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Valve deactivation followed by multiple compression-expansion strokes was employed to remove intake-generated turbulence from the bulk gas in an internal combustion engine. The result was a nearly quiescent flowfield that retains the same time-varying geometry and, to a first approximation, thermodynamic conditions as a standard engine. Mass loss, and more significantly heat loss were found to contribute to a reduction in the peak cylinder pressure in the cycle following two compression-expansion strokes. The reduction of the turbulence was verified both computationally and by performing premixed combustion studies. Mixing studies of both liquid spray jets and gaseous jets were performed. Laser-induced fluorescence images of high spatial resolution and signal-to-noise ratio were acquired, allowing the calculation of the two in-plane components of the scalar dissipation rate.

A spectroscopic diagnostic system was designed to study the effects of different engine parameters on the chemiluminescence characteristic of HCCI combustion. The engine parameters studied in this work were intake temperature, fuel delivery method, fueling rate (load), air-fuel ratio, and the effect of partial fuel reforming due to intake charge preheating. At each data point, a set of time-resolved spectra were obtained along with the cylinder pressure and exhaust emissions data. It was determined that different engine parameters affect the ignition timing of HCCI combustion without altering the reaction pathways of the fuel after the combustion has started. The chemiluminescence spectra of HCCI combustion appear as several distinct peaks corresponding to emission from CHO, HCHO, CH, and OH superimposed on top of a CO-O continuum. A strong correlation was found between the chemiluminescence light intensity and the rate of heat release.

Measurements were made of the in-cylinder fluid velocities in a crankcase compression, piston ported two-stroke engine under both motored and fired operating conditions to investigate the effect of combustion on the scavenging process. The engine was modified to allow optical access to the clearance volume and was operated in a burst fired manner, where the firing sequence was controlled by modulating the fuel delivered to the crankcase. The burst fired sequence consisted of 30 cycles, of which there were twelve consecutive cycles where fuel was injected into the crankcase. The engine was operated at a speed of 500 RPM, with a delivery ratio of 0.54, and a fuel-air equivalence ratio of 1.28. Laser Doppler Velocimetry was used to measure two components of the in-cylinder fluid velocity at five locations in the cylinder head cup during the burst fired operation of the engine.

A direct calibration has been performed on laser-induced fluorescence measurements of the oil film in a single cylinder air-cooled research engine by simultaneously measuring the minimum oil film thickness by the capacitance technique. At the minimum oil film thickness the capacitance technique provides an accurate measure of the ring-wall distance, and this value is used as a reference for the photomultiplier voltage, giving a calibration coefficient. This calibration coefficient directly accounts for the effect of temperature on the fluorescent properties of the constituents of the oil which are photoactive. The inability to accurately know the temperature of the oil has limited the utility of off-engine calibration techniques. Data are presented for the engine under motoring conditions at speeds from 800 - 2400 rpm and under varying throttle positions.

The contribution of fuel adsorption in engine oil and its subsequent desorption following combustion to the engine-out hydrocarbon (HC) emissions of a spark-ignited, air-cooled, V-twin utility engine was studied by comparing steady state and cycle-resolved HC emission measurements from operation with a standard full-blend gasoline, and with propane, which has a low solubility in oil. Experiments were performed at two speeds and three loads, and for different mean crankcase pressures. The crankcase pressure was found to impact the HC emissions, presumably through the ringpack mechanism, which was largely unaltered by the different fuels. The average and cycle-resolved HC emissions were found to be in good agreement, both qualitatively and quantitatively, for the two fuels. Further, the two fuels showed the same response to changes in the crankcase pressure. The solubility of propane in the oil is approximately an order of magnitude lower than for gasoline.

Simultaneous fuel distribution images (by shadowgraph and laser-induced fluorescence) and cylinder pressure measurements are reported for a combusting stratified-charge engine with a square cup in the head at 800 RPM and light load for two spark locations with and without swirl. Air-assisted direct-injection occurred from 130°-150° after bottom dead center (ABDC) and ignition was at 148° ABDC. The engine is ported and injection and combustion take place every 6th cycle. The complicated interaction of the squish, fuel/air jet, square cup, spark plug geometry and weak tumble gives rise to a weak crossflow toward the intake side of the engine with no swirl, but toward the exhaust side in the presence of strong swirl, skewing the spray slightly to that side.

The mixing between the flows introduced through different intake valves of a four-valve engine was investigated optically. Each valve was fed from a different intake system, and the relative sensitivity to different flow parameters (manipulated with the goal of enhancing the bulk in-cylinder stratification) was investigated. Flow manipulation was achieved in three primary ways: modifying the intake runner geometry upstream of the head, introducing flow-directing baffles into the intake port, and attaching flow break-down screens to the intake valves. The relative merits of each flow manipulation method was evaluated using planar laser-induced fluorescence (PLIF) of 3-pentanone, which was introduced to the engine through only one intake valve. Images were acquired from 315° bTDC through 45° bTDC, and the level of in-cylinder stratification was evaluated on an ensemble and cycle-to-cycle basis using a novel column-based probability distribution function (PDF) contour plot.

Results of experiments performed on a direct-injection two-stroke engine using an air-assisted injector are presented. Pressure measurements in both the engine cylinder and injector body coupled with backlit photographs of the spray provide a qualitative understanding of the spray dynamics from the oscillating poppet system. The temporal evolution of the spatial distribution of both liquid and vapor fuel were measured within the cylinder using the Exciplex technique with a new dopant which is suitable for tracing gasoline. However, a temperature dependence of the vapor phase fluorescence was found that limits the direct quantitative interpretation of the images. Investigation of a number of realizations of the vapor field at a time typical of ignition for a stratified-charge engine shows a high degree of cycle to cycle variability with some cycles exhibiting a high level of charge stratification.

