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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.

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.

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.

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.

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.

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.

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 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 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.

Extending the lean limit or/and exhaust-gas-recirculation (EGR) limit/s are necessary for improving fuel economy in spark ignition engines. One of the major problems preventing the engine to operate at lean conditions is stable and successful initial ignition kernel formation. A repeatable, stabilized ignition and early flame development are quite important for the subsequent part of the combustion cycle to run smooth without partial burn or cycle misfire. This study aims to develop an innovative plasma ignition system for reciprocating combustion engines with an aim to extend lean limit and for high pressure applications. This ignition system utilizes microwaves to generate plasma as an ignition source. This microwave plasma igniter is much simplified device compared to conventional spark plug. The microwave plasma ignition system consists of microwave oscillator, co-axial cable and microwave discharge igniter (MDI).