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Technical Paper

Diesel Engine Cold Start Combustion Instability and Control Strategy

2001-03-05
2001-01-1237
Combustion instability and white smoke emissions are serious problems during cold starting of diesel engines. In this investigation, a model has been applied to predict misfiring based on an analysis of the autoignition process. The effect of injection timing on combustion instability during the cold start transient, at different ambient temperatures is investigated, both theoretically and experimentally. Maps have been developed to show the zones where misfiring would occur. The experimental work was conducted on a direct injection heavy-duty diesel engine in a cold room. The room temperature covered a range from 21 ° C to -10 ° C. The cycle-by-cycle data analysis was made and results plotted on the developed maps. The experimental results correlated fairly well with the model prediction. Based on the analysis, a new strategy for cold starting can be developed to reduce combustion instability and white smoke emissions.
Technical Paper

Combustion Visualization of DI Diesel Spray Combustion inside a Small-Bore Cylinder under different EGR and Swirl Ratios

2001-05-07
2001-01-2005
An experimental setup using rapid compression machine to provide excellent optical access to visualize simulated high-speed small-bore direct injection diesel engine combustion processes is described. Typical combustion visualization results of diesel spray combustion under different EGR, swirl, and injection pressure and nozzle conditions are presented. Different swirl intensities are achieved using an air nozzle with variable orientations and a check valve to connect the compression chamber and the combustion chamber. Different EGR ratios are achieved by pre-injection of diesel fuel prior to the main observation sequence. Clear visualization of the high-pressure fuel injection, ignition, combustion and spray/wall/swirl interactions is obtained. The injection system is a high-pressure common-rail system with either a VCO or a mini-sac nozzle. High-speed movies up to 35,000 frame-per-second are taken using a framing drum camera to record the combustion events.
Technical Paper

Development of High Temperature Diesel Engine Piston Ring and Cylinder Liner Tribology

2003-03-03
2003-01-1104
Adiabatics, Inc. with the support of the U.S. Army Tank Automotive & Armaments Command has examined the feasibility of using Diamond Like Carbon (DLC) films and Iron Titanate (Fe2TiO5 or IT) for sliding contact surfaces in Low Heat Rejection (LHR) diesel engines. DLCs have long been a popular candidate for use in sliding contact tribo-surfaces where a perceived reduction of friction losses will result in increased engine efficiency [1]. There exists a broad range of technologies for applying DLC films. This paper examines several types of these technologies and their future application to automotive internal combustion engines. Our work focuses upon DLC use for LHR military diesel engines where operating temperatures and pressures are higher than conventional diesel engines. However, a direct transfer of this technology to automotive diesel or gasoline engines exists for these thin films.
Technical Paper

Simplified Elasto-Hydrodynamic Friction Model of the Cam-Tappet Contact

2003-03-03
2003-01-0985
The paper analyses the particularities of the lubricating conditions at the contact between the cam and a flat tappet in the valve train of an internal combustion engine and develops a method for the calculation of the friction force. The existing lubrication models show the predominance of the entraining speed and oil viscosity on the thickness of the oil film entrapped between cam and tappet, predicting a very small value (less than 0.1 μm) of the oil film thickness (OFT). The oil viscosity increases exponentially with pressure in the Hertzian contact, determining non-Newtonian behavior of the oil in the contact zone. Using the model developed by Greenwood and Tripp [11] for the contact of two rough surfaces and the Eyring model [2] for the oil it is shown that non-Newtonian behavior of the oil prevails and that the OFT plays a secondary role on the friction force.
Technical Paper

Analysis of Current Spray Penetration Models and Proposal of a Phenomenological Cone Penetration Model

1996-02-01
960773
A phenomenological zero-dimensional spray penetration model was developed for diesel-type conditions for a constant volume chamber. The spray was modeled as a protruding cone which is well-mixed at its tip after passing through initial primary and secondary breakup zones. The resulting cone model is strictly dependent on injection parameters; density ratio, injection and chamber pressure, nozzle characteristics, and cone angle. The proposed model was compared with data from three different sources and performed well in most cases except for low density environments.
Technical Paper

