Search Results

One of the key functions of lubricating oil additives in diesel engines is to control oil thickening caused by soot accumulation. Over the last several years, it has become apparent that the composition of the base oil used within the lubricant plays an extremely important role in the oil thickening phenomenon. In particular, oil thickening observed in the Mack T-8 test is significantly affected by the aromatic content of the base oil. We have found that the Mack T-8 thickening phenomenon is associated with high electrical activity, i.e., engine drain oils which exhibit high levels of viscosity increase show significantly higher conductivities. These findings suggest that electrical interactions are involved in soot-induced oil thickening.

Synthetic Diesel-like soots were prepared according to a methodology reported in the literature, and their physico-chemical characteristics and properties determined as a function of the operating parameters. These Diesel-like soots were synthesized following a two stage process where carbon-black oil mixtures were firstly oxidized at 400 °C in a tubular furnace and the resulting solid was next oxidized between 75°C and 175 °C. The products obtained after the removal of residual oil were characterized morphologically, via elemental analysis, solid state 13C-NMR, XPS and rheologically. Results were compared with those achieved from the characterization of a “reference” soot sample extracted from an oil recovered after an XUD11 engine test. Synthetic soots have chemico-physical characteristics that are different than those of the precursor carbon black and that can be controlled changing the operative conditions of the second step of the synthesis.

The requirements for emission control, lower fuel consumption and higher engine output have changed the engine valve train system to 4-valve/cylinder and higher cam lift designs, and these changes make the cam/tappet lubrication conditions more severe than before. Under such a working condition, there is a high possibility that cam/tappet surface damages such as scuffing, pitting and wear may occur. Among the damages, the wear of cam/tappet is the most difficult to predict since the wear mechanism still remains unclear. To understand the lubrication condition and therefore, the wear mechanism at the cam/tappet contact, friction was measured with a newly developed apparatus. Measurement results showed that the lubrication condition between cam and tappet is predominantly in the mixed and boundary lubrication conditions.

Minimum bearing oil film thickness (MBOFT) was measured in both a main and a connecting-rod bearing of a production V-6 engine using the total capacitance method (TCM). MBOFT was measured at 1500 rpm and at three different engine loads (64, 128, and 192 Nm). The oil sump temperature was controlled at 100°C. Five engine oils were tested (SAE grades 5W-20, 20W-20, 5W-30, 10W-30, and 20W-50) with emphasis given to the SAE 5W-30 and 10W-30 oils. MBOFT was also calculated using a computer code. The absolute minimum of the MBOFT (MBOFTmin, closest approach between the journal and the bearing) increased with increasing values of a Sommerfeld parameter (viscosity/load) and this dependence was similar in both the main and the connecting-rod bearings. But, for the main bearing the MBOFTmin values showed a higher dependence on the Sommerfeld parameter than those for the connecting-rod bearing. Similar results were obtained with the theoretical calculations of the MBOFT_min values.

The friction reducing capability of engine oils in the piston ring/cylinder bore contact was investigated under fully-flooded and starved lubrication conditions at 100° C using a laboratory piston ring/cylinder bore friction rig. The rig is designed to acquire instantaneous transient measurements of applied loads and friction forces at the ring/bore interface in reciprocating motion over a 50.8 mm stroke. The effects of increasing load and speed on the friction coefficient have been compared with new and used engine oils of different viscosity that were formulated with and without friction modifying additives. Test results with fully formulated engine oils containing molybdenum dithiocarbamate (MoDTC) show that friction is always lower than that obtained with non-friction modified oils but in regions of persistent starvation the coefficient of friction can increase significantly, approaching levels equivalent to fully-flooded non-friction modified formulations.

Exhaust-gas recirculation (EGR) causes the piston rings and cylinder liners of a Diesel engine to suffer abnormal wear on the sliding parts. The present study aimed at making clear such abnormal wear structurally by examining the state of lubrication of the piston with a floating liner method, observing directly a visualized cylinder and experimenting on a Diesel engine for wear. As a result, it was confirmed that soot in EGR gas would change a lot the characteristics of the piston friction force. There are two mechanisms: one directly enters the sliding surfaces, and the other enters the ring rear, applying more load to them. It was also confirmed that the level of wear on the piston ring would vary to a large extent as the state of lubrication changed.

We will introduce two methods with which hydrogen peroxide (H2O2) is injected into the combustion chamber of a DI Diesel engine during main time of combustion. One method is using a second injection system to inject the H2O2 and the other method is the injection of a fuel-H2O2 emulsion into the combustion chamber. Hereby the emission of soot can be considerably reduced without a large influence to NOx, even with the second method a reduction of NOx is measured. From calculations on soot kinetics and measurements it is known that the majority of soot is already being oxidized within the cylinder itself. Considering the high temperatures during the combustion, it is mainly the OH radical that leads to soot oxidation. By injecting H2O2 and in this way increasing the concentration of OH later on during the combustion, soot can almost completely be reduced provided that there is an ideal mixture.

