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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.

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.

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 paper describes the development and application of a spark plug sensor using a 3.392 μm infrared absorption technique to quantify the instantaneous gasoline concentration near the spark plug. We developed an in situ laser infrared absorption method using a spark plug sensor and a 3.392 μm He-Ne laser as the light source; this wavelength coincides with the absorption line of hydrocarbons. First, we established a database of the molar absorption coefficients of premium gasoline at different pressures and temperatures, and determined that the coefficient decreased with increasing pressure above atmospheric pressure. We then demonstrated a procedure for measuring the gasoline concentration accurately using the infrared absorption technique. The history of the molar absorption coefficient of premium gasoline during the experiment was obtained from the established database using measured in-cylinder pressures and temperatures estimated by taking the residual gas into consideration.

One of the authors has proposed to use the decay rate of EHRR, the effective heat release rate, d2Q/dθ2 as an index for the rapid local combustion [1]. In this study, EHRR profiles and the cylinder gas pressure oscillations of the low and high speed knock are analyzed by using this index. A delayed rapid local combustion, such as an autoignition with small burned mass fraction can be detected. In the cases of the low speed knock, it has been agreed that a rapid local combustion is an autoignition. Although whether the cylinder gas oscillation is provoked by an auto ignition in a certain cycle or not is an irregular phenomenon, the auto ignition takes place in almost all of the cycles in the knocking condition. Mixture mass fraction burned by an auto ignition is large. A small auto ignition may induce a secondary auto ignition, in many cases, mass burned by the secondary auto ignition is extremely large.

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).

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.