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Implementing triple injection strategies in partially premixed charge-based gasoline compression ignition (GCI) engines has shown to achieve improved engine efficiency and reduced NOx and smoke emissions in many previous studies. While the impact of the triple injections on engine performance and engine-out emissions are well known, their role in controlling the mixture homogeneity and charge premixedness is currently poorly understood. The present study shows correspondence between the triple injection strategies and mixture homogeneity/premixedness through the experimental tests of second/third injection proportion and their timing variations with an aim to explain the observed GCI engine performance and emission trends. The experiments were conducted in a single cylinder, small-bore common-rail diesel engine fuelled with a commercial gasoline fuel of 95 research octane number (RON) and running at 2000 rpm and 830 kPa indicated mean effective pressure conditions.

A prototype of measurement device that compresses a sample of engine oil at constant temperature and calculates its void fraction from the magnitude of volume change and pressure was proposed. During compression, the oil sample was pressurized to several hundreds of kPa above atmospheric pressure. Because the gas can be regarded as an ideal gas at this pressure level, the estimation of void fraction can be based on a simple formula derived from the ideal gas law, the law of conservation of mass and Henry’s law. The calibration line is represented by a linear equation of the void fraction, and from the coefficient of void fraction or the constant term the volume fraction of the dissolved gas in the initial state can be known. That is, by experimentally determining the calibration line, not only void fraction but also the volume fraction of the dissolved gas in the initial state can be known. Then, the results of measurement principle confirmation tests were given.

The present study explores the effect of in-cylinder generated non-thermal plasma on hydroxyl and soot development. Plasma was generated using a newly developed Microwave Discharge Igniter (MDI), a device which operates based on the principle of microwave resonation and has the potential to accentuate the formation of active radical pools as well as suppress soot formation while stimulating soot oxidation. Three diagnostic techniques were employed in a single-cylinder small-bore optical diesel engine, including chemiluminescence imaging of electronically excited hydroxyl (OH*), planar laser induced fluorescence imaging of OH (OH-PLIF) and planar laser induced incandescence (PLII) imaging of soot. While investigating the behaviour of MDI discharge under engine motoring conditions, it was found that plasma-induced OH* signal size and intensity increased with higher in-cylinder pressures albeit with shorter lifetime and lower breakdown consistency.

The Microwave Discharge Igniter (MDI) was developed to create microwave plasma for ignition improvement inside combustion engines. The MDI plasma discharge is generated using the principle of microwave resonance with microwave (MW) originating from a 2.45 GHz semiconductor oscillator; it is then further enhanced and sustained using MW from the same source. The flexibility in the control of semiconductors allows multiple variations of MW signal which in turn, affects the resonating plasma characteristics and subsequently the combustion performance. In this study, a wide range of different MW signal parameters that were used for the control of MDI were selected for a parametric study of the generated Microwave Plasma. Schlieren imaging of the MDI-ignited propane flame were carried out to assess the impact on combustion quality of different MW parameters combinations.

Exhaust gas recirculation (EGR) has proven to be beneficial for not only fuel economy improvement but also knock and emissions reduction. Combined with lean burning, it can assist gasoline engines to become cleaner, more efficient and to meet the stringent emissions limit. However, there is a practical limit for EGR percentage in current engines due to many constraints, one of which being the ignition source. The Microwave Discharge Igniter (MDI), which generates, enhances and sustains plasma discharge using microwave (MW) resonance was tested to assess its ability in extending the dilution limit. A combination of high-speed Schlieren imaging and pressure measurements were performed for propane-air mixture combustion inside a constant volume chamber to compare the dilution limits between MDI and conventional spark plug. Carbon dioxide addition was carried out during mixture preparation to simulate the dilution condition of EGR and limit the oxygen fraction.

Requirements for reducing consumption of hydrocarbon fuels, as well as reducing emissions force the scientific community to develop new ignition systems. One of possible solutions is an extension of the lean ignition limit of stable combustion. With the decrease of the stoichiometry of combustible mixture the minimal size of the ignition kernel (necessary for development of combustion) increases. Therefore, it is necessary to use some special techniques to extend the ignition kernel region. Pulsed microwave discharge allows the formation of the ignition kernels of larger diameters. Although the microwave discharge igniter (MDI) was already tested for initiation of combustion and demonstrated quite promising results, the parameters of plasma was not yet studied before. Present work demonstrates the results of the dynamics of spatial structure of the MDI plasma with nanosecond time resolution.

