Efficiency Improvement of Common-Rail Pumps by Gap Compensation Based on Hollow Pistons

2015 ◽  
Author(s):  
Stefan Heitzig ◽  
Gregor Bultel ◽  
Hubertus Murrenhoff
Keyword(s):  
Operating Conditions ◽  
Geometric Parameters ◽  
Common Rail ◽  
Injection System ◽  
Dominant Factor ◽  
Efficiency Improvement ◽  
Lubricating Film ◽  
Piston Cylinder ◽  
Low Viscosity ◽  
Gap Height

In the scope of the cluster of excellence “Tailor-Made Fuels from Biomass” new biofuels are developed. To ensure safe and reliable functioning of the injection system operating with the new fuels, the tribological characteristics of the fuel candidates have to be investigated. The biofuel candidates which have been studied so far tend to have a lower viscosity compared to diesel [1]. This has an enormous impact on the efficiency of common-rail piston pumps. For low viscosity fuels the volumetric losses become the dominant factor. These losses are influenced by the geometric parameters of the pump, the operating conditions and the rheological characteristics of the fuels. Regarding the geometric parameters, the gap height in the piston-cylinder-contact is the predominant factor. In modern common-rail pumps the nominal gap height is in the range of 2–3 μm [2]. A further reduction of the height is limited by tolerances of the manufacturing process and the risk of the piston getting stuck in the cylinder due to different temperature gradients and consequently different thermal expansions of piston and cylinder. Besides the nominal gap height, the high pressure in the lubricating film in operation leads to an expansion of the gap. If this expansion can be limited or even avoided, a significant reduction of the leakage losses will be possible. In the scope of this paper an approach to a gap compensation of the sealing and lubricating contact between piston and cylinder is presented. Based on a detailed study of the state of the art design, including efficiency measurements of pumps and EHD-simulation, a modified piston design is investigated and optimized. The results show a great potential for efficiency improvement of common-rail pumps, especially if operated with biofuels, which provide low viscosities.

Reducing Friction and Wear in Common-Rail Pumps by Grooved and Contoured Pistons

2016 ◽  
Author(s):  
Marcel Rückert ◽  
Stefan Heitzig ◽  
Hubertus Murrenhoff
Keyword(s):  
Alternative Fuels ◽  
Friction And Wear ◽  
Operating Conditions ◽  
Common Rail ◽  
Reliable Operation ◽  
Lubricating Film ◽  
Piston Cylinder ◽  
Lower Viscosity ◽  
Common Rail Injection ◽  
Solid Friction

Within the cluster of excellence “Tailor-made Fuels from Biomass” at RWTH Aachen University new biofuels are developed and investigated. Because common-rail injection pumps are generally lubricated by the fuel itself, the tribological characteristics of the fuel candidates is of interest. The lubricity and viscosity of the alternative fuels differ from diesel. Hence, a reliable function of the tribological contacts, which are designed for the operation with diesel, cannot be guaranteed. To achieve a reliable operation even for fuels with, for instance, a lower viscosity or worse lubricity an optimisation of the tribological contacts is necessary. The focus of the investigations presented in this paper lies on the piston-cylinder-contact. Prior to the simulative study the losses in a pump operating with various fuel candidates are quantified by means of efficiency measurements. By these measurements the great impact of the fuel’s rheology on the pump performance is clarified. Based on detailed EHD-simulations with various fuels under typical operating conditions, an optimisation of the piston-cylinder-contact is presented. The optimisation aims for the reduction of solid friction by changing the pressure field on the piston. The approaches can basically be separated into grooved and contoured pistons. The potential of the different approaches is discussed based on simulation results and effects, which occur in the lubricating film of the optimised contacts.

scholarly journals Tailoring the Bore Surfaces of Water Hydraulic Axial Piston Machines to Piston Tilt and Deformation

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5997
Author(s):  
Meike Ernst ◽  
Andrea Vacca ◽  
Monika Ivantysynova ◽  
Georg Enevoldsen
Keyword(s):  
Experimental Testing ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Surface Shape ◽  
Working Fluid ◽  
Total Efficiency ◽  
Positive Displacement ◽  
Piston Cylinder ◽  
Low Viscosity ◽  
Axial Piston

