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An experimental study of partially premixed compression ignition combustion with low octane fuel was conducted on a single-cylinder engine. The effects of the external exhaust gas recirculation and intake boost on this partially premixed compression ignition combustion and emissions were investigated. During the experiments, a trade-off relationship between the NOx and smoke emissions was observed in this partially premixed compression ignition combustion. However, heavy exhaust gas recirculation usage has the potential to decrease NOx and soot emissions simultaneously at the expense of the fuel economy. It is determined that at an increased intake port pressure, the maximum in-cylinder pressure increases, and the ignition timing of the high-temperature combustion is retarded. Also, the peak value of the low-temperature combustion is slightly depressed, the peak value of the high-temperature heat release decreases significantly, and the maximum value of the diffusing burn increases to some extent. Compared to natural aspirated condition, the partially premixed compression ignition combustion with intake boost has the capability of simultaneously reducing NOx and soot emissions to ultra-low levels, that is, the intake boost could be an important strategy for the combustion and emission improvement in this advanced engine combustion mode. [ABSTRACT FROM AUTHOR]

This paper investigates the combustion and emission characteristics of dual-fuel compound homogeneous charge compression ignition combustion. n-heptane and oxygen-containing alcohols were chosen as the port-injection fuel and the in-cylinder direct-injection fuel, respectively. It is found that compound homogeneous charge compression ignition combustion with n-heptane port injection and alcohol direct injection exhibits a three-stage combustion process containing n-heptane low-temperature reactions, high-temperature reactions and alcohol combustion. The crank angle position at which 10% of the mass fraction is burned is mainly dominated by the fuel heat value per cycle of premixed fuel, and is advanced with increasing the fuel heat value per cycle of premixed fuel and premixed ratio. The crank angle position at which 50% of the mass fraction is burned shows remarkable sensitivity to the premixed ratio, and is advanced considerably as the premixed ratio and the fuel heat value per cycle of premixed fuel increase. Burn duration increases with increasing total fuel heat value per cycle and fuel heat value per cycle of directly injected fuel. The results show that compound homogeneous charge compression ignition combustion could successfully reach the full load of the prototype engine. The indicated thermal efficiency is very close to the prototype engine. However, their CO and hydrocarbon emissions are relatively higher. It is worth noting that compound homogeneous charge compression ignition combustion with alcohol direct injection can reduce nitrogen oxide and soot emissions simultaneously. Nitrogen oxide emissions can be reduced below 100 ppm, and smoke opacity is below 15% at the full-load ranges. Moreover, with increasing oxygen content of directly injected fuels, soot emission of compound homogeneous charge compression ignition combustion decreases. Ethanol direct injection could make compound homogeneous charge compression ignition combustion nearly smoke free at the full-load ranges. [ABSTRACT FROM AUTHOR]

In this paper, the combustion stabilities and cycle-by-cycle variations of homogeneous charge compression ignition (HCCI) combustion using neat n-heptane, PRF20, PRF40, PRF50, and PRF60 were investigated. In-cylinder pressures of 100 combustion cycles for each test fuel on a single-cylinder engine were recorded. Consequently, cycle-to-cycle variations of the main combustion parameters and performance parameters were analysed, and the interdependency between the combustion parameter and performance parameters were also evaluated. The results reveal that the cycle-by-cycle variations deteriorate with the increase of the research octane number (RON). Especially, the coefficient of variations (COVs) of all parameters increase substantially when the RON of test fuels exceeds 40. For a certain test fuel, the COVs of combustion parameters that were used to depict the combustion characteristics during the early stage of combustion are very small, the COVs of combustion parameters that were used to describe the combustion characteristics of the post stage of the combustion are the largest, and the COVs of the i.m.e.p. and Pmax maintain at a middle level. Furthermore, a better interdependency also exists between the ignition timing of the low temperature reaction (LTR) and high temperature reaction (HTR), between the maximum pressure rise rate and its corresponding crank angle, between the peak values of the heat release and its corresponding crank angle. [ABSTRACT FROM AUTHOR]

Abstract: The control of ignition timing in the homogeneous charge compression ignition (HCCI) of n-heptane by port injection of reaction inhibitors was studied in a single-cylinder engine. Four suppression additives, methanol, ethanol, isopropanol, and methyl tert-butyl ether (MTBE), were used in the experiments. The effectiveness of inhibition of HCCI combustion with various additives was compared under the same equivalence ratio of total fuel and partial equivalence ratio of n-heptane. The experimental results show that the suppression effectiveness increases in the order MTBE

Abstract: In the present study, the detailed combustion characteristics and emissions of biodiesel-fueled engines with premixed ethanol by port injection were investigated. The experiments were carried out on a single-cylinder, four-stroke, natural aspirated direct injection engine at a fixed speed. The heat release analysis indicates that, with the introduction of ethanol fuel by port injection, the ignition timing of the overall combustion event delays remarkably, while the maximum heat release rate increases smoothly. At a leaner fuel/air mixture, the peak value of the heat release rate (HRR) increases slightly, the maximum in-cylinder gas pressure and temperature decrease, and the indicated thermal efficiency (ITE) deteriorates with the increase of ethanol proportion. While at a rich fuel/air mixture, with the increase of the ethanol proportion, the maximum HRR increases rapidly, the overall combustion event is completed at an earlier crank angle. Moreover, the maximum values of the HRR reach the peak point in a certain premixed ratio which ranges from 20% to 40%. Also, the ITE reaches the largest value at this operation point. Due to the introduction of the ethanol fuel by port injection, both the NO x emission and smoke opacity decrease to a very low level under overall operation conditions. During the experimental points of this test, NO x and smoke opacity simultaneously decrease about 35–85% compared to those of the neat biodiesel-fueled engines. [Copyright &y& Elsevier]