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The post-flame oxidation of unburned hydrocarbons released from the ring-pack crevice was investigated for a small, air-cooled, spark-ignition utility engine. Spark timing sweeps were performed at 50, 75 and 100% load and speeds of 1800, 2400 and 3060 RPM while operating at a 12:1 air-fuel ratio, which is typical for these engines. A global HC consumption rate (GCR) was introduced based on the temporal profile of the mass released from the ring pack; the mass release after CA90 and up to the point where the remainder of the ring pack HC mass is equal to the exhaust HC level was taken as the mass oxidized, and a rate was defined based on this mass and the corresponding crank angle period over which this took place. For all conditions tested, the GCR varied with the spark timing; advanced spark timing gave higher GCR.

Comparison of particulate size distribution measurements from different combustion strategies was conducted with a four-stroke single-cylinder diesel engine. Measurements were performed at four different load-speed points with matched combustion phasing. Particle size distributions were measured using a scanning mobility particle sizer (SMPS). To study the influence of volatile particles, measurements were performed with and without a volatile particle remover (thermodenuder) at low and high dilution ratios. The use of a single testing platform enables quantitative comparison between combustion strategies since background sources of particulate are held constant. A large number of volatile particles were present under low dilution ratio sample conditions for most of the operating conditions. To avoid the impact of volatile particles, comparisons were made based on the high dilution ratio measurements with the thermodenuder.

An experimental investigation was conducted to explore the impact in-cylinder pressure oscillations have on piston heat transfer. Two fast-response surface thermocouples embedded in the piston top measured transient temperature and a commercial wireless telemetry system was used to transmit thermocouple signals from the moving piston. Measurements were made in a light-duty single-cylinder research engine operated under low temperature combustion regimes including Homogeneous Charge Compression Ignition (HCCI) and Reactivity Controlled Compression Ignition (RCCI) and Conventional Diesel (CDC). The HCCI data showed a correlated trend of higher heat transfer with increased pressure oscillation strength, while the RCCI and CDC data did not. An extensive HCCI data set was acquired. The heat transfer rate - when corrected for differences in cylinder pressure and gas temperature - was found to positively correlate with increased pressure oscillations.

The effect of direct-injected fuel on particle size distributions (PSDs) of particulate matter emitted from dual-fuel combustion strategies was investigated. The PSD data were acquired from a light-duty single-cylinder diesel engine operated using conventional diesel combustion (CDC) and two diesel/natural gas dual-fuel combustion strategies. Three different direct-injection (DI) fuels (diesel, 2,6,10-trimethyldodecane, and a primary reference fuel blend) and two different injector nozzles were studied. The DI fuels were chosen to have similar energy and ignition characteristics (heat of combustion and cetane number) but different physical and chemical properties (volatility, aromatics %, viscosity, density). The two nozzles (with different orifice diameter and spray angle) allowed a wide range in DI fuel quantity for the dual-fuel combustion strategies.

High resolution planar laser-induced fluorescence (PLIF) measurements were performed in an optically accessible internal combustion (IC) engine to investigate the behavior of scalar dissipation and the fine-scale structures of the turbulent scalar field. The fluorescent tracer fluorobenzene was doped into one of the two intake streams and nitrogen was used as the carrier gas to permit high signal-to-noise ratio fluorescence measurements without oxygen quenching effects. The resulting two-dimensional images allowed for an analysis of the structural detail of the scalar and scalar dissipation fields defined by the mixing of the two adjacent intake streams. High levels of scalar dissipation were found to be located within convoluted, sheet-like structures in accordance with previous studies. The fluorescence data, which were acquired during the intake stroke, were also used to examine the scalar energy and dissipation spectra.

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 ability to make fully resolved turbulent scalar field measurements has been demonstrated in an internal combustion engine using one-dimensional fluorobenzene fluorescence measurements. Data were acquired during the intake stroke in a motored engine that had been modified such that each intake valve was fed independently, and one of the two intake streams was seeded with the fluorescent tracer. The scalar energy spectra displayed a significant inertial subrange that had a −5/3 wavenumber power dependence. The scalar dissipation spectra were found to extend in the high-wavenumber regime, to where the magnitude was more than two decades below the peak value, which indicates that for all practical purposes the measurements faithfully represent all of the scalar dissipation in the flow.

The effect of the presence of liquid fuel in the intake manifold on unburned hydrocarbon (HC) emissions of a spark-ignited, carbureted, air-cooled V-twin engine was studied. To isolate liquid fuel effects due to the poor atomization and vaporization of the fuel when using a carburetor, a specially conditioned homogeneous, pre-vaporized mixture system was developed. The homogeneous mixture system (HMS) consisted of an air assisted fuel injection system located approximately 1 meter upstream of the intake valves. The results from carburetor and HMS are compared. To verify the existence of liquid fuel in the manifold, and to obtain an estimate of its mass, a carburetor-mounted liquid fuel injection (CMLFI) system was also implemented. The conditions tested were 10% and 25% load at 1750 RPM, and 25%, 50%, and 100% at 3060 RPM. The results of the comparison show that the liquid fuel in the intake manifold does not have a statistically significant influence on the averaged HC emissions.

