Engine Friction Research Articles

Dynamic method of controlling friction losses in the mechanism of converting reciprocating motion into rotary inline piston internal combustion engines

The task of reducing friction in internal combustion engines is an important task of the development of transport engineering. As the analysis of literature sources shows, the problem of reducing friction losses in relation to internal combustion engines is usually solved for each individual friction pair, for example, a cylinder-skirt of a piston or a cylinder - compression ring. In this case, the measurement of friction is carried out mainly in stationary conditions. However, such approaches do not allow to identify the most critical, in terms of friction in all friction pairs of internal combustion engines, operating modes and do not allow to study and control the friction processes of all friction pairs in of the internal combustion engines. The developed dynamic methods of control of mechanical parameters of engines of rotational action and drives on their basis allow to synthesize a dynamic method of control of friction losses in the internal combustion engines, the scientific and technical justification of which is devoted to this work. Critical, from the point of view of the developed method, is the calculation of the value given to the axis of rotation of the crankshaft moment of inertia of the parts of the crank mechanism, changing during one revolution of the crankshaft.

One-Dimensional Modeling of Mechanical and Friction Losses Distribution in a Four-Stroke Internal Combustion Engine

AbstractAs the road transport accounts between 15%–18% of worldwide CO2 emissions, the automotive sector has a deep commitment to mitigate global warming. Consequently, stricter regulations have been adopted by the European Union and worldwide to reduce that big impact. Approximately, 10% of the energy generated by fuel combustion in the engine is destined to the auxiliaries components activation and the movement of mechanical elements with relative motion between themselves. A reduction on that figure or alternatively a mechanical efficiency improvement can be directly translated on target alignment. The aim of this work is developing a model to predict the mechanical and friction losses and its distribution in a four-stroke direct injection-diesel engine and simulating different strategies, which increment the engine efficiency. A 1D model has been developed and fitted in gt-suite based on the experimental results of a 1.6-L diesel engine. Additionally, a description of the tribological performance has been realized in different parts of the engine where friction is present. Finally, the engine friction maps have been broken down in order to quantify the friction losses produced in the piston ring assembly, crankshaft bearings, and valvetrain.

Reduction of Friction and Parasitic Losses of Large-bore Diesel Engines

Reduction of Friction and Parasitic Losses of Large-bore Diesel Engines

Predictive tool for frictional performance of piston ring-pack/liner conjunction

Fundamental understanding of piston ring-pack lubrication is essential in reducing engine friction. This is because a substantial portion of engine frictional losses come from piston-ring assembly. Hence, this study investigates the tribological impact of different piston ring profiles towards engine in-cylinder friction. Mathematical models are derived from Reynolds equation by using Reynolds’ boundary conditions to generate the contact pressure distribution along the complete piston ring-pack/liner conjunction. The predicted minimum film thickness is then used to predict the friction generated between the piston ring-pack and the engine cylinder liner. The engine in-cylinder friction is predicted using Greenwood and Williamson’s rough surface contact model. The model considers both the boundary friction and the viscous friction components. These mathematical models are integrated to simulate the total engine in-cylinder friction originating from the studied piston ring-pack for a complete engine cycle. The predicted minimum film thickness and frictional properties from the current models are shown to correlate reasonably with the published data. Hence, the proposed mathematical approach prepares a simplistic platform in predicting frictional losses of piston ring-pack/liner conjunction, allowing for an improved fundamental understanding of the parasitic losses in an internal combustion engine.

Experimental investigation of the effects of CR, hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty NGSI engine fueled with 99% methane content

In order to analyze and improve thermodynamic process of NGSI engine and achieve better energy utilization, a low CR (11.6) SI engine was modified by replacing pistons with different bowl volumes and an experimental investigation of the effects of CR (13.6 and 14.5), hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty NGSI engine fueled with 99% methane content was conducted. The results showed that the PCP, maximum HRR and in-cylinder temperature increased obviously with the increase of hydrogen contents, CR and engine speed, and the locations of PCP and maximum HRR advanced towards TDC, which led to the advance of 50% combustion position, shorter combustion duration and more output work. Secondly, with the increase of hydrogen contents and CR, the proportions of indicated work and heat transfer energy to coolant turned larger but the unaccounted losses and combustion loss became smaller. In addition, with the increase of engine speed, both indicated work and friction loss were large, which caused the decrease of BTE, besides, the percentage of friction loss and pumping loss turned up. And the hydrogen contents and CR had little effect on exhaust energy and exergy. Finally, comparing the energy and exergy of NGSI engine under operated conditions, the change trends of exergy terms were similar to their corresponding energy, however, the exergy efficiency was 7.97–9.70% lower than BTE and the percentage of exhaust energy and heat transfer energy to coolant was 2.46–2.51 and 7.09–8.09 times larger than corresponding energy, respectively.

