bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Effect of Volute Tongue Design on Radial Turbine Performance
Authors: Suhrmann Jan F. , Peitsch Dieter , Gugau Marc , Heuer Tom
Published: July 2013

With an increasing need for gas turbines with rather low flow rates in many industrial applications, e.g. decentralized power generation, aircrafts or automotive turbochargers, the development of small size radial turbines becomes more and more important.

A major step in the development of a radial turbine stage is the preliminary design, which is the definition of basic geometrical features and the calculation of general turbine flow parameters at the design point and within the operating range. These are mainly the rotational speed, the expansion ratio, the flow rate and in particular the expected turbine efficiency.

In a radial turbine stage, the volute component delivers the flow to the rotor wheel and according to the geometrical form it defines major flow parameters like the mass flow parameter or the absolute rotor inlet flow angle. Amongst others, the way the flow enters the turbine wheel represents one of the most important loss generating factors. Thus, on the one hand an approach is necessary for the calculation of the optimum rotor inlet flow angle, in order to avoid dispensable losses due to secondary flow in the turbine wheel region. On the other hand, the volute tongue generates flow non-uniformity which has an effect on the overall circumferential averaged rotor inlet flow angle. Furthermore, the local flow pattern downstream of the volute tongue can generate suboptimal flow conditions for the turbine wheel. Hussain and Bhinder [1] measured the flow field at the outlet of a vaneless volute at different circumferential positions and detected a variation of the outlet angle of about Δα = 10°. The authors conclusion was, that the influence on the stage performance of flow non-uniformity generated by the volute could exceed the one of pressure losses through the volute.

In this paper, the effect of different geometrical volute parameters on the flow condition especially at the turbine wheel inlet area is investigated. Experimental data of the influence of different volute tongue geometries on the flow field is difficult to generate. Hence, comprehensive numerical investigations are made using steady 3D-CFD calculations of the turbine volute as well as calculations of complete turbine stages including a turbine wheel geometry.

Based on the numerical results, a design guideline is developed to estimate the influence of the geometric volute parameters on the flow and to raise the quality of the preliminary design process.
Interpretation of Adjoint Solutions for Turbomachinery Flows
Authors: Shankaran Sriram , Marta Andre , Venugopal Prem , Barr Brian , Wang Qiqi
Published: July 2013

While the mathematical derivation of the adjoint equations and their numerical implementation is well established, there is a scant discussion on the understanding of the adjoint solution by itself. As this is a field solution of similar resolution of the flow-field, there is a wealth of data that can be used for design guidance. This paper addressess this specific topic. In particular, we take representative cases from turbomachinery aerodynamic problems and use the adjoint solution to identify the “physical insight” it provides. We aim to tie the adjoint solution to the flow-field which has physical properties. Towards this end, we first look at three problems 1) a fan, 2) a compressor rotor and stator, 3) a low pressure turbine. In all three of them, we focus on changes related to geometry, but one can also realize the changes using other inputs to the flow solver (eg. boundary conditions). We show how the adjoint counter-part of the density, the velocity fields and the turbulence quantities can be used to provide insights into the nature of changes the designer can induce to cause improvement in the performance metric of interest. We also discuss how to use adjoint solutions for problems with constraints to further refine the changes. Finally, we use a problem where it is not immediately apparent what geometry changes need to be used for further evaluation with optimization algorithms. In this problem, we use the adjoint and flow solution on a turbine strut, to determine the kind of end-wall treatments that reduce the loss. These changes are then implemented to show that the loss is reduced by close to 8%.
Use of Transition Modeling to Enable the Computation of Losses for Variable-Speed Power Turbine
Authors: Ameri Ali A.
Published: July 2013

To investigate the penalties associated with using a variable speed power turbine (VSPT) in a rotorcraft capable of vertical takeoff and landing, various analysis tools are required. Such analysis tools must be able to model the flow accurately within the operating envelope of VSPT. For power turbines low Reynolds numbers and a wide range of the incidence angles, positive and negative, due to the variation in the shaft speed at relatively fixed corrected flows, characterize this envelope. The flow in the turbine passage is expected to be transitional and separated at high incidence. The turbulence model of Walters and Leylek was implemented in the NASA Glenn-HT code to enable a more accurate analysis of such flows. Two-dimensional heat transfer predictions of flat plate flow and two and three dimensional heat transfer predictions on a turbine blade were performed and reported herein. Heat transfer computations were performed because it is a good marker for transition. The final goal is to be able to compute the aerodynamic losses. Armed with the new transition model, total pressure losses for three-dimensional flow of an Energy Efficient Engine (E3) tip section cascade for a range of incidence angles were computed in anticipation of the experimental data. The results obtained form a loss bucket for the chosen blade.
Unsteady Wake-Blade Interaction: A Correlation Between Surface Pressure Fluctuations and Loss Generation
Authors: Biester Marc H.-O. , Henke Michael , Seume Jörg R. , Gündogdu Yavuz , Engel Karl
Published: July 2013