High speed, time resolved Particle Image Velocimetry (PIV) diagnostics was applied to an optical SI engine to study the interactions between in-cylinder flow field and flame development. Optimisation and certain adaptations have been made to the diagnostic setup to enable time-resolved, simultaneous measurements of both PIV data and flame tomography imaging from the same original captured image set. In this particular study, interactions between flow and flame during lean-burn operating conditions at various tumble strength have been investigated and compared to a standard stoichiometric operation. Diagnostics were performed for both the vertical plane (x-y) and the horizontal plane (r-⊖) of the combustion chamber with a particular focus in the pent-roof area. Some major differences in the tumble flow-field prior to ignition has been observed between the lean and stoichiometric conditions.

The present study aims to evaluate the effects of engine speed on gasoline compression ignition (GCI) combustion implementing double injection strategies. The double injection comprises of near-BDC first injection for the formation of a premixed charge and near-TDC second injection for the combustion phasing control. The engine performance and emissions testing of GCI combustion has been conducted in a single-cylinder light-duty diesel engine equipped with a common-rail injection system and fuelled with a conventional gasoline with 91 RON. The double injection strategy was investigated for various engine speeds ranging 1200~2000 rpm and the second injection timings between 12°CA bTDC and 3°CA aTDC.

The effect of microwave enhanced plasma (MW Plasma) on diesel spray combustion was investigated inside a constant volume high pressure chamber. A microwave-enhanced plasma system, in which plasma discharge generated by a spark plug was amplified using microwave pulses, was used as plasma source. This plasma was introduced to the soot cloud after the occurrence of autoignition, downstream of the flame lift-off position to allow additional plasma-generated oxidizers to be entrained into the hot combustion products. Planar laser induced incandescence (PLII) diagnostics were performed with laser sheet formed from 532 nm Nd:YAG laser to estimate possible soot reduction effect of MW plasma. A semi-quantitative comparison was made between without-plasma conventional diesel combustion and with-plasma combustion; with LII performed at different jet cross-sections in the combustion chamber.

A plasma combustion system was developed to improve fuel economy and efficiency without modifying the engine configuration. Non-thermal plasma generation technology with microwave was applied. Plasma was generated by spark discharge and expanded using microwaves that accelerated the plasma electrons, generating non-thermal plasma. Even at high pressures, spark discharge occurred, allowing plasma generation under high pressures. The durability and practicality of previous plasma combustion systems was improved. The system consisted of a spark plug without a resistor, a mixer circuit, and a control system. The mixer unit used a standard spark plug for plasma combustion and functioned as a high-voltage and high-frequency isolator. A commercially available magnetron produced microwaves of 2.45 GHz. The spark and microwave control system used a trigger signal set to the given crank angle, from the engine control unit.

This study aims to develop innovative plasma combustion system to improve fuel economy and achieve higher efficiency without any modification of current engine configuration. A new plasma generation technique, that used a combination of spark discharge and microwave, was proposed. This technique was applied to gasoline engine as an ignition source, which was intensive and stable even in lean condition. In this technique, firstly, small plasma source was generated by spark discharge. Secondly, microwave was radiated to the plasma source to expand the plasma. The microwave power was absorbed by the plasma source and large non-thermal plasma was formed. In non-thermal plasma, the electron temperature was high and the gas temperature was low. Then many OH radicals were generated in the plasma. The frequency of the microwave was 2.45 GHz because we used a magnetron for microwave oven. Magnetrons for microwave oven were high efficiency and reasonable.

An in-spark-plug flame sensor was developed to measure local chemiluminescence near the spark gap in a practical spark-ignition (SI) engine in order to study the development of the initial flame kernel, flame front structure, transient phenomena, and the correlation between the initial flame kernel structure and cyclic variation in the flame front structure, which influences engine performance directly. The sensor consists of a commercial instrumented spark plug with small Cassegrain optics and an optical fiber. The small Cassegrain optics were developed to measure the local chemiluminescence intensity profile and temporal history of OH*, CH*, and C2* at the flame front formed in a turbulent premixed flame in an SI engine. A highresolution monochromator with an intensified chargecoupled device (ICCD) and spectroscopy using optical filters and photomultiplier tubes (PMTs) were used to measure the time-series of the three radicals, as well as the in-cylinder pressure.

The chemiluminescence emission intensity can be measured with high temporal resolution, leading to understanding the chemical reaction. Time-series chemiluminescence measurements of OH*, CH* and C2* were carried out to understand flame propagation speed, its thickness and A/F ratio of combustion status. The optical piston head (quartz) allows us to visualize combustion chamber. It is found that the chemiluminescence intensity ratio of CH*/OH* and C2*/OH* can estimate local A/F. The A/F measured by O2 sensor was used for evaluation and the results indicate this method can be applicable to estimate A/F.

