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Fuel wall impingement commonly occurs in small-bore diesel engines. Particularly during engine starting, when wall temperatures are low, the evaporation rate of fuel film remaining from previous cycles plays a significant role in the autoignition process that is not fully understood. Pre-injection chemiluminescence (PIC), resulting from low-temperature oxidation of evaporating fuel film and residual gases, was measured over 3200 μsec intervals at the end of the compression strokes, but prior to fuel injection during a series of starting sequences in an optical diesel engine. These experiments were conducted to determine the effect of this parameter on combustion phasing and were conducted at initial engine temperatures of 30, 40, 50 and 60°C, at swirl ratios of 2.0 and 4.5 at 1000 RPM. PIC was determined to increase and be highly correlated with combustion phasing during initial cycles of the starting sequence.

EGR is a proven technology used to reduce NOx formation in both compression and spark ignition engines by reducing the combustion temperature. In order to further increase its efficiency the recirculated gases are subjected to cooling. However, this leads to a higher load on the cooling system of the engine, thus requiring a larger radiator. In the case of turbocharged engines the large variations of the pressures, especially in the exhaust manifold, produce a highly pulsating EGR flow leading to non-steady-state heat transfer in the cooler. The current research presents a method of determining the pulsating flow field and the instantaneous heat transfer in the EGR heat exchanger. The processes are simulated using the CFD code FIRE (AVL) and the results are subjected to validation by comparison with the experimental data obtained on a 2.5 liter, four cylinder, common rail and turbocharged diesel engine.

As a result of recent focus on the control of Low Temperature Combustion (LTC) modes, dual-fuel combustion strategies such as Reactivity Controlled Compression Ignition (RCCI) have been developed. Reactivity stratification of the auto-igniting mixture is thought to be responsible for the increase in allowable engine load compared to other LTC combustion modes such as Homogenous Charge Compression Ignition (HCCI). The current study investigates the effect of ethanol intake fuel injection on in-cylinder formaldehyde formation and stratification within an optically accessible engine operated with n-heptane direct injection using optical measurements and zero-dimensional chemical kinetic models. Images obtained by Planar Laser Induced Fluorescence (PLIF) of formaldehyde using the third harmonic of a pulsed Nd:YAG laser indicate an increase in formaldehyde heterogeneity as measured by the fluorescence signal standard deviation.

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.

The simulation of I.C. Engines operation, especially during transients, requires a fairly accurate estimation of the internal mechanical losses of the engine. The paper presents generic friction models for the main friction components of the engine (piston-ring-liner assembly, bearings and valve train), considering geometry of the engine parts and peculiarities of the corresponding lubrication processes. Separate models for the mechanical losses introduced by the injection system, oil and water pumps are also developed. All models are implemented as SIMULINK modules in a complex engine simulation code developed in SIMULINK and capable to simulate both steady state and transient operating conditions. Validation is achieved by comparison with measurements made on a four cylinder, common rail diesel engine, on a test bench capable to run controlled transients.

This paper presents an experimental investigation conducted to determine the parameters that control the behavior of autoignition in a small-bore, single-cylinder, optically-accessible diesel engine. Depending on operating conditions, three types of autoignition are observed: a single ignition, a two-stage process where a low temperature heat release (LTHR) or cool flame precedes the main premixed combustion, and a two-stage process where the LTHR or cool flame is separated from the main heat release by an apparent negative temperature coefficient (NTC) region. Experiments were conducted using commercial grade low-sulfur diesel fuel with a common-rail injection system. An intensified CCD camera was used for ultraviolet imaging and spectroscopy of chemiluminescent autoignition reactions under various operating conditions including fuel injection pressures, engine temperatures and equivalence ratios.

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).