This paper presents loss mechanisms associated with unsteady flows in axial turbines due to the interaction of wakes with downstream blade-rows. To evaluate the effect of wake induced loss mechanisms, extensive 3D-URANS computations of an 1.5-stage low pressure turbine rig have been performed. The investigation of the flow field shows how the wake influences well-known effects like the negative-jet effect and resulting flow structures. A detailed view on the impact of these time-dependent flow structures on the fluctuating pressure distribution on the blade is presented by evaluation in both, the time and frequency domains. The effects causing the fluctuations are identified in detail and attributed to their corresponding sources. Unsteady pressure induced by potential effects is distinguished from unsteadiness induced by wake passage. Regarding the latter, it is shown that the amplitude of the pressure fluctuations correlates with the instantaneous state of the wake. In order to describe this behavior, an analytical model is proposed and referred to as the conservation of wake circulation. The evaluation of the entropy generation caused by wake deformation allows the distinction of different loss mechanisms. Finally, an empirical correlation between the amplitude of pressure fluctuation and loss generation is shown.
Unsteady Aerodynamics of a Centrifugal Compressor Stage: Validation of Two Different CFD Solvers
Authors: Borm Oliver , Kau Hans-Peter
Published: July 2013

The unsteady flow field of a centrifugal compressor stage with vaned diffuser has been numerically investigated. Three dimensional steady as well as unsteady numerical simulations have been carried out with the CFD programs Numeca and OpenFOAM. The investigated numerical approaches range from a steady state mixing-plane simulation to an unsteady full annulus 360° computation. The numerical investigation was done at 80% design speed with the Spalart-Allmaras as well as the k-w SST turbulence model. All numerical simulations were compared to the experiments in the compressor map. The velocity field of one operating point near the surge line was analysed in more detail. Similarities and differences between numerical and experimental results are discussed and their causes and effects pointed out.
Numerical and Experimental Analysis of the Airflow Inside an A250 Diffuser Tube
Authors: Lee G. G. W. , Allan W. D. E. , Goni Boulama K.
Published: July 2013

The diffuser tube of the Allison 250 gas turbine has been investigated in this paper. It consists of a diverging conical section that transitions into a constant diameter S-shaped tube, and connects the exit of the compressor to the inlet of the combustion chamber. The shear stress transport model (SST) in ANSYS-CFX has been used for the numerical prediction of the flow and an experimental rig was built in order to collect data in four directions and at three stations along the diffuser tube. The calculated results perfectly matched the experimental data. The development of the stream-wise velocity profile, the velocity contours at different stream-wise stations, and the friction and pressure coefficients were calculated and discussed. A secondary flow in the plane of the cross-section has thus been evidenced, and resulted in a shift towards the outer wall of the first bend of the region of the flow where the velocity is greatest. It has also been shown that the friction coefficient decreased as the Reynolds number was increased, while the opposite trend was observed for the pressure coefficients. The effect of the inlet turbulence intensity on the main flow features was generally small.
Performance Limits of Axial Compressor Stages
Authors: Hall D. K. , Greitzer E. M. , Tan C. S.
Published: July 2013

This paper presents a framework for estimating the upper limit of compressor stage efficiency. Using a compressor stage model with a representative design velocity distribution with turbulent boundary layers, losses are calculated as the sum of selected local irreversibilities, rather than from correlations based on data from existing machines. By considering only losses that cannot be eliminated and optimizing stage design variables for minimum loss, an upper bound on stage efficiency can be determined as a function of a small number of stage design parameters. The impact of the stage analysis results are evaluated in the context of gas turbine cycle performance. The implication from the results of the stage level and cycle analyses is that compressor efficiency improvements that result in substantial increases in cycle thermal efficiency are still to be realized.
The Effect of Four Part Gap Geometry Configurations for Variable Stator Vanes in a Compressor Cascade
Authors: Gottschall Marcel , Vogeler Konrad , Mailach Ronald
Published: July 2013

The article describes numerical investigations on the influence of four different endwall clearance topologies for variable stator vanes to secondary flow field development and the performance of high pressure compressors. The aim of this work is to quantify the characteristics of different clearance configurations depending on the penny-axis position and the penny diameter for a typical operating range. All clearance configurations were implemented to a linear cascade of modern stator profiles. The analysis was introduced using a relative clearance size of 1.3% chord at three stagger angles and two characteristic Reynolds numbers to model the operating range on aircraft engines. 3D numerical calculations were carried out to gain information about the flow field inside the cascade. They were compared with measurements of a 5-hole-probe as well as pressure tappings on the airfoil and the endwall.