A novel virtual prototyping algorithm has been developed to design one of the most critical lubricating interfaces in axial piston machines of the swash plate type—the piston–cylinder interface—for operation with water as the working fluid. Due to its low viscosity, the use of water as a lubricant can cause solid friction and wear in these machines at challenging operating conditions. The prototyping algorithm compensates for this by tailoring the shape of the bore surface that guides the motion of each piston in this type of positive displacement machine to conform with the piston surface, taking into account both the piston’s tilt and its deformation. Shaping these surfaces in this manner can render the interface more conducive to generating hydrodynamic pressure buildup that raises its load-carrying capacity. The present work first outlines the structure of the proposed algorithm, then presents a case study in which it is employed to design a bore surface shape for use with two prototypes, one virtual and one physical—both modified versions of a 444 cc commercial axial piston pump. Experimental testing of the physical prototype shows it to achieve a significantly higher maximum total efficiency than the stock unit.

Impact of Intake Induced Swirl on Combustion and Emissions on a Single Cylinder Diesel Engine

2016 ◽  
Author(s):  
Eduardo Barrientos ◽  
Ivan Bortel ◽  
Michal Takats ◽  
Jiri Vavra
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Operating Conditions ◽  
Common Rail ◽  
Injection System ◽  
Nox Emissions ◽  
Cylinder Pressure ◽  
Swirl Ratio ◽  
Single Cylinder ◽  
Optimal Values

Engine induced swirl improves mixing of fuel and air and at optimal values accelerates burn, improves the combustion stability and can decrease particulate matter (PM). However, swirl increases convective heat loss and cylinder charge loss and could increase nitrogen oxides (NOx) emissions. High intensity of swirl could impede flame development and increases emissions of total hydrocarbons (THC) and carbon monoxide (CO). Therefore, careful and smart selection of optimal swirl values is paramount in order to obtain beneficial impact on combustion and emissions performance. This study is conducted on a 0.5L single cylinder research engine with common rail (CR) diesel injection system, with parameters corresponding to modern engines of passenger cars. The engine has three separate ports in the cylinder head. The change of swirl ratio is defined by closing appropriate ports. There are three levels of swirl ratio under study — 1.7, 2.9 and 4.5, corresponding to low, medium and high swirl levels respectively. This study highlights the influence of intake induced swirl on combustion parameters and emissions. Assessed combustion parameters are, among others, heat release rate, cylinder pressure rise and indicated mean effective pressure. Assessed emissions are standard gaseous emissions and smoke, with emphasis on PM emissions. An engine speed of 1500 rpm was selected, which well represents common driving conditions of this engine size. Various common rail pressures are used at ambient inlet manifold pressure (without boost pressure) and at 1 bar boosted pressure mode. It is found that when the swirl level is increased, the faster heat release during the premixed combustion and during early diffusion-controlled combustion causes a quick increase in both in-cylinder pressure and temperature, thus promoting the formation of NOx. However, since swirl enhances mixing and potentially produces a leaning effect, PM formation is reduced in general. However, maximum peak temperature is lower for high swirl ratio and boosted modes due to the increase of heat transfer into cylinder walls. Furthermore, it is necessary to find optimal values of common rail pressures and swirl ratio. Too much mixing allows increase on PM, THC and CO emissions without decrease on NOx emissions in general. Common rail injection system provides enough energy to achieve good mixing during all the injection time in the cases of supercharged modes and high common rail pressure modes. Positive influence of swirl ratio is found at lower boost pressures, lower revolution levels and at lower engine loads. The results obtained here help providing a better understanding on the swirl effects on diesel engine combustion and exhaust emissions over a range of engine operating conditions, with the ultimate goal of finding optimal values of swirl operation.

