Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xii, 153 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 133-135).

Non-contact ignition of TIG welding arcs has been studied. The variation of dc voltage with dc current of combined acdc discharges indicated that an ac-dominated discharge, a dc-dominated discharge and a transition region exist during the initial current rise after breakdown from cold. These measurements enabled the conditions for reliable ignition of dc arcs using a continuous sinusoidal hf source to be predicted. The minimum current to sustain a cold arc and the time taken to reach the steady-state were investigated using a novel capacitor discharge supply. The results showed that to initiate a3 mm TIG welding arc from cold supplied by a power supply with an open circuit voltage of 80 V, a minimum current of about 0.9 A may be required and the time taken for the arc to reach the steady-state may take several hundred milliseconds. The results of investigations on combined ac-dc discharges, minimum current to sustain a cold arc and the time taken to reach the steady-state indicated that for safe, interference-free and reliable non-contact arc ignition, a continuous sinusoidal hf supply was the best method. A high voltage (about 3 kV) and high current (about 1 A) were required simultaneously to initiate a3 mm TIG arc from cold. A single continuous sinusoidal hf supply required an ignition power of the order of 1.35 kW which was not feasible. An arc ignition method using two continuous sinusoidal hf supplies has been devised which provides safe, interference-free and reliable arc ignition, and which requires less than 75% of the output power of a single continuous sinusoidal hf system. A solid-state hf ignition system based on the new method was designed and constructed.

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The effects of swirl and spark location on combustion duration were studied in a constant volume cylindrical chamber of length-to-diameter ratio of 0.5. A chemically balanced methane-air mixture was swirled up to 628 radians per second by tangential injection. The chamber was closed by a valve before ignition by a spark gap of variable location and electrode geometry. The burning duration, indicated by repeated measurements of combustion pressure rise, was found to be a strong function of swirl intensity and spark location. Increased swirl resulted in decreased burning duration; mid-radius ignition location combined with high swirl resulted in the shortest combustion durations. Spark gap was found to have an important effect on the standard deviation of the burning duration, especially with high swirl. Various "flame holders" were installed to achieve shorter burning durations and lower cyclic variation. Results indicated that the best ignition source geometry was an unshielded, low-drag probe. This gave the least burning durations and the least cyclic variation at the higher swirl values. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Current diesel technologies involve a broad spectrum of combustion regimes. Previous diesel combustion models either lack the universality across various combustion regimes or suffer computational cost. This dissertation discusses the development of a phenomenological framework to identify and understand key in-cylinder processes that influence the overall performance of a compression ignition engine. The first part of this research is focused on understanding the ignition delay (ID) of diesel fuel in a pilot-ignited partially premixed, low temperature natural gas (NG) combustion engine. Lean premixed low temperature NG combustion is achieved by using small pilot diesel sprays (2-3% of total fuel energy) injected during early compression stroke (about 60° BTDC). Modeling ignition delay at advanced pilot injection timings (50°-60°BTDC) presents unique challenges. In this study, single component droplet evaporation model in conjunction with the Shell hydrocarbon autoignition (SAI) model is used to obtain ignition delay predictions of pilot diesel over a wide range of injection timings (20°-60° BTDC). Detailed sensitivity analysis of several SAI model parameters revealed that the model parameter Aq, which influences chain initiation reactions, was most important to predict ignition delays at very lean equivalence ratios. Additional studies performed to ascertain critical model parameters revealed that ignition delay was particularly sensitive to intake manifold temperature over the range of injection timings investigated. Finally, the validated SAI model was used to predict ignition delays of pilot diesel fuel at various exhaust gas recirculation (EGR) substitutions, intake manifold temperatures and engine loads (bmep = 6 bar and 3 bar, respectively). The second part of this research involved the development of a phenomenological simulation of diesel/biodiesel combustion, which included sub-models for diesel spray entrainment, evaporation, ignition and premixed and mixing-controlled combustion. In the simulation, the cylinder contents consisted of an unburned zone, packet zones, and a burned zone. The simulation, after appropriate calibration, was capable of predicting cylinder pressure and heat release rates at different engine load conditions over the injection timing range of 0°BTDC to 10°BTDC. The total number of packets, droplet evaporation rates, air entrainment rates; ignition delay and premixed/mixing-controlled reaction rate parameters had a profound influence on combustion predictions.