The CFD shows the clearance characteristics in good agreement with the measurements for the lower and the nominal stagger angle. Small gaps in the rear part of the vane have a beneficial effect on the flow field. In contrast, a clearance in the higher loaded front part of the vane always resulted in increased losses. Otherwise, the significant enhanced performance of a rear part gap, which was measured at the higher stagger angle, was not reflected by the CFD. The reduced mixing losses and the higher averaged flow turning even compared to a configuration without a clearance are not verified with the calculations. Large flow separations at the high stagger angle result in a two to four times higher underturning of the CFD in comparison to the experiments. The clearance effects to the characteristic radial loss distribution up to 40 % bladeheight also deviate from the measurements due to heavy mixing of clearance and reversed separated flow.
Selection of One-Dimensional Design Parameter ‘Reaction Degree’ for 1st Stage of a Cooled Gas Turbine
Authors: Noor Hina , Genrup Magnus , Fransson Torsten
Published: July 2013

The recommendations available today in open literature for the choice of design parameter such as flow coefficient, stage loading and reaction degree incorporates mainly the influence of aerodynamics loss on efficiency. However, it is difficult to find the recommendation relating the influence of not only the aerodynamics loss but also cooling mass flow and cooling losses on varying most influential design parameters. In this paper, preliminary design and performance guidelines are presented for a cooled turbine stage using the 1D design tool LUAXT. The intention is to provide recommendations on the selection of design parameters, mainly reaction degree, which is found to be highly influenced by not only the aerodynamics loss but also the cooling mass flow and cooling loss such as in 1st stage of a High Pressure Turbines (HPT). The One-Dimensional (1D) design methods used to perform this task are verified and validated against experimental test data. A comparison of different loss models has been performed to provide most accurate outcomes for certain tested ranges. Based on the outcomes of this study, ‘Craig & Cox’ loss model has been considered to perform subsequent investigations for HPT design and performance estimation while formulating a parametric study. From this study, the design recommendations for the selection of performance parameter reaction degree are developed for cooled turbines. The results shows that for a HPT 1st stage, the recommended reaction degree range of 0.20 to 0.37 seems to provide the optimum stage design when chosen for stage loading in between 1.40 to 1.80 along with the stator exit flow angle in range of 74° to 78°.
Effects of Using Hydrogen-Rich Syngas in Industrial Gas Turbines While Maintaining Fuel Flexibility on a Multistage Axial Compressor Design
Authors: Nucara Pascal , Sayma Abdulnaser
Published: July 2013

Current gas turbine technology for power generation is generally optimised for natural gas. Recently the use of Low Calorific Value (LCV) fuels gained interest, particularly, Hydrogen rich syngas resulting from coal and solid waste gasification. When LCV fuels are used the performance and behaviour of the engines could significantly change and modifications may be needed. For instance, due to the relatively low heating value of the syngas, higher fuel mass flow rate is required compared to the natural gas combustion case. This leads to a decrease of demand for air from the compressor, which results in increased back pressure, reduction of stall margin and possible compressor instability.

In a previous work an exploration of some compressor geometry modifications to allow for high fuel flexibility was conducted on a single axial compressor rotor. The investigation provided insights into the effect of blade shape modifications, such as stagger, lean and sweep on rotor performance. With the same purpose of identifying trends rather than producing optimum design, in this study the analysis is extended to a multistage axial compressor. Two different investigations have been performed, both having, as objective, the shifting of the original mass flow rate towards a lower value while maintaining high performance. In the first study the effect of IGV and stator vanes stagger variations only was considered while in a second approach the re-design of the original machine included modifies to rotor’s stagger angles.

In order to understand the change in each single blade performance when modifying the original geometry, the variation of critical parameters such as blade loading and diffusion factor has been here considered in first analysis.
Performance Investigation of a Turbocharger Compressor
Authors: de Wet A. L. , von Backström T. W. , van der Spuy S. J.
Published: July 2013

The compressor section of a diesel locomotive turbocharger was re-designed to increase its maximum total-to-total pressure ratio and efficiency. Tests conducted on the prototype compressor showed possible rotating stall in the diffuser section before the designed higher pressure ratio could be achieved. It was decided to simulate the prototype compressor’s operation by using one-dimensional theory [1], followed by a three-dimensional CFD analysis of the compressor. This publication focuses on implementation of the impeller, vaneless annular passage and vaned diffuser one-dimensional theories. A verification process was followed to show the accuracy of the one- and three-dimensional modelling methods using two well-known centrifugal compressor test cases found in the literature [2–5]. Comparing the test case modelling results to available experimental results indicated sufficient accuracy to investigate the prototype compressor’s impeller and diffuser. Conclusions drawn on the prototype compressor’s performance using the one- and three-dimensional modelling methods led to a recommendation to redesign the impeller and diffuser of the prototype compressor.
Through-Flow Analysis of Air-Cooled Gas Turbines
Authors: Petrovic Milan V. , Wiedermann Alexander
Published: July 2013

This paper describes the development of a new through-flow method for the analysis of axial multistage turbines with cooling by air from compressor bleed. The method is based on a stream function approach and a finite element solution procedure. It includes a high-fidelity loss and deviation model with improved correlations. A radial distribution model of losses and a new spanwise mixing model are applied to simulate 3D flow effects.