The effects of residual gas mixing were studied in a single-cylinder, air-cooled utility engine using both external exhaust gas recirculation (EGR) and internal residual retention. EGR was introduced far upstream of the throttle to ensure proper mixing. Internal residual was changed by varying the length of the valve overlap period. EGR was measured in the intake system; the total in-cylinder diluent was directly measured using a skip-fire, cylinder dumping technique. A sweep of diluent fraction was performed at different engine speeds, engine loads, fuel mixture preparation systems, and ignition timings. An optimum level of diluent, where the combined hydrocarbon and NOx emissions were minimal, was found to exist for each operating condition. Higher levels of diluent, either through internal retention or external recirculation, caused the combined emissions to increase.

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.

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 effects of augmented mixing through the use of an auxiliary gas injection (AGI) were investigated in a direct-injection gasoline engine operated at a 22:1 overall air-fuel ratio, but with retarded injection timing such that the combustion was occurring in a locally rich mixture as evident by the elevated CO emissions. Two AGI gas compositions, nitrogen and air, were utilized, the gas supply temperature was ambient, and a wide range of AGI timings were investigated. The injected mass was less than 10% of the total chamber mass. The injection of nitrogen during the latter portion of the heat release phase resulted in a 25% reduction in the CO emissions. This reduction is considered to be the result of the increased mixing rate of the rich combustion products with the available excess air during a time when the temperatures are high enough to promote rapid oxidation.

A simple model to simulate cycle-by-cycle variation that is suitable for use in Monte-Carlo approaches has been developed and validated with a wide range of experimental data. The model is intended to be diagnostic rather than predictive in nature, with a goal of providing realistic in-cylinder pressures. The individual-cycle cumulative rate of heat release was curve fit with a four-parameter Wiebe function. It was found that the distribution of the Wiebe b-parameter was quite small, so its value was obtained from the ensemble-averaged condition. The remaining three Wiebe function parameters, θig, θcomb and m were found to be distributed over a moderate range, and were linearly correlated to each other. Using the cumulative density function of θig, and the linear fit of θcomb and m to θig, with a random component added, a Monte-Carlo scheme was developed.

The objective of this work is to compare and contrast standard metrics that are used to quantify engine knock phenomena. Several methods found in the literature were investigated, and the fundamental bases for the methods were elucidated. A new knock onset metric was developed and compared to the commonly used threshold value exceeded metric. The standard knock intensity metrics were categorized based on the underlying signal (pressure, heat release), domain of analysis (time or frequency), and the calculation method (single-valued or integral). Each category was evaluated based on the fundamental advantages and disadvantages of that category. Single-value methods were found to be inadequate because they are prone to biases due to wave interference and beating. Heat release-based metrics were found to be redundant and be based on flawed assumptions.

The light-medium load operating range (4-7 bar net IMEP) presents many challenges for advanced low temperature combustion strategies utilizing low cetane fuels (specifically, 87-octane gasoline) in light-duty, high-speed engines. The overly lean overall air-fuel ratio (Φ≺0.4) sometimes requires unrealistically high inlet temperatures and/or high inlet boost conditions to initiate autoignition at engine speeds in excess of 1500 RPM. The objective of this work is to identify and quantify the effects of variation in input parameters on overall engine operation. Input parameters including inlet temperature, inlet pressure, injection timing/duration, injection pressure, and engine speed were varied in a ~0.5L single-cylinder engine based on a production General Motors 1.9L 4-cylinder high-speed diesel engine.

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.

Schlieren visualization was performed to investigate hydrogen injection into a quiescent chamber. The injection pressures investigated were 52 and 104 bar, and the chamber density ranged from 1.15 to 12.8 kg/m3, giving rise to underexpanded jets for all conditions. The expansion waves outside the nozzle were clearly visible with hydrogen, and the effect was confirmed with studies of nitrogen injected into a nitrogen environment. The distance between the expansion wave fronts was found to scale directly with the ratio of the exit pressure to the chamber pressure. The jet tip penetration rate was measured and was found to increase with injection pressure, and decrease with chamber density as expected. A mass- and momentum-preserving scheme was developed to relate the underexpanded jet to a subsonic jet of larger diameter.

High-resolution planar laser-induced fluorescence (PLIF) measurements were performed on the scalar field in an optical engine. The measurements were of sufficient resolution to fully resolve all of the length scales of the flow field through the full cycle. The scalar dissipation spectrum was calculated, and by fitting the results to a model turbulent spectrum the Batchelor scale of the turbulent flow was estimated. The scalar inhomogeneity was introduced by a low-momentum gas jet injection. A consistent trend was observed in all data; the Batchelor scale showed a minimum value at top dead center (TDC) and was nearly symmetric about TDC. Increasing the engine speed resulted in a decrease of the Batchelor scale, and the presence of a shroud on the intake valve, which increased the turbulence intensity, also reduced the Batchelor scale. The effect of the shrouded valve was less significant compared to the effect of engine speed.

High frame rate particle image velocimetry (PIV) measurements were performed in a motored engine at speeds of 600 and 1200 rpm under both throttled and unthrottled conditions. Data were acquired at 1 kHz throughout the entire engine cycle, allowing the temporal and spatial evolution of the flow to be observed. The data were both temporally and spatially filtered to study the turbulent flowfield. The mean (over the spatial domain) kinetic energy of the high-pass filtered data, and its evolution with cutoff frequency or length, was used to quantitatively compare differences between operating conditions and different cycles at the same condition. The difference in fluctuation kinetic energy, when normalized, between different operating conditions was found to be comparable to the difference between cycles. A comparison between spatially and temporally filtered data at the same level of fluctuation kinetic energy was performed.

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).