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Predictions of the volume flow rate through an inlet port were produced by four different commercially available CFD programs suitable for use in a steady flow simulation. These predictions were compared with experimental measurements of an inlet port's discharge coefficients. The experiment performed was a typical steady state flow bench test for an inlet port. Volume flow rates were measured at five different valve lifts. The largest valve lift tested (12.24mm) was the maximum value of lift under actual operation. The smallest valve lift was typical of early valve opening. The tests were performed at two different pressure differences across the inlet port and valve at each of the five different valve lifts. All predictions were made using an RNG k-ε turbulence model. Standard wall functions were used to predict wall friction effects and the energy equation was included to account for compressibility effects.

A Rotary Valve combustion System (RVS) is being developed which is a potential alternative to the conventional poppet valve combustion chamber systems currently in use on four-stroke reciprocating automotive engines. The RVS has been developed to operate in a Variable Valve Timing (VVT) mode, termed RVS/VVT. The system accomplishes variation of intake-valve-closure from 50 degrees After-Top-Center (ATC) to 250 degrees ATC. This broad range of variability is necessary to achieve throttleless power control from idle to full power. The RVS was evaluated for characteristics which were independent of its valve timing mode. These included: (1) system friction, (2) seal effectiveness, and (3) combustion performance at full load. System friction for the RVS valve train was measured by a pulley transducer on the drive-belt. Seal effectiveness was evaluated by static differential compression tests and dynamic blowby measurements.

An in-cylinder optical sensor has been developed and tested for use in spark-ignition engine combustion analysis and control, This sensor measures the luminous emission in the near infrared region. Results of these tests show good correlation between the measured luminosity and traditional combustion parameters, such as location and magnitude of maximum cylinder pressure, and location and magnitude of maximum heat release. Engine performance indicators, such as the indicated mean effective pressure (IMEP), also can be determined accurately with the measured luminosity combined with other engine operating parameters, e.g. intake manifold pressure. In-cylinder air-fuel ratio can be determined with accuracy over an ensemble of 100 cycles.

Conditional sampling of cylinder-pressure data is used to investigate cyclic variability in a premixed-charge spark-ignited engine operating under fuel-lean conditions. Unlike straight ensemble averaging of pressure data, conditional sampling applies a set of constraints to the pressure data such that like combustion events can be identified and grouped together. Ensemble averaging of pressure data from an engine that exhibits significant cycle-to-cycle variation is shown to produce a mean pressure history that is not representative of the combustion process. Conditional sampling provides a means of identifying and analyzing the different groups of pressure histories and therefore the different types of combustion processes that occur in an engine that exhibits cyclic variability.

Cyclic variation is examined by: (1) conditional grouping and heat-release analysis to reveal different modes of combustion, (2) considering the order in which the burn modes occur to establish prior-cycle effects and (3) comparing the measured variation in IMEP with data generated by simple models. Results show that several burn modes may exist, particularly under fuel-lean conditions. Prior-cycle effects also become more obvious as the air-fuel ratio is increased. Finally, comparisons with data generated by simple models show that the nature of cyclic variation may range from completely stochastic to a superposition of a non-chaotic deterministic process on a stochastic process.

Three different carburetor types have been tested to observe differences in the characteristics of the fuel/air mixtures produced. To characterize the fuel/air mixtures, two diagnostics have been applied: 1) High speed movies and subsequent analysis of the exit flow, and 2) measurement of the A/F ratio found in different positions within the intake manifold. The three different carburetor types that have been studied include a fixed-venturi, fixed-jet butterfly carburetor, a slide-valve carburetor, and a constant-velocity carburetor. Each carburetor type produced a unique set of exit flow characteristics, with differences in the optical density of fuel exiting the carburetor, and differences in the apparent amount of fuel on the intake manifold wall, entrained in the air flow, and in vapor phase.

Measurements are presented for the turbulence intensities and mean velocities obtained in a research engine in which a grid was used to create a flow field characterized by negligible mean motions and homogeneous and isotropic turbulence at the time of ignition. Pressure measurements for homogeneous stoichiometric combustion indicate a very low level of cyclic variation. The combustion-induced mean flow field is shown to be characteristic of a one-dimensional compression of the unburned gases, which produces a small increase in the bulk turbulent kinetic energy ahead of the flame. Most of the effect of combustion appears to occur locally, as the turbulence in the preflame gases close to the flame front is strongly amplified in the direction of flame propagation. Parallel to the flame surface there is little effect until the flame has propagated nearly all the way across the chamber.