Ultraviolet chemiluminescence has been observed in a diesel engine cyclinder during compression, but prior to fuel injection under engine starting conditions. During a portion of the warm-up sequence, the intensity of this emission exhibits a strong correlation to the phasing of the subsequent combustion. Engine exhaust measurements taken from a continuously misfiring, motored engine confirm the generation of formaldehyde (HCHO) in such processes. Fractions of this compound are expected to be recycled as residual to participate in the following combustion cycle. Spectral measurements taken during the compression period prior to fuel injection match the features of Emeleus' cool flame HCHO bands that have been observed during low temperature heat release reactions occurring in lean HCCI combustion. That the signal from the OH* bands is weak implies a buildup of HCHO during compression.

The non-uniform character of the torque produced by a reciprocating I.C. engine is reflected in the cyclic variation of the crankshaft's speed. Because the crankshaft is an elastic structure, its response to the different harmonic components of the torque is different and changes with engine speed. The lowest harmonic components of the engine torque do not excite torsional vibrations and correlate fairly well with the corresponding harmonic orders of the crankshaft's speed. Based on a random vector model of the harmonic components of the gas-pressure torque, a statistical correlation is obtained between amplitudes and phases of the same harmonic component of the gas-pressure torque and of the crankshaft's speed. The lowest major harmonic order determines the average IMEP of the engine and the half-order detects if a cylinder is a lesser contributor to the total engine output and identifies the deficient cylinder.

Even under steady state operating conditions, the pressure variation in individual cylinders, and the corresponding gas-pressure torque are subjected to small random fluctuations from cycle to cycle. The gas-pressure torque of a cylinder may be expressed as a sum of harmonically variable components, each harmonic being affected by these fluctuations. A probabilistic model of the vector interpreting such a harmonic component is developed and used to determine the statistical parameters of the resultant random vector representing the corresponding harmonic order of the engine torque. At the low frequencies of the lowest harmonic orders of the engine torque the crankshaft behaves like a rigid body. This behavior permits to correlate the statistical parameters of the same harmonic components of the resultant torque and of the measured engine speed. This correlation is proved by experiments and used to identify faulty cylinders.

The paper presents a method of determining the Indicated Mean Effective Pressure (IMEP) and the gas pressure torque of a multi-cylinder engine using data obtained from the measurement of the crankshaft's speed variation. At steady state operating conditions a Fourier series describe the gas pressure torque of a cylinder and the resultant torque may be obtained by adding the harmonic components corresponding to all cylinders. Only the major harmonic orders, having the same phase for all cylinders add algebraically appearing with large contributions in the spectrum of the resultant torque. The lowest major component has a low frequency and, at this frequency, the crankshaft behaves dynamically like a rigid body. In this situation it is possible to correlate the amplitude of this harmonic order of the gas pressure torque to the same harmonic order of the crankshaft speed.

A dimensionless relationship that estimates the maximum bearing load of a 4-cylinder 4-stroke in-line engine has been found. This relationship may assist the design engineer in choosing a desired counterweight mass. It has been demonstrated that: 1) the average bearing load increases with engine speed and 2) the maximum bearing load initially decreases with engine speed, reaches a minimum, then increases quickly with engine speed. This minimum refers to a transition speed at which the contribution of the inertia force overcomes the contribution of the maximum pressure force to the maximum bearing load. The transition speed increases with an increase of counterweight mass and is a function of maximum cylinder pressure and the operating parameters of the engine.

The paper analyses the friction in the valve train of an internal combustion engine trying to separate the contribution of the different components to the total friction losses in the valve train. The measurements are performed on a running engine in order to avoid extraneous factors introduced by simulating rigs. The experimental engine is instrumented with strain gauge bridges on the rocker arm, the push rod and the camshaft to measure forces and moments acting on these components. Original techniques are developed to isolate and determine the friction forces between the valve stem and its guide, the friction force in the rocker arm bearing and the combined friction between cam/tappet and tappet/bore. It was found that the friction in the rocker arm bearing never reaches hydrodynamic conditions and that the friction coefficient between cam and tappet reduces with an increase in the engine speed.

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.

