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A model has been developed for estimating the oil vaporization rate from the cylinder liner of a reciprocating engine. The model uses input from an external cycle simulator and an external liner oil film thickness model. It allows for the change in oil composition and the change in oil film thickness due to vaporization. It also estimates how the passage of the compression and scraper rings combine with the vaporization to influence the steady-state composition of the oil layer in the upper ring pack. Computer model results are presented for a compression-ignition engine using a range of liner temperatures, several engine speeds, and two different oils. Vaporization is found to be highly dependent on liner temperature and steady-state oil composition. The steady-state oil composition near the top of the cylinder is found to be significantly different than the composition of the oil near the bottom of the cylinder.

The use of hydrogen as a fuel supplement for lean-burn engines at higher compression ratios has been studied extensively in recent years, with good promise of performance and efficiency gains. With the advances in reformer technology, the use of a gaseous fuel stock, comprising of substantially higher fractions of hydrogen and other flammable reformate species, could provide additional improvements. This paper presents the performance and emission characteristics of a gas mixture of equal volumes of hydrogen, CO, and methane. It has recently been reported that this gas mixture can be produced by reforming of ethanol at comparatively low temperature, around 300C. Experiments were performed on a 1.8-liter passenger-car Nissan engine modified for single-cylinder operation. Special pistons were made so that compression ratios ranging from CR= 9.5 to 17 could be used. The lean limit was extended beyond twice stoichiometric (up to lambda=2.2).

The challenge posed by the long run times necessary to accurately quantify ash effects on diesel aftertreatment systems has led to numerous efforts to artificially accelerate ash loading, with varying degrees of success. In this study, a heavy-duty diesel engine was outfitted with a specially designed rapid lubricant degradation and aftertreatment ash loading system. Unlike previous attempts, the proposed methodology utilizes a series of thermal reactors and combustors to simulate all three major oil consumption mechanisms, namely combustion in the power cylinder, evaporative and volatile losses, and liquid losses through the valve and turbocharger seals. In order to simulate these processes, each thermal reactor allows for the precise control of the level of lubricant additive degradation, as well as the form and quantity of degradation products introduced into the exhaust upstream of the aftertreatment system.

This paper presents a numerical model of the rotational and lateral dynamics of the piston (secondary motion) and piston slap in mixed lubrication. Piston dynamic behavior, frictional and impact forces are predicted as functions of crank angle. The model considers piston skirt surface waviness, roughness, skirt profile, thermal and mechanical deformations. The model considers partially-flooded skirt and calculates the pressure distributions and friction in the piston skirt region for both hydrodynamic and boundary lubrication. Model predictions are compared with measurements of piston position using gap sensors in a single-cylinder engine and the comparison between theory and measurement shows remarkable agreement.

A complete one-dimensional mixed lubrication model has been developed to predict oil film thickness and friction of the piston ring-pack. An average flow model and a roughness contact model are used to consider the effects of surface roughness on both hydrodynamic and boundary lubrication. Effects of shear-thinning and liner temperature on lubricant viscosity are included. An inlet condition is applied by considering the unsteady wetting location at the leading edge of the ring. A ‘film non-separation’ exit condition is proposed to replace Reynolds exit condition when the oil squeezing becomes dominant. Three lubrication modes are considered in the model, namely, pure hydrodynamic, mixed, and pure boundary lubrication. All of these considerations are crucial for studying the oil transport, asperity contact, and friction especially in the top dead center (TDC) region where the oil control ring cannot reach.

Engine oil consumption is an important source of hydrocarbon and particulate emissions in automotive engines. Oil evaporating from the piston-ring-liner system is believed to contribute significantly to total oil consumption, especially during severe operating conditions. This paper presents an extensive experimental and theoretical study on the contribution of oil evaporation to total oil consumption at different steady state speed and load conditions. A sulfur tracer method was used to measure the dependence of oil consumption on coolant outlet temperature, oil volatility, and operating speed and load in a production spark ignition engine. Liquid oil distribution on the piston was studied using a one-point Laser-Induced-Fluorescence (LIF) technique. In addition, important in-cylinder variables for oil evaporation, such as liner temperature and cylinder pressure, were measured. A multi-species cylinder liner oil evaporation model was developed to interpret the oil consumption data.

Engine oil consumption is recognized to be a significant source of pollutant emissions. Unburned or partially burned oil in the exhaust gases contributes directly to hydrocarbon and particulate emissions. In addition, chemical compounds present in oil additives poison catalytic converters and reduce their conversion efficiency. Oil consumption can increase significantly during critical non-steady operating conditions. This study analyzes the oil consumption behavior during ramp transients in load by combining oil consumption measurements, in-cylinder measurements, and computer-based modeling. A sulfur based oil consumption method was used to measure real-time oil consumption during ramp transients in load at constant speed in a production spark ignition engine. Additionally in-cylinder liquid oil behavior along the piston was studied using a one-point Laser-Induced-Fluorescence (LIF) technique.

