in a Turbine Stage
Authors: Wang Zhong-Nan , Yuan Xin
Published: July 2013

Hydrogen or syngas derivative turbines in IGCC power plant promise increased efficiency with exceptional low NOx and CO2 emission. On one hand, the working flow in hydrogen turbines will be primarily water steam mixed with nitrogen, which leads to special aero-thermal characteristics in the turbine. On the other hand, the diluting and cooling air in combustors forms a cushion around the hot combustion gas, which results in both temperature and gas species non-uniformity at the turbine inlet. The goal of this paper is to study the concurrent effect of the two non-uniform inlet conditions on aerodynamics and heat transfer characteristics of the downstream turbine. In this paper, three-dimensional unsteady Navier-Stokes simulation was performed primarily on two cases: one with both hot streak and a range of species concentrations, and the other with only hot streak at the turbine inlet. The hot streak and species concentration migration was investigated to reveal their interaction. The results indicated that the steam concentration, among the range of species concentration, have the influential impact on the streak migration. It will enhance radial hot streak migration and promote the hot gas accumulation the rotor pressure side. Also, the tip leakage flow was also increased by the species concentration. Based on the understanding of their migration behaviors, the adiabatic wall temperature distribution was discussed to reveal the inlet species concentration effects on the blade heat load. The maximum blade surface temperature increase, due to the inlet species concentration, is about 1.5% of inlet total temperature (about 25 K) on the pressure side. The research in this paper will provide a practical guideline for the cooling strategy design of hydrogen turbines in the future.
Experimental Investigation of the Effects of Waveform Tip Injection in a Low Pressure Turbine Cascade
Authors: Mercan Bayram , Doğan Eda , Ostovan Yashar , Uzol Oğuz
Published: July 2013

This paper presents the results of an experimental study that investigates the effects of uniform/waveform tip injection along the camberline on the total pressure loss and wake flow characteristics downstream of a row of Low Pressure Turbine (LPT) blades. The experiments are performed in a low speed cascade facility. This injection technique involves spanwise jets at the tip that are issued from a series of holes along the camber line normal to the freestream flow direction. The injection mass flow rate from each hole is individually controlled using computer driven solenoid valves and therefore the flow injection geometrical pattern at the tip can be adjusted to any desired waveform shape, and can be uniform as well as waveform along the camber. Measurements involve Kiel probe traverses for different injection scenarios 0.5 axial chords downstream of the blades as well as Time-Resolved Particle Image Velocimetry (Tr-PIV) measurements at different spanwise locations. Results show that tip injection significantly reduces the total pressure loss levels created by the leakage vortex. Highest overall loss reduction occurs in the case of reversed-triangular injection. The least effective waveform is triangular injection. Loss levels do not seem to get reduced significantly in the passage vortex zone. Velocity, vorticity and turbulence fields created by the passage and leakage vortices get influenced by tip injection. There is significant reduction in the extent of the low momentum zone of the leakage vortex with injection. This effect is much less pronounced for the passage vortex. On the other hand, complex flow patterns are observed within the passage vortex, especially in the case of reversed-triangular injection, such as a possible embedded vortical structure along the passage vortex core, which creates double peaks in the velocity and turbulent kinetic energy fields and complex patterns in Reynolds shear stress.
Experimental and Numerical Investigation of the Flow Field in the Radial Inlet of a Centrifugal Compressor
Authors: Han Fenghui , Qi Datong , Tan Jiajian , Wang Li , Mao Yijun
Published: July 2013

This paper presents an experimental and numerical study of the flow field in a typical geometry of a centrifugal compressor radial inlet. A five-hole probe system, which makes the probe calibration and the data acquisition automatically controlled by computer, was developed and used to measure the pressure, velocity and flow angle distributions inside the radial inlet. The testing portion consists of the entrance and exit of the radial inlet, the outlet section of the suction nozzle and the exit of the plenum, including 46 sampling holes and 923 measuring points. In parallel with the experiment, a computational analysis was also carried out to simulate the internal flow of the radial inlet with a commercial CFD Code. The numerical results are compared with the experimental data. It shows a good agreement between CFD and the measurement on most sections.

