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Technical Paper

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

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

Experimental Determination of the Instantaneous Frictional Torque in Multicylinder Engines

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

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

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

Diesel Cold-Starting Study Using Optically Accessible Engines

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

In-Situ Phase-Shift Measurement of the Time-Resolved UBHC Emissions

The UBHC emissions during cold starting need to be controlled in order to meet the future stringent standards. This requires a better understanding of the characteristics of the time resolved UBHC signal measured by a high frequency FID and its phasing with respect to the valve events. The computer program supplied with the instrument and currently used to compute the phase shift has many uncertainties due to the unsteady nature of engine operation during starting. A new technique is developed to measure the in-situ phase shift of the UBHC signal under the transient thermodynamic and dynamic conditions of the engine. The UBHC concentration is measured at two locations in the exhaust manifold of one cylinder in a multicylinder port injected gasoline engine. The two locations are 77 mm apart. The downstream probe is positioned opposite to a solenoid-operated injector which delivers a gaseous jet of hydrocarbon-free nitrogen upon command.
Technical Paper

Determination of the Gas-Pressure Torque of a Multicylinder Engine from Measurements of the Crankshaft's Speed Variation

The local variation of the crankshaft's speed in a multicylinder engine is determined by the resultant gas-pressure torque and the torsional deformation of the crankshaft. Under steady-state operation, the crankshaft's speed has a quasi-periodic variation and its harmonic components may be obtained by a Discrete Fourier Transform (DFT). Based on a lumped-mass model of the shafting, correlations are established between the harmonic components of the speed variation and the corresponding components of the engine torque. These correlations are used to calculate the gas-pressure torque or the indicated mean effective pressure (IMEP) from measurements of the crankshaft's speed.
Technical Paper

A Diagnostic Technique for the identification of Misfiring Cylinder(s)

This paper introduces a diagnostic technique for the detection of misfiring cylinders in internal combustion engines. The technique requires the analysis of the instantaneous angular velocity of an engine flywheel. The results show that the mean cyclic acceleration, maximum variation in angular velocity, and the cyclic period of acceleration can be used as a measure for the mean net torque and the mean net expansion pressure torque produced by each cylinder. The proposed technique has proven to be effective in identifying a faulty cylinder using efficient and simple computations.
Technical Paper

Transient Engine and Piston Friction During Starting

The instantaneous frictional torque (IFT) of the engine and the piston-ring assembly frictional force (PRAFF) were determined during cranking and starting of a direct injection single cylinder diesel engine. The measurements included the cylinder gas pressure, the instantaneous torque of the electric starter, the angular velocity of the crankshaft and the axial force on the connecting rod. The engine and piston friction were determined every crank angle degree for all the cycles from the time the starter was engaged to the time the engine reached the idling speed. The data was analyzed and a comparison was made between the friction in successive cycles.
Technical Paper

Dynamic Parameters for Engine Diagnostics: Effect of Sampling

Several dynamic parameters for the diagnosis of reciprocating combustion engines are investigated. Emphasis is made on the effect of sampling. The dynamic parameters include the frequency analysis, autocorrelation function, the frequency analysis of the autocorrelation function, variation of the angular velocity peaks, variation of the angular velocity depressions, variation of the angular velocity from before to after top dead center, velocity index and acceleration index. Two sampling techniques are used to measure the instantaneous angular velocity of a six cylinder, four-stroke-cycle diesel engine, under healthy and faulty conditions. The most effective dynamic parameters for engine diagnostics are determined.
Technical Paper

Cetane Scale: Function, Problems and Possible Solutions

This paper identifies the original function of the Cetane Scale and examines some problem of concern to the technical community. The following six problems have been analyzed: i) inability of the ASTM D-613 method to rate low ignition quality fuels, ii) instability of the ignition delay meter, iii) inconformity of the CFR combustion system with actual diesel systems, iv) invalidity of Cetane number in correlating the I.D. for different fuels, engines and operating conditions, v) inaccuracy of Cetane number in ranking the overall performance and emission behaviour of fuels in diesel engines and vi) inability of Cetane number in rating the cold startability of diesel engines on different fuels. Possible solutions to the above problems have been examined.
Technical Paper

Compression Ratio Optimization in a Direct-Injection Diesel Engine: A Mathematical Model

This paper describes the development and results of a mathematical model for a single cylinder, naturally-aspirated, direct-injection diesel engine, used to study the effect of compression ratio on the different performance parameters. The parameters investigated include; thermal and mechanical efficiency, ignition delay, mean effective pressure, maximum cylinder pressure, mechanical friction, and blowby. The model simulates a full thermodynamic cycle and considers the intake and exhaust processes, instantaneous heat transfer, instantaneous friction, and instantaneous blowby. Based on the model results, a prediction of an optimum CR for the engine is made.
Technical Paper

Diesel Starting: A Mathematical Model

A mathematical model Is developed to study the transient behavior of a four-stroke, single cylinder naturally-aspirated, DI diesel engine during cranking and starting. The model simulates the full thermodynamic cycle of the engine and includes detailed sub-models for the intake and exhaust gas flow processes, autoignition combustion, heat transfer, mechanical friction, blowby, and engine dynamics. The model considers the period of time from starter on until the engine reaches the idle speed. Experimental data and results obtained from the engine are used to calibrate and validate the model. A comparison of results from the model and the experiments generally show good agreement for the starting conditions investigated.
Technical Paper