How much mixed/boundary friction is there in an engine — and where is it?

Automotive engines are believed to operate predominantly in the hydrodynamic regime, as evidenced by the (1) the successful strategy of reducing lubricant viscosity to reduce engine friction and improve vehicle fuel consumption, and (2) for most engine operating conditions, direct measurements of engine friction (either motored or fired) find that engine friction increases with increasing engine speed. However, certain components in an engine are known to operate mainly in the mixed/boundary lubrication (e.g. the valve train) and other components (such as the piston rings) operate in the mixed/boundary regime for a portion of the time. In order to quantify the amount of mixed/boundary lubrication in an engine, and in the individual components of the engine, motored and fired friction tests have been carried out for a range of lubricants (of differing viscosity grade, and with/without friction modifier additives). A full discussion of the implications of this work, which includes the impact of fuel dilution and “running-in” is included with insights given into how the work reported here guides the development of future fuel-efficient engine lubricants.

Strain Engineering Modulates Graphene Interlayer Friction by Moiré Pattern Evolution.

The sliding friction of a graphene flake atop strained graphene substrates is studied using molecular dynamics simulation. We demonstrate that in this superlubric system, friction can be reduced nonmonotonically by applying strain, which differs from previously reported results on various 2D materials. The critical strain needed for significant reduction in friction decreases drastically when the flake size increases. For a 250 nm flake, a 0.1% biaxial strain could lead to a more than 2-order-of-magnitude reduction. The underlying mechanism is revealed to be the evolution of Moiré patterns. The area of the Moiré pattern relative to the flake size plays a central role in determining friction in strain engineering and other scenarios of superlubricity as well. This result suggests that strain engineering could be particularly efficient for friction modification with large contacts.

Film breakup of tilted impinging spray under various pressure conditions

Fuel film on engine walls caused by spray impingement would dramatically cause engine friction deterioration, incomplete combustion, and significant cycle-to-cycle variations. In a previous work, it has been demonstrated that fuel film would break up via wave entrainment induced by the high-speed coflow. Meanwhile, the film breakup dynamics depend on various boundary conditions, such as injection pressure, ambient pressure, and so on. However, such impact on the wall film formation was not investigated thoroughly in existing literature. This work aims to perform a parameter study to investigate possible means to enhance wave entrainment effect as to reduce the amount of impingement fuel mass. In this study, simultaneous measurements of macroscopic structure and its corresponding footprint of impinging spray are conducted using a single-hole, prototype injector in a constant volume chamber. The macroscopic spray structure was captured by high-speed backlit imaging, and the film was obtained using laser-induced fluorescence under different conditions. The laser-induced fluorescence signal is converted to film thickness following a calibration procedure where laser-induced fluorescence signals from a series of known-thickness film are captured. A mathematical processing method is used to analyze both the dynamic behavior of film thickness and amount of droplet detachment caused by high-speed coflow. It is found that at the leading edge of film waves, a remarkable amount of liquid droplets detaches from the liquid film and the quantity of film mass on the wall decreases during this process. Quantitative analysis is conducted and the mass ratio of detached droplets over residual liquid film is estimated. We hold that the film breakup percentage increases with both ambient and injection pressure due to the enhanced high-speed coflow. Then, variation laws for various boundary conditions are obtained based on the observations.