The Impact of the Surface Shape of the Piston on Power Losses

2014 ◽  
Author(s):  
Ashley M. Wondergem ◽  
Monika Ivantysynova
Keyword(s):  
Energy Dissipation ◽  
Cost Effective ◽  
Operating Conditions ◽  
Surface Shape ◽  
Critical Gap ◽  
Piston Cylinder ◽  
Wide Range ◽  
Load Carrying ◽  
Gap Height ◽  
The Impact

Axial piston machines are widely used in industry thus new cost-effective and highly efficient designs are needed. One way to increase efficiency and decrease cost is by altering the geometry along with the configuration of the piston/cylinder interface influencing the fluid film generation and in turn the energy dissipation and load carrying capacity while still having a design that is cost effective and easy to manufacture. This paper presents a study on a reduction of energy dissipation between the piston and cylinder over a wide range of operating conditions at both full and partial displacements based on the surface shape of the piston along with the minimum clearance. First, it is necessary to measure a base design and then compare those results to simulations in order to verify the simulation results. Once a baseline is established, various piston surface shapes and minimum clearances are then also simulated and compared back to the simulated baseline. Not only is energy dissipation important to compare, but also the minimum gap height over one revolution. The minimum gap height is in direct correlation to friction loss and wear. Therefore, this paper also includes an understanding of how the gap height affects the total losses thus leading to the importance of finding a relative clearance that satisfies a median between torque losses and leakage along with the importance of reducing the occurrence of critical gap heights to reduce the need for wear in in the machine.

Influence of a New Hollow Piston Design on Volumetric Losses of a Common-Rail Pump

2017 ◽  
Author(s):  
Marcel Rückert ◽  
Hubertus Murrenhoff ◽  
Stefan Heitzig
Keyword(s):  
Common Rail ◽  
Hydrodynamic Properties ◽  
Compression Behavior ◽  
Piston Cylinder ◽  
Low Viscosity ◽  
Measurement Results ◽  
Common Rail Injection ◽  
Global Emissions ◽  
Viscosity Fluid ◽  
Critical Contact

The cluster of excellence „Tailor-Made Fuels from Biomass“ at RWTH Aachen University develops and investigates new biofuel candidates, to reduce global emissions and create an alternative and sustainable diesel fuel. Biofuels pose a new challenge to existing common-rail injection pumps. Since fuels are used as lubricants for tribological contacts in these pumps, the deviating hydrodynamic properties in comparison to diesel can cause high leakage, wear, and a low overall-efficiency. In order to ensure a reliable pump performance, especially for low-viscosity fuels or fuels with worse lubricity than diesel, an optimization of the tribological contacts is necessary. The most critical contact is the piston-cylinder contact. One possibility to reduce the leakage in this contact is the use of a hollow piston design. This design can reduce the gap between piston and cylinder by minor pressure-dependent elastic deformations of the piston. In this paper, a first simulative look is taken at the compression behavior of the new piston design. The focus lies on the delayed pressure build-up due to the additional capacity caused by the shape of the piston. Based on the results, a new design approach is proposed subsequently in order to ensure a sufficient pressure build-up. The manufactured contour of the new design is investigated in order to ensure the geometric properties and first measurement results are discussed. For the measurement, a low-viscosity fluid is used to compare leakage rates of the standard and the new hollow piston design. Based on the results, a conclusion is made, deriving further usage of the hollow piston.

Spray Characterization From Common Rail Injection System for Use in Locomotive Engines

2007 ◽  
Author(s):  
Essam El-Hannouny ◽  
Douglas Longman ◽  
Steven McConnell ◽  
Xingbin Xie ◽  
Ming-Chai Lai ◽  
...  
Keyword(s):  
High Speed ◽  
Alternative Fuels ◽  
Operating Conditions ◽  
Common Rail ◽  
Pollutant Emissions ◽  
Injection System ◽  
Emissions Reduction ◽  
Common Rail Injection System ◽  
Spray Structure ◽  
Common Rail Injection

New U.S. Environmental Protection Agency regulations are forcing locomotive manufacturers and railroads to reduce pollutant emissions from locomotive operation. Locomotive engines will be required to meet the applicable standards at the time of original manufacture. A variety of emissions-reduction technologies can be used, such as alternative fuels, additives in lubricant oil, and aftertreatment technologies (e.g., selective catalytic reduction and particulate traps). Emissions reduction can also be accomplished inside the cylinder, using advanced diesel fuel injectors that have a significant impact on the quality of spray and charge preparation before engine combustion and subsequent events. High-speed optical measurements have been collected at elevated ambient pressures for sprays from a modular common rail injection system at Argonne National Laboratory in order to investigate spray structure and dynamics. High-speed laser imaging was used to explore the effects of various parameters on the spray structure. The experimental parameters included were ambient gas density, injection pressure, number of spray holes, injection strategy, and internal orifice size. Spray symmetry and structure were found to depend significantly on the nozzle geometry or manufacturing variances and the operating conditions.

