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On urban and emission homologation cycles, engines operate predominantly at low speeds and part loads where engine friction losses represent around 10% of the consumed fuel energy but would account for 25% of the fuel consumption once combustion efficiency is taken into account. Under such mild conditions, engine and engine oil temperatures are also lower than ideal. The influence of oil viscosity on friction losses are significant. By reducing lubricant viscosity, engine friction, fuel consumption and emissions are reduced. Tribological and machine learning models were investigated to predict the effect of oil viscosity on fuel consumption during the FTP75 emission cycle with the use of detailed actual emission test measurements. Oil viscosity was calculated with the measured oil temperature. As the same vehicle transient is followed in the cold and hot phases, the models were evaluated by comparing their prediction of fuel consumption in the hot phase versus the measured value.

In the present work, a system approach to the tribological optimization of passenger car engines is demonstrated. Experimental data and simulation results are presented to demonstrate the role of surface specifications, ring pack, and lubricant on the piston/bore tribology. The importance of in-design “pairing” of low-viscosity motor oils with the ring pack and the cylinder bore characteristics in order to achieve maximum reduction in GHG emissions and improvement in fuel economy without sacrificing the endurance is elucidated. Earlier motored friction data for two different gasoline engines - Ford Duratec and Mercedes Benz M133 - using motor oils of different viscosity grades are now rationalized using AVL EXCITE® piston/bore tribology simulations. The main difference between the engines was the cylinder bore surface: honed cast iron vs thermally sprayed, and the valve train type: direct-acting mechanical bucket (DAMB) vs roller finger follower (RFF).

With the current use of bio-renewable fuel, the application of Ethanol in Flex-Fuel vehicles presents a very low CO2 emission alternative when the complete cycle, from plantation, fuel production, till vehicle use, is considered. In Brazil more than 80% of the car production is composed of Flex-Fuel vehicles. Due to the lower heating content of the Ethanol, more aggressive combustion calibrations are used to obtain the same engine power than when burning gasoline. Such Ethanol demands, associated with the continuous increase of engine specific power has lead to thermo-mechanical loads which challenges the tribology of piston rings. The ethanol use brings also some specific tribological differences not very well understood like fuel dilution in the lube oil, especially on cold start, corrosive environment etc. Under specific driving conditions, incipient failures like spalling on nitrided steel top rings have been observed.

Wear of piston ring and cylinder was modelled through a computer code that calculates the hydrodynamic and roughness contact pressures acting on the contact surfaces. Both pressures are fully and coupled solved through, respectively, Reynolds equation and Greenwood-Williamson model. Piston secondary motion and piston groove thermal deformations are considered. The latter was discovered to be fundamental in defining the top ring worn profile. Due to the rough contact pressures, the model predicts material removal from both piston ring and cylinder surfaces and recalculates the system, hence simulating the evolution of the worn sliding surface of both parts. The predicted wear of the piston ring pack and the cylinder wall are compared with a medium duty diesel engine tested for 750 hours in dynamometer.

The present study looks into different possibilities for tribological optimization of the piston/bore system in heavy duty diesel engines. Both component rig tests and numerical simulations are used to understand the roles of surface specifications, ring pack, and lubricant in the piston/bore tribology. Run-in dynamics, friction, wear and combustion chamber sealing are considered. The performance of cylinder liners produced using a conventional plateau honing technology and a novel mechanochemical surface finishing process - ANS Triboconditioning® - is compared and the importance of in-design “pairing” of low-viscosity motor oils with the ring pack and the cylinder bore characteristics in order to achieve maximum improvement in fuel economy without sacrificing the endurance highlighted. A special emphasis is made on studying morphological changes in the cylinder bore surface during the honing, run-in and Triboconditioning® processes.

The evolution of internal combustion engines has led to friction reduction as well as to gaseous emissions reduction, demanding the use of narrower rings. Nodular cast iron is used satisfactorily for compression piston rings, with wear resistant coatings to improve their durability. However, for more severe applications and rings narrower than 1.2mm, even the nodular cast iron mechanical resistance is not enough. In this way, the use of steel is recommended, which may have its tribological properties improved by the nitriding thermochemical treatment. This paper presents the characteristics of the materials and of the nitriding process of compression and oil control rings as well as bench and dynamometric test results run during the development of these products.

