Eiji Tomita

In situ measurement of hydrocarbon fuel concentration near a spark plug in an engine cylinder using the 3.392 μm infrared laser absorption method: Application to an actual engine

An infrared absorption method with a 3.392 µm He–Ne laser was used to determine the hydrocarbon fuel concentration near the spark plug in a spark-ignition engine. Iso-octane was used for the fuel. The pressure and temperature dependence of the molar absorption coefficient was clarified. The molar absorption coefficients of a multi-component fuel such as gasoline were estimated by using the coefficient of each component and considering the mass balance. A sensor was developed and installed in a spark plug, which was substituted in place of an ordinary spark plug in a spark-ignition engine. Light can pass from the sensor through the engine cylinder to measure the fuel concentration. The effects of liquid droplets inside the engine cylinder, mechanical vibrations and other gases such as H2O and CO2 on the measurement accuracy were considered. Four main conclusions were drawn from this study. First, the pressure and temperature effects on the molar absorption coefficient of liquid fuel vapour were determined independently in advance using a constant-volume vessel. The pressure and temperature dependence of the molar absorption coefficient was determined under engine firing conditions. Second, the molar absorption coefficients of a multi-component hydrocarbon fuel such as gasoline were estimated by considering the molar fraction of each component. Third, in situ measurements of the hydrocarbon fuel concentration in an actual engine were obtained using the spark plug sensor and the molar absorption coefficient of iso-octane. The concentration near the spark plug just before ignition was almost in agreement with the mean value that was obtained from the measurement of the flow rate made with a burette, which represented the mean value averaged over many cycles. And fourth, no liquid droplets were observed at near-idling conditions. The effects of other gases, such as CO, CO2 and H2O, can be neglected.

Use of an optical probe for time-resolved in situ measurement of local air-to-fuel ratio and extent of fuel mixing with applications to low NOx emissions in premixed gas turbines

The lower temperatures associated with lean premixed combustion generally lead to lower NOx emissions; however, the benefit of lean premixed combustion may be lost if the fuel and air are poorly mixed. In this paper, we describe the development of an inexpensive fiber optic probe capable of measuring the extent of mixing. The fuel concentration is determined by laser light absorption at 3.39 μm over a short path length created by using infrared transmitting fiber optics. A hydrogen-piloted, CH4-in-air turbulent flame with a variable fuel injection location is used to vary the degree of mixedness at the burner exit. We use the optical probe to measure the level of mixedness (nonreacting) at the burner exit. The level of mixing and the mean concentration profiles are also measured by using planar laser-initiated Rayleigh scattering. NOx measurements are reported for several mixing distances. We show that at lean conditions (=0.6), incomplete mixing causes a dramatic increase in NOx production because of the exponential temperature dependence of NOx formation about =0.6. We also numerically investigate how the extent of mixing affects NOx production at various equivalence ratios and pressures. Modeling the effect of incomplete mixing on NOx formation is done with a distribution ofconvolved with numerical results from a perfectly stirred reactor in series with a plug flow reactor. The model does an excellent job of predicting the NOx increase caused by incomplete mixing at lean conditions. Model predictions at higher pressures that are typical of gas turbine conditions show good agreement with available data. In particular, for lean premixed combustion, NOx is not a function of pressure if the air and fuel are well mixed.

Premixed mixture ignition in the end-gas region (PREMIER) combustion in a natural gas dual-fuel engine: operating range and exhaust emissions:

This paper is concerned with engine experiments and spectroscopic analysis of premixed mixture ignition in the end-gas region (PREMIER) combustion in a pilot fuel ignited, natural gas dual-fuel engine. The results reveal the characteristics and operating parameters that induce and affect this combustion mode. The PREMIER combustion is followed by natural gas flame propagation. Pilot-injected diesel fuel ignites the natural gas/air mixture, and the flame propagates before the natural gas/air mixture is autoignited in the end-gas region. This combustion cycle differs from a knocking cycle in terms of combustion and emission characteristics. The PREMIER combustion can be controlled by pilot fuel injection timing, the equivalence ratio, and the exhaust gas recirculation (EGR) rate, and can be used as an effective method for high load extension on a dual-fuel engine. An analysis of the relationship between the maximum in-cylinder pressure and its crank angle (CA) is used to compare combustion dynamics during conventional, PREMIER, and knocking combustion. In PREMIER combustion, the heat release gradually transforms from the slower first-stage flame rate to the faster second-stage rate. During PREMIER combustion, the maximum indicated mean effective pressure (IMEP) and thermal efficiency increase by about 25 per cent compared with those of conventional combustion, and low carbon monoxide (CO) and total hydrocarbon (HC) emissions can be achieved. However, nitrogen oxide (NO x ) emissions increase. Spectroscopic analysis shows that the intensity of the OH* emissions in the end-gas region increases as the combustion mode transforms from conventional to PREMIER to knocking. In all three modes, emission fluctuations above 650 nm can be observed in the end-gas region. These emissions are attributed to the luminosity from soot particles formed during the concurrent diesel fuel combustion.

