Floating Liner Engine Research Articles

Analysis of the Piston Group Friction in a Single-Cylinder Gasoline Engine When Operated with Synthetic Fuel DMC/MeFo

<div class="section abstract"><div class="htmlview paragraph">Synthetic fuels for internal combustion engines offer CO<sub>2</sub>-neutral mobility if produced in a closed carbon cycle using renewable energies. C1-based synthetic fuels can offer high knock resistance as well as soot free combustion due to their molecular structure containing oxygen and no direct C-C bonds. Such fuels as, for example, dimethyl carbonate (DMC) and methyl formate (MeFo) have great potential to replace gasoline in spark-ignition (SI) engines. In this study, a mixture of 65% DMC and 35% MeFo (C65F35) was used in a single-cylinder research engine to determine friction losses in the piston group using the floating-liner method. The results were benchmarked against gasoline (G100). Compared to gasoline, the density of C65F35 is almost 40% higher, but its mass-based lower heating value (LHV) is 2.8 times lower. Hence, more fuel must be injected to reach the same engine load as in a conventional gasoline engine, leading to an increased cooling effect. To determine this effect, the temperatures of the cylinder liner and piston of the research engine were measured. Depending on the load point, friction losses were reduced by up to 12.6% compared to gasoline operation. Although the floating-liner engine is operated with port fuel injection (PFI), the temperatures of the cylinder liner dropped by up to 4°C and those of the piston by up to 8°C. C65F35 therefore not only shows decreased emissions, but also leads to a reduction in friction losses, mainly due to the lower temperatures in the combustion chamber.</div></div>

Measurement of Piston Friction with a Floating Liner Engine for Heavy-Duty Applications

<div class="section abstract"><div class="htmlview paragraph">The further increase in the efficiency of heavy-duty engines is essential in order to reduce CO<sub>2</sub> emissions in the transport sector. This is also valid for the future use of alternative fuels, which can be CO<sub>2</sub>-neutral, but can cause higher total costs of ownership due to higher prices and limited availability. In addition to thermodynamic optimization, the reduction of mechanical losses is of great importance. In particular, there is a high potential in the piston bore interface, since continuously increasing cylinder pressures have a strong influence on the frictional and lateral piston forces. To meet these future challenges of increasing heavy-duty engine efficiency, AVL has developed a floating liner engine for heavy-duty applications based on its tried and tested passenger car floating liner concept. This article describes the concept of the friction single-cylinder engine developed to measure both the frictional forces and the lateral forces that occur between the piston assembly and cylinder liner during fired engine operation. Four force sensors convert the floating movement of the liner group into the corresponding frictional force. Due to the crank angle based measurement, a very detailed analysis of measures to increase mechanical efficiency of the piston bore interface is possible. In addition, the frictional power can be derived and used to evaluate the CO<sub>2</sub> potential of the technologies investigated. The design of the single-cylinder engine has a high degree of flexibility to enable quick component changes and the use of different cranktrains. In a first study, a variation in the crankshaft offset and the potential of this measure to increase engine efficiency are investigated. The results show a clear influence of the cranktrain geometry on the lateral piston force and also on the frictional force during the upstrokes and downstrokes. This measurement campaign confirms the possibilities of the system to contribute to the development of future highly efficient heavy-duty engines.</div></div>

Effects of a Cylinder Liner Microstructure on Lubrication Condition of a Twin-Land Oil Control Ring and a Piston Skirt of an Internal Combustion Engine

It is hypothesized that structured sliding-surfaces improve the lubrication condition by forming an oil sump on the sliding surface, redistributing the oil, and trapping wear debris. For these reasons, structured sliding-surfaces have been used as a friction reduction method for a long time. In this work, effects of microstructure laid on the cylinder liner of an internal combustion engine on twin-land oil control ring (TLOCR) and piston skirt lubrication condition were investigated by comparing friction between a conventional fine-honed liner (CFL) and a micro-structured liner with the CFL. The measurements using a floating liner engine showed that the microstructure improved lubrication condition by reducing hydrodynamic friction. On the other hand, it was also observed that the microstructure could result in elevated friction under certain engine operating conditions.Graphical Abstract

Comparative study on the friction behaviour of piston/bore interface technologies

Engine crank case designs for passenger car applications are based today on two main material technologies: grey cast iron and an increasing share of aluminium-based concepts. Due to the low wear resistance of aluminium, the latter concepts require a wear protective layer for the cylinder bore surface. Iron-based thermal spray coats are widely used for this purpose. The coating improves the tribological behaviour significantly, as previous studies have shown. Additionally, aluminium-based concepts offer advantages regarding engine weight and thermal management. The aim of the presented work was the discussion of these technological concepts regarding the tribological and sealing properties of the piston/bore interface. The study was carried out based on the AVL FRISC Floating Liner Engine. While the basic engine remained unchanged, the cylinder bore surface was varied. In addition to the floating liner friction measurement, the blow-by and lube oil consumption were also measured. A state-of-the-art multi-body dynamic simulation model complements the experimental study, while both simulation and measurement lead to similar conclusions.

Resource-efficient piston ring/cylinder liner pairing

PurposeThe purpose of this paper is to investigate the influence of different finish processes on the surface integrity and tribological behaviour of cylinder running surfaces for internal combustion engines.Design/methodology/approachThe cutting force during finishing and the resulting surface topography was measured for a variety of cylinder running surfaces made of EN-GJL-250, EN-GJV-400 and thermal sprayed aluminium alloy. A separate conditioning tool was developed and tested. Different analysis methods (SEM, EDX, SIMS and FIB) for the characterisation of the boundary conditions were used. By an oscillating friction wear test and a single cylinder floating liner engine, the running-in and frictional behaviour was rated.FindingsIt was shown that honing with low cutting forces and silicon carbide cutting material decreases the friction in operation. The characteristics of the boundary layers after running-in depend on the finish machining process. A preconditioning with a separate tool can adjust the boundary layer and running-in behaviour. Based on the experimental results, a multi-body and computational fluid dynamics simulation was developed for the floating liner engine.Originality/valueThe results demonstrate the potential of finishing with low process forces to reduce friction and the need for a complete consideration of the tribological system piston ring/cylinder liner surface.

