Tsuneaki Ishima

Effect of Fuel Injection Timing Relative to Ignition Timing on the Natural-Gas Direct-Injection Combustion

The effect of fuel injection timing relative to ignition timing on natural gas direct-injection combustion was studied by using a rapid compression machine (RCM). The ignition timing was fixed at 80 ms after the compression start. When the injection timing was relatively early (injection start at 60 ms), the heat release pattern showed a slower burn in the initial stage and a faster burn in the late stage, which is similar to that of flame propagation of a premixed gas. In contrast to this, when the injection timing was relatively late (injection start at 75 ms), the heat release rate showed a faster burn in the initial stage and a slower burn in the late stage, which is similar to that of diesel combustion. The shortest duration was realised at the injection end timing of 80 ms (the same timing as the ignition timing) over a wide range of equivalence ratio. The degree of charge stratification and the intensity of turbulence generated by the fuel jet are considered to cause this behavior. Early injection leads to longer duration of the initial combustion, whereas late injection leads to a longer duration of the late combustion. Early injection showed relatively lower CO concentration in the combustion products while late injection gave relatively lower NO x . It was suggested that early injection leads to combustion with weaker stratification, and late injection leads to combustion with stronger stratification. Combustion efficiency was kept at a high value over a wider range of equivalence ratio.

Combustion characteristics of natural-gas direct-injection combustion under various fuel injection timings

Abstract The characteristics of natural-gas direct-injection combustion under various fuel injection timings were studied by using a rapid compression machine. Results show that natural-gas direct injection can result in combustion that is much faster than homogeneous combustion while shortening the time interval between injection timing and ignition timing can markedly decrease the combustion duration. Unburned hydrocarbon would increase over a wide range of equivalence ratios, shortening the time interval between injection timing and ignition timing can decrease the value to that of homogeneous-mixture combustion. The NOx level is high but the CO level is low over a wide range of equivalence ratios and is little affected by fuel injection timing. High values of pressure rise due to combustion can be realized and it is insensitive to the variation in fuel injection timing. High combustion efficiency can be achieved, which is also independent of injection timing.

Study of cycle-by-cycle variations of natural gas direct injection combustion using a rapid compression machine

Abstract Cycle-by-cycle variations of natural gas direct injection (CNG DI) combustion were studied by using a rapid compression machine. Results show that CNG DI combustion can realize high combustion stability with less cycle-by-cycle variation in the maximum pressure rise, the maximum rate of pressure rise and the maximum rate of heat release at the given equivalence ratios. Mixture stratification and fast flame propagation with the aid of turbulence produced by the high speed fuel jet are considered to be responsible for these behaviours. Cycle-by-cycle variations in combustion durations and combustion products present higher magnitudes than those of maximum pressure rise and maximum rate of heat release. Cycle-by-cycle variations of CO and unburned CH4 show an interdependence with the variation of the late combustion duration, and the variation of NO x shows an interdependence with the variation of the rapid combustion duration. Cycle-by-cycle variations are found to be insensitive to the equivalence ratios in CNG DI combustion.

PDA and LDA Measurements of Large Angle Hollow Cone Spray Proposed for Hot-Premixed Combustion Type Diesel Engine

To study the characteristics of flow velocity and particle diameters in large angle conical spray proposed for hot-premixed combustion type Diesel engines, steady, and unsteady conical sprays have been analyzed using laser Doppler anemometry (LDA), and phase Doppler anemometry (PDA). Three injection pressures were used in steady experiments. In unsteady experiments, the frequency of injection was 20.7 Hz and the amount of injection fuel was 10.3 mg or 25.6 mg in each cycle. Distributions of bulk velocity, fluctuation intensity of the velocity, air entrainment rate, Sauter mean diameter of particles and correlation between particle diameter and velocity of the spray were obtained.

Correlation of Ignitability with Injection Timing for Direct Injection Combustion Fuelled with Compressed Natural Gas and Gasoline

Abstract A study on the correlation of ignitability with fuel injection timing for direct injection combustion fuelled with natural gas and gasoline was carried out by using a rapid compression machine. The injection pressure of natural gas is 9 MPa and the injection pressure of gasoline is 7 MPa. The study results show that natural gas direct injection possesses higher momentum than that of gasoline, and this is beneficial to the combustion enhancement since a higher intensity of turbulence could be induced. Correlation of ignitability with injection timing shows better behaviour in natural gas direct injection, and this correlation is insensitive to injection modes in the case of natural gas. Thus, natural gas direct injection would have better engine applicability under cold-start conditions. The lean burn limits of natural gas and gasoline direct injection can extend to extremely low equivalence ratio when the ignitable stratified mixture exists around the spark electrode gap by optimizing the injection timing.