In situ measurement of hydrocarbon fuel concentration near a spark plug in an engine cylinder using the 3.392 μm infrared laser absorption method: Discussion of applicability with a homogeneous methane-air mixture

A fibre optic system was developed to determine the fuel concentration near a spark plug using an infrared absorption method. The system was linked to an optical sensor installed in the spark plug, from which light could pass through the combustion chamber. By using this modified spark plug, successive measurements of the fuel concentration near the spark plug before ignition were performed in a spark-ignition engine burning homogeneously mixed methane–air. The fuel concentration was determined from the Lambert–Beer law by considering the dependence of the methane molar absorption coefficient on pressure and temperature. Three main conclusions were drawn from this study. First, the methane molar absorption coefficient was greater for lower pressures and decreased with increasing temperature and pressure above atmospheric pressure. The temperature and pressure effects were offset by each other, since the temperature effects were positive and the pressure effects were negative. Second, precise time-series data for the local fuel concentration were obtained by considering the in-cylinder pressure and temperature from an estimate of the methane molar absorption coefficient. And third, the measured air/fuel ratio near the spark plug before ignition agreed with the preset value when the developed optical sensor was used under motoring and firing conditions.

Measurement of hydrocarbon fuel concentration by means of infrared absorption technique with 3.39 μm HeNe laser

Abstract The infrared absorption technique with a 3.39 μm HeNe laser is useful for measuring hydrocarbon concentrations. First, molar absorption coefficients of propane or methane for the 3.39 μm wavelength were investigated in the temperature range of 285–420 K and in the pressure range of 100–800 kPa. It was found that the molar absorption coefficient, ϵ, is independent of temperature, and that pressure has little effect on ϵ in propane, but a strong effect in methane. Second, by applying this technique to a spark ignition engine, the fuel concentration in the vicinity of a spark plug and the hydrocarbon concentration in the exhaust pipe were measured under the c conditions of no residual gas and homogeneous mixture. For the lean mixture, although cycle-to-cycle fluctuation of the fuel concentration was very small, the fluctuation of pressure in the cylinder was large.

Ion current measurement in a homogeneous charge compression ignition engine

Abstract An ion current probe using a spark plug was applied to gasoline-fuelled homogeneous charge compression ignition (HCCI) combustion with hot residual gas in order to verify the possibility of using it as a combustion sensor. The ion current signal for single-cycle HCCI combustion had a simple profile and effectively one maximum value. There is a possibility that a similar ion current signal corresponding to the completed reaction can be obtained, depending on the location of the probe during HCCI combustion. The ionization reaction for HCCI combustion is affected by the chemical ionization reaction with heat release, and there is a possibility that the ion current can be used to detect heat release corresponding to the chemical ionization reaction. A strong correlation between the timing of the integrated ion current and the timing of the mass fraction burned is observed. The timing of the mass fraction burned is assumed from the timing of the integrated ion current, and the mass fraction burned (up to 70 per cent) can be determined, even if the engine driving condition changes within the scope of the test. There is a correlation between the timing of the maximum ion-current and the maximum rate of heat release, and there is a possibility that the maximum value of the rate of heat release can be inferred by detecting the timing of the maximum ion current. There is a correlation between the timing of the maximum ion current and the timing of the maximum pressure at each cycle. Therefore, it may be possible to monitor the variation of the HCCI combustion phasing.