A means of validating numerical simulations has been developed which utilizes chemiluminescence measurements from an internal combustion engine. By incorporating OH*, CH2O* and CO2* chemiluminescence sub-mechanisms into a detailed n-heptane reaction mechanism, excited species concentration and chemiluminescence light emission were calculated. The modeled line-of-sight chemiluminescence emission allows a direct comparison of simulation results to experimentally measured chemiluminescence images obtained during combustion in an optically accessible compression ignition engine using neat n-heptane fuel. The spray model was calibrated using in-cylinder liquid penetration length Mie scattering measurements taken from the jets of the high-pressure piezo injector.

In recent years much interest has been shown for the possibilities to determine, on-line, the torque or power delivered by an i.c. engine running on site under normal operating conditions. In this paper, a method is developed which permits to estimate the average value, for the whole engine, of the mean indicated pressure (MIP), based on measurements of the angular speed fluctuations of the crankshaft. In order to establish the correlation between the MIP and some characteristic magnitudes of the angular speed fluctuations, three different ways to solve the system of differential equations of motion for the torsional oscillating system of the shafting are presented and discussed: transfer matrices (TM), direct numerical integration (DI) and modal analysis (MA). A comparison with experiment shows acceptable coincidence between measurements and simulation for all three methods.

The paper tries to establish the possible correlations between the fluctuations of the angular motion of the crankshaft -which may be easily measured-with the variations of the pressure time-histories in the engine's cylinders. The model of the dynamic system of an engine shafting and the appropriate computing code are validated by comparison with measured angular motion of the front-end of the crankshaft. The algorithm of the code - based on the transfer matrix method - is then reversed in order to obtain the harmonic components of the exciting torques acting along the crankshaft from the harmonic components of the motion of the free-end of the crankshaft. Different ways of performing this task and the influence of nonuniform cylinder contributions are investigated and discussed.

In marine propulsion systems with direct-coupled two-stroke large diesel engines, the angular position of the propeller with respect to the crankshaft remains unchanged during the whole operation of the engine. The interference between major harmonic orders of the engine torque is avoided by choosing a number of blades, different from any divisor of the cylinder number. However, interferences between other harmonic orders of the engine torque and the major harmonic order of the propeller torque -which is equal to the number of blades- may increase the amplitude of torsional vibrations. The paper shows that there is an optimum Phasing between crankshaft and propeller for which a decrease, up to 20%, of the dynamic shear stress of the shafting -in comparison with the worst possible phasing- may be achieved. This results points out the importance of being able to calculate, in the design stage, the best phasing of engine and propeller

Among the excitation sources of vibration for the marine propeller shafting, the propeller itself plays a significant role. It is the main source of excitation for the axial vibrations and a major contributor among the excitation sources for torsional vibrations. Thus, the possibility to predict the harmonic structure of the torque and thrust, in the design stage of the propeller system has a great importance for the designer. In this direction, the paper presents an analytical method of calculation for the propeller torque and thrust based only on the propeller series diagrams and general empirical formula for the wake and suction coefficients. A vortex model of the marine propeller, based on Prandtl lifting-line theory, has been developed. Considering the system of bounded and free vortices representing the propeller blade and its interaction with the incipient wake generated by hull motion, the velocity field around the blade profile is determined.

The problem of torsional vibrations of a shafting acted by an internal combustion engine has a very complex character due to the large frequency spectrum of the exciting torques produced by the engine's cylinders. Torsional vibration dampers, which are widely used in conjunction with i.c. engines in order to reduce vibration amplitudes and accompanying stresses, have as a principal drawback the energy dissipation by internal friction. This energy consumption affects the mechanical efficiency of the powerplant and may become important, especially for large engines. Theoretically, the classic dynamic vibration absorber doesn't dissipate mechanical energy; it only exchanges energy with the vibrating system, having as a result the reduction of the vibration amplitude. Such a device -built only with passive mechanical elements - shall be tuned to the vibrating system, being able to control torsional vibration only for a single engine speed.