The calibration of the models is performed by calculation of a number of test cases with different configurations, with the aim of achieving high accuracy and optimum robustness for each of the test cases considered.

Various types of cooling air injection were encompassed: film cooling, trailing edge injection and disc/endwall coolant flow. There are two effects of air cooling: (i) increase in mass flow downstream of the injection surface and (ii) reduction of the gas total temperature connected with total pressure losses. For both of these effects, the appropriate 2D models were developed and applied.

The code was applied to flow analysis and performance prediction of a newly developed industrial gas turbine. Comparison of the predicted results and measured test data for a number of parameters showed good agreement. The results of the validation confirmed that this method based on calibrated correlations can be considered a reliable tool for flow analysis and parameter variation during the design phase.
Influence of a Novel Three-Dimensional Leading Edge Geometry on the Aerodynamic Performance of Transonic Cascade Vanes
Authors: Bouchard D. , Asghar A. , Hardes J. , Edwards R. , Allan W. D. E. , LaViolette M.
Published: July 2013

This paper addresses the issue of aerodynamic performance of a novel 3D leading edge modification to a reference vane. An analysis of tubercles found in nature and some engineering applications was used to synthesize new leading edge geometry. Three variations of the reference low pressure turbine vane were obtained by changing the characteristic parameters of the tubercles. Shock structure, surface flow visualization and total pressure measurements were made through experiments in a cascade rig, as well as through computational fluid dynamics. The tests were carried out at design zero incidence and off-design ±10-deg and ±5-deg incidences. The performance of the new 3D leading edge geometries was compared against the reference vane. Some leading edge tubercle configurations were effective at decreasing total pressure losses at positive inlet incidence angles. Numerical results supplemented experimental results.
Validation of a Surge Model by Full Scale Testing
Authors: Smeulers Jan P. M. , Díez Néstor González , Slot Harmen
Published: July 2013

Surge of turbo compressors can cause large almost step like changes in flow and pressure, which can potentially damage the compressor and any equipment that is in direct connection with the compressor. In spite of an anti-surge controller (ASC), at extreme events surge cycles may occur. In order to design the compressor and attached equipment such that surge cycles can be sustained without damage, the characteristics of a surge cycle should be known.

This paper presents a model that describes the surge cycle in centrifugal compressors, which is a combination of the model developed by Greitzer and a model of the suction and discharge pipe system.

The surge model has been validated with tests on a full scale compressor system. The simulations compare very well with the test results, although the model required tuning of one parameter. The validation demonstrates that the model is robust and can be effectively applied for the evaluation of surge cycles in newly designed compressor systems.
Time-Resolved Numerical Investigation of the Effects of Blade-Row Spacing on the Turbine Efficiency
Authors: Behre S. , Restemeier M. , Jeschke P. , Guendogdu Y. , Engel K.
Published: July 2013

Numerical investigations of a 1.5 stage axial flow turbine geometry were performed to determine the effects of a variation of the inter-blade row axial gap on turbine efficiency. In order to study the influence of blade row spacing, both steady and unsteady RANS simulations were conducted. State of the art meshing including fillet radii and high grid density was used. In addition to an overall improvement of the aerodynamic efficiency with a decreasing axial distance between the rows, the numerical results showed differences in radial distribution of efficiency downstream of the trailing edges. Furthermore, transition on the blades’ suction side was investigated and compared to former fully turbulent numerical results [1]. The intermittency distributions showed that the laminar fraction of the boundary layer on the rotor, as well as on the second stator suction side, decreases with increasing gap.
Flow-Rate Observers in the Suppression of Compressor Surge Using Active Magnetic Bearings
Authors: Yoon Se Young , Lin Zongli , Jiang Wei , Allaire Paul E.
Published: July 2013

Surge is a dynamic flow instability that can cause extensive damage to compressors and other components. One common challenge that many surge control methods in the literature face when implemented in industrial applications is the unavailability of the high performance actuators and accurate flow rate measurements that are required to suppress surge. In this paper we present experimental results of employing active magnetic bearings in order to suppress the surge instability in a centrifugal compressor. Also, we compare how the selection of the flow estimation method affects the effectiveness of the implemented surge suppression controller. Experimental data demonstrates that the best combination of controller and flow estimator tested in this work allows the compressor to operate deep into the former surge region when the controller is activated, moving the minimum flow rate at the surge initiation point by 21%. This allows the compression system to operate at the highest efficiency/pressure point in the characteristic curve, while still retaining a very conservative surge margin separating the allowed compressor operating region from the surge inception point even if unexpected system changes occur.
Performance Improvement of Multi-Blade Centrifugal Fan by Using Optimal Bionic Blade
Authors: Liu Xiaomin , Wang Xing , Tang Hu , Xi Guang
Published: July 2013

