Search Results

Two models used for the prediction of noise attenuation in silencers have been evaluated. One is a full non-linear one-dimensional fluid-dynamic model, representing the entire engine (from the air cleaner to the tail pipe). The other is a linear acoustic model, representing a silencer and the exhaust and tail pipes. The evaluation was made by comparing the models' predictions to transmission lose measurements obtained with a set of concentric-tube resonators under speaker excitation at room temperature. This represents a test of the models in the linear range (small pressure pulsation amplitudes). The comparisons showed that both of the models performed well under these conditions. For the non-linear model this comparison represents validation for only one special case, since the main application of the model is to prediction of engine performance, insertion loss in silencer, absolute level of noise radiated from tailpipe and engine backpressure.

Diesel engine control has already become complex, and in order to meet future emissions standards (such as Euro 4) it is likely to be the control system that will provide the needed performance increment. Common rail fuel injection offers yet more degrees of freedom which will need to be exploited as new emissions standards emerge. Whatever the emissions standards, there is a need to reduce risk at the earliest stages in the development of the powertrain. This will involve early and extensive simulation of the powertrain including its control system, sensors and actuators. What is the best way to achieve this using current tools? The result lies in a combination of a phenomenological model of the engine and a flexible controls environment. To illustrate the principles of developing prototype control systems, we will use the example of the CPower environment, which is a combination of a detailed engine simulation code (GT-Power) and the Simulink simulation environment.

An important aspect of calculation of engine combustion chamber heat transfer with a multi-dimensional flow code is the modeling of the near wall flow. Conventional treatments of the wall layer flow employ the use of wall functions which impose the wall boundary conditions on the solution grid points adjacent to solid boundaries. However, the use of wall functions for calculating complex flows such as those which exist in engines has numerous weaknesses, including dependence on grid resolution. An alternative wall modeling approach has been developed which overcomes the limitations of the wall functions and is applicable to the calculation of in-cylinder engine flows. In this approach the wall layer flow is solved dynamically on a grid spanning a very thin boundary layer region adjacent to solid boundaries which is separate from the global grid used to solve the outer flow.

Selective reinforcement of squeeze-cast aluminum pistons by fiber matrix inserts is a method of improving high temperature strength in piston zones subject to severe thermal and mechanical loads in highly loaded diesel engines. An investigation was carried out into the effects of selective fiber-matrix reinforcement on the thermal and stress state of an aluminum piston for a heavy-duty truck diesel engine application. Specifically, effects of geometry of the reinforced zone (fiber matrix), fiber density in the matrix, fiber orientation and piston combustion bowl shape were sought. Thermal and structural finite element analysis of the configurations were carried out. Thermal analyses were fully coupled to a simulation of a highly rated heavy-duty diesel.

The warmup characteristics of an engine have an important impact on a variety of design issues such as performance, emissions and durability. A computer simulation has been developed which permits a detailed transient simulation of the engine warmup period from initial ambient conditions to a fully warmed up state. The simulation combines a detailed crankangle-by-crankangle calculation of in-cylinder processes and of engine air flow, with finite element heat conduction calculations of heat transfer from the gases, through the structure to the coolant. The paper describes one particular application of the simulation to the warmup of a 2.5ℓ spark ignited engine from cold start to a fully warmed up state at several speeds ranging from 1600 to 5200 rpm and loads ranging from 25% to 100% at each speed. The response of structure temperatures, charge temperature at IVC and of the exhaust temperature has been calculated and is documented in terms of characteristic warmup times.

A combined experimental/analytical study was made of a 2.2ℓ production engine. The objective was to characterize the performance of the engine and the pressure wave dynamics in its manifolds, and to compare the data/predictions obtained using an engine simulation program. Description of the computer program is given, providing an overview of its capabilities and of the models it contains. The data was obtained at wide open throttle, at four engine speeds from 1600 rpm to 4800 rpm. The comparisons showed the ability of the simulation to predict the major features of the wave dynamics, including the amplitude, frequency and phasing of the waves, and their tuning and de-tuning at the various engine speeds.

This article describes a system level 1D simulation tool that has been constructed on the Quasi-steady (QS) method. By assuming that spatial changes are much greater than the temporal ones, rigorous 1D governing equations can be considerably simplified thus becoming less computationally demanding to solve and therefore suitable for control oriented modeling purposes. With the proposed tool exhaust pipe wall temperature profiles, including multiple-wall-layer configurations, are solved through a finite difference scheme. Momentum equation is included for predicting pressure losses due to frictions and geometric irregularity. Exhaust fluid properties (transport and thermodynamic) are evaluated according to NASA or JANAF polynomial thermal data basis. The proposed tool allows the consideration of an arbitrary number of chemical species and reactions in the entire system. A novel semi-automatic approach was developed to handle catalytic reaction kinetics intuitively.