Zero-Dimensional Analysis of Combustion in a Multiple-Injection CRDI Engine Using Wiebe Law

2015 ◽  
Vol 787 ◽  
pp. 707-711 ◽  
Author(s):  
G. Sudarshan ◽  
S. Rajkumar
Keyword(s):  
Engine Speed ◽  
Direct Injection ◽  
Combustion Process ◽  
Combustion Characteristics ◽  
Operating Conditions ◽  
Common Rail ◽  
Injection System ◽  
Empirical Constant ◽  
Rate Law ◽  
Burn Rate

Common rail direct injection system (CRDI) offers the potential to achieve optimal combustion and emission characteristics. An empirical analysis of engine combustion process incorporating Wiebe type burn rate law approach is useful not only in understanding the combustion characteristics of a CRDI engine but also aids in diagnosis and control of the combustion process wherever required from the performance and emission standpoint. This paper presents a methodology for applying the burn rate law for common rail direct injection diesel engines adopted with split injection by using Wiebe’s correlation. The analysis reveals that while the empirical constant ‘m’ (shape factor) for both pilot and main injections is independent of engine load and seems to be affected by engine speed only, the constant ‘a’ (efficiency parameter) seems to be influenced by the engine speed, load and injection conditions. A correlation for these empirical constants with the respective parameters of dependence can be formulated which can be used to analyze the effect of change in engine operating conditions on combustion characteristics without conducting engine experiments.

scholarly journals Octane Index Applicability over the Pressure-Temperature Domain

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 607
Author(s):  
Tommy R. Powell ◽  
James P. Szybist ◽  
Flavio Dal Forno Chuahy ◽  
Scott J. Curran ◽  
John Mengwasser ◽  
...  
Keyword(s):  
High Efficiency ◽  
National Laboratory ◽  
Operating Conditions ◽  
Dominant Factor ◽  
Compression Ignition ◽  
Oak Ridge ◽  
Operating Modes ◽  
Wide Range ◽  
Thermodynamic Conditions ◽  
Si Engines

Modern boosted spark-ignition (SI) engines and emerging advanced compression ignition (ACI) engines operate under conditions that deviate substantially from the conditions of conventional autoignition metrics, namely the research and motor octane numbers (RON and MON). The octane index (OI) is an emerging autoignition metric based on RON and MON which was developed to better describe fuel knock resistance over a broader range of engine conditions. Prior research at Oak Ridge National Laboratory (ORNL) identified that OI performs reasonably well under stoichiometric boosted conditions, but inconsistencies exist in the ability of OI to predict autoignition behavior under ACI strategies. Instead, the autoignition behavior under ACI operation was found to correlate more closely to fuel composition, suggesting fuel chemistry differences that are insensitive to the conditions of the RON and MON tests may become the dominant factor under these high efficiency operating conditions. This investigation builds on earlier work to study autoignition behavior over six pressure-temperature (PT) trajectories that correspond to a wide range of operating conditions, including boosted SI operation, partial fuel stratification (PFS), and spark-assisted compression ignition (SACI). A total of 12 different fuels were investigated, including the Co-Optima core fuels and five fuels that represent refinery-relevant blending streams. It was found that, for the ACI operating modes investigated here, the low temperature reactions dominate reactivity, similar to boosted SI operating conditions because their PT trajectories lay close to the RON trajectory. Additionally, the OI metric was found to adequately predict autoignition resistance over the PT domain, for the ACI conditions investigated here, and for fuels from different chemical families. This finding is in contrast with the prior study using a different type of ACI operation with different thermodynamic conditions, specifically a significantly higher temperature at the start of compression, illustrating that fuel response depends highly on the ACI strategy being used.

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