The aim of this paper is to obtain a higher flow rate and lower noise multi-blade centrifugal fan by employing a type of optimized bionic blade. The design of experiment with orthogonal array tables is used in the optimization process. The factors of the geometric parameters of the bionic blade which selected in the present study are leading edge curvature, leading edge thickness, the leading edge angle and pressure side surface curvature. The contribution of each factor to the performance of bionic blade is investigated numerically by solving Navier-Stokes equation and FW-H equation. The pressure side surface curvature of the blade is considered as the most effective factor. Compared with the original blade, the optimal bionic blade not only improve the flow rate of multi-blade centrifugal fan, but also suppress noise occurred on the blade surface effectively. The values of the flow rate and the A-weighted sound pressure level (SPL) for the fan with optimal bionic blade are 2.75m3/s, 44.9dB(A) respectively against the initial fan of 2.55m3/s, 52.4dB(A). The optimization results demonstrate considerable improvement of the multi-blade centrifugal fan in both flow rate and A-weighted SPL when the optimized bionic blade is used.
Simulation and Validation of Centrifugal Impeller Shock Wave and Acoustic Power Prediction
Authors: Schlinker Robert H. , Blanc Arthur , Lurie Elizabeth , Joo Jongwook , Reimann Aaron , Shannon Daniel , Simonich John
Published: July 2013

In this paper, we describe the development and validation of a simulation based methodology for predicting centrifugal impeller rotor locked noise generated at supersonic relative tip speeds when shock waves dominate the acoustic field. Propagating shock waves were calculated in the compressor inlet with a RANS code using an acoustic quality grid to track the sound power as the shocks transition from non-linear to linear propagating wavefronts. The predicted shocks were compared with unsteady pressure measurements obtained from sensors installed on the impeller shroud wall as part of the validation procedure. Calculated shock signatures compared well with the directly measured pressure field propagating over the shroud wall. An independent measurement of acoustic power was also conducted in the free field outside of the test cell. The predicted acoustic power compared within 1dB of the direct measurement validating the simulation based methodology for centrifugal impeller rotor locked shock noise. The resulting study provides both prediction and measurement of the generation, evolution, and far field acoustic power of centrifugal impeller blade passage shock wave noise.
Effect of EGR in a Gasoline Operated Diesel Engine in LTC Mode
Authors: Ciatti Stephen , Subramanian Swami Nathan , Ferris Alison
Published: July 2013

Conventional combustion techniques struggle to meet the current emissions’ regulations while retaining high engine efficiency. Specifically in automotive diesel engines, oxides of nitrogen (NOx) and particulate matter (PM) emissions have limited the utilization of diesel fuel in compression ignition engines. By comparison, throttled, knock-limited conventional gasoline operated SI engines tend not to be fuel efficient. Advanced combustion systems that simultaneously address PM and NOx while retaining the high efficiency of modern diesel engines, are being developed around the globe [1]. One of the most difficult problems in the area of advanced combustion technology development is the control of combustion initiation [2] and retaining power density [3]. During the past several years, significant progress has been accomplished in reducing emissions of NOx and PM through strategies such as LTC/HCCI/PCCI/PPCI and other advanced combustion processes; however control of ignition and improving power density has suffered to some degree — advanced combustion engines tend to be limited to the 10 bar BMEP range and under [4].

Experimental investigations have been carried out on a light duty, DI, multi cylinder, diesel automotive engine. The engine is operated in low temperature combustion technology with 87 RON (Research Octane Number) fuel [7]. Using an Ignition Quality Test (IQT) device, the equivalent Cetane Number (CN) was measured to be 25. In the present work, various EGR rates are examined to determine the effect on the combustion, emissions and performance. Experiments were conducted at three different engine load/speed combinations that are part of General Motors’ reference points for vehicle operation. To reduce the complexity, boost pressure and injection pressure and timing were kept constant while EGR percentage and intake temperature were used as parameters in this study. The intake temperature was not truly independent, as it trended with EGR level, but based upon the boost level and the available EGR cooling, Intake Air Temperature (IAT) was kept in the range of 40–80 deg C. Additional cooling capacity will be added in future work in an effort to keep IAT more consistent. EGR rates have a detrimental effect on engine efficiencies at lower load while it appears to have little effect on efficiency at higher loads. A more significant effect at very low load appears to be higher intake temperatures (hot EGR) as opposed to the very slight decrease in oxygen concentration.
3D-CFD Lagrangian Spray Simulations for Large Two Stroke Marine Diesel Engines Compared With Experimental Data of a Spray Combustion Chamber
Authors: Bolla M. , Cattin M. A. , Wright Y. M. , Boulouchos K. , Schulz R.
Published: July 2013