Insulated Miller Cycle Diesel Engine

1996-02-01
961050
This paper investigates theoretically the benefits of the Miller cycle diesel engine with and without low heat rejection on thermodynamic efficiency, brake power, and fuel consumption. It further illustrates the effectiveness of thin thermal barrier coatings to improve the performance of military and commercial IC engines. A simple model which includes a friction model is used to estimate the overall improvement in engine performance. Miller cycle is accomplished by closing the intake valve late and the engine components are coated with PSZ for low heat rejection. A significant improvement in brake power and thermal efficiency are observed.
Technical Paper

A Large Scale Mixing Model for a Quiescent Chamber Direct Injection Diesel

1996-02-01
961040
The methodology for predicting the transient mixing rate is presented for a direct injection, quiescent chamber diesel. The mixing process is modeled as a zero-dimensional, large-scale phenomena which accounts for injection rate, cylinder geometry, and engine operating condition. As a demonstration, two different injection schemes were investigated for engine speeds of 1600, 2100, and 2600 rpm. In the first case, the air-fuel ratio was fixed while the injection rate was allowed to vary, but for the second case, the injection duration was fixed and the air-fuel ratio was allowed to vary. For the former case, the resulting mixing rate was also compared with the experimentally determined fuel burning rate. These two quantities appeared to be correlated in some manner for the various engine speeds under investigation.
Technical Paper

Experimental Determination of the Instantaneous Frictional Torque in Multicylinder Engines

1996-10-01
962006
An experimental method for determining the Instantaneous Frictional Torque (IFT) using pressure transducers on every cylinder and speed measurements at both ends of the crankshaft is presented. The speed variation measured at one end of the crankshaft is distorted by torsional vibrations making it difficult to establish a simple and direct correlation between the acting torque and measured speed. Using a lumped mass model of the crankshaft and modal analysis techniques, the contributions of the different natural modes to the motion along the crankshaft axis are determined. Based on this model a method was devised to combine speed measurements made at both ends of the crankshaft in such a way as to eliminate the influence of torsional vibrations and obtain the equivalent rigid body motion of the crankshaft. This motion, the loading torque and the gas pressure torque are utilized to determine the IFT.
Technical Paper

Emissions Comparisons of an Insulated Turbocharged Multi-Cylinder Miller Cycle Diesel Engine

1998-02-23
980888
The experimental emissions testing of a turbocharged six cylinder Caterpillar 3116 diesel engine converted to the Miller cycle operation was conducted. Delayed intake valve closing times were also investigated. Effects of intake valve closing time, injection time, and insulation of piston, head, and liner on the emission characteristics of the Miller cycle engine were experimentally verified. Superior performance and emission characteristic was achieved with a LHR insulated engine. Therefore, all emission and performance comparisons are made with LHR insulated standard engine with LHR insulated Miller cycle engine. Particularly, NOx, CO2, HC, smoke and BSFC data are obtained for comparison. Effect of increasing the intake boost pressure on emission was also studied. Poor emission characteristics of the Miller cycle engine are shown to improve with increased boost pressure. Performance of the insulated Miller cycle engine shows improvement in BSFC when compared to the base engine.
Technical Paper

Improving the Fuel Economy of Insulated Engine by Matching the Fuel System

1998-02-23
980885
This paper deals with the analysis of heat release characteristics of an insulated turbocharged, six cylinder, DI contemporary diesel engine. The engine is fully insulated with thin thermal barrier coatings. Effect of insulation on the heat release was experimentally verified. Tests were carried over a range of engine speeds at 100%, 93%, 75% and 50% of rated torque. Fuel injection system was instrumented to obtain injection pressure characteristics. The study shows that rate of heat release, particularly in the major portion of the combustion, is higher for the insulated engine. Improvement in heat release and performance are primarily attributed to reduction in heat transfer loss due to the thin thermal barrier coating. Injection pressure at the rated speed and torque was found to be 138 MPa and there was no degradation of combustion process in the insulated engine. Improvements in BSFC at 93% load are 3.25% and 6% at 1600 and 2600 RPM, respectively.
Technical Paper