Engine developments have led to higher mechanical and thermal loads on the components, at the same time that lower friction losses are also sought. Therefore, the development of better materials and of surface treatments has received great emphasis. This paper presents the results of dynamometric engine tests with a proposed piston ring pack, composed of a gas nitrided steel top ring, a nitrided gray cast iron second ring and a normal production chrome plated oil ring. The proposed pack showed very low wear when applied to a medium duty diesel engine, besides being a cost-effective alternative to the conventional pack with moly coated and chrome plated (respectively in the top and second) rings. The proposed pack also caused very low wear on the cylinder bore, specially near the TDC, where the bore wear is usually maximum.

The cylinder bore honing quality is an essential factor for a good engine performance and durability. A bad surface finish can result in an excessive lubricant oil consumption, high piston ring wear and scuffing occurrence. In this paper the most important characteristics of bore honing for cast iron cylinders and their influence in the combustion engine performance are described and discussed. Despite its importance, the bore honing is commonly undervalued due to various reasons including the difficulty of a practical but sufficient method of quality qualifying. Some honing commonly misunderstood concepts are detailed and SEM photographs of bore surface from both good and bad finish are presented. At the end of this paper it is also presented a recommendation for a practical evaluation method of honing quality.

Due to several market demands of higher wear and scuffing resistance, Duplex PVD (Physical Vapor Deposition) CrN top ring has been used in Heavy Duty Diesel (HDD) engines. The ring comprises a nitrided high chromium stainless steel with a PVD ceramic CrN coating. For High Speed Diesel (HSD) vehicles with lower demands, MAHLE has developed an alternative PVD coated ring, which balances the cost and performance ratio. This alternative, named High Value PVD (HV-PVD), consists of applying the best resistant coating for wear and scuffing, PVD, onto a less costly ring material, Ductile Cast Iron. The HV-PVD top ring has been tested in HSD engines and shown excellent performance. Additional advantages of the HV-PVD are its lower friction coefficient and better tribological compatibility with the cylinder bore materials when compared to the traditional galvanic chrome based coatings. Such features lead to reduced engine friction and lower cylinder wear.

In lubricating and specialty oil industries, blending is routinely used to convert a finite number of distillation cuts produced by a refinery into a large number of final products matching given specifications regarding viscosity, flash point, pour point or other properties of interest. To find the right component ratio for a blend, empirical or semi-empirical equations linking blend characteristics to those of the individual components are used. Mathematically, the problem of finding the right blend composition boils down to solving a system of equations, often non-linear ones, linking the desired properties of the blend with the properties and percentage of the blend components. This approach can easily be extended to crankcase lubricants, in which case major blend constituents are base oils, additive packages, and viscosity index improvers. Artificial intelligence (AI) tools allow accurate predictions of the basic physicochemical properties of such blends.

With the increase of thermal and mechanical loads, some spark ignition (SI) engines may present excessive wear on the piston top groove. The problem was studied first by numerical simulation. Several parameters were found to influence the groove wear. E.g., ring side face roughness and hardness. But the main influence found was the relative attitude between groove flank and ring side face. As the instantaneous attitude varies during the engine cycle, the problem was studied with a commercial ring dynamics computer program and considering thermal and mechanical deformations that occur in the piston during engine operation. The expected groove wear was estimated by the accumulated “wear load” during critical engine operation regimes. Experimental results of engines with groove wear solved by design optimization are shown.

With the worldwide trend towards CO2 emission reduction, renewable fuels such as ethanol are gaining further importance. However, the use of ethanol as a fuel can bring some tribological impacts. Friction and wear of engine parts when lubricants are contaminated with ethanol are not very well understood. Within this scenario, the present paper introduces a new procedure to investigate the ethanol dilution on the performance of engine oils. Friction and wear of actual piston ring and liner were evaluated in a reciprocating test designed to emulate real thermomechanical conditions of both urban and highway car use. In addition to fresh oil, lubricant/ethanol emulsions were prepared carefully following two different procedures - unheated and heated mixing. The former to emulate cold start and “bakery” driving use, the latter to reproduce what happens after the engine heats in normal conditions.