One of the most critical elements in diesel engine design is the selection and matching of the fuel injection system. The injection largely controls the combustion process, and with it also a wide range of related issues, such as: fuel efficiency, emissions, startability, load acceptance (acceleration) and combustion noise. Simulation has been a valuable tool for the engine design engineer to predict and optimize key parameters of the fuel injection system. This is a problem that spans a number of subsystems. Historically, simulations of these subsystems (hydraulics, gas dynamics, engine performance and 3-D CFD cylinder modeling) have typically been done in isolation. Recently, a simulation tool has been developed, which models the different subsystems in an integrated manner. This simulation tool combines a 1-D simulation tool for modeling of hydraulic and gas dynamics systems, with 3-D CFD code for modeling the in-cylinder combustion and emissions.

An integrated simulation tool has been developed, which is applicable to a wide range of design issues. A key feature introduced for the first time by this new tool is that it is truly a single code, with identical handling of engine, powertrain, vehicle, hydraulics, electrical, thermal and control elements. Further, it contains multiple levels of engine models, so that the user can select the appropriate level for the time scale of the problem (e.g. real-time operation). One possible example of such a combined simulation is the present study of engine block vibration in the mounts. The simulation involved a fully coupled model of performance, thermodynamics and combustion, with the dynamics of the cranktrain, engine block and the driveline. It demonstrated the effect of combustion irregularity on engine shaking in the mounts.

Recently, several theories have been offered as possible explanations for claimed increases in diesel engine heat transfer when combustion chamber surface temperatures are raised through insulation. A multi-dimensional computational fluid dynamics (CFD) analysis, using a recently developed near wall turbulent heat transfer model, has been employed to investigate the validity of two of these theories. The proposed mechanisms for increased heat transfer in the presence of high wall temperatures are: 1 piston-induced compression heating of the near wall gas which increases the near wall temperature gradient when wall temperatures are high; 2 increased penetration of hot, burned gases into the near wall flow during combustion through reduction of the flame quench distance.

A set of methods is described to calculate boundary conditions for thermal and mechanical finite element (FE) analyses and to assess and present the results of those analyses in a clear and understandable way. The approach utilizes a combination of engine simulation programs and an empirical database of engine measurements developed over many years. The methodology relies on the use of specialized FE pre- and post-processors dedicated to the analyses of engine components. Gas-side thermal boundary conditions for combustion chamber components are calculated using an engine simulation code for standalone FE analyses or for FE analyses directly coupled to the engine simulation code itself. Coolant side boundary conditions are calculated using multidimensional flow analysis (computational fluid dynamics). Boundary conditions in intake and exhaust manifolds are calculated using a one-dimensional gas dynamics code.

This paper presents the results of an investigation into the comparison between measured and simulated intake system dynamics of the General Motors Quad 4 engine. Simulations of the engine were conducted at eleven wide-open-throttle operating conditions ranging in engine speed from 2500 rpm to 6000 rpm under both firing and motoring operation. Comparisons of basic engine performance (torque, volumetric efficiency, BSFC), as well as dynamic pressure at two locations within the intake manifold (runner and plenum) showed good correlation between measurements and simulation. The total sound pressure level radiated from the intake orifice was also calculated and compared to measured data. The results of this study show that the simulation program has the ability to accurately capture the major features of engine intake system wave dynamics, including amplitude, phasing, and excitation of system resonances throughout the engine operating range.

The use of engine simulation is rapidly increasing throughout the engine industry. In the present paper, the major contributing factors which drive this trend are discussed. These include the increasing sophistication of the simulations, both in the area of high accuracy and in user-friendliness. Also, the decreasing cost of engineering computer workstations places them on the desktop of engineers and makes them readily available. Furthermore, the steadily rising computer processing power now provides the response needed in the engine development environment. The advances seen in simulations now open a new area for their application--as a tool fully complementary to test and measurement in a “concurrent test and simulation” process. The wide-ranging benefits and opportunities offered by the process are described in detail.