Diesel Engine Cold Starting: Combustion Instability

Combustion instability is investigated during the cold starting of a single cylinder, direct injection, 4-stroke-cycle, air-cooled diesel engine. The experiments covered fuels of different properties at different ambient air temperatures and injection timings. The analysis showed that the pattern of misfiring (skipping) is not random but repeatable. The engine may skip once (8-stroke-cycle operation) or twice (12-stroke-cycle operation) or more times. The engine may shift from one mode of operation to another and finally run steadily on the 4-stroke cycle. All the fuels tested produced this type of operation at different degrees. The reasons for the combustion instability were analyzed and found to be related to speed, residual gas temperature and composition, accumulated fuel and ambient air temperature.
Technical Paper

Comparative Analysis of Stirling and Other Combustion Engines

The development of the Stirling engine has recently gained momentum because of technological advances as well as the need to explore alternative power systems for meeting environmental concerns. An overview of the Stirling engine principles, taking into account the ideal as well as the actual cycle, is presented. The analysis examines the various design aspects and the performance and emission characteristics. A comparison is made between the Stirling and other continuous and cyclic combustion engines, such as the gasoline, diesel, gas turbine, and steam engines. This includes recent designs for the Rankine cycle and gas turbine combustors being considered for automotive applications.
Technical Paper

Combustion and Emission Formation in the Stirling Engine with Exhaust Gas Recirculation

The combustion and emission formation in continuous combustion burners have been studied both theoretically and experimentally. The theoretical study is concerned with the combustion and emission formation in idealized sprays in quiescent air. The effects of the spray rotation and the air axial and radial velocities have been examined. A model has been developed for the emission formation in an actual Stirling engine. This model showed that the incomplete combustion products are primarily formed in the heterogeneous eddies zone near the burner walls. In this region, surface combustion takes place. The nitric oxide is primarily formed in the premixed-eddies zone where microvolume combustion is believed to take place. The experimental results deal with the effect of diluting the charge by using excess air or exhaust-gas recirculation on performance and emissions. The emissions measured are the nitric oxide, carbon monoxide, unburned hydrocarbons, and carbon.
Technical Paper

The Diesel as an Alternative Automobile Engine

An evaluation has been made of the use of the diesel as an alternative engine in passenger cars. This includes the technological feasibility for meeting the different emission standards and the techniques for emission control. The emissions studied include both the presently regulated species--hydrocarbons, carbon monoxide, and nitrogen oxides--and the following nonregulated emissions: aldehydes, ammonia, smoke and particulates, polynuclear aromatics, and sulfur compounds. A comparison has been made between the emissions, performance and economy of currently produced diesel powered cars and gasoline powered cars. Other cars which are being developed and powered by the stratified charge, Wankel, and the gas turbine engines are also included in the comparison. Intrinsic problem areas in the diesel engine that need further research are also identified and discussed.
Technical Paper

Starting of Diesel Engines: Uncontrolled Fuel Injection Problems

Many problems can develop from the uncontrolled fuel injection during cranking and starting of diesel engines. Some of the problems are related to excessive wear as a result of the high peak pressures reached upon combustion after misfiring, the relatively low rotating speeds and the lack of formation of a lubricating oil film between the interacting surfaces. Another problem is the emission of high amounts of unburned hydrocarbons and white smoke. Experimental results are given for a single cylinder and a multicylinder diesel engine, for the instantaneous angular velocity and cylinder pressures from the starter-on point until the engine fires. The causes of misfiring during cranking are investigated. The role of the increased blow-by gases on the autoignition process at the low cranking speeds is analyzed both analytically and experimentally. The contribution of the instantaneous angular velocity at the time of injection, on the autoignition process is investigated.
Technical Paper

A New Approach to Evaluate Instantaneous Friction and Its Components in Internal Combustion Engines

A new approach referred to as (P-ω) method, has been developed at Wayne State University to determine the instantaneous friction and its components in internal combustion engines. The method is based on the fact that the instantaneous cylinder gas forces and the instantaneous frictional, inertia and load forces cause the instantaneous variation in the flywheel angular velocity. The instantaneous total friction forces have been computed for a single diesel engine, under idling conditions. A breakdown of the friction into its components and a formulation for each component has been made. By applying linear regression, correlations between the individual components of the friction losses and the different parameters have been developed. The components are classified into two categories: piston assembly losses and crankcase assembly losses.
Technical Paper

Correlation between Physical Properties and Autoignition Parameters of Alternate Fuels

The correlations between the physical properties and autoignition parameters of several alternate fuels have been examined. The fuels are DF-2 and its blends with petroleum derived fuels, coal derived fuels, shale derived fuels, high aromatic naphtha sun-flower oils, methanol and ethanol. A total of eighteen existing correlations are discussed. An emphasis is made on the suitability of each of the correlations for the development of electronic controls for diesel engines when run on alternate fuels. A new correlation has been developed between the cetane number of the fuels and its kinematic viscosity and specific gravity.
Technical Paper

Cycle-To-Cycle Variation with Low Ignition Quality Fuels in a CFR Diesel Engine

Cycle-to-cycle cylinder pressure variation has been observed in a CFR prechamber diesel engine when low ignition quality (low cetane number) fuels are burned. A statistical analysis of this phenomenon for various fuels and blends with cetane numbers as low as zero has been made. Operating conditions used were those specified by the ASTM Cetane Method for rating diesel fuels, in which the inlet air temperature is 150°F. Additional analysis was made at increased inlet air temperatures of 250°F and 350°F. The cycle-to-cycle variation has been characterized by the variation in the ignition (or pressure rise) delay time. It has been found to increase sharply as fuel cetane number is decreased below 20. The variation in dynamic injection timing was also measured and correlated with that for ignition delay.