Two distinct atomization strategies are contrasted through the measurement of time and spatially dependent mass flux. The two systems investigated include a pressure atomizer (6.9 MPa opening pressure) and an air-assist atomizer. Both systems have potential for use in direct injection spark ignition engines. The mass flux data presented were obtained using a spray patternator that was developed to allow phased sampling of the spray. The temporal mass related history of the spray was reconstructed as volume versus time plots and interpolated mass flux contour plots. Results indicate substantial differences in the distribution of both mass and mass flux in space and time for the two injection systems. For example, the pressure atomizer at high mass delivery rates produced a spray that collapsed into a dispersed cylindrical shape while at low rates, generated a hollow cone structure.

Two sets of comparisons were made in an attempt to provide a mechanism for understanding the behavior of transient sprays. First, detailed measurements of drop size and velocity in a transient spray were compared to established stability criteria for different droplet breakup mechanisms, specifically criteria for bag breakup and boundary layer stripping. Then, probability-density-functions were determined from the experimental data and compared, where appropriate, to different computed distributions (such as the Chi-square or log-hyperbolic distributions). Comparison with the stability criteria indicates that the a majority of droplets in the spray are susceptible to both breakup mechanisms near the injector tip. However, downstream, the spray appears to stabilize and any redistribution of droplet size must apparently be a result of collisions. The experimentally-determined PDF's for size and velocity are functions of both position and time in the spray.

Simultaneous droplet sizes and velocities were obtained for a transient diesel fuel spray in a quiescent chamber at atmospheric temperature and pressure. Instantaneous injection pressure, needle lift, and rate of injection were also measured, allowing calculation of the instantaneous nozzle discharge coefficient. Short-exposure still photographs were obtained at various chamber pressure and densities to further investigate this spray. Correlations between droplet size and velocity were determined at each crank angle to observe the detailed nature of the transient events occurring in this transient diesel fuel spray. As expected, peak mean and rms velocities are observed in the center of the spray. Measured average velocities are consistent with a calculated value, using the discharge coefficient for the nozzle and the known rate of fuel injection.

Pilot injection and two other forms of auxiliary fuel introduction have been studied for their effects on diesel engine combustion and emissions. A two-stroke diesel has been equipped with an electronic solenoid-controlled unit injector such that the injector can operate with pilot injection. In addition, the engine has been fitted with experimental air-blast atomizing injectors in the inlet port and intake manifold. In-cylinder pressure, Bosch smoke, exhaust hydrocarbons, NO and NOx emissions measurements have been made for a range of engine conditions. In addition, two fuels have been tested to observe the effects of fuel blend on the auxiliary fuel behavior. In general, the effect of auxiliary fuel introduction is to reduce ignition delay and rate-of-pressure rise. This tends to result in a decrease in NO emissions. Unburned hydrocarbons and smoke tend to increase, although not in every case.

In-cylinder heat flux and temperature measurements were obtained in an air-cooled four-stroke utility engine for a range of air-fuel ratios. For these measurements, the magnitude of the integrated heat flux peaked at the stoichiometric air-fuel ratio, with an approximately linear decrease on either side of stoichiometric. Advancing the spark generally increased the magnitude of the integrated heat flux. Evaluation of the Brake Specific Integrated Heat Flux (BSIHF) mitigated these trends, and, the effects of changes in timing were eliminated for some operating conditions Examination of the BSIHF from the compression and expansion stroke showed behavior mimicking the full cycle BSIHF. However, the fraction of the total flux contributed by this portion of the cycle varied greatly from approximately 98% of the total to approximately 75% of the total.

A laboratory-based fuel mixture system capable of delivering a range of fuel/air mixtures has been used to observe the effects of differing mixture characteristics on engine combustion through measurement and analysis of incylinder pressure and exhaust emissions. Fuel air mixtures studied can be classified into four different types: 1) Completely homogeneous fuel/air mixtures, where the fuel has been vaporized and mixed with the air prior to entrance into the normal engine induction system, 2) liquid fuel that is atomized and introduced with the air to the normal engine induction system, 3) liquid fuel that is atomized, and partially prevaporized but the air/fuel charge remains stratified up to introduction to the induction system, and 4) the standard fuel metering system. All tests reported here were conducted under wide open throttle conditions. A four-stroke, spark-ignited, single-cylinder, overhead valve-type engine was used for all tests.