Based on the experiment and simulation, this study reveals the detailed flow conditions in a radial inlet, which helps to figure out how the complex flow pattern in a radial inlet forms and develops as well as the influences on the downstream components. It yields an improved understanding of the principle of flow phenomena in radial inlets, and gives recommendations for optimizing the structure design of the radial inlet of centrifugal compressors.
On the Assessment of Turbine Efficiency From Experimental Data for Low Pressure Turbines at Low Reynolds Numbers
Authors: Schneider C. , Rose M. G. , Staudacher S. , Heisler A. , Lippl F. , Raab I.
Published: July 2013

The isentropic efficiency of a turbo machinery device is assessed using a defined control volume. Representative stagnation pressures and temperatures are measured at inlet and exit of the volume. This task is mainly accomplished by radial rake measurements. It is assumed to measure a representative flow quantity for an area with a defined number of circumferentially and radially distributed probes. The assumption incorporates biases into the assessed efficiency. The sensitivities of a radial rake measurement at the exit of a two-stage turbine to the unresolved area, the spatial resolution, and the averaging method are studied at a low Reynolds number working point (ReV1 = 75000). A method of analysis has been developed to assess the changes in turbine efficiency. For the case studied, the results show that the applied averaging method represents a minor contributor to the overall uncertainty. The effects of the spatial resolution and the unresolved area constitute up to ∼0.6% of turbine efficiency. Methods are presented to reduce the bias of the unresolved area significantly. The circumferential and the radial direction are observed separately which allows drawing conclusions for the design of rake measurement systems. The method of analysis is based on CFD completely, and thus it can be used to optimize or to design rake measurement systems prior to turbine testing. Additionally, the knowledge gained of the remaining biases can be used for an improved uncertainty analysis.
Advanced Numerical Methods for the Prediction of Tonal Noise in Turbomachinery: Part I—Implicit Runge Kutta Schemes
Authors: Ashcroft Graham , Frey Christian , Heitkamp Kathrin , Weckmüller Christian
Published: July 2013

This is the first part of a series of two papers on unsteady CFD methods for the numerical simulation of aerodynamic noise generation and propagation. In this part, the stability, accuracy and efficiency of implicit Runge-Kutta schemes for the temporal integration of the compressible Navier-Stokes equations are investigated in the context of a CFD code for turbomachinery applications. Using two model academic problems, the properties of two Explicit first stage, Singly Diagonal Implicit Runge-Kutta (ESDIRK) schemes of second- and third-order accuracy are quantified and compared with more conventional second-order multi-step methods. Finally, to assess the ESDIRK schemes in the context of an industrially relevant configuration, the schemes are applied to predict the tonal noise generation and transmission in a modern high bypass ratio fan stage and comparisons with the corresponding experimental data are provided.
Experimental Investigation of Purge Flow Effects on a High Pressure Turbine Stage
Authors: Regina K. , Kalfas A. I. , Abhari R. S.
Published: July 2013

In the present paper an experimental investigation of the effects of hub purge flow on the performance of a high pressure axial turbine stage is presented. The test configuration consists of a one-and-a-half stage, unshrouded, highly loaded axial turbine, with a blading representative of high pressure gas turbines. The test configuration has the capability of integrating purge flow from the cavity under the rotor/stator platform.

Efficiency measurements for various purge flow injection levels have been carried out with pneumatic probes at the exit of the rotor and show a reduction of isentropic total-to-total efficiency of 0.8 % per percent of injected mass flow.

For three purge flow conditions the unsteady aerodynamic flow field at rotor inlet and rotor exit has been measured with the in-house developed Fast Response Aerodynamic Probe (FRAP): one condition is with sucking at a mass flow fraction of −0.1 % and two conditions are with injection at a mass flow fraction of 0.8 % and 1.2 %. The time-resolved data shows the unsteady interaction of the purge flow with the secondary flows of the main flow and the impact on the radial displacement of the rotor hub passage vortex.

Steady measurements at off-design conditions show the impact of the rotor incidence and of the stage flow factor on the resulting stage efficiency and the radial displacement of the rotor HPV.

A comparison of the effect of purge flow and of the off-design conditions on the rotor incidence and stage flow factor shows that the detrimental effect of the purge flow on the stage efficiency caused by the radial displacement of the rotor hub passage vortex is dominated by the increase of stage flow factor in the hub region rather than by the increase of negative rotor incidence.
The Effects of Tip Clearance on Performance of a Heavy Duty Multi Stages Axial Turbine
Authors: Shirzadi Mohammad Reza , Saeidi Hossein
Published: July 2013

In this article aerodynamic effects of tip clearance on a heavy duty axial turbine are studied. Three different tip clearances are considered for each rotor. For simplicity, a simple tip profile is assumed and cooling air is not modeled. Aerodynamic behavior of all stages is studied in terms of polytropic efficiency, leakage mass flow, secondary and total losses, penetration length, and total mass flow rate for different pressure ratios. Also three well established correlations of tip clearance loss are compared with CFD results to obtain the best model for performance calculation of such a large-scale turbine. The steady states, viscous and compressible flow governing equations representing the flow field with k-epsilon turbulence model are solved using commercial code ANSYS CFX.12. Useful data are presented to predict the variation of efficiency of each individual rotor, as well as entire turbine, as a function of relative tip gap (k/h). This information may be useable in design and troubleshooting. According to the results, even though pressure drop in rear stages across tip gap is lower than pressure drop in front stages, leakage mass flow rate is considerably high for this LP stages. Consequently, tip clearance losses of rear stages have significant effect on the entire turbine efficiency.
Numerical Investigation of the Behavior of Tip Leakage Flow in a Low-Speed Axial Compressor Rotor at Near-Stall Condition
Authors: Duan Zhenzhen , Liu Yangwei , Lu Lipeng
Published: July 2013