A Multiscale Cylinder Bore Honing Pattern Lubrication Model for Improved Engine Friction

A Multiscale Cylinder Bore Honing Pattern Lubrication Model for Improved Engine Friction

Effect of piston ring geometries on lubrication and friction in diesel engine

Lubrication and friction in piston rings are of a greater importance which has been receiving significant attention from tribologists for a long time. The main subsystems which contribute to friction include the ring-pack/liner, piston-skirt/liner, piston-pin/connecting-rod and connecting rod-crankshaft bearings. Piston rings are used in engines mainly to reduce leakage of gas in the combustion chamber and simultaneously provide a lubrication film in order to reduce friction during its motion. Wear between piston rings and liner is inevitable and therefore in order to reduce it, different types of ring geometries are being used which has its own advantages and disadvantages. Another major problem being faced during operation is that oil from the liner gets transported by pumping, reverse blow by, inertia and squeezing of oil due to ring dynamics into the combustion chamber. The present work focuses on to investigate different ring geometries and their effects on friction and lubrication oil consumption. It was found that Tangential force has an inverse relationship with Oil Film Thickness and Oil filling ratio. Top ring friction is high at Top dead centres due to boundary lubrication. Ring Barrel height has a direct relationship with asperity friction and an inverse relationship with Oil Film Thickness. Axial width is directly proportional to the wear of rings, which is due to the area exposed to back pressure on the rings exerted by gases from combustion chamber. Second ring closed gap has a direct relationship with Inter-ring pressure thus increasing reverse blowby. Rings with a Positive twist are found to be stable during operation. For this analysis, AVL Excite software is being used and results are validated with an experimental model.

Optimal Pressure Relief Groove Geometry for Improved NVH Performance of Variable Displacement Oil Pumps

<div class="section abstract"><div class="htmlview paragraph">Variable Displacement Oil Pump (VDOP) is becoming the design of choice for engine friction reduction and fuel economy improvement. Unfortunately, this pump creates excessive pressure ripples, at the outlet port during oil pump shaft rotation, causing oscillating forces within the lubrication system and leading to the generation of objectionable tonal noises and vibrations. In order to minimize the level of noise, different vanes spacing and porting geometries are used. Moreover, an oil pressure relief groove can be added, at the onset of the high pressure port, to achieve this goal.</div><div class="htmlview paragraph">This paper presents an optimization method to identify the best geometry of the oil pressure relief groove. This method integrates adaptive meshing, 3D CFD simulation, Matlab routine and Genetic Algorithm based optimization. The genetic algorithm is used to create the required design space in order to perform a multi-objective optimization using a large number of parameterized groove geometries. Results of this optimization method are discussed and a design guideline for the oil pressure relief groove is disclosed.</div></div>

Numerical Investigation on Oil Pan Design Parameters to Improve Engine Performance During Oil Cool Down and Warm Up Periods

For developing automotive industry, one of the focusing point is reduction of engine friction level to decrease both engine emissions and fuel consumption. Important part of researchers have focused on cold engine start period, which has higher friction loses. Shorter warm up period and faster heating of engine oil help to provide better engine performance. Not only warm up time but also better cool down period after engine stops, dramatically effects engine efficiency. If oil temperature stays hot for longer time during the vehicle key-off duration, it brings an important advantageous at the next start. Main purpose of this study is to investigate oil temperature changes depending on the design parameters of the oil pan. This investigation is done for oil warm up and cool down periods by mathematical model, which is validated for 2.0 L and 4 cylinders diesel engine. Design improvement combinations against base steel oil pan has been examined throughly in terms of oil temperature changes, warm up and cool down time, fictional loses and weight reduction opportunity. As a result, 5 mm thickness plastic oil pan with windage tray application is the best solution option since it brings both 12.5 % friction decreasing in cold start after 2 hours key-off duration, and 43 % weight reduction.

Experimental development of apparatus to measure piston assembly friction in an eco-mileage vehicle engine

Apparatus was developed to measure piston assembly friction with a floating cylinder liner against crank angle, using components of an eco-mileage vehicle engine as much as possible. This apparatus was then used to investigate the effect of different sets of piston rings on piston assembly friction in an eco-mileage vehicle engine. Results indicated that, compared to the piston with all three rings (a top ring, a second ring and an oil ring), the piston with two rings (a top ring and an oil ring) reduced piston assembly friction at all engine temperatures and engine speeds. Another configuration of two rings, with the top ring and the second ring, but without the oil ring, reduced friction at a lower engine temperature and speed, but was almost the same as the three-ring set at a higher engine temperature and speed. Finally, a one-ring set, with only the top ring, further reduced friction, except at a higher temperature and speed, where friction was greater than the two-ring set without the second ring.