Visualization study of natural gas direct injection combustion

Abstract A visualization study of natural gas direct injection combustion was carried out by using a high speed video camera. The results show that the distribution of the stratified mixture di ers with the injection mode, with parallel and single injection tending to form a higher degree of mixture stratification than opposed injection. Flame propagates toward the downstream direction in the cases of parallel and single-injection combustion, and flame propagates outward from the centre of the combustion chamber in the case of opposed injection combustion. A characteristic of turbulent combustion with a wrinkled flame front is presented in natural gas direct injection combustion. Super-lean combustion can be realized owing to the formation of an ignitable stratified mixture with the optimum setting of the fuel injection timing.

Basic characteristics of direct injection combustion fuelled with compressed natural gas and gasoline using a rapid compression machine

Abstract The basic characteristics of direct injection (DI) combustion fuelled with compressed natural gas (CNG) and gasoline was studied using a rapid compression machine. The characteristics of stratified combustion and emission of natural gas and gasoline direct injection at the optimum injection settings over a wide range of equivalence ratios were investigated. The results showed that, similar to premixed combustion, natural gas stratified combustion was of shorter duration than gasoline DI combustion. In contrast to this, the heat release pattern for gasoline DI combustion was similar to that of diesel combustion, which seems to have both a premixed phase and a diffusion phase. This phenomenon tends to be more obvious at a lower overall equivalence ratio, which suggests that fuel and charge stratification have a great influence on DI stratified charge combustion. Thus, this faster burn for natural gas promotes extremely lean combustion and a higher pressure rise. However, natural gas DI stratified combustion produces more hydrocarbons (HC) than gasoline DI stratified combustion at a low overall equivalence ratio. Combustion effciency is at the same level for the two fuels, and natural gas DI combustion was shown to have a slightly leaner combustion capability than gasoline DI combustion, which suggests the better feasibility of natural gas stratified combustion.

Turbulence Structure of a Liquid-Solid Two-Phase Jet by Means of Laser Techniques

Characteristics on particle motion in a liquid-solid two-phase jet flow were studied in the paper. The water jet including glass particle of 389 μm in mean diameter was injected into water bath. The experimental conditions were 0.21% of initial particle volume ratio, 5mm in pipe diameter and 1.84 m/s of mean velocity on outlet of the jet. A laser Doppler anemometer (LDA) with size discrimination was applied for measuring the time serious velocities of the single-phase flow, particle and water phase flow. A particle image velocimetry (PIV) was also applied in the two-phase flow. The normal PIV method can hardly measure the particle size and perform the particle size discrimination. In the experiment, using the gray scales related with the scattering light intensity, measuring method with size discrimination in two-phase flow was carried out. The experimental results show less difference between velocities of single-phase flow and water-phase flow under this low particle volume ratio condition. Particles have the relative motion with the water-phase and large rms velocity. The PIV used in this experiment, which is called multi-intensity-layer-PIV: MILP, can measure water-phase velocity with good accuracy.Copyright

Impact force measurement of a spherical body dropping onto a water surface

We propose a method for measuring the impact force of a spherical body dropping onto a water surface. The velocity of the center of gravity of a metal spherical body, in which a cube corner prism is embedded so that its optical center coincides with the center of gravity of the sphere, is accurately measured using an optical interferometer. The acceleration, displacement, and inertial force of the sphere are calculated from the velocity. The sphere is also observed using a high-speed camera. The uncertainty in measuring the instantaneous value of the impact force with a sampling interval of approximately 1 ms is estimated to be 8 mN, which corresponds to 0.8% of the maximum force of approximately 1.0 N.

Characteristics of HCCI Diesel Combustion Operated with a Hollow Cone Spray

Thie paper presents two factors for improving the performance and emissions characteristics in HCCI diesel combustion, one is reducing compression ratio and another is changing the injector position. In a previous study,it was shown that HCCI diesel combustion could be realized by utilizing a hollow-cone spay with normal injection pressure. However there remained two major problems of engine instability and increase in BSFC (decrease in brake thermal efficiency). By reducing the compression ratio from 18.8 to 16.8, the engine stability was much improved to the level of conventional diesel combustion and the increase in BSFC became almost half, which was mainly due to the change of combustion phasing. In addition to this, application of 5 mm inside position of the injector realized almost no penalty of BSFC at higher load condition. At around 15 deg BTDC, small increment of pressure rise was observed, which must be due to the occurrence of cool flame, and the heat released during this stage did not vary with load. Then this cool flame energy is shown to be another important factor for the increase in BSFC at lighter load.