In the present work, time-accurate simulations were performed to investigate the unsteady flow fields in the tip region of a low-speed large-scale axial compressor rotor at near-stall condition. Firstly, the steady performance characteristic of the rotor was obtained by steady simulations. Secondly, a series of unsteady simulations were carried out to investigate the physical processes as the rotor approaching stall and the role of complex tip flow mechanism on flow instability in the rotor.

The characteristics of tip leakage vortex were compared between design condition and near-stall condition. Detailed analyses were then employed to emphasize the development of stall inception and the comprehensions of the internal flow field. Two flow phenomena, spillage at the leading edge and backflow at the trailing edge, are found beyond the flow solution limit, which are both linked to the tip leakage flow. And the breakdown of the tip leakage vortex has been captured.

The flow visualization and the quantification of passage blockage expose that the tip leakage vortex and corner vortex contribute most to the total passage blockage. Therefore, they are considered to be the key flow structures contributing to the rotating stall. Further analyses indicate that, in the current rotor, the interaction of the tip leakage flow and the corner vortex is clarified to be the key factor that leads to the rotating stall.

In addition, the very initial disturbances of stall inception are discussed. And the interaction of the boundary layer migration on the blade suction side and the tip leakage vortex also plays a significant role in the stall inception.
Flow Mechanics in Tandem Rotors
Authors: Qian Yuping , Li Zhiping , Lu Yajun , Li Qiushi
Published: July 2013

Tandem cascade is quite a useful way to reduce losses in design of stator with a large turning angle. The dominant flow mechanism for reducing loss is to control the wake development induced by the front row in tandem cascade. However, the wake effect is not dominant but the potential influence of the back rotor is far more important. This paper establishes the principles for arranging the circumferential location of the back rotor in tandem rotors to achieve a high efficiency in a high loading design.
Full Design of a Highly Loaded Fan by Multi-Objective Optimization of Through-Flow and High-Fidelity Aero-Mechanical Performances
Authors: Joly Michael , Verstraete Tom , Paniagua Guillermo
Published: July 2013

An innovative design methodology for axial flow compressors is developed utilizing a multi-objective optimization. The full design of a highly-loaded fan is considered, including through-flow and high-fidelity performance evaluations. To augment the explored design space and smoothen the whole process, optimization techniques are integrated into the different steps in the design.

As an alternative to the traditional parametric studies performed for the flow path design, an optimization of the through-flow configuration is performed to initiate the aerodynamic design of the fan. To bypass two-dimensional sub-optimal results, the detailed design of the fan rotor geometry is then directly processed with a three-dimensional optimization, including several section profiles along the span, as well as lean and sweep. The multi-objective algorithm enables one to consider fluid and structure performances simultaneously. High-fidelity CFD (Computational Fluid Dynamics) and CSM (Computational Structural Mechanics) methods are used to guarantee the flow efficiency and the structural integrity of the finalized design. This methodology is applied to the design of a transonic fan achieving a pressure ratio of 2.1.
Axial Loss Development in Low Pressure Turbine Cascades
Authors: Muth Bastian , Niehuis Reinhard
Published: July 2013

The objective of this work presented in this paper is to study the performance of low pressure turbines in detail by extensive numerical simulations. The numerical flow simulations were conducted using the general purpose code ANSYS CFX. Particular attention is focused on the loss development in axial direction within the flow passage of the cascade. It is shown that modern CFD tools are able to break down the integral loss of the turbine profile into its components depending on attached and separated flow areas. In addition the numerical results allow to show the composition of the loss depending on the Reynolds number. The method of the analysis of axial loss development presented here allows for a much more comprehensive investigation and evaluation of the quality of the numerical results. For this reason the paper also demonstrates the capability of this method to quantify the influence of the axial velocity density ratio, the inflow turbulence level, the inflow angle and the Reynolds number on the loss configuration and the flow angle of the cascade as well as a comparison of steady state and transient results. The validation data of this LPT-Cascade have been obtained at the High Speed Cascade Wind Tunnel of the Institute of Jet Propulsion. For this purpose experiments were conducted within the range of Re2th = 40’000 to 400’000. To gather data at realistic engine operation conditions, the wind tunnel allows for an independent variation of Reynolds and Mach number. The experimental results presented herein contain detailed pressure measurements as well as measurements with 3-D-hot-wire anemometry. However, this paper shows only integral values of the experimental as well as the numerical results to protect the proprietary nature of the LPT-design.
Numerical and Experimental Investigations of Steady and Unsteady Characteristics of a Counter Rotating Fan Model With Thickened Blades of Working Wheel
Authors: Mileshin Victor , Brailko Igor , Stepanov Alexander , Korzhnev Vladimir
Published: July 2013

Under VITAL Project funded by the European Community, Snecma as a project leader developed a counter rotating low-speed fan concept for a high bypass ratio engine [1–4].