The behavior of lagrangian spray models for the application in large two stroke marine engines is investigated. 3D-CFD simulations of a Spray Combustion Chamber (SCC) with a single hole (0.875 mm diameter) injector are presented and compared with experimental results. Shadow images of the spray under evaporating and non-evaporating conditions, with and without swirl flow and for different chamber pressures are available by means of which the simulation results are validated. A novel post processing methodology for 3D CFD spray simulations is introduced, which converts the numerical data into images which allows for a more rigorous quantitative comparison with the experimental data. Good agreement of the simulation results with the experiment is reported both in terms of spray penetration as well as concerning the evaporation of the fuel. Since the appropriate discretization of the large volumes typical of 2-stroke marine engines presents a substantial challenge, the influence of the grid resolution is investigated. In addition, the influence of fuel quality on the evolution of the spray morphology is assessed. For this purpose, simulations with heavy fuel oil (HFO) are compared with experiment.
Effect of Pilot Injection on Diesel Knock in a Small-Bore Optical Engine
Authors: Rusly Alvin M. , Kook Sanghoon , Hawkes Evatt R. , Zhang Renlin
Published: July 2013

Diesel knock is a phenomenon that generates undesirable noise and vibration that can be destructive to diesel engine structures and components for long-term operation. The diesel knock occurs when a large quantity of air-fuel is mixed prior to combustion when the ignition delay is long. This leads to a drastic pressure rise during the premixed phase of the combustion, which is followed by a pressure ringing. The main focus of this study is to examine effect of pilot injection on the pressure ringing and associated in-cylinder flame behaviour. In a single-cylinder small-bore optical engine, in-cylinder pressure measurement and high-speed imaging of the natural combustion luminosity have been performed. Results demonstrate that pilot injection helps reduce the in-cylinder pressure ringing by reducing the pressure rise rate of the main injection. Moreover, oscillation of the flames observed during the knocking events appears to diminish when the pilot injection is applied. How the pilot injection duration and timing affect the diesel knock behaviour is also discussed in detail.
On-Engine Study of the Thermal and Performance Impacts of a Variable Displacement Oil Pump
Authors: Burke Richard , Brace Chris , Lewis Andy , Stark Roland , Pegg Ian
Published: July 2013

Variable displacement lubricant pumps allow oil flow to be matched to engine requirements over the whole operating range, reducing energy losses through excessive pumping work. An experimental investigation has been performed on-engine to understand the effects of such devices. Significant instrumentation was fitted to the production, EURO IV specification, 2.4L Diesel engine to assess the impacts of lubricant flow on thermal state. The reduced oil flow was measured as a reduction in engine oil pressure with the production pump supplying 4–6bar whereas the variable flow device provided pressures as low as 1–2bar.

The reduction in oil flow significantly reduced the oil pump energy consumption, measured as a change in indicated work, resulting in a 4% benefit in fuel economy over both hot and cold start NEDC. The reduced oil flow also impacted oil and metal temperatures: during engine warm-up, oil temperatures were approximately 4°C colder with the lower flow as a result of less work input from the oil pump. Conversely, cylinder liner temperatures were 2–6°C hotter both during warm-up and fully warm conditions as a result of reduced piston cooling from piston cooling jets. The changes in thermal state were reflected by changes in emissions with a 3% increase in NOx and a 3–5% reduction in HC and CO.

The calibration of the variable flow device follows a fuel consumption/NOx trade-off that is more favourable to fuel economy than conventional control parameters. However, these benefits are strongly linked to engine duty cycle with larger benefits at higher engine speeds.
Friction Under Transient Mixed Regime of Lubrication in Conjunction of an Elastic Ring Within a Real Cylinder
Authors: Baker C. E. , Theodossiades S. , Rahnejat H.
Published: July 2013

Fuel efficiency is now the over-riding engine development objective. With approximately 50–60% of the input fuel energy in an internal combustion engine lost through thermal and mechanical inefficiencies, friction has been targeted as the arch nemesis in any engine development program. A significant portion of the parasitic frictional losses is due to the top compression ring. This suggests that optimization of tribological performance of the compression ring conjunction warrants much more attention that it has been hitherto afforded. Studies reported thus far take into account ring-bore conformance, based on static fitment of the ring within an out-of-round bore, whose out-of-circularity is affected by manufacturing processes, surface treatment and assembly. The various static fitment analyses presume quasi-static equilibrium between ring tension and gas pressure loading with the generated conjunctional pressures. This is an implicit assumption of ring rigidity whilst in situ, which is in fact not the case in practice. The transient nature of combustion variation means that mere static or quasi-static force balance is inappropriate. Furthermore, the bore is not a right circular cylinder. Thus, its radial cross-sectional out-of-roundness and its axial variation introduce further transience in the ring-bore conformance. Consequently, the net force applied to the ring induces its modal behaviour, which accounts for its instantaneous in situ shape within the bore. These considerations are not taken into account in the often idealized ring-bore tribology. The paper provides transient solution of ring-bore conjunction, when subjected to ring in-plane modal behavior, when the conjunction is subjected to a mixed regime of lubrication, comprising hydrodynamic viscous action and boundary interactions.
Effect of Stationary Natural Gas Engine Oils on Fuel Economy
Authors: Dayanand Nikhil , Palazzotto John D. , Beckman Alan T.
Published: July 2013

In order to investigate the possible environmental and economic benefits of lubricants optimized for stationary natural gas engine efficiency, a decision was made to develop a test stand to quantify the effects of lubricant viscosities and formulations on the brake specific fuel consumption.

