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Mass-related properties of four atomizers were estimated with the use of a mechanical transient patternator. The properties presented on a temporal and spatial basis are the axial liquid mass flux, liquid fuel to air ratio, and liquid axial velocity. The data are presented in two formats. The first format consists of the mass-related properties that occurred radially between two planes positioned 2.0 cm and 2.25 cm along the atomizer axis. A second format consists of interpolated contour plots of the axial liquid mass flux for all of the spray systems studied. The atomizers used in the study consisted of three liquid-only high-pressure systems and one air-assist system. Two of the liquid-only high-pressure systems and the air - assist system were operated with a volumetric delivery of 20 mm3 per injection while injecting into ambient conditions. A third liquid-only high-pressure system was operated with a delivery of 15 mm3 per injection.

This study investigates the relationship between intake port geometry, flame position and stability, and combustion rate and emissions in an air-cooled four-stroke engine where three intake ports of differing geometry have been tested. In particular, the production intake port geometry, and directed and helical intake port geometries were tested. It was a specific intent of this study to investigate the interaction between inlet port geometry, equivalence ratio and ignition timing, without interference from mixture preparation effects. Thus all tests were performed using a homogeneous mixture of propane and air. Significant differences in combustion stability, flame position and stability, burn rate and emissions were observed. For example, the flow induced by the helical port, which should be characterized by a dominant swirl motion, resulted in stabile, asymmetric flames at many of the operating conditions studied.

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.

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.

To study the near-wall velocity characteristics, gas velocity measurements have been made near the cylinder head of a motored four-stroke engine using Laser Doppler Velocimetry (LDV), and near-wall flow characteristics have been observed in three different two-stroke geometries using Particle Image Velocimetry (PIV) and particle photographs. The results of these studies show that the behavior of the fluid near the wall depends on the engine intake geometry, combustion chamber geometry, and operating condition. The near-wall velocity characteristics tend to be one of two forms. In one form, the behavior is one of an extended region of low momentum fluid, where an imbalance in radial pressure gradient forces and centripetal forces exists because of the combined effects of fluid rotation and shear. Such a flow can be seen in engines with gas exchange systems that do not promote scrubbing of the wall, and in cylinder geometry that does not cause flow normal to the wall.

Particle image velocimetry (PIV) was used to study the velocity field characteristics in motored two-stroke ported engines. Measurements of the two-dimensional velocity field were made at the midplane of the clearance volume for bowl-in-head and disk combustion chamber geometries. Measurements were also obtained for two scavenging port geometries, i.e. a loop-scavenged engine and a loop-scavenged engine with a boost port. Results from this study show that in-cylinder geometry had a dominant effect on the flow structure observed at TDC. For example, with the boost-port scavenging crankcase, the disk-shaped chamber showed a turbulent flow-field at TDC with little large scale motion. In contrast, addition of a squish flow from the bowl-in-head geometry produced an organized cross-chamber flow. The addition of a boost port also changed the flow structure markedly. A large-scale swirl flow was observed in the engine that did not contain a boost port.

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.

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.

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.

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.

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. Factorial experiments were designed in order to quantify, in a statistically representative manner, the effects of pilot (or ‘split’) and port auxiliary injection on main fuel combustion. Results indicated that interactions between experimental parameters (such as between pilot fuel quantity and pilot-to-main spacing), as well as main effects are important in analyzing auxiliary fuel injection. The bulk gas temperature at main injection was determined primarily by the experimental parameters acting independently of one another, which is a case where main effects only are important. Conversely, analysis of indicated specific fuel consumption and peak cylinder pressure involved interactions of the experimental parameters in both cases.

This paper describes the development of diagnostics and testing methods for the characterization of carburetor exit flow conditions in small utility engines. These diagnostics include: 1) Three different methods of acquiring intake flow photographs. 2) A technique to measure the thickness of the fuel film running along the bottom of the intake manifold using the electrical properties of the fuel. 3) A system for measuring the A/F ratio across the carburetor exit using a heated catalyst to oxidize the sampled mixture and a wide-range oxygen sensor to determine the A/F of the reacted sample.

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.

Control of the flow of thermal energy in an air-cooled engine is important to the overall performance of the engine because of potential effects on engine performance, durability, design, and emissions. A methodology is being developed for the assessment of thermal flows in air-cooled engines, which includes the use of cycle simulation and in-cylinder heat flux measurements. The mechanism for the combination of cycle simulation, the measurement of in-cylinder heat flux and wall temperatures, and comparison of predicted and measured heat flux in the methodology is presented. The methodology consists of both simulation and experimental phases. To begin, a one-dimensional gas dynamics code (WAVE) has been used in conjunction with a detailed in-cylinder flow and combustion model (IRIS) in order to simulate engine operation in a variety of operating conditions. The methods used to apply the model to the air-cooled engine case are described in detail.

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.

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.

This paper reports on the investigation of injection pressure upon the droplet behavior in transient diesel sprays. Phase/Doppler results for a Diesel spray with a maximum fuel injection line pressure of 105 MPa are compared with previously acquired droplet size and velocity measurements for a Diesel spray with an injection pressure of 21 MPa. All measurements reported here were made in atmospheric conditions at a position near the nozzle. It is shown in these results that the droplet velocity and size profiles do maintain similarity despite the substantial change in injection pressure. Specific characteristics, for example, the appearance of subtle waves in the time-dependent spray data, are present in both data sets. Comparison of the measured droplet velocities and diameters with Weber number based stability criteria shows that increased injection pressure produces a higher percentage of droplets that are likely to breakup.

Previous experiments using an air-assisted spray in a two-stroke direct-injected engine demonstrated a significant improvement in combustion stability at part-load conditions when a wide injection spray was used. It was hypothesized that the decrease in variability was due to the spray following the combustion chamber wall, making it less affected by variations in the in-cylinder gas flows. For this study, experiments were conducted to investigate engine spray combustion for cases where engine performance was not dominated by cyclic variation. Combustion and emission performance data was collected for a wide range of injection timings at several speed/load conditions. Experimental data for combustion shows that combustion stability is relatively unaffected by injection timing changes over a 40 to 100 degree window, and tolerant to spark gap projections over a range of 0.7 to 5.2 mm, depending on operating conditions.

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.