The goal of this study is to assess conventional and low temperature dual fuel combustion in light- and heavy-duty multi-cylinder compression ignition engines in terms of combustion characterization, performance, and emissions. First, a light-duty compression ignition engine is converted to a dual fuel engine and instrumented for in-cylinder pressure measurements. The primary fuels, methane and propane, are each introduced into the system by means of fumigation before the turbocharger, ensuring the airuel composition is well-mixed. Experiments are performed at 2.5, 5, 7.5, and 10 bar BMEP at an engine speed of 1800 RPM. Heat release analyses reveal that the ignition delay and subsequent combustion processes are dependent on the primary fuel type and concentration, pilot quantity, and loading condition. At low load, diesel-ignited propane yields longer ignition delay periods than diesel-ignited methane, while at high load the reactivity of propane is more pronounced, leading to shorter ignition delays. At high load (BMEP = 10 bar), the rapid heat release associated with diesel-ignited propane appears to occur even before pilot injection, possibly indicating auto-ignition of the propane-air mixture. Next, a modern, heavy-duty compression ignition engine is commissioned with an open architecture controller and instrumented for in-cylinder pressure measurements. Initial diesel-ignited propane dual fuel experiments (fumigated before the turbocharger) at 1500 RPM reveal that the maximum percent energy substitution (PES) of propane is limited to 86, 60, 33, and 25 percent at 5, 10, 15, and 20 bar BMEP, respectively. Fueling strategy, injection strategy, exhaust gas recirculation (EGR) rate, and intake boost pressure are varied in order to maximize the PES of propane at 10 bar BMEP, which increases from 60 PES to 80 PES of propane. Finally, diesel-ignited propane dual fuel low temperature combustion (LTC) is implemented using early injection timings (50 DBTDC) at 5 bar BMEP. A sweep of injection timings from 10 DBTDC to 50 DBTDC reveals the transition from conventional to low temperature dual fuel combustion, indicated by ultra-low NOx and smoke emissions. Optimization of the dual fuel LTC concept yields less than 0.02 g/kW-hr NOx and 0.06 FSN smoke at 93 PES of propane.

The Design Institute for Physical Properties (DIPPR) maintains the DIPPR 801 database for the American Institute of Chemical Engineers. Autoignition temperature (AIT) is one of the properties included in the database and is the focus of this work including improvement of the overall state of AIT in the database. Phenomena related to AIT as well as the relevant literature are reviewed. Likewise, the database is presented to respond to significant misuse of the DIPPR 801 database in the literature. The database is evaluated, respecting AIT, as a whole to show where improvement is needed. An experimental study of minimum autoignition temperatures reveals unexpected behavior of pure n-alkanes not predicted by current current phenomenological understanding of autoignition processes. Measurements show an increase at C16 and a dramatic and previously unexplained step increase between C25 and C26. Experimental modifications are presented to compensate the effect of altitude. Measured values for several n-alkanes are reported and compared to the literature. Other ignition experiments and decomposition measurements using differential scanning calorimetry are also reported and examined to elucidate the unexpected trends. Explanations for these trends are proposed. Finally, the implications of this for trends in other chemical families are discussed. A comprehensive examination of AIT family trends reveals variation from the n-alkane family trend. Measured AIT values are presented and discussed. Evaluated AIT values are recommended for several single-group chemical families. Phenomenological explanations for observed differences are proposed and discussed along with the broader implications for these trends. Methods for predicting autoignition temperatures (AIT) have been historically inaccurate and are rarely based on the underlying physical phenomena leading to observed AIT. An improved method for predicting AIT based on the method by the late Dr. William H. Seaton is presented and discussed. The method of Seaton is described in detail. An evaluated data set is used to regress new parameters for the Seaton method parameters. Improvements to Seaton's model and underlying principles are presented and discussed. Finally, an improved AIT prediction method is presented and recommended.

While the operating conditions are the main factors that influence engine design, it is important to understand ignition in any potential design to ensure reliable light-ability. Ignition probability maps can be generated, either experimentally or numerically, to inform design of ignition mechanisms. Recent models have been proposed to estimate ignition probability using non-reacting computational fluid dynamic (CFD) simulations. These models have not been applied to scramjet flame holding cavities. A qualitative model is described that uses tracer particles that probe CFD data and are removed when the conditions are adverse to flame survivability. The parameters that influence ignition are investigated by changing the criteria to define the flammable region. A quantitative model is developed based on a frozen flow assumption and the assumption that a region exists such that the geometry can be considered ignited if a flame is able to be propagated to this region. A virtual flame begin in this "ignition region" and propagates backwards in time to all the cells that would be successful if forward time was used. This model is implemented with an Eulerian and a Lagrangian scheme (IMIT and LIMIT, respectively). The results are compared to a previous coldlow model, I-CRIT-LES, on a low speed, lifted jet geometry and a supersonic cavity geometry. The models generate similar results on the jet case. A diffusion-like effect in IMIT allows the virtual flame to propagate over streamlines and into cells that the flame should not be able to reach. Thus the cavity ignition map generated by IMIT overpredicts ignition. The diffusion-like problem is solved by using particles following the streamlines. Therefore, LIMIT results match the qualitative experimental data in the cavity better than the other models.

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