At first, a counter rotating fan model (hereinafter referred to as CRTF1) with solid titanium blades was designed, manufactured and tested in CIAM’s C-3A anechoic chamber. The CRTF1 fan model had blades with a conventional thickness distribution in order to provide optimal mechanical properties and weight characteristics [1, 2]. To simulate blades made of composite materials, CRTF2a [3] and CRTF2b [4] counter-rotating fan models were designed with thickened blades (by 20–40%) as compared with the CRTF1 fan model to ensure mechanical properties.

The CRTF2a counter-rotating fan model with thickened blades to simulate blades made of a composite material was tested in CIAM’s C-3A anechoic chamber. Fan local and integral performances within rotational speeds from ncor = 40% to ncor = 100% were measured.

The numerical investigations were based on 3DFS software package developed for RANS and URANS solutions. The solution procedure is based on a modified S.K. Godunov’s scheme of implicit finite-difference second-order approximation [5].

The numerical investigations were subdivided into three stages corresponding to various problem definitions. Numerical investigations at the first stage and second stages were carried out without flow nonuniformity at the CRTF inlet. The first stage meets the requirements of the stationary problem definition. CRTF performances at this stage were calculated in the “mixing plane” approximation and compared with test data.

Numerical investigations at the second stage were completed for non-stationary problem definition without flow nonuniformity at the inlet (the same as at the first stage). Calculations at this stage were carried out for the problem definition with a common period corresponding to calculations covering 5 blade channels in Rotor 1 (R1) and 7 blade channels in Rotor 2 (R2). Results of non-stationary calculations at the second stage were in good agreement with computed data at the first stage (the stationary calculation).

The third stage of numerical investigations was in line with the numerical simulation of CRTF operation with total pressure nonuniformity at the inlet. At this stage the numerical investigations were carried out for non-stationary problem definition for all blade channels in Rotor 1 and Rotor 2 (10 and 14, respectively). The computed data were in good agreement with test results for CRTF integral characteristics as well as for local flow characteristics at the CRTF outlet (instantaneous and averaged by time values of flow parameters distributed in radial and circumferential directions).
An Evaluation of 1D Design Methods for the Off-Design Performance Prediction of Automotive Turbocharger Compressors
Authors: Harley Peter , Spence Stephen , Filsinger Dietmar , Dietrich Michael , Early Juliana
Published: July 2013

Several one-dimensional design methods have been used to predict the off-design performance of three modern centrifugal compressors for automotive turbocharging. The three methods used are single-zone, two-zone, and a more recent statistical method. The predicted results from each method are compared against empirical data taken from standard hot gas stand tests for each turbocharger. Each of the automotive turbochargers considered in this study have notably different geometries and are of varying application. Due to the non-adiabatic test conditions, the empirical data has been corrected for the effect of heat transfer to ensure comparability with the 1D models. Each method is evaluated for usability and accuracy in both pressure ratio and efficiency prediction. The paper presents an insight into the limitations of each of these models when applied to one-dimensional automotive turbocharger design, and proposes that a corrected single-zone modelling approach has the greatest potential for further development, whilst the statistical method could be immediately introduced to a design process where design variations are limited.
An Experimental Assessment of the Effects of Stator Vane Tip Clearance Location and Back Swept Blading on an Automotive Variable Geometry Turbocharger
Authors: Walkingshaw Jason , Spence Stephen , Ehrhard Jan , Thornhill David
Published: July 2013

Off-design performance is of key importance now in the design of automotive turbocharger turbines. Due to automotive drive cycles, a turbine which can extract more energy at high pressure ratios and lower rotational speeds is desirable. Typically a radial turbine provides peak efficiency at U/C values of 0.7, but at high pressure ratios and low rotational speeds the U/C value will be low and the rotor will experience high values of positive incidence at the inlet. The positive incidence causes high blade loading resulting in additional tip leakage flow in the rotor as well as flow separation on the suction surface of the blade.

An experimental assessment has been performed on a scaled automotive VGS (Variable Geometry System). Three different stator vane positions have been analysed; minimum, 25% and maximum flow position. The first tests were to establish whether positioning the endwall clearance on the hub or shroud side of the stator vanes produced a different impact on turbine efficiency. Following this, a back swept rotor was tested to establish the potential gains to be achieved during off-design operation. A single passage CFD model of the test rig was developed and used to provide information on the flow features affecting performance in both the stator vanes and turbine.