Diesel Engine Diagnosis Based on Analysis of the Crankshaft's Speed Variation

1998-10-19
982540
The variation of the crankshaft's speed is influenced by the action of the cylinders and shall reflect the contribution of each cylinder to the total engine output. At the same time, the speed variation is influenced by the torsional stiffness of the cranks, the mass moments of inertia of the reciprocating mechanisms and the average speed and load of the engine. As the result, the variation of angular motion of the crankshaft is complex, each particular influence changing its importance as speed and load are modified. The diagnostic method presented in the paper is based on the analysis of the amplitudes and phases of the lowest harmonic orders of the measured speed and is capable to determine the average Indicated Mean Effective Pressure (IMEP), to detect nonuniformities in cylinder operation and to identify the faulty cylinder(s).
Technical Paper

Microscopic Characterization of Diesel Sprays at VCO Nozzle Exit

1998-10-19
982542
A long-distance microscope with pulse-laser as optical shutter up to 25kHz was used to magnify the diesel spray at the nozzle hole vicinity onto 35-mm photographic film through a still or a high-speed drum camera. The injectors examined are high-pressure valve-covered-orifice (VCO) nozzles, from unit injector and common rail injection systems. For comparison, a mini-sac injector from a hydraulic unit injector is also investigated. A phase-Doppler particle analyzer (PDPA) system with an external digital clock was also used to measure the droplet size, velocity and time of arrival relative to the start of the injection event. The visualization results provide very interesting and dynamic information on spray structure, showing spray angle variations, primary breakup processes, and spray asymmetry not observed using conventional macroscopic visualization techniques.
Technical Paper

Diesel Cold-Starting Study Using Optically Accessible Engines

1995-10-01
952366
An experimental and numerical study was carried out to simulate the diesel spray behavior during cold starting conditions inside two single-cylinder optically accessible engines. One is an AVL single-cylinder research diesel engine converted for optical access; the other is a TACOM/LABECO engine retrofitted with mirror-coupled endoscope access. The first engine is suitable for sophisticated optical diagnostics but is constrained to limited consecutive fuel injections or firings. The second one is located inside a micro-processor controlled cold room; therefore it can be operated under a wide range of practical engine conditions and is ideal for cycle-to-cycle variation study. The intake and blow-by flow rates are carefully measured in order to clearly define the operation condition. In addition to cylinder pressure measurement, the experiment used 16-mm high-speed movie photography to directly visualize the global structures of the sprays and ignition process.
Technical Paper

Recent Development of Tribological Coatings for High Temperature Engines

1995-02-01
950979
Lubrication of advanced high temperature engines has been one of the greatest obstacles in the development of the Adiabatic engine. Liquid lubricants which gave lubricating properties as well as heat removal function can no longer carry out this duty when piston ring top ring reversal temperatures approach 540°C. Solid lubricants offer some hope. Since solid lubricants cannot perform the heat removal function, its coefficient of friction must be very low, at least <0.10, in order to prevent heat build up and subsequent destruction to the piston rings and cylinder liners. The Hybrid Piston concept developed in the U.S. Army Advanced Tribology program offers some hope, since the top solid lubricant ring slides over the bottom hydrodynamic lubricant film section during each stroke. This paper presents the progress made with the solid lubricant top ring in the Hybrid Piston. Four materials have shown promise in the laboratory to fullfil its mission.
Technical Paper