Ash, primarily derived from diesel engine lubricants, accumulates in diesel particulate filters directly affecting the filter's pressure drop sensitivity to soot accumulation, thus impacting regeneration frequency and fuel economy. After approximately 33,000 miles of equivalent on-road aging, ash comprises more than half of the material accumulated in a typical cordierite filter. Ash accumulation reduces the effective filtration area, resulting in higher local soot loads toward the front of the filter. At a typical ash cleaning interval of 150,000 miles, ash more than doubles the filter's pressure drop sensitivity to soot, in addition to raising the pressure drop level itself. In order to evaluate the effects of lubricant-derived ash on DPF pressure drop performance, a novel accelerated ash loading system was employed to generate the ash and load the DPFs under carefully-controlled exhaust conditions.

A laser fluorescent diagnostic method was employed to measure lubricant film thickness on the cylinder wall/piston interface of two engines. The system output signal was calibrated using lubricant samples of known thickness, and by comparison of a known piston ring profile to measured lubricant film contours. Agreement of the results of the two calibration methods was within 5%. A relative calibration was performed with three oils having different additive packages, and with an oil contaminated through use in a commercially operated engine. The calibration coefficients for the oils, relating output voltage to film thickness, varied within a factor up to two, depending on lubricant type and age. The laser fluorescent apparatus was installed for use with a single cylinder test version of the Cummins VT-903 diesel engine. An optical passage was created through the block and cylinder wall using a quartz window.

In this study, changes in the composition of lubricant additives in the power cylinder oil are examined. Samples are extracted from a single cylinder heavy-duty diesel engine in two locations during engine operation; the crankcase and the top ring groove of the piston. Emissions of lubricant-derived ash-forming elements are lower than would be expected based on oil consumption and crankcase oil composition. This occurs partly because the inorganic additive compounds are less volatile than light-end hydrocarbons in the base oil. The tribology of the piston ring pack also affects the composition of the oil consumed in the power cylinder system. The elemental composition of oil extracted from the top ring groove is significantly different than the crankcase oil. Additive metals are concentrated in the top ring groove of the power cylinder. Detergent compounds (i.e. Ca and Mg) concentrate due to the volatility of the base oil. The metals associated with ZDDP (i.e.

This paper is a direct continuation of a previous study that addressed the performance and design of a variable compression engine, the Alvar-Cycle Engine [1]. The earlier study was presented at the SAE International Conference and Exposition in Detroit during February 23-26, 1998 as SAE paper 981027. In the present paper test results from a single cylinder prototype are reviewed and compared with a similar conventional engine. Efficiency and emissions are shown as function of speed, load, and compression ratio. The influence of residual gas on knock characteristics is shown. The potential for high power density through heavy supercharging is analyzed.

An apparatus was designed and applied to measure the oil-film thickness in a production engine using the principle of laser-induced fluorescence. The apparatus incorporated fiber optics technology in its design with an aim to improve the ease of installation, portability, durability, spatial resolution and signal-to-noise ratio of previous designs using conventional optics, which hitherto have been used almost exclusively in studying oil-film characteristics in detail. Bench tests and engine tests were conducted to study the optimum combination of system components and to evaluate the performance of the design. These tests indicate that the goals of the design have been achieved. The increased spatial resolution enabled more precise identification of important lubricant features around the piston rings.

The oil film thickness distribution between the top ring and liner was observed using laser fluorescence (LF). Five different commercial lubricants, two single grades and three multigrades, were studied at two azimuthal, mid-stroke locations for five speed/load combinations in a small IDI diesel engine. Cavitation is never observed. The lubricant always separates tangent to the ring surface. The rheology of the oil flow under the ring is consistent with a non-Newtonian viscosity without elasticity. The difference between lubricant type (single or multigrade) corresponds to differences in inlet and outlet conditions. Using an analytical model together with the measured oil distributions, calculations demonstrate a difference in friction between single and multigrade lubricants. The multigrade lubricants have a lower friction coefficient, consistent with improvements in fuel economy reported in the literature.

The wear patterns of the rings and grooves of a diesel engine were analyzed by using a ring dynamics/gas flow model and a ring-pack oil film thickness model. The analysis focused primarily on the contact pressure distribution on the ring sides and grooves as well as on the contact location on the ring running surfaces. Analysis was performed for both new and worn ring/groove profiles. Calculated results are consistent with the measured wear patterns. The effects of groove tilt and static twist on the development of wear patterns on the ring sides, grooves, and ring running surfaces were studied. Ring flutter was observed from the calculation and its effect on oil transport was discussed. Up-scraping of the top ring was studied by considering ring dynamic twist and piston tilt. This work shows that the models used have potential for providing practical guidance to optimizing the ring pack and ring grooves to control wear and reduce oil consumption.