It was seen that off-design performance was improved by implementing clearance on the hub side of the stator vanes rather than on the shroud side. Through CFD analysis and tests it was seen that two leakage vortices form, one at the leading edge and one after the spindle of the stator vane. The vortices affect the flow angle at the inlet to the rotor, in the hub region. The flow angle is shifted to more negative values of incidence, which is beneficial at the off-design conditions but detrimental at the design point. The back swept rotor was tested with the hub side stator vane clearance configuration. The efficiency and MFR were increased at the minimum and 25% stator vane position. At the design point the efficiency and MFR were decreased. The CFD investigation showed that the incidence angle was improved at the off-design conditions, for the back swept rotor. This reduction in the positive incidence angle along with the improvement caused by the stator vane tip leakage flow, reduced flow separation on the suction surface of the rotor. At the design point both the tip leakage flow of the stator vanes and the back swept blade angle caused flow separation on the pressure surface of the rotor. This resulted in additional blockage at the throat of the rotor reducing MFR and efficiency.
Engine Performance Prediction for Varied LPT Vane Geometry Utilizing Test Rig Data and Combined CFD and Cycle Models
Authors: van Rooij Michel , Kogenhop Oscar , Rademaker Edward , Woodason Ray , Soemarwoto Bambang
Published: July 2013

Engine performance is a result of the interaction between individual components. Any deviation from the design geometry does not only affect the flow locally, but can also lead to significantly altered whole engine performance. Specifically for Low Pressure Turbine (LPT) vanes, erosion and subsequent refurbishment can lead to considerable changes in geometry. Following vane refurbishment, the part’s effective flow area may be measured and adjusted to meet turbine nozzle matching requirements for the engine build. Other parameters such as pressure loss and outlet flow angle are not evaluated, but rather assumed equivalent to a new part. Consequently, a large portion of vanes is rejected only after engine test, making it an expensive process.

A new methodology is presented here that promises to reduce the cost of acceptance tests by predicting the performance of an engine with a refurbished vane. It follows a multi-fidelity approach involving experimental testing, zero-dimensional cycle modeling and three-dimensional Computational Fluid Dynamics (CFD).

Baseline performance maps of the LPT stage with varied vane geometries are generated using CFD. The obtained performance maps are incorporated into an engine cycle model. A multiple map feature for the cycle model was developed for this purpose. It enables accessing a plurality of stored maps representing a single LPT. Using performance parameters derived from test data of the isolated vane, a performance map is generated through interpolation of the baseline maps. The expected engine performance can now be readily predicted, and a well-founded decision on acceptance of the refurbished vane made.
On the Physics of Vortex Formation at the Tip of a Turbine Blade
Authors: El-Ghandour Mohamed , Shatat Mohammed M. E. , Nakamura Yoshiaki
Published: July 2013

The vortical flow at the blade tip area of a turbine rotor has a great effect on the aerothermal performance of the blade tip of turbine rotor however its physics is not fully understood. The present paper is a numerical study to investigate the physics behind vortex formation at the blade tip area. The blade under investigation is a linear model of the tip section of the GE-E3 high-pressure turbine first stage rotor blade. Calculations were carried out for three tip geometries, namely, conventional double squealer, thick pressure side squealer and thick suction side squealer. The code used in this study is an in-house, unstructured, finite volume, multiblock, 3D, compressible, viscous solver. The turbulent viscosity was calculated using the Delayed Detached Eddy Simulation (DDES) model. Computational results show that the vortex formation depends on the vorticity imparted with the incoming flow. Therefore, the flow with high velocity gradient caused larger vortex than that with low velocity gradient. This result is valid for both the cavity vortex as well as the leakage vortex.
An Air Hybrid Engine With Higher Efficiency and Cam-Based Valvetrain System
Authors: Fazeli Amir , Khajepour Amir
Published: July 2013

In this paper, a new configuration for air hybrid engines is introduced which increases the energy storing capacity of the system during braking and simplifies significantly the valvetrain needed for the hybridized engine by relaxing the need for a fully flexible valvetrain system. The proposed configuration allows easy implementation of various air hybrid operational modes. Moreover, the specific configuration of the system avoids irreversible gas exchange in the cylinder during regenerative mode which results in the significant increase of the energy recovering efficiency. One of the most important advantages of the proposed system is that the engine torque in the regenerative braking mode is controlled by the same throttle system used in the conventional ICE mode. The performance and feasibility of the proposed configuration is shown through simulation and experimental work.
Prediction of Ring-Bore Conformance and Contact Condition and Experimental Validation
Authors: Theaker M. , Rahmani R. , Rahnejat H.
Published: July 2013

One of the key conjunctions in the IC engine is that made by the top compression ring to the cylinder liner. Although the compression ring has seen considerable improvements since its introduction into steam engines by John Ramsbottom in the 1850s, its multiple and often contradictory functions still remain a challenge today. The primary aim has always been to seal the combustion chamber and guard against leakage of combustion gasses. The ring is also required to conduct some of the generated heat away. These requirements call for good ring-bore conformance, but often at the expense of increased friction.