Assessment of Thin Thermal Barrier Coatings for I.C. Engines

1995-02-01
950980
This paper investigates theoretically the effects of heat transfer characteristics, such as crank-angle phasing and wall temperature swings, on the thermodynamic efficiency of an IC engine. The objective is to illustrate the fundamental physical basis of applying thin thermal barrier coatings to improve the performance of military and commercial IC engines. A simple model illustrates how the thermal impedance and thickness of coatings can be manipulated to control heat transfer and limit the high temperatures in engine components. A friction model is also included to estimate the overall improvement in engine efficiency by the proper selection of coating thickness and material.
Technical Paper

Design of High Temperature Engine Components

1995-02-01
950982
The successful design of engine components for high temperature applications is very dependent on the use of advanced finite element methods. Without the use of thermal and structural modeling techniques it is virtually impossible to establish the reliable design specifications to meet the application requirements. Advanced modeling and design of two key engine components, the cylinder head thermal insulating headface plate and the capped air gap insulated piston, are presented. Prior engine test experience contributes to further understanding of the important factors in recognizing successful design solutions. It has been found that the modeling results are only as good as the modeling assumptions and that all modeling boundary conditions and constraints must be reviewed carefully.
Technical Paper

A Simplified Analytical Methodology for Selecting Element Density for Low Heat Rejection Diesel Heat Thermal Analysis

1996-02-01
960507
The authors have conducted extensive finite element (FE) thermal and stress analysis on the heads of low heat rejection diesel engines. Throughout these analyses, model mesh construction was based on conventional rule-of-thumb criteria. In this paper a simple analytical methodology is presented for selecting a mesh to conduct thermal analysis. This is intended to remove some of the arbitrary appearance of these prior meshes. Results of the FE thermal solution based on a mesh using this methodology is compared to a known convergent FE thermal solution.
Technical Paper

White Smoke Emissions Under Cold Starting of Diesel Engines

1996-02-01
960249
More stringent regulations have been enforced over the past few years on diesel exhaust emissions. White smoke emission, a characteristic of diesel engines during cold starting, needs to be controlled in order to meet these regulations. This study investigates the sources and constituents of white smoke. The effects of fuel properties, design and operating parameters on the formation and emissions of white smoke are discussed. A new technique is developed to measure the real time gaseous hydrocarbons (HC) as well as the solid and liquid particulates. Experiments were conducted on a single cylinder direct injection diesel engine in a cold room. The gaseous HC emissions are measured using a high frequency response flame ionization detector. The liquid and solid particulates are collected on a paper filter placed upstream of the sampling line of the FID and their masses are determined.
Technical Paper

An Investigation of the Effects of Node Density on Finite Element Thermal/Stress Analysis as Applied to Low Heat Rejection Diesel Heads

1994-03-01
940950
In our prior analytical work concerning a finite element methodology for thermal stress analysis of minimum cooled low heat rejection (LHR) engine cylinder heads, a very fine mesh with strict aspect ratio and element density criteria was used. In this current study, these criteria were relaxed and two other finite element models with different element densities were used to solve the same thermal stress problem. The thermal and stress results of the relaxed models are compared to those of the earlier very fine mesh results. It is the aim of this paper to show in a semi-quantified manner, how mesh density can affect thermal stress solutions in LHR engine heads. Hopefully this will enable other analysts working in this area to make some judgement on mesh density before starting an actual modelling effort, resulting in a savings of time and manpower resources.
Technical Paper

100 Hour Endurance Testing of a High Output Adiabatic Diesel Engine

1994-03-01
940951
An advanced low heat rejection engine concept has successfully completed a 100 hour endurance test. The combustion chamber components were insulated with thermal barrier coatings. The engine components included a titanium piston, titanium headface plate, titanium cylinder liner insert, M2 steel valve guides and monolithic zirconia valve seat inserts. The tribological system was composed of a ceramic chrome oxide coated cylinder liner, chrome carbide coated piston rings and an advanced polyolester class lubricant. The top piston compression ring Included a novel design feature to provide self-cleaning of ring groove lubricant deposits to prevent ring face scuffing. The prototype test engine demonstrated 52 percent reduction in radiator heat rejection with reduced intake air aftercooling and strategic forced oil cooling.
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