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Cycle-resolved measurements of the fuel concentration near a spark plug in a commercial rotary engine were performed. An in situ laser infrared (IR) absorption method was developed using a spark plug sensor and a 3.392-μm He–Ne laser as the light source. This wavelength coincided with the absorption line of hydrocarbons. The newly developed IR spark plug sensor had a higher signal-to-noise ratio than its previous version due to the optimization of its quartz lens and two optical fibers. The new sensor provided quantitative cycle-resolved fuel concentration measurements around the spark plug with a high temporal resolution. At lean preset air/fuel (A/F) ratios, fuel was mixed with the surrounding air gradually by the rotor motion in the plug hole of the rotary engine. Strong mixture inhomogeneities were measured during the compression stroke; the magnitude of these inhomogeneities decreased throughout the compression stroke. Cycle-resolved measurements were made to investigate the effects of the fuel concentration near the spark plug on the combustion characteristics of the commercial rotary engine. There was a strong correlation between the fuel concentration measured with the spark plug sensor and the combustion characteristics during the initial combustion period, which occurred faster when conditions were slightly richer than stoichiometric near the spark plug. The indicated mean effective pressure (IMEP) was slightly related to the A/F ratio near the spark plug. It was possible to measure the cycle-resolved A/F ratio near the spark plug and investigate its cycle-to-cycle fluctuations to achieve stable operation using the newly developed spark plug sensor.

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.

Effects of squish area location on tumble and squish flow were investigated to control the knock in an SI engine. For the exhaust squish piston, tumble flow is collapsed by the exhaust squish clearance during the compression stroke, so that the compression-squish flow is strong. For the intake squish piston, tumble flow impinges on the edge of squish area and the induction of it into the squish area is controlled. The compression-squish flow is weakened and reverse-squish flow grows strong. This led to realization of a high heat release at late stage combustion. Simultaneously, the decrease of cycle-by-cycle variation of initial burn is realized. Consequently, knocking is controlled compared with a flat piston.

Planar Laser-Induced-Fluorescence technique was applied to measure the NO fluorescence distribution in a spark ignition engine. The fluorescence intensity had high value near the flame front, and gradually decreased from the flame front to the postflame gas. The fluorescence was distributed in the broad flame zone as compared with the case of the constant-volume combustion chamber. The effect of equivalence ratio on the NO fluorescence intensity were investigated. At the flame-development duration, the total NO fluorescence intensity was high as the equivalence ratio became rich. However, at the rapid-burning duration, the total NO fluorescence intensity of a slightly lean condition had a maximum value. As the equivalence ratio became lean, the peak intensity of the radial NO fluorescence distribution increased and the width of the high intensity zone in radial distance broadened. The peak intensity and the width of the radial distribution reached the maximum value at a slightly lean condition.

The Sauter mean diameter and size distribution of a diesel spray in a vaporizing process were studied to obtain detailed information of the diameter change of the spray in an elevated-temperature and-pressure environment. In this study, direct photographs of the diffracted light from particles or spray drops were taken using a pulsed laser and analyzed directly. The mean particle size could be measured even if the diffracted light from particles passed through a high-ambient-temperature and-pressure environment. The liquids used for studying a vaporizing diesel spray were diesel fuel and n-heptane. The Sauter mean diameter increased to a maximum, then decreased with a further increase of the ambient temperature. The change of the Sauter mean diameter was different for different fuel evaporation rates. The increase of the Sauter mean diameter of n-heptane spray occurred at a lower ambient temperature condition than did that for the diesel spray.

The new empirical equations to represent the Sauter mean diameter of a spray injected from a diesel nozzle were reported in this paper. In order to determine the new equations of the mean diameter, drop sizes of a diesel spray were analyzed by a laser diffraction technique. Liquids with different viscosities and different surface tensions were tested. The maximum injection pressure and the maximum ambient pressure were 90 MPa and 3 MPa, respectively. According to the tendencies of break-up length and drop sizes of a spray for an injection velocity and an ambient pressure, the spray formation mechanism could be divided into two categories as a function of the injection velocity and physical properties of the liquid. Finally, dimensionless analysis for each category of a spray could lead tot the empirical equations of the Sauter mean diameter.

The purpose of this study is to clarify the effect of liquid viscosity on the Sauter mean diameter and the spray angle. The spray injected by a diesel nozzle of hole type was observed by the laser diffraction technique system and the direct photography method. The tests were carried out over a wide range of injection pressures and viscosities of glycerine solution at ambient pressure of 3 MPa. With an increasing liquid viscosity, the spray angle decreases and the Sauter mean diameter gradually increases. With further increase of the Viscosity, the Sauter mean diameter suddenly increases. There is an upper limit of the viscosity to be atomized as a spray of fine droplets. At a high injection pressure, the effect of viscosity on the Sauter mean diameter still remains but the viscosity has no effect on the spray angle.

To study the effect of fuel viscosity, injection pressure and surface tension on the mean droplet size and spray angle, the diesel fuel spray droplets were measured by a Laser diffraction technique. Several kinds of glycerine solution with water and residual fuel oil were used. The tests were carried out over a wide range of injection pressure [3 to 90 MPa (30.6 to 917.7 kgf/cm2) ] and of kinematic viscosity of liquid [1×10-6 to 200×10-6 m2 /s (1 to 200 cSt) ] at ambient pressure of 3 MPa (30.6 kgf/cm2) .The main results obtained are as follows:(1) Sauter mean diameter increases with increasing kinematic viscosity of liquid, but decreases with increasing injection pressure. There are an upper limit of viscosity and a lower limit of the pressure to produce a fine spray.(2) At high injection pressure, the effect of viscosity on Sauter mean diameter still remains, but the viscosity has no effect on the spray angle.(3) When the viscosity is the same at low injection pressure, Sauter mean diameter of glycerine solution spray is larger than that of residual oil. Surface tension has no effect on the Sauter mean diameter at high injection pressure.