The Homogeneous Charge Compression Ignition (HCCI) engine is a promising engine concept that emits low concentrations of NOx and particulates and still has a high efficiency. Since the charge is auto-ignited, the auto-ignition quality of the fuel is of major importance. It has been shown in several studies that neither of the classical measures of auto-ignition quality of gasoline-like fuels, RON and MON, can alone describe this in all conditions in HCCI combustion. However, even in such cases it is possible to combine RON and MON into an octane index, OI, that describes the auto-ignition quality well in most conditions. The octane numbers are combined into the OI with the variable K according to the following equation: OI = (1-K)RON + K MON = RON – K S The OI of a sensitive fuel is the equivalent of the octane number of a primary reference fuel with the same resistance to auto-ignition in the tested condition. The K-value is dependent on the temperature and pressure history. A generic parameter Tcomp15, the temperature at 15 bar during the compression, was introduced to describe the temperature and pressure history. It was found that the K-value increases with increasing Tcomp15 and two linear equations have been suggested to describe this relationship. At high or low Tcomp15 it has been found that the sensitivity of the fuel octane quality on combustion phasing is small and the auto-ignition quality defined by the OI scale does no longer play a big role. NO affects the combustion phasing of gasoline-like fuels. This effect is most significant at low concentration where it advances the combustion phasing considerably. At higher conditions its influence is different for different fuels. A sensitive fuel is considered a good HCCI fuel since its OI changes in the same direction as the octane requirement of the engine, which would make the engine management easier. It is also likely that a sensitive fuel will enable a wider operating range. The auto-ignition quality of diesel-like fuels was studied in tests with three different strategies of mixture formation. In these tests it was found that the ignition delay increased with lower cetane number and that the cetane number described the auto-ignition quality well, even for fuels of significantly different physical properties. The experiments were, however, made at a limited range of operating conditions and low load. A good diesel-like HCCI fuel should be easy to vaporize to facilitate homogeneity. It should have a high resistance to auto-ignition, not necessarily the highest, one that allows both high and low loads at a given compression ratio. Finally, it should also function well with the injection system without a significant decrease in injection system life length. / QC 20100917

Hydrogen Assisted Jet Ignition (HAJI) is an advanced ignition process that allows ignition of ultra-lean mixtures in an otherwise standard gasoline fuelled spark ignition engine. Under typical operating conditions, a small amount of H2 (~ 2 % ofthe main fuel energy or roughly the equivalent of 1 g/km of H2) is injected just before ignition in the region of the spark plug. By locating the spark plug in a small prechamber (less than 1 % of the clearance volume) and by employing a H2 rich mixture, the content of the prechamber is plentiful in the active species that form radicals H and OH on decomposition and has a relatively high energy level compared to the lean main chamber contents. Thus, the vigorous jets of chemically active combustion products that issue through orifices, which connect to the main chamber, burn the main charge rapidly and with almost no combustion variability (less than 2% coefficient of variation in IMEP even at λ = 2.5). / The benefits from the low temperature combustion at λ = 2 and leaner are that almost zero NOx is formed and there is an improvement in thermal efficiency. Efficiency improvements are a result of the elimination of dissociation, such as CO2 to CO, which normally occurs at high temperatures, together with reduced throttling losses to maintain the same road power. It is even possible to run the engine in an entirely unthrottled mode, but at λ = 5. / Although only a small amount of H2 is required for the HAJI process, it is difficult to both refuel H2 and store it onboard. In order to overcome these obstacles, the viability of a variety of more convenient fuels was experimentally assessed based on criteria such as combustion stability, lean limit and emission levels. The prechamber fuels tested were liquefied petroleum gas (LPG), natural gas, reformed gasoline and carbon monoxide. Additionally, LPG was employed as the main fuel in conjunction with H2 or LPG in the prechamber. Furthermore, the effects of HAJI operation under sufficient exhaust gas recirculation to allow stoichiometric fuel-air supply, thus permitting three-way catalyst application were also examined. / In addition to experiments, prechamber and main chamber flame propagation modeling was completed to examine the effects of each prechamber fuel on the ignition of the main fuel, which consisted of either LPG or gasoline. The modeling and experimental results offered similar trends, with the modeling results giving insight into the physiochemical process by which main fuel combustion is initiated in the HAJI process. / Both the modeling and experimental results indicate that the level of ignition enhancement provided by HAJI is highly dependent on the generation of chemical species and not solely on the energy content of the prechamber fuel. Although H2 was found to be the most effective fuel, in a study of a very light load condition (70 kPa MAP) especially when running in the ultra-lean region, the alternative fuels were effective at running between λ = 2-2.5 with almost zero NOx formation. These lean limits are about twice the value possible with spark ignition (λ = 1.25) in this engine at similar load conditions. In addition, the LPG results are very encouraging as they offer the possibility of a HAJI like system where a commercially available fuel is used as both the main and prechamber fuel, while providing thermal efficiency improvements over stoichiometric operation and meeting current NOx emission standards.

Thesis (Ph.D.)--North Carolina State University. / Includes vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 331-360). Also available on the World Wide Web.

Thesis (M.S.C.E.)--University of Toledo, 2008. / Typescript. "Submitted as partial fulfillments of the requirements for The Master of Science in Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 81-92.

Thesis (M.S.)--Ohio University, March, 2008. / Title from PDF t.p. Includes bibliographical references.

Thesis (M. Sc.)--University of Hong Kong, 1995. / Includes bibliographical references.

Thesis (Ph.D.)--Mississippi State University. Department of Agricultural and Biological Engineering. / Title from title screen. Includes bibliographical references.

Diss. (sammanfattning) Karlstad : Karlstads universitet, 2009. / Härtill 5 uppsatser.

Thesis (M.Sc.) -- Memorial University of Newfoundland. / Typescript. Bibliography: leaves 228-249. Also available online.