In-situ fuel concentration measurement near spark plug in spark-ignition engines by 3.39 μM infrared laser absorption method

Recently, improving the thermal efficiency and reducing the exhaust emissions of internal combustion engines have become crucial. To this end, it is important to determine the fuel concentration in the vicinity of the spark plug near the spark timing, because initial combustion affects the subsequent main combustion in spark-ignition engines. In this study, a fiber optic system linked to an optical sensor installed in the spark plug, by means of which light can pass through the combustion chamber, was developed to determine the fuel concentration near the spark plug using an IR absorption method. A He−Ne laser with a wavelength of 3.39 μ m that coincides with the absorption line of hydrocarbons was used as a light source. By exchanging an ordinary spark plug for this spark plug with the optical sensor, successive measurement of fuel concentration before the spark timing near the spark plug was performed in a port-injection spark-ignition engine fueled with iso-octane under the firing condition. The effects of pressure and temperature on the molar absorption coefficient of fuel were clarified in advance. The air/fuel ratio averaged for many cycles near the spark plug with this optical system agreed with that measured with a buret, which represented the mean value averaged over a protracted period. Next, this sensor was applied to determine the air/fuel ratio quantitatively in a direct-injection gasoline engine. As a result, it was clarified that the air/fuel ratio and its standard deviation near the spark plug have a strong relationship to stable engine operation.

Direct microscopic image and measurement of the atomization process of a port fuel injector

The main objective of this study is to observe and investigate the phenomena of atomization, i.e. the fuel break-up process very close to the nozzle exit of a practical port fuel injector (PFI). In order to achieve this objective, direct microscopic images of the atomization process were obtained using an ultra-high-speed video camera that could record 102 frames at rates of up to 1 Mfps, coupled with a long-distance microscope and Barlow lens. The experiments were carried out using a PFI in a closed chamber at atmospheric pressure. Time-series images of the spray behaviour were obtained with a high temporal resolution using backlighting. The direct microscopic images of a liquid column break-up were compared with experimental results from laser-induced exciplex fluorescence (LIEF), and the wavelength obtained from the experimental results compared with that predicated from the Kelvin–Helmholtz break-up model. The droplet size diameters from a ligament break-up were compared with results predicated from Webers analysis. Furthermore, experimental results of the mean droplet diameter from a direct microscopic image were compared with the results obtained from phase Doppler anemometry (PDA) experimental results. Three conclusions were obtained from this study. The atomization processes and detailed characterizations of the break-up of a liquid column were identified; the direct microscopic image results were in good agreement with the results obtained from LIEF, experimental results of the wavelength were in good agreement with those from the Kelvin–Helmholtz break-up model. The break-up process of liquid ligaments into droplets was investigated, and Webers analysis of the predicated droplet diameter from ligament break-up was found to be applicable only at larger wavelengths. Finally, the direct microscopic image method and PDA method give qualitatively similar trends for droplet size distribution and quantitatively similar values of Sauter mean diameter.

Temperature measurement of end gas under knocking condition in a spark-igniyion engine by laser interferometry

Abstract Knocking is one of the most significant problems that limits the efficiency of an internal combustion engine. It is caused by autoignition of the unburned gas ahead of the flame. In order to understand the knock phenomenon, it is important to measure the temperature of the unburned gas. In this study, with polarization preserving fibers, the laser interference measurement of the unburned gas temperature was performed in a constant-volume and a specially designed engine which could be ignited only once. The engine was fueled with n- butane , oxygen and argon, and was operated under knocking conditions. When the density of the gas changes, the change of the optical path length of the test beam corresponds to the change of the refractive index. The temperature history of the unburned gas was determined by measuring the pressure and the change of interference signal. The optical fiber interference system had the advantage of resisting mechanical vibration because the test and reference beams were transmitted in the same optical fiber and were separated only in the test section.

Laser-induced plasma generation and evolution in a transient spray.

The behaviors of laser-induced plasma and fuel spray were investigated by visualizing images with an ultra-high-speed camera. Time-series images of laser-induced plasma in a transient spray were visualized using a high-speed color camera. The effects of a shockwave generated from the laser-induced plasma on the evaporated spray behavior were investigated. The interaction between a single droplet and the laser-induced plasma was investigated using a single droplet levitated by an ultrasonic levitator. Two main conclusions were drawn from these experiments: (1) the fuel droplets in the spray were dispersed by the shockwave generated from the laser-induced plasma; and (2) the plasma position may have shifted due to breakdown of the droplet surface and the lens effect of droplets.