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In-cylinder heat flux, cylinder pressure, and flame arrival and position data were obtained at air fuel ratios ranging from 11 - 16 at 3060 rpm and approximately 80% load. The engine used was a single cylinder, 5 hp, fixed timing, four stroke, overhead valve, air-cooled engine. Methods of mixture preparation include that produced with the stock carburetor, and with a system designed to provide the engine with a homogeneous mixture (HMS). Heat flux was measured using a thermopile device consisting of 300 thermocouple pairs. A thin film platinum RTD was used to measure the temperature at the thermopile and correct for sensitivity of the thermopile output to thermopile temperature. Flame arrival near the sensor was found through the analysis of an ion voltage signal from a probe located next to the heat sensor. An effort was made to identify and account for the variables which influence in-cylinder heat transfer.

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.

Consideration of the heat transfer effects in low-heat-rejection engines has prompted further study into engine heat transfer phenomena. In a previous study, an approximate solution of the one-dimensional energy equation was acquired for transient, compressible, low-Mach number, turbulent boundary layers typical of those found in engines. The current study shows that an approximate solution of the one-dimensional energy equation with arbitrarily-distributed heat release can also be obtained. Using this model, the effects of high temperature walls, combustion, and autoignition on heat transfer can be studied. In the case of high temperature walls, the model predicts the expected behavior unless the quench distance gets very small. For combustion, the reaction must occur close to the wall for a direct effect on the heat transfer to be observed. With autoignition, instantaneous values of heat flux reach levels as high as 6 MW/m2, and oscillate in phase with the pressure wave.

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.

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.

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.

To help understand the fundamental processes involved in direct injection, a research project was conducted using a single-cylinder, two-stroke research engine at a mid-speed, boat load operating condition. A 24 statistical factorial experimental design was applied. Of the factors tested at this operating condition, spray type was the most important factor affecting hydrocarbon emissions, followed by in-cylinder flow-related factors. Injection spray was also most important for nitrogen oxide emissions, carbon monoxide emissions, and efficiency. The dominant mechanism influencing the results was misfire, with other mechanisms present for specific responses.