Chrysler began a limited development program directed toward a new automatic transmission fluid (ATF) early in 1989 and launched a full time effort in 1994. The development process for the new ATF involved a significant level of bench testing and eventually vehicle tests to evaluate the durability and shift quality of the ATF. The bench tests included those that pertain to oxidation and shear stability, anti-wear, frictional properties and torque converter shudder. Vehicle tests were primarily extended durability in both internal vehicle fleets and at external taxi sites. The mileage accumulated in this phase of the development program exceeded two million miles, all with no fluid drains out to 100,000 miles. Additionally, shift feel tests were conducted in Chrysler vehicles to verify compliance to targets. This paper summarizes the tests and results that lead to the development of the new Chrysler fill-for-life automatic transmission fluid.

This paper discusses four methods for measuring the resistance of transmission fluids to permanent viscosity loss through shear. The four methods include the Fuel Injector Shear Stability test, the Sonic shear test, the DEXRON®-III Cycling test and the KRL test. Each of these methods and their advantages are discussed and data provided for many OEM fluids and the effects of these methods on the final viscosity. The data indicates the KRL generates the maximum shear stress on the fluids compared to the other methods. The data also indicates the sonic shear method results are similar to those of the KRL test. The fuel injector test imparts the least stress to the fluid. Data is presented to show the correlation between viscosity changes obtained using these methods and viscosity changes observed with mileage accumulation in vehicle transmissions.

As part of the International Lubricant Standardization and Approval Committee's (ILSAC) goal of developing a global automatic transmission fluid (ATF) specification, members have been evaluating test methods that are currently used by various automotive manufacturers for qualifying ATF for use in their respective transmissions. This report deals with comparing test methods used for determining torque capacity in friction systems (shifting clutches). Three test methods were compared, the Plate Friction Test from the General Motors DEXRON®-III Specification, the Friction Durability Test from the Ford MERCON® Specification, and the Japanese Automotive Manufacturers Association Friction Test - JASO Method 348-95. Eight different fluids were evaluated. Friction parameters used in the comparison were breakaway friction, dynamic friction torque at midpoint and the end of engagement, and the ratio of end torque to midpoint torque.

Interactions between automatic transmission fluid (ATF) components and composite friction materials and their effect on friction system performance continues to be an active area of interest to the automotive industry. A more fundamental understanding is needed of how base fluids, ATF additives, friction materials, and transmission design interact to produce the observed transmission system performance and durability. We herein report results from investigations carried out using a relatively thermo-oxidatively stable polyalphaolefin (PAO) base fluid treated with components representative of several additive types we previously reported to have significant negative effects on frictional performance. Secondly, we investigated a conventionally refined 150 N base oil treated with a calcium sulfonate detergent previously shown to improve friction performance.

This paper describes the design and construction of a dynamic flow apparatus for the measurement of air entrainment and release characteristics of lubricants, specifically automatic transmission fluids. Data are provided on test method development and correlation with transmission cycling tests. The results obtained using this apparatus and method are compared with those obtained from readily available, and newly developed, foaming and air entrainment tests. The existing tests give an inconsistent picture of fluid foaming and air entrainment characteristics. Foaming tests contained in the major ATF service fill specifications have been found incapable of identifying lubricants with poor fluid level control in an automatic transmission cycling test. The newly developed dynamic flow apparatus is capable of correctly ranking the fluid level control of tested lubricants as determined in the transmission cycling test.

Most of liquid jet breakup models now available in combustion codes only apply to high pressure sprays (Diesel … ). When gasoline is injected in the intake pipe of a chamber (S.I. engines), the relative pressure between the injector and the intake gas flow is quite low (3-4 bars). In this case, the spray looks like a long continuous liquid non-evaporating phase. Generally, the jet collapses, giving droplets, far from the tip of the injector. Vaporization is negligible within the pipe. Thus, the assumption generally made that the fuel is gaseous in the chamber fails. The fluid phase can no more be considered fully atomized and dispersed. We propose here a breakup model for low Weber non-evaporating fuel jets. It takes into account the continuous nature of the spray. The liquid core is represented by cylindrical blobs. The main assumption is that the breakup of a blob is caused by the growth of its surface. A new equation gives the evolution of the surface for each blob.

A review of flame kernel growth in SI engines and the regimes of premixed turbulent combustion showed that a misfire model based on regimes of premixed turbulent combustion was warranted[1]. The present study will further validate the misfire model and show that it has captured the dominating physics and avoided extremely complex, yet inefficient, models. Results showed that regimes of turbulent combustion could, indeed, be used for a concept-simple model to predict misfire limits in SI engines. Just as importantly, the entire regimes of premixed turbulent combustion in SI engines were also mapped out with the model.