A comprehensive study of the effects of honing patterns on twin-land oil control rings friction using both a numerical model and a floating liner engine

Engine bores are finished with a multi-stage honing process and the finished surface roughness contributes significantly to the piston ring hydrodynamic pressure generation, especially for twin-land oil control rings whose land profile is parallel to the liner surface. In this paper, five different honing patterns on a cast iron liner and one on a spray-coated aluminum liner are studied with a floating liner engine and numerical models. The liner temperature and engine speed were varied such that all the lubrication regimes, namely boundary, mixed, and fully hydrodynamic, are present. It is found that the models based on deterministic approach with a patch of carefully measured liner roughness can match the trend of the Stribeck curves for different liner finishes observed in the experiment. Furthermore, the results show that the roughness height and structure of the honing affect the twin-land oil control rings lubrication differently. With the same honing structure, although rougher liner experiences mixed and boundary lubrication in larger range of Gumbel–Hersey number, it renders less friction than the smoother ones in the hydrodynamic regime. With the same plateau roughness height, a more continuous plateau can provide more flow resistance and thus generate higher hydrodynamic pressure at the ring–liner interface and less friction.

Improvement in Accuracy of Piston Frictional Force Measurement Using Floating Liner Engine

Improvement in Accuracy of Piston Frictional Force Measurement Using Floating Liner Engine

Friction Reduction Effect Between Piston and Cylinder Surface Treatment Using Floating Liner Engine

Friction Reduction Effect Between Piston and Cylinder Surface Treatment Using Floating Liner Engine

Component test for simulation of piston ring – Cylinder liner friction at realistic speeds

The piston ring cylinder liner contact is a large contributor to mechanical friction losses in internal combustion engines. It is therefore important to have methods and tools available for investigations of these frictional losses. This paper describes the design of a novel component test rig which is developed to be run at high speeds with unmodified production piston rings and cylinder liners from heavy duty diesel engines. A simplified floating liner method is used and the test equipment is developed to fill the gap in between a full floating liner engine and typical component bench test equipment. The functionality and repeatability of the test are investigated and an unexpected behaviour of the twin land oil control ring is found.

A Study of the Friction of Oil Control Rings Using the Floating Liner Engine

A Study of the Friction of Oil Control Rings Using the Floating Liner Engine

Practical challenges in determining piston ring friction

Practical challenges from both experiment and calculation sides were discussed for determining two piece twin land oil control ring friction. A floating liner engine was used for twin land oil control ring study. Effects of floating liner engine system dynamics and piston skirt friction were addressed and methods to mitigate them were discussed. A deterministic twin land oil control ring model was used for ring friction calculation. Variation of the surface roughness at different spots of the liner and its effects on both hydrodynamic and boundary lubrication predictions were discussed. A multi-point correlation method was introduced to address surface variation effects on the twin land oil control ring model. Ring land width variation between two lands as well as along the circumference and its effects on calculation were shown, and methods to address it were discussed. By taking all these necessary steps in both experiments and calculations, this study shows that a reasonable match can be achieved between the measured and calculated friction, which covers all three lubrication regimes. This study lays a foundation for realistically predicting the friction of piston rings in internal combustion engines.

Tri-Axial Force Measurements on the Cylinder of a Motored SI Engine Operated on Lubricants of Differing Viscosity

Friction is a determining factor in the efficiency and performance of internal combustion engines. Losses in the form of friction work typically account for 10–20% of an engine’s output. Improvements in the friction characteristics of the power cylinder assembly are essential for reducing total engine friction and improving the mechanical efficiency of internal combustion engines. This paper describes the development and implementation of a new concept of the “floating liner” engine at Colorado State University that allows 0.5 crank angle deg resolved measurement of the forces on the cylinder along three axes—in the axial direction, the thrust direction, and along the wrist pin. Three different lubricants with differing properties were tested to observe the friction characteristics of each. The experimental results showed that the floating liner engine was able to resolve changes in friction characteristics coinciding with changes in lubricant viscosity and temperature. The axial force increases at TDC and BDC were observed as lubricant viscosity was decreased and larger amounts of mixed and boundary lubrication began to occur. For each test the axial friction force data was used to calculate total cycle friction work. The thrust and off-axis (wrist pin direction) forces are discussed under the same circumstances.

Analysis of Piston Skirt Friction in a Gasoline Engine

In order to reduce the friction of the piston system, it is important to understand the friction and lubrication at the skirt and ring. In gasoline engines, the friction of the skirt is often equal to or larger than that of the ring pack, then the reduction of the friction at the skirt is indispensable. In this study, the piston skirt friction was measured by the floating liner engine which consists of independent measuring devices for skirt and ring pack friction. In addition, the skirt friction was calculated by a simulation model considered surface roughness, boundary lubrication, skirt profile and skirt stiffness. The calculated skirt friction compared with experimental data measured by floating liner method. As a result, the calculated skirt friction showed good agreement with the measured results, thus it was confirmed that the calculation accuracy of the skirt friction was sufficient. Furthermore, calculations of the skirt friction were carried out to clarify the influence of friction factors. It was also found that the skirt friction was affected by the skirt stiffness, skirt profile and skirt bearing area at the case of gasoline engines.