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Technical Paper

Development of a Two-Zone HCCI Combustion Model Accounting for Boundary Layer Effects

2001-03-05
2001-01-1028
The Homogeneous Charge Compression Ignition (HCCI) combustion concept is currently under widespread investigation due to its potential to increase thermal efficiency while greatly decreasing harmful exhaust pollutants. Simulation tools have been developed to explore the implications of initial mixture thermodynamic state on engine performance and emissions. In most cases these modeling efforts have coupled a detailed fuel chemistry mechanism with empirical descriptions of the in-cylinder heat transfer processes. The primary objective of this paper is to present a fundamentally based boundary layer heat transfer model. The two-zone combustion model couples an adiabatic core zone with a boundary layer heat transfer model. The model predicts film coefficient, with approximately the same universal shape and magnitudes as an existing global model.
Technical Paper

A Global Model for Steady State and Transient S.I. Engine Heat Transfer Studies

1996-02-01
960073
A global, systems-level model which characterizes the thermal behavior of internal combustion engines is described in this paper. Based on resistor-capacitor thermal networks, either steady-state or transient thermal simulations can be performed. A two-zone, quasi-dimensional spark-ignition engine simulation is used to determine in-cylinder gas temperature and convection coefficients. Engine heat fluxes and component temperatures can subsequently be predicted from specification of general engine dimensions, materials, and operating conditions. Emphasis has been placed on minimizing the number of model inputs and keeping them as simple as possible to make the model practical and useful as an early design tool. The success of the global model depends on properly scaling the general engine inputs to accurately model engine heat flow paths across families of engine designs. The development and validation of suitable, scalable submodels is described in detail in this paper.
Technical Paper

Transient Heat Conduction in Low-Heat-Rejection Engine Combustion Chambers

1987-02-01
870156
Predicting the effects of transient heat conduction in low-heat-rejection engine components have been analyzed by applying instantaneous boundary conditions throughout a diesel engine thermodynamic cycle. This paper describes the advantages and disadvantages of one-dimensional finite difference and two-dimensional finite element methods by analyzing simple and complicated geometries like diesel bowl-in pistons. Also the performance characteristics of plasma sprayed zirconia, partially stabilized zirconia, and a monolithic reaction bonded silicon nitride ceramic materials are discussed and compared. Finite element studies have indicated that the steep temperature gradients associated with cyclic temperature swings in excess of 400 K may contribute to the failure of ceramic coatings near the corner joining the surface of the piston and the surface of the bowl for bowl-in pistons.
Technical Paper

Piston-Ring Assembly Friction Modeling by Similarity Analysis

1993-03-01
930794
A semi-empirical engine piston/ring assembly friction model based on the concept of the Stribeck diagram and similarity analysis is described. The model was constructed by forming non-dimensional parameters based on design and operating conditions. Friction data collected by the Fixed-Sleeve method described in [1]* at one condition, were used to correlate the coefficient of friction of the assembly and the other non-dimensional parameters. Then, using the instantaneous cylinder pressure as input together with measured and calculated design and operating parameters, reasonable assembly friction and fmep predictions were obtained for a variety of additional conditions, some of which could be compared with experimental values. Model inputs are component dimensions, ring tensions, piston skirt spring constant, piston skirt thermal expansion, engine temperatures, speed, load and oil viscosity.
Technical Paper

Effect of Some Piston Variables on Piston and Ring Assembly Friction

1987-02-01
870088
The piston and ring assembly friction of a lightweight piston with lower compression height has been compared to that of a production assembly. Additional weight was added to the lightweight piston to study the effect of that variable alone. The lightweight piston reduced friction, especially in motoring tests. Within the speed range tested (up to 1640 rpm) the friction reduction of the lightweight piston could not be attributed to the lower mass itself.
Technical Paper

Measurement of Piston and Ring Assembly Friction Instantaneous IMEP Method

1983-02-01
830416
An experimental technique termed the Instantaneous IMEP Method has been developed to measure piston and ring assembly friction. The technique requires very accurate measurements of cylinder pressure, connecting rod force and calculation of inertial forces. Friction force is the difference of these forces in consideration of the slider-crank geometry. A grasshopper linkage has been used to transmit the connecting rod force signal measured by a strain gage bridge. Inertial forces have been calculated with the assumption of distributed connecting rod mass. The test engine was a Chevrolet 5 litre V-8, modified for single cylinder operation. Piston and ring assembly friction has been determined under motoring conditions with and without compression as well as firing. Friction measurements have been made with SAE 30 and 50 grade oils at different temperatures. Boundary friction has been observed especially near top and bottom dead centers.
Technical Paper

Effect of Some Lubricant and Engine Variables on Instantaneous Piston and Ring Assembly Friction

1984-02-01
840178
The Instantaneous IMEP method has been used to measure piston and ring assembly friction in a production Chevrolet 1.8 litre L-4 and a 5 litre V-8 engine modified for single-cylinder operation. Friction measurements are reported at different loads and speeds up to 1640 RPM under firing and motoring conditions with various oils and before and after break-in of the oil ring. Oils used were SAE viscosity grades 30, 50 and 30 with a friction modifier. Differences were found between motoring and firing friction, especially on the power and exhaust strokes. These differences diminished at higher speeds and lower loads where lubrication was more hydrodynamic. Differences in response to viscosity and friction modifier changes were noted between the two engines.
Technical Paper

Oil and Ring Effects on Piston-Ring Assembly Friction by the Instantaneous IMEP Method

1985-02-01
850440
This paper describes the friction characteristics of a 1.8 Litre J-car piston and ring assembly as influenced by oil rings of conventional design, but of varying tensions. In addition, the piston-ring assembly friction characteristics are reported for a set of oil viscosities ranging from 2 to 20 cSt with and without a molybdenum friction modifier. Multigrade oil results are shown also. Finally comparisons are presented between changes in friction measured by the Instantaneous IMEP Method and those measured by the dynamometer for the engine as a whole. Our results show large differences in piston-ring assembly friction as oil ring tension was varied. However, these differences became moderate after the oil ring broke-in. Both high and low oil viscosities increased piston and ring assembly friction. The friction modifier was most effective with a mid-range viscosity and provided virtually no benefit at viscosity extremes.
Technical Paper

Quantification of Local Ozone Production Attributable to Automobile Hydrocarbon Emissions

2001-11-12
2001-01-3760
When automobile hydrocarbons are exhausted into the atmosphere in the presence of NOx and sunlight, ground-level ozone is formed. While researchers have used Maximum Incremental Reactivity (MIR) factors to estimate ozone production, this procedure often overestimates Local Ozone Production (LOP) because it does not consider local atmospheric conditions. In this paper, an enhanced MIR methodology for estimating actual LOP attributable to a vehicle in a particular ozone problem area is presented. In addition to using tabulated MIR factors, the procedure also uses local hydrocarbon reaction terms and a relative mechanistic reactivity term that account for local atmospheric conditions. Through this approach, the effects of hydrocarbon reaction rates, hydrocarbon residence times, and prevailing HC/NOx ratio are accounted for. The procedure is intended to enable automotive engineers to more realistically estimate actual local ozone production resulting from hydrocarbon emissions.
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