Particulate emission measurements were performed on a direct-injection two-stroke engine that employed a lost-oil lubricating system. The particulate emissions were sampled using a partial-flow dilution system. Particulate mass emission rates were measured using a tapered element microbalance (TEOM), and the results were found to compare favorably with gravimetric tests performed simultaneously. The size distribution was measured using a scanning mobility particle sizer (SMPS), and the cumulative mass from the measured size distribution was found to agree well with the values measured by the TEOM. The particulate mass emission were found to be dominated by particulate matter derived from the engine oil. The particulate emissions were found to decrease substantially as the oil flow to the engine was reduced from the baseline case of 1:100 (oil-to-fuel mass ratio).

Planar instantaneous fuel concentration measurements were made by laser-induced fluorescence of 3-pentanone in the spark gap just prior to ignition in a direct-injection spark-ignition engine operating at a light load, highly stratified condition. The distribution of the average equivalence ratio in a circle of 1.9 mm diameter centered on the spark plug showed that a large fraction of the cycles had an equivalence ratio below the lean limit, yet acceptable combustion was achieved in those cycles. Further, weak correlation was found between the local average equivalence ratio near the spark plug and the time required to achieved a 100 kPa pressure rise above the motoring pressure, as well as other parameters which characterize the early stages of combustion. The cause for this behavior is assessed to be mixture motion during the spark discharge which continually convects fresh mixture through the spark gap during breakdown.

An axisymmetric one-dimensional finite difference model has been developed to investigate the optimization of external fins on a cylindrical tube with a non-uniform heat flux applied to the inner surface. The heat flux boundary condition applied to the inner surface was determined from detailed 3-dimensional calculations using the KIVA code. The external convective boundary condition was determined from published correlations. This model encompasses the basic geometry of an air-cooled engine cylinder. The model was computationally efficient and allowed for the optimization of the fin length of each fin and its location. A genetic algorithm optimization procedure was utilized. The results show that optimum usage of material is obtained from fins of comparable length distributed over the entire outer cylinder, in spite of the concentrated heat flux at the upper end of the cylinder. The results indicate the important role of axial conduction in the thermal energy balance of this system.

To experimentally investigate evaporating sprays under conditions experienced in high speed direct-injection (HSDI) diesel engines, the exciplex LIF technique with the TMPD / naphthalene dopant system was applied in a combustion-type constant-volume spray chamber. The chamber allows spark ignition of a slightly rich C2H2-air mixture, and subsequent fuel injection into the high temperature and pressure products. A detailed set of calibration experiments has been performed in order to quantify the TMPD fluorescence signal. It has been demonstrated that the TMPD fluorescence intensity is directly proportional to concentration, is independent of the chamber pressure, and was not sensitive to quenching by either water vapor or carbon dioxide. Therefore, the temperature dependence of the TMPD fluorescence was the only correction factor required for quantitative measurements. Using a dual heated-jet experiment, the temperature dependence of TMPD fluorescence up to 1000 K was measured.

The residual gas fraction was measured in an air-cooled single-cylinder utility engine by directly sampling the trapped cylinder charge during a programmed misfire. Tests were performed for a range of fuel mixture preparation systems, cam timings, ignition timings, engine speeds and engine loads. The residual fraction was found to be relatively insensitive to the fuel mixture preparation system, but was, to a moderate degree, sensitive to the ignition timing. The residual fraction was found to be strongly affected by the amount of valve overlap and engine speed. The effects of engine speed and ignition timing were, in part, due to the in-cylinder conditions at EVO, with lower temperatures favoring higher residual fractions. The data were compared to existing literature models, all of which were found to be lacking.

The effect of the ring pack storage mechanism on the hydrocarbon (HC) emissions from an air-cooled utility engine has been studied using a simplified ring pack model. Tests were performed for a range of engine load, two engine speeds, varied air-fuel ratio and with a fixed ignition timing using a homogeneous, pre-vaporized fuel mixture system. The integrated mass of HC leaving the crevices from the end of combustion (the crank angle that the cumulative burn fraction reached 90%) to exhaust valve closing was taken to represent the potential contribution of the ring pack to the overall HC emissions; post-oxidation in the cylinder will consume some of this mass. Time-resolved exhaust HC concentration measurements were also performed, and the instantaneous exhaust HC mass flow rate was determined using the measured exhaust and cylinder pressure.

The role of mixture stratification on combustion rate has been investigated in a constant volume combustion vessel in which mixtures of different equivalence ratios can be added in a spatially and temporally controlled fashion. The experiments were performed in a regime of low fluid motion to avoid the complicating effects of turbulence generated by the injection of different masses of fluid. Different mixture combinations were investigated while maintaining a constant overall equivalence ratio and initial pressure. The results indicate that the highest combustion rate for an overall lean mixture is obtained when all of the fuel is contained in a stoichiometric mixture in the vicinity of the ignition source. This is the result of the high burning velocity of these mixtures, and the complete oxidation which releases the full chemical energy.

Time-resolved measurements were made of the gas composition at the exhaust port of a direct-injection two-stroke engine operating at 2000 rpm and an air-fuel ratio of 30:1. A high-speed sampling valve capable of 1.0 ms (12 CAD) time resolution was used to collect samples 1 cm downstream of the exhaust port of the engine. The time-resolved NOx, CO2 and CO concentrations decreased continuously during the scavenging process due to the dilution by short-circuited air. The hydrocarbon emissions, however, behaved significantly differently from the other species. At the time of exhaust port opening the concentration was low, it reached a maximum value by BDC, then decreased slightly in the latter part of the scavenging event. The dilution rates calculated for the hydrocarbon data gave negative values, indicating that there was a significant production of hydrocarbons during the gas exchange period.