Many fuel economy tests already exist for evaluating gasoline and heavy duty diesel motor oils which have proven the benefit of fuel economy from different lubricant formulations. These engines would not be suitable tools for evaluating the fuel economy performance of lubricating oils formulated specifically for stationary natural gas engines, since there are significant differences in operating conditions, fuel type, and oil formulations. This paper describes the adaptation of a Waukesha VSG F11 GSID as a tool to evaluate fuel consumption performance. The performance of brake specific fuel consumption when using different formulations was measured at selected high loads and rated speed.

The results of the testing program discuss the viscosity and additive effects of stationary natural gas engine oil formulations on brake specific fuel consumption. The results will detail the change in brake specific fuel consumption between natural gas engine oil formulations blended to varying viscosities and compared to a typical natural gas engine oil formulation with a viscosity of 13.8 cSt @ 100°C. The second portion of the test program explores the effect of different additive packages that were blended to the same finished oil viscosity.

It was acknowledged that there were statistical differences in brake specific fuel consumption characteristics between lubricants different in viscosity and additive formulations.
Development and Analysis of a Controlled Hot Surface Ignition System for Lean Burn Gas Engines
Authors: Scholl Fino , Neher Denis , Kettner Maurice , Hügel Philipp , Kubach Heiko , Klaissle Markus
Published: July 2013

Spark ignition constitutes the most common way of mixture inflammation for gas engines of CHP units (combined heat and power). However, spark plug durability is limited due to spark erosion. High maintenance costs as a result of frequent spark plug replacements are the consequence. Beside the durability aspect, the inflammation of lean mixtures makes high demands on the inflammation process itself. Due to the small reactive mixture volume, the level of air-fuel ratio as well as the efficiency increase is limited. The ignition by means of a hot surface enables an increase of the reactive mixture volume and, as a result, an enhancement of the lean burn limit.

A hot surface ignition (HSI) system was developed for stationary lean burn operation in due consideration of low manufacturing costs and electrical characteristics that allow a reliable control of the ignition timing. The main component of the inflammation element is a pin-shaped glow plug, whose temperature can be regulated by adjusting the electrical power. Due to external influences such as fluctuating ambient pressure and gas quality a control unit is essential for securing an optimal combustion phasing of the engine.

Several designs of hot surface ignition, including passive prechamber and shielded versions, were tested on a single cylinder test bed engine operating with a homogeneous air-petrol mixture. The engine tests were accompanied by 3D flow simulations. The trials showed that the power consumption, and hence the temperature of the hot surface, as well as the flow conditions around the glow plug have a strong influence on the ignition timing. Furthermore, a strong correlation between the mean combustion chamber temperature and combustion phasing became evident. Based on this coherence, it was possible to develop a closed-loop control that adjusts the combustion phasing by controlling the combustion chamber temperature at a stationary operating point.

The shielded inflammation element stood out to be the target-aiming version of hot surface ignition. It is characterised by an accelerated inflammation which allows reducing the cycle-to-cycle variations compared to prechamber spark ignition and, hence, to enhance the lean burn limit. As a result, a significant improvement of the efficiency-NOx trade-off is possible.

The obtained results provide the basis for further trials on a gas engine CHP module operating with natural gas.
Fast Emission Measurements in the Exhaust Port of Large Two-Stroke Engines
Authors: Ioannou Marios , Kyrtatos Nikolaos P. , Larsson David , Mayer Stefan
Published: July 2013

Ultra-fast emission measurements can provide important information about the combustion system of an engine, especially during its development phase. The ability to measure NOx as soon as it exits the cylinder provides an insight to engine designers and combustion engineers about the in-cylinder process with regards to formation of NOx emissions. There are mainly two areas where such information can be used. First, the fast measurements can be used for the tuning of CFD models that are used during the development phase of an engine. Secondly, such a method could be useful in the first phases of engine testing during the development of the combustion system where engine tuning could lead to an overall superior compromise between an engine’s fuel economy and emission behaviour.

The current research work investigated the potential of performing ultra-fast emission measurements in the exhaust port, immediately downstream of the exhaust valve, of a specified engine cylinder of a two-stroke large engine. A methodology was therefore developed and tested, by which emission measurements with fast temporal response can be conducted for individual engine cylinders.

