Methods for heat transfer and temperature field analysis of the insulated diesel

Work done during phase 1 of a three-year program aimed at developing a comprehensive heat transfer and thermal analysis methodology oriented specifically to the design requirements of insulated diesel engines is reported. The technology developed in this program makes possible a quantitative analysis of the low heat rejection concept. The program is comprehensive in that it addresses all the heat transfer issues that are critical to the successful development of the low heat rejection diesel engine: (1) in-cylinder convective and radiative heat transfer; (2) cyclic transient heat transfer in thin solid layers at component surfaces adjacent to the combustion chamber; and (3) steady-state heat conduction in the overall engine structure. The Integral Technologies, Inc. (ITI) program is comprised of a set of integrated analytical and experimental tasks. A detailed review of the ITI program approach is provided, including the technical issues which underlie it and a summay of the methods that were developed

Methods for heat transfer and temperature field analysis of the insulated diesel, phase 3

Work during Phase 3 of a program aimed at developing a comprehensive heat transfer and thermal analysis methodology for design analysis of insulated diesel engines is described. The overall program addresses all the key heat transfer issues: (1) spatially and time-resolved convective and radiative in-cylinder heat transfer, (2) steady-state conduction in the overall structure, and (3) cyclical and load/speed temperature transients in the engine structure. These are all accounted for in a coupled way together with cycle thermodynamics. This methodology was developed during Phases 1 and 2. During Phase 3, an experimental program was carried out to obtain data on heat transfer under cooled and insulated engine conditions and also to generate a database to validate the developed methodology. A single cylinder Cummins diesel engine was instrumented for instantaneous total heat flux and heat radiation measurements. Data were acquired over a wide range of operating conditions in two engine configurations. One was a cooled baseline. The other included ceramic coated components (0.050 inches plasma sprayed zirconia)-piston, head and valves. The experiments showed that the insulated engine has a smaller heat flux than the cooled one. The model predictions were found to be in very good agreement with the data

The effect of insulated combustion chamber surfaces on direct-injected diesel engine performance, emissions, and combustion

The combustion chamber of a single-cylinder, direct-injected diesel engine was insulated with ceramic coatings to determine the effect of low heat rejection (LHR) operation on engine performance, emissions, and combustion. In comparison to the baseline cooled engine, the LHR engine had lower thermal efficiency, with higher smoke, particulate, and full load carbon monoxide emissions. The unburned hydrocarbon emissions were reduced across the load range. The nitrous oxide emissions increased at some part-load conditions and were reduced slightly at full loads. The poor LHR engine performance was attributed to degraded combustion characterized by less premixed burning, lower heat release rates, and longer combustion duration compared to the baseline cooled engine

Modeling of Piston Secondary Dynamics and Tribology

This paper describes a general, design-oriented model for the analysis of secondary motions in conventional and articulated piston assemblies. The model solves for the axial, lateral and rotational departures in positions and motions from the nominal kinematics, resulting from clearances within the piston assembly and also between the piston assembly components and the cylinder. In order to accurately represent the effect of oil films, the model includes comprehensive treatments of hydrodynamic and boundary lubrication of the skirt and of wristpin bearings. The skirt lubrication submodel also allows representation of oil starvation at the cylinder end of the skirt. The methodology allows the characterization of conventional and articulated piston secondary motions in the thrust plane of the cylinder. Oil and contact pressure and film thickness distributions in skirt-bore and wristpin interfaces are also solved for. Motions of the piston, pin, rod and (for articulated pistons) skirt are separately calculated, by integrating equations of motion for individual components and dynamic degrees of freedom. Various configurations with respect to rigid attachment of the wristpin to other components can also be represented. In the equations of motions solved, all gas pressure, inertia, friction and oil or contact pressure forces are accounted for. All pertinent operating parameters (engine speed and cyclic pressure variation) as well as design parameters, such as component masses, moments of inertia, mass centers, pin offsets, skirt profile, roughness and lubricated area, bore distortion etc. are specifiable to the model as inputs. The integrated model was applied in a number of parametric studies, to conventional and articulated pistons. Effects of speed, load and piston configuration as well as viscosity, skirt design and profile were investigated. Results indicate that the skirt friction predictions of the model correspond to known levels and trends. Further, design parameters such as nominal clearance, skirt profile, circumferential lubrication extent as well as oil viscosity are shown to have key influences on the action of the oil films and thereby on piston motions and skirt friction

A Comprehensive Model of Piston Skirt Lubrication

This paper describes a comprehensive model of piston skirt lubrication, developed for use in conjunction with piston secondary dynamic analysis, to accurately characterize the effects of the skirt-cylinder oil film on piston motions. The model represents both hydrodynamic and boundary lubrication modes and applies an asperity contact pressure when surfaces are in close proximity with each other. In addition to skirt dimensions and surface roughness properties, the circumferential extent of lubrication, an arbitrary skirt profile and bore distortion are specifiable inputs to the model. The model is also extended to represent the oil starvation at the cylinder end of the skirt by allowing the axial extent of lubrication on the skirt surface to vary circumferentially and with time to satisfy continuity of oil. Using a finite difference solution of the Reynolds equation and an asperity contact submodel, the model calculates oil and contact pressure distributions in the skirt-bore oil film as a function of all input design parameters and positions and motions of the skirt relative to the cylinder. In the context of a piston secondary dynamic analysis the computed oil and asperity pressures are integrated to calculate axial, lateral forces and moments on the skirt, in the thrust plane. The model was coupled to a piston secondary dynamics analysis and applied, in a number of parametric studies, to conventional and articulated pistons. Results indicate that the skirt friction predictions of the model correspond to known levels and trends. Further design parameters such as nominal clearance, skirt profile, circumferential lubrication extent as well as oil viscosity are shown to have key influences on the action of the oil films and thereby on piston motions and skirt friction

Simulation of Secondary Dynamics of Articulated and Conventional Piston Assemblies

This paper describes a general model for the analysis of secondary motions in conventional and articulated piston assemblies. The model solves for the axial, lateral and rotational departures in positions and motions from the nominal kinematics, resulting from clearances within the piston assembly and also between the piston assembly components and the cylinder. The methodology allows the characterization of conventional and articulated piston secondary motions in the thrust plane of the cylinder. Motions of the piston, pin, rod and (for articulated pistons) skirt are separately calculated, by integrating equations of motion for individual components and dynamic degrees of freedom. Various configurations with respect to rigid attachment of the wristpin to other components can also be represented. In the equations of motions solved, all gas pressure, inertia, friction and oil or contact pressure forces are accounted for. Detailed submodels of skirt and wristpin lubrication are utilized to calculate the effect of these oil films. All pertinent operating parameters (engine speed and cyclic pressure variation) as well as design parameters, such as component masses, moments of inertia, mass centers, pin offsets etc. are specifiable to the model as inputs. The model was applied, in conjunction with the skirt and wristpin lubrication submodels, to conventional and articulated pistons, in a number of parametric studies. Effects of speed, load and piston configuration were investigated