Experiments were done to quantify the dynamic motion of the piston and oil-film during piston impact on the cylinder bore, commonly known as “piston slap.” Parameters measured include engine block vibration, piston-skirt to liner separation, oil-film thickness between the piston and liner, and other engine operating conditions. Experimental parametric studies were performed covering the following: engine operating parameters - spark timing, liner temperature, oil-film thickness, oil type, and engine speed; and engine design parameters - piston-skirt surface waviness, piston-skirt/cylinder-liner clearance, and wrist-pin offset. Two dynamic modes of piston-motion-induced vibration were observed, and effects of changes in engine operating and design parameters were investigated for both types of slap. It was evident that engine design parameters have stronger effects on piston slap intensity, with piston-skirt/liner clearance and wrist-pin offset being the dominant parameters.

The effects of combustion chamber and intake valve deposit build-up on the knocking characteristics of a spark ignition engine were studied. A Chrysler 2.2 liter engine was run continuously for 180 hours to build up intake valve and combustion chamber deposits. In the tests reported here, the gasoline used contained a deposit controlling fuel additive. The engines's octane requirement increased by 10 research octane numbers during this extended engine operating period. At approximately 24 hour intervals during these tests, the engine was audibly knock rated to determine its octane requirement. Cylinder pressure data was collected during knocking conditions to investigate the knocking characteristics of each cylinder, and deposit build-up effects on those statistics. Cylinder-to-cylinder variations in knock statistics were studied. Analysis of the data indicated that some 20 to 40 percent of cycles knock before the knock is audibly detected.

Parallel measurements of lubricant-film behavior and oil consumption in two identical small production IDI diesel engines are presented. Oil consumption was measured using tritium as a radioactive tracer, and instantaneous film thickness data between the piston and liner were obtained using laser fluorescence diagnostics. The data covered single- and multi-grade lubricants and five different ring configurations (two-piece vs three-piece rings at various ring tensions). The data illustrate (a) oil-film profiles under the rings, especially around the leading and trailing edges, (b) accumulation of oil on piston lands and skirt, (c) circumferential variations around the bore, (d) observations on ring rotation, and (e) the piston-skirt oil-pumping mechanism. Effects of lubricants and piston-ring configurations on oil-film characteristics are investigated, and the oil consumption data are compared with oil-film thickness measurements.

The increased use of biodiesel fuels has raised concerns over the fuel's impact on engine performance and hardware compatibility. While these issues have received much attention in recent years, less well-known are the effects of biodiesel on engine-out ash emissions and lubricant properties. Significant differences in composition between biodiesel and petroleum diesel fuels have the potential to influence ash emissions, thereby affecting aftertreatment system performance. Further, the fuel also interacts directly with the lubricant through fuel dilution, and may impact lubricant properties. In this study, a 5.9L, 6 cylinder, Cummins ISB 300 diesel engine was outfitted with a specially designed rapid lubricant aging system and subjected to a set of steady-state engine operating conditions. The lubricant aging system allows for the investigation of the interactions of emissions and combustion products, as well as fuel dilution, on lubricant properties in an accelerated manner.

Lowering lubricant viscosity to reduce friction generally carries a side-effect of increased metal-metal contact in mixed or boundary lubrication, for example near top ring reversal along the engine cylinder liner. A strategy to reduce viscosity without increased metal-metal contact involves controlling the local viscosity away from top-ring-reversal locations. This paper discusses the implementation of insulation or thermal barrier coating (TBC) as a means of reducing local oil viscosity and power cylinder friction in internal combustion engines with minimal side-effects of increased wear. TBC is selectively applied to the outside diameter of the cylinder liner to increase the local oil temperature along the liner. Due to the temperature dependence of oil viscosity, the increase in temperature from insulation results in a decrease in the local oil viscosity.

Frictional losses in the piston ring-pack of an engine account for approximately half of the total frictional losses within the power cylinder of an engine. Three-dimensional honing groove texture was modeled, and its effect on piston ring-pack friction and engine brake thermal efficiency was investigated. Adverse effects on engine oil consumption and durability were also considered. Although many non-conventional cylinder liner finishes are now being developed to reduce friction and oil consumption, the effects of surface finish on ring-pack performance is not well understood. A rough surface flow simulation program was developed to calculate flow and stress factors that adjust the solution of the Reynolds equation for the effects of surface roughness as has been done in the literature. Rough surface contact between the ring and liner was modeled using a previously published methodology for asperity contact pressure estimation between rough surfaces.