A laboratory-based fuel mixture preparation system has been developed that is capable of generating a wide range of fuel/air mixtures, including production of a premixed, prevaporized homogeneous charge, beginning with liquid gasoline fuel. This system has been developed to allow the study of the effects of fuel/air mixture preparation characteristics on engine combustion, in-cylinder pressure, and exhaust emissions. For the study to be described here, engine combustion behavior and emissions measurements were obtained for a wide range of A/F's with the fuel mixture preparation being produced in one case, by the stock carburetor operating with fixed throttle position, and the other case, with the custom-built system producing a homogeneous mixture (HM.) A four-stroke, spark-ignited, single-cylinder, overhead valve-type utility engine was used for all tests.

The objective of this study was to observe and attempt to understand the effects of equivalence ratio and simulated exhaust gas recirculation (EGR) on the exhaust emissions and performance of a L-head single cylinder utility engine. In order to isolate these effects and limit the confounding influences caused by poor fuel mixture preparation and/or vaporization produced by the carburetor/intake port combination, the engine was operated on a premixed propane/air mixture. To simulate the effects of EGR, a homogeneous mixture of propane, air, and nitrogen was used. Engine measurements were obtained at the operating conditions specified by the California Air Resources Board (CARB) Raw Gas Method Test Procedure. Measurements included exhaust emissions levels of HC, CO, and NOx, and engine pressure data.

Laser Doppler velocimeter results are presented for the mean velocity and turbulence intensity measured during combustion in a research engine. Simultaneously with each LDV measurement, the cylinder pressure and gas state (unburned or burned) were measured so that conditional sampling techniques could be used in the data-averaging procedure. Measurements of the mean velocity component in the direction of flame propagation agree well with a computer simulation of the induced velocities generated by the volume expansion of the burned gases. Mean velocities measured parallel to the flame surface are shown to be complex because a small amount of swirl was present. Conditional sampling on the time of flame arrival at the LDV probe volume revealed a thirty percent cyclic-variation bias error in the turbulence component normal to the flame.

Instantaneous heat flux and flame position were measured on a silicon nitride diesel engine head. Ionization probes and thin-film platinum temperature detectors were applied directly to the head surface. The ionization probes showed that the flame exited the bowl and propagated asymmetrically from the centerline of the combustion bowl. The temperature measurements revealed that average surface temperatures varied with position by more than 200°C. Spatial variations in the temperature swings were also present with large swings resulting from direct combustion effects on heat transfer at locations near the lip of the piston bowl. Peak instantaneous heat flux values varied from 0.3 to 2.0 MW/m2. Five of the seven probe locations exhibited heat transfer rates that were limited due to the combustion rate. At three different positions, the peak heat flux magnitude and phasing were independent of load.

In the first part of this study, a one-dimensional code was used to compare predictions from six different two-equation turbulence models. It is shown that the application of the traditional k-ε models to the viscous-dominated region of the boundary layer can produce errors in both the calculated heat flux and surface friction. A low-Reynolds-number model does not appear to predict similar non-physical effects. A new one-dimensional model, which includes the effect of compression, has been formulated by multiparameter fit to the numerical solution of the energy equation. This model can be used in place of the law-of-the-wall to calculate the surface heat flux. The experiments were performed in a specially-instrumented engine, allowing optical access to the clearance volume. Measurements of heat flux, swirl velocities, and momentum boundary layer thickness were made for different engine speeds.

Experiments were conducted using three different ignition systems on a single cylinder, two-stroke research engine. The ignition systems included a transistorized coil ignition (TCI), a capacitive discharge ignition (CDI), and a commercially available multistrike system (JCI). The sparks produced by each ignition system were characterized using three different types of spark plugs. Spark voltage and current data along with simultaneous high speed images of the spark process in a pressurized chamber were obtained. Each ignition system was evaluated in a two-stroke research engine in terms of cyclic variability, misfire rate, and indicated power produced. In addition, ion sensing was used to detect cycle misfires and various strategies were used to improve engine performance.

A two-stroke diesel engine was outfitted for operation with an electronic solenoid-controlled unit injector and an additional solenoid-controlled air-assisted injector at the inlet ports. Access through an existing pressure transducer port allowed installation of a sapphire window to the combustion chamber with very little disturbance to the combustion system. A coherent fiber optic bundle permitted remote visualization of the combustion event. Use of a gateable intensified solid-state camera permitted imaging at high effective shutter speeds at arbitrary times in the engine cycle. Imaging and two-color temperature and soot concentrations measurements were performed. Imaging results indicated a low-intensity diffuse ignition, away from the injector tip, for both the pilot spray in pilot-main tests and the main spray in the main-only runs. Remnants of the burning pilot spray congregated near the injector tip where a region of flame remained until main injection arrived.