A computational model is proposed and analysis is carried out to study the atomization processes of hollow-cone fuel sprays from pressure-swirl injectors for a Gasoline Direct-Injection (GDI) Spark Ignition (SI) engine. The flow field inside a swirl injector is numerically analyzed, and characteristics of the liquid sheet at the nozzle exit are predicted. The intact length (i.e., breakup length) of the sheet is calculated from a semi-empirical correlation and a Sauter Mean Diameter (SMD) at the breakup location is estimated based on the classical wave instability theory. The spray dynamics that address the interactions between liquid drops and surrounding gas phase are simulated using FIRE code with modified spray models. The objective is to understand the effects of nozzle geometry and engine operating conditions on spray characteristics so that the spray structure can be optimized through the injector design to meet the fundamental requirements of GDI engines.

The instability of a viscous liquid jet surrounded by a swirling air stream subject to a 3-D disturbance is predicted by a linear stability model. The effect of flow conditions, fluid properties and nozzle geometry on the disintegration of the liquid jet are investigated by conducting a parametric study. It is observed that the relative velocity between the liquid and gas phases promotes the interfacial aerodynamic instability. The predicted range of wave numbers in which asymmetric modes have higher growth rates than the axisymmetric mode and dominate the instability agrees very well with experimental data. The density ratio significantly enhances the instability as does the axial Weber number. Liquid viscosity inhibits the disintegration process and damps higher helical modes more significantly than the axisymmetric mode. It is observed that air swirl has a stabilizing effect on the liquid jet.

Their high fuel economy is making light-duty vehicles with spark-ignition direct-injection (SIDI) engines attractive. However, the implications for exhaust emissions and the effects of fuel quality on emissions are not clear for this type of engine. A Mitsubishi Legnum with a 1.8-L GDI™ engine was tested on federal test procedure (FTP) and highway fuel economy cycles. The results were compared with those for a production Dodge Neon vehicle with a 2.0-L port fuel-injection (PFI) engine. The Mitsubishi was tested with Indolene, Amoco Premium Ultimate, and a low-sulfur gasoline. The Neon was tested only with Indolene. Both engine-out and tailpipe emissions were measured. Second-by-second emissions and hydrocarbon speciation were also evaluated. The SIDI engine provided up to 24% better fuel economy than the PFI engine on the highway cycle. Tailpipe emissions of oxides of nitrogen (NOx) from the SIDI vehicle using low-sulfur fuel were 40% less than those when using Indolene.

Diesel exhaust contains a lower level of hydrocarbons, which serve as the reductant for the NOx catalyst, than gasoline engine exhaust. An investigation was made of several methods for maximizing the performance of NOx catalysts for direct-injection diesel engines. First, the catalysts were given an HC adsorption capability and then their characteristics were tailored to the HC species contained in diesel exhaust. This HC adsorption capability is designed to achieve better utilization of the HC species in diesel exhaust as a reductant. Second, catalyst performance was examined under passive and active conditions. Excellent catalyst performance was obtained under a passive condition, because at high engine loads, NOx catalysts with an HC adsorption capability can utilize HCs adsorbed under low engine load conditions to reduce NOx.

Increasing interest in lean NOx catalysis at temperatures between about 300-550°C has led to development of catalytic materials with thermal durability considerably improved over academic benchmark catalysts such as Cu-ZSM-5. The breaching of thermal durability barriers brings new obstacles into focus. Practical implementation of high temperature HC-based lean NOx catalysis entails delivery of hydrocarbons to the catalyst inlet at high temperatures. We have found initially unexpected, but scientifically precedented, phenomena regarding gas-phase kinetic instability of hydrocarbons in diesel exhaust atmospheres above 300°C. Around 300°C, homogeneous hydrocarbon oxidation can begin to occur. Rates of oxidation decrease between about 350-450°C and then increase again at higher temperatures. Some apparent NOx disappearance that does not correspond to chemical reduction of NOx can also occur homogeneously throughout this temperature range.

An expanding cylindrical laminar flame kernel affected by random external strain rates and diffusivity is numerically simulated in order to gain insight into the influence of small-scale turbulence on the combustion variability in engines. In the simulations, the kernel is strained, as a whole, by external velocity gradients randomly generated with either Gaussian or log-normal probability density functions. The influence of small-scale turbulent heat and mass transfer is modeled by turbulent diffusivity, the randomness of which is controlled by the fluctuations in the viscous dissipation averaged over the kernel volume. The computed results show that small-scale phenomena can substantially affect the quenching characteristics of a small flame kernel and the kernel growth history rj(t); the scatter of the computed curves of rf(t) being mainly controlled by the scatter of the duration of the initial stage of kernel development.