A simplified inter-ring gas flow model, as well as the measured chamber pressure using a Kistler pressure transducer is carried out under motored conditions to obtain the net gas pressure acting behind the ring. This and the elastic pressure as the result of ring restoring tension force in fitment constitute the contact load, which is usually carried by a mixed-hydrodynamic regime of lubrication. The conjunction pressures are treated as a combination of hydrodynamic generated pressures and asperity-pair interactions. The former is obtained by solution of two dimensional Reynolds equation, whilst the latter is determined assuming a Gaussian distribution of asperities on the counterfaces. Surface topography of the bounding solids; the compression ring and the liner are measured and used as appropriate statistical functions in the Greenwood and Tripp model.

Using an analytical flow model, pressure acting behind the ring (on the inner periphery of the ring) is obtained, leading to the calculation of ring-bore friction. A floating liner is used to measure friction of piston and ringpack in situ. The characteristic of the predicted variations are compared with the measured data. However, a quantitative comparison is not possible as the measured data corresponds to all the conjunctions of piston system, including the oil control rings as well as the piston skirt. The results show that variation of gas force behind the ring significantly changes the ring-bore contact, thus friction and the nature of interactions.
Particle Number Emissions of Non-Road Diesel Engines of Various Ages
Authors: Niemi Seppo , Ekman Krister , Nousiainen Pekka
Published: July 2013

Over the two last decades, gaseous and particle mass emissions of new diesel engines have been reduced effectively and progressively in response to the emissions legislation and due to the applied new technologies.

There is, however, increasing concern about whether the engine modifications, while improving combustion and reducing emissions, have increased the number emissions of ultrafine and nanoparticles. So far, emissions regulations have solely been based on particulate matter (PM) mass measurements, not on particle number. Nanoparticles, however, form a major part of the PM emissions, but they do not considerably contribute to the PM mass and can not be seen as a problem, if only PM mass is determined.

Therefore, there is increasing interest in expanding the scope of the regulations to also include particle number emissions, e.g. Euro VI for on-road engines. The PM number limit will also be enforced for non-road engines slightly later. Thus, more information is required about the particle number emissions themselves, but also about the effects of the engine technology on them.

Wall-flow diesel particulate filters (DPFs) reduce the particle number very effectively within the entire particle size range. Nevertheless, in order to keep the DPF as small as possible and to lessen the need for regeneration, the engine-out PM number should also be minimized.

If the DPF could be left out or replaced by a simpler filter, there would be greater freedom of space utilization or cost savings in many non-road applications. This might be realized in installations where the engine is tuned at high raw NOx and an SCR system is adopted for NOx reduction. However, it is not self-evident that new engine technologies would reduce the PM number emissions sufficiently.

In this study, particle number emissions were analyzed in several non-road diesel engines representing different engine generations and exploiting different emissions reduction technologies: 4- or 2-valve heads, exhaust gas recirculation (EGR), different injection pressures and strategies, etc. All engines were turbocharged, intercooled, direct-injection non-road diesel engines. Most engines used common-rail fuel injection technology. Comparisons were, however, also performed with engines utilizing either a distributor-type or an in-line fuel injection pump to see the long-term development of the particle number emissions.

In this paper, the PM number emissions of nine (9) non-road diesel engines are presented and compared. Gaseous exhaust emissions and fuel consumption figures are also provided.
Investigation on Amorphous Particles Evolution of the Diesel Engine
Authors: Liang Xingyu , Chen Yu , Dong Lihui , Song Chonglin
Published: July 2013

Analysis of the changes in mass and size of particles formed during the diesel combustion process, the morphological characteristics, and the trace elements within these amorphous particles was carried out using a total cylinder sampling system installed on a direct injection diesel engine. Utilizing field emission transmission electron microscope technology, the results showed that the amorphous particles formed during the combustion process were abundant in metallic and non-metallic elements mainly derived from the lubrication oil, which was found to have entered the combustion process, oxidized and combusted, further increasing the absorbed carbon particles during the later stages of combustion.
Empirical Study of Simultaneously Low NOx and Soot Combustion With Diesel and Ethanol Fuels in Diesel Engine
Authors: Han Xiaoye , Gao Tongyang , Asad Usman , Xie Kelvin , Zheng Ming
Published: July 2013

Diesel low temperature combustion (LTC) is capable of producing diesel-like efficiency while emitting ultra-low nitrogen oxides (NOx) and soot emissions. Previous work indicates that well controlled single-shot injection with exhaust gas recirculation (EGR) is an operative way of achieving diesel LTC from low to mid engine loads. However, as the engine load is increased, demanding intake boost and injection pressure are necessary to suppress high soot emissions during the transition to LTC. The use of volatile fuels such as ethanol are deemed capable of promoting the cylinder charge homogeneity, which helps to overcome the high soot challenge and thus potentially expand the engine LTC load range.