The purpose of this study is to reveal the flame propagation characteristics. Planar OH* image and local radical emission were measured simultaneously. Planar OH* images were used to analyze the flame propagation characteristics by high-speed camera. These images were then used to evaluate the speed of distribution and the direction of flame propagation. By comparing local point radical emission and planar OH*, the flame propagation characteristics was measured and evaluate that. And the time history of the radical intensity and planar OH* distribution were compared. The relation ship between flame propagation speed and initial heat generation was discussed. The variation of flame propagation speed and the difference of propagation speed in both port sides were confirmed.

The purpose of this study was to examine the cause of fluctuations in combustion. It is important to understand the changes that occur in flame kernel development and in flame propagation during cyclic variation. In this study, a comparison was made between time-series variations in OH emission with THC concentration, and the intensity of the combustion reaction and the direction of flame propagation are also discussed. Early flame development and cyclic variation at an early stage of combustion were demonstrated by simultaneously measuring a two-dimensional image of flame emission and the time-series variation of local flame emission. The instantaneous intensity at Cassegrain measurement point agreed with the intensity of time-series variation in local flame propagation at CCD recorded timing. Variations in THC concentration in the cylinder were compared with time-series variations in local flame emission.

The purpose of this study is to examine the cause of combustion fluctuation in a partially loaded two-stroke engine with respect to the hydrocarbon (HC) concentration in the cylinder. HC concentration in the cylinder, exhaust gas velocity and pressure were simultaneously measured in order to determine the influence of HC concentration on combustion fluctuation. A correlation between cyclic variation in HC concentration in the cylinder and IMEP was confirmed. The way in which the HC concentration influenced the combustion states in the next cycle made clear. A decrease of HC concentration cause the delay of early flame development and combustion, the decrease of HC concentration had an great influence on the combustion states. The relationship between combustion states and HC concentration was discussed. The relative value of IMEP and HC concentration were closely related to the HC concentration in the cylinder.

The purpose of this study was to detect a misfiring cycle in terms of the transfer-passage and the exhaust-pipe flow rate by experimental measurements. Simultaneous measurements of flow rates and in-cylinder pressure were carried out. The flow rate data were grouped into the different combustion classes by the in-cylinder pressure. A large flow rate of exhaust blow-down and a large reverse flow rate were observed in the cycle before misfiring, compared with in the cycle before firing. It showed that high concentration of the residual burnt gas in the cylinder was the main source of misfiring, this feature was also demonstrated by the complementary measurement of CO and CO2 concentrations.

The purpose of this study is to experimentally investigate in-cylinder flows with cyclic variation in a practical part-loaded two-stroke engine. First, the in-cylinder LDV measurements are introduced, which were carried out above the port layout and the combustion chamber as well as the exhaust pipe or the transfer port together with the simultaneous pressure measurements. Second, the in-cylinder flow characteristics in different combustion groups were discussed. The in-cylinder flow and the combustion-chamber flow were not simply characterized by the pressure variation in the engine or the other passage flow in the exhaust pipe or the transfer port. Finally, the in-cylinder flow structure with three stages was shown using the vector variation analysis and the drawing of the velocity profiles in the engine parts.

The purpose of this study is to experimentally understand the cyclic variation of combustion state in a two-stroke engine with respect to the variations in scavenging flow and the CO and CO2 emissions. The criteria of grouping combustion states into misfiring were established using the in-cylinder pressure at the crankangle of maximum variability in peak pressure instead of indicated mean effective pressure. The CO and CO2 emissions and the flow velocity variations in the transfer port and the exhaust pipe were measured. Combustion of each cycle was grouped into misfiring, incomplete firing or firing by the criteria of the in-cylinder pressure. In the cycle before misfiring, the CO and CO2 concentration showed high level and the first peak of the exhaust flow showed large velocity and the positive velocity remained for long duration, and the exhaust and the transfer port flow were steeply decelerated to negative velocity midway between scavenge port opening and bottom dead center.

The velocity variations of the burnt exhaust gas in a practical fired two-stroke engine operating under wide-open-throttle conditions were measured by a fiber LDV ( FLDV ). The characteristics of the exhaust flow are discussed in comparison with those in motoring and in a transfer port. The relation between velocity variation and pressure wave propagation in the exhaust pipe are also investigated. The measured results show that the velocity distribution in the exhaust pipe can be characterized as pulsative flow. The flow characteristics had large influence by the combustion pressure wave propagation. During exhaust and transfer-port opening, the intake flow and the blow-down flow have similar velocity gradient and peak location. The velocity distribution in the exhaust pipe was also measured, which showed pulsative flow variation having no recirculating vortex.