Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

Ambient gas density and fuel vaporization effects on the penetration and dispersion of diesel sprays were examined over a gas density range spanning nearly two order of magnitude. This range included gas densities more than a factor of two higher than top-dead-center conditions in current technology heavy-duty diesel engines. The results show that ambient gas density has a significantly larger effect on spray penetration and a smaller effect on spray dispersion than has been previously reported. The increased dependence of penetration on gas density is shown to be the result of gas density effects on dispersion. In addition, the results show that vaporization decreases penetration and dispersion by as much as 20% relative to non-vaporizing sprays; however, the effects of vaporization decrease with increasing gas density. Characteristic penetration time and length scales are presented that include a dispersion term that accounts for the increased dependence of penetration on ambient density. These penetration time and length scales collapse the penetration data obtained over the entire range of conditions examined in the experiment into two distinct non-dimensional penetration curves: one for the non-vaporizing conditions and one for the vaporizing conditions. Comparison of the two nondimensional penetration curves to a theoretical penetration correlation for non-vaporizing sprays helped isolate and explain the effects of droplets and vaporization on penetration. The theoretical penetration correlation was derived using the penetration time and length scales and simple model for a non-vaporizing spray that has been previously presented in the literature. The correlation is in good agreement with the non-vaporizing data from this experiment and other commonly quoted penetration data sets. It also provides a potential explanation for much of scatter in the penetration predicted by various correlations in the literature.

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Effects of Gas Density and Vaporization on Penetration and Dispersion of Diesel Sprays

Scaling Liquid-Phase Fuel Penetration in Diesel Sprays Based on Mixing-Limited Vaporization

An improved understanding of the mechanisms of unstable combustion in lean premixed combustors is essential to the development of stable gas turbine combustion systems. To obtain such understanding, detailed experimental studies of the phenomenology of unstable combustion are required. A number of experimental diagnostic techniques for characterizing unstable combustion and the underlying instability mechanisms are discussed. This includes techniques based on pressure, chemiluminescence emission, infrared absorption, and laser-induced fluorescence measurements. The techniques themselves are discussed briefly; however, the primary objective is to present and discuss results illustrating how these techniques can be used to characterize the mechanisms of unstable combustion, to gain an improved understanding of unstable combustion, and to develop strategies for suppressing unstable combustion in lean premixed gas turbine combustors.

Experimental Diagnostics for the Study of Combustion Instabilities in Lean Premixed Combustors

Effects of ultra-high injection pressure and micro-hole nozzle on flame structure and soot formation of impinging diesel spray

Fundamental study on combustion diagnostics using a spark plug as ion probe

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.

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

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 339 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

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

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. (A)

Sadami Yoshiyama

Papers

Fundamental study on combustion diagnostics using a spark plug as ion probe

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

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

Ion current measurement in a homogeneous charge compression ignition engine

Combustion diagnostics of a spark ignition engine using a spark plug as an ion probe