In this work, LTC investigations have been carried out on a high compression ratio (18.2:1) engine. The engine was firstly fuelled with diesel, and LTC operation at 8 bar indicated mean effective pressure (IMEP) was enabled by sophisticated control of the injection pressure, injection timing, intake boost and EGR application. The engine performance was characterized as the baseline, and the challenges were identified. Further tests were aimed to improve the engine performance against these baseline results.

Experiments were hence conducted on the same engine with secondary ethanol port injection (PI). Single-shot diesel direct injection (DI) was applied close to top dead center (TDC) to ignite the ethanol and control the combustion phasing. The control sensitivity has been studied through injection timing sweeps and EGR sweeps. Additional tests were performed to investigate the ethanol-to-diesel ratio effects on the mixture reactivity and the engine emissions. Engine load was also raised to 10 bar IMEP while keeping the simultaneously low NOx and soot emissions. Significant improvement of engine control and emissions was achieved by the DI+PI strategy.
On the Computer-Aided Conversion of a Diesel Engine to CNG-Dedicated or Dual Fuel Combustion Regime
Authors: Donateo Teresa , de Risi Arturo , Laforgia Domenico
Published: July 2013

The paper proposes a cost-saving analytical methodology using empirical based models to efficiently evaluate design alternatives in the optimization of a CNG converted diesel engine. The procedure is performed in five steps. Firstly, a database of different combustion chambers that can be obtained from the original piston is obtained. The chambers in the database differ for the shape of the bowl, the value of the compression ratio, the offset of the bowl and the size of the squish region. The second step of the procedure is the selection, from the first database, of the combustion chambers able to resist to the mechanical stresses due to the pressure and temperature distribution at full load. For each combination of suitable combustion chamber shape and ignition timing, a CFD simulation is used to evaluate the combustion performance of the engine. Then, a post-processing procedure is used to evaluate the detonation tendency and intensity of each combination. All the tools developed for the application of the method have been linked in the ModeFrontier optimization environment in order to perform the final choice of the combustion chamber.

The overall process requires not more of a week of computation on the 4 processor servers considered for the optimization. Moreover, the selected chambers can be obtained from the original piston of the engine. Therefore, the conversion cost of the engine is quite small compared with the case of a completely new piston. The procedure can be applied to diesel engines to be converted to either CNG dedicated or dual fuel combustion. The main aspects and challenges to be taken into account in both cases are also analyzed.
Assessment of a Low-Throughput Predictive Model for Indicated Cycle, Combustion Noise and NOx Calculation in Diesel Engines in Steady-State and Transient Operations
Authors: Catania Andrea Emilio , Finesso Roberto , Spessa Ezio
Published: July 2013

A predictive zero-dimensional low-throughput combustion model that was previously developed by the authors has been refined and applied to a EURO V diesel automotive engine.

The model is capable of simulating, in real time, the time-histories of the HRR (Heat Release Rate), in-cylinder pressure, in-cylinder temperatures and NOx (nitrogen oxides) concentrations, on the basis of a few quantities estimated by the ECU (Engine Control Unit), such as the injection parameters, the trapped air mass, the intake manifold pressure and temperature. It has been developed for model-based feedforward control purposes in DI (Direct Injection) diesel engines featuring an advanced combustion system or new combustion-mode concepts, such as LTC/PCCI (Low Temperature Combustion/Premixed Charge Compression Ignition) engines.

In the present work, the model has been assessed in detail by analyzing a wide set of experimental engine data that were acquired during the engine calibration phase. The experimental data set has been defined according to the DoE (Design of Experiment) methodology currently used for engine calibration purposes, and applied to six ‘key-points’ that are representative of engine working operations during an NEDC (New European Driving Cycle) for a D-class passenger car. Different injection strategies (pilot-main, double pilot-main; pilot-main-after; double pilot-main-after) have been considered for each key point, and all the main engine operating parameters (rail pressure, injected quantities, boost level, intake temperature, EGR rate,…) have been included in the DoE variation list. Therefore, about 1000 steady-state engine operating conditions have been investigated.

In addition, several NEDC driving cycles have been realized with the engine installed on a dynamic test rig, and the combustion parameters and emission levels have continuously been measured during the transient operations.