A mathematical model of a bolted connection based on Florida contact theory to study the influence of the friction coefficient on structural performance

Bolted joints are widely used for the mechanical assembly of engineering structures and friction coefficient of the contact surface of a bolted connection is the main factor that influences its structural performance. This article presents a mathematical model based on the Florida contact model to obtain the friction coefficient for the contact surface of a bolted joint. The pressure distribution function of the bolted joint is introduced into the mathematical model and elastic, elastic–plastic, and full plastic deformation of asperities at the microscale is also considered. By varying the peak height of asperities, an improved exponential distribution function was constructed. In addition, the proposed model was verified by comparing simulation results to experimental values obtained using a CETR UMT-5 high-precision ball-on-disk friction and wear tester. Then the theoretical friction coefficient was used in the finite element model of the bolted joint, and through numerical simulation, the state of the contact surface of the tightened bolted connection was analyzed. Increasing the friction coefficient was shown to improve the structural performance of the bolted joint. The results provide a theoretical basis for designing uniform preloading of bolted joints and reducing micro-slip at the joint interface.

Investigations of the Friction Losses of Different Engine Concepts. Part 1: A Combined Approach for Applying Subassembly-Resolved Friction Loss Analysis on a Modern Passenger-Car Diesel Engine

This work presents the application of a combined approach to investigate the friction losses in a modern four-cylinder passenger-car diesel engine. The approach connects the results from engine friction measurements using the indication method and the results from journal-bearing simulations. The utilization of the method enables a subassembly-resolved friction loss analysis that yields the losses of the piston group, crankshaft journal bearings, and valve train (including the timing drive and crankshaft seals). The engine and engine subassembly friction losses are investigated over the full speed and load range, covering more than 120 engine operation points at different engine media supply temperatures ranging from 70 to 110 ∘ C. The subsequently decreasing lubricant viscosity due to higher engine media supply temperatures allow for the identification of friction reduction potentials as well as possible risks due to an onset of mixed lubrication. Furthermore, additional strip-tests have been conducted to determine the friction losses of the crankshaft radial lip seals, the timing drive, and the crankshaft journal bearings, thus enabling a verification of the calculated journal-bearing friction losses with measurement results. For the investigated diesel engine, a friction reduction potential of up to 21% could be determined when increasing the engine media supply temperature from 70 to 110 ∘ C, at engine speeds higher than n = 1500 rpm and part load operating conditions. At low engine speeds and high load operations, the friction loss reduction potential is considerably decreased and below 8%, indicating mixed lubrication regimes at the piston group and valve train.

Further Experimental Investigation of Motored Engine Friction Using Shunt Pipe Method

<div class="section abstract"><div class="htmlview paragraph">Mechanical friction is a significant power dissipater in the internal combustion engine. In the effort of designing more efficient and less pollutant engines, friction reduction is certainly on the agenda to be investigated. Such investigation cannot be possible without an accurate measurement of the same quantity. This publication regards a continued study on the mechanical friction determination in an internal combustion engine using the Pressurised Motoring Method. In this work, the friction mean effective pressure of a four-cylinder compression ignition engine was investigated with varying engine speed and manifold pressurisation, using a dedicated high precision sensor for the correct determination of the cylinder Top Dead Centre position. Two different measurement sessions were carried out; in the first, air was employed as pressurisation medium, testing 32 different setpoints; in the second, instead, with the aim to test the effect of the variation of thermochemical properties of fluids on the thermodynamic loss angle, Argon was used in place of air in 18 different setpoints. In the motored condition it is widely accepted that the brake torque is a measure of the losses of the engine and therefore has to be supplied by the driver, in our case the AC motor. The 2000 rpm region was explored with the aim to investigate the high motoring brake torque observed in a previous work from the same authors [<span class="xref">1</span>]. An investigation of the volumetric efficiency effect on motoring brake torque is also presented in the paper. Values of IMEP, BMEP, FMEP, peak in-cylinder pressure, loss angle and other parameters are given. The loss angle measured at each setpoint using the TDC sensor is compared with the loss angle evaluated by the use of two thermodynamic methods developed by Stas’ [<span class="xref">2</span>] and Pipitone [<span class="xref">3</span>].</div></div>