More specifically, an ultra-fast NOx measurement sampling probe was designed and developed to be applied mainly to 2-stroke engines, with the flexibility to also be applicable to 4-stroke engines. The development of the sampling system was done by initially performing NO measurements on the 4-stroke MAN L16/24 research engine, installed at the test bed of the Laboratory of Marine Engineering (LME), at the National Technical University of Athens (NTUA). Once developed, the final fast sampling system was then used for measurements of NO at the exhaust port of the 2-stroke MAN 4T50ME-X engine, at the MAN Diesel & Turbo test-centre in Copenhagen. The employed NO emissions measurement method provided the results on a cycle-by-cycle basis, and also as phase averaged values. The extremely fast response time of the instrument captured important details of the NO concentration in the exhaust gases, as soon as they exit the cylinder.
Numerical Investigation on DI Diesel Engine Running With Eucalyptus Biodiesel and its Blends
Authors: Tarabet L. , Loubar K. , Lounici Mohand S. , Hanchi S. , Tazerout M.
Published: July 2013

The aim of the present work is to investigate the possibility of using eucalyptus biodiesel and its blends with diesel fuel as an alternative fuel for diesel engines. Eucalyptus oil is converted to biodiesel with ethanol using sodium hydroxide as a catalyst. The characterization of the obtained biodiesel shows that the thermo-physical properties are in the range recommended by American Standard (ASTM D6751). Innovative biodiesel development tests on the diesel engine require a lot of time and efforts. Here, mathematical model, which is based on the thermodynamic single zone model, is developed to analyze the combustion characteristics such as cylinder pressure and the performance characteristics such as brake power, brake thermal efficiency and specific fuel consumption of a DI diesel engine.
A Numerical Analysis of Hydrogen Underexpanded Jets
Authors: Bonelli F. , Viggiano A. , Magi V.
Published: July 2013

The aim of this work is the study of the fluid dynamic structure of underexpanded hydrogen jets by using a High Performance Computing (HPC) methodology. An axial symmetric two-dimensional turbulent flow model, which solves the Favre-averaged Navier-Stokes equations for a multicomponent gas mixture, has been implemented and validated. In order to predict the decrease in spreading rate with increasing Mach number, a compressibility correction has been added to the turbulence closure model.

The flow model has been assessed by comparing spreading and centerline property decay rates of subsonic jets at different Mach numbers with those obtained both by theoretical considerations and experimental measurements. Besides, the Mach disk structure of an underexpanded jet has been analysed, thus confirming the suitability of the computational model.

To take into account the effects of real gases, both van der Waals and Redlich-Kwong equations of state have been implemented. The computations performed under ICEs conditions show that the values of Mach number and pressure just behind the Mach disk are affected by the use of real gas equations.
Simulation of Turbocharged Marine Diesel Engine for Electrical Power System Trainer
Authors: Boley Matthew , Hagen Christopher L.
Published: July 2013

This paper presents an application of the mean value combustion model to simulate large bore turbocharged diesel engines, coupled with large electric AC synchronous generators, to mimic power generation within a training simulator for a ship board electrical power system. A mean value engine model has been developed to simulate the most prevalent phenomena occurring in diesel direct injection internal combustion engines. The combustion process is modeled as a mean value system where characteristics of combustion are averaged over the entire cycle. Detailed models of the air intake, fuel delivery, and internal/external cooling systems have been developed using concepts from fluid dynamics and thermodynamics. The engine model has been created in MATLAB® Simulink® to simulate actual hardware signals sent to the power management controller to facilitate the development of the power system trainer. The model has been structured so that it is highly adaptable and is capable of simulating a wide variety of engine bore sizes and cylinder numbers which has significantly increased the utility of the work presented herein.
Nozzle Flow Characteristics of Alternate Fuels for Compression Ignition Engine Applications
Authors: Som Sibendu , Longman Douglas E.
Published: July 2013

Inner nozzle flow characteristics (e.g., cavitation, turbulence, injection velocity) are known to affect spray development and hence combustion and emissions. Our previous studies showed that petrodiesel and biodiesel (soybean-based fuels) had very different cavitation and turbulence characteristics, which caused differences in spray breakup, penetration, dispersion, etc. Specifically, the atomization characteristics of biodiesel were worse than those of diesel; they were a direct consequence of biodiesel’s reduced cavitation and turbulence levels at the nozzle exit. In this study, the nozzle flow characteristics of biodiesel (from different feedstocks like tallow, soy, rapeseed, cuphea, and hydrotreated vegetable oil [HVO]) were compared with those of diesel. The first step was to obtain data on the physical properties of these fuels (e.g., their density, viscosity, surface tension, vapor pressure) at different temperatures. At full-needle open position, the cavitation contours scaled with the vapor pressure and viscosity; hence, methyl esters such as soy (SME), rapeseed (RME), and tallow (TME) exhibited less cavitation. The nozzle discharge coefficient, exit velocity, turbulent kinetic energy, and dissipation rate at the orifice exit were also compared for these fuels. Transient effects due to needle movement upon the inception of cavitation were studied. The effects of different needle-lift profiles (pertaining to various load conditions) on the nozzle flow development of these fuels were also characterized. This study also provides data on the critical boundary conditions for spray simulations from using the Kelvin Helmholtz-aerodynamic cavitation turbulence (KH-ACT) model, which accounts for cavitation and turbulence-induced breakup in addition to aerodynamic breakup.