The flow around a bluff body with a slanted rear surface is influenced very dramatically by changing the angle of the rear surface slant and at some slant angles an excessively high drag is generated. To learn more about this critical behavior a series of detailed experiments was conducted on a vehicle-like bluff body, investigating the effect of ground proximity, Reynolds number, free-stream turbulence and of rounding of the upper edge of the slanted surface. The results of these experiments showed that although these various factors could change the critical slant angle and the size of the drag overshoot, the basic critical behavior was always present.

The flow produced by an experimental high-swirl intake port was studied by several techniques. These included measurements of flow rate and swirl as a function of valve lift on a steady state bench rig, hot-wire measurements of flow issuing from the valve, and flow visualization in water and air. By applying these techniques together to a single port, a body of data was generated which is presented as an addition to what is known about intake port flows and swirl generation. Data include flow and swirl coefficients, information on the effects of valve offset and port orientation angle, swirl generation by velocity non-uniformity around the valve, swirl decay in the rig due to air friction on the walls, and forward/backward flow coefficients. The definition of the appropriate dimensionless parameters for port flow characterization is also discussed.

A new model for corrective in-cylinder heat transfer has been developed which calculates heat transfer coefficients based on a description of the in-cylinder flow field. The combustion chamber volume is divided into three regions in which differential equations for angular momentum, turbulent kinetic energy and turbulent dissipation are solved. The resultant heat transfer coefficients are strongly spatially non-uniform, unlike those calculated from standard correlations, which assume spatial uniformity. When spatially averaged, the heat transfer coefficient is much more peaked near TDC of the compression stroke as compared to that predicted by standard correlations. This is due to the model's dependence on gas velocity and turbulence, both of which are amplified near TDC. The new model allows a more accurate calculation of the spatial distribution of the heat fluxes. This capability is essential for calculation of heat transfer and of component thermal loading and temperatures.

The heat flux from the gases to the walls of I.C. engines is highly transient, producing temperature transients in thin layers of the walls adjacent to the combustion chamber. The resulting surface temperature swings affect engine performance, and also increase the maximum temperature of the engine components. To analyze these effects, a one-dimensional, time-dependent heat conduction model was developed, with the capability to handle layered or laminated walls and temperature-dependent material properties. The model is driven by a thermodynamic cycle code coupled to a steady-state heat conduction model of the engine structure. A parametric study was carried out in which boundary conditions representing a heavy duty diesel engine were applied to materials with a wide range of thermal properties.

An analysis was made of the effect of insulation strategy on diesel engine heat transfer, performance and structure temperatures. The analysis was made using a thermodynamic cycle code with a new heat transfer correlation which takes into account the gas velocity and turbulent intensity and provides a spatially and time resolved description of the heat transfer process. The cycle code is directly coupled to a steady state heat conduction code representing the engine structure, and a transient heat conduction code tracking wall temperature swings along the combustion chamber surfaces. The study concentrated on the effects of different insulation strategies and insulating materials placed at various locations within the combustion chamber. Among the outputs of these analyses were the thermodynamic efficiency, peak firing pressure, exhaust gas temperature, component temperatures (time-average and maximum), volumetric efficiency, major heat paths and fuel energy balance.

A set of heat flux data was obtained in a Cummins single cylinder NH-engine coated with zirconia plasma spray. Data were acquired at two locations on the head, at several speeds and several load levels, using a thin film Pt-Pt/Rh thermocouple plated onto the zirconia coating. Careful attention was given to the probe design and to data reduction to assure high accuracy of the measurements. The data showed that the peak heat flux was consistently reduced by insulation and by the increasing wall temperature. The mean heat flux was also reduced. The results agree well with a previously developed flow-based heat transfer model. This indicates that the nature of the heat transfer process was unchanged by the increased wall temperature. Based on these results, the conclusion is drawn that insulation and increasing wall temperatures lead to a decrease in heat transfer and thus contribute positively to thermal efficiency.

Detailed heat transfer measurements were made in the combustion chamber of a Cummins single cylinder NH-engine in two configurations: cooled metal and ceramic-coated. The first configuration served as the baseline for a study of the effects of insulation and wall temperature on heat transfer. The second configuration had several in-cylinder components coated with 1.25 mm (0.050″) layer of zirconia plasma spray -- in particular, piston top, head firedeck and valves. The engine was operated over a matrix of operating points at four engine speeds and several load levels at each speed. The heat flux was measured by thin film thermocouple probes. The data showed that increasing the wall temperature by insulation reduced the heat flux. This reduction was seen both in the peak heat flux value as well as in the time-averaged heat flux. These trends were seen at all of the engine operating conditions.