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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.

The flow velocity in a scavenging port of a small two-stroke engine was measured directly by a specially developed fiber LDV. The measurement was carried out under motored conditions at engine speeds of 1500 to 5000 rpm, and with throttle-opening ratios of 100, 50, and 20 %. The performance of the FLDV was improved for measuring the scavenging velocity in the backscatter mode. The flow in the scavenging port changed significantly from -11 m/s to 47 m/s with the engine cycle, and the pressure difference between the crankcase and the exhaust pipe provided the typical features of the flow but not the absolute values. The results show that the scavenging flow entered the cylinder just before scavenging port opening (SO) and reached a maximum at the crank angle of 145°, which was constant for all conditions. A second velocity peak was formed by the back pressure from the exhaust pipe. The charging rate of the fresh air into the cylinder was obtained to evaluate the engine performance.

The objective of this study was to develop an innovative microwave-induced plasma ignition system to improve the fuel economy of a current engine and achieve a higher efficiency without any configuration modifications. A new plasma generation technique was proposed for a stable and intense ignition source. A microwave plasma combustion system was developed consisting of a spark plug, microwave transfer system, and control system. A magnetron, like that found in a microwave oven, was used as a microwave oscillator. The spark plug had a microwave antenna inside that generated plasma in the engine cylinders. The microwave transfer system transmitted microwave power from the oscillator to the antenna. Combustion experiments were performed using a single-cylinder research engine. The microwave plasma expanded the range of lean operating conditions. The single-cylinder engine had an indicated mean effective pressure (IMEP) of 275 kPa at an engine speed of 2000 rpm.

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.

Misfiring cycles were detected by a conditional sampling method to demonstrate the differences between firing and misfiring of the scavenging flow characteristics at the scavenging port and exhaust pipe using LDV method. The results show that the flow at the scavenging port was not influenced significantly by misfiring, but the blowdown flow in the exhaust pipe greatly depended on the combustion status. The blow-down flow of fired cycles at a light-load condition was very similar to the flow at a full-load condition. It was also found that measured flow characteristics at partial load should not be considered by averaging firing and misfiring cycles. The occurrence pattern of misfiring should be quantified and considered in the analysis.

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.

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 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 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 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.

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.

Recent trend in gasoline-powered automobiles focuses heavily on reducing the CO2 emissions and improving fuel efficiency. Part of the solutions involve changes in combustion chamber geometry to allow for higher turbulence, higher compression ratio which can greatly improve efficiencies. However, the changes are limited by the ignition-source and its location constraint, especially in the case of direct injection SI engines where mixture stratification is important. A new compact microwave plasma igniter based on the principle of microwave resonance was developed and tested for propane combustion inside a constant volume chamber. The igniter was constructed from a thin ceramic panel with metal inlay tuned to the corresponding resonance frequency. Microwaves generated by semiconductor based oscillator were utilized for initiation of discharge. The small and flat form factor of the flat panel igniter allows it to be installed at any locations on the surface of the combustion chamber.

The flow vector variations at the transfer port exit in a small two-stroke engine under firing condition were investigated experimentally. A fiber LDV system was used to measure the two-dimensional velocities near the cylinder to obtain the scavenging flow vector. The scavenging flow vector variations at different engine speeds were discussed, and the relation between its vector behavior and the pressure differences between the exhaust pipe and the crankcase was examined. The measurement results show that the velocity profiles at the scavenging port were not uniform and to obtain the representative velocity at the port exit was impossible. But the major features of the scavenging flow can be understood from the pressure difference between the exhaust pipe and the crankcase. The start timing of the scavenging flow was delayed due to the residual gas and high pressure in the cylinder when the scavenging port was opened.

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.

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.

The extension of the lean stability limits of gasoline-air mixtures using a microwave-assisted spark plug has been investigated. Experiments are conducted on a 1200 RPM single-cylinder Waukesha Cooperative Fuel Research (CFR) engine at two compression ratios: 7:1 and 9:1; and four different levels of microwave energy input per cycle (prior to accounting for transmission losses): 0 mJ (spark only), 130 mJ, 900 mJ, and 1640 mJ. For various microwave energy inputs, the effects upon stability limits are explored by gradually moving from stoichiometric conditions to increasingly lean mixtures. The coefficient of variation (COVIMEP) of the indicated mean effective pressure (IMEP) is used as an indication of the stability limits. Specific characteristics of microwave-assisted ignition are identified. Microwave enhancement extends stability limits into increasingly lean regions, but slow and partial burning at the leanest mixtures curb efficiency gains.

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 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.

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.

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.