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An investigation was made into two approaches to air-fuel mixture formation in direct injection SI engines in which charge stratification is controlled by swirl or tumble gas motions, respectively. Particle image velocimetry (PIV), laser-induced fluorescence (LIF) and air-fuel ratio measurement by infrared absorption were used to analyze fuel transport from the fuel injector to the spark plug and the fuel vaporization process. The results obtained were then compared with measured data as to combustion stability. As a result, the reason why the effects of injection timing on combustion stability were different between the two approaches was made clear from the standpoint of the mixture formation process.

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.

A new technique for combustion diagnostics of a spark ignition engine was developed. In this method the ion sensor with the circular configuration was installed into the cylinder head gasket. This sensor is expected to be applied for production engine. The signal measured by the ion sensor was similar with that of cylinder pressure. The peak timing of ion current was consistent with the peak timing of pressure. There was a strong correlation between IMEP and the peak timing of ion current. This sensor is available to detect combustion quality in a spark ignition engine.

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.

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.

This study measured the fuel concentration near a spark plug using a laser infrared absorption method. An IR spark plug sensor with a double-pass measurement length was developed. A He-Ne laser with a wavelength of 3.392 μm, which coincides with the absorption line of hydrocarbons, was used as the light source. In order to confirm the measurement accuracy, the concentrations of a methane-air mixture were measured in a compression-expansion engine. Then, the IR spark plug sensor was used for measurements in a 4-stroke spark-ignition engine fuelled with isooctane. The air/fuel ratio measured using this system clearly agreed with the mean air/fuel ratio.

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.

A heterodyne interferometry system with a fiber-optic sensor was developed to measure the temperature history of unburned gas in a spark-ignition engine. A polarization-preserving fiber and metal mirror were used as the fiber-optic sensor to deliver the test beam to and from the measurement region. This fiber-optic sensor can be assembled in an engine cylinder head without a lot of improvements of an actual engine. Adjustment system in the sensor was revised to face the distributed index lens with metal mirror. Before the flame arrived at the developed fiber-optic sensor, measured temperature was almost same with the temperature history after the spark, assuming that the process that changes the unburned gas is adiabatic. In situ unburned gas temperature measurements before knocking in a commercially produced SI engine can be carried out using developed fiber-optic heterodyne interferometry system.

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.

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.

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.

In this study, fuel concentration measurements in a spark-ignition (SI) engine with ethanol blended gasoline were carried out using an optical sensor installed in the spark plug with laser infrared absorption technique. The spark plug sensor for in-situ fuel concentration measurement was applied to a port injected SI engine. The molar absorption coefficients of ethanol blended gasoline were determined for various pressures and temperatures in advance using a constant volume vessel with electric heating system. Ethanol blended gasoline with high volumetric ratios shows lower molar absorption coefficients due to lower molar absorption coefficients of ethanol. The molar absorption coefficients of ethanol blended gasoline can be estimated by considering the molar fraction of each component.

In this research, a spark plug with an optical fiber has been developed to obtain the emission spectra from the spark discharge and flame kernel. This developed spark plug with an optical fiber can obtain the time series of emission spectra from the spark discharge and Initial flame kernel in the real spark-ignition engine using EMCCD spectrometer. The plasma vibrational temperature of the spark discharge can be measured using the emission spectra from the electrically excited CN violet band system. The plasma of the spark discharge and gas rotational temperature of the initial flame kernel can be also measured using emission spectra from OH* radicals (P and R branches). The plasma temperature of the spark discharge was almost 8,000 K and the gas temperature of the Initial flame kernel approached that of the adiabatic flame temperature.

In this study, residual gas fraction measurements in a spark-ignition engine were carried out using an optical sensor installed in the spark plug with infrared absorption method. The residual gas fraction inside engine cylinder is proportional to the CO2 concentration. Infrared absorption method was applied and an infrared lamp and optical filter (center wavelength: around 4.3 μm) that coincides with the absorption lines of CO2 was used as a light source.The molar absorption coefficient of CO2 is discussed and compared to results in the HITRAN database. The effect of water vapor absorption doesn't affect the absorption of CO2. The absorption characteristics of CO2 were determined in advance using a constant volume vessel. Molar absorption coefficient depends on the CO2 concentration and ambient pressure and temperature, and wavelength of absorption line.

Investigation of knocking combustion in a hydrogen spark-ignition engine is one of the major challenges for future vehicle development. The knock phenomenon in a Spark-Ignition (SI) engine is caused by autoignition of the unburned gas ahead of the flame. The explosive combustion of the end-gas creates a pressure wave that leads to damage of the cylinder wall and the piston head of the engine. We observed autoignition in the end-gas region due to compression by the propagating flame front using a high-speed colour video camera through the optically accessible cylindrical quartz window on the top of the cylinder head. Moreover, a high-speed monochrome video camera operating at a speed of 250, 000 frame/s was used to measure the pressure wave propagation. The goal of this research was to improve our ability to describe the effect of the autoignition process on the end-gas and propagating pressure wave during knocking combustion with the help of a high-speed video camera.