Film Forming Capability of Polymer-Base Oil Lubricants in Elastohydrodynamic and Very Thin Film Regimes

The development of high-performance lubricants to insure the separation of mechanical parts, to reduce engine friction and consequently fuel consumption remains a major challenge for oil manufacturers. Polymer additives called viscosity index improvers (VII) have been extensively used to reduce the dependency of the lubricant’s viscosity on temperature, to maintain an acceptable hydrodynamic lubrication in extreme conditions. This work focuses on understanding the role of VII in engine lubricants to bridge their tribological response with their rheological behavior. Simplified lubricants are studied, composed of polymers of different chemistries, molecular weights and conformations added to a mineral base oil. Film thickness measurements are carried out in pure rolling and isothermal conditions to quantify and clarify the effect of polymer addition on the lubricants behavior in the elastohydrodynamic (EHD) and very thin film (VTF) regimes. They are compared with accurate analytical predictions based on rheological models which lead to a good agreement with measured film thicknesses in the EHD regime, whereas some polymer solutions present a significant deviation to EHD predictions at lower thickness, i.e. in the VTF regime. Several explanations are considered, among them the non-Newtonian behavior of the lubricants and the adsorption of some polymers on the surface of the solid bodies.

Reply to Kim et al. (2019): Commentary on “Correction to: On the Calculation of fuel savings through lightweight design in automotive life cycle Assessments” by Koffler and Rohde-Brandenburger (2018)

In addition, the reply contains several arguments that speak against the allocation of engine friction losses in the context of automotive lightweighting. In conclusion, the authors cannot follow Kim et al's proposed solution and maintain their recommendation to follow the approach published in their 2010 methodology paper to assess the fuel savings due to automotive lightweighting for internal combustion engine (ICE) vehicles.

Modeling and Optimization Control for an Engine Electrified Cooling System to Minimize Fuel Consumption

The engine friction and actuator power are the main factors of the cooling system affecting the fuel economy of a spark ignition (SI) engine. An electrified cooling system containing an electric fan, pump, and thermostat provides an opportunity to reduce fuel consumption. The coolant temperature is always kept at a high fixed value within the safe temperature range to avoid friction losses caused by overcooling; however, the actuator power is not typically considered. Recent publications have attempted to minimize the actuator power and the coolant temperature is maintained in a range. Nevertheless, neither method quantitatively considers both factors. In this paper, the integrated consideration of engine friction and actuator power is presented to minimize engine fuel consumption. The accuracy of a control-oriented model of a cooling system is improved first in an attempt to exert the full potential of the model. Then, the proposed strategy for minimum fuel consumption is constructed as an optimization problem and the improvement of fuel economy obtained by the proposed strategy is evaluated using a causal suboptimal controller and dynamic programming (DP)-based global optimal controller. Compared with a causal coolant temperature tracking controller, the causal suboptimal controller and the global optimal controller based on the proposed strategy both achieve significant improvements. Compared with a global optimal controller for minimum actuator power, the global optimal controller based on the proposed strategy achieves a certain improvement and this effect can increase as the environmental temperature decreases. Finally, a real-time implementation of the proposed strategy on a hardware platform using model predictive control (MPC) with a limited horizon is presented, which shows the feasibility of the proposed strategy.

Hydrodynamic Conjunction of Textured Journal Surface—Bearing for Improved Frictional Response during Warm-Up of an Internal Combustion Engine

Considerable prime global energy is used in the transport sector. Significant energy is lost to overcome the internal friction of engines in transport vehicles. Journal bearings are crucial tribo-pairs and passive components that cause energy loss. Frictional losses increase extensively during the warm-up period of an engine due to high lubricant viscosity. Recent tribological developments have shown that surface textures can be a potential solution to reduce friction. A numerical investigation is performed to evaluate the effect of surface texture on the frictional and lubrication performance of a journal bearing at varying thermal operating conditions in an internal combustion engine. Temperature variations during engine warm-up are considered with oil rheology to observe texture-based improvements. Surface texture substantially reduces frictional energy loss during engine warm-up. Eight different monograde and multigrade engine oils are considered, and consistency is observed in texture-based improved outcomes.