The model has been applied to all the investigated conditions. It has shown excellent accuracy in estimating the values of the main combustion parameters, and a good matching between the calculated and predicted NOx concentrations was found, for both steady-state and transient operations.
Detailed Evaluation of a New Semi-Empirical Two-Zone NOx Model by Application on Various Diesel Engine Configurations
Authors: Provataris Stelios , Savva Nicholas , Hountalas Dimitrios
Published: July 2013

Over a significant period of time, efforts have been made towards a valid and accurate estimation of DI diesel engine NOx emissions. Considering the fact that experiments have a high cost in both time and money, modelling approaches have been developed in an effort to overcome these issues. It is well known that accuracy in the prediction of NOx emissions lies specifically on the accurate estimation of local temperature and O2 histories inside the combustion chamber that govern NOx formation, fulfilled by an accurate estimation of the combustion mechanism. To account for the actual effect of parameters that control NOx formation and overcome inefficiencies introduced from existing purely empirical models or artificial neural networks, valid only on the combustion systems for which they were developed [1], an alternative solution is the introduction of physically based semi-empirical models. Towards this direction, in the present work is presented and evaluated a new modelling approach, based on the combustion rate obtained from the measured cylinder pressure trace using Heat Release Rate Analysis. The model used is a semi-empirical two-zone one which makes use of the estimated elementary fuel mass burnt at each crank angle interval. The combustion process is considered to be adiabatic, while chemical dissociation is also considered. With this approach, temperature distribution throughout the combustion chamber is considered for, together with its evolution during the engine cycle. In addition, O2 availability is also considered for through the calculated charge composition. The result is an extremely fast computational model, combining the advantages of both empirical and physically based ones. In the present work is given a detailed validation of the model, from its application on two different types of diesel engines: a heavy-duty DI diesel engine and a light-duty DI diesel engine with pilot fuel injection. A significant number of cases where tested for both engine configurations, considering different operation points and variation of operating parameters, such as rail pressure and EGR. The twelve points of the European Stationary Cycle (ESC) were covered for the case of the heavy duty DI diesel engine, whilst for the light-duty DI engine a total number of forty-six operating points was studied. For both engine configurations the model reveals a very good predictive ability, considering for the effect of all operating parameters examined on NOx emissions. However, there is potential for improvement and development on its physical base for even more accurate predictions. The merits of good accuracy in prediction trends with varying engine operating parameters — even without calibration — and low computational time establish a potential for model use in engine development, optimization studies and model based control applications.
Combustion Phasing Effect on Cycle Efficiency of a Diesel Engine Using Advanced Gasoline Fumigation
Authors: Northrop William F. , Fang Wei , Huang Bin
Published: July 2013

Advanced premixed compression ignition (CI) combustion using fumigation has been shown to yield significant improvements in indicated efficiency over traditional diesel combustion strategies while simultaneously reducing engine-out soot and NOX emissions. To better interpret these findings, a breakdown of the ways in which actual performance deviates from ideal engine cycles is helpful. Non-ideal combustion phasing is one cause of such deviations. In this paper, the centroid of the calculated apparent heat release rate is used to estimate an adjusted maximum possible thermal efficiency based on constant volume combustion using an effective compression ratio concept. Using these metrics, experimental engine data are evaluated from a single cylinder direct-injection diesel engine operating in premixed CI mode enabled by gasoline fumigation and a diesel pilot injection. Indicated gross cycle efficiency was found to be higher for premixed fumigation compared with a conventional diesel condition at the same load. A key finding of the work is that the peak indicated cycle efficiency for fumigated premixed CI combustion occurs with combustion phased very close to TDC. Shorter heat release duration and lower heat losses from the cylinder are thought to be the cause of differences in cycle efficiency between conventional combustion and premixed CI fumigation modes.
Model-Based Methodology for Estimating Engine Cylinder Pressure Imbalance for Combustion Feedback Control Applications
Authors: Al-Durra Ahmed
Published: July 2013

One of the principal issues of alternative combustion modes for Diesel engines (such as HCCI, PCCI and LTC) is related to imbalances in the distribution of air and EGR across the cylinders, which ultimately cause significant differences in the pressure trace and indicated torque for each cylinder. In principle, a cylinder-by-cylinder control approach could compensate for air, residuals, and temperature imbalance. However, in order to fully benefit from closed-loop combustion control, it is necessary to obtain feedback from each engine cylinder to reconstruct the pressure trace. Therefore, cylinder imbalance is an issue that can be detected in a laboratory environment, wherein each engine cylinder is instrumented with a dedicated pressure transducer. The objective of the work in this paper is to estimating the individual in-cylinder pressure traces in a multi-cylinder engine, relying on a very restricted sensor set, namely a crankshaft speed sensor, a single production-grade pressure sensor. In doing so, a crankshaft model will be developed and a sliding mode observer will be employed to estimate the cylinder pressure using only crankshaft speed fluctuation measurement. Furthermore, as an added enhancement, the cylinder pressure signal from one cylinder will be utilized to adapt the friction and heat release parameters for more accurate estimation in all cylinders.