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“Flashing” is a process where high temperature liquids held in a subcooled state, explosively release large amounts of stored energy when depressurized. The rapid volume expansion that results from the flashing has been harnessed to drive an expansion engine working on a cycle called “The Superheated Liquid Flash, Boiling” (S.L.F.B) cycle. In cyclic operation, the expansion engine power output was seen to be directly related to the mass and temperature of the injected subcooled water. At low levels of subcooling, smaller masses of water were able to achieve higher levels of efficiency in converting the total enthalpy of injected subcooled water to work, than larger injection masses with the same level of subcooling. However, with higher levels of subcooling, smaller injection masses show a reduction in efficiency.

High temperature liquids held in a subcooled state are capable of storing large amounts of energy and then explosively releasing this energy when depressurized in a phase change process known as “Flashing”. The rapid volume expansion that results from this flashing has been harnessed to drive an expansion engine working on a cycle called “The Superheated Liquid Flash, Boiling” (S.L.F.B) cycle. The first stage showed that multiphase convective boiling of the unflashed water off the heated walls of the expansion unit supplemented the Flash work output. Furthermore, Flashing was seen to improve the effectiveness of convective boiling off the walls. The results were shown to be repeatable in a modified piston engine. Convective boiling was again shown to be able to supplement the power output under specific conditions.

In order to detect the combustion quality in a production SI engine, the ion sensor of gasket type was used. The relationship between the ion current and the rate of heat release has been discussed. Under varying equivalence ratio, intake pressure and engine speeds, the averaged start and peak timings of the ion current for 8 electrodes correspond to timings of 50% MFB and 90% MFB respectively, are also discussed. The waveforms accumulated for all signals of the 8 electrodes are discussed as being analogues to the waveform of a ring ion sensor. Coincidentally, the cycle resolved ion current waveforms accumulated from the 8 electrodes is seen to vary with the rate of heat release. The ion current fraction accumulated (ICFA), has been defined using the summation waveforms of ion current from a gasket ion sensor. It was found that the timing of 5% ICFA corresponds with that of 50% MFB and the timing of 50% ICFA corresponds with that of 90% MFB.

Homogeneous charge compression ignition (HCCI), has the potential to improve the fuel economy and to reduce NOx emission significantly. Spark plug in SI engine and fuel injector in diesel engine can be used directly to control the start of combustion and the combustion period. However, the combustion of HCCI engine is controlled by the chemical kinetic mainly due to the temperature histories in the cylinder. Therefore the combustion process of HCCI engine cannot be directly controlled. Ion sensors such as a spark plug or a gasket are useful to detect the combustion information in production engines. In this study, the ion current was measured in an HCCI engine with the heated charge mixture of fuel and air without EGR when the charge temperature, equivalence ratio and fuel were varied. Simultaneously in-cylinder pressure was measured and the rate of heat release was calculated. The relationship between the rate of heat release and the ion current is mainly discussed.

Recently, in order to warm up the catalyst temperature rapidly, the retard ignition management has been developed. However, the excess retard of ignition causes the combustion instability and misfire. In this case, the ion sensor has been used for detecting the combustion quality for the late burned cycle under the idling condition. Several researchers have focused on the potential of ion-current measurement for the retard ignition management. However, the interpretation of ion-current during the exhaust process under the idling condition is not clear. In this study the source of ion-current for the late burned cycle during the exhaust process is focused. In order to measure the flame propagation process in the cylinder and the exhaust pipe, the single-cylinder test engine was used instead of production engine. Several ion probes were mounted on the cylinder head gasket, the piston head and the exhaust pipe for detecting the flame front.

In order to reduce the exhaust emission and the fuel consumption in a spark ignition engine, the combustion diagnostics had been developed. However, there are few sensors which can detect the combustion quality for the individual cycle and cylinder in production engines. In previous study, the new technique using a gasket ion sensor for measuring the combustion quality has been proposed. In present study, the flame propagation pattern in a spark ignition engine was detected by using a gasket ion sensor with a circular electrode. The waveforms of ion current obtained from a circular ion sensor were compared with the flame propagation pattern obtained from multiple ion sensors. When the mixture was ignited in offset center of the cylinder, the flame propagation pattern was distorted from the spherical pattern. Then the waveforms of ion current from the circular ion sensor were varied from the waveform for a center ignition.

It is important to develop the technique for measuring the cycle-to-cycle variation of combustion in order to reduce the fuel consumption of the commercial spark ignition engine. In previous study, we had proposed using the spark plug as an ion probe to measure the appearance time of maximum pressure under the lean mixture conditions of the research engine. In this paper the combustion diagnostics for the commercial engine was performed using the spark plug as an ion probe. Under idling conditions the ion current often appeared during the exhaust process. This ion current is dominated by the flame contact area and the flame velocity. In this case there is good correlation between the characteristic value of the ion current and the indicated mean effective pressure (IMEP). Finally using the spark plug as an ion probe can detect the combustion quality under conditions with large cyclic variation.

The several burning models based on the wrinkled laminar flame concept had been proposed and applied to the turbulent premixed flame in a spark ignition engine. Fractal burning model is one of the flamelet burning models. However the formulations of fractal characteristics such as fractal dimension, inner cutoff scale and outer cutoff scale weren't established. These formulations based on the results of the fractal analysis in a constant volume vessel and a spark ignition engine were proposed in this study. The fractal dimension is expressed as a function of non-dimensional turbulence intensity and the density of mixture. Non-dimensional inner cutoff scale is expressed a function of Karlovitz number. Outer cutoff scale is equal to the flame radius. Finally the quasidimensional model for turbulent combustion was performed by using the fractal burning model with our formulations.

In order to investigate the relation between ion current and combustion characteristics, the ion current signal from a spark plug as an ion probe, pressure history and flame development were measured in a homogeneous propane-air mixture in closed combustion chambers. The flame propagation was measured by Schlieren photography technique. When negative bias is applied to the central electrode of the spark plug, the ion current flows only due to an early flame kernel existing near the spark plug. When positive bias is applied to the central electrode, the ion current flows from the central electrode to the combustion chamber wall and to the ground electrode. Consequently, the ion current is dominated by the contact area between the flame and the combustion chamber wall. The appearance period of ion-current is related to the combustion duration. This method was applied to the combustion analysis of the spark ignition engine.

The structures of the turbulent premixed flame in the engine cylinder under lean burn conditions were investigated using ion probe method. The flow fields were measured with an LDA for two tumble ratios and two compression ratios. And ion-current signal was analyzed to discuss the interaction between the turbulence and the flame structure. The effects of turbulence and equivalence ratio on the characteristic values of the turbulent flame, that is to say number of ion-current peaks, thickness of flame front and thickness of burning zone of the flamelet, were investigated. In normal combustion, the structure of the turbulent flame front is almost the same as the laminar flame. In the lean limit, the flamelet is broken and stretched and then the structure may change.