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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.

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.

A small Cassegrain optics sensor was developed to measure local chemiluminescence spectra and the local chemiluminescence intensities of OH*, CH*, and C2* in a four-stroke spark-ignition (SI) engine in order to investigate the propagation characteristics of the turbulent premixed flame. The small Cassegrain optics sensor was an M5 type that could be installed in place of a pressure transducer. The measurements could be used to estimate the flame propagation speed, burning zone thickness, and local air/fuel (A/F) ratio for each cycle. The specifications of the small Cassegrain optics sensor were the same as those used for previous engine measurements. In this paper, measurements were made of several A/F ratios using gasoline to fuel the model engine. The performances of two Cassegrain optics sensors were compared to demonstrate the advantages of the new small sensor by measuring the local chemiluminescence intensities of a turbulent premixed flame in the model engine.

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 droplet characteristics of the air-assisted gasoline injector was investigated. A Phase Doppler technique was used to measure droplet diameter and its velocity. The size-classes technique was employed and found to be the best way to understand what kind of droplet is existing in shear flow induced mushroom vortex at spray shell. The detail spray characteristics near nozzle was discussed and the double shell structure was found. The droplets of less than 20 μm can be entrained into mushroom vortex, while the larger of over 30 μm penetrates straight to downstream. The slip velocity and relative Reynolds number were used in data analysis in order to understand the momentum transfer occurrence region due to strong drag force. The spray animation was demonstrated with the ensembled / size-classified droplet, which was found to be the